HUMAN ANATOMY MORRIS ARRANGEMENT OF SUBJECTS AND AUTHORS. OSTEOLOGY. By J. Bland Sutton, F.R.C.S., Lecturer on Compara- tive Anatomy, and Senior Demonstrator of Anatomy, Middlesex Hospital; Hunterian Professor Royal College of Surgeons, etc. JOINTS. By the Editor, Henry Morris, F.R.C.S., Surgeon to, and Lecturer on Surgery at, Middlesex Hospital; Examiner on Anatomy in Royal College of Physicians and Royal College of Surgeons, etc. MUSCLES. By J. H. Davies-Colley, F.R.C.S., Mem. Path, and Clin. Soc., London; Fellow Medico-Chir. Soc.; Surgeon to, and Lecturer on Surgery (late Lecturer on Anatomy), Guy’s Hospital, etc. BLOOD-VESSELS AND LYMPHATICS. By Wm. J. Walsham, f.r.c.s., Author of “Manual of Practical Surgery,” Assistant Surgeon to, and Lecturer on Anatomy at, St. Bartholomew’s Hospital, etc. NERVOUS SYSTEM. By H. St. John Brooks, M.D., of Dublin, Secretary for Ireland of Anat. Soc. of Great Britain; Chief Demon- strator of Anatomy University of Dublin, etc. EYE. By R. Marcus Gunn, F.R.C.S., Mem. Path., Ophthal., and Neurol. Soc.; Surgeon to Royal London and to the Western Ophthal- mological Hospitals, etc. TONGUE, NOSE, EAR, HEART, VOICE, RESPIRATION. By Arthur Hensman, F.R.C.S., Aural Surgeon (late Senior Demonstrator of Anatomy) Middlesex Hospital, Lecturer on Aural Surgery and Anatomy Middlesex Hospital Medical School. ORGANS OF DIGESTION. By Frederick Treves, F.R.C.S., Sur- geon and Lecturer on Anatomy London Hospital, etc. URINARY AND GENERATIVE ORGANS. By William Ander- son, f.r.c.s., Assistant Surgeon, Lecturer on Anatomy, and Surgeon to Skin Department St. Thomas’ Hospital, Professor of Surgery and Path- ology Royal College Surgeons, etc. SURGICAL AND TOPOGRAPHICAL ANATOMY. By W. H. A. Jacobson, f.r.c.s., Assistant Surgeon to Guy’s Hospital, Surgeon to Royal Hospital for Children and Women, Lecturer on Anatomy (late Teacher of Operative Surgery) Guy’s Hospital Medical School. Author of “ The Operations of Surgery,” etc. PUBLISHERS’ NOTICE. The Illustrations in this book have all been cut on wood from drawings made by special artists. They are mostly from original sources; those that are not have been duly credited; all, however, owing to re-drawing and engraving, are protected by copyright. HUMAN ANATOMY A COMPLETE SYSTEMATIC TREATISE BY VARIOUS AUTHORS INCLUDING A SPECIAL SECTION ON SURGICAL AND TOPOGRAPHICAL ANATOMY EDITED BY HENRY MORRIS, M.A. AND M.B. Lond. SURGEON TO, AND LECTURER ON SURGERY, FORMERLY LECTURER ON ANATOMY, AT THE MIDDLESEX HOSPITAL, LATE EXAMINER IN ANATOMY IN THE UNIVERSITY OF DURHAM, AND FOR THE ROYAL COLLEGE OF PHYSICIANS ON THE? CONJOINT BOARD _____ ILLUSTRATED BY SEVEN HUNDRED AND NINETY-ONE WOODCUTS 214 OF WHICH ARE PRINTED IN COLORS FROM DRAWINGS MADE EXPRESSLY FOR THIS WORK P.Y SPECIAL ARTISTS PHILADELPHIA P. BLAKISTON, SON & CO. IOI2 WALNUT STREET 1893 Copyright, 1893, by P. Blakiston, Son & Co. Press of Wm F. Fell & Co. 1220-24 Sansom St., PHILADELPHIA. PREFACE. This Treatise on Human Anatomy is designed for the use of students, and aims at being a complete and systematic description of every part and organ of the body, so far as it is studied in the dissecting room. Histology and development—except the mode and dates of development of the bones, and in a few other instances—are not included, as it is felt that these subjects are more appropriately dealt with in books on Physiology than they can conveniently be in works on Anatomy. The different sections have been written by separate authors who are known to have devoted special attention to the subjects allotted to them. To these gentlemen my best thanks are due for their generous assistance and able co-opera- tion. Whilst each author is alone responsible for the subject-matter of the article which follows his name, the proof-sheets of other articles besides his own have in certain cases been submitted to him, so that several of the articles may be con- sidered to have received the approval and endorsement of two, three, or more authors. This has been particularly the case with the sections on Osteology, Arthrology, Myology, and Neurology. There is, therefore, reason to believe that such important points as the attachments of ligaments and of muscles, and the nerve-supply of muscles, etc., will be found to be in perfect accord in the various sections in which they are referred to or described. In the illustrations of the bones the origins of muscles are indicated by red lines, the insertions by blue lines, and the attachments of ligaments by dotted black lines. A feature of the work which, it is confidently hoped, will facilitate the work of students, is the mode of describing the illustrations. Several of the illustrations are repeated in different parts of the book, with the object of sparing the reader the trouble of referring from one section to another when reference is made in the letter-press to such figures. As much uniformityas possible has been observed in the size and general style of the drawings. But exceptions will be found in the section on Surgical and Topographical Anatomy, for which many of the illustrations have been borrowed from another work published by Messrs. J. and A. Churchill, namely, Bellamy’s “ Surgical Anatomy.” V VI PREFA CE. I have to acknowledge with grateful thanks the assistance I have received from Mr. Gordon Brodie, who made several dissections from which drawings were taken ; from Mr. J. Bland Sutton and Mr. Frank Steele in reading over proof-sheets; from Mr. Burghard for the care with which he has drawn up the Index and Tables of Contents; and from the following artists who have so care- fully prepared the drawings: Messrs. Berjeau, Balcomb, Collins, Griffin, Lewin, Mannix, Parker, Smit, Tonks, and Wesley. Mr. Berjeau and Mr. Balcomb have done a very large proportion of the figures; and, with Mr. Smit and Mr. Parker, have shown a degree of interest in, and have given an amount of time and trouble to, the illustrations, for which they merit the fullest recognition. The beautiful anatomical dissections in the Hunterian Museum, which have been, by permission, copied for this Treatise, are from the hand of Mr. William Pearson, to whose great skill in dissecting I have much pleasure in referring. I need only say, in conclusion, shall not consider my prolonged and laborious task has been in vain if it be found that the Treatise adequately meets the requirements of students, for whom it is written. Henry Morris. 8 Cavendish Square, January, i8gy. CONTENTS. SECTION I. OSTEOLOGY. By J. B. Sutton. PAGE The Skeleton, 17 A Classified List of the Bones to show their Mode of Development, . . 18 The Spine, 21 Characters of a Typical Vertebra, . 21 The Cervical Vertebrae, 23 The Thoracic or Dorsal Vertebrae, . 27 The Lumbar Vertebrae, 29 The Sacral and Coccygeal Verte- brae, 31-35 The Spinal Column in general, . . 35 Ossification of the Vertebrae, ... 36 Serial Morphology of the Vertebrae, 39 The Bones of the Skull, 41-80 The Appendicular Elemenls of the Skull, 80 Mandible (inferior Maxilla), ... 80 Hyoid Bone, 84 Styloid Process, 84 Ear Bones, 84 PAGE The Skull as a whole: Exterior of the Skull, 87 The Orbits 96 The Nasal Fossae, ’ 98 Interior of the Skull, 100 The Teeth, 105 Morphology of the Skull, .... 108 Metamorphosis of the Branchial Bars, 109 Skull at Birth, 109 Peculiarities of Individual Bones at Birth, ... hi Nerve-Foramina of the Skull, ... 114 The Ribs and Sternum, 117 The Thorax, 127 The Clavicle and Scapula, 128-134 The Bones of the Upper Extremity, . 135-157 The Hip-Bone, 157 The Pelvis, 164 The Bones of the Lower Extremity, . 165-194 SECTION II. THE ARTICULATIONS. By Henry Morris. PAGE Structures entering into the formation of Joints . 195 The various kinds of Articulations, ... 196 The various Movements of Joints, ... 197 The Articulations of the Skull 198 The Temporo-mandibular Articula- tion, 198 The Ligaments and Joints between the Skull and Spinal Column, and between the Atlas and Axis, . . 201 PAGE The Articulation of the Atlas with the Occiput, 201 The Articulations between the Atlas and Axis, 204 The Ligaments uniting the Occiput and Axis, 207 The Articulations of the Trunk, .... 208 The Articulations of the Vertebral Column, 209 VII VIII CONTENTS. PAGE The Articulations of the Bodies of the Vertebrae, 209 The Ligaments connecting the Ar- ticular Processes, . • 213 The Ligaments uniting the Laminae, 213 The Ligaments connecting the Spin- ous Processes, 214 The Ligaments connecting the Transverse Processes, 214 The Articulations of the Pelvis with the Spine, 216 The Articulations of the Pelvis, ... 218 The Sacro-iliac Synchondrosis and Sacro-sciatic Ligaments, .... 218 The Sacro-coccygeal Articulation, . 221 The Inter-coccygeal Joints, .... 223 The Symphysis Pubis, • 223 The Articulations of the Ribs with the Vertebrae, 225 The Costo-central Articulation, . . 226 The Costo-Transverse Articulation, . 228 The Articulations at the Front of the Thorax, 229 The Chondro-sternal Articulations, . 229 The Costo-chondral Joints, .... 231 The Union of the Segments of the Sternum, 231 The Interchondral Articulations, . . 231 Movements of the Thorax as a whole, 232 The Articulations of the Upper Extremity, 233 The Sterno-clavicular Articulation, . . 233 The Scapulo-clavicular Union, . . . 236 The Acromio-clavicular Joint, . . . 236 The Coraco-clavicular Union, . . . 237 The Proper Scapular Ligaments, . . 238 The Shoulder Joint, 239 The Elbow Joint, 244 The Union of the Radius with the Ulna, 247 The Superior Radio-ulnar Joint, . . 247 The Mid Radio-ulnar Joint, .... 247 The Inferior Radio ulnar Joint, . . 249 The Radio-carpal Articulation, ... 251 The Carpal Joints, . . • 254 The Union of the First Row of Car- pal Bones, 254 The Union of the Pisiform with the Bones of the First Row, .... 254 The Union of the Second Row of Carpal Bones, 255 The Medio-carpal Joint, 255 The Carpo-metacarpal Joints, .... 258 The Four Inner Carpo-metacarpal Joints, 258 PAGE The Carpometacarpal Joint of the Thumb, 259 The Inter-metacarpal Articulations, . 260 The Union of the Heads of the Metacarpal Bones, 260 The Metacarpo-phalangeal Joints, . . 260 The Metacarpo-phalangeal Joints of the Four Inner Fingers, .... 260 The Metacarpo-phalangeal Joint of the Thumb, 262 The Inter-phalangeal Articulations, . 262 The Articulations of the Lower Limb, . 263 The Hip Joint, 263 The Knee Joint, 271 The Tibio-fibular Union, 281 The Superior Tibio-fibular Joint, . . 281 The Middle Tibio-fibular Union, . . 282 The Inferior Tibio-fibular Articula- tion 282 The Ankle Joint, 283 The Tarsal Joints, 286 The Calcaneo-astragaloid Union, . . 286 The Posterior Calcaneo-astragaloid Joint, 286 The Anterior Calcaneo-astragaloid Joint, 286 The Articulations of the Anterior Part of the Tarsus, 288 The Cubo-scaphoid Union, . . . 288 The Scapho-cuneiform Articula- tion, 288 The Inter-cuneiform Articulations, 289 The Cubo-cuneiform Articulation, 289 The Medio-tarsal or Transverse Tar- sal Joints, 290 The Astragalo-scaphoid Articula- tion, 290 The Calcaneo cuboid Articulation, 290 The Tarso-metatarsal Articulations, . 293 The Internal Tarso-metatarsal Joint, 293 The Middle Tarso-metatarsal Joint, 294 The Cubo metatarsal Joint, . . . 293 The Inter-metatarsal Articulations, . . 295 The Union of the Heads of the Metatarsal Bones, 296 The Metatarso-phalangeal Articu- lations, 296 The Metatarso-phalangeal Joints of the Four Outer Toes, . . . 296 The Metatarso-phalangeal Joints of the Great Toe, 296 The Inter-phalangeal Joints, .... 297 Morphology of Ligaments, 297 CONTENTS. IX SECTION III. THE MUSCLES. J. N. C. Davies-Colley. PAGE Muscles of the Upper Extremity, .... 305 Posterior Division of the Group of Muscles passing from the Trunk to the Upper Extremity, .... 305 First Layer, 305 Second Layer, 307-310 Anterior Division of the Group of Muscles passing from the Trunk to the Upper Extremity, .... 311 First Layer, 311-313 Second Layer, 313-316 Third Layer, 316-317 Muscles which pass from the Scapula to the Upper Limb, 318-323 Group of Muscles which move the Elbow Joint, 323 Fasciae of the Upper Arm, .... 323 Flexors of the Forearm, . . . 324-327 Extensors of the Forearm, .... 327 Muscles of the Forearm, 329 Muscles of the Front of the Fore- arm 330 First Layer, 33°~333 Second Layer, 334-336 Third Layer 336-339 Fourth Layer, 339 Radial Group of Muscles, .... 340 Muscles of the Back of the Fore- arm. 343 Superficial Layer, .... 343-346 Deep Layer, 346-351 The Fasciae of the Hand, 351 The Palmar Fasciae, 351 Muscles of the Hand, 352 Superficial, 352 Deep Muscles of the Palm, . . . 354 Central Group, 354-358 Muscles of the Thenar Emin- ence, 3587362 Muscles of the Hypothenar Em- inence, 362 Muscles and Fasciae of the Thigh, . . . 363 Muscles of the Front of the Thigh, 365-370 The Gluteal Muscles, 370 First Layer, 370-372 Second Layer, 372 Third Layer, 373 The External Rotators of Thigh, 374-377 The Adductors of the Thigh,. . 377-382 The Hamstring Muscles, . . . 382-385 The Anterior Muscles of the Thigh, . 385 The Deep Fascia of the Leg and Annular Ligaments, 388 Muscles of the Back of the Leg, . . 389 PAGE First Layer, 389-391 Second Layer, 391-393 Third Layer, 393 Fourth Layer, 396 The Fascia and Muscles of the Sole of the ,Foot> 397 First Layer, 398-400 Second Layer, 400-402 Third Layer, 402-405 Fourth Layer, 405 Muscles of the Front of the Leg, . . 407-410 Muscle on the Dorsum of the Foot, ... 411 Muscles on the Outer Side of the Leg, 412-414 Muscles of the Thorax, 414-419 The Diaphragm, 419 The Abdominal Parietes, 421 The Abdominal Muscles, .... . 422 Anterior Vertical Muscles, 422 Transverse and Oblique Muscles, 424-431 Posterior Vertical Muscle, 431 Muscles of the Back, 432 Third Layer, 432-434 General Arrangement of the Muscles acting upon the Spinal Column, . 434 The Vertebral Aponeurosis, .... 434 Fourth Layer 435 Fifth Layer, 435-441 Sixth Layer, 441-444 Seventh Layer, 444 The Suboccipital Muscles, 445 Muscles of the Head and Neck 447 Superficial Muscles of Neck and Scalp, 447-450 Muscles of the Eyelids and Eyebrows, 450-452 Extrinsic Muscles of the Auricle, .... 452 Muscles of the Nose, 453 Muscles of the Mouth, 455 Transverse Muscles of the Mouth, . 457 Angular Muscles of the Mouth, . . . 458 Labial Group of Muscles, 460 Muscles radiating from the Mouth, . 461 Muscles of Mastication, 462-466 Muscles and Fasciae of the Front of the Neck, 466 First Group, 467 Second Group—Infra-hyoid, .... 468 Superficial Layer, 468 Second Layer, 470 Third Group—Supra-Hyoid, . . 471-473 Extrinsic Muscles of the Tongue, . . 473-476 Deep Muscles of the Front of the Neck, . 476 Outer Group, 476 Inner Group, 477 Abnormal Muscles, 479 X CONTENTS. SECTION IV ARTERIES, VEINS, AND LYMPHATICS. By W. T. Walsham. PAGE The Arteries, 483 The Pulmonary Artery, 483 The Right, 487 The Left, 487 The Systemic Arteries, 487 The Aorta, 487 Arch of the Aorta, 488 Variations of the Arch of the Aorta, 492 Branches of the Arch of the Aorta, 493 Coronary Arteries and their Varia- tions, 494 Innominate Artery, 495 Branches and Variations, . . . 496 Common Carotid Arteries, .... 496 Thoracic Portion of Left Com- mon Carotid, 497 Common Carotid in the Neck, . 498 Branches and Variations, . . . 500 External Carotid Artery, .... 501 Branches and Variations, . 502-518 Internal Carotid Artery, 519 Branches, 521-526 Subclavian Artery, 527 Variations, 530 Branches, . 530 Distribution of the Cerebral Arter- ies, 535 Axillary Artery 542 Branches and Variations, . . . 543 Brachial Artery, 548 Branches and Variations, . . . 551 Ulnar Artery, 553 Branches and Variations, . . . 555 Superficial Palmar Arch, .... 558 Variations, 560 Branches, 560 Radial Artery, 561 Variations, 563 Branches, 565 Deep Palmar Arch, 565 Branches and Variations, . 566-567 Descending, or Thoracic Aorta, .... 568 Visceral Branches, 570 Parietal Branches 570 Abdominal Aorta, 573 Variations, 574 Parietal Branches, 575—577 Visceral Branches, 577—5S6 Terminal Branches, 586 Middle Sacral Artery, 586 Branches and Variations, . . . 587 Common Iliac Arteries, 587 Variations, 588 Collateral Circulation, 588 Branches, 589 Internal Iliac Artery, 589 Variations, 589 PAGE Branches of Posterior Division, 589-592 Branches of Anterior Division, 593-600 External Iliac Artery, 600 Branches and Variations, . . . 600 Collateral Circulation 600 Femoral Artery, 602 Branches and Variations, . . . 604 Popliteal Artery, 609 Branches and Variations, . 611-613 Posterior Tibial Artery, 614 Branches, 615 External Plantar Artery, 616 Branches, 618 Internal Plantar Artery, 619 Branches, 619 Anterior Tibial Artery, ..... 620 Branches, 620 Dorsalis Pedis Artery, ...... 622 Branches, 624 The Veins, 626 Veins of the Thorax, 626 Pulmonary Veins, 626 Vena Cava Superior, 627 Innominate, or Brachio - cephalic Veins, 627 Variations, 628 Azygos Veins, 630 Veins of the Heart, 633 Veins of the Head and Neck, . . . 635 Superficial Veins of the Head and Neck, 636-642 Deep Veins of the Head and Neck, 642 Veins of the Diploe, 642 Venous Sinuses of the Cranium, 643 Veins of the Brain, 648 Veins of the Nasal Cavities, . . 649 Veins of the Ear, 650 Veins of the Orbit, 650 Veins of the Pharynx and Larynx, 651 Deep Veins of the Neck, ... 651 Spinal Veins, 653 Veins of the Abdomen and Pelvis, . 655 Inferior Vena Cava, 656 Variations, 658 Common Iliac Veins, 658 Variations, 659 Portal Vein and its Tributaries, . . 659 Veins of the Pelvis, 663 Veins of the Upper Extremity, . . . 664 Superficial Veins of the Upper Extremity, 664 Deep Veins of the Upper Ex- tremity, 668 Veins of the Lower Extremity, . . . 669 Superficial Veins of the Lower Extremity, 669 CONTENTS. XI PAGE Deep Veins of the Lower Ex- tremity, 671 The Lymphatics, 673 Lymphatics of the Head and Neck, 673 Superficial Lymphatic Vessels and Glands of the Head and Neck, 674 Deep Lymphatic Vessels and Glands of the Head and Neck, 676 Lymphatics of the Upper Extremity, 678 Superficial Lymphatic Vessels and Glands of the Upper Ex- tremity, 678 Deep Lymphatic Vessels and Glands of the Upper Extremity, 678 Lymphatics of the Thorax, .... 680 Parietal Lymphatic Vessels and Glands of the Thorax, .... 680 PAGE Visceral Lymphatic Vessels and Glands of the Thorax, .... 681 Thoracic Duct, 683 Variations, 684 Lymphatics of the Abdomen and Pelvis, 684 Parietal Lymphatic Vessels and Glands of the Abdomen and Pelvis, 684 Visceral Lymphatic Vessels and Glands of the Abdomen and Pelvis, 686 Lymphatics of the Lower Extremity, 689 Superficial Lymphatic Vessels and Glands of the Lower Extremity, 689 Deep Lymphatic Vessels and Glands of the Lower Extremity, 691 SECTION V. THE NERVOUS SYSTEM. H. St. John Brooks. PAGE Neurology, 692 The Meninges, 694 Lymphatics of the Brain and Spinal Cord, 701 The Encephalon, 7°2 Base of the Brain, 703 Cerebral Hemispheres, 704 | Lobes of Cerebral Hemispheres with the Fissures and Convolutions,. . 707 i Basal Ganglia of the Hemispheres, 722 The Thalamencephalon, 728 The Mesencephalon, ....... 733 The Epencephalon, 736 The Metencephalon 743 Cranio-cerebral Topography, 749 The Spinal Cord, 754 External Characters, 757 Internal Structure, 759 Deep Origin of the Spinal Nerves, . 761 j The Peripheral Nervous System 768 Cranial Nerves, 769 First or Olfactory Nerve, .... 77° Second or Optic Nerve, .... 772 Third or Oculo-motor Nerve, . . 774 Fourth or Trochlear Nerve, . . . 775 Fifth or Trigeminal Nerve, . . . 776 First or Ophthalmic Division, . 777 Lenticular Ganglion, 779 Second or Maxillary Division, . 780 | Meckel’s Ganglion, 782 Third or Mandibular Division. . 783 j Submandibular (Submaxillary) Ganglion, 787 Otic Ganglion, 787 Sixth or Abducent Nerve, . . . 787 PAGE Seventh or Facial Nerve, .... 788 Eighth or Auditory Nerve, . . . 792 Ninth or Glosso pharyngeal Nerve, 794 Tenth or Pneumogastric Nerve, . 796 Eleventh or Spinal Accessory Nerve, 800 Twelfth or Hypoglossal Nerve, . 801 Spinal Nerves, 803 Posterior Primary Divisions, . . . 806 Anterior Primary Divisions, . . . 809 Cervical Nerves, 809 Cervical Plexus, 809 Superficial Branches, . . 810 Deep Branches, 812 Brachial Plexus, 813 Branches given off above the Clavicle, . . . . 814 Branches given off below the Clavical, 815 Thoracic Nerves, 823 Lumbar Nerves, 826 Lumbar Plexus, 827 Sacral and Coccygeal Nerves, . . . 833 Fourth Sacral Nerve, 833 Coccygeal Plexus, 834 Sacral Plexus, 834 The Great Sciatic Nerve, .... 838 Sympathetic Nerves, 843 Gangliated Cords of the Sympa- thetic, 844 Cervical Portion, 844 Superior Cervical Ganglion, . 845 Middle Cervical Ganglion, , 847 Inferior Cervical Ganglion, . 847 Thoracic Portion, 848 XII CONTENTS. PAGE Lumbar Portion, 848 Sacral Portion, 849 Great Prevertebral Plexuses, . . 849 Cardiac Plexus, 849 PAGE Solar Plexus, 850 Hypogastric Plexus, 852 Pelvic Plexuses, 852 SECTION VI. ORGANS OF SPECIAL SENSE. By R. Marcus Gunn and Arthur Hensman PAGE The Eye, 854 The Eyeball and its Surroundings, . 854 General Surface View, 854 Examination of the Eyeball, . . 858 Cavity of the Orbit, 870 General Arrangement of its Con- tents, 870 The Optic Nerve, 877 Blood-vessels and Nerves of the Orbit, 879 PAGE The Eyelids, 881 The Lachrymal Apparatus, . . . 883 The Ear 886 The External Ear 886 The Middle Ear, 889 The Internal Ear or Labyrinth, . 895 The Tongue, 900 The Nose, 905 SECTION VII. THE THORAX, INCLUDING THE ORGANS OF VOICE, RESPIRATION, AND CIRCULATION. Arthur Hensman. PAGE The Thorax, 914 The Organs of Voice, 917 The Larynx, 917 The Trachea, 929 The Bronchi, 931 The Thyroid Body or Gland, ... 931 The Thymus Body or Gland, . . . 935 The Organs of Respiration 936 The Lungs, 936 The Pleurae, 936 PAGE The Organs of Circulation, 941 The Pericardium, 941 The Heart, 942 The Openings and their Valves, . 947 The Position of the Chief Open- ings one to the other and to the Chest Wall 950 The Vessels and Nerves, . . . , 951 Peculiarities of the Foetal Heart, . 955 CONTENTS. XIII SECTION VIII. THE ORGANS OP DIGESTION Arthur Hensman. * PAGE The Organs above the Diaphragm, . . . 958 The Mouth, 958 The Palate, 959 The Salivary Glands, 961 The Pharynx, 964 The (Esophagus, 966 The Abdominal Viscera, 968 The Peritoneum, 968 The Abdomen, 973 The Stomach, 974 PAGE The Intestines, 978 The Small Intestine, 978 The Large Intestine 983 The Liver, 990 Varieties of the Liver, 1001 The Pancreas, 1001 The Spleen, 1003 The Evolution of the Peritoneum and an Explanation of its Arrangement in the Human Body, 1006 SECTION IX. THE URINARY AND REPRODUCTIVE ORGANS. William Anderson. PAGE The Kidneys, 1020 The Suprarenal Bodies, 1028 The Renal Ducts, 1029 The Bladder, 1031 The Male Reproductive Organs, .... 1036 The Prostate, . . 1036 The Testicles and their Appendages and Coverings, 1038 The Spermatic Cord, 1045 The Penis, 1046 The Urethra, 1050 The Female Organs of Generation, . . . 1053 The Vagina, 1056 PAGE The Uterus, 1058 The Fallopian Tubes or Oviducts, . 1065 The Ovaries, 1066 Vessels and Nerves of the Uterus and its Appendages, 1067 Development of the Genito-urinary Organs, ’ * . . . 1069 The Perineum, 1072 The Male Perineum, 1073 The Pelvic Fasciae and Muscles, . . 1074 The Perineum Proper, 1080 The Female Perineum, 1083 The Mammae, 1084 SECTION X. SURGICAL AND TOPOGRAPHICAL ANATOMY. W. H. A. Jacobson. PAGE Superficial Anatomy of the Head and Neck, 1088 The Head and Face, 1088 The Eyelids and Lachrymal Appa- ratus, 1097 PAGE The Mouth, 1098 The Palate, noi The Neck, 1101 Superficial Anatomy of the Thorax, . . 1111 The Abdomen, 1118 XIV CONTENTS. PAGE The Perineum and Genitals, 1126 Female External Genitals 1132 Hernia, 1135 Parts concerned in Inguinal Hernia, 1135 Parts concerned in Femoral Hernia, 1141 Parts concerned in Umbilical Hernia 1145 The Back 1146 Superficial Anatomy of the Upper Limb, 1156 .The Shoulder, 1156 The Arm, - . 1162 The Elbow, 1164 PAGE The Forearm, 1168 The Wrist and Hand, 1173 The Lower Extremity, 1186 The Thigh, . 1186 The Buttocks 1192 The Knee 1196 The Popliteal Space, 1200 The Leg, ... 1204 The Ankle, 1209 The Foot, 1214 Arches of the Foot, ..#... 1218 The Regions of the Abdomen, .... 1223 INDEX, 1227 LIST OF ILLUSTRATIONS. FIG. PAGE 1. The Tibia and Fibula in section, to show the Epiphyses, .... 19 2. A Vertebral Centrum to show the Pressure Curves, ...... 20 3. A Diagram to show the Pressure and Tension Curves of the Femur, . . 20 After Wagstaffe, 4. A Diagram showing Pressure and Tension Curves in the Head of the Humerus, 20 After Wagstaffe, 5. A Thoracic Vertebra (side view), ......... 22 6. A Thoracic Vertebra, ............ 22 7. A Cervical Vertebra, 23 8. The First Cervical Vertebra or Atlas 24 9. The Axis, .............. 24 10. The Cervical Vertebra (anterior view) {Colored), ...... 25 11. The Cervical Vertebra (posterior view) {Colored), ...... 26 12. Peculiar Thoracic Vertebra, ..... Atodifiedfrom Gray, 28 13. A Lumbar Vertebra (side view) 29 14. A Lumbar Vertebra. (Showing the compound nature of the transverse pro- cesses. Upper view), 29 15. Variation in the Fifth Lumbar Vertebra, ..... After Turner, 30 16. A Variation in the Fifth Lumbar Vertebra, .... After Turner, 30 17. The Sacrum and Coccyx (anterior view) {Colored), . . . . . 31 18. The Sacrum (posterior view) {Colored) 32 19. Base of Sacrum, 33 20. The Spine (lateral view), ........... 34 21. A Divided Thoracic Vertebra, ....... After Turner, 35 22. A Vertebra at Birth, ............ 36 23. Lumbar Vertebra at Eighteenth Year, with Secondary Centres, ... 36 24. Immature Atlas (third year), .......... 37 25. Development of the Atlas, 37 26. The Axis (from an Adult) in Section, 37 27. An Immature Cervical Vertebra, ......... 38 28. Ossification of the Fifth Lumbar Vertebra, ........ 38 29. Morphology of the Transverse and Articular Processes, ..... 40 30. The Occipital (external view) {Colored), ........ 42 31. Occipital Bone (cerebral surface), ......... 43 32. Cerebral Surface of the Occipital, showing an Occasional Disposition of the Channels, ............. 43 33. The Foramen Magnum at the Sixth Year, ........ 44 34. The Occipital at Birth (anterior view), ........ 45 35. The Occipital with a Separate Interparietal, ....... 46 36. The Sphenoid (viewed from above), ......... 47 37. The Left Half of the Sphenoid, 47 38. The Sphenoid (anterior view), 48 39. The Right Half of the Sphenoid (anterior view) {Colored), .... 49 40. The Under Surface of the Pre-Sphenoid at the Sixth Year, .... 5° 41. The Sphenoid at Birth 5° 42. The Jugum Sphenoidale, . . . . . . . . . . • 51 LIST OF ILLUSTRATIONS. FIG. PAGE 43. The Left Temporal Bone (outer view), ........ 52 44. The Left Temporal Bone (inner view), 52 45. The Foramina in the Fundus of the Left Internal Auditory Meatus of a Child at Birth diagrammatic), 53 46. The Left Temporal Bone (inferior view), ........ 54 47. The Temporal Bone with Muscle Attachments (Colored) -55 48. The Inner Wall of the Tympanum (Colored) 57 49. The Left Osseous Labyrinth (from a cast), .... After Henle, 57 50. The Cochlea in Sagittal Section, After Henle, 58 51. The Temporal Bone at Birth (outer view), ........ 59 52. The Temporal Bone at Birth (inner view), ....... 60 53. The Temporal Bone at the Sixth Year, . 6o( 54. The Mastoid Antrum at the Third Year, .... After Symington, 61 55. The Mastoid Antrum at the Ninth Year, .... After Symington, 61 56. The Mastoid Antrum of an Adult, . . . . . After Symington, 61 57. The Left Parietal (outer surface), 62 58. The Left Parietal (inner surface), ......... 63 59. The Frontal (anterior view), . . 64 60. The Frontal Bone (inferior view), . 65 61. The Frontal Bone at Birth, ........... 65 62. Section through the Nasal Fossa to show the Mesethmoid, .... 67 63. The Ethmoid (side view), 67 64. Section through the Nasal Fossa to show the Lateral Mass of the Ethmoid, . 68 65. The Sphenoidal Turbinal at the Sixth Year, ....... 69 66. The Sphenoidal Turbinals from an Old Skull, .69 67. The Inferior Turbinal, Adult Sphenoidal Turbinal, and Lachrymal Bones, . 70 68. The Vomer (side view), . . . . . . . . . . .71 69. The Vomer at Birth, ............ 72 70. The Left Nasal Bone, .72 71. The Left Maxilla (outer view), .......... 73 72. The Left Maxilla (inner view), .74 73. Ossification of the Maxilla, ........... 76 74. The Left Palate Bone (inner view), ......... 77 75. The Palate Bone (posterior view), . 78 76. The Left Malar Bone, 79 77. The Mandible (outer view) {Colored), ........ 81 78. The Mandible (inner view) [Colored), 82 79. The Mandible at Birth, 82 80. The Skull of an Old Woman eighty-three years old, to show the changes in the Mandible and Maxilla, 83 81. The Hyoid 85 82. The Ear Bones, ........ Modified from Henle, 86 83. The Skull (norma lateralis) (Colored), 88 84. A Section of the Skull, showing the Inner Wall of the Orbit, the Base of the Antrum, and the Spheno-maxillary Fossa 89 85. Hard Palate of a Child five years old, ........ 90 86. The Skull (norma basilaris) {Colored), ........ 92 87. The Skull (norma basilaris), 93 88. The Skull (norma facialis) {Colored), 94 89. The Skull (norma facialis), 95 90. The Inner Wall of the Orbit, .......... 97 91. Section through the Nasal Fossa to show the Septum, 97 92. Section through the Nasal Fossa to show the Outer Wall with the Meatuses, . 98 93. The Posterior Nares, 99 94. The Skull in Sagittal Section, 101 LIST OF ILLUSTRATIONS. XVII FIG. PAGE 95. The Skull in Horizontal Section, ......... 102 96. The Skull in Horizontal Section, ......... 103 97. The Teeth of an Adult, ........... 106 98. A Molar Tooth in Section, and a Canine Tooth, ...... 106 99. The Temporary Teeth, ........... 107 100. The Chondro-Cranium, ........... 108 101. The Cranium at Birth 109 102. The Cranium at Birth, no 103. The Cranium at Birth in Sagittal Section (Colored), . . . . .110 104. The Occiptal at Birth, 111 105. The Sphenoid at Birth 112 106. The Temporal Bone at Birth, . . . . . . . . . .112 107. The Temporal Bone at Birth (outer view), 113 108. The Temporal Bone at Birth (inner view), 113 109. The Frontal at Birth, 114 no. The Maxilla at Birth, . . . . . . . . . . . .114 in. The Mandible at Birth, 115 1x2. The Seventh Rib of the Left Side (seen from below) 118 113. The First and Second Ribs (Colored), 119 114. The Vertebral Ends of Tenth, Eleventh, and Twelfth Ribs 120 115. Rib at Puberty, 121 116. The Thorax at the Eighth Month (Colored) 123 117. The Sternum (anterior view) (Colored) 124 118. The Sternum (posterior view) (Colored) ........ 125 119. Two Stages in the Formation of the Cartilaginous Sternum, . After Ruge, 126 120. The Thorax (front view), . . . . . . . . . . .128 121. The Left Clavicle (superior surface) (Colored), 129 122. The Left Clavicle (inferior surface) (Colored), ....... 129 123. The Left Scapula (dorsal surface) (Colored) 131 124. The Left Scapula (ventral surface) (Colored), 132 125. Ossification of the Scapula, 134 126. The Left Humerus (anterior view) (Colored), 136 127. The Left Humerus (posterior view) (Colored), 137 128. The Left Humerus with a Supracondyloid Process and some Irregular Muscle attachments (anterior view) (Colored), 138 129. Ossification of the Humerus, 139 130. The Head of the Humerus at the Sixth Year(in section), 140 131. The Upper End of the Left Ulna (outer view) (Colored), ..... 141 132. The Left Ulna and Radius (antero-internal view) (Colored), . . . .142 133. The Left Ulna and Radius (postero-external view) (Colored), .... 143 134. The Articular Facets on the Lower End of Left Radius and Ulna, . . . 145 135. Posterior View of the Lower End of the Radius and Ulna, . . . .145 136. Ossification of the Radius and Ulna, 146 137. The Left Hand (dorsal surface) (Colored), ....... 148 138. The Left Hand (palmar surface) (Colored), ....... 149 139. The Left Scaphoid, 150 140. The Left Semilunar, . . . . . . . . . . . .150 141. The Left Cuneiform, 150 142. The Left Pisiform, . . . . . . . . . . . .150 143. The Left Trapezium,. . . . . . . . . . . • I5I 144. The Left Tfapezoid, . . . . . . . . . . . 151 145. The Left Magnum, ............. I51 146. The Left Unciform, . . . . . . . . . . . • I52 147. The First (Left) Metacarpal 153 xviii LIST OF ILLUSTRATIONS. FIG. PAGE 148. The Second (Left) Metacarpal, . . . . . . . . . 153 149. The Third (Left) Metacarpal, . . . . . . . . . . 154 150. The Fourth (Left) Metacarpal, . . . . . . . . . 155 151. The Fifth (Left) Metacarpal, .......... 155 152. The Phalanges of the Third Digit of the Hand (dorsal view), . . . .156 153. Ossification of the Metacarpals and Phalanges, . . . . . . 157 154. The Left Hip-Bone (internal surface) {Colored) 159 155. The Left Hip-Bone (posterior view) (Colored) 160 156. An Immature Innominate Bone, showing a Cotyloid Bone, . . . .161 157. The Pelvis of a Foetus at Birth, to show the three portions of the Innominate Bones, . . . . . . . . 163 158. Hip-Bone, showing Secondary Centres, ........ 163 159. The Pelvis (Male), ............ 164 160. The Left Femur (anterior view) (Colored), . . . . . . .166 161. The Left Femur (posterior view) (Colored), . . . . . . .167 162. The Femur at Birth, ............ 169 163. The Left Femur at the Twentieth Year (posterior view), 170 164. The Left Patella, . . . . . . . . . . . 171 165. The Left Tibia and Fibula (anterior view) (Colored), 173 166. The Left Tibia and Fibula (posterior view) {Colored), 174 167. The Tibia and Fibula at the Sixteenth Year, , . 175 168. The Left Foot (dorsal surface) {Colored), ........ 179 169. The Left Foot (plantar surface) (Colored), . . . . . . .180 170. The Left Astragalus (plantar view), . . . . . . . . .181 171. An Astragalus with the Os Trigonum 181 172. The Left Calcaneum (dorsal view), 183 173. The Calcaneum at the Fifteenth Year, showing the Epiphysis,. . . . 183 174. The Left Cuboid (inner view), 184 175. The Left Cuboid (inner view), 184 176. The Left Scaphoid (anterior view), 185 177. The Left Scaphoid, showing a Facet for the Cuboid, 185 178. The Left Internal Cuneiform (internal surface), . . . . . .186 179. The Left Internal Cuneiform (external surface), ...... 186 180. The Left Middle Cuneiform (internal surface), 187 181. The Left Middle Cuneiform (external surface), . . . . . . .187 182. The Left External Cuneiform (internal surface), . . . . . .187 183. The Left External Cuneiform (external surface), ...... 187 184. The First Left Metatarsal, . . . . . . . . . . .188 185. The Second (Left) Metatarsal, 189 186. The Third (Left) Metatarsal, 189 187. The Fourth (Left) Metatarsal, . . . . . . . . . .190 188. The Fifth (Left) Metatarsal, 190 189. The Phalanges of the Middle Toe, . . 192 190. A Longitudinal Section of the Bones of the Lower Limb at Birth, . . . 192 191. The Secondary Ossific Centres of the Foot, 193 192. External View of the Temporo-mandibular Joint, ...... 199 193. Internal View of the Temporo-mandibular Joint, ...... 200 194. Vertical Section through the Condyle of the Jaw to show the two Synovial Sacs and the Interarticular Fibro-Cartilage, . 200 195. Anterior View of the Upper End of the Spine, . 202 196. Vertical Antero-posterior Section of Spinal Column through the Median Line showing Ligaments, 203 197. Horizontal Section through the Lateral Masses of the Atlas and the Top of the Odontoid Process 205 LIST OF ILLUSTRATIONS. XIX FIG. PAGE 198. The Superficial Layer of the Posterior Common Vertebral Ligament has been removed to show its Deep or Short Fibres (These Deep Fibres form the Oc- cipito-cervical Ligament), .......... 206 199. Vertical Transverse Section of the Spinal Column and the Occipital Bone, to show Ligaments, ........... 207 200. Horizontal Section through an Intervertebral Disc and the corresponding Ribs, 209 201. The Anterior Common Ligament of the Spine, the Stellate, and the Superior Costo-transverse Ligaments, . . . . . . . . .210 202. Posterior Common Ligament of the Spine (Thoracic Region), .211 203. Posterior Common Ligament (Lumbar Region), . . . .212 204. Ligamenta Subflava in the Lumbar Region, . . . . . 213 205. The Interspinous and Supraspinous Ligaments in the Lumbar Region, . .215 206. Anterior View of the Pelvis, .......... 217 207. Vertical Antero-posterior Section of the Pelvis, 219 208. Sacro-sciatic Ligaments (Posterior View), 220 209. Ligaments connecting Sacrum and Coccyx posteriorly, ..... 222 210. Anterior View of the Symphysis Pubis (Male), showing the Decussation of the Fibres of the Anterior Ligament, ........ 223 211. Anterior View of the Symphysis Pubis (Female), showing the Greater Width between the Bones, . 224 212. Posterior View of the Symphysis Pubis, showing the Backward Projection of the Symphysial Substance and the Decussation of the Fibres from the In- ferior Pubic Ligament, .......... 224 213. Section of the Symphysis to show the Synovial Cavity, ..... 225 214. The Capsular Ligaments of the Costo-vertebral Joints, ..... 226 215. Showing the Anterior Common Ligament of the Spine, and the Connection of the Ribs with the Vertebrae, 227 216. Horizontal Section through the Intervertebral Disc and Ribs, . . 227 217. The Sternum 230 218. Diagram of Axis of Rib-movement, ..... After Kirkes, 232 219. Posterior View of the Sterno-clavicular Joint, ....... 234 220. Anterior View of Sterno-clavicular Joint, ........ 234 221. Section through Sterno-clavicular Joint, • 235 222. Anterior View of Shoulder, showing also Coraco-clavicular and Coraco-acro- mial Ligaments 237 223. Posterior View of the Shoulder Joint, showing also the Acromio-clavicular Joint and the Proper Ligaments of the Scapula, ..... 239 224. Vertical Section through the Shoulder Joint to show the Gleno-humeral Liga- ment, 240 225. Foetal Shoulder Joint, showing the Gleno-humeral Ligament, and also the Short Head of the Biceps being continuous with the Coraco-acrominal Ligament, ............. 241 226. Outer View of the Shoulder Joint, showing the Coraco-humeral and Trans- verse Humeral Ligaments, 242 227. Biceps Tendon, bifurcating and blending on each side with the Glenoid Fibro- cartilage 243 228. Internal View of the Elbow Joint, ......... 245 229. External View of the Elbow Joint, ......... 246 230. Orbicular Ligament, 248 231. Anterior View of Wrist, ........... 251 232. Posterior View of Wrist, ........... 252 233. Front of Wrist with Anterior Annular Ligament, ...... 253 234. Posterior View of Wrist, with Capsule cut to show Articular Surfaces, . . 256 235. Synovial Membranes of Wrist, Hand, and Fingers, ..... 257 XX LIST OF ILLUSTRATIONS. FIG. PAGE 236. Anterior and Posterior View of Ligaments of the Fingers, . . . . 261 237. Anterior View of the Capsule of the Hip Joint, ...... 264 238. Posterior View of the Capsule of the Hip Joint, ...... 265 239. Section through the Hip Joint, showing the Cotyloid Ligament, Ligamentum Teres, and Retinacula, 266 240. Hip Joint after dividing the Capsular Ligament, and disarticulating the Femur, 267 241. Portions of Ischium and Pubes, showing the Cotyloid Notch and the Ligamen- tum Teres attached outside the Acetabulum, ...... 268 242. Ligamentum Teres, lax in Flexion, 269 243. Ligamentum Teres, very lax in complete Extension, ..... 269 244. Ligamentum Teres, drawn tight in Flexion combined with Rotation outward and Adduction, ............ 270 245. Posterior View of the Knee Joint, . . . . . . . . 272 246. Anterior View of the Internal Ligaments of the Knee Joint, .... 273 247. Structures lying on the Head of the Tibia (Right Knee), .... 274 248. Anterior View of the Knee Joint, showing the Synovial Ligaments, . -275 249. Vertical Section through the Knee Joint in the Antero-posterior Direction, . 277 250. The Lateral Ligaments of the Knee in Flexion and Extension, . . . 278 251. Section of Knee, showing Crucials in Extension, ...... 279 252. Crucial Ligaments in Flexion, .......... 280 253. Inner View of the Ankle and the Tarsus, showing the Groove for the Tendon of the Tibialis Posticus, .......... 283 254. Ligaments seen from the Back of the Ankle Joint, ...... 284 255. External View of the Ligaments of the Foot and Ankle, .... 287 256. View of the Foot fromabove, with the Astragalus removed to show the Inferior and External Calcaneo-scaphoid Ligaments, ...... 291 257. Ligaments of Sole of Foot. Long Plantar, ....... 292 258. Section to show the Synovial Cavities of the Foot, ...... 294 259. Diagram showing Penniform Muscle, the Peroneus Longus ; and Bipenniform, the Tibialis Posticus, ........... 301 260. Diagram illustrating the advantage of Oblique Insertion of Tendons, . . 303 261. Diagram illustrating the advantage of Oblique Insertion of Tendons, . . 304 262. First Layer of Muscles of the Back, . . . . . . . . 306 263. The Levator Anguli Scapulae and Rhomboidei, ...... 308 264. The Pectoralis Major and Deltoid, 312 265. The Subclavius and the Upper Portion of the Serratus Magnus, . . . 314 266. The Pectoralis Minor, Obliquus Internus, Pyramidalis, and Rectus Abdominis, 315 267. Serratus Magnus, . . . - 316 268. Back View of the Scapular Muscles and Triceps, 320 269. Front View of the Scapular Muscles, ........ 322 270. Superficial View of the Front of the Upper Arm, ...... 324 271. Deep View of the Front of the Upper Arm, ....... 325 272. Front of the Forearm: First Layer of Muscles, ...... 331 273. Front of the Forearm : Second Layer of Muscles, ...... 334 274. Diagram of the Great Palmar Bursa, . . . . . . . -335 275. Front of Forearm : Third Layer of Muscles, ....... 337 276. Muscles of the Radial Side of the Back of the Forearm, . . . .341 277. Tendons upon the Dorsum of the Hand, ....... 344 278. The Deep Layer of the Back of the Forearm, 347 279. Diagram of a Vertical Section through the Middle of the Hand, . . . 353 280. The Superficial Muscles of the Palm of the Hand, . . . . -355 281. The Palmar Interossei, . . . . . . . . . . -356 282. The Dorsal Interossei 357 283. The Deeper Muscles of the Palm of the Hand, ...... 359 LIST OF ILLUSTRATIONS. XXI FIG. PAGE 284. The Pronator Quadratus and Deep View of the Palm, ..... 361 285. Obliquus Externus and Fascia Lata, ......... 364 286. Psoas, Iliacus, and Quadratus Lumborum 366 287. Muscles of the Front of the Thigh, ......... 369 288. The External Rotators and the Hamstring Muscles, 375 289. The Deep Muscles of the Front of the Thigh, 378 290. The Deep Muscles of the Back of the Thigh, ....... 379 291. Superficial Muscles of the Back of the Thigh and Leg 390 292. The Deep Muscles of the Back of the Leg, 394 293. First Layer of the Muscles of the Sole, ........ 397 294. Second Latyer of the Muscles of the Sole, ....... 401 295. Third Layer of the Muscles of the Sole, ........ 403 296. Fourth Layer of the Muscles of the Sole, ........ 405 297. The Muscles of the Front of the Leg, 408 298. The Muscles of the Dorsum of the Foot 411 299. The External Intercostals and Levatores Costarum, 415 300. The Intercostal Muscles, ........... 416 301. The Muscles attached to the Back of the Sternum, 418 302. Diaphragm, ............. 420 303. External Oblique and Ilio-tibial Band, 425 304. Transversalis Abdominis and Sheath of Rectus, ...... 429 305. The Third and Fourth Layers of the Muscles of the Back, .... 433 306. The Fifth Layer of the Muscles of the Back, ....... 437 307. The Fifth Layer of the Muscles of the Back, after separating the Outer and Middle Divisions 439 308. The Sixth Layer of the Muscles of the Back 442 309. The Superficial Muscles of the Head and Neck, 448 310. The Tensor Tarsi and Corrugator Supercilii, ....... 452 311. The Deeper Layer of the Muscles of the Face and Neck, .... 457 312. The Temporal Muscle, ........... 463 313. The Pterygoid Muscles 465 314. Anterior and Lateral Cervical Muscles, 467 315. Side View of the Muscles of the Tongue, ....... 475 316. The Muscles of the Front of the Neck, 478 317. Anterior View of the Heart with the Large Arteries and Veins (Colored), . 484 Royal College of Surgeons Museum 318. The Heart, with the Arch of the Aorta, the Pulmonary Artery, the Ductus Arteriosus, and the Vessels concerned in the Foetal Circulation (Colored), , 485 St. Bartholomew's Hospital Museum 319. Diagram of the Relations of the Pulmonary Artery and its Right and Left Branches (Colored), ........... 486 320. Posterior View of Heart and Greater Vessels, {Colored'), ..... 486 Royal College of Surgeons Museum 321. The Arch of the Aorta, with the Pulmonary Artery and Chief Branches of the Aorta (Colored'), .... St. Bartholomew's Hospital Museum 488 322. Scheme of the Relations of the First Portion of the Arch of the Aorta (Colored), 489 323. Scheme of the Relations of the Transverse Portion of the Arch of the Aorta {Colored), ............. 490 324. The Heart and Great Vessels with the Root of the Lungs, seen from behind . 491 {Colored), St. Bartholomew's Hospital Museum 325. Scheme of the Relations of the Third Portion of the Arch of the Aorta {Colored), 492 326. Scheme of the Coronary Arteries {Colored), ....... 494 327. Scheme of the Relations of the Innominate Artery {Colored), .... 496 328. Scheme of the Relations of the Left Common Carotid and Left Subclavian Arteries within the Thorax {Colored), ........ 497 XXII LIST OF ILLUSTRATIONS. PIG. PAGE 329. The Common Carotid, the External and Internal Carotid, and the Subclavian Arteries of the Right Side and their Branches {Colored), .... 499 St. Bartholomew s Hospital Museum 330. The Collateral Circulation after Ligature of the Common Carotid and Subcla- vian Arteries {Colored), 500 331. Scheme of Ascending Pharyngeal Artery {Colored), ..... 503 332. Scheme of Superior Thyroid Artery {Colored), . ...... 504 333. Scheme of the Lingual Artery {Colored), ........ 506 334. Scheme of the Facial Artery {Colored), ........ 508 335. Scheme of Occipital and Posterior Auricular Arteries {Colored), . . . 510 336. Scheme of Internal Maxillary Artery {Colored), . . . • . 514 337. The Middle Meningeal Artery within the Skull {Colored), . . . .516 338. The Internal Carotid Artery, and Deep Branches of the External Carotid Artery {Colored), .... Royal College of Surgeons Museum 519 339. The Ophthalmic Artery and Vein {Colored), ....... 522 340. The Arteries of the Brain {Colored), . St. Bartholomew's Hospital Museum 526 341. The Subclavian Artery {Colored), ......... 529 342. Scheme of the Vertebral Artery {Colored), ....... 531 343. Diagram of the Anastomoses of the Scapular Arteries {Colored), . . . 537 344. Scheme of the Internal Mammary Artery {Colored), ..... 539 345. Scheme of the Superior Intercostal Artery {Colored), ..... 541 346. The Lower Part of the Axillary, the Brachial, and the Radial and Ulnar Arteries {Colored), . . . Royal College of Surgeons Museum 544 347. The Dorsal Scapular Artery ( Colored), Royal College of Surgeons Museum 546 348. The Posterior Circumflex Artery {Colored), ....... 547 St. Bartholomew's Hospital Museum 349. The Anastomoses about the Scapula {Colored), ...... 548 350. The Brachial Artery {Colored), . . Royal College of Surgeons Museum 549 351. The Brachial Artery at the Bend of the Elbow {Colored), .... 550 352. The Arteries of the Forearm, with the Deep Palmar Arch {Colored), . . 554 353. The Back of the Forearm, with the Posterior Interosseous Artery and Branches of the Radial at the Back of the Wrist {Colored), ..... 556 Royal College of Surgeons Museum 354. Anastomoses and Distribution of the Arteries of the Hand {Colored), . . 558 355. The Arteries of the Forearm and the Deep Palmar Arch {Colored), . . 559 356. Diagram of the Relation of the Arteries of the Forearm to the Bones {Colored), 561 357. The Bend of the Elbow {Colored), . St. Bartholomew's Hospital Museum 562 358. The Radial Artery at the Wrist {Colored), Royal College of Surgeotis Museum 564 359. Anastomoses and Distribution of the Arteries of the Hand {Colored), . . 566 360. The Arch of the Aorta, the Thoracic Aorta, and the Abdominal Aorta, with the Superior and Inferior Vena Cava and the Innominate and Azygos Veins {Colored) 567 361. Scheme of the Thoracic Aorta {Colored), ........ 569 362. Scheme of Intercostal Artery {Colored), ........ 572 363. The Abdominal Aorta and its Branches, with the Inferior Vena Cava and its Tributaries {Colored), ........... 574 364. Scheme of the Abdominal Aorta {Colored), ....... 575 365. The Coeliac Artery and its Branches {Colored), ...... 578 366. The Superior Mesenteric Artery and Vein {Colored), ..... 582 367. The Inferior Mesenteric Artery and Vein {Colored), ..... 586 368. Side View of the Pelvis and Upper Third of Thigh, with the External Iliac, Internal Iliac, and Femoral Arteries and their Branches {Colored), . . 590 Si. Bartholomew's Hospital Museum 369. The Gluteal Region with the Gluteal, Sciatic, and Pudic Arteries {Colored), . 592 St. Bartholomew's Hospital Museum LIST OF ILLUSTRATIONS. xxiii FIG. PAGE 370. Scheme of the Ovarian, Uterine, and Vaginal Arteries {Colored), . . . 594 370A. The Arteries of the Perineum {Colored), ....... 598 371. Scheme of the Pudic Artery and its Branches, 599 372. The Femoral Artery in Scarpa’s Triangle {Colored), ..... 603 St. Bartholomew's Hospital Museum 373. To show the Anastomoses of the Arteries of the Lower Extremity {Colored), . 605 After Smith and Walsham 374. Relations of the Popliteal Artery to Bones and Muscles {Colored), . . . 610 375. Side View of the Popliteal Artery {Colored), 611 376. The Anastomoses about the Knee Joint (semi-diagrammatic) {Colored), . . 613 377. The Popliteal, the Posterior Tibial, and the Peroneal Artery {Colored), . . 614 378. The Plantar Arteries {Colored), . St. Bartholomew's Hospital Museum 617 379. The Deep Plantar Arteries {Colored), Royal College of Surgeons Museum 619 380. The Anterior Tibial Artery, Dorsal Artery of the Foot, and Anterior Peroneal Artery, and their Branches {Colored), . . . . . . . .621 381. Diagram of the Distribution and Anastomoses of the Arteries of the Foot {Colored), ............. 623 38ia. The Vena Cava Superior and the Innominate Veins {Colored), . . . 629 St. Bartholomew's Hospital Museum 382. The Superior and Inferior Venae Cavae, the Innominate Veins, and the Azygos Veins {Colored), 631 383. The Coronary Sinus {Colored), . ......... 634 384. The Scheme of the Coronary Veins {Colored), ....... 635 385. The Superficial Veins and Lymphatics of the Scalp, Face, and Neck {Colored), 637 386. The Veins of the Diploe {Colored), . St. Bartholomew's Hospital Museum 643 387. The Venous Sinuses {Colored), . . St. Bartholomew's Hospital Museum 644 388. The Venous Sinuses (longitudinal section) {Colored), ..... 645 389. The Veins of the Orbit {Colored), ......... 650 390. The Spinal Veins {Colored), .......... 654 391. The Abdominal Aorta and Inferior Vena Cava {Colored), .... 657 392. The Veins of the Stomach and Portal Vein {Colored), 660 393. The Superior Mesenteric Vein {Colored), 661 394. The Inferior Mesenteric Vein {Colored), ........ 662 395. The Bend of the Elbow with the Superficial Veins {Colored), .... 666 St. Bartholomew's Hospital Museum 396. Superficial Veins and Lymphatics of the Forearm and Arm {Colored), . . 667 397. The Superficial Veins and Lymphatics of the Lower Limb {Colored), . . 670 398. The Superficial Lymphatics of the Scalp, Face, and'Neck {Colored), . . 675 399. The Superficial Lymphatics of the Upper Limb and Axillary Glands {Colored), 679 400. The Superficial Lymphatics of the Lower Limb {Colored), .... 690 401. Diagrammatic Sagittal Section of a Vertebrate Brain, . . After Huxley 692 402. Diagrammatic Horizontal Section of a Vertebrate Brain,. . After Huxley 693 403. Coronal Section of the Head passing through the Mastoid Process . . . 696 Anatomical Department, Trinity College, Dublin 404. Coronal Section of the Head passing through the Posterior Horns of the Lateral Ventricles, . Anatomical Department, Trinity College, Dublin 697 405. The Cranium opened to show the Falx Cerebri, the Tentorium Cerebelli, and the places where the Cranial Nerves pierce the Dura Mater {Colored), 698 Sappey 406. Coronal Section through the Great Longitudinal Fissure, showing the Meninges, ......... Key and Retzius 699 407. The Cranial Nerves in the Base of the Skull {Colored), ..... 700 408. View of the Base of the Brain, ....... After Beaunis 703 409. The Fissures and Convolutions of the Cerebrum, viewed from above {Colored), 705 410. Lateral View of the Fissures and Convolutions of the Cerebrum {Colored), . 707 XXIV LIST OF ILLUSTRATIONS. FIG. PAGE 411. Convolutions and Fissures on the Mesial and Tentorial Surfaces of the Hemisphere (Colored), . . . . . . . . . . 714 412. Mesial Section of Entire Brain, . ...... After Henle 716 413. A Dissection of the White Matter of the Posterior Part of the Right Cerebral Hemisphere (viewed from the inner side), .... .Schwalbe 717 414. Diagrammatic Coronal Section of the Third and Lateral Ventricles {Colored), 718 From Schwalbe, slightly modified 415. Coronal Section of the Hemispheres, passing through the Anterior Cornua of the Lateral Ventricles, Anatomical Department, Trinity College, Dublin 719 416. Coronal Section of the Head, passing through the Posterior Horns of the Lateral Ventricles, . Anatomical Department, Trinity College, Dublin 721 417. A Dissection of the Descending Cornu of the Lateral Ventricle, with a Sagittal Section through the Basal Ganglia, ........ 722 418. A Dissection showing the Free or Intraventricular Portion of the Caudate Nucleus. The Mesial and Tentorial Surfaces of the Hemisphere are also shown, .... Anatomical Department, Trinity College, Dublin 723 419. Horizontal Section of the Cerebrum, . . After Landois and Stirling 724 420. Horizontal Section of the Cerebral Hemispheres, 727 Anatomical Department, Trinity College, Dublin 421. Coronal Section through the Anterior Part of the Third Ventricle, . . . 729 Anatomical Department, Trinity College, Dub lift 422. Coronal Section through the Middle Commissure of the Third Ventricle, . 730 Schwalbe 423. Coronal Section through the Third Ventricle behind the Middle Commissure 731 Gegenbaur 424. Deep Origin of the Third Nerve, ...... After Krause 733 425. Lateral View of Mesencephalon, Pons, and Medulla, . . Gegenbaur 734 426. Inferior Surface of the Cerebellum, ......... 738 Anatomical Department, Trinity College, Dublin 427. Right Half of the Encephalic Peduncle as seen from the inside of a Median Section, Allen Thomson, after Reichert 740 428. Metencephalon, Mesencephalon, and Thalamencephalon, from the Dorsal Surface, After Obersteiner 742 429. Transverse Section through the Upper Part of the Pons, . . Schwalbe 745 430. Transverse Section of the Pons near the Centre of the Fourth Ventricle, 746 Schwalbe 431. Transverse Section of the Medulla, a little above the Lower Extremity of the Fourth Ventricle, 4 After Krause 747 432. Transverse Section of the Medulla in the Region of the Decussatio Lemnisci 748 Schwalbe 433. Drawing of a Cast of the Head of an Adult Male {Colored), . Cunningham 751 434. Drawing of a Cast of the Head of a Newly-born Male Infant {Colored), 753 Cunningham 435. Transverse Section through the Spinal Cord and its Membranes, . . . 754 After Key and Retzius 436. View of the Membranes of the Spinal Cord, Ellis 755 437. Posterior View of the Medulla Oblongata and of the Spinal Cord, with its Coverings and the Roots of the Nerves, . . Hirschfeld and Leveille 756 438. Anterior and Posterior View of the Spinal Cord, . Modified from Quain 758 439. Sections through different Regions of the Spinal Cord, . After Schwalbe 760 440. Diagram of the Tracts of the Spinal Cord and of the Deep Origins of the Spinal Nerves {Colored), ........... 763 441. Surface Origin of the Cranial Nerves, . After Allen Thompson.— Quain 770 442. Nerves of the Nasal Cavity, .......... 771 443. Deep Origin of the Third Nerve, ...... After Krause 774 LIST OF ILLUSTRATIONS. XXV FIG. PAGE 444. Sections through the Origin of the Fourth Nerve, .... Stilling 775 445. Nerves of the Orbit, from the Outer Side, ....... 778 From Sappey after Hirschfeld and Leveille 446. The Maxillary Nerve, seen from without, ...... Beatmis 780 447. Distribution of the Mandibular Division of the Trigeminal Nerve, . Henle 784 448. Diagrammatic Lateral View of the Origin of the Facial Nerve, . Krause 789 449. Superficial Distribution of the Facial and other Nerves of the Head, 791 After Hirschfeld and Leveille 450. Transverse Section of the Pons, passing through the most Distal of the Striae Medullares, Krause 793 451. Distribution of the Pneumogastric Nerve, viewed from behind, . Krause 797 452. Distribution of the Posterior Primary Divisions of the Spinal Nerves, Henle 807 453. Diagram of the Cervical Plexus 810 454. Superficial Branches of the Cervical Plexus, . After Hirschfeld and Leveille 811 455. Diagram of the Brachial Plexus, . . . . . . . . .814 456. Distribution of Cutaneous Nerves on the Anterior and Posterior Aspects of the Superior Extremity, . ■ . . . . . . . . . .817 457. A Dissection showing the Arrangement of the Nerves in front of the Elbow 818 ('Colored), . . . Anatomical Department, Trinity College, Dublin 458. Superficial Nerves of the Palm, ........ Ellis 820 459. A Dissection of the Cutaneous Nerves on the Dorsal Aspect of the Hand and Fingers (Colored), H. St. J. Brooks 821 460. Cutaneous Nerves of the Thorax and Abdomen, viewed from the side, . . 824 After Henle 461. Diagram of the Lumbar and Sacral Plexuses, . Modified from Paterson 827 462. Branches of the Lumbar and Sacral Plexuses, viewed from before, . . 828 After Hirschfeld and Leveille 463. Anterior Crural and Obturator Nerves, Ellis 830 464. Distribution of Cutaneous Nerves on the Posterior and Anterior Aspects of the Inferior Extremity, . . . . . . . . . . .831 465. Diagram of the Lumbar and Sacral Plexuses, . Modified from Paterson 835 466. A Dissection of the Lumbar and Sacral Plexuses, from behind, . . . 836 467. A Dissection of the Nerves in the Gluteal Region {Colored), .... 837 468. Distribution of the Musculo-cutaneous and Anterior Tibial Nerves on the Anterior Aspect of the Leg, and on the Dorsum of the Foot, . . . 840 Hirschfeld and Leveille 469. Superficial Nerves in the Sole of the Foot, ..... Ellis 842 470. The Cervical Portion of the Sympathetic, and the Distribution of the Pneumo- gastric Nerve, viewed from behind, ...... Krause ■ 846 471. Lumbar Portion of the Gangliated Cord, with the Solar and Hypogastric Plexuses, ........... Henle 851 472. View of the Eyeball, etc., obtained on drawing the Lids forcibly apart, . . 856 After Merkel, slightly modified 473. Left Fundus Oculi, as seen by direct Ophthalmoscopic Method, After Fuchs 858 474. Diagrammatic View of the Insertions of the Ocular Muscles, After Merkel 859 475. Equatorial Section of Eyeball: Anterior Segment viewed from behind, . . 860 After Merkel 476. Diagrammatic Horizontal Section of Eyeball and Orbit {Colored). . . 863 After Fuchs, much modified 477. Semi-diagrammatic Horizontal Section through Eyeball and Optic Nerve, . 865 After Elfinger, reduced and altered 478. Diagrammatic Representation of the Blood-vessels of the Eyeball {Colored), 866 Leber 479. Surface of Choroid and Iris exposed by removal of Sclerotic and Cornea, showing Distribution of Blood-vessels and Nerves {Colored), After Zinn 867 XXVI LIST OF ILLUSTRATIONS. FIG. PAGE 480. The Lymphatics of the Eyeball (Colored), . Diagrammatic, after Fuchs 868 481. Left Eyeball seen in its Normal Position in the Orbit, with View of the Ocular Muscles, After Merkel, modified 869 482. Section through Contents of Right Orbit, 8-11 mm. behind the Eyeball, viewed from behind {Colored), ...... After Lange 871 483. Diagrammatic Representation of Origins of Ocular Muscles at the Apex of the Right Orbit, ..... After Schwalbe, slightly altered 872 484. View of Left Orbit from above, showing the Ocular Muscles, .... 873 From Hirschfeld and Leveille 485. Vertical Section through the Eyeball and Orbit in the direction of the Orbital Axis, with closed Eyelids (Colored), ........ 874 Semi-diagrammatic, after Schwalbe, modified to show fascice 486. Horizontal Section through Left Orbit, viewed from above, . . . .875 After Von Gerlach, to show check ligaments, etc. 487. Transverse Section through Optic Nerve, showing the Relations of its Sheaths and Connective-tissue Framework, 877 488. Longitudinal Section through Termination of Optic Nerve, .... 877 489. The Blood-vessels of the Left Orbit, viewed from above {Colored), . . 878 490. Section through Contents of Right Orbit, 1-2 mm. in front of the Optic Foramen, viewed from behind {Colored), .... After Lange 879 491. Vertical Transverse Section through Upper Eyelid, After Waldeyer and Fuchs 882 492. Lachrymal Apparatus, ....... After Schwalbe 884 493. External View of the Left Auricle, ......... 886 494. Section through the Orifice of the Right External Auditory Meatus, . . 887 495. External and Internal Surface of the Cartilage of the Right Pinna and its Muscles, etc., 888 496. Section of the Middle and External Ear, ....... 889 497. External View of the Left Membrana Tympani, . . . . . . 890 498. Internal View of the Right Membrana Tympani, ...... 891 499. Section of the Tympanum, etc., 893 500. Osseous Labyrinth of the Right Side, . Modified from Soemmerring, enlarged 895 501. Interior of the Osseous Labyrinth of the Left Side, ...... 896 Modified from Soemmering, enlarged 502. Interior of the Osseous Cochlea, 896 503. Section of the Osseous Cochlea, ......... 897 504. Membranous Labyrinth (magnified), with Nerves, Modified from Bresch'et 898 505. Enlarged Diagrammatic View of Membranous Labyrinth, .... 898 506. Enlarged View of Longitudinal Section of the First Turn of the Cochlea, showing the Positions and Boundaries of the Three Scalae, . . . 899 507. Dorsum of the Tongue, . . . . . . . . . . 901 508. The Foetal Tongue, ............ 902 509. Under Surface of the Tongue with Muscles, ....... 902 510. Transverse Section through the Left Half of the Tongue (magnified), . . 903 Middlesex Hospital Museum 511. Side View of the Tongue, with its Muscles, ....... 903 512. Side View of the Nose, showing its Cartilages, etc., ..... 905 513. Anterior View of the Nose, showing its Cartilages, etc 906 514. Under View of the Nose, showing its Cartilages, etc 907 515. Section showing Bony and Cartilaginous Septum, 908 516. Muscles of the Nose, ....... After Bourgery 909 517. Oblique Section passing through the Nasal Fossae, just in front of the Posterior Nares, seen from behind, .......... 910 518. Section of the Nose, showing the Turbinal Bones and Meatuses, with the Open- ings in dotted outline, 911 LIST OF ILLUSTRATIONS. xxvii FIG PAGE 519. Transverse Section passing through the Nasal Fossae and Antra at the posterior extremity of the Middle Turbinal Bone, 911 520. Nerves of the Nasal Cavity, . . . . . . . . . .912 521. Anterior View of the Thorax, with Outlines of the Diaphragm and Lungs, . 915 522. Superior View of a Section of the Thorax, passing through the Sternum immediately below the First Costo-sternal Articulation, through the Trachea at its Division, and through Body of the Fourth Thoracic Vertebra, Braune 916 523. Front View of the Cartilages of the Larynx, Modified from Bourgery and Jacob 918 524. Side View of the Cartilages of the Larynx {Colored}, ..... 919 Modified from Bourgery and Jacob 525. Front View of the Cricoid and Arytenoid Cartilages {Colored), . . . 921 Modified from Bourgery and Jacob 526. Back View of the Cricoid and Arytenoid Cartilages {Colored), . . .921 Modified from Bourgery and Jacob 527. Superior View of the Cartilages of the Larynx, 922 528. Side View of the Muscles and Ligaments of the Larynx, .... 923 529. Scheme of the Rima, showing Action of Crico-arytenoideus Posticus {Colored), 924 Modified from Stirling 530. Posterior View of Thyroid Cartilage, with Epiglottis, ..... 925 531. Scheme showing Action of Thyro-Arytenoid {Colored), ..... 925 532. Scheme showing Action of Arytenoideus {Colored), ..... 926 533. View of the Interior of Larynx as seen during Inspiration, .... 927 534. View of the Interior of the Larynx as seen during Vocalization, . . . 927 535. Nerves of the Larynx (posterior view), ........ 928 536. Anterior View of Larynx, with Trachea and Bronchi, Modified from Bourgery 930 537. View of the Thyroid Body, .......... 932 538. Thyroid Body, with Middle Lobe and Levator Muscle, 933 539. The Suspensory Ligaments of the Thyroid Body, . . . After Berry 933 540. Thymus Gland in a Child at Birth, 934 541. Thymus Gland in a Child at the Age of Two Years, ..... 935 542. Anterior View of the Foetal Fleart, Vessels, and Lungs, ..... 937 543. Anterior View of the Thorax, with Chest Wall removed, showing the Lungs, 937 Modified from Bourgery 544. Posterior View of the Thorax, with Chest Wall removed, showing the Lungs, 938 Modified from Bourgery 545. Anterior View of the Lungs: Pericardium, . . Modified from Bourgery 939 546. Anterior View of the Heart, with the Larger Vessels {Colored), . . . 943 Royal College of Surgeons Museum 547. Showing the Position of the Heart and its Valves in Relation to the Chest Walls {Colored), . . . Reduced from Hensman and Fisher 944 548. Transverse Section passing through the Auricles of the Heart, showing the Auriculo-ventricular Orifices and the Semilunar Valves of the Pulmonary Artery and Aorta (seen from above), . . . . . . . -945 549. Anterior View of the Right Chambers of the Heart, with the Great Vessels, . 946 550. Transverse Section through the Heart, near its Apex, showing the relative thickness of its Muscular Walls, the bulging of the Septum toward the Right Ventricle, and the shape of the Cavities, ..... 947 551. Interior View of the Aortic Semilunar Valves, ...... 948 552. View of the Auricular Cavities from below (the Transverse Section passing above their middle), ........... 948 553. Posterior View of the Left Chambers of the Heart, with the Great Vessels and the Coronary Sinus laid open, ......... 949 554. Showing the Position of the Heart and its Valves to the Chest Wall {Colored), 951 Reduced from Hensman and Fisher 555. Anterior View of the Heart, showing its Arteries and Veins {Colored), . . 952 xxviii LIST OF ILLUSTRATIONS. FIG. PAGE 556. Posterior View of the Heart, showing its Arteries and Veins (Colored), . . 953 557. Anterior View of a Foetus. The Heart, Vessels, and Chief Organs displayed, with the Placenta and Umbilical Cord (Colored) 954 558. Anterior View of the Heart and Great Vessels of Foetus, the Anterior Chest Wall being removed and the Heart Sac opened, ..... 956 559. The Salivary Glands, ........... 962 560. Section showing the Posterior Wall of the Pharynx, with the Pharyngeal Bursa, Fauces, etc., . . . . . . . . . . . 965 561. Transverse Section of the Peritoneal Sac at about the Level of the Umbilicus, 968 562. Transverse Section of the Abdomen at the Level of the Foramen of Winslow, 969 563. Diagram to show the Peritoneum, as seen in a Vertical Section, Allen Thomson 970 564. Diagram to show the Peritoneum, as seen in Vertical Section, Allen Thomson 972 565. The Viscera, as seen on fully opening the Abdomen, without Disarrangement of the Internal Parts, ....... After Sarazin 974 566. Posterior Surface of the Stomach, . . . . . . . . -975 567. Anterior Surface of the Stomach, 975 568. Muscular Coat of the Stomach, ....... Luschka 977 569. Muscular Coat of the Stomach, ....... Luschka 977 570. The Duodenum, from the front, ......... 979 571. The Duodenum, from behind, .......... 979 572. The Fossa Duodeno-jejunalis, ........ Treves 980 573. Portion of the Small Intestine, laid open, to show the Valvulae Conniventes, . 982 Brin ton 574. Vessels of the Small Intestine, .......... 983 575. The Four Types of Caecum Treves 984 576. Section of the Ascending Colon, ..... Allen Tkomson 986 577. View of the Deeper Abdominal Viscera, Riidinger 988 578. The Viscera of the Foetus, ........ Riidinger 991 579. Superior Surface of the Liver, .......... 992 580. The Inferior Surface of the Liver 993 581. Posterior Surface of the Liver, .......... 994 582. Relation of the Abdominal Viscera to the Parietes, .... Treves 995 583. Relation of the Abdominal Viscera to the Parietes, .... Treves 996 584. Relation of Structures at and below the Transverse Fissure, . . Thane 998 585. Structure of a Portal Canal, ........ Quain 999 586. Abdominal Viscera, from behind, ....... Riidinger 1000 587. The Pancreas and its Duct, 1002 588. Outer Aspect of the Spleen, . . . . . . . . . . 1003 589. Inner Aspect of the Spleen 1004 590. Transverse Section of the Body at the Lower Part of the Epigastric Region 1004 Riidinger 591. View of the Spleen, etc., from behind Riidinger 1005 592. Diagram of the Primitive Alimentary Canal 1008 593. Diagram of the Primitive Alimentary Canal, ....... 1008 594. Alimentary Canal of Salamandra maculosa, ....... 1009 595. Alimentary Canal of Salamandra maculosa, ....... 1010 596. Alimentary Canal of Cholceptis Hoffmanni, 1011 597. Diagram to show the Rotation of the Intestinal Canal 1012 598. Diagram to show the Relation of the Peritoneum to the Duodenum, . . 1013 599. Diagram to show the Lines along which the Peritoneum leaves the Wall of the Abdomen to invest the Viscera, . . . . . Cunningham 1015 600. Diagram to show the Formation of the Great Omentum, 1016 601. Great Omentum in Macropus penicillatus, ....... 1016 602. Formation of Great Omentum, as seen in Vertical Section, .... 1017 603. Relation of Great Omentum to Transverse Colon, ...... 1017 LIST OF ILLUSTRATIONS. XXIX FIG. PAGE 604. Transverse Section of the Abdomen at the Level of the Foramen of Winslow, 1018 605. Intestine of Macropus penicillatus, ......... 1018 606. Duodenal Fold of Macropus penicillatus, ....... 1019 607. Postero-internal Aspect of Left Kidney, ........ 1020 608. Diagram showing Relation of Kidney to Capsule, ...... 1021 609. Section of Kidney, showing the Sinus, . . ... . After Henle 1022 610. Diagram of Relations of the Posterior Surface of the Kidney, . . . 1022 611. The Abdominal Viscera, seen from behind, . . From the model of His 1023 612. Diagram showing Anterior Relations of Kidneys and Suprarenal Bodies, . 1024 613. Horizontal Section of Kidney, showing the Sinus, ...... 1026 614. Scheme of Tubules and Vessels of the Kidney, . . After Macalister 1027 615. Diagram showing Relations of the Kidneys and Suprarenal Bodies, . . 1029 616. Upper Portion of Duct, ........ After Henle 1030 617. Median Sagittal Section of the Male Pelvis, St. Thomas's Hospital Museum 1032 618. The Posterior Wall of the Bladder, ...... After Henle 1034 619. Section of the Female Pelvis, After Henle 1035 620. Semi-diagrammatic Section of the Male Pelvis, ...... 1037 621. Horizontal Section of the Scrotum and Testicle (diagrammatic), . . . 1039 622. The Left Testicle, with Vessels and Duct, .... After Sappey 1040 623. Diagram of the Testicular Tubules, ......... 1042 624. Vasa Deferentia and Vesiculse Seminales, .... After Sappey 1043 625. Vas Deferens and Vesicula Seminalis dissected, . . . After Sappey 1044 626. Section of the Spermatic Cord, After Henle 1046 627. Transverse Section through the Body of the Penis, 1047 628. Transverse Section of the Penis through the base of the Gians, . . . 1047 629. The Male Perineum, . . . Modified from Hirschfeld and Leveille 1048 630. The Male Urethra, cleft dorsally to show Ventral Mucous Wall, . . . 1051 631. The External Genitals of the Female, After Sappey 1053 632. Diagrammatic Representation of the Perineal Structures in the Female, . 1054 633. Section of the Female Pelvis, After Henle 1055 634. Horizontal Section of Vagina and adjacent Structures, . . After Henle 1057 635. The Female Organs of Generation, .... Modified from Sappey 1059 636. The Posterior Surface of the Uterus, ..... After Sappey 1059 637. Frontal Section of the Virgin Uterus, After Sappey 1060 638. Sagittal Section of the Virgin Uterus, ..... After Sappey 1060 639. The Broad Ligament and its Contents, seen from the Front, . After Sappey 1062 640. Diagrammatic Section of the Broad Ligament, . . . ... 1063 641. Section of the Pelvis showing the Ligaments of the Uterus, . ... . 1064 642. The Broad Ligament and its Contents, seen from the Front, . After Sappey 1066 643. Diagram of the Arteries and Lymphatics of the Female Generative Organs, . 1068 644. Diagram of the Primitive Genito-urinary Organs before Differentiation of Sex, 1069 After Henle 645. Development of the Urino-generative Organs, Female Type, After Henle 1070 646. Development of the Urino-generative Organs, Male Type, . After Henle 1071 647. The Male Perineum, . . . Modified from Hirschfeld and Leveille 1073 648. Diagram of the Pelvic Fascia, ,. . . 1075 649. Muscles of the Floor of the Pelvis, 1076 650. Diagram showing Lines of Attachment of the Fasciae and Muscles of the Pelvis 1077 651. Muscles of the Floor of the Pelvis, ......... 1078 652. Sagittal Section through the Perineal Ledge and Ischio-rectal Fossa to the . left of the Middle Line (diagrammatic), 1078 653. Section showing the Ischio-rectal Fossa in its relations to the Pelvic Viscera, . 1079 654. Diagram of the Superficial and Deep Triangular Ligaments, .... 1080 655. Vertical Frontal Section of the Pelvis, showing Fasciae, Modified from Braune 1081 656. Diagrammatic Representation of the Perineal Structures in the Female, . 1083 XXX LIST OF ILLUSTRATIONS. PIG. PAGE 657. The Female Mamma during Lactation, .... After Luschka 1085 658. Development of the Mamma of the Female Embryo, . . After Langer 1086 659. The Skull in Sagittal Section (Colored), ........ 1089 660. The Cranium at Birth (Colored), ......... 1089 661. The Skull (norma lateralis) (Colored'), ........ 1090 662. Drawing of a Cast of the Head of an Adult Male (Colored ), Cunningham 1091 663. Section through the Scalp, Skull, and Dura Mater, .... Tillaux 1092 664. The Course of the Occipital Artery {Colored), ....... 1094 665. Scheme of the Facial Artery {Colored'), ........ 1095 666. Vertical Transverse Section through Upper Eyelid, After Waldeyer and Fuchs 1096 667. The Lachrymal Apparatus and Nasal Duct, ..... Bellamy 1097 668. Side of the Face and Mouth Cavity, showing the three Salivary Glands (Colored) 1098 669. Section of the Skull and Brain in the Median Plane, . . . Braune 1099 670. Section of the Nose, showing the Turbinal Bones and Meatuses, with the Openings in dotted outline, 1100 671. Section showing Bony and Cartilaginous Septum, . . . . . . 1100 672. Thymus Gland in a Child at Birth, ......... 1102 673. Anterior and Lateral Cervical Muscles, ........ 1103 674. The Internal Carotid Artery, and Deep Branches of the External Carotid Artery {Colored) Royal College of Surgeons Museum 1104 675. The Common Carotid, the External and Internal Carotid, and the Subcla- vian Arteries of the Right Side and their Branches {Colored}, . . . 1105 St. Bartholomew's Hospital Museum 676. The Subclavian Vessels {Colored), . Royal College of Surgeons Museum 1106 677. Region of the Third Part of the Subclavian Artery {Colored), . . Bellamy 1107 678. The Collateral Circulation after Ligature of the Common Carotid and Subcla- vian Arteries {Colored), 1108 679. Diagram of the Layers of the Deep Cervical Fascia in an Antero-posterior Section opposite to the Sternum Tillaux 1109 680. Diagram of the Arrangement of the Deep Cervical Fascia, the section passing through the Clavicle, Tillaux 1109 681. Section of Neck through the Sixth Cervical Vertebra, . . . Braune mo 682. The Arch of the Aorta, with the Pulmonary Artery and Chief Branches of the Aorta (Colored), .... St. Bartholomew's Hospital Museum 1112 683. Section of the Sixth Left Intercostal Space, at the Junction of the Anterior and Posterior Thirds, Tillaux 1113 684. Anterior View of the Lungs : Pericardium, . . Modified from Bourgery 1114 685. Outline of the Heart, its Valves, and the Lungs (shaded), . . Holdeti 1115 686. Diagram of the Relations of the Thoracic Viscera to the Walls of the Chest 1116 Bellamy 687. Anterior View of Foetal Heart, Vessels, and Lungs, . . . . .1117 688. The Obliquus Externus and Fascia Lata, . . . . . . .1119 689. The Pectoralis Minor, Obliquus Internus, Pyramidalis, and Rectus Abdominis 1120 690. The Viscera as seen on fully opening the Abdomen without Disarrangement of the Internal Parts, ........ AfterSarazin 1122 69x. Section of Abdomen between the Third and Fourth Lumbar Vertebras, Braune 1123 692. Diagram showing Relation of Kidney to Capsule 1123 693. Transverse Section of the Abdomen through the Kidneys and Pancreas, at the level of the First Lumbar Vertebra, ..... Braune 1124 694. The Abdominal Aorta and Inferior Vena Cava {Colored), .... 1125 695. The Male Perineum, . . . Modified from Hirschfeld and Leveille 1127 696. The Male Perineum, ......... Roser 1128 697. The Arteries of the Perineum {Colored'), ........ 1129 698. Sagittal Section of the Male Pelvis in the Mesial Line, . . . Braune 1130 LIST OF ILLUSTRATIONS. xxxi FIG. PAGE 699. Section showing the Ischio-rectal Fossa in its Relations to the Pelvic Viscera 1130 700. Scheme of the Pudic Artery and its Branches, . . . . . . .1131 701. The Muscles attached to the Pubes, . Royal College of Surgeons Museum 1131 702. Diagram of the Pelvic Fascia 1132 703. External Genitals of the Virgin,with Diaphragmatic Hymen, . After Sappey 1133 704. Diagrammatic Representation of the Perineal Structures in the Female, . 1133 705. Section of the Female Pelvis, After Henle 1134 706. The Parts concerned in Inguinal Hernia, Royal College of Surgeons Museum 1136 707. Dissection of the Lower Part of the Abdominal Wall from within, the Perito- neum having been removed, ....... Wood 1138 708. Vertical Section of Pelvis, through the Heads of the Thigh Bones, . Blandin 1139 709. Transversalis Abdominis and Sheath of Rectus 1140 710. Superficial Dissection of the Inguinal and Femoral Regions, . . Wood 1142 711. Section through the Crural Arch and Sheath of the Femoral Vessels, Blandin 1143 712. Irregularities of the Obturator Artery, ..... After Gray 1144 713. The First Layer of the Muscles of the Back 1147 714. The Levator Anguli Scapulae and Rhomboidei, 1148 715. Diagram and Table showing the Approximate Relation to Spinal Nerves of the various Motor, Sensory, and Reflex Functions of the Spinal Cord, 1149 Gowers 716. Chief Arterial Anastomoses of the Scapula, Royal College of Surgeons Museum 1150 717. Arrangement of Lumbar Aponeurosis at Level of Third Lumbar Vertebra, . 1151 718. Relation of the Abdominal Viscera to the Anterior Parietes, . . Treves 1152 719. Relation of the Abdominal Viscera to the Posterior Parietes, . . Treves 1153 720. Abdominal Viscera, seen from behind, ..... . Rudinger 1154 721. The Superior and Inferior Venae Cavae, the Innominate Veins, and the Azygos Veins {Colored), . 1155 722. View of the Spleen, etc., from behind, Riidinger 1156 723. Transverse Section through the Right Shoulder Joint, showing the Structures in contact with it, ......... Braune 1157 724. The Pectoralis Major and Deltoid, . . . . . . . . . 1157 725. Superficial View of the Front of the Upper Arm, ...... 1158 726. The Brachial Artery {Colored), . . . Royal College of Surgeons Museum 1159 727. Section through the Middle of the Right Upper Arm, . . . Heath 1160 728. The Lower Part of the Axillary, the Brachial, and the Radial and Ulnar Arteries {Colored), . . . Royal College of Surgeons Museum 1161 729. Back View of the Scapular Muscles and Triceps, ...... 1162 730. Deep View of the Front of the Upper Arm, ....... 1163 731. Vertical Section of the Elbow, ........ Braune 1164 732. Longitudinal Section of the Elbow Joint, Braune 1165 733. Bend of the Elbow, Blandin 1165 734. The Bend of the Elbow, with the Superficial Veins {Colored), . . . 1166 St. Bartholomew's Hospital Museum 735. The Brachial Artery at the Bend of the Elbow {Colored), .... 1167 736. The Arteries of the Forearm with the Deep Palmar Arch {Colored), . . 1168 737. Front of the Forearm: First Layer of Muscles, ...... 1169 738. Front of the Forearm: Second Layer of Muscles, ...... 1170 739. Section through the Middle of the Right Forearm, .... Heath 1171 740. Superficial Nerves of the Forearm, ......... 1172 741. Distribution of Cutaneous Nerves on the Anterior and Posterior Aspects of the Superior Extremity, ........... 1173 742. Superficial Veins and Lymphatics of the Forearm and Arm {Colored), . . 1174 743. Relation of the Palmar Arches to the Folds of the Palm, . . Tillaux 1175 744. Anastomoses and Distribution of the Arteries of the Hand {Colored), . . 1176 745. The Deep Layer of the Back of the Forearm, ...... 1177 xxxii LIST OF ILL USTRA 7IONS. FIG. PAGE 746. The Superficial Muscles of the Palm of the Hand, 1178 747. Muscles of the Radial Side and the Back of the Forearm, .... 1179 748. The Deeper Muscles of the Palm of the Hand, ...... 1180 749. Section through Region of Wrist, a little above the Joint. Right side, upper half of the section, ......... Tillaux 1181 750. Transverse Section of the Wrist, through the Middle of the Pisiform Bone, . 1181 751. Diagram of the Great Palmar Bursa, .1182 752. Section of Carpus, through Unciform Bone, . . Bellamy after Henle 1183 753. Horizontal Section of the Hand through the Carpo-metacarpal Joints, . . 1183 Bellamy after Henle 754. Tendons upon the Dorsum of the Hand, 1184 755. Diagram of a Vertical Section through the Middle of the Hand, . . . 1185 756. Transverse Section of the Hip Joint and its Relations, . . . Braune 1187 757. Muscles of the Front of the Thigh, 1188 758. Section of the Right Thigh at the Apex of Scarpa’s Triangle, . Heath 1189 759. Superficial Dissection of the Front of the Thigh, . Hirschfeld and Leveille 1190 760. Anterior Crural and Obturator Nerves, ...... Ellis 1191 761. Side View of the Pelvis and Upper Third of Thigh, with the External Iliac, Internal Iliac, and Femoral Arteries and their Branches {Colored'), . . 1192 St. Bartholotnew's Hospital Museum 762. The Deep Muscles of the Front of the Thigh, ....... 1193 763. Superficial Muscles of the Back of the Thigh and Leg 1194 764. Section through the Hip and Gluteal Region, 1195 765. The Gluteal Region, with the Gluteal, Sciatic, and Pudic Arteries (Colored), . 1196 St. Bartholomew's Hospital Museum 766. Deep Dissection of the Gluteal Region, Royal College of Surgeons Museum 1197 767. Horizontal Section of the Knee Joint, ........ 1197 768. The Deep Muscles of the Back of the Thigh, ....... 1199 769. Vertical Section of the Knee Joint in the antero-posterior direction, . . 1200 770. The External Rotators and the Hamstring Muscles, ..... 1201 771. Side View of the Popliteal Artery {Colored), Royal College of Surgeons Museum 1202 772. Deep View of the Popliteal Space, .... Hirschfeld and Leveille 1203 773. The Popliteal, the Posterior Tibial, and the Peroneal Arteries (Colored), . 1204 774. The Anterior Tibial Artery, the Dorsal Artery of the Foot, and Anterior Peroneal Artery, and their Branches (Colored) 1205 775. Relations of the Popliteal Artery to Bones and Muscles (Colored), . . . 1206 776. Section of the Right Leg in the Upper Third, ..... Heath 1207 777. Branches of the External Popliteal Nerve 1208 778. The Muscles of the Front of the Leg, ........ 1210 779. Transverse Section through the Lower Third of the Left Leg, immediately above the Ankle Joint, Braune 1211 780. Relations of Parts behind the Inner Malleolus, .... Heath 1211 781. The Deep Muscles of the Back of the Leg, . 1212 782. Articulations of the Foot, Dorsal Aspect, ...... Bellamy 1215 783. Vertical Section through the Cuneiform and Cuboid Bones, .... 1215 784. Superficial Nerves in the Sole of the Foot, ..... Ellis 1216 785. The Plantar Arteries (Deep) {Colored), Royal College of Surgeons Museum 1217 786. Longitudinal Section of Foot, Braune 1218 787. The Arch in the Ordinary Position of Standing, . Ellis {of Gloucester) 1219 788. The Effect of Muscular Action in throwing up the Arch, Ellis {of Gloucester) 1219 789. Fourth Layer of the Muscles of the Sole, ........ 1220 790. The Superficial Veins and Lymphatics of the Lower Limb {Colored), . . 1221 791. Distribution of Cutaneous Nerves on the Posterior and Anterior Aspects of the Inferior Extremity, ... 1222 ERRATA. Page 26, Fig. 11, for Splenius capitis Scalenus medius (origin) read Splenius colli Scalenus medius (insertion) “ 42, “ 30, for Sterno-mastoid read Middle nuchal line For Middle nuchal line read Sterno-mastoid “ 119, “ 113, insertion of the Serratus posticus superior should be blue, not red “ 142, “ 132, for External lateral ligament read Internal lateral ligament “ 142 and 143, Figs. 132 and 133, at the lower end of the bone substitute Anterior and Posterior radio-carpal ligament for Capsular ligament and Capsule respectively “ 173 and 174, Figs. 165 and 166, substitute Coronary for Capsule at the head of the tibia. At the lower end, substitute Anterior and Posterior ligament of ankle joint for Capsule “ 260, line 1, for the Intercarpal Articulations read the Intermetacarpal Articulations “ 303, “ 7, after elbow, should be inserted : “ it therefore forms a lever of the second order” “ 355. Fig- 280, for Anterior annular ligament read Deep fascia of forearm “ 460, line 4, “ 461, 10 lines from foot, “ 462, line 11, for supramaxillary read supramandibular “ 463, lines 1 and 2, “ 464, line 10, “ 464, “ 43. “ 465, last line, for inferior maxillary nerve read mandibular or third division of the fifth nerve “ 471, lines 16 and 17 from foot, for inferior dental branch of the inferior maxillary read mandibular nerve “ 473, line 2, for inferior dental read mandibular nerve “ 481, “ 3%, for thyroidea read thyroidem “ 509, “ 36, for inferior dental read mandibular nerve “ “ “ 43, for arteria septum narium read arteria septi nasi “ 538, “ 43, for external intercostal membrane read anterior (or external) intercostal membrane “ 567, Fig. 360, The commencement of the left common carotid, and left subclavian arteries should have been colored red. “ 574, “ 363, The cystic artery has been omitted on the red block : its position on the gall bladder is, however, indicated. “ 59°, “ 368, “ 6°3. “ 372> There is an accidental red colored blot at the end of the pointer of Iliacus muscle. This error is corrected on page 1192, where the figure is repeated. “ 611, “ 375, The long or internal saphenous nerve is inadvertently colored blue where seen above the insertion of the Adductor magnus. This error is corrected in the repetition of the figure on page 1202. “ 657, “ 391, The cystic artery has been omitted on the red block : its position on the gall bladder is, however, indicated. “ 7°8, 5 lines from foot, for external orbital gyrus read posterior orbital gyrus “ 762, 14 lines from foot, omit in “ 765, line 16, omit and “ 800, line 5, for pharynx read larynx “ 802, line 11, for concavity read convexity “ 816, line 4 from foot, for posterior cord read outer cord “ 831, line 5, for hip joint read knee joint “ 847, headline, for Ganglion read Ganglia “ 936, line 6, for thyroid body read thymus gland “ “ “ 12, for thyroid gland read thymus gland “ 944 and 951, Figs. 547 and 554, The red and blue valves are not accurately registered ; the blue are slightly too low; the red both too low and too much to the right of the reader. “ 960, line 29, for enervated read innervated “ 1041, “ 42, for one-sixteenth read one-sixtieth Note.—The nerve-supply of the Lumbrical muscles of the foot, and of the External Oblique muscles of the abdo- men, is somewhat differently given in the two sections. See respectively pages 402 and 843 ; and pages 426 and 826. XXXIII SECTION I. OSTEOLOGY. BY J. BLAND SUTTON, F. R. C. S. Eng., Assistant-Surgeon to the Middlesex Hospital, London. THE SKELETON. The skeleton contains 206 distinct bones. They are arranged by anatomists in two sets : the bones of the trunk and the bones of the limbs. The skeleton of the trunk is made up of the skull, which contains 29 bones exclusive of the teeth ; the vertebral column, consisting of 26 separate bones ; 24 ribs, and the sternum. The skeleton of the upper limbs comprises 64 bones; and that of the lower limb including the patella, 62. Several of the skull bones are compound, that is, in the immature skeleton they consist of separate elements which ultimately unite to form a single bone. In order to comprehend the nature of such bones, it is necessary to examine them in the various stages through which they pass in the embryo and child. Thus the student, anxious to convince himself of Man’s place in nature, studies carefully the development and ossification of bones, and compares them with the bones ot other Vertebrata. He then finds that many elements which make a compound bone are osteological units for the Comparative Anatomist. Comparisons of this nature constitute the science of Morphology, one of the most fascinating departments of Biology. It is the duty of the student to follow the descriptions with the actual bones in his hand. He should also remember that many variations occur in the outlines and markings of bones. Hence the various types described and figured represent the average of a large number of bones examined. It is very rare to meet with bones which accurately correspond to the description in every detail. In order to appreciate the morphology of the skeleton, the osteogenesis or mode of development of bones must be studied as well as their topography or position. Some bones arise by ossification in membrane, others in cartilage. In the early embryo, many portions of the skeleton are represented by cartilage which becomes infiltrated by lime salts—calcification. This earthy material is taken up and redeposited in a regular manner—ossification. Portions of the original cartilage persist at the articular ends of bones, and, in young bones, at the epiphysial lines. Long bones increase in length at the epiphysial cartilages, and increase in thickness by ossification of the deeper layers of the investing membrane or periosteum. These processes—intercartilaginous and intermembranous ossification—proceed concurrently in the limb-bones of a young and growing mammal. 17 18 THE SKELETON. There is no bone in the human skeleton which, though pre-formed in carti- lage, is perfected in this tissue. The ossification is completed in membrane. On the other hand, there are numerous instances in the skull, of bones the ossification of which begins in, and is perfected by, the intermembranous method. Ossifi- cation in a few instances commences in membrane, but later invades tracts of cartilage ; occasionally the process begins in perichondrium and remains restricted to it, never invading the underlying cartilage, which gradually disappears as the result of continued pressure exerted upon it by the growing bone. The vomer and nasal bones are the best examples of this mode of development. A Classified List of the Bones to Show their Mode of Development. i. All the limb-bones and those of the vertebral column are pre-formed in cartilage and perfected in membrane, with the exception of the clavicles. These begin in membrane, proceed in cartilage, and are finally perfected in membrane. 2. The Skull. Parietals. Frontal. Squamosals. Maxillae. Malars. Palates. Nasals. Membrane-Bones.. Interparietal portion of occipital. Wormian bones and the epipterics. Tympanies. Mandible (except part near the symphysis). Lachrymals. Vomer. Cartilage Bones. Sphenoid. Petrosals. Mallei. Stapes. Hyoid. Inferior turbinals, Occipital (except interparietal portion). Ethmoid. Incudes. Styloid processes. Symphysial portion of the mandible. Internal pterygoid plate. Many of the skull bones are composite, that is, they consist of two or more elements which remain separate in other vertebrates. To this group belong : — The Occipital, Temporals. Ethmoid. Maxillae. Hyoid. Sphenoid. Frontal. Malars. Mandible. The details of the development and ossification of each bone are added to the description. The limb-bones differ in several important particulars from those of the skull. Some of the long bones have many centres of ossification, but the centres are of very different morphological value to those of the skull. Speaking gen- erally, it is only the primary nuclei that have any especial value for the morphologist. The primary nucleus of a long bone appears before birth. In only three instances does a secondary centre appear before birth; e.g., the condyles of the femur, the head of the tibia, and occasionally in the head of the humerus. Many primary ossific nuclei appear after birth ; for example, those for the carpal bones, the cuneiform and scaphoid bones of the foot, the coracoid, and the third, fourth, and fifth pieces of the sternum. When a bone ossifies from one nucleus only, this nucleus may appear before or after birth. Examples: the astragalus at the seventh month of embryonic life, and the trapezoid at the eighth year. When a bone possesses one or more secondary centres, the primary nucleus, as a rule, appears early. Examples: the femur, humerus, phalanges, and the calcaneum. Secondary centres which remain for a time distinct from the main portion of a bone are termed epiphyses. An epiphysis may arise from a single nucleus, as is the case with the lower end of the femur; or from several, as at the upper end of the humerus. Prominences about the ends of long bones may be capped by RULES OF EPIPHYSES. 19 separate epiphyses, as is the ease at the upper end of the femur. Epiphyses, though of no morphological value, seem to follow certain rules, thus: — 1. Those epiphyses which appear last are the first to unite with the shaft. Exception.—The distal epiphysis of the fibula is visible three years before the proximal, but fuses with the shaft much earlier than it. It should be remembered that the proximal end of the fibula in man and many mammals is vestigial. 2. The epiphysis toward which the nutrient artery is directed unites first with the shaft. Fig. 1.—The Tibia and Fibula in Section, to Show the Epiphyses. •Epiphysis. ■Centre of ossification of epiphysis. ■Epiphysial line. .Shaft oi fibula, •Shaft of tibia in section Epiphysis of tibia, Epiphysis of fibula. 3. When a bone has only one epiphysis, the nutrient artery is directed toward the extremity which has no epiphysis. 4. The centres of ossification appear earliest for those epiphyses which bear the largest relative proportion to the shafts of the bones to which they belong. 5. When an epiphysis ossifies from more than one centre, the various nuclei coalesce before the shaft and epiphysis consolidate. On section the shaft of a foetal long bone is found occupied with red marrow 20 THE SKELETON. lodged in bony cells which do not present any definite arrangement. In an adult, the central portion of the shaft of a long bone is filled with fat, or marrow, held together by a delicate reticulum of connective tissue; the space containing the marrow is the medullary cavity. The expanded ends of the bone contain a net- work of cancellous tissue, the spaces being filled with red marrow. This cancel- Fig. 2.—A Vertebral Centrum in Section to Show the Pressure Curves. lous tissue differs from that of the foetal bone in that it is arranged in a definite manner according to the direction of pressure and tension exerted by muscles. Pressure lines are well shown in the vertebrge. In a vertical section through the centrum of a vertebra the fibres of the cancellous tissue are seen to be arranged vertically and horizontally; the vertical fibres are curved with their concavities directed toward the centre of the bone. The horizontal fibres are slightly curved Fig. 3.—A Diagram to Show the Pres- sure and Tension Curves of the Femur. {After Wagstaffe.) Fig. 4.—A Diagram Showing Pressure and Tension Curves in the Head of the Humerus. {After Wagstaffe.) parallel with the upper and lower surfaces, with their convexities toward the centre of the bone. They are not so defined as the vertical set. (Wagstaffe.) The arrangement of the cancelli in individual bones is a consequence of the mechanical conditions to which the bone is subject. This is well illustrated in the femur. In the upper end of this bone the cancellous tissue is arranged in divergent curves. One set springs from the inner wall and spreads into the greater THE SPINE. 21 trochanter ; a second series of curves crosses this and forms a set of Gothic arches, and is continued into the neck and head; a third set springs from the lower thick wall of the neck and spreads into the upper part of the head, and ends perpen- dicularly in the articular surface mainly along the lines of greatest pressure. A nearly vertical plane of compact tissue projects into the neck of the bone from the inferior cervical tubercle toward the great trochanter. This is placed in the line through which the weight of the body falls, and adds to the stability of the neck of the bone : it is said to be liable to absorption in old age. In the lower end of the bone the vertical and horizontal fibres are so disposed as to form a rectan- gular meshwork. The plan of construction exhibited by the femur is the most complex in the skeleton, but the principles involved are the same in all bones. An interesting disposition of these curves is exhibited in the head of the humerus. The pressure curves radiate in two directions: one set at right angles to the articular surface of the head of the bone ; the other at right angles to the greater tuberosity. The last set, like those in the trochanter, are the result of tension exerted by the muscles attached to these prominences. The shafts of long bones at the time of birth are mainly cylindrical and free from ridges. The majority of the lines and ridges so conspicuous on the shafts of long bones in adults are due to the ossification of muscle-attachments. The more developed the muscles, the larger the ridges become. The surfaces of bones are variously modified by environing conditions. Pressure at the extremities causes enlargement, and movement renders them smooth. The two causes combined produce an articular surface. When rounded and supported upon a constricted portion of bone, an articular surface is termed a head, sometimes a condyle ; when depressed, a glenoid fossa. Blunt, non- articular processes are called tuberosities; smaller ones, tubercles; sharp projections, spines. Slightly elevated ridges of bones are crests ; when narrow and pronounced, lines and borders. A shallow depression is a fossa; when narrow and deep, a groove ; a perforation is usually called a foramen. The majority of terms—such as canal, spine, notch, sulcus, and the like—are so obvious as to render explanation needless. THE SPINE. The spine (vertebral column) consists of thirty-three superimposed bones termed vertebrae. Of these the upper twenty-four remain separate throughout life and form three groups. The first seven are called cervical, the succeeding twelve thoracic (dorsal), and the last five lumbar. In adult life the last nine vertebrae ankylose to form two composite bones named the sacrum and the coccyx. The sacrum is formed by the fusion of five vertebrae from the twenty- fifth to the twenty-ninth inclusive; the four terminal are vestigial, and form the coccyx. In order to gain a general notion of the characters of a vertebra, it is desirable to select a bone from the middle of the thoracic series. A vertebra presents the following parts: The body or centrum is a solid disc of bone slightly concave on its superior and inferior aspects, and wider transversely than antero-posteriorly. The upper and lower surfaces are rough for intervertebral discs, and the margins are slightly lipped. The circumference of the body is, in front, concave vertically, but convex from side to side; posteriorly it is excavated, and presents foramina for the escape of veins from the cancellous tissue. On the sides of the body, at the upper and lower angles, there are four demi-facets; when two vertebrae are superimposed, the adjacent demi-facets form a complete articular facet for the head of a rib. The pedicles are two constricted short piers of bone projecting horizontally backward from the upper angles of the posterior surface. The lower border of 22 THE SKELETON. each pedicle is deeply notched ; hence, when two vertebrae are in position the notches are converted into intervertebral foramina for the transmission of spinal nerves and vessels. The laminae are broad plates of bone continuous with the pedicles; each lamina meets its fellow dorsally to complete the neural arch, and conjointly Fig. 5.—A Thoracic Vertebra. {Side view.) Demi-facet for head of lib Superior articular pro- cess. Facet for tubercle of rib. Transverse process Demi-facet for head of rib. Inferior articular process. Spinous process. form the spinous process. The superior borders of the laminae are rough for the insertion of ligamenta subflava. The anterior surface, in its upper part is smooth where it bounds the neural canal. The lower part is rough for the origin of the ligamenta subflava. This rough surface is continuous with the inferior border of the spinous process. Fig. 6.—A Thoracic Vertebra. Facet for tubercle of rib. Demi-facet for head, of rib. The spinous process projects backward and downward from the confluent laminae. To its upper and lower borders the interspinous ligaments are attached ; its tip is rounded for the supraspinous ligament. It is mainly a muscular process. The articular processes are four in number : two are superior and have the articular facets directed backward with a slight outward tendency ; their anterior THE CERVICAL VERTEBRA. 23 surfaces complete the intervertebral foramina; posteriorly their margins give attachment to capsular ligaments. The inferior articular processes are slightly concave oval facets on the lower and outer angles of the anterior surface of the laminae. They are directed forward and slightly inward. The transverse processes are two in number, and jut outward from the laminae between the superior and inferior articular processes. The tip presents an oval facet for articulation with the tubercle of the rib. When the rib is in situ its neck forms with the process a costo-transverse foramen. The transverse pro- cesses, in addition to supporting the ribs, afford powerful leverage to muscles. THE CERVICAL VERTEBRAE. A typical cervical vertebra (from the third to sixth inclusive) presents the following characters. The centrum is smaller than in other regions of the column, and is of oval shape, the major axis being transverse. The upper surface has its lateral margins raised into prominent lips, whilst the lower surface is somewhat concave, its anterior margin being lipped so as to slightly overlap the anterior surface of the vertebra below. The inferior lateral margins are rounded, and come into relation with the raised edges of the centrum next below. Fig. 7.—A Cervical Verterra. Costal process. Costo-transverse foramen._ Transverse process.- Superior articular process.- Inferior articular process. - Lamina.- Spinous process— The pedicles are directed obliquely outward, and the intervertebral notch is narrower above than below. The laminae are long and narrow. The spinous process is short, and bifid at the extremity. The superior articular processes look backward and upward; the inferior are directed forward and downward. The transverse process presents near its base the costo-transverse foramen for the transmission of the vertebral artery, vein, and a plexus of sympathetic nerves. The process behind the foramen has a shallow groove for the correspond- ing spinal nerve. The extremity of the transverse process is bifid ; each arm is terminated by a tubercle, referred to as anterior and posterior. The costo- transverse foramen is very characteristic of a cervical vertebra. It is bounded posteriorly by the pedicle, externally by the rudimentary transverse process, and anteriorly by a narrow bar of bone springing from the centrum posterior to the neuro-central suture. This thin bar is a vestigial rib, and will be referred to as the costal process. The spinal foramen of all the cervical vertebrae is large, and somewhat triangular in form. Peculiar cervical vertebrae.—The various cervical vertebrae possess dis- tinguishing features. The first, second, and. seventh have characters so different from their fellows as to render them peculiar. 24 THE SKELETON. The Atlas. This vertebra has neither body nor spinous process; it is an irregular ring of bone with two thicker portions, the lateral masses, united anteriorly by a bridge, the anterior arch, which constitutes one-fifth of the entire circumference. This arch presents a tubercle on its anterior face for the anterior vertebral liga- ment and the longus colli muscle ; its posterior surface has a circular facet for the odontoid process of the axis. The upper and lower borders are for ligaments. The lateral masses are united posteriorly by a larger arch of bone, forming Anterior tubercle. Superior articular process. Costal process. Costo-transverse foramen. Transverse pro- cess. Groove for verte- bral artery. Posterior tubercle. Fig. 8.—The First Cervical Vertebra or Atlas. r TUBERCLES for transverse ligament. two-fifths of the circumference. Posteriorly this arch has a tubercle, representing a rudimentary spinous process. The upper and under surfaces of the arch afford attachment to ligaments. At the junction of the arch with the lateral masses there is, on the upper surface, a deep groove which lodges the vertebral artery and the suboccipital (first spinal) nerve. A bridge of bone sometimes converts this into a foramen. A similar, but much shallower, notch is present on the under surface ; this, with the axis, forms an intervertebral foramen for the second nerve. Fig. 9.—The Axis. Odontoid process Facet for atlas. Groove for transverse liga- ment. — Lamina. Superior articular process. Costo-transverse foramen. Body. Costal process. Spine. Inferior articular process. The atlas and axis are peculiar in that the first and second spinal nerves issue behind the articular processes, whereas the remaining spinal nerves emerge in front of the articular facets of the vertebrae. Each lateral mass has, on its upper surface, an elongated, deeply concave articular fossa or cup. These articular cups converge anteriorly. Occasionally each presents two oval facets united by an isthmus. These cups receive the occipital condyles and permit nodding move- ments of the head. The inferior articular processes are circular and almost flat; they are directed downward, with an inclination inward, and rest upon the axis THE AXIS. 25 and permit rotatory movements of the head. Between the upper and lower articular surfaces on the inside of the ring two tubercles exist for the transverse ligament. This ligament divides the space within the ring into an anterior smaller segment for the odontoid process of the axis, and a larger portion—the spinal foramen of other vertebrae—for the spinal cord and its membranes. The transverse processes are large, to serve for the attachment of muscles which help to rotate the head. The costo-transverse foramina are large, but the costal processes are slender. Fig. io.—The Cervical Vertebra. (.Anterior view.) Anterior tubercle of atlas to which the longus colli is inserted. Rectus capitis anticus minor, The upper ob- lique portion of longus colli. This and the three succeed- ing processes give origin to the rectus ca- pitis a n t i c u s major and in- sertion to the scalenus anti- cus. The upper ob- lique portion of longus colli and in- sertion of in- ferior ob- lique por- tion. Origin of vertical portion of the longus colli. It is inserted into the second, third, and fourth vertebrae. The Axis. The Axis is easily recognized by the large rounded odontoid process which surmounts its upper surface. The centrum has a more prominent lip than the other cervical vertebrae, and the interior surface has a median ridge separating two lateral depressions. The odontoid process is an irregularly rounded peg of bone. The anterior surface has an oval facet for the anterior arch of the atlas. Posteriorly it presents a deeply cut smooth groove for the transverse ligament. To the apex a thin, narrow, fibrous band (the suspensory ligament) is attached. On each side of the apex there is an oblique facet for the check ligaments which connect it with the occipital bone. The pedicles are stout and broad; they support the oval, 26 THE SKELETON. upwardly directed, articular surfaces for the atlas. The inferior articular sur- faces do not differ from the cervical type. The transverse are smaller than the costal processes. The spinous process is stout and strong, deeply concave on its under aspect, and affords firm attachment for muscles, especially those which help to rotate the head. Fig. ii.—The Cervical Vertebra. (.Posterior view.) Rectus capitis posticus minor. Rectus capitis lateralis. A Transverse pro- f cess of atlas. —— Levator anguli scapulae (origin). Splenius colli (insertion). Levator anguli scapulae Splenius capitis. Scalenus medius (ori- gin)- Levator anguli scapulae Splenius colli. Scalenus medius. -Complexus. Levator anguli scapulae .Splenius colli (sometimes) Scalenus medius. .Complexus and multi- fidus spinae. Scalenus medius. Scalenus posticus. Complexus and trachelo-mastoid. Multifidus spinae. Scalenus medius. "Scalenus posticus. Complexus and • trachelo-mastoid. Multifidus spinae. Scalenus medius. Scalenus posticus. -Complexus and trachelo-mastoid. Multifidus spinae. (The large surface is for the multifidus spinae.) Multifidus spinae (and to each spinous pro- cess as high as the second). Superior oblique. Inferior oblique, Rectus capitis posticus major. (The pointer crosses the origin of the inferior oblique.)- Semispinalis colli." Cervicalis transversus." Semispinalis colli." Cervicalis transversus.- Cervicalis ascendens. Semispinalis colli - Cervicalis transversus._ Cervicalis ascendens. Cervicalis transversus.r Cervicalis ascendens/ Semispinalis colli.- Levator costae (origin). Accessorius (insertion). Interspinales- Interspinales. Trapezius. Rhomboideus minor. Serratus posticus supe- Splenius. [rior. Complexus. The Seventh Cervical Vertebra. This vertebra has a longer spinous process than any other cervical vertebra,, hence it is sometimes called vertebra prominens. The extremity of this process is not bifid, but has two small lateral tubercles which give attachment to the liga- mentum nuchse. The transverse processes are of large size; the costal processes are very small; and the costo-transverse foramina are the smallest of the series. Very frequently the costal process is segmented off, and constitutes a cervical rib, sometimes of large size. THE THORACIC OR DORSAL VERTEBRA. 27 Occasionally a demi-facet exists on each side of the lower border of the centrum for the head of the first rib. When this demi-facet is present, there is usually a well-developed cervical rib. The cervical vertebrae also exhibit great variation in regard to the extremities of their spinous processes. As a rule among Europeans, the second, third, fourth, and fifth vertebrae possess bifid spines. The sixth and seventh exhibit a tendency to bifurcate, their tips presenting two small lateral tubercles; sometimes the sixth has a bifid spine, and more rarely the seventh presents the same condition. Occasionally all the cervical spines, with the exception of the second, are non- bifid, and even in the axis the bifurcation is not extensive. In the lower races ot men the cervical spines are relatively shorter and more stunted than in Europeans generally, and, as a rule, are simple. The only cervical vertebra which presents a bifid spine in all races is the axis; even this may be non-bifid in the Negro, and occasionally in the European. (Owen, Turner, Cunningham.) The laminae of the lower cervical vertebrae frequently present over the inferior articular processes distinct tubercles from which fasciculi of the multifidus spina muscle arise. They are usually confined to the sixth and seventh vertebrae, but are fairly frequent on the fifth, and are occasionally seen on the fourth. A large number of muscles are attached to the cervical vertebrae. To the atlas:—Rectus capitis anticus minor, rectus capitis posticus minor, rectus capitis lateralis, superior oblique, inferior oblique, longus colli, splenius colli, intertransversales, levator anguli scapulae. To the axis:—Rectus capitis posticus major, inferior oblique, longus colli, splenius colli, intertransversales, interspinales, levator anguli scapulae, transversalis cervicis, the scalenus medius, semispinalis colli, and multifidus spinae. To the seventh :—Trapezius, complexus, serratus posticus superior, splenius, rhomboideus minor, multifidus spinae, semispinalis, eight intertransversales, inter- spinales, levator costae, scalenus posticus, accessorius, scalenus medius, trachelo- mastoid, and the longus colli. THE THORACIC OR DORSAL VERTEBRA. The general characters of the thoracic vertebrae have already been considered in the description of the type vertebra. Their most distinguishing features are the facets on the transverse processes and sides of the bodies for the tubercles and heads of ribs. Peculiar thoracic vertebrae.—Several vertebrae in this series differ from the type form. The exceptional are—the first, ninth, tenth, eleventh, and twelfth. The first has a body resembling a cervical vertebra, the upper surface being concave and lipped laterally; it has two entire facets above for the first pair, and two demi-facets below for the second pair of ribs. The spinous process is thick, strong, almost horizontal, and more prominent than the vertebra prominens. Occasionally the transverse process is perforated near its root. The ninth has demi-facets above, and usually none below ; when the inferior demi-facets are present, this vertebra is not exceptional. The tenth usually has an entire costal facet at its upper border, on each side, but occasionally only demi-facets. It has no lower demi-facets, and the facets on the transverse processes are usually small. The eleventh has a large body resembling a lumbar vertebra. The rib facets are on the pedicles ; they are complete and of large size. The transverse processes are short and have no facets for the tubercles of the eleventh pair of ribs. In many mammals the spines of the anterior vertebra are directed backward, and those of the posterior directed forward ; in the centre of the column there is usually one spine vertical. This is called the anti-clinal vertebra. It is at this point that the thoracic begin to assume the characters of lumbar vertebra. In man, the eleventh thoracic is the anti-clinal vertebra. The twelfth resembles in general characters the eleventh, but may be distin- 28 THE SKELETON. guished from it in having the inferior articular processes convex and turned outward as in the lumbar vertebra. It also resembles a lumbar vertebra by possessing well-marked mammillary and accessory tubercles. These tubercles are occasionally present on the tenth and eleventh vertebrae. Fig. 12.—Peculiar Thoracic Vertebra;. (Modified from Gray.) An entire facet above ; a demi-facet below. In shape the body resem- bles that of a cervical vertebra. Usually a demi - facet above (sometimes it has a demi-facet be- iow). Usually an entire facet above. Occasionally this facet is incomplete. The facet on the trans- verse process is usually small. An entire facet above. None on transverse process, which is small. Sometimes it has a well-marked mammil- lary tubercle. This is the anti-clinal vertebra. An entire facet above; no facet on transverse process. Centrum large. Inferior articular pro- cesses turn outward as in a lumbar vertebra ; it has also a well- marked mammillary process. A peculiarity, more frequent in the thoracic and lumbar than in the cervical and sacral regions of the column, is the existence of a half-vertebra. Such speci- mens have a wedge-shaped half-centrum, to which are attached a lamina, a transverse, superior and inferior articular, and half a spinous process. As a rule, a half-vertebra is ankylosed to the vertebrae above and below. LUMBAR VERTEBRA. 29 The distinguishing features of lumbar vertebrae are their large size; the margins of the centrum are prominent; the pedicles are stout and strong; the inferior intervertebral notches are deep, and the laminae are thick and strong. LUMBAR VERTEBRAE. Fig. 13.—A Lumbar Vertebra. (Side view.) •Superior articular process. Mammillary process, • Transverse process. Accessory process. Inferior articular process.— Fig. 14.—A Lumbar Vertebra, [Showing the compound nature of the transverse process. Upper view.') Accessory pro- cess or tip of the true transverse process. Costal element Costo - trans- verse fora- mina. Mammillary _ process. The superior articular processes have concave facets directed backward and inward, and their posterior borders are surmounted by rounded mammillary processes or tubercles. The inferior articular processes have facets which look THE SKELETON. forward and outward. The transverse processes are long, slender, and each presents near the base, on the posterior aspect, a small accessory tubercle. The spinous processes are thick, broad, and project horizontally backward. The transverse processes of the lumbar vertebrae are more complex than they at first appear. Each is compounded of a transverse and a costal process. The accessory process represents the tip of the partially suppressed transverse process, and the part in front is an undifferentiated rib. Between the transverse and costal elements some large vas- cular foramina are usually present, representing the costo-transverse foramina of other Fig. 15.—Variation in the Fifth Lumbar Vertebra. {After Turner.') Pedicle.. Fissure, Lamina vertebrae. Occasionally the costal element differentiates and becomes a well-developed lumbar rib. A glance at the spine will show that the accessory tubercles are in line with the thoracic transverse processes, and the costal elements are in series with the ribs (see also Fig. 29). The fifth lumbar vertebra has several distinguishing features. The centrum is much thicker in front than behind. The inferior articular processes are widely separated to articulate with the first sacral vertebra. The transverse processes are of large size, and the spinous process is small. Fig. 16.—A Variation in the Fifth Lumbar Vertebra. {After Turner.') ■ Centrum. Fissure. Lamina. I he pedicles of this vertebra are liable to a remarkable deviation from the condi- tions found in other parts of the spine. The peculiarity consists of a complete solution in the continuity of the arch immediately behind the superior articular processes. In such specimens the anterior part consists of the body carrying the pedicles, transverse and superior articular processes; whilst the posterior segment is composed of the laminae, spine, and inferior articular processes. The posterior segment of the ring of this vertebra may even consist of two pieces. There is reason to believe that this abnormality of the fifth lumbar vertebra occurs in five per cent, of all subjects examined. THE SACRUM. Sir William Turner, in his report on the human skeletons in the “ Challenger ” Reports, found seven examples among thirty skeletons examined. The skeletons in which this occurred were : a Malay, an Andamanese, a Chinese, two Bushmen, an Esquimaux, and a Negro. Turner has also seen it in the skeleton of a Sandwich Islander. THE SACRAL AND COCCYGEAL VERTEBRAE. In the adult skeleton, the five vertebrae succeeding the lumbar series are firmly ankylosed to form a single bone, the sacrum ; the components of the sacrum are termed sacral vertebrae. Beyond the fifth sacral, four, and occasionally five, other rudimentary vertebrae to which the adjective coccygeal is applied, are ankylosed in adult life, to form a single piece, the coccyx. In advanced life the coccyx unites with the sacrum. Fig. 17.—The Sacrum and Coccyx. (Anterior view.) lliacus, Pyriformis. -Coccygeus. _Coccygeus. _ Levator ani. THE SACRUM is a large, triangular-shaped bone, firmly wedged between the innominate bones. It forms the posterior boundary of the true pelvic cavity. The sacrum is curved upon itself with the concavity looking forward. The upper end of the curve forms, with the body of the fifth lumbar vertebrae, an anterior projection known as the promontory. The middle portion of the anterior face of the sacrum exhibits four transverse ridges corresponding to the intervertebral spaces. The intervening portions are the bodies of the vertebrae. The upper two sacral vertebrae are almost equal in size to those of the lumbar series, but the three lower rapidly diminish in size from above downward. The ridges terminate laterally in the anterior sacral foramina, four pairs in all, which are the intervertebral foramina of the sacral vertebrae, and transmit the anterior divisions of the first 3 2 THE SKELETON. four sacral nerves. The upper two are also traversed by the lateral sacral arteries. The bone immediately outside the foramina corresponds to the costal processes, and the portion formed by the second, third, and fourth sacral vertebrae gives origin to the pyriformis muscle. The lateral part of the fifth sacral vertebra gives partial insertion to the coccygeus. The posterior surface is strongly convex and rough. The middle line is occu- pied by four tubercles representing the suppressed spinous processes. Of these the first is the largest, the second and third may be confluent, and the fourth is often absent. The bone on each side of the spines is formed by the ankylosed laminae. In the fourth sometimes, but always in the fifth, the laminae fail to meet in the middle line, and this leaves a gap, the hiatus sacralis. lhe median borders of this hiatus are prolonged downward as rounded processes, the sacral cornua, to which the posterior sacro-coccygeal ligaments are attached. External to the laminae is a second series of small prominences: these are the articular processes. The first pair are large for the last lumbar vertebra, the second and third are small, and the fourth and fifth are inconspicuous. Fig. i8.—The Sacrum. {Posterior view.) Articular pro-. cess. Auricular sur- face. Multifidus spinae. Erector spinae. Spinous process. Latissimus dorsi, Articular process. Transverse process. Sacral foramen. Gluteus maximus Hiatus sacralis leading into the sacral canal. Sacral cornu. Notch for fifth sacral nerve. Apex. Immediately external to the articular processes are the posterior sacral foramina, four on each side; they are smaller than the anterior, and give exit to the posterior divisions of the first four sacral nerves. External to the foramina there are five eminences on each side, representing the transverse processes. The first pair are large and conspicuous; the second form part of the articular surface for the ilium ; the third, fourth, and fifth give attachment to ligaments and muscles. The furrow formed by the laminae, and bounded on the median aspect by the spinous, and externally by the articular processes, is known as the sacral groove, and lodges the erector spince. muscle. The upper surface, or base, of the sacrum resembles the corresponding aspect of a lumbar vertebra, and its articular processes have well-marked mammillary tubercles. The conjoint transverse and costal processes form on each side a broad surface, the wing or ala. From its margin the iliacus has a small point of origin. THE COCCYX. 33 The apex is directed downward and forward, and is formed by the inferior aspect of the body of the fifth sacral vertebra; it articulates by means of an inter- vertebral disc with the coccyx. In advanced life the coccyx and sacrum ankylose at this point. The lateral surface presents in the upper two-thirds a broad irregular tract called the auricular process, which is rough and, in the recent state, covered with fibro-cartilage for union with the ilium. The margins are rough for ligaments. Below the auricular surface the lateral borders are sharp and give attachment to the greater and lesser sacro-sciatic ligaments. Near the extremity it presents a notch which is converted into a foramen by articulation with the coccyx. Through the space thus enclosed the anterior branch of the fifth sacral nerve issues. Some- times the foramen is represented by a notch even when the sacrum and coccyx are articulated. The middle of the sacrum is occupied by a continuation of the spinal canal. It is triangular in form at the base and flattened toward the apex. It lodges the terminal branches of the cauda equina, the filum terminale, and the lower extremity of the dura mater. The sacrum exhibits sexual differences. In the female it it usually wider, much less curved, and is directed more obliquely backward than in the male. Muscles.—The following muscles are attached to the sacrum : Pyriformis, coccygeus, iliacus, latissimus dorsi, multifidus spinse, erector spinse, gluteus Fig. 19.—Base of Sacrum. SPINE- Articular pro- cess. Lamina. Sacral canal. maximus; and the occasional muscles, namely, curvator coccygis, extensor coccygis, and the agitator caudse. Ligaments.—Anterior and posterior common ligaments of the spine; an- terior and posterior sacro-coccygeal; greater and lesser sacro-sciatic, anterior and posterior sacro-iliac, two capsular, ligamenta subflava, and the supraspinous. THE COCCYX. The coccyx in the adult is made up of four and occasionally five vestigial verte- brae ankylosed to one another. Rarely the number of segments is reduced to three. The first two segments contain, in addition to the body of a vertebra, traces of articular and transverse processes : the rest are mere nodules of bone, representing centra. The anterior surface gives attachment to the anterior sacro-coccygeal ligament; and near its tip to the levator ani; it is in relation with the lower end of the rectum. The posterior surface is convex, and along its margin affords attachment to the gluteus maximus muscle. The lateral borders are thin : they receive parts of the greater sacro-sciatic ligaments and of the coccygeus muscle. The base has an oval facet for the fifth 34 THE SKELETON. Fig. 20.—The Spine. (Lateral view.) Atlas._ Axis._ Vertebra prominens, The eleventh thoracic is the anti clinal vertebra. THE SPINAL COLUMN. 35 sacral vertebra, and presents the two long coccygeal cornua for the posterior sacro-coccygeal ligament. The junction of the coccyx and sacrum completes the foramen of exit for the fifth sacral nerve. In many skeletons the foramen is incomplete externally. The apex is rounded and gives attachment to the sphincter ani, and in front to the levator ani muscles. THE SPINAL COLUMN IN GENERAL. When the various vertebrae are in their relative positions, the whole is termed the spinal column. It occupies the median line of the posterior aspect of the trunk. Superiorly it supports the head; laterally it gives attachment to ribs; these in their turn receive the weight of the upper limbs. Inferiorly, the sacrum affords attachment to the innominate bones, by which the weight of the trunk is transmitted to the lower limbs. The spinal column is the axis of the skeleton. It varies in length in different persons, but on an average it measures, from the atlas to the tip of the coccyx, following the curve, 70 cm. (28"). Of this the cervical spine measures 12.5 cm. (5"), the thoracic 27.5 cm. (n"), the lumbar 17.5 cm. (7"), and the sacro-coccygeal portion 12.5 cm. (5"). Viewed in profile, the column presents four curves : the first, or cervical, is convex anteriorly; the thoracic is much larger and longer, with its concavity Fig. 21.—A Divided Thoracic Vertebra. (After Turner.) forward ; the lumbar curve has its convexity directed anteriorly, and ends some- what abruptly at the sacro-vertebral angle ; and to this succeeds the pelvic curve, which corresponds to the hollow of the sacrum. In addition to these, the whole column has a slight lateral curve with the convexity to the right, probably due to muscular action. Viewed from the front, the superimposed bodies present three pyramids. The first is formed by the cervical vertebrae from the second to the seventh. The bodies of the lumbar and thoracic vertebrae form a much longer pyramid. The third is inverted, and formed by the sacrum and coccyx. Posteriorly, the column presents a median and two lateral rows of processes. The median row is formed by the spinous processes. In the cervical spine, with the exception of the first and the seventh, they are bifid. In the thoracic set they end in rounded tubercles, are long, and for the most part directed obliquely downward, but in the lower part they become more horizontal until the eleventh is reached. The spine of the eleventh thoracic vertebra is small and almost horizontal; this is the anti-clinal vertebra. In the lumbar region the spinous processes are short, stout plates of bone, with their borders set vertically ; in the sacrum they are vestigial, and in the coccyx completely suppressed. The lateral rows are formed by the transverse processes, which are most marked in the thoracic region, where they are rib-bearers. In the cervical spine they are 36 THE SKELETON. in the same plane as the ribs. The articular processes in the cervical region are in series with the transverse processes of the thoracic vertebrae. Between the ridges formed by the spinous and transverse processes we recognize the vertebral grooves in which muscles are lodged. The floor of each groove ; formed by the laminae and articular processes, with their mammillary tubercles in the lumbar and lower thoracic regions. Similar tubercles are present on the inferior articular processes of the three lower cervical vertebrae. The interverte- bral foramina, oval in shape, are small in the cervical, but gradually increase in size in the thoracic, and are largest in the lumbar region. Ossification.—The various ossific centres for the vertebrae are deposited in Fig. 22.—A Vertebra at Birth. Lateral mass. Neuro-central suture. Centrum or body. the cartilage which, very early in embryonic life, surrounds the notochord and gradually encloses the spinal cord. A typical vertebra arises from three primary and numerous secondary centres. The primary centres appear during the sixth week of embryonic life. In the thoracic region the nucleus for the body is first seen, but in the cervical region the lateral centres make their appearance somewhat earlier. The nucleus for the body is deposited around the centre, and quickly becomes bilobed. This bilobed, or dumb-bell, shape is often so pronounced as to give rise to the appearance of two distinct nuclei. Sometimes the nucleus is double, and remains separate throughout life, the vertebra being divided by a vertical fissure (Fig. 21). The bifid character of the nucleus of the vertebral body is further emphasized by the Fig. 23.—Lumbar Vertebra at the Eighteenth Year, with Secondary Centres. Epiphysial plate or disc. ■Mammillary tubercle. Transverse process. Spinous process. Epiphysial plate or disc. occasional occurrence of half-vertebrse. The lateral centres are deposited near the bases of the superior articular processes, and give rise to the pedicles, laminae, articular processes, and a large part of the transverse and spinous processes. At birth a vertebra consists of three parts—a body and two lateral masses connected by hyaline cartilage. The line of union of the lateral masses with the bodies is known as the neuro-central suture (Fig. 22), and this is not obliterated for several years after birth. An examination of a thoracic vertebra at the fifth year will show that a portion of the body of each vertebra is derived from the lateral masses, and that the demi-facets for the rib-heads are situated behind the neuro-central suture, and therefore belong to the pedicles. During the early years growth progresses rapidly, and at puberty the secondary THE VERTEBRA. 37 centres make their appearance in the cartilaginous tips of the transverse and spi- nous processes. During the seventeenth year a meniscus of bone forms around the margins of the superior and inferior surfaces of the centra. These are the epiphysial discs; they are thickest at the periphery, and gradually become thin Fig. 24.—Immature Atlas. [Thirdyear.) toward the central perforation. By the twenty-fifth year the various secondary nuclei have coalesced with the main bone, and the vertebra is then complete. In several vertebrae the mode of ossification deviates from the account given above, and requires separate consideration. Fig. 25.—Development of the Atlas Suspensory ligament. Nucleus for tip of odontoid process. Lateral centres for odontoid process. Epiphysial plate or disc. Pedicle Centrum or body. Epiphysial plate. The atlas.—This bone has three primary centres—one for each lateral mass (neural arch) appearing in the sixth week of embryonic life. The third appears a few months after birth for the anterior arch. The lateral portions coalesce Fig. 26.—The Axis (from an Adult) in Section. Odontoid process Cartilage representing the intervertebral disc be- tween the odontoid pro- cess and the body of the axis. Body of axis. posteriorly about the third year; the union with the anterior nucleus is delayed until the sixth year. An additional centre occasionally appears for the posterior segment. The axis.—This is the most exceptional of all the vertebrae. It has the usual 38 THE SKELETON. three primary nuclei—one for the body, and one on each side for the neural arch. The centre for the body appears in the embryo about the fifth month, and a few weeks later two laterally disposed nuclei are seen for the base of the odontoid process; these fuse together in the middle line, and by the third year ankylose peripherally to the centrum of the axis. The line of union between the body of the axis and the odontoid process is indicated even in advanced life by a persistent lenticular-shaped cartilage. During the second year a nucleus appears at the tip of the odontoid process. An epiphysial meniscus for the inferior and superior surfaces of the centrum of the axis appears about the seventeenth year. As a rule, the superior meniscus is represented by a few earthy granules. Fig. 27.—An Immature Cervical Vertebra Neuro-central suture. The sixth and seventh vertebrae.—In the cervical vertebrae the pedicles, or anterior extremities of the neural arches, take a much larger share in forming the centrum than is the case with the remaining vertebrae. The sixth, seventh, and possibly other cervical vertebrae present an additional centre on each side of the neural arch for the costal process; it appears before birth. The costal pro- cesses of the seventh cervical not infrequently fail to ankylose with the vertebra; when this is the case, the processes become cervical ribs. Sometimes these ribs are of large size. The lumbar vertebrae.—In the lumbar vertebrae two additional centres make their appearance, about puberty, namely, for the mammillary tubercles on the posterior aspect of each superior articular process. Fig. 28.—Ossification of the Firm Lumbar Vertebra. Lamina. Suture. Pedicle. Neuro-central suture. Centrum. The fifth lumbar occasionally differs in the mode of ossification of its arch ; in many skeletons this arch is derived from four nuclei. There is a nucleus on each side for the pedicle, the transverse process, and the superior articular pro- cess; and one on each side for the lamina, inferior articular process, and the lateral half of the spinous process (Fig. 28). The pedicles may fail to join the laminae; more rarely the laminae fail to fuse (Fig. 16). The sacral vertebrae.—In addition to the three primary vertebral centres, the three upper sacral vertebrae have each an extra pair corresponding to the costal processes of the seventh cervical vertebra. These processes are very large THE VERTEBRA. 39 in the first sacral, smaller in the second, and very small in the third. Although the various primary centres of the sacral vertebrae appear much later than in other regions of the column, yet they are all visible at birth. The centrum of each sacral vertebra develops a superior and inferior epiphysial meniscus, and eventually the five vertebrae fuse to form a single bone, the sacrum. Even in advanced life the intervertebral discs between the sacral vertebrae persist in the centre of the bone. The ear-shaped lateral articular facet on the side of the sacrum arises from two additional centres on each side, about the eighteenth year. The total number of ossific centres for the sacrum is thirty-five. The coccygeal vertebrae.—These are cartilaginous at birth. A few months later the first segment ossifies. The remaining three ossify from above downward before the fifteenth year. By the twentieth year the first three have usually coalesced. The fourth fuses with them later, and the coccyx ankyloses with the sacrum, as a rule, late in life. Although at first sight many of the vertebrae exhibit peculiarities, nevertheless a study of the mode by which they develop, and their variations, indicates the serial homology of the constituent parts of the vertebra in each region of the column. The centrum, or body of the vertebra, is that part which immediately surrounds the notochord. This part is present in all the vertebrae of man, but the centrum of the atlas is dissociated from its neural arch, and ankylosed to the body of the axis. The reasons for regarding the odontoid process as the body of the atlas are these : In the embryo the notochord passes through it on its way to the base of the cranium. Between the odontoid process and the body of the axis there is a swelling of the notochord in the early embryo as in other intervertebral regions. This swelling is later indicated by a small inter- vertebral disc hidden in the bone, but persistent even in old age. The odontoid process arises from primary centres, and in chelonians it remains as a separate ossicle throughout life ; in Ornithorhynchus it remains distinct for a long time, and it has been found sep- arate even in an adult man. Lastly, in man and many mammals, an epiphysial plate develops between it and the true body of the axis. The anterior segment of the atlas is in no sense homologous with a centrum, and is most probably an enlarged hypapophysis or subvertebral wedge-bone, which, in lizards, exists on the ventral aspect of the column between individual centra. Similar ossicles occur in the lumbar region of the mole. The neural arches and spinous processes are easily recognized throughout the various parts of the column in which complete vertebrae are present. The articular processes are of no morphological value, and do not require con- sideration here. The transverse processes offer more difficulty. They present themselves in the simplest form in the thoracic series. Here they articulate with the tubercles of the ribs. The transverse process and the neck of the rib enclose an arterial foramen, the costo- transverse. In the cervical region this rib, or costal element, and the transverse process are fused together, but the conjoint process thus formed is pierced by the costo-transverse foramen. The compound nature of the process is indicated by the fact that the anterior or costal processes in the lower cervical vertebrae arise from additional centres and occasionally retain their independence as cervical ribs. These processes in Sauropsida (birds and reptiles) are represented by free ribs. In the lumbar region the compound nature of the transverse process is further marked. The true transverse process is greatly suppressed, and its extremity is indicated by the accessory tubercle. Anterior to this in the adult vertebra a group of holes represent the costo-transverse foramen, and the portion in front of this is the costal element. Occasionally it will persist as an independent ossicle, the lumbar rib. In the sacral series the costal elements are peculiarly modified in the first three verte- brae to form piers of bone for articulation with the ilium. The costo-transverse foramina are completely obscured. In rare instances the first sacral vertebra will articulate with the ilium on one side, but remain free on the other. Under such conditions the free process exactly resembles the elongated transverse process of a lumbar vertebra. The first three sacral vertebrae which develop a costal process (rib) for articulation with the ilium are true sacral vertebrae. Those ankylosed below these are pseudo-sacral. A glance at Fig. 29 will show the homology of the various parts of a vertebra from the cervical, thoracic, lumbar and sacral regions. The mammillary processes are vestiges of the greatly elongated articular processes of such mammals as the dog, armadillo, etc. The Serial Morphology of the Vertebrce. 40 THE SKELETON. Fig. 29.—Morphology of the Transverse and Articular Processes. Cervical vertebra. Transverse process Costo-transverse foramen Neuro-central suture. Cervical rib. Costal process. Thoracic vertebra. .Transverse process, .Costo-transverse foramen Neuro-central suture. Rib. Lumbar vertebra. Transverse process. Lumbar rib. Sacral vertebra. Neuro-central suture. Costal process. THE OCCIPITAL. 41 THE BONES OF THE SKULL. The skeleton of the head is called the skull: it contains, in the adult, twenty- nine separate bones. For descriptive purposes they are divided in two groups : those of the skull proper, and the appendicular elements. Occipital. Sphenoid. Temporals. I. The Skull. Ethmoid. Sphenoidal tur- binals. Turbinals. Lachrymals. Vomer. Nasals. (a) Basilar Bones Parietals. Frontal. Epipterics. (c) Nasal Region (b) Roof Bones (d) Facial Bones Maxillae. Palatines. Malars. Mandible. Malleus. Incus. Stapes. II. Appendicular Elements. Hyoid. Styloid. Internal pterygoid. The epipierics are not always separate in the adult skull: the styloid ankyloses with the temporal, and the internal pterygoid with the sphenoid. THE OCCIPITAL. This bone forms the back and a portion of the base of the skull. At birth it consists of four distinct parts disposed around the foramen magnum (Fig. 34). These, in the adult, fuse together and form a single bone, which ankyloses with the sphenoid. The four parts of the occipital are—the squamo-occipital, two ex-occipitals, and a basi-occipital. The lines of union of these parts are easily distinguished even in the oldest skull. The squamo-occipital is saucer-shaped deeply concave on its cerebral, but convex on its external aspect. It consists of two parts which have different modes of origin. The posterior surface is divided by a ridge, the superior nuchal line, into a lozenge-shaped superior portion with a smooth surface and an inferior rough portion. The upper is the interparietal, and the lower the supra-occipital segment. The interparietal portion not infrequently persists as an independent ossicle (Fig. 35). The supra-occipital is divided into two lateral halves by a median vertical ridge—the external occipital crest—which ascends from the middle of the posterior margin of the foramen magnum, to terminate at the external occipital protuberance, or inion, near the middle of the squamo-occipital. The pro- tuberance and crest give attachment to the ligamentum nuchse. Each lateral half of the supra-occipital presents three pairs of transverse ridges, the nuchal lines. Of these the superior is usually the least conspicuous, but most curved ; frequently it is absent; beginning at the external occipital pro- tuberance, it curves outward to the lateral angle. It affords attachment to the epicranial aponeurosis and to few fibres of the occipito-frontalis muscle. The middle nuchal line (sometimes called the superior curved line) com- mences a little distance below the protuberance, and curves outward to end below the lateral angle. In some cases the superior and middle nuchal lines are confluent in their outer thirds, and form a prominent ridge for the insertion of the sterno- mastoid and splenius capitis muscles. When these muscles are well-developed, there is a fairly wide interval between the lines. The inferior nuchal line begins near the middle of the crest and curves downward to the jugular process. Of the spaces deliminated by these lines, that between the superior and middle 42 THE SKELETON. is occupied by the trapezius, and frequently by the sterno-mastoid and spletuus capitis muscles. The space between the middle and inferior receives the complexus, and the space between the inferior line and the foramen magnum is occupied by the rectus capitis posticus minor, rectus capitis posticus major, and the superior oblique muscles. The cerebral surface is deeply concave, and divided by crucial ridges into four fossae, of which the upper two accommodate the occipital lobes of the cere- brum, the lower pair the cerebellar hemispheres. The ridges intersect each other, and at the point where they cross an eminence, the internal occipital pro- tuberance, is seen. The vertical ridge runs upward to the superior angle of the bone and furnishes attachment for the falx cerebri; the portion of the ridge below the protuberance, the internal occipital crest, is for the falx cerebelli. As it nears the foramen magnum this ridge divides, becoming lost upon its margins. The angle of divergence is often occupied by a shallow fossa for the extremity of the vermiform process of the cerebellum, and is called the vermiform fossa. The horizontal ridge is deeply grooved ; to the edges of the groove the tentorium Fig. 30.—The Occipital. (External view.) Trapezius. Inion, or external-occipital protuberance. Superior nucha line. Occipito-frontalis Sterno-mastoid Middle nuchal line Rectus cap. post min. Splenius capitis Rectus cap. post maj. Superior oblique Inferior nuchal line. FORAMEN MAGNUM Posterior condy loid foramen. Rectus capiti: lateralis. ICON DYLE Jugular process Basi-occipital. cerebelli is attached, the grooves lodge the greater part of the lateral sinuses. To one side of the internal occipital protuberance, usually the right, the furrow for the sinus is deeper and frequently forms a circular fossa which receives the torcular. This fossa is sometimes exactly in the middle line. The squamo-occipital has three angles and four borders. The superior angle fits into the space formed by the union of the two parietals. The lateral angles mark the external limits of the middle nuchal lines, and occupy the angle formed by the parietal and mastoid portion of the petrosal on each side. The ridge between the superior and lateral angles is the superior border; it is serrated deeply, and articulates with the posterior border of the parietal to form the lambdoid suture. The inferior border extends from the lateral angle to the jugular process ; it articulates with the mastoid portion of the petrosal. The ex-occipitals form the lateral boundaries of the foramen magnum, and extend from the ridge immediately behind the groove for the termination of the lateral sinus to the tubercle in front of the anterior condyloid foramen. The lateral surface of each ex-occipital is extended outward to form a quadrilateral buttress of bone, the jugular process. This has an outer rough surface for articu- THE OCCIPITAL. 43 lation with the jugular surface of the petrosal. Its anterior border is deeply notched to form the posterior boundary of the jugular foramen, and is directly Fig. 31.—Occipital Bone, Cerebral Surface. Superior angle. For superior longi- tudinal sinus and falx cerebri. Cerebral fossa. Groove for lateral sinus. Lateral angle. Cerebellar fossa. Groove for lateral sinus. Jugular process.- For petrosal._ Cut surface of the basi-occipital. Fig. 32.—Cerebral Surface of the Occipital, showing an Occasional Disposition of the Channels. Torcular. Vermiform fossa Posterior condy loid foramen. Anterior condy loid foramen. continuous with a groove which lodges the termination of the lateral sinus. Its undef surface gives attachment to the rectus capitis lateralis and the oblique 44 THE SKELETON. occipito-atlantal ligament. The pneumatic mastoid cells occasionally extend into this process. Rarely a process of bone extends from its under surface and represents the par-occipital process present in many mammals. The rest of the ex occipitals enter into the formation of the condyles, and will be separately described. The basi-occipital is a quadrilateral plate of bone. Its superior surface is concave for the medulla oblongata. Inferiorly it is rough, and presents the pharyngeal tubercle, to which the median portion of the fibrous bag of the pharynx is attached. The rectus capitis anticus major and minor muscles are inserted into this surface. Anteriorly the basi-occipital is, in the adult, ankylosed to the basi-sphenoid. Posteriorly it has a smooth, rounded, narrow, concave border forming the anterior boundary of the foramen magnum. The extremities of this border enlarge to join the ex-occipitals, and form the anterior extremities of the condyles. The lateral borders are rough, and articulate with the inferior border of the petrosals. The foramen magnum is oval in shape, with its major axis in the long axis of the skull. Near the middle it is encroached upon by the condyles. It is bounded posteriorly by the supra-occipital, anteriorly by the basi-occipital, and laterally by the ex-occipitals. Sometimes a facet exists at the anterior margin for Fig. 33.—The Foramen Magnum at the Sixth Year Posterior condyloid foramen. Ex-occipital portion of the condyle. Jugular process Anterior condyloid foramen. Basi-occipital portion of the condyle. Basi-occipital. articulation with the odontoid process. This is the tertiary occipital condyle. The margin of the foramen gives attachment behind the condyles to the posterior occipito-atlantal ligament. The condyles are two oval processes of bone, with smooth articular surfaces, covered in the recent state with cartilage. They are received into the superior articular cups of the atlas. The condyles converge anteriorly but diverge poste- riorly. Their margins give attachment to capsular ligaments, and a prominent tubercle in the middle of the median border of each condyle is for the check liga- ment. A foramen, the anterior condyloid, traverses the upper part of each condyle; it transmits the hypoglossal nerve, and a twig of the ascending pha- ryngeal artery with its venae comites. Frequently the foramen is divided by a delicate spicule of bone. Posterior to each condyle is a depression, the posterior condyloid fossa, which receives the hinder edge of the articular cavity of the atlas when the head is extended ; the floor of this depression is occasionally perforated by the posterior condyloid foramen, which transmits a vein from the lateral sinus. Articulations.—The occipital bone is connected by suture with the two parie- tals, the two temporals, and the sphenoid ; by means of the condyles it articulates with the atlas; and, under the exceptional condition of a tertiary occipital con- dyle, with the odontoid process of the axis. THE OCCIPITAL. 45 Muscles.—Attached to the occipital bone: — Occipitofrontalis. Trapezius. Sterno-cleido-mastoid. Complexus and biventer cervicis. Splenius capitis. Superior oblique. Rectus capitis anticus major. Rectus capitis anticus minor. Rectus capitis posticus major. Rectus capitis posticus minor. Rectus capitis lateralis. Azygos pharyngei (when present). Ligaments :— Ligamentum nuchae. Capsular. Posterior occipito-atlantal. Anterior occipito-atlantal. Oblique occipito-atlantal. Suspensory ligament. Check ligaments. Vertical slip of the crucial. Posterior common ligament of spine. Anterior common ligament of spine. The fibrous bag of the pharynx. Fig. 34.—The Occipital at Birth. {Anterior view.) Interparietal portion (Develops in membrane) The interparietal and supra-occipital por- tions form the squa- mo-occipital of the adult. Supra occipital portion. (Develops in cartilage.) Ex-occipital FORAMEN MAGNUM Basi-occipital Blood-supply.—The occipital bone receives branches from the occipital, posterior auricular, middle meningeal, vertebral, and ascending pharyngeal arteries. Development.—The interparietal portion of the occipital is a membrane bone, and arises by two or more centres about the twelfth week ; these nuclei rapidly become confluent and fuse with the supra-occipital portion about the fifteenth week. Occasionally this fusion fails. The centres for the rest of the bone are deposited in cartilage. The nucleus for the basi-occipital appears in the tenth week, and is quickly followed by a nucleus for each ex-occipital; the supra- occipital ossifies from two laterally disposed nuclei, which quickly coalesce and fuse with the interparietal portion near the situation of the future occipital protu- berance. For many weeks two deep lateral fissures separate the interparietal and supra-occipital portions, and a membranous space, extending from the centre of the squamo-occipital to the foramen magnum, partially separates the lateral portions of the supra-occipital. This space becomes occupied by a spicule of bone, and is 46 THE SKELETON. of interest, because through it hernia of the brain and its membranes, known as meningocele or encephalocele, occurs. At birth the occipital consists of four parts: the squamo-occipital, two ex- occipitals, and the basi-occipital, united by strips of cartilage. The ex-occipitals and squamo-occipital fuse together about the fifth year, and unite with the basi- Fig. 35.—The Occipital with a Separate Interparietal. occipital before the seventh year. The posterior two-thirds of each occipital condyle belongs to the ex-occipitals, and the anterior third to the basi-occipital (Fig. 33). Not infrequently the interparietal portion remains separate throughout life, and may even be represented by numerous detached ossicles or Wormian bones. By the twenty-fifth year the basi-occipital is firmly ankylosed to the sphenoid. THE SPHENOID. The sphenoid forms a large part of the base of the skull in the region of the anterior and middle fossse. It is very irregular in shape, and is best described as consisting of a body, two pairs of wings, and two pairs of processes. The body is irregularly cuboidal in shape. The superior surface presents the following points for examination. In front, there is a prominent spine, which is received between the diverging alse of the crista galli, and known as the ethmoidal spine. The surface behind this is smooth, and is formed by the lesser or orbital wings; it frequently presents two parallel longitudinal grooves for the olfactory nerves. This smooth surface is terminated by the optic groove, which lodges the optic chiasma, and leads on each side into the optic foramen. The groove is bounded posteriorly by the olivary eminence, a ridge of bone indicating the line of union of the pre- and post-sphenoid. Behind this ridge the bone presents a deep hollow, the pituitary fossa, in which the pituitary body is lodged. The floor of this fossa presents numerous foramina for blood- vessels, and at birth the superior orifice of a narrow passage termed the cranio- pharyngeal canal. The pituitary fossa presents on each side, slightly pos- terior to the olivary eminence, a tubercle of variable size, the middle clinoid process. This is occasionally prolonged to meet the anterior clinoid process on the orbital wing. The posterior boundary is formed by a quadrilateral plate of bone, the dorsum ephippii. The superior angles of this plate are surmounted by the posterior clinoid processes, which give attachment to the tentorium cerebelli. A little below the clinoid process, on each side of the dorsum ephippii, there is a deep notch, converted into a foramen by the dura mater, for the passage THE SPHENOID. of the sixth cranial nerve. The dorsum is slightly concave posteriorly, and sup- ports the basilar artery and the pons Varolii. The inferior surface of the body has a prominent median ridge, the rostrum, which is received between the alse of the vomer. The rest of the surface is rough, and covered by the mucous membrane belonging to the roof of the pharynx. The anterior surface presents in the middle line a vertical ridge of bone, the sphenoidal crest, which articulates with the perpendicular plate of the Fig. 36.—The Sphenoid. ( Viewed front above). Optic foramen Sphenoidal fissure, Foramen rotundum Foramen ovale. Foramen spinosum, -Spine of the sphenoid. .External pterygoid plate. -Internal pterygoid plate. -Pterygoid notch. -Hamular process. ethmoid. On each side of the crest, a more or less circular orifice leads into the sphenoidal sinuses. These sinuses are irregularly shaped, unsymmetrical cavi- ties, separated from each other by a thin vertical septum ; in adult bones they may extend into the roots of the pterygoid processes, and even into the base of the occipital bone. The sinuses communicate with the nasal fossa of their respective sides. The lateral margins of the anterior surface are serrated for articulation with the posterior border of the os planum on each side of the ethmoid. The superior margin articulates with the cribriform plate of the ethmoid. Fig. 37.—The Left Half of the Sphenoid. Ethmoidal spine. Anterior clinoid process.. Middle clinoid process.- Posterior clinoid process. - .Optic groove. ■Olivary eminence. Dorsum ephippii. For occipital The posterior surface is, in the adult, ankylosed to the basi-occipital. The two bones are separated by a disc of hyaline cartilage until the eighteenth year; by the twenty-fifth year ankylosis is complete. On each side of the body there is the broad, sinuous, cavernous groove, which lodges the internal carotid artery and the cavernous sinus. The process of bone over which this artery turns is the lingula; it constitutes a flying buttress for the support of the greater wings. 48 THE SKELETON. The lesser or orbital wings forbito-sphenoids) are thin, triangular, hori- zontal plates of bone resting upon that portion of the sphenoid anterior to the olivary ridge (pre-sphenoid). The superior surface of each wing is smooth and slightly concave, and forms the posterior part of the anterior fossa of the skull; the under surfaces constitute a portion of the roof of each orbit, and bound superiorly the sphenoidal fissures. The anterior border is serrated for articu- lation with the horizontal plate of the frontal bone. (The orbital wings meet over the pre-sphenoid and almost exclude it from the cranial cavity.) 1 he posterior border, smooth and rounded, is received into the Sylvian fissure of the cerebrum. The inner extremity is prolonged to form the anterior clinoid process to which the tentorium cerebelli is attached. Each lesser wing is connected to the body of the bone by two processes or roots ; of these, the upper is thin and flat, the lower one is thicker, and presents near its junction with the body a small tubercle for the attachment of the common tendon of three ocular muscles. 1 he space between the roots is the optic foramen, and transmits the optic nerve and ophthalmic artery. The greater wings (ali-sphenoids) are two large plates of bone ankylosed to the body by means of the lingulae. Each wing has three surfaces. 1 he superior or cerebral surface is concave and smooth ; it receives the temporo-sphenoidal Fig. 38.—The Sphenoid. {Anterior view.} Optic fora- men. Sphenoidal fissure. Orbital surface. (The pointer crosses the malar crest.) Foramen rotundum .Vidian canal. Ext. pterygoid plate Pterygoid notch Hamular process Fterygo-palatine canal. lobe of the cerebrum, and presents several foramina. At the anterior and internal part is the foramen rotundum for the second division of the fifth nerve; behind and external to this is the foramen ovale, for the motor root and the third division of the fifth nerve, the small petrosal nerve, and the small meningeal artery. Behind and external to the foramen ovale is the small circular foramen spinosum, for the middle meningeal artery and its venae comites. To the inner side of the foramen ovale a small opening, the foramen Vesalii, is occasionally present; it transmits a vein. A foramen may exist near the foramen ovale for the small superficial petrosal nerve. The external surface is divided by the prom- inent malar crest into an orbital and a temporo-zygomatic portion. The orbi- tal surface forms the chief part of the outer wall of the orbit; its internal segment forms part of the spheno-maxillary fossa, and presents the anterior orifice of the foramen rotundum. Near the middle of the upper border there is a small tubercle for the origin of the outer head of the external rectus muscle; and at the highest part of this surface one or more foramina are often present, for the transmission of twigs from the middle meningeal artery to the orbit and the lach- rymal gland. The malar crest is serrated for articulation with the malar bone ; its lower angle, in many bones, articulates with the maxilla. A foramen exists in the suture, between the sphenoid and malar, for the temporal twig of the orbital nerve. The surface of bone outside this ridge is subdivided by a low crest, the THE SPHENOID. 49 pterygoid ridge. The surface above the ridge forms part of the temporal fossa, and affords attachment to the temporal muscle; the part behind the crest be- longs to the zygomatic fossa, it furnishes attachment to the external pterygoid muscle, and is continuous with the outer surface of the external pterygoid plate ; it contains the inferior orifices of the foramina spinosum, ovale, and Vesalii. The circumference of the great wing, commencing at its anterior attachment to the body, is at first smooth, and forms the lower boundary of the sphenoidal fissure ; this serves for the passage of the third, fourth, first division (ophthalmic) of the fifth and the sixth nerves, with the ophthalmic vein. Ex- ternal to this, the margin is broad and serrated for the frontal bone ; quite at the tip it is beveled on its inner aspect for the anterior inferior angle of the parietal; behind this, the edge, at first thin and beveled, becomes gradually broader, and deeply serrated for the squamosal, and runs into the prominent alar spine of the sphenoid, to which the spheno-mandibular ligament is attached. That portion of the circumference extending from the spine to the body of the sphenoid articulates by the outer third with the petrosal, but the inner two-thirds forms the anterior boundary of the foramen lacerum medium, and contains the posterior orifice of the Vidian canal. Projecting at right angles from the greater wing, near its junction with the lingulae, are the pterygoid processes. Of these the external, broad and thin, Fig. 39.—Right Half of Sphenoid. (Anterior view.) Temporal surface Ridge which forms the upper boundary of the spheno - maxillary fissure. Sphenoidal crest. Sphenoidal sinus. Ext. pterygoid muscle.. The alar spine forms by its outer surface the inner wall of the zygomatic fossa, and affords attach- ment to the external pterygoid muscle. From its inner surface the internal pterygoid takes origin. The internal pterygoid plate is narrower and longer than the external. Its inner surface forms part of the outer boundary of the nasal fossa, and by a thin ledge of bone, called the vaginal process, extends to the under surface of the basi- sphenoid to articulate with the ala of the vomer, and anteriorly with the sphenoidal process of the palate bone. Immediately above this ledge of bone is the pterygo- palatine groove (converted into a canal by the sphenoidal process of the palate bone), for an artery and nerve of the same name. At the point where the internal pterygoid plate comes into relation with the great wing and the lingula, there is the Vidian canal. This canal is 3 cm. long, and transmits the Vidian nerve and artery. The outer surface of the internal pterygoid plate forms the inner boundary of the pterygoid fossa; its posterior border is prolonged into a hamular pro- cess, smooth on its under aspect, for the bursa between it and the tensor (circum- flexus) palati. From the lower third of the posterior border and the hamular process the superior constrictor of the pharynx takes origin. The anterior borders of these processes diverge below, and have rough edges for articulation with the tuberosity of the palate bone; the gap between them is the pterygoid notch. Above, the pterygoid processes form a triangular surface, THE SKELETON. which constitutes the posterior boundary of the spheno-maxillary fossa, and presents above the anterior orifice of the Vidian, and more internally the commencement of the pterygo-palatine canals. The anterior border of the internal pterygoid plate articulates with the posterior border of the vertical plate of the palate bone. The recess between the two pterygoid plates posteriorly is subdivided. The upper, smaller, and shallower depression is the scaphoid fossa; it gives origin to the tensor (circumflexus) palati. The lower, deeper, and larger, is the ptery- goid fossa ; it lodges the internal pterygoid and tensor palati muscles. The fossa is completed by the tuberosity of the palate bone. Articulations.—The sphenoid articulates with the following bones: ethmoid, Fig. 40.—The Under Surface of Pre-sphenoid at the Sixth Year Lesser wing Optic foramen Pre-sphenoid Vidian canal. Pterygo-palatine groove Vaginal process. frontal, parietal, temporal, epipteric, palate, vomer, occipital, malar, sphenoidal turbinals, and occasionally with the maxilla. Muscles.—It gives origin to the following muscles :— Temporal. Internal pterygoid. External pterygoid. Tensor tympani. Tensor palati. . External rectus of the eyeball Internal rectus “ “ Superior rectus “ “ Superior oblique “ “ Levator palpebrae. Ligaments.—The sphenoid has numerous intrinsic ligaments which occa Fig. 41.—The Sphenoid at Birth. Vidian canal. Lingula. sionally ossify and produce adventitious foramina. Of these the more important are:— Inter-clinoid.—This passes from the anterior to the posterior clinoid processes. Carotico-clinoid.—From the anterior to the middle clinoid process. The ossi- fication of this ligament gives rise to a ring of bone through which the internal carotid artery passes. Pterygo-spinous.—This is attached to the spine of the sphenoid and the external pterygoid plate near the upper third. The spheno-mandibular ligament (long internal lateral ligament of the jaw). Several other insignificant bands have received names, but they are of no importance. THE TEMPORAL BONES. Blood-supply.—The sphenoid is supplied by branches of the middle and small meningeal arteries; also the anterior deep temporal and other branches of the internal maxillary, such as the Vidian, pterygo-palatine, and spheno-palatine. The body of the bone also receives twigs from the internal carotid. Ossification.—The sphenoid is ossified in cartilage from twelve ossific nuclei which appear in pairs. The nuclei are divisible into two sets—those for the pre- sphenoid and those for the post-sphenoid. The post-sphenoid centres consist of four pairs disposed as follows :—One for each ali-sphenoid (great wing). A pair of median nuclei for the basi- sphenoid, and a nucleus for each lingula (sphenotic nucleus), and one for each internal pterygoid. The external pterygoid is an outgrowth from the great wing. The pre-sphenoid centres consist of a nucleus for each orbito-sphenoid (lesser Fig. 42.—The Jugum Sphenoidaie. wings), and a median pair for the body of the pre-sphenoid. These nuclei appear at intervals from the eighth week to the end of the third month in the following order: ali-sphenoid, basi-sphenoid, lingulae, internal pterygoids, orbito-sphenoid, and pre-sphenoid. The various earthy spots fuse together, so as to form at birth three pieces. The median piece consists of the basi-sphenoid and lingulae, con- joined with the pre-sphenoid carrying the lingulae; the two lateral pieces are the ali-sphenoids (greater wings) carrying the internal pterygoid plates. The greater wings are joined to the lingulae by cartilage. The dorsum ephippii is cartilaginous at birth. In the course of the first year the orbito-sphenoids fuse in the middle line to form the jugum sphenoidale, which excludes the anterior part of the pre-sphenoid from the cranial cavity. The greater wings fuse with the lingulae in the course of the first year. THE TEMPORAL BONES. The adult temporal bone consists of three parts, so firmly united as to afford little trace of its complex origin. At birth the three parts are easily separable as the squamosal, petrosal, and tympanic (Fig. 103). The squamosal resembles a large scale; .it is attached at right angles to the petrosal, and forms part of the side wall of the skull. It is thin, and in places translucent. The outer surface is smooth and forms part of the temporal fossa ; it presents one, and occasionally two, nearly vertical grooves for the deep temporal arteries. A ridge of bone, the supra-mastoid crest, runs immediately above the external auditory meatus, and is continued onward to the zygoma. The zygoma is a narrow, projecting bar of bone, jutting forward and lying parallel with the squamosal. It has two surfaces and two borders. The outer surface is subcutaneous ; the inner looks toward the temporal fossa. The inner surface and lower border give origin to the masseter muscle. The upper border receives the temporal fascia. The tip of the zygoma is serrated for articulation with the malar. Posteriorly the lower border ends in a tubercle, which is the meeting point of two ridges ; of these, the anterior passes inward at right angles to the zygoma, and expands into the articular eminence which serves as an articular facet for the condyle of the mandible when the mouth is opened. The second ridge runs backward and forms the upper boundary of the glenoid fossa, 52 THE SKELETON. and curving downward ends in a tubercle, the post-glenoid tubercle, imme- diately anterior to the Glaserian fissure. The oval deep depression between these ridges is the glenoid fossa, which receives the condyle of the mandible. This fossa is limited posteriorly by the Glaserian fissure. The inner surface of the squamosal presents furrows for the convolutions of the brain and grooves for the middle meningeal arteries. The line of union between Fig. 43.—The Left Temporal Bone. (Outer view.) Temporal fossa Post-glenoid tubercle. Auditory meatus. Zygomatic tubercle Glenoid fossa Glaserian fissure Tympanic plate Styloid process. Auricular fissure. the squamosal and petrosal is sometimes indicated by a persistent petro-squa- mosal suture. Rarely the two portions remain permanently separate. The superior border of the squamosal is thin, and beveled on the cerebral surface where it overlaps the parietal; anteriorly it is serrated for the posterior border of the greater wing of the sphenoid. Posteriorly it joins the rough serrated margin of the petrosal to form the parietal notch. The petrosal element is a four-sided pyramid of very dense bone. Its base Fig. 44.—The Left Temporal Bone. (Inner view.) For middle meningeal artery The groove for superior petrosal sinus. Lateral sinus Mastoid foramen Remnant of floccular fossa. Internal auditory meatus. Aqueductus vestibuli Aqueductus cochleae For occipital is formed by the mastoid process; the apex is rough and forms part of the boun- dary of the foramen lacerum medium. Two sides of the pyramid project into the cranial cavity, of which one forms the posterior boundary of the middle fossa, and the other the anterior boundary of the posterior fossa of the cranium. Of the two remaining surfaces, one appears on the under surface of the skull, and the fourth constitutes the inner wall of the recess called the tympanum. The posterior surface is bounded above by the superior border, which serves for the attachment of the tentorium cerebelli, and is grooved for the superior pe- THE TEMPORAL BONES. 53 trosal sinus ; near the apex this border presents the trigeminal notch (converted into a foramen by the tentorium) for the transmission of the trigeminal nerve. This border in old skulls sometimes terminates in a spiculum of bone—the petro- sphenoidal process—and extends to the dorsum ephippii, and completes a foramen (petro-sphenoidal) which transmits the sixth nerve. Near the middle of the posterior surface is an oblique inlet, the internal auditory meatus, which receives the auditory and facial nerves and the auditory artery. The meatus is about 10 mm. deep, and to be properly examined the surface of the bone should be cut away, or the parts studied in the petrosal of a foetus at or near the ninth month, for it is at this date relatively large and shallow. The fundus of the meatus is divided by a transverse ridge of bone, the falciform crest, into a superior and inferior fossa. Of these, the superior is the smaller, and pre- sents anteriorly the beginning of the aqueduct of Fallopius ; this transmits the seventh nerve. The rest of the surface above the crest is dotted with small foramina (the supe- rior cribriform area) which transmit nerve-twigs to the fovea hemielliptica and the ampullae of the superior and external semicircular canals. Below the crest there are two depressions and an opening. Of these, an anterior curled tract (the spiral cribriform tract) with a central foramen (foramen centrale cochleare) marks the base of the cochlea; the central foramen indicates the qrifice of the canal of the modiolus, and the smaller foramina transmit the cochlear twigs of the auditory nerve. The posterior open- ing (foramen singulare) is for the nerve to the ampulla of the posterior semicircular canal. The middle depression (middle cribriform area) is dotted with minute foramina Fig. 45.—The Foramina in the Fundus of the Left Internal Auditory Meatus of a Child at Birth (T). (Diagrammatic.) Superior fossa. Entrance to the aqueduct of Fallo- pius. Falciform crest. Superior cribriform area Middle cribriform area Orifice of the canal of the modiolus. Foramen singulare Spiral cribriform tract Inferior fossa. for the nerve-twigs to the saccule, which is lodged in the fovea hemispherica. The inferior fossa is subdivided by a low vertical crest. The fossa in front of the crest is the fossula cochlearis, and the recess behind it is the fossula vestibularis. Behind the meatus is a small slit (large in the foetus) which formerly lodged the aqueductus vestibuli (ductus endolymphaticus) ; in the adult it is occupied by a small arteriole and venule and a process of dura mater. Occasionally a bristle can be passed along this passage into the vestibule. Above, and anterior to this, is a second slit also lodging a process of the dura mater. This is a remnant of the floccular fossa, so conspicuous in the foetus. Posteriorly, this surface has a deep groove for the lateral sinus. The anterior face of the pyramid is separated from the squamosal by the petro squamous suture, which may persist throughout life. It presents the fol- lowing points of interest: near the apex it has a shallow depression for the Gas- serian ganglion, and the recess of dura mater (Meckel’s cave) in which it lies ; below this is the termination of the carotid canal. Behind these are two small foramina, overshadowed by a thin osseous lip. Of these, the larger and more internal is the hiatus Fallopii, which transmits a small artery from the middle meningeal and the greater petrosal nerve. The smaller and external foramen is for the lesser petrosal nerve. Still more externally there is a thin translucent plate of bone, the tegmen tympani. Behind, and slightly internal to this, there is a ridge formed by the superior semicircular canal. The inferior or basilar surface is very irregular, and has the following points 54 THE SKELETON. of interest. At the apex is a quadrilateral smooth space for the tensor tympani and levator palati muscles. Behind this is the large circular orifice of the carotid canal, for the transmission of the carotid artery and a plexus of sympathetic nerves. Internal to this, near the inner border of the bone, is the orifice of the aqueductus cochleae (ductus perilymphaticus). In the adult it transmits a small vein from the cochlea to the internal jugular. Posteriorly is the elliptical jugular fossa with smooth walls for the ampulla which receives the lateral and inferior petrosal sinuses, and forms the commencement of the internal jugular vein. In the ridge of bone between the fossa and the carotid canal there is a small foramen, the tympanic canaliculus, for the tympanic branch of the glosso-pharyngeal nerve. On the inner wall of the fossa a similar minute foramen, the auricular canaliculus, permits the passage inward of the auricular branch of the vagus nerve. Behind the fossa is the rough jugular surface, which receives the jugular process of the occipital. Firmly ankylosed to the inner surface of the tympanic plate is the styloid process, varying in length from one to five cm. At its base is the stylo-mastoid foramen, from which issues the facial nerve; the stylo- mastoid artery enters the Fallopian canal through this opening. Running backward from this foramen are two grooves ; the outer is the digastric groove, from which the digastric muscle arises. The inner is narrower and shallower; it lodges the occipital artery. Carotid canal.- Surface for sphenoid. - Tensor tympani and levator palati. Tympanic canaliculus. - Aqueductus cochleae - Auricular canaliculus. - Jugular fossa. - Jugular surface.- Stylo-mastoid foramen.- Articulation for occipital.- Occipital groove._ Fig. 46.—The Left Temporal Bone. (.Inferior view.) Articular eminence. ~ Zygomatic tubercle. - Glaserian fissure. " Styloid process. External auditory meatus, - Auricular fissure. - Mastoid process. - Digastric groove. Of the outer surface, the only part which appears externally is the mastoid process; the rest is occupied by a recess known as the tympanum. The mastoid process is a nipple-shaped prominence of bone, formed partly by the squamosal, but mainly by the petrosal. Its upper limit is the supra-mastoid crest. Below the crest an irregular furrow crosses the surface of the process from the parietal notch downward, to the middle of the meatus. This furrow (squamo-mastoid) is often dotted with holes, and represents the line of union of squamosal and petrosal. The mastoid process gives attachment to the sterno-?nastoid, splenius capitis, trachelo-mastoid, occipito-frontalis, and retrahens auretn muscles. The tympanum is hidden by the tympanic plate, which extends downward from the Glaserian fissure to form the vaginal process. Anteriorly it ex- tends forward and ankyloses with the outer wall of the carotid canal. The Glase- rian fissure separates it from the squamosal. This fissure transmits the tympanic branch of the internal maxillary artery, and lodges the slender process of the malleus. A narrow subdivision of this fissure, canal of Huguier, is traversed by the chorda tympani nerve. The tympanic plate forms the anterior, lower, and part of the posterior walls of the external auditory meatus. It is limited pos- teriorly by the auricular fissure, through which the auricular twig of the vagus nerve issues. THE TEMPORAL BONES. 55 The external auditory meatus assumes the form of an elliptical bony tube. Its outer margin is rough and gives attachment to the cartilaginous portion of the pinna. Between the posterior edge of the meatus and the mastoid process is the auricular fissure. The tympanic orifice of the meatus is smooth, and presents a well-marked groove for the tympanic membrane. This is very conspicuous in young bones. The direction of the-meatus is somewhat oblique. In children, and occasionally in adults, a circular opening exists in the anterior wall of the meatus (Fig. 53). Articulations.—The temporal bone articulates with the occipital, parietal, sphenoid, malar, and by a movable joint with the mandible. Occasionally the squamosal presents a process which articulates with the frontal. A fronto- squamosal suture is common in the skulls of the lower races of men, and is normal in the skulls of the chimpanzee, gorilla, and gibbon. Fig. 47.—Temporal Bone with Muscle Attachments •Temporal. Retrahens aurem. Occipito-frontalis. Masseter. Sterno mastoid. Tympanic plate./ Trachelo-mastoid. Splenius capitis. Stylo-glossus. | Stylo-pharyngeus. Stylo-hyoid. The muscles connected with the temporal bone are :— Sterno-mastoid. Splenius capitis. T rachelo-mastoid. Digastric. Occipito-frontalis. Attrahens aurem. Retrahens aurem. Attollens aurem. To the mastoid process, To the styloid process, Stylo-glossus. Stylo-hyoid. Stylo pharyngeus. To the zygoma, Masseter. Intrinsic muscles, Stapedius. Tensor tympani. Ligaments :— To the petrosal, Levator palati, Capsular Interarticular Internal lateral External lateral of temporo-mandi- bular joint. Stylo-hyoid. Stylo-maxillary. Petro-sphenoidal. Ligaments connected with the ear-bones :— Anterior ligament of malleus (laxator tympani). External ligament of malleus. Superior ligament of malleus. Ligament of incus. 56 THE SKELETON. The blood-supply.—Arteries supplying the temporal bone are derived from various sources. The chief are :— Stylo-mastoid from posterior auricular : it enters the stylo-mastoid foramen. Tympanic from internal maxillary: it passes through the Glaserian fissure. Petrosal from middle meningeal: transmitted by the hiatus Fallopii. Tympanic from internal carotid whilst in the carotid canal. Auditory from the basilar : it enters the internal auditory meatus, and is distri- buted to the cochlea, vestibule, etc. Other less important twigs are furnished by the middle meningeal, the menin- geal branches of the occipital, and by the ascending pharyngeal artery. The squamosal is supplied on its internal face by the middle meningeal, and externally by the branches of the deep temporal from the internal maxillary. The tympanum is an irregular cavity in the temporal bone. At birth it is a recess in the outer wall of the petrosal, partially closed externally by the squamosal. When the various elements of the temporal bone coalesce, and the tympanic plate becomes fully developed, then the cavity is completely surrounded by bony walls, except where it communicates with the external auditory meatus. The roof, or tegmen tympani, is a translucent plate of bone belonging to the petrosal; it separates the tympanum from the middle fossa of the skull. The floor is the plate of bone which forms the roof of the jugular fossa. The inner wall is formed by the external surface of the petrosal bone, and presents the following points for study: In the angle between it and the roof is a horizontal ridge which extends backward as far as the posterior wall, and then turns downward in the angle between the inner and posterior wall. This is the Fallopian canal; it is occupied by the facial nerve (seventh). Near the roof, but below the Fallopian canal, is the fenestra ovalis, which leads into the vesti- bule : this fenestra receives the base of the stapes. Below the fenestra ovalis is the promontory, which contains the commencement of the first turn of the cochlea. In the lower and posterior part of the promontory is the fenestra rotunda ; this, in the recent state, is closed by the secondary membrane of the tympanum. In the macerated bone it leads into the spiral canal of the cochlea. The promon- tory is also furrowed by some delicate channels (sometimes canals) for the tym- panic branch of the glosso-pharyngeal nerve, which enters the tympanum through the tympanic canaliculus. The posterior wall of the tympanum is formed by the mastoid process. At the superior and internal angle of this wall an opening leads into the mastoid antrum. Immediately below this opening there is a small hollow cone, the posterior pyramid; its cavity is continuous with the descending limb of the Fallopian canal. One or more bony spiculae often con- nect the apex of the pyramid with the promontory. The cavity of this cone is occupied by the stapedius and the tendon of the muscle emerges at the apex. The roof and floor converge toward the anterior extremity of the tympanum, which is, in consequence, very narrow, and occupied by two canals : the lower for the Eustachian tube, the upper for the tensor tympani muscle. These grooves are sometimes described together as the canalis musculo-tubarius. In carefully prepared bones the upper canal is a small horizontal hollow cone (anterior pyra- mid), 12 mm. in length, which lodges the tensor tympani muscle; the apex is just in front of the fenestra ovalis, and is perforated to permit the passage of the ten- don of the muscle. As a rule the thin walls of the canal are damaged, and repre- sented merely by a thin ridge of bone. The posterior portion of this ridge pro- jects into the tympanum, and is known as the processus cochleariformis. The thin septum between the canal for the tensor tympani and the tube is pierced by a narrow canal which is traversed by the small deep petrosal nerve. The outer wall is occupied mainly by the external auditory meatus. This opening is closed in the recent state by the tympanic membrane. The rim of bone to which the membrane is attached is incomplete above ; the defect is known as the notch THE TYMPANUM. THE TYMPANUM. 5 7 of Rivinus. Anterior to this notch, in the angle between the squamosal and the tympanic plate, is the Glaserian fissure, and the small passage which transmits the chorda tympani nerve sometimes called the canal of Huguier. The tympanic cavity may be divided into three parts. The part below the level of the superior margin of the external auditory meatus is the tympanum proper ; the portion above this level is the attic of the tympanum ; it receives the head of the malleus, the body of the incus, and leads posteriorly into a recess known as the mastoid antrum. The mastoid antrum.—This is quite distinct from the mastoid cells. It is an air-chamber communicating with the attic of the tympanum. It is separated Fig. 48.—The Inner Wall of Tympanum. External semicircu- lar canal. Mastoid antrum. Fallopian canal. Carotid canal Tensor tympani. Groove for Eustachian tube. Levator palati Canal for small deej petrosal nerve. Iter chordae posterius. ,Stylo-mastoid foramen Stylo-pharyngeus. - Stylo-hyoid.- Stylo-glossus. ■ from the middle cranial fossa by the posterior portion of the tegmen tympani; the floor is formed by the mastoid portion of the petrosal; it communicates with the mastoid cells. The outer wall is formed by the squamosal below the supra- mastoid crest. In children the outer wall is exceedingly thin, but in the adult it is of considerable thickness. The external semicircular canal projects into the antrum on its inner wall, and is very conspicuous in the fcetus. A canal occasionally leads from the mastoid antrum through the petrous bone to open in the recess which indicates the position of the floccular fossa; it is termed the petro-mastoid canal. (Gruber.) Fig. 49.—The Left Osseous Labyrinth. {After Henle. From a Cast.) Superior semicircular canal The cochlea External semicircular canal. Posterior semicircular canal. Fenestra rotunda or cochleae. Fenestra ovalis or vestibuli. The Fallopian canal.—This canal begins at the anterior angle of the superior fossa of the internal auditory meatus, and passes directly outward to the hiatus Fallopii; it then turns abruptly backward and forms a horizontal ridge on the inner wall of the tympanum lying in the angle between it and the tegmen tympani. It passes immediately above the fenestra ovalis, and extends as far backward as the entrance to the mastoid antrum ; here it comes in contact with the inferior aspect of the projection formed by the external semicircular canal. It then turns vertically downward, running in the angle between the internal and posterior wall of the tympanum to terminate at the stylo-mastoid foramen. The canal is traversed by the facial (seventh) nerve. Numerous openings exist in the walls of this passage. At the hiatus the greater and smaller superficial pe- 58 THE SKELETON. trosal nerves escape from, and a branch from the middle meningeal artery enters, the canal. In the vertical part of its course the cavity of the posterior pyramid opens into it. There is also a small orifice by which the auricular branch of the vagus joins the facial, and near its termination the iter chordae posterius for the chorda tympani nerve leads from it to the tympanum. The vestibule.—This is an oval chamber situated between the base of the internal auditory meatus and the inner wall of the tympanum, with which it com- municates by way of the fenestra ovalis. Anteriorly the vestibule leads into the cochlea, and posteriorly it receives the extremities of the semicircular canals. It measures about 3 mm. transversely, and is somewhat longer antero-posteriorly. Its inner wall presents at the anterior part a circular depression, the fovea hemispherica, which is finely perforated for the passage of nerve-twigs. This fovea is separated bv a vertical ridge (the crista vestibuli) from the vestibular orifice of the aqueductus vestibuli (ductus endolymphaticus), which passes obliquely backward to open on the posterior surface of the petrosal bone. The roof contains an oval depression—the fovea hemielliptica. Anteriorly the vestibule leads into the cochlea. Posteriorly it receives the five openings of the semicircular canals. The semicircular canals are three in number. Each forms about two-thirds of a circle; they lie in different planes. One extremity of each canal is dilated to form an ampulla. The superior canal lies transversely to the long axis of the petrosal, and is Fig. 50.—The Cochlea in Sagittal Section. {After Hen/e.) Internal auditory meatus. The spiral canal. nearly vertical; its highest limb makes a projection on the anterior surface of the bone. The ampulla is at the outer end ; the inner end opens into the vestibule conjointly with the superior limb of the posterior canal. The posterior canal is nearly vertical and lies antero-posteriorly. It is the longest of the three ; its upper extremity joins the inner limb of the superior canal, and opens in common with it into the vestibule. The lower is the ampul- lated end. The external canal is placed horizontally and arches outward; its external limb forms a prominence in the mastoid antrum. This canal is the shortest; its ampulla is at the outer end near the fenestra ovalis. The cochlea.—This is a cone-shaped cavity lying with its base upon the in- ternal auditory meatus, and the apex directed outward. It measures about five millimetres in length, and the diameter of its base is about the same; The centre of this cavity is occupied by a column of bone—the modiolus—around which a delicate bony lamella appears to be wound. This lamella is the osseous spiral lamina, which gives attachment to the structures which form collectively the membranous cochlea. The lamina makes two and a half turns in all. The first turn is the largest, and forms a bulging, the promontory, on the inner wall of the tympanum. The lamina terminates at the apex of the cochlea in a hooklike process—the hamulus. The modiolus is traversed by a central canal, and presents many canaliculi for the transmission of the twigs of the cochlear division of the auditory nerve. THE TYMPANUM. 59 There is also a canal which winds round the modiolus at the base of the spiral lamina, known as the spiral canal of the modiolus. The portion of the cochlea above the lamina is the scala vestibuli; the part below, that is, on the basal aspect of the lamina, is the scala tympani; it opens into the tympanum by way of the fenestra rotunda. Near the commence- ment of the scala tympani, and close to the fenestra rotunda, is the cochlear orifice of the aqueductus cochleae (ductus perilymphaticus). In the adult this opens on the inferior surface of the petrosal near the apex, and transmits a small vein from the cochlea to the jugular fossa. Measurements of the principal parts connected with the auditory organs:— Internal auditory meatus . . Length of anterior wall, 13-14 mm. “ posterior wall, 6.7 mm. External auditory meatus . . 14-16 mm. (Gruber.) Tympanum .... Length, 13 mm. Height in centre of cavity, 15 mm. Width opposite the membrana tympani, 2 mm. “ “ tubal orifice, 3-4 mm. (Von Troltsch.) The capsule of the osseous labyrinth is in length 22 mm. (Schwalbe.) Superior semicircular canal measures along its convexity 20 mm. The posterior “ “ “ “ “ 22 mm. The external “ “ “ “ “ 15 mm. The canal is in diameter 1.5 mm. (Huschke.) The ampulla of the canal, 2.5 mm. Fig. 51.—The Temporal Bone at Birth. {Outer view.) Petro-squamous suture. Post-glenoid tubercle, Petrosal. Glaserian fissure Tympanic fissure Stylo-mastoid foramen. Tympano-hyal. Carotid canal At birth the temporal bone consists of three parts easily separable in the macerated skull: they are the petrosal, squamosal, and the tympanic. (The styloid process is car- tilaginous with the exception of its basal element, the tympano-hyal, which, with the ear-bones, will be described with the appendicular elements of the cranium.) The squamosal and tympanic bones develop in membrane. The squamosal is formed from one centre, which appears as early as the eighth week. Ossification extends into the zygoma, which grows concurrently with the squamosal. At first the tympanic border is nearly straight, but soon assumes its characteristic horseshoe shape. At birth the post-glenoid tubercle is conspicuous, and at the hinder end of the squamosal there is a recess where it comes into relation with the mastoid antrum. The centre appears for the tympanic bone about the twelfth week. At birth it is a horseshoe-shaped ossicle slightly ankylosed to the lower border of the squamosal; the open arms being directed up- ward. The tip of the anterior arm terminates in a small irregular process, and the inner aspect presents, in the lower half of its circumference, a groove for the reception of the tympanic membrane. Up to the middle of the fifth month the periotic capsule is cartilaginous ; it then ossifies so rapidly that by the end of the sixth month its chief portion is converted into porous bone. The ossific material is deposited in four centres, or groups of centres, named according to their relation to the ear-capsule in its embryonic position. The nuclei are deposited in the following order:— i. The opisthotic appears at the end of the fifth month. The osseous material is seen first on the promontory, and it quickly surrounds the fenestra rotunda from above The Ossification of the Temporal Bone. 60 THE SKELETON. downward, and forms the floor of the vestibule, the lower part of the fenestra ovalis, and the internal auditory meatus; it also invests the cochlea. Subsequently a plate of bone arises from it to surround the internal carotid artery and form the floor of the tympanum. 2. The pro-otic nucleus is deposited behind the internal auditory meatus near the inner limb of the superior semicircular canal. It covers in a part of the cochlea, the vestibule, and the internal auditory meatus, completes the fenestra ovalis, and invests the superior semicircular canal. Fig. 52.—Temporal Bone at Birth. (Inner view) Hiatus fallopii. Floccular fossa Aqueductus vestibuli. Internal auditory meatus. 3. The pterotic nucleus ossifies the tegmen tympani and covers in the external semi- circular canal; the ossific matter is first deposited over the outer limb of this canal. 4. The epiotic is the last to appear, and is first seen at the most posterior part of the posterior semicircular canal; often it is double. This centre gives rise to the mastoid process. At birth the bone is of loose and open texture, resembling biscuit or unglazed porcelain, thus offering a striking contrast to the dense and ivory-like petrosal of the adult. It also differs from the adult bone in several other particulars. • The floccular Fig. 53.—Temporal Bone at the Sixth Year. Wormian bone in’the pa- rietal notch. Auditory meatus Opening in the tympanic plate Glaserian fissure fossa is widely open and conspicuous. Voltolini has pointed out that a small canal leads from the floor of the floccular fossa and opens posteriorly on the mastoid surface of the bone ; it may open in the mastoid antrum. The hiatus Fallopii is unclosed, and the tympanic recess is filled with gelatinous connective tissue. The mastoid process is not developed, and the jugular fossa is a shallow depression. After birth the parts grow rapidly. The tympanum becomes permeated with air; the various elements fuse; and the tympanic annulus grows rapidly and forms the tympanic plate. Growth in the tympanic bone takes place most rapidly from the tuber- THE TYMPANUM. 61 cles at its upper extremities, and in consequence of the slow growth of the lower segment a deep notch is formed ; gradually the tubercles coalesce, leaving a foramen in the anterior part of the bony meatus which persists until puberty, and even in the adult. In most skulls a cleft capable of receiving the nail remains between the tympanic Fig. 54.—The Mastoid Antrum at the Third Year. [After Symington.) Mastoid antrum Vestibule. Lateral sinus. Fig. 55.—The Mastoid Antrum at the Ninth Year. (After Symington.) Mastoid antrum P&sterior semi circular canal Lateral sinus. Digastric, Fig. 56.—The Mastoid Antrum of an Adult. [After Symington.) Mastoid antrum Semicircular canals Air cells of mastoid, Lateral sinus element and the mastoid process; this is the auricular fissure. The anterior portion of the tympanic plate forms with the inferior border of the squamosal a cleft known as the Glaserian fissure, which is subsequently encroached upon by the growth of the petrosal. As the tympanic plate increases in size it joins the outer wall of the carotid canal and presents a prominent lower edge, known as the vaginal process. 62 THE SKELETON. The mastoid process becomes distinct about the first year, coincident with the ob- literation of the petro-squamous suture. It increases in thickness by deposit from the periosteum. Toward puberty, rarely earlier, the process becomes pneumatic, the air- cells being lined by delicate mucous membrane. In old skulls the air-cells may extend into the jugular process of the occipital bone. At birth the mastoid antrum is relatively large and bounded externally by a thin plate of bone belonging to the squamosal. As the mastoid increases in thickness the antrum comes to lie at a greater depth from the surface and becomes relatively smaller. The size of the antrum and the variations in thickness of its outer wall at the age of three years, nine years, and in the adult, are shown in Figs. 54> 55> and 56. In each case the sections were made slightly posterior to the external auditory meatus. In 20 per cent, of skulls there are no air-cells in the mastoid process. THE PARIETAL. The two parietals form a large portion of the vault and sides of the skull ; they are interposed between the frontal anteriorly and the occipital posteriorly. Each parietal presents two surfaces, four borders, and four angles. The external Fig. 57.—The Left Parietal. (Outer surface.) Superior border. Parietal foramen. Portion cov- ered by apo- neurosis of' occ ipito- frontalis. Superior tem poral ridge, Inferior tem- poral ridge. For temporal muscle, and forms part of the tem- poral fossa. Anterior in ferior angle surface is convex and smooth : the convexity, best marked in young bones, is greatest near the centre, which is termed the parietal eminence. Crossing the middle of the bone are the two temporal ridges ; the lower is the better marked, and limits the origin of the temporal muscle. The upper ridge is less constant, and it gives attachment to the temporal fascia. The internal surface is concave and marked with depressions corresponding to the cerebral convolutions. Numerous vertical deep furrows for the branches of the middle meningeal artery radiate from the anterior inferior angle and lower border of the bone. Along the superior margin of the bone there is a groove which, when articulated with the opposite bone, forms a furrow which receives the superior longitudinal sinus. In adult bones numerous deep circular depressions for Pacchionian bodies are found near this groove. The superior border is deeply serrated for the opposite parietal, THE FRONTAL. 63 the union with which forms the sagittal suture. The anterior and posterior borders are deeply serrated: the anterior articulates with the frontal to form the coronal, and the posterior with the squamo-occipital to form the lambdoid sutures. The inferior border is beveled and overlapped by the squamosal to form the squamous suture. Of the angles, the anterior inferior is prolonged downward and articulates with the summit of the greater wing of the sphenoid. The posterior inferior angle articulates with the mastoid portion of the petrosal; on its inner surface it has a horizontal groove for lodging a portion of the lateral sinus. The superior angles present nothing worthy of note. Parietal foramen. Fig. 58.—The Left Parietal. (Inner surface.) Groove for superior longitudinal sinus. Depressions for pacchionian bodies. Groove for lateral sinus. Grooves for middle meningeal artery. Articulations.—The parietal articulates with its fellow, the occipital, squa- mosal, frontal, sphenoid, and epipteric bones. Occasionally the squamosal and epipteric may exclude the parietal from union with the greater wing of the sphenoid. Blood-supply.—From the middle meningeal, occipital, and supraorbital arteries. Ossification.—The parietal ossifies from an earthy spot deposited in the outer layer of the dura mater about the seventh week. This bone is sometimes divided by a horizontal suture. THE FRONTAL. This bone bears much the same relation to the anterior part of the skull that the occipital bears to the posterior. It has, not inaptly, been compared to a cockle shell. The inner or posterior surface is concave, forming a deep fossa for the reception of the frontal lobes of the cerebrum. There is a gap in the lower part of the bone known as the ethmoidal notch, which overlaps by its thin edges the cribriform plate of the ethmoid and forms, with that bone, the internal 64 THE SKELETON. orifices of the anterior and posterior ethmoidal canals. The anterior part of this notch articulates with the crista galli, and the small hole in the line of suture is the foramen caecum. Prolonged vertically upward from ihe point of union with the crista is a ridge of bone, which gradually opens out to form a furrow for the reception of the superior longtitudinal sinus ; the ridge serves for the attach- ment of the anterior part of the falx cerebri. The thin laminae of bone on each side of the ethmoidal notch are termed orbital plates, because they form the greater part of the roof of each orbit. As a rule, they present deep depressions for the convolutions on the orbital surface of the cerebrum. rl he rest of the cerebral surface of the frontal is fairly smooth, and presents a few furrows for meningeal arteries, and, near the median groove, pits for Pacchionian bodies. The external surface is convex and smooth, often divided by an imperiect fissure, the remains of the metopic suture, which indicates the line of union of the two bones representing the frontal in early life. On each side of this suture a little below the centre is the frontal eminence. Below the eminences, sepa- Fig. 59.—The Frontal. (Anterior view.) FRONTAL EMIN ENCE Temporal ridge. Supraorbital notch. External angular process. Internal angular process. Nasal spine. rated by shallow grooves, are the two converging superciliary ridges, which approach each other in the median line to form the nasal eminence. The smooth space bounded by the converging superciliary ridges is the glabella. Below these ridges the bone presents the sharp supraorbital ridges which end internally at the internal angular, and externally at the external angular processes. Each ridge has a narrow, deep supraorbital notch (sometimes a complete foramen) at its inner third. At the bottom of this notch or foramen a small opening communicates with the diploe. The external angular processes are prominent and articulate with the malar bones ; from each process a ridge extends upward and backward, marking off the lateral aspect of the bone, where it assists in the formation of the temporal ridge and fossa. The internal angular processes articulate with the lachrymal bones, and are separated by a serrated interval, the nasal notch, which receives the upper borders of the nasal bones, and outside these the nasal processes of the maxillae. The notch has in the middle a long, pointed process, the nasal spine, which lies between the upper part of the nasal THE FRONTAL. 65 bones and the mesethmoid. On each side of the spine an opening leads into the large frontal sinuses. The under surfaces of the orbital plates are smooth and concave ; they form the roofs of the orbits. Each is sharply limited anteriorly by the supraorbital ridge, and presents at the outer angle the lachrymal fossa for the reception of the lachrymal gland. Near the internal angle there is a small, shallow supra- trochlear fossa for the pulley of the superior oblique muscle. A sharp ridge runs backward from the internal angular process and articulates successively with Fig. 60.—The Frontal Bone. (Inferior viezv.) Nasal spine. Articulation with nasal bone. Articulation with maxilla. Articulation with1 lachrymal. Trochlear fossa. Articulation with_ os planum. Articulation with- in alar. Articulation with- greater wing of sphenoid. Articulation with- lesser wing of sphenoid. Lachrymal fossa. - Orbital surface. -Ethmoidal notch. the lachrymal and the os planum of the ethmoid. It has two notches, which are converted into the anterior and posterior ethmoidal canals by articulation with the os planum. The posterior border of each orbital plate articulates with the lesser wing of the sphenoid (orbito-sphenoid), and is continuous with a rough triangular surface for the greater wing (ali-sphenoid). This triangular surface is continuous anteriorly with the serrated malar ridge of the sphenoid, and, laterally, with that border of the bone which articulates with the parietals to form the coronal Fig. 6i.—The Frontal Bone at Birth. suture. Between the ethmoidal notch and the inner margin of the orbital surface there is an irregular surface which forms the roofs of the ethmoidal cells. Articulations.—The frontal articulates with the parietal, sphenoid, ethmoid, lachrymal, malar, maxilla, and nasal bones. With the epipterics when present, and occasionally (as explained on page 55) with the squamosal, and with the sphenoidal turbinal when it creeps into the orbit. It has the following ?nuscles attached to it :— Corrugator supercilii. Temporal. Occipito-frontalis. Orbicularis palpebrarum 66 THE SKELETON. The blood-supply.—Arterial twigs derived from the middle and small menin- geal arteries enter it on the cerebral, and branches from the frontal and supra- orbital arteries on the outer surface. The horizontal plate derives twigs from the ethmoidal and other branches of the ophthalmic artery. Ossification.—The frontal develops from two earthy spots deposited in the outer layer of the dura mater, in the situations ultimately known as the frontal eminences. These nuclei appear about the eighth week, and quickly spread through the membrane. At birth the bones are quite distinct. Subsequently they articulate with each other in the median line to form the metopic suture. In a few cases the bones remain distinct throughout life. In the majority of cases the suture is obliterated; ankylosis commences about the sixth year. In adult skulls, traces of the metopic suture may often be seen in the region of the glabella. After the two halves of the bone have united, osseous material is deposited at the lower end of the metopic suture to form the nasal spine, which is one of the distinguishing features of the human frontal bone. The spine appears about the twelfth year, and soon consolidates with the bone above. Accessory nuclei are sometimes seen between this bone and the lachrymal; they may persist as Wor- mian ossicles. The frontal sinuses appear about the seventh year as prolongations from the anterior ethmoidal cells. Occasionally they invade the horizontal plate, and extend over the roof of the orbit. THE EPIPTERIC AND WORMIAN BONES. These are bones of variable size which occupy the anterior lateral fontanelles, regions indicated in the adult skull by the name pterion. Each epipteric bone is wedged between the squamosal, frontal, greater wing of sphenoid, and the parietal, and is present in most skulls between the second and fifteenth year. After that date it may persist as a separate ossicle, or unite with the frontal or the squamosal. In this case it will cause a fronto-squamosal suture, and exclude the parietal from the sphenoid. More commonly the epipteric joins the sphenoid. In some skulls it is scarcely as large as a split pea, in others it is as broad as the thumb-nail. The epipteric bone is pre-formed in membrane, and appears in the course of the first year. The Wormian bones are small, irregular-shaped ossicles, often found in the sutures of the skull, especially those in relation with the parietal bones. Wormian bones sometimes occur in great number; as many as a hundred have been counted in one skull. They are rarely present in the facial sutures. THE ETHMOID. The ethmoid is a bone of delicate texture, situated at the anterior part of the skull-base; it is roughly cuboidal in shape, and its delicacy is due to the fact that it is honeycombed by air-cells. The bone consists of four parts : the horizontal or cribriform plate, two lateral masses, and a perpendicular plate. The cribriform plate forms part of the anterior cerebral fossa, and is received into the ethmoidal notch of the frontal bone. Standing vertically upon this plate is the crista galli. To the posterior border of the crista the falx cerebri is attached ; this border divides posteriorly to enclose the ethmoidal spine of the sphenoid. The anterior aspect of the base of the crista constitutes the anterior border of the cribriform plate; it is rough for articulation with the frontal. In the suture between the two bones there is an opening, the foramen caecum, which trans- mits a small vein. On each side of the crista galli the cribriform plate lodges the olfactory bulb, and is perforated for the transmission of the filaments of the olfactory nerves. On each side, near the anterior part of the crista, there is a narrow longitudinal slit for the nasal branch of the fifth nerve. The perpendicular plate (mesethmoid) is directly continuous with the crista THE ETHMOID. 67 on the under aspect of the cribriform plate. It is a lamella of bone, trapezoid in shape, which forms the upper part of the nasal septum ; usually it is laterally deflected. Its anterior border articulates with the nasal spine of the frontal and the crest of the nasal bones. The inferior border has the triangular cartilage attached to it. The posterior border is subdivided : the upper half articulates with Fig. 62.—Section through the Nasal Fossa to show the Mesethmoid. Crista galli. Nasal spine of frontal, Crest of sphenoid, Groove for nasal nerve. Crest of palate bone. Spine of palate bone. Crest of maxilla. the crest of the sphenoid, and the lower articulates with the vomer. The surfaces of this plate present, especially in their upper parts, numerous foramina for vessels, and grooves for filaments of the olfactory nerves. The lateral mass, or labyrinth, of the ethmoid consists of two scroll-like pieces of bone, the superior and inferior turbinals (ethmo-turbinals) ; a smooth, quadrilateral plate of bone, the os planum, and a number of air-cells. Fig. 63.—The Ethmoid. (Side view.) Crista galli. Anterior ethmoidal groove. Posterior ethmoidal groove. Sphenoidal turbinal Middle turbinal. Unciform process. Inferior turbinal The os planum is on the outer side of the lateral mass, and forms a large por- tion of the inner wall of the orbit. By the anterior border it articulates with the lachrymal, by the posterior border with the sphenoid and the orbital process of the palate bone ; the inferior border articulates with the inner margin of the orbital 68 THE SKELETON. plate of the maxilla, and by the superior border with the horizontal plate of the frontal. Two notches in the superior border lead into grooves running horizontally across the lateral masses to the cribriform plate. These ethmoidal grooves are converted into ca?ials by the frontal bone. The anterior canal transmits the an- terior ethmoidal artery and nasal nerve ; the posterior is for the posterior ethmoidal artery. The turbinals project on the inner aspect of the lateral mass; they coalesce anteriorly, but are separated posteriorly by a space, termed the superior meatus. Each turbinal has an attached upper, and a free, slightly convoluted, lower border. In the recent state they are covered with mucous membrane, and present numerous foramina for blood-vessels, and grooves for twigs of the olfactory nerves. On the under surface of each lateral mass, near the anterior corner of the os planum, an irregular lamina of bone projects downward and backward. This is the unciform process ; it articulates with the ethmoidal process of the inferior turbinal, and forms a small part of the inner wall of the antrum. The ethmoidal cells occupy the space between the os planum and the tur- binals ; they are divided by a thin septum into an anterior and posterior set. The Fig. 64.—Section through the Nasal Fossa to show the Lateral Mass of the Ethmoid. Crista galli. - Frontal sinus. Body of sphenoid. Sphenoidal sinus. Spheno-palatine foramen. Middle meatus. Internal pterygoid plate. Palate bone. r Superior turbinal. _ Middle turbinal. - Infundibulum. - Inferior turbinal. nasal spine. Anterior palatine fora- “ men. cells are imperfect in the ethmoid, they require the juxtaposition of other bones to make them complete. Above, they are closed by the horizontal plate of the frontal, posteriorly by the sphenoidal turbinal and the orbital process of the pal- ate, inferiorly by the maxilla, and anteriorly by the lachrymal, The anterior set communicate with the frontal cells above, whilst below they open into the middle meatus of the nose by a sinuous canal, the infundibulum. The posterior cells open into the superior meatus, and occasionally communicate with the sphenoidal cells. The cells are sometimes divided into groups, according to the bone which lies in immediate juxtaposition. Those along the superior edge are the fronto- ethmoidal; those beneath the lachrymal, lachrymo ethmoidal, usually two in number. Those along the lower edge are the maxillo-ethmoidal; and pos- teriorly there are the spheno-ethmoidal, completed by the sphenoidal-turbinals, and a palato ethmoidal cell. Articulations.—The ethmoid articulates with the frontal, sphenoid, two pal- ate bones, two nasals, vomer, two inferior turbinals, the sphenoidal turbinals, two maxillse, and two lachrymal bones. The hinder surface of each lateral mass comes into relation with the sphenoid on each side of the crest and rostrum, and helps to close in the sphenoidal sinus. THE SPHENOIDAL TURBINAL. 69 Blood-supply.—The anterior and posterior ethmoidal, and from the nasal or spheno-palatine branch of the internal maxillary. Ossification.—The ethmoid has three centres of ossification. Of these, a nucleus appears in the fourth month of intra-uterine life in each lateral cartilage. At birth this bone is represented by two scroll-like bones, very delicate, and covered with irregular depressions, which give it a worm-eaten appearance. Six months after birth a nucleus appears in the ethmo-vomerine plate for the mesethmoid. This gradually extends into the crista galli. During the third year the lateral masses and the mesethmoid (perpendicular plate) ankylose. The cribriform plate is derived from the lateral masses. The ethmoidal cells do not make their appearance before the third year, and they gradually produce attenuation of the lateral masses. In many places there is so much absorption of bone that the cells perforate the ethmoid in situations where it is overlapped by other bones. Along the lower border of the bone, near its articulation with the maxilla, the absorption leads to the partial detachment of a narrow strip known as the uncinate or unciform process. Sometimes a second but smaller hook-like process is formed, above and anterior to the large one. This process is so very fragile that it is difficult to preserve it in disarticulated bones. The relations of the uncinate process are best studied by removing the outer wall of the antrum. These bones (often referred to as the bones of Bertin) are two hollow cones, flattened externally in three planes. They may be obtained as distinct ossicles about the fifth year. At this date they are wedged in between the under surface THE SPHENOIDAL TURBINAL Fig. 65.—The Sphenoidal Turbinal at the Sixth Year. of the pre-sphenoid and the orbital and sphenoidal processes of the palate bone. The apex of the cone is directed backward, and appears near the vaginal process of the sphenoid. Of its three surfaces, the outer one is in relation with the spheno-maxillary fossa, and occasionally extends upward between the sphenoid and the os planum of the ethmoid to appear on the inner wall of the orbit (Fig. Fig. 66—The Sphenoidal Turbinals from an Old Skull, Sphenoidal turbinal Rostrum of sphenoid 6y). The inferior surface forms the upper boundary of the spheno-palatine fora- men, and enters into the formation of the posterior part of the roof of the nasal fossa. The superior surface lies flattened against the under surface of the pre- sphenoid. The base of the cone is in contact with the posterior surface of the lateral mass of the ethmoid. At birth these bones are visible as small triangular ossifications in the peri- 70 THE SKELETON. chondrium of the ethmo-vomerine plate near its junction with the pre-sphenoid. By the third year they become hollow cones, the circular orifice representing the base eventually becoming the orifice of the sphenoidal sinus. As the cavity en- larges, the median wall atrophies so that the inner wall of the sinus is formed by the pre-sphenoid. As the turbinal enlarges it ankyloses with adjacent bones. In many skulls it joins the lateral mass of the ethmoid ; more frequently it fuses with the pre-sphenoid; less frequently with the palate. After the twelfth year they can rarely be separated from the skull without damage. In many disarticulated skulls they are so broken up that a portion is found on the sphenoid, fragments on the palate bones, and the remainder attached to the ethmoid. Sometimes, even in very old skulls, they are represented by a triangular plate of extreme tenuity on each side of the rostrum of the sphenoid (tig. 66). These are a pair of delicate, scroll-like bones, and may be regarded as dismem- berments of the lateral masses of the ethmoid, with which they are closely related. Each bone presents two surfaces, two borders, and two extremities. The outer surface is concave, and overhung by the auricular or maxillary THE INFERIOR TURBINAL. Pig. 67.—The Inferior Turbinal, Adult Sphenoidal, Turbinal, and Lachrymal Bones. The crest of lachrymal. Tensor tarsi. The orbital surface.. Lachrymal groove/ Hamular process. Turbinal process. The lachrymal process. The ethmoidal process. The maxillary process. OS PLANUM The sphenoidal turbinal with an orbital process. Middle turbinal. process. The inner surface is convex and pitted with depressions. The su- perior border presents from before backward three processes: the first is called the lachrymal process, because it articulates with the turbinal process of the lachrymal bone. The margin of bone at the base of this process comes into rela- tion with the nasal process of the maxilla. The second vertical spiculum is the ethmoidal process, which joins the uncinate process of the ethmoid. The third or maxillary process is a thin lamella of bone, turned downward ; it overhangs the orifice of the maxillary sinus, and serves to fix the bone firmly to the outer wall of the nasal fossa. The margin posterior to the maxillary process comes into relation with the inferior turbinal crest of the palate bone. The inferior border is rounded and free. It is the thickest part of the bone. The extremities are nar- row, the posterior being the more pointed. Articulations.—The inferior turbinal articulates with the maxilla, lachrymal, palate, and ethmoid. The inferior turbinal is ossified from a single nucleus which appears about the fifth month of intra-uterine life. At birth it is a relatively large bone, and fills up the lower part of the nasal fossa. THE LACHRYMAL AND VOMER. THE LACHRYMAL. The lachrymal bones are extremely thin and delicate, quadrilateral in shape, and situated at the anterior part of the inner wall of the orbit. They are the smallest of the facial bones. The outer or orbital surface is divided by a vertical ridge into two unequal portions. The anterior smaller portion is deeply grooved to form the lachrymal sulcus, which lodges the lachrymal sac and forms the commencement of the lachrymal duct. The portion behind the ridge is smooth, and forms part of the inner wall of the orbit. The ridge gives origin to the tensor tarsi muscle, and terminates interiorly in a hook-like process, the hamulus, which curves forward to articulate with the lachrymal tubercle of the maxilla and completes the superior orifice of the lachrymal canal. The inner surface is in relation with the two anterior cells of the ethmoid (lachrymo-ethmoid) and forms part of the infundi- bulum. The superior border is short, and articulates with the internal angular process of the frontal. The lower border posterior to the crest joins the inner edge of the orbital plate of the maxilla. The narrow piece, anterior to the ridge, is prolonged downward to join the lachrymal spine of the inferior turbinal, and is called the turbinal process. The anterior border comes into relation with the posterior border of the nasal process of the maxilla. The posterior border articulates with the os planum of the ethmoid. Articulations.—The lachrymal articulates with the ethmoid, maxilla, frontal, and inferior turbinal bones. Blood-supply.—Its arteries are derived from the infraorbital, the nasal branch of the ophthalmic, and the anterior ethmoidal. Ossification.—This bone arises in the membrane overlying the cartilage of the fronto-nasal plate. Its mode of ossification is very variable. As a rule it is described as coming from one nucleus. Not infrequently the hamulus is a separate element. Sometimes the bone is divided horizontally, and a process of the os planum projects between the two halves to join the nasal process of the maxilla. More rarely the bone is represented by a group of detached ossicles resembling Wormian bones. THE VOMER The vomer is an irregular four-sided plate of bone constituting the lower portion of the nasal septum. It is usually described as resembling a ploughshare in shape. Each lateral surface is covered with the thick mucous membrane of the nasal sinus, Fig. 68.—The Vomer. (Side View.) Groove for naso-palatine nerve. Anterior border. — Ala. Groove for septal cartilage Posterior border. Inferior border. and is traversed by a narrow but well-marked groove, which lodges the naso- palatine nerve from the spheno-palatine ganglion ; hence it is sometimes called the naso-palatine groove. The superior border of the bone is expanded laterally into two alee. The groove between them lodges the rostrum of the sphenoid, whilst the margin of each ala comes into contact with the sphenoidal process of the palate bone. Between the alae and the sphenoid a canal exists on each side of the rostrum for blood-ves- sels. The inferior border is uneven, and is received into the groove formed by the crests of the opposed maxillae and the palatine bones of each side. The ante- rior border joins posteriorly the mesethmoid, and in front the triangular (median) 72 THE SKELETON. nasal cartilage. The posterior border, smooth, rounded, and covered with mucous membrane, serves to separate the posterior nares. The anterior and inferior bor- ders meet each other at the apex of the bone. Articulations.—The vomer articulates with the sphenoid, palates, ethmoid, and maxillae, and with the triangular cartilage. Blood-supply.—Its arteries are derived from the anterior and posterior ethmoidal, the naso-palatine, and the pterygo-palatine arteries, and twigs from the posterior palatines through Stenson’s canals. Fig. 69.—The Vomer at Birth. Ossification.—The vomer is a membrane bone, and arises from a single centre deposited in the lower border of the perichondrium of the ethmo-vomerine plate as early as the eighth week. From this single centre a lamina of bone ex- tends on each side of the cartilage plate. For many weeks the vomer is a shallow, bony trough. Gradually it presses upon and induces absorption of the inclosed cartilage, and by degrees the laminae fuse, and form a rectangular plate of bone. At birth the vomer presents an expanded lower border, especially in cases of cleft palate. These are two oblong bones situated in the middle line at the upper part of the face, and forming the bridge of the nose. Each bone has two surfaces and four borders. The facial surface is concave from above downward, but convex from side to side. Near its centre is a foramen for the transmission of a small tributary to the facial vein. The posterior or nasal surface is concave laterally, and traversed by a longitudinal groove for the nasal branch of the ophthalmic nerve. THE NASAL. Fig. 70.—The Left Nasal Bone. Superior border. —Median border. Median border. — Outer border. — Groove for nasal nerve. Inferior border. — In life this surface has a covering of mucous membrane. The short superior bor- der is thick and serrated for articulation with the nasal notch of the frontal. The inferior border is thin, and serves for the attachment of the lateral nasal cartilages. Each bone articulates with its fellow by the median border, which is prolonged backward to form a crest; this crest comes into relation with the nasal spine of the frontal and the anterior border of the mesethmoid. The outer border articu- lates with the nasal process of the maxilla. THE MAXILLA. 73 Articulations.—The nasal bone articulates with its fellow, the frontal, maxilla, and ethmoid. Blood-supply.—Twigs to this bone are furnished by the nasal branch of the ophthalmic, the frontal, the angular, and the anterior ethmoidal arteries. Ossification.—Each nasal bone is developed from a single earthy nucleus in the membrane overlying the fronto-nasal cartilage. The nucleus is easily seen in the eighth week. The bone by its pressure soon produces absorption of the underlying cartilage. At birth the nasal bones are nearly as wide as they are long, whereas in the adult the length of the bones is three times greater than the width. THE MAXILLA. The maxillae are two hollow, irregular cuboidal bones with two prominent processes. They form a large portion of the facial skeleton. This bone is occupied by a large cavity, the antrum. The body presents four surfaces. Of these the facial surface looks forward and outward and pre- sents the following points of interest: The socket for the canine tooth causes a low elevation, the canine eminence, having to its inner side the incisive fossa, from which the depressor alee nasi arises. On the outer side of the emi- Fig. 71.—The Left Maxilla. {Outer view.) Border of sphenomaxillary fissure. Infraorbital foramen For sphenoid. Zygomatic surface. Malar process. Nasal notch Canine fossa Nasal spine. Incisive fossa. Posterior dental canals. Canine eminence Tuberosity. nence is the canine fossa, which gives origin to the levator anguli oris. Above this fossa is the infraorbital foramen, through which the terminal branches of the infraorbital nerve and artery emerge. From the ridge above this foramen the levator labii superioris arises. A ridge of bone extending upward from the socket of the second molar tooth separates the facial from the zygomatic surface. Near the middle of the zygo- matic surface are the orifices of the canals for the posterior dental nerves and vessels. The posterior inferior angle of this surface is termed the tuberosity; from it a few fibres of the internal pterygoid muscle arise. This tuberosity is most prominent after eruption of the wisdom tooth; the rough surface along its inner border is for the tuberosity of the palate bone ; the smooth surface immediately above forms the anterior boundary of the spheno-maxillary fossa, and enters into the formation of the descending palatine canal. The orbital surface is irregularly triangular and forms the floor of the orbit. Anteriorly it is rounded and forms part of the circumference of the orbit; exter- nally it is rough for suture with the malar bone ; the rough surface ends in a backwardly projecting spine which occasionally joins the sphenoid and forms the anterior limit of the spheno-maxillary fissure. The posterior margin, smooth and rounded, forms the inferior limit of the spheno-maxillary fissure. The internal border is nearly straight; quite at the posterior part is a gap for the orbital process 74 THE SKELETON. of the palate bone ; anteriorly it articulates with the os planum of the ethmoid ; beyond this it receives the lachrymal bone, and in the anterior angle it is smooth and rounded, forming part of the circumference of the orbital orifice of the lachrymal duct. The orbital surface is traversed by the infraorbital groove, which, commen- cing at the posterior border, deepens as it passes forward and enters the infra- orbital canal. This groove receives the second division of the fifth nerve and the infraorbital artery. The infraorbital canal runs under the margin of the orbit and opens on the facial surface. It transmits the infraorbital artery and nerve. At the termination of the groove a smaller canal tunnels the anterior wall of the antrum, and conveys the anterior dental nerves and vessels to the upper incisor, canine, and bicuspid teeth. External to the commencement of the lachrymal duct there is a shallow depression from which the inferior oblique takes origin. The internal or nasal surface forms the outer wall of the nasal fossa, and is prolonged inward to form part of the floor of this fossa. The posterior half of this surface is deficient, and leads by a large irregular aperture into the antrum ; below and behind this opening the bone is rough for articulation with the vertical plate of the palate bone. The extreme posterior border receives the tuberosity of the palate bone ; the groove in front of it forms part of the posterior palatine canal. Anterior to this surface the bone becomes suddenly smooth; between the smooth Fig. 72.—The Left Maxilla. (Inner view.) Nasal process. Ridge for middle turbinal. Lachrymal groove. Ridge for inferior turbinal. Nasal spine. Crest. Anterior palatine groove. Antrum. Posterior palatine groove. Palatine process. and rough portions is the maxillary fissure for the reception of the thin maxillary process on the anterior border of the vertical plate of the palate bone. In the angle between this surface and the nasal process is a deep groove converted by the lachrymal and inferior turbinal into the nasal duct. Running backward from the anterior margin is the inferior turbinated crest which articulates with the lowest turbinal bone. The surface above the crest forms part of the middle meatus, and the surface below belongs to the inferior meatus of the nose, and is directly continuous with the superior surface of the palatine process. Near its anterior border is the orifice of the anterior palatine canal. The inferior or palatine surface is formed by the palatine process and the alveolar border. The palatine process forms the anterior part of the roof of the mouth. It is concave, rough, and pitted with foramina for vessels. Where it joins the alveolar border a groove (sometimes a canal) exists for the anterior pala- tine nerve and posterior palatine vessels. When the bones of opposite sides are placed in apposition the palatine fossa is formed ; running outward from this to the space between the second incisor and canine tooth, the maxillo-pre- maxillary suture can be detected in young bones. The posterior border articulates with the horizontal process of the palate bone, whilst the median border joins its fellow to form, above, a prominent crest upon which the vomer is received. The anterior palatine fossa is situated in the meso-palatine suture near THE MAXILLA. 75 its anterior termination. In its typical form the fossa contains four passages: two are small and disposed one behind the other exactly in the suture ; these are the foramina of Scarpa for the naso-palatine nerves, the left nerve emerging from the anterior foramen. The lateral and larger orifices diverge to open on each side of the crest. They are called Stenson’s canals, and lodge recesses of the nasal mucous membrane and remnants of Jacobson’s organs. The alveolar ridge forms the outer limit of this surface; it is crescentic in shape, spongy in texture, and presents cavities in which teeth are lodged. When the teeth are complete in number, eight cavities are present; of these the pit for the canine tooth is the deepest, those for the molars are the widest and present subdivisions. Along the outer aspect of the alveolar border the buccinator arises as far forward as the first molar tooth. The nasal process is somewhat triangular, standing vertically from the nasal angle of the maxilla. Its outer surface gives attachment to the orbicularis palpe- brarutn, the tendo oculi, and the levator labii superioris alceque nasi. The internal surface forms one of the lateral boundaries of the nasal fossa. Superiorly it articulates with the frontal; below this is the superior turbinated crest for articulation with the middle turbinal. The space between this and the inferior tubin&ted crest forms part of the middle meatus. The anterior border articu- lates with the nasal bone ; the posterior is thick and vertically grooved to form part of the nasal duct. The inner margin of this groove articulates with the lachrymal bone. The point where the outer margin of the groove joins the orbital plate is indicated by the lachrymal tubercle. The malar process is rough and triangular, and forms the summit of the ridge of bone separating the facial and zygomatic surfaces. It articulates with the malar bone, and from its inferior angle a few fibres of the masseter take origin. The antrum or maxillary sinus, as the air-chamber occupying the body of the bone is called, is somewhat pyramidal in shape, the base being represented by the nasal or internal surface, and the apex corresponding to the malar process. In addition to these it has four walls : the superior is formed by the orbital plate and the inferior by the alveolar ridge. The anterior wall corresponds to the facial surface of the maxilla, and the posterior is formed by the zygomatic surface. The inner boundary or base presents a very irregular orifice at its posterior part; this is partially filled in by the vertical plate of the palate bone, the uncinate process of the ethmoid, the maxillary process of the inferior turbinal, and a small portion of the lachrymal bone. Even when these bones are in situ, the nasal orifice is very irregular in shape, and requires the mucous membrane to form the definite rounded aperture (or apertures, for they are often multiple) known as the open- ing of the antrum. The cavity of the antrum varies considerably in size and shape. In the young it is small and the walls are thick: as life advances, the antrum enlarges at the expense of its walls, and in old age they are often of extreme tenuity; occasionally the cavity extends into the substance of the malar bone. The floor of the antrum is, as a rule, very uneven, due to prominences corresponding to the roots of the molar teeth. In most cases the bone separating the teeth from the antrum is very thin, and not rarely the roots project uncovered into it. The teeth which come into closest relationship with the antrum are the first and second molars, but the sockets of any of the teeth lodged in the maxilla may, under diseased conditions, communicate with it. Although, as a rule, the cavity of the antrum is single, yet specimens occasionally come to hand in which it is divided by bony septa into chambers, and it is far from uncommon to find it divided into recesses by bony processes. In many maxillae, the roof of the antrum presents near its anterior aspect what appears to be a thick rib of bone; this is hollow and corresponds to the infraorbital canal. The most satisfactory method of studying the relation of the bones closing in the base of the antrum is to cut away the outer wall of the cavity (see Fig. 84). Articulations.—The maxilla articulates with its fellow, and with the frontal, nasal, lachrymal, ethmoid, palate, vomer, malar, and inferior turbinal bones. Oc- casionally it articulates with the greater wing, and less frequently with the ptery- goid process of the sphenoid bone. 76 THE SKELETON. The muscles attached to it are mainly those known as muscles of expression :— Compressor naris. Orbicularis palpebrarum. Orbicularis oris. Levator labii superior proprius. Levator labii superioris alaeque nasi. Levator anguli oris. Inferior oblique. Depressor alae nasi. Buccinator. Internal pterygoid. Masseter. Blood-supply.—The maxilla is a very vascular bone, and its arteries are numerous and large. They are derived from the infraorbital, alveolar, descending palatine, naso-palatine,ethmoidal, frontal, nasal, and facial branches. Ossification.—The maxilla arises from four centres which are deposited in membrane. The various centres may be termed pre-maxillary, maxillary, malar, and pre-palatine. They arise about the eighth week of embryonic life, and fuse very rapidly. (a) The pre-maxillary nucleus gives rise to that portion of the bone wfliich lodges the incisor teeth. It sends a narrow process upward which forms part of the outer boundary of the anterior narial aperture. On the palatine aspect it furnishes a spiculum which surrounds the anterior and mesial aspect of Stenson’s canal. The posterior limit is indicated up to the end of the first dentition by the Fig. 73.—Ossification of the .Maxilla. Pre-maxillary portion. Outer view. Inferior view. Inner view. maxillo-premaxillary suture. The greater part of this centre is formed in mem- brane, but the inner part subsequently invades the ethmo-vomerine cartilage. (b) The maxillary nucleus forms the nasal process and the greater part of the body of the maxilla. (<) The malar centre gives origin to that portion of the bone lying external to the infraorbital groove. (d) The pre-palatine centre gives rise to the nasal surface of the maxilla and the palatine process posterior to Stenson’s canal. This portion is in shape similar to the palate bone. The palate bone is rectangular in shape, and wedged between the maxilla and the pterygoid processes of the sphenoid. It has a horizontal and a vertical plate, a tuberosity, and two processes. The horizontal plate is smaller than the vertical; it is quadrilateral in shape. The upper surface forms the floor of the nasal fossa; the inferior surface com- pletes the hard plate posteriorly, and presents near its posterior border a transverse ridge, which gives attachment to the tensorpalati muscle. The anterior border is rough for articulation with the palatine process of the maxilla. The posterior border is free, curved, and sharp; it gives attachment to the soft palate. The inner border is broad, and rough for articulation with its fellow. When the palate THE PALATE BONE. THE PALATE BONE. 77 bones are in apposition, these borders form a ridge continuing the crest formed by the palatine processes of the maxillae; this crest receives the inferior border of the vomer. The posterior extremity of the crest forms the posterior nasal spine, from which the azygos uvula arises. The vertical plate is thin ; of its two surfaces, the outer is rough for articu- lation with the maxilla, except a small portion near the middle close to the ante- rior border where it looks into the antrum, and a small triangular surface at the upper end where it forms part of the spheno-maxillary fossa. Toward the posterior border there is a vertical groove, which forms with the maxilla the posterior pala- tine canal; it transmits the descending palatine nerves and vessels. The canal may be more or less complete in the palate bone. The internal surface has two transverse ridges separating three shallow depressions. Of these depressions the lower forms part of the inferior meatus of the nose, and the limiting ridge or crest articulates with the inferior turbinal. Above this is the depression for part of the middle meatus; the ridge above is for the second turbinal. The upper groove is narrower and deeper than the lower two, and forms a large part of the superior meatus. The ridges are known as the turbinated crests. The borders of the vertical plate are terminated by irregular prominences, which enter into complex union with surrounding bones. The posterior border is vertical, and comes into relation with the anterior Fig. 74.—Palate (Left) Bone. [Inner view.) Orbital process. (Ethmoidal surface.) Superior meatus. Superior turbinated crest. Middle meatus. — Inferior turbinated crest. ~ Inferior meatus. Sphenoidal process. Spheno-palatine notch. (When the foramen is complete in the palate bone, it is due to ankylosis with the sphenoidal tur- binal.) border of the internal pterygoid process; below, it terminates in a prominent tuberosity. This presents three grooves or flutes : the inner receives the inter- nal pterygoid, the outer the external pterygoid process, while the middle groove completes the pterygoid fossa, and affords attachment to a few fibres of the internal pterygoid muscle ; the superior constrictor of the pharynx also arises from this process. The tuberosity is tunneled by canals : to the nasal side are the accessory palatine canals; near its junction with the horizontal plate is the orifice of the posterior palatine canal; and outside this occasionally may be found the minute external palatine canals (Fig. 85). The sphenoidal process, which is a process of variable shape, surmounts the posterior border; it has three surfaces and two borders. The superior surface comes into apposition with the sphenoidal turbinal bone, and forms part of the pterygo-palatine canal. The internal surface forms part of the outer wall of the nasal fossa, and is prolonged on to the roof, and comes in contact with the ala of the vomer. The outer surface is subdivided by a thin lip into an anterior smooth portion for the spheno-maxillary fossa, and a posterior rough part for the base of the internal pterygoid plate. Of the borders, the posterior is thin and articulates with the internal pterygoid plate; the anterior border forms the posterior boundary of the spheno-palatine foramen. The anterior border of the vertical plate is thin, sharp, and presents near 78 THE SKELETON. the middle the maxillary process, which is received into the maxillary fissure of the maxilla near the lower border of the opening of the antrum. Superiorly this border is terminated by the orbital process. This process presents five surfaces; of these, three are articular. The posterior surface joins the walls of the sphenoidal turbinal bone, its air-cells extending occasionally into this part of the palate bone. In the same way the posterior ethmoidal cells ex- tend into the inner surface of the orbital process, where they articulate with the lateral mass. The anterior surface is a continuation of the outer aspect of the vertical plate, and rests upon the maxilla. Of the two non-articular surfaces, the one directed upward and outward is slightly concave, and forms part of the floor of the orbit at its junction with the inner wall. The outer smooth surface looks directly into the zygomatic fossa, and extends into thespheno-maxillary fossa, and forms the anterior boundary of the spheno-palatine foramen. These surfaces are often conveniently named according to the bones with which they articulate or the fossae which they help to form: thus, the anterior or maxillary; internal or ethmoidal; posterior or sphenoidal; superior or orbital; external or zygomatic. Between the orbital and sphenoidal processes is the spheno-palatine notch, which is converted by the sphenoid turbinal bone into a complete foramen. Oc- casionally it is complete in the palate bone. It transmits the spheno-palatine Fig. 75.—Palate Bone. (Posterior view.) Orbital surface Zygomatic surface Orbital process. (Surface for sphenoidal turbinal.) Spheno-palatine foramen. (Usually a notch.) Sphenoidal process Groove for external pterygoid, Groove for pterygoid fossa, Groove for internal pterygoid, Tuberosity Spine of palate, nerve and artery; the foramen opens into the back part of the nasal fossa, close to its roof. When the spheno-palatine foramen is complete in the palate bone, it is often due to ankylosis between the palate and the sphenoidal turbinal; the latter, being extremely, fragile, easily breaks during the process of disarticulation. Articulations.—The palate bone articulates with its fellow the sphenoid, maxilla, vomer, sphenoidal turbinal, inferior turbinal, and ethmoid bones. As the surfaces and lines of union of the orbital and sphenoidal processes are some- what intricate, the student should, when studying this bone, refer to the following figures. The orbital and zygomatic surfaces are shown in Fig. 48 ; the relation of the sphenoidal process to the nasal fossa in Fig. 64; the relations of the pterygoid processes to the tuberosity of the palate are shown in Fig. 85. With the help of these drawings the student will be able to understand the position of this bone, which assists in forming the boundary of the following cavities : viz., the nasal, orbital, spheno-maxillary, antral, and the ethmoidal cells. The muscles attached to it are : — Internal pterygoid. Tensor palati. Azygos uvulae. Superior constrictor of pharynx. Blood-supply.—Its arteries are derived from the descending palatine, the spheno-palatine, and pterygo-palatine. THE MALAR BONE. 79 Ossification.—The palate bone arises from one nucleus, which is deposited in membrane, and appears about the eighth week of embryonic life. The spot where the earthy matter is first seen ultimately becomes the angle where the ver tical and horizontal plates join. At birth the two plates are nearly equal, but as the nasal sinuses increase in height the vertical plate is lengthened, until it be- comes twice the length of the horizontal plate. The malar bone, somewhat quadrilateral in shape, is situated at the outer and upper side of the face, and forms the prominence known as the cheek. Each bone has a convex external surface, presenting near the centre one or two minute orifices for the transmission of the malar nerves and arteries. This surface is largely covered by the orbicularis palpebrarum, and gives origin to the zygomatici major and minor. The internal surface is concave, and abruptly excluded from the orbit by a THE MALAR. Fig. 76.—The Left Malar Bone. Frontal process. Orbital border. Posterior border. Malar canal. Zygomatic process. Maxillary process.— Anterior border. Inferior border. Notch for temporal nerve. For sphenoid. Orbital process. Malar canal. Malar canal. Maxillary process. Maxillary surface. prominent ledge of bone, the orbital process, which forms the anterior boundary of the temporal fossa. A large part of this surface is rough for articulation with the malar process of the maxilla. The orbital process of the malar is at right angles with the external surface, and presents the orbital orifice of the malar canal; this canal is usually single, but it may bifurcate as it traverses the bone, one branch emerging on the external, the other on the internal surface. The thin edge of this process articulates inferiorly with the orbital plate of the maxilla, and ends in a point known as the maxillary process. The superior portion articulates with the malar crest on the external surface of the greater wing of the sphenoid ; in the suture between these bones a notch (sometimes a foramen) exists for the temporal branch of the fifth nerve. When the orbital surface is large, it excludes the sphenoidal wing from articulation with the maxilla at the anterior extremity of the spheno-maxillary fissure. When this is the case, the border presents near its middle a short non-serrated margin. The malar bone presents superiorly the frontal process, which articulates with the external angular process of the frontal bone. The maxillary process 80 THE SKELETON. articulates with the maxilla, and occasionally forms the superior segment of the infraorbital foramen. The zygomatic process is directed backward, and is serrated mainly on its inner aspect for articulation with the zygoma. Of the four borders, the orbital is the longest, and extends from the frontal to the maxillary process. It is thick, rounded, and forms the outer and a large portion of the inferior circumference of the orbit. The inferior is continuous with the zygoma, and gives origin to the anterior fibres of the masseter. The anterior border is in relation with the maxilla, and near the margin of the orbit gives origin to a portion of the levator labii superioris proprius. The posterior border extends from the frontal to the zygomatic process, and presents a double curve; it gives attachment to the temporal fascia. This border is directly continu- ous below with the upper border of the zygoma, and above with the temporal ridge. Articulations.—The malar articulates with the maxilla, frontal, sphenoid, and temporal bones. Blood-supply.—The arteries of the malar are derived from the infraorbital, lachrymal branches of the ophthalmic, transverse facial, and deep temporal arteries. The muscles connected with it are :— Zygomaticus major. Masseter. Zygomaticus minor. Ossification.—The malar is a membrane-bone, and arises from two and occa- sionally three centres, which appear in the eighth week of embryonic life, and grow with astonishing rapidity; the bone quickly attains a relatively large size. Occasionally the two primary nuclei fail to coalesce, and the bone is repre- sented in the adult by two portions separated by a horizontal suture. Such bipar- tite malars have been observed in skulls obtained from at least a dozen different races of men. Bipartite malars have been seen with the suture vertical. That the bone may arise from three centres is shown by the fact that tripartite malars have been observed. At birth the maxillary process reaches as far forward as the outer border of the infraorbital canal; subsequently it may send a process over the canal. THE APPENDICULAR ELEMENTS OF THE SKULL. The bones which form this group are the mandible (lower jaw), malleus, incus, stapes, hyoid, the styloid process of the temporal bone, and the internal pterygoid process of the sphenoid. THE MANDIBLE OR LOWER JAW. The mandible (lower jaw or inferior maxilla) is in shape like a horseshoe; it consists of a horizontal portion or body, and two vertical portions or rami. The body consists of a right and a left half, meeting in the middle line to form the symphysis. Each half presents two surfaces and two borders. The external surface is smooth and generally convex, and presents the following points of interest: The symphysis ends inferiorly in a triangular surface which forms the chin. Near the symphysis is the incisive fossa, from which the levator menti arises; external to this is the mental foramen through which the mental nerve and artery issue. This foramen is in a line with the second bicuspid tooth. Extending backward and upward from the mental protuberance, so as to become continuous with the anterior border of the coronoid process, is the external oblique line ; along its upper border the depressor labii inferioris and THE MANDIBLE. 81 depressor anguli oris arise ; the platysma is attached to its lower edge. The internal surface presents, at a point corresponding to the symphysis, two pairs ot genial tubercles. The upper pair give origin to the genio-hyo-glossi, and the lower pair afford insertion to the genio-hyoid muscles. The tubercles occasionally form a single, median, irregularly shaped eminence. By the side of the genial tubercles there is a shallow, smooth depression, the sublingual fossa ; below this is the digastric fossa for the insertion of the anterior belly of the digastric muscle. Posterior to the genial tubercles, the internal oblique line (mylo- hyoid ridge) commences and extends backward, becoming more and more prom- inent as it approaches the alveolar border. The mylo-hyoid muscle is inserted along the whole length of this ridge. At the posterior part the superior constrictor takes origin, and the pterygo-maxillary ligament is attached to its posterior ex- tremity. Below the internal oblique line is the submaxillary fossa, which is in relation with the submaxillary gland. Fig. 77.—The Mandible. {Outer view.) Temporal. Coronoid process. Sigmoid notch. External pterygoid. Condyle. Neck. Capsular and External lateral ligament. Mental foramen. Levator menti. Depressor labii inf. The chin or mental protuber- ance. - Angle. Platysma. | Groove for facial artery. Depressor anguli oris, external oblique line. The inferior border of the body of the mandible is smooth and rounded ; near its junction with the ramus there is a groove for the facial artery. The superior border is composed of spongy bone, and is named the alveolus ; it presents sockets for eight teeth. From the outer edge of the alveolus, as far forward as the first molar tooth, the buccinator muscle takes origin. The ramus is quadrilateral in shape. It has two surfaces, four borders, and two processes. The external surface is for the insertion of the masseter muscle. The internal surface presents near its middle the mandibular (inferior dental) foramen which leads into the mandibular (inferior dental) canal which traverses the body of the bone and emerges at the mental foramen. This canal presents a series of fine apertures above, through which filaments of the mandibular nerve and artery pass to the teeth. In its posterior two-thirds the canal is nearer the internal, in its outer third it is nearer the external surface of the mandible. The posterior orifice of the canal is surmounted by the mandibular spine, to which the spheno-mandibular ligament is attached. Running obliquely downward behind 6 82 THE SKELETON. this spine is the mylo-hyoid groove, which lodges the mylo-hyoid nerve and artery. In the embryo, Meckel’s cartilage also occupies the groove. The trian- gular rough space behind this groove is for the insertion of the internal pterygoid muscle. The inferior border of the ramus is thick, rounded, and continuous with the Fig. 78.—The Mandible. (Inner View). External pterygoid. Capsule. Temporal. Mandibular spine. Mandibular foramen. . Spheno-mandi- bular ligament.. Superior con-, strictor. Mylo-hyoid" groove. Internal pterygoid." Stylo-mandi bular ligament. Buccinator Groove for sublingual gland. Genio-hyo- glossus. Genio- hyoid. Digastric. Mylo-hyoid. Internal oblique line. Groove for submaxillary gland. lower border of the body of the bone. The posterior border is rounded ; to its lower part the stylo-maxillary ligament is attached. This border is surmounted by the condyle, which is connected with the ramus by a somewhat constricted por- tion, the neck. The condyle is oval in shape, with it long axis transverse to the upper border Fig. 79.—The Mandible at Birth. Outer view. Inner view. of the ramus, but oblique with regard to the median axis of the skull, so that the outer is more anterior than the inner angle, and presents the condyloid tubercle for the external lateral ligament of the temporo-mandibular articulation. The convex surface of the condyle is covered with cartilage and rests in the glenoid THE MANDIBLE. 83 fossa; the neck is flattened in front and presents a pit for the insertion of a portion of the external pterygoid muscle. The superior border of the ramus is known as the sigmoid notch; it is terminated anteriorly by the coronoid pro- cess. This is a pointed process with two borders and two surfaces ; the inner sur- face presents a ridge, commencing at the tip and becoming continuous with the inner edge of the alveolus. To this ridge, to the area of bone in front of it and the tip of the coronoid process, the temporal muscle is inserted ; its outer surface affords attachment to the masseter and a few fibres of the temporal. The anterior border of the ramus is continuous with the external oblique line on the body of the bone. Blood-supply—The mandible is very vascular, and receives a large supply from the mandibular branch of the internal maxillary artery. This constitutes its main supply. It receives twigs also from the facial artery. Fig. 8o.—The Skull of an Old Woman Eighty-three Years Old, to Show the Changes in the Mandible and Maxilla. It gives attachment to the following muscles : — Buccinator. Depressor labii inferioris. Depressor anguli inferioris. Levator menti. Genio-hyo-glossus. Superior constrictor of pharynx. Masseter. Internal pterygoid. External pterygoid. PlatySma myoides. Geniohyoid. Mylo-hyoid. Digastric. Temporal. Ossification.—The mandible has six points of ossification for each lateral half. All these, with the exception of one, are deposited in membrane. The nuclei are deposited very early (between the sixth and eighth week), and fuse so rapidly that observations on the development of this bone are unusually difficult. Its six centres are mainly named according to their position. The mento-Meckelian.—This is deposited in the distal end of Meckel’s (mandibular) cartilage, and gives rise to that portion of the bone between the symphysis and the mental foramen. Orbicularis oris 84 THE SKELETON. The dentary.—This forms the lower border and outer plate, and supports the teeth, hence its name. The coronoid.—This gives rise to the process of that name. The condyloid.—This forms the condyle and adjacent portion of the neck of the bone. The angular.—This gives rise to the angle of the bone. The splenial.—This centre appears three weeks later than the portions already mentioned. It forms the inner plate of the mandible from near the sym- physis to the mandibular foramen. The mandibular spine represents the posterior extremity of the splenial. Its line of junction with the dentary is indicated in the adult bone by the mylo-hyoid groove. At birth the mandible is represented by two nearly horizontal troughs of bone lodging unerupted teeth. Each half is joined at the symphysis by fibrous tissue. The upper edge of the symphysis and the condyles are nearly on a level. The mandibular nerve lies in a shallow groove between the dentary and splenial plates. During the first year the two halves ankylose, union taking place from below upward, but the ankylosis is not complete until the second year. After the first dentition, the ramus forms with the body of the mandible an angle of about 140°, and the mental foramen is situated midway between the upper and lower borders of the bone opposite the second milk-molar. In the adult, the angle formed by the ramus and body is nearly a right angle, and the mental foramen is opposite the second bicuspid, so that its relative position remains unaltered after the first dentition. In old age, after the fall of the teeth, the alveolar margin is absorbed, the angle formed by the ramus and body becomes obtuse, and the mental foramen approaches to the alveolar margin. In a young and vigorous adult the mandible is, with the exception of the petrosal, the densest bone in the skeleton, and resists decay longest; in old age it becomes exceedingly porous, and often so soft that it may be broken easily. THE HYOID, THE STYLOID PROCESS, AND THE EAR BONES. The hyoid or lingual bone consists of a body and four processes. The body (basi-hyal) forms the central portion of the bone ; it is somewhat oblong in shape. Its anterior aspect is convex and divided by a longitudinal ridge into a superior and an inferior portion. Frequently it presents a median vertical ridge, and at the point where the horizontal and vertical ridges intersect, a tubercle, sometimes measuring four millimetres in length, is formed. The whole of the anterior surface is crowded with the origin and insertions of muscles. The posterior surface is deeply concave, and frequently presents several small depressions near the middle line which lodge accessory thyroid bodies. The inferior border is free, the superior gives attachment to the thyro-hyoid membrane. Between this membrane and the concavity of the hyoid a large bursa is occasionally found. The lateral borders are in relation with the greater cornua, but remain separated from them until late in life. The greater cornua (thyro-hyals) project backward and upward. Their upper and lower borders and anterior surfaces are occupied with muscles. Each cornu terminates posteriorly in a rounded tubercle, to which the thyro-hyoid ligament is attached. The lesser cornua (cerato-hyals) are small conical pieces of bone occupying the upper part of the suture between the body and the greater cornua. Their tips are continuous with the stylo-hyoid ligaments. Muscles attached to the hyoid bone :— Lingualis. Genio-hyo-glossus. Middle constrictor. Sterno-hyoid. Digastric. Genio-hyoid. Thyro-hyoid. Omo-hyoid. Mylo-hyoid. Hyo-glossus. Hyo-epiglottideus (when present). HYOID BONE AND STYLOID PROCESS. 85 Ligaments :— Thyro-hyoid. Stylo-hyoid ; and the thyro-hyoid membrane. Blood-supply.—The hyoid receives twigs from the arteries supplying the muscles attached to it, in addition to direct supply from the superior thyroid and lingual arteries. Ossification.—At the third month the hyoid consists of hyaline cartilage; it is directly continuous with the styloid process. In the fourth month a nucleus appears on each side of the middle line; they become quickly confluent to form the body of the bone. In the fifth month each greater cornu has a conspicuous nucleus. The centres for the lesser cornua are delayed until the second year. The greater cornua remain separate from the body until alter middle life. The lesser cornua rarely ankylose with the body of the bone. As a rule, they are small and inconspicuous; occasionally they are very long, and are sometimes continu- ous with the styloid process of their respective sides. The styloid process is a thin, cylindrical spike of bone wedged in between the tympanic plate and the petrosal immediately anterior to the stylo-mastoid foramen. It consists of two parts: a tympano-hyal segment which in the adult is hidden behind the tympanic plate, and a free projecting portion of variable length. As a rule, it varies from five to fifty millimetres. When short it is hidden by the vaginal process, but it may reach to the hyoid bone. Its base forms the Fig. 81.—The Hyoid. Greater cornu Lesser cornu anterior boundary of the stylo-mastoid foramen. The free portion gives origin to the following muscles : The stylo-pharyngeus arises from the base posteriorly; the stylo-hyoid from the outer aspect near the middle; and the stylo-glossus from the front near the tip. The extremity of the process is continuous with the stylo-hyoid ligament. A band of fibrous tissue—the stylo-mandibular ligament—passes from the process below the origin of the stylo-glossus to the angle of the mandible. Muscles attached to the styloid process :— Ligaments :— Stylo-glossus. Stylo-hyoid. Stylo-pharyngeus. Stylo-hyoid. Stylo-mandibular. The morphology and development of this process are described on page 109. The malleus.—This is the most external of the auditory ossicles, and comes in relation with the tympanic membrane. Its upper portion, or head, is lodged in the attic of the tympanum. It is of rounded shape, and presents posteriorly an elliptical depression for articulation with the incus. Below the head is a con- stricted portion or neck. From beneath the neck three processes diverge. The largest is the handle or manubrium, which is slightly twisted and flattened. It forms an obtuse angle with the head of the bone, and lies between the mem- brana tympani and the mucous membrane covering its inner surface. The tensor tympani tendon is inserted into the manubrium near its junction with the neck on the inner side. The slender process (gracilis or Folian) is a long, 86 THE SKELETON. slender, delicate spiculum of bone (rarely seen of full length except in the foetus), projecting nearly at right angles to the anterior aspect of the neck, and extending obliquely downward. It lies in the Glaserian fissure, and in the adult usually becomes converted into connective tissue, except a small basal stump. The short process is a conical projection from the outer aspect of the base of the manu- brium. Its apex is connected to the upper part of the tympanic membrane, and its base receives the external ligament of the malleus. The malleus also gives Fig. 82.—The Ear Bones. (Modified fro??i Henle.) INCUS |MALLEUS STAPES Left malleus. Fossa for incus— -Head of malleus. -Short process. “Slender process. “Handle or manubrium. Left incus. -Articular surface for malleus. Short process.— - Long process. Anterior crus. x .Orbicular tubercle. Left stapes. Base.- Base of stapes. Posterior crus. Neck. attachment to the suspensory ligament, and to the long anterior ligament of the malleus which was formerly described as the laxator tympani muscle. The incus.—This bone is situated between the malleus externally and the stapes internally. It presents for examination a body and two processes. The body is deeply excavated anteriorly for the reception of the head of the malleus. The short process projects backward, and is connected by means of liga- mentous fibres to the posterior wall of the tympanum, near the entrance to the THE EXTERIOR OE THE SKULL. 87 mastoid antrum. The long process is slender, and directed downward and inward; it lies parallel with the handle of the malleus. On the inner aspect of the distal extremity of this process is the orbicular tubercle, connected with the process by a narrow neck. Its free surface articulates with the head of the stapes. The orbicular tubercle is separate in early life. The stapes is the innermost ossicle. It has a head directed horizontally out- ward, capped at its outer extremity by a disc resembling the head of the radius. The cup-shaped depression receives the orbicular tubercle of the incus. The base occupies the fenestra ovalis, and like this opening the inferior border is straight and the superior curved. The base is connected with the head by means of two crura, and a narrow piece of bone called the neck. Of the two crura, the ante- rior is the shorter and straighter. The crura with the base form a stirrup-shaped arch, of which the inner margin presents a groove for the reception of the mem- brane which is stretched across the hollow of the stapes. In the early embryo this hollow is traversed by the stapedial artery. The neck is very short, and receives on its posterior border the tendon of the stapedius muscle. THE EXTERIOR OF THE SKULL. The skull, when viewed from above, presents an oval outline; the posterior part is broader than the anterior. The bones seen in this view are the frontal, parietals, and the interparietal portion of the occipital. In a skull of average width the zygomata come into view, but in very broad skulls they are obscured. The sutures of the vertex are:— The metopic, which is, in most skulls, merely a median fissure in the frontal bone just above the glabella; occasionally it involves the whole length of the bone. It is due to the persistence of the fissure normally separating the two halves of the bone in the infant. The sagittal is situated between the two parietals, and extends from the bregma to the lambda. The coronal lies between the frontal and parietals, and extends from pterion to pterion. The lambdoid is formed by the parietals and interparietal portion of the occipital. It extends from asterion to asterion. The occipital suture is only present when the interparietal exists as a separate element (Fig. 35). The more important regions are :— The bregma, which indicates the situation of the anterior fontanelle and marks the confluence of the coronal, sagittal, and, when present, the metopic sutures. The lambda, where the sagittal enters the lambdoid suture ; it marks the situation of the posterior fontanelle. The obelion, a little anterior to the lambda, is usually indicated by a median or two lateral foramina. It indicates the spot where the sagittal suture first suffers obliteration. Viewed from behind, the skull appears irregularly globular, the inferior part of its circumference being somewhat flattened. The limits of the flattened portion are indicated by the mastoid processes. The centre is occupied by the occipital protuberance ; this, with the occipital crest and the three pairs of nuchal lines, give to the lower half a rough and uneven appearance. The sutures in this view are the terminations of the sagittal, lambdoidal, and, when present, the occipital suture. The occipital point (Fig. 94) is the most posterior part of the skull, and is exactly opposite the ophryon. The inion corresponds to the external occipital protuberance. The lateral aspect of the skull is very uneven ; it presents three recesses or fossae. Its irregularity is increased by the zygoma. 88 THE SKELETON. The temporal fossa, semilunar in shape, is limited above by the superior temporal ridge, and below by the zygoma. The temporal ridge begins at the external angular process of the frontal bone, and curves upward and backward to cross the frontal and parietal bones; it then descends along the mastoid portion of the temporal bone to become con- tinuous with the upper border of the zygoma. In many skulls this ridge is double. The lower ridge gives origin to the temporal muscle. The upper is the least con- stant ; it diverges from the lower ridge as it approaches the coronal suture. At the middle of the parietal bone the two ridges are often ten millimetres apart. This ridge gives attachment to the temporal fascia. The fossa is almost entirely occupied by the temporal muscle. Fig. 83.—The Skull. (ATorma lateralis.) ' External pterygoid, The zygomatic fossa is limited anteriorly by the zygomatic surface of the maxilla ; internally by the external pterygoid plate; externally by the zygomatic arch and the ramus of the mandible; and posteriorly by a line drawn from the foramen spinosum to the zygomatic tubercle. The outer surface of the greater wing of the sphenoid behind the pterygoid ridge and a small piece of the squamosal form part of the upper boundary of the fossa. The chief objects of interest in this region are :—The spheno-maxillary and pterygo-maxiilary fissures, the pterygoid ridge on the sphenoidal wing, the foramen ovale, foramen spinosum, and the articular eminence of the squamosal. The spheno-maxillary fissure is horizontal in position, and lies between the orbital border of the maxilla and the greater wing of the sphenoid ; externally THE SPHENO-MAXILLARY FOSSA. 89 it is completed usually by the malar; frequently the sphenoid will join the maxilla and exclude the malar bone from the fissure; internally it is terminated by the zygomatic surface of the orbital process of the palate bone. Through this fissure the orbital, spheno-maxillary, and zygomatic fossae communicate. The zygomatic fossa lodges the temporal, external pterygoid, and internal pterygoid muscles. The pterygo-maxillary fissure forms a right angle with the preceding. It is situated between the maxilla and the anterior border of the external pterygoid process. At its lower angle the external pterygoid plate occasionally articulates with the maxilla. The pterygo-maxillary fissure leads from the zygomatic fossa directly into the spheno-maxillary fossa, a small space shaped like an inverted pyramid, situated between the maxilla and the roots of the pterygoid processes. The roof of this fossa is formed by the under surface of the greater wing of the sphenoid. The anterior boundaries are a small portion of the zygomatic surface of the maxilla and the orbital process of the palate; posteriorly it has the roots of the pterygoid processes, and the lower part of the orbital surface of the greater wing of the sphenoid ; and internally the vertical plate of the palate bone. The apex of the pyramid leads into the posterior palatine canal. The inner wall Fig. 84.—A Section of the Skull, showing the Inner Wall of the Orbit, the Base of the Antrum, and the Spheno-maxillary Fossa. Frontal sinus Nasal bone. Anterior ethmoid canal. -Posterior ethmoid canal. Nasal process of maxilla. Lachrymal. Lachrymal canal Optic foramen Os planum of ethmoid. Orifice of antrum. Inferior turbinal. Spheno-palatine foramen. Vidian canal leading into the spheno-maxillary fossa. Sphenoid. Anterior nasal spine, Palate bone External pterygoid plate. Palate bone. presents the spheno-palatine foramen which leads into the nasal fossa. The posterior wall has three openings in the following order, from without inward, and from above downward: the foramen rotundum, Vidian canal, and pterygo-palatine canal. Anteriorly it communicates with the orbit by the spheno-maxillary fissure ; and externally the pterygo-maxillary fissure leads into the zygomatic fossa. This fossa is mainly of interest on account of its relation to the spheno-palatine (Meckel’s) ganglion. The various foramina and canals connected with the fossa serve for the transmission of the nerves connected with this ganglion and the terminal branches of the internal maxillary artery. In addition to the fossae, the lateral region presents the glenoid fossa with its articular eminence, the external auditory meatus, the mastoid and styloid pro- cesses, and the following sutures: — The spheno-parietal, which lies between the greater wing of the sphenoid and the anterior inferior angle of the parietal. The squamous is formed by the squamosal overlapping the lower border of the parietal. 90 THE SKELETON. The parieto-mastoid, which lies between the posterior inferior angle of the parietal and the mastoid portion of the petrosal. The zygomatic suture is formed by the union of the zygoma with the malar bone. The squamo-sphenoidal is situated between the anterior border of the squamosal and the greater wing of the sphenoid. The spheno-malar suture is formed by the orbital process of the malar and the malar ridge on the greater wing of the sphenoid. Near its middle the suture is perforated by the spheno-malar foramen, which allows the temporal branch of the orbital nerve and a branch of the lachrymal artery to escape from the orbit. This foramen in some adult skulls is complete in the malar. The fronto-squamosal is an occasional suture; when it is present, the anterior inferior angle of the parietal is excluded from the greater wing of the sphenoid. The more important regions are :— The pterion, which marks the situation of the anterior lateral fontanelle, is the meeting-place of the coronal, squamous, spheno-parietal, squamo-sphenoidal, and the fronto-squamosal sutures. Frequently it is occupied in the adult by the epipteric ossicle. Fig. 85.—Hard Palate op a Child Five Years Old. Gubernacular canals. Anterior palatine fossa. Maxillo-premaxillary suture. Palate process of maxilla. Palate bone, Posterior palatine foramen. Accessory palatine canals. The asterion indicates the situation of the posterior lateral fontanelle and marks the confluence of the squamosal, parieto-mastoid, lambdoid, the occipito- mastoid, and occasionally the occipital sutures. Sometimes it is occupied by a Wormian bone. The stephanion is the spot where the superior temporal ridge cuts the coronal suture. The auricular point is the centre of the external auditory meatus. The base of the skull is very irregular, and extends from the incisor teeth to the occipital protuberance. Laterally it is limited by the zygomatic arches. Anteriorly it presents the hard palate. When the skull is inverted the hard palate stands at a higher level than the rest; it is bounded anteriorly and laterally by the alveolar ridges containing the teeth. The bones appearing in the intermediate space are the pre-maxillary and palatine portions of the maxillae, and the horizontal plates of the palate bones. The bone is rough for the attachment of the muco-periosteum. The following points are readily recognized (Fig. 85) :— The meso-palatine suture commences at the alveolar point, traverses the anterior palatine fossa, and terminates at the posterior nasal spine. The transverse palatine suture between the palate bones and palatine processes of the maxillae. THE BASE OE THE SKULL. 91 In young skulls the maxillo-premaxillary sutures, and behind the incisor teeth four small openings known as the gubernacular canals. The anterior palatine fossa containing the termination of four canals: two small orifices, foramina of Scarpa, situated one behind the other in the meso- palatine suture ; and two larger openings, the foramina of Stenson. Scarpa’s formina transmit the naso-palatine nerves; Stenson’s are in relation with Jacob- son’s organs. At the posterior angles of the hard palate are the posterior palatine fora- mina, through which the posterior palatine vessels and the anterior palatine nerves emerge on to the palate; a thin lip of bone separates them from the accessory palatine foramina for the posterior palatine nerves. The accessory foramina are in the tuberosity of the palate bone. The hamular process of the internal pterygoid plate is the most posterior limit of the hard palate. At the posterior extremity of each alveolar ridge is the tuberosity of the maxilla. Between the tuberosities of the maxilla and the palate bone are a few minute foramina (variable in number and not always present), the external palatine canals for the external palatine nerves. Behind the hard palate are the posterior nares, separated from each other by the vomer. Each is bounded externally by the internal pterygoid plate ; below by the horizontal plate of the palate bone ; above by the under surface of the body of the sphenoid, with the ala of the vomer and a portion of the sphenoidal process of the palate bone. External to the nares there is on each side a vertical fossa lying between the pterygoid plates. It extends upward to the under surface of the greater wings of the sphenoid ; it is completed anteriorly by the coalescence of the pterygoid plates, and below by the tuberosity of the palate bone. It contains the following points of interest:— An elongated furrow, the scaphoid fossa, for the tensor palati muscle. The general cavity of the pterygoid fossa, which lodges the tensor palati and internal pterygoid muscles. Frequently there is a notch in the external pterygoid plate close beside the foramen ovale. The posterior termination of the Vidian canal. If a line be drawn across the skull base from one zygomatic tubercle to the other, it will fall immediately behind the external pterygoid plate and bisect the foramen spinosum on each side. A second transverse line, drawn across the opisthion or posterior margin of the foramen magnum, will fall behind the mastoid processes. The space between these imaginary lines may be called the sub-cranial region ; that behind the second line the sub-occipital region. In addi- tion to these there is a lateral space anterior to the first line known as the zygo- matic region. Each will require separate consideration. The sub-cranial region is formed by the following bones: In the centre, the under surface of the bodies of the sphenoid and occipital bones. Laterally, the petrosal, a small piece of the greater wing of the sphenoid, and of the squamosal, and part of the occipital. It presents the following points in the middle line for study: — The pharyngeal tubercle. The foramen magnum and the occipital condyles. The most anterior point of the foramen is termed the basion, and the most posterior point the opisthion. On each side will be seen :—The anterior condyloid foramen for the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery. The posterior condyloid fossa with the posterior condyloid foramen (this foramen is not constant). The sphenotic (middle lacerated) foramen and the orifice of the Vidian canal. The canalis musculo-tubarius for the tensor tympani muscle and Eustachian tube. 92 THE SKELETON. Fig. 86.—The Skull. (Norma basilaris.) Mass eter Tensor palati. Azygos uvulae. Superior constrictor. Internal pterygoid. Tensor palati. Tensor tympani. Levator palati. Rectus capitis anticus major. Rectus capitis anticus minor. Anterior common liga- ment of spine. Vertical part of crucial ligament. Check ligament. Capsular ligament. Posterior occipito-at- lantal ligament. Superior oblique. Rectus capitis posticus major. Rectus capitis posticus minor. Ligamentum nuchae. Trapezius. EXTERIOR OF THE SKULL. 93 Fig. 87.—The Skull. (Norma bdsilaris.) Scarpa’s foramen. Stenson’s foramen. Scarpa’s foramen. Anterior palatine fossa. Palatine groove. Posterior palatine foramen. Spine of the palate bone. Hamular process. Sphenoidal process of palate bone. Sphenotic (middle lacerated) foramen. Pharyngeal tubercle. Carotid canal. Anterior condyloid foramen. Basion. Tubercle for check ligament. Posterior condyloid foramen. Opisthion. External occipital crest. External occipital protuberance. 94 THE SKELETON. The carotid canal. Aqueductus cochleae, or ductus perilymphaticus. The jugular foramen and fossa for the glosso-pharyngeal, vagus, and spinal accessory nerves, the internal jugular vein, and a meningeal branch of the ascend- ing pharyngeal artery. The tympanic canaliculus for Jacobson’s nerve. (Tympanic of glosso- pharyngeal). Fig. 88.—The Skull. (Norma facialis.) Surface covered by occipito- frontalis. Corrugator sup- ercilii. Tendo oculi. Orbicularis palpebra- rum. Levator labii superions alaeque nasi. Levator labii su- periors. Levator anguli oris. Compressor na- ris. Depressor alse nasi. Orbicularis oris. Zygomaticus major. Zygomaticus minor. The alar spine of the sphenoid; this is sometimes fifteen millimetres in length. The glenoid fossa with the Glaserian fissure. This lodges the slender process of the malleus, the tympanic twig of the internal maxillary artery. A small passage beside it, the canal of Huguier, conducts the chorda tympani nerve from the tympanum. The external auditory meatus. EXTERIOR OE THE SKULL. 95 The auricular fissure for the tympanic branch of the vagus. The tympanic plate and vaginal process. The styloid process. The stylo-mastoid foramen for the stylo-mastoid artery and the exit of the facial nerve. The mastoid process with the digastric and occipital grooves. Fig. 89.—The Skull. \Norma facialis.) Ophryon Superciliary ridge Glabella Nasion Nasal sinus. Subnasal point, Canine fossa. Canine eminence Alveolar point, The sub• occipital region presents chiefly muscular ridges. They are the superior, middle, and inferior nuchal lines, with the external occipital protuberance and the external occipital crest. Behind the mastoid process is an opening of variable size, the mastoid foramen ; a branch of the occipital artery enters, and a vein from the lateral sinus issues from this foramen. The anterior aspect of the skull is oval in outline, but presents a very irregular surface. Its upper portion, or forehead, presents the frontal eminences and 96 THE SKELETON. superciliary ridges. In the middle line is the prominence formed by the nasal bones, with a deep pyramidal recess, the orbits, on each side. Below the nasal bones are the entrances to the nasal sinuses and the various recesses connected with them. The teeth form a conspicuous feature in this view of the skull, the outline of which is completed by the mandible. The bones visible in this view of the skull are : the frontal, nasals, lachrymals, orbital surfaces of the lesser and the greater wings, and a portion of the body of the sphenoid, the ossa plana of ethmoid, and the orbital processes of the palate bones, the malars, maxillse, inferior turbinals, and the mandible. The foramina are : the supraorbital, infraorbital, optic, temporal, and mental; the lachrymal duct; the malar and ethmoidal canals; and the spheno-maxillary and sphenoidal fissures. The orbits are two cavities of pyramidal shape, which lodge the eyeball and its associated muscles, nerves, and vessels. The apex of each orbit corresponds to the optic foramen, a circular orifice which transmits the optic nerve and ophthalmic artery. The base looks forward and outward. It is formed by the frontal bone above, the nasal process of the maxilla on the inner side, the malar bone externally, and below by the malar and body of the maxilla. The following points are seen around the base: The suture between the external angular process of the frontal bone and the malar; the supraorbital notch (sometimes a complete foramen); and the suture between the frontal bone and the nasal process of the maxilla; and in the inferior segment of the circumference is the malo-maxillary suture. Occasionally, the infraorbital foramen opens by a narrow fissure into the orbit. The roof of the orbit is formed mainly by the orbital plate of the frontal bone, and completed posteriorly by the lesser wing of the sphenoid. At the outer angle it presents the lachrymal fossa for the lachrymal gland, and at the inner angle a depression for the pulley of the superior oblique muscle. The floor is formed by the orbital plate of the maxilla, the orbital process of the malar, and the orbital process of the palate bone. At its inner angle it presents the lachrymal canal, and near this a depression for the origin of the inferior oblique muscle. The floor has a furrow for‘the infraorbital artery and the superior maxil- lary division of the fifth nerve. The furrow terminates anteriorly in the infra- orbital canal, through which the infraorbital nerve and artery emerge on the face. Near the commencement of the canal a narrow passage, the anterior dental canal, runs forward and downward in the anterior wall of the antrum; it conducts nerves to the incisor and canine teeth. The outer wall is very oblique ; it is formed by the orbital surface of the greater wing of the sphenoid, and the malar. Between it and the roof, near the apex, is the sphenoidal fissure, by means of which the third, fourth, ophthalmic division of the fifth, and sixth nerves enter the orbit from the cranial cavity. The lower margin of the fissure presents near the middle a small tubercle, from which one head of the external rectus muscle arises. Between the outer wall and the floor, near the apex, is the spheno-maxillary fissure, which allows the superior maxillary nerve to enter the infraorbital groove from the spheno-maxillary fossa. At the anterior margin of the fissure, the sphenoidal wing occasionally articulates with the maxilla, but frequently it is excluded by the malar. In front of the anterior extremity of this fissure is the orbital orifice of the malar canal. Near the outer extremity of the sphenoidal fissure a few small foramina may be seen, especially in old skulls, which allow branches of the middle meningeal artery to creep into the orbit. A vertical fissure, the spheno-malar, traverses the outer wall. It contains a very small foramen (the spheno-malar), which allows the temporal branch of the orbital nerve to escape from the orbit. This foramen is sometimes confined to the malar bone. The inner wall, narrow and straight, is formed by the lachrymal, os planum of the ethmoid, and a part of the body of the sphenoid. The ethmoid section of the transverse suture contains the orifices of the anterior and posterior eth- moidal canals : the former transmits the nasal nerve and anterior ethmoidal artery; the latter the posterior ethmoidal artery. THE ORBITS. 97 Anteriorly is the lachrymal groove, and behind this the crest which gives origin to the tensor tarsi. This wall has three vertical sutures: one between the nasal process of the maxilla and the lachrymal, the ethmo-lachryrfial, and one between the os planum and body of the sphenoid. Occasionally the sphenoidal turbinal bone appears in the orbit between the os planum of the ethmoid and the body of the sphenoid (Fig. 67). The orbit communicates with the cranial cavity by the optic foramen and Fig. 90.—The Inner Wall of the Orbit. Frontal sinus. Nasal bone. Nasal process of maxilla. Lachrymal. Lachrymal canal. Orifice of antrum. Inferior turbinal. Palate bone. Anterior nasal spine. ■Anterior ethmoid canal. •Posterior ethmoid canal. Optic foramen. Os planum of ethmoid. .Spheno-palatine foramen. ■Vidian canal leading into the spheno-maxillary fossa. Sphenoid. •External pterygoid plate Palate bone. Fig. 91.—Section through the Nasal Fossa to show the Septum. Crista galli Crest of sphenoid Nasal spine of frontal, Groove for nasal nerve. Crest of palate bone. Spine of palate bone. Crest of maxilla. sphenoidal fissure; with the nasal fossa by means of the lachrymal duct; with the zygomatic and spheno-maxillary fossae by way of the spheno-maxillary fissure. In addition to these large openings, the orbit has six other foramina—the infra- orbital, malar, spheno-malar, anterior and posterior ethmoidal canals, and the anterior dental canal—opening into it or leading from it. In old skulls the frontal sinuses occasionally extend into that portion of the horizontal plate of the frontal bone which forms the roof of the orbit. 98 THE SKELETON. The following muscles arise within the orbit : the four recti, the superior oblique, and levatorpalpebrce superioris, near the apex ; the inferior oblique on the floor of the orbit external to the lachrymal canal; and the tensor tarsi from the lachrymal crest. The margins of the spheno-maxillary fissure give attachment to the orbitalis muscle. The nasal fossae or sinuses are two irregular cavities situated on each side of a median vertical septum, extending from the anterior part of the skull-base to the superior surface of the hard palate. They are somewhat oblong in section, but are narrower above than below. Each fossa presents a roof, floor, inner and outer wall, and opens in front by the anterior naris, and communicates behind with the pharynx by the posterior naris. The roof resembles that of a house with two sloping edges and an intermediate level portion. The anterior slope is formed by the posterior surface of the nasal bone and the nasal spine of the frontal. The horizontal portion corresponds to the cribriform plate of the ethmoid and the sphenoidal turbinal. The posterior slope is formed by the inferior surface of the body of the sphenoid, an ala of the vomer, and a small portion of the sphenoidal process of each palate bone. Fig. 92.—Section Through the Nasal Fossa to Show the Outer Wall with the Meatuses. Crista galli. - Frontal sinus. Body of sphenoid. Sphenoidal sinus. Spheno-palatine foramen. Middle meatus. Internal pterygoid plate. Palate bone. - Superior turbinal. ■ Middle turbinal. - Infundibulum. - Inferior turbinal. -interior nasal spine. Anterior palatine fora- men. The floor is wider than the roof, concave from side to side, and has a slight backward slope. It is formed mainly by the palatine process of the maxilla, and completed posteriorly by the horizontal plate of the palate bone. Near its anterior part, close beside the septum, is the anterior palatine canal. The septum, or inner wall, is formed by the crest of the sphenoid, the crest of the nasal bones, nasal spine of frontal, the mesethmoid, vomer, and the median crest formed by the apposition of the palatine plates of the maxillae and the hori- zontal plates of the palate bones. The anterior border has a triangular outline, limited above by the mesethmoid, and below by the vomer. This receives the triangular cartilage of the nose. The posterior border is formed by the pharyngeal edge of the vomer. The septum is usually deflected to one side, and is occasionally perforated. Sometimes a strip of cartilage, continuous with the triangular cartil- age, persists between the vomer and mesethmoid. The outer wall is formed by the nasal process and inner wall of the maxilla, the lachrymal, the ethmoidal and inferior turbinals, the vertical plate of the palate bone, and the inner surface of the internal pterygoid plate. The outer wall pre- sents three recesses or meatuses. The superior meatus is situated between THE NASAL FOSSAE. 99 the superior and middle turbinal; it opens posteriorly; three orifices are in rela- tion with it, namely, the orifice of the posterior ethmoidal cells, the spheno- palatine foramen, and the opening of the sphenoidal sinus. The middle meatus lies between the middle and inferior turbinals. It opens anteriorly and posteriorly. This meatus has two orifices communicating with it—the opening of the antrum (which is of very irregular shape) and the termination of the infun- dibulum. The inferior meatus is situated between the inferior turbinal and the floor of the fossa ; it presents near its anterior part, under cover of the turbinal, the terminal orifice of the nasal duct. This is the largest meatus, and, like the middle, opens anteriorly and posteriorly. The anterior narial orifices are bounded above by the lower border of the nasal bones, laterally by the maxillae, and inferiorly by the premaxillary portions of the maxillae. In the recent state they are separated by the triangular cartilage; in the dried skull the most anterior inferior limit is the anterior nasal spine. The posterior narial orifices are bounded above by the alae of the vomer, the sphenoidal process of the palate bones, and the under surface of the sphenoid ; externally by the internal pterygoid plates; and inferiorly by the posterior border Fig. 93.—The Posterior Nares. Pterygo-palatine canals. Vidian canal Foramen ovale. Scaphoid fossa - Vomer. Pterygoid fossa. External pterygoid plate. Internal pterygoid plate. Tuberosity of palate bone. Hamular process. Spine of palate or posterior nasal spine. of the horizontal plates of the palate bones. They are divided by the posterior border of the vomer and the posterior nasal spine. The nasal fossae communicate with all the more important fossae and sinuses of the skull. By means of the foramina in the roof they are in connection with the cranial cavity. The infundibulum brings each fossa in communication with the frontal and anterior ethmoidal cells. The posterior ethmoidal and the sphenoidal cells open into the superior meatuses. The spheno-palatine foramina connect them with the spheno-maxillary fossae, and an irregular orifice in each outer wall causes them to communicate with the antra. The nasal ducts connect them with the orbits, and the anterior palatine canals with the buccal cavity. The sutures visible in an anterior view of the skull are numerous, and for the most part unimportant:— The transverse suture extends from one external angular process to the other. The upper part of the suture is formed by the frontal bone ; below are the malar, greater and lesser wing of the sphenoid, os planum, lachrymal, maxillary, and nasal bones. A portion of this complex suture, lying between the sphenoid and frontal bones, appears in the anterior cranial fossa. Other and less important fissures are the internasal, naso-maxillary, inter- 100 THE SKELETON. maxillary, and malo-maxillary. The small sutures visible in the orbit have been already mentioned in describing that cavity. The following points are seen in an anterior view of the cranium : — The glabella, a smooth space between the converging superciliary ridges. The ophryon is the most anterior point of the metopic suture. The nasion is the central point of the transverse suture. The subnasal point is the middle of the inferior border of the anterior nasal aperture at the base of the nasal spine. The alveolar point is the centre of the anterior margin of the upper alveolar arch. THE INTERIOR OF THE SKULL. In order to study the interior of the skull it is necessary to make sections in three directions—sagittal, coronal, and horizontal. This enables the student to examine the various points with facility, and displays the great proportion the brain cavity bears to the rest of the skull. The sagittal section should be made slightly to one side of the median line in order to preserve the nasal septum. The black line (Fig. 94) drawn from the basion (anterior margin of the foramen magnum) to the gonion (the anterior extremity of the sphenoid) represents the basi-cranial axis ; whilst the line drawn from the gonion to the sub-nasal point lies in the basi-facial axis. These two axes form an angle termed the cranio-facial, which is useful in making comparative measurements of crania. A line prolonged vertically upward from the basion will strike the bregma. This is the basi-bregmatic axis, and gives the greatest height of the cranial cavity. A line drawn from the ophryon to the occipital point indicates the greatest length of the cranium. Near its middle, the cranial cavity is encroached upon by the petrosal; the walls are channeled vertically by narrow grooves for the middle and small meningeal arteries, and toward the base broader furrows are found for the venous sinuses. The coronal section is most instructive when made in the basi-bregmatic axis. The section will pass through the petrosal in such a way as to traverse the two external auditory passages and expose the tympanum and vestibule, and will also partially traverse the internal auditory meatuses. Such a section will divide the parietal bones slightly posterior to the parietal eminences, and a line drawn transversely across the section at the mid-point will give the greatest transverse measurement of the cranial cavity. A skull divided in this way facilitates the examination of the parts about the posterior nares. The horizontal section of the skull should be made through a line extending from the ophryon to the occipital point, passing laterally a few millimetres above the pterion on each side. It is of great advantage to study the various parts on the floor of the cranial cavity in a second skull having the dura mater and its various processes in situ. The floor of the cranial cavity presents three irregular depressions termed the anterior, middle, and posterior fossae. The anterior fossa.—The floor of this fossa is on a higher level than the rest of the cranial floor. It is formed by the horizontal plate of the frontal bone, the cibriform plate of the ethmoid, and the lesser wings of the sphenoid, which meet each other and exclude the pre-sphenoid from the anterior fossa. The free margins of the lesser wings and the optic groove mark the limits of this fossa posteriorly. The central portion of the fossa is depressed on each side of the crista galli, the depressions forming a part of the roofs of the nasal sinuses; laterally, the floor of this fossa is convex where it corresponds to the roof of the orbits, and is marked by irregular furrows. It supports the frontal lobes of the cerebrum. The sutures traversing the floor of the fossa are the fronto-ethmoidal, forming three sides of a rectangle, that portion of the transverse facial suture which traverses the roof of the orbit, and the ethmoido-sphenoidal suture, the centre of which corresponds to the gonion. The points of interest in the fossa are :— INTERIOR OF THE SKULL. 101 A groove for the superior longitudinal sinus. The foramen caecum which transmits a small vein. The crista galli. The ethmoidal fissure for the nasal branch of the fifth nerve. The cranial orifice of the anterior ethmoidal canal, transmitting the nasal branch of the fifth and a meningeal branch of the anterior ethmoidal artery. Ethmoidal foramina for the olfactory filaments. Cranial orifice of the posterior ethmoidal canal, transmitting a meningeal branch of the posterior ethmoidal artery The ethmoidal spine of the sphenoid. Furrows for meningeal arteries. The middle cranial fossa presents a central isthmus and two lateral depressed portions. It is limited anteriorly by the posterior border of the lesser wings of the sphenoid and the anterior margin of the optic groove. The posterior limits Fig. 94.—The Skull in Sagittal Section BREGMA BASION are the dorsum ephippii and the superior border of the petrosals. Laterally it is bounded by the squamosals and the parietal bones. The floor is formed by the body and greater wings of the sphenoid, and the anterior surface of the petrosal. It contains the following sutures: spheno-parietal, petro-sphenoid, squamo- sphenoidal, squamous, and a portion of the transverse suture. The central portion or isthmus of the middle fossa possesses the following points from before back- ward :— The optic groove, which lodges the optic chiasma. The optic foramina, transmitting the optic nerve and ophthalmic artery. The olivary process, indicating the line of ankylosis between pre- and post- sphenoid. The anterior clinoid processes. The pituitary fossa, with the middle clinoid processes, and grooves for the internal carotid arteries. The dorsum ephippii, with the posterior clinoid processes, and notches for the third pair of cranial nerves. 102 THE SKELETON. Fig. 95.—The Skull in Horizontal Section, Ethmoidal fissure for nasal nerve. Anterior ethmoidal canal (for nasal nerve). Ethmoidal foramina for olfactory nerve. Optic foramen (for second or optic nerve). Foramen rotundum (second division of fifth nerve). Foramen ovale (third division of fifth nerve). Notch for sixth nerve Depression for fifth nerve. Hiatus fallopii. Interior auditory meatus (seventh and eighth nerves). Jugular foramen (ninth, tenth, and eleventh nerves). Anterior condyloid foramen (twelfth nerve). INTERIOR OF THE SKULL. 103 Fig. 96.—The Skull in Horizontal Section. Frontal bone. Ridge for falx cerebri. Crista galli. Anterior fossa. Cribriform plate. Lesser wing of sphenoid. Optic groove. Pituitary fossa. Dorsum ephippii. Petro-sphenoidal process. Middle fossa. The clivus. Foramen mag- num. Posterior fossa. Internal occipital crest. Internal occipital protuberance. Occipital bone. 104 THE SKELETON. This central depression is in direct relation with the parts of the brain sur- rounding the circle of Willis. The lateral depressions receive the temporo-sphenoidal lobes of the brain, and are marked by numerous furrows roughly corresponding to the convolutions of the cerebrum. Numerous narrow diverging channels pass upward from the fossa toward the vertex; these lodge the ramifications of the middle and small menin- geal arteries. The following openings occur on each side of this fossa :— The sphenoidal fissure, leading into the orbit and transmitting the third, fourth, ophthalmic division of the fifth, the sixth nerve, and ophthalmic vein. In the greater wing of the sphenoid near its union with the frontal bone there are small openings allowing twigs of the middle meningeal artery to enter the orbit. The foramen rotundum, which conducts the second division of the fifth nerve into the spheno-maxillary fossa. The foramen ovale : this transmits the third division of the fifth with its motor root, the small meningeal artery, and the small superficial petrosal nerve. The foramen Vesalii (not always present) for a small vein. The foramen spinosum, for the middle meningeal artery and its venae comites. The sphenotic foramen (middle lacerated foramen), which transmits at its inner angle the internal carotid artery, with the carotid plexus of nerves. On the posterior wall of this fossa the objects of interest are: — A depression which lodges the Gasserian ganglion. The hiatus Fallopii, for the great superficial petrosal nerve, and a twig from the middle meningeal artery. A foramen for the small superficial petrosal nerve. An eminence formed by the superior semicircular canal. Anterior and slightly external to the ridge formed by the- superior semicircular canal, the bone is exceedingly thin and translucent. This is the roof of the tym- panum (tegmen tympani). When the dura mater is in situ, the depression lodging the Gasserian ganglion is converted into a foramen, traversed by the fifth nerve. The notch in the side of the dorsum ephippii for the third nerve is also a foramen when the dura mater is present. In many skulls the middle clinoid process is pro- longed to meet the anterior clinoid process, and thus forms a foramen for the internal carotid artery. The grooves for the middle meningeal arteries are some- times canals or tunnels in a part of their course, especially in old skulls. The grooves radiate from the foramen spinosum and extend to the vault. The bones most deeply marked are the squamosal, the greater wing of the sphenoid, and the parietal. The posterior cranial fossa is the deepest portion of the cavity. It is bounded by the dorsum ephippii and the superior borders of the petrosals, the mastoid portion of the petrosals, the posterior inferior angle of the parietals, and the squamo-occipital below the level of the crest (supra-occipital). The upper limits are indicated by the grooves for the lateral sinuses. It is marked by the following sutures : the pretro-occipital, occipito-mastoid, parieto-mastoid, and, in young skulls, the basilar suture. The ridges limiting this fossa give attachment to the tentorium cerebelli, and the fossa lodges the cerebellum with the pons and medulla. It communicates with the general cranial cavity by means of the foramen of Pacchionius when the tentorium is in situ. It has the following objects of interest: — The clivus, extending from the dorsum ephippii to the anterior margin of the foramen magnum. This is in relation with the basilar artery, the pons, and medulla. The notch for the sixth nerve on each side of the dorsum ephippii. This is sometimes a foramen, termed the petro-sphenoid. The foramen magnum, presenting on each side a tubercle for the check liga- ments; and the anterior condyloid foramen (sometimes subdivided by a spiculum of bone) for the hypoglossal nerve. Behind the foramen there is a ver- THE TEETH. tical ridge of bone, the internal occipital crest, for the falx cerebelli. This some- times presents a depression known as the vermiform fossa. The anterior boundaries of the fossa present:— A notch for the passage of the fifth nerve. This is a foramen when the ten- torium is present. The internal auditory meatus, for the facial and auditory nerves, and the auditory branch of the basilar artery. The jugular foramen, which transmits the glosso-pharyngeal, vagus, and spinal accessory nerves, the internal jugular vein, and the meningeal branch of the ascending pharyngeal artery. The termination of the groove for the lateral sinus, with the internal orifice of the mastoid foramen. The cranium of an average European has a capacity of 1450 c. c. The circum- ference, taken in a plane passing through the ophryon anteriorly, the occipital point posteriorly, and the pterion laterally, is 52 cm. The length from the ophryon to the occipital point is 17 cm. ; the width between the parietals at the level of the zygomata is 12.5 cm. ; and the height from the basion to the bregma is nearly the same. The cranio-facial angle is about 96°. THE TEETH. An adult individual with perfect dentition possesses thirty-two teeth, equally distributed to the maxilla and mandible. The four central teeth in each dental arch are termed incisors ; the tooth next these on each side is the canine; behind these are two pre-molars or bicuspids; and, lastly, three molars. This relation of teeth is expressed by means of a formula : — 2 1 2 2 I — C — prm — m — — 32. 21 23 Each tooth has a portion coated with enamel exposed above the gum—named the crown ; and a portion coated with cementum embedded in bone—this is the root. The line of union of the crown and root is termed the neck. The surface of the tooth directed toward the lips and cheek is called labial, and that toward the tongue lingual. It is also necessary to apply definite terms to the opposed surfaces of teeth, hence the surface directed toward the middle line of the mouth if the alveolar arch were straightened out is median, and the op- posite side is distal. Each tooth has distinguishing features. The incisors.—The central upper incisors are very much larger than the lateral, the crown is somewhat oblong in outline, its length exceeding the breadth. The median is longer than the distal border. The labial surface is convex, the lingual concave, and terminates near the gum in a low eminence, the basal ridge or cingulum. In recently erupted teeth, the cutting edge is elevated into three small cusps; these soon wear down and leave a straight edge. The root is long, single, and flattened laterally. The upper lateral incisors are much smaller than the centrals, which they resemble in the general contour of the crown. The distal angle of the crown is more rounded than in the central incisors, and the cingulum is more pronounced. The root is single. The lower central incisors are much narrower than those of the upper set, and less than half their width in the cutting edges, and the crown becomes contracted toward the neck. The cingulum is scarcely marked, and the root single. The lower lateral incisors are distinctly larger than the lower centrals in every direc- tion. The distal angle of the crown is rounded off; the root is single and fre- quently presents on each side a longitudinal groove. The canines.—These differ from the incisors in possessing larger crowns, and thick, long roots. The crown ends in a blunt point', and the cutting edge slopes away on each side. The slope toward the bicuspid is the longer, and causes the crown to be asymmetrical. The lingual surface presents a median and 106 THE SKELETON. two lateral ridges; they converge toward the well-marked cingulum, which is often produced into a distinct cusp. The lower canines have not such pronounced features as the upper; the point is blunter, and the median ridge is absent from the lingual surface. Premolars or bicuspids.—The crown of the first upper premolar has a grinding surface which is somewhat quadrilateral in outline ; the labial is, however, longer than the lingual border. It has two cusps, of which the labial is much the Incisors. Canine. Fig. 97.—The Teeth of an Adult. Bicuspids. Molars. Wisdom tooth. Upper set. Lower set. larger. The cusps are separated by a pit, but are connected by a narrow ridge along the median and distal borders. The median border is nearly straight, the distal is convex. The root may be single, or marked by a longitudinal depression, or be double throughout the greater part of its length ; it may in some specimens have three distinct roots like a molar. The second bicuspid differs from the first in having its cusps nearly equal in size. Its root is double. Fig. 98.—A Molar Tooth in Section, and a Canine Tooth. Crown Cusp. Neck, -Pulp cavity Root Root. - - Neck. Cingulum. -Crown. The lower bicuspids are smaller than the upper and differ from them in shape. The labial cusp is larger than the lingual; the cusps are connected by a low ridge; the grinding surface presents two small pits. The root is single, rounded, and tapering. The second lower bicuspid is larger than the first. The inner cusp is higher and stouter, and the distal border is much more pronounced. Its root is also single and tapering. THE TEETH. 107 The upper molars.—The first and second resemble each other so closely that one description will serve for the two. The grinding surface is quadrilateral but with rounded angles. It has four cusps, two labial and two lingual. Of these, the anterior lingual is the largest, and is connected with the posterior labial by a ridge of enamel. The groove separating the labial and lingual cusps extends on to the sides of the crown and is lost near the neck. The median and distal bor- ders usually present a slight ridge. The roots are three in number, two on the labial, and one on the lingual aspect; this last is usually referred to as the palatine root, and often diverges from the crown at a considerable angle. The lower molars.—The first is the most constant in form. It has five cusps on the grinding surface. Four occupy the angles and are separated by a crucial fissure. The fifth cusp is situated at the posterior extremity of the longi- tudinal ridge. It has two roots, placed one in front of the other; they are in- clined somewhat backward, and present a vertical groove which is sometimes so deep as to divide each root, producing four roots. One root only may divide in this way. The second molar differs from the first in the frequent absence of the fifth cusp ; when present it is feebly developed. The roots have a tendency to become confluent. Fig. 99.—The Temporary Teeth. Incisors. Canine. Milk molars. Upper set. Lower set. The third molars (wisdom teeth).—The upper third molar resembles in its grinding surface the adjacent molars. The two lingual tubercles are usually blended, and the roots coalesce and taper to a cone. The apex is often bent. The characters of this tooth are very variable. The third lower molar has a larger crown than the corresponding tooth in the upper set; it resembles the adjacent molars and has usually five cusps. It has two roots which may be confluent. The Relations of the Crowns of the Upper and Lower Teeth to Each Other.— In a normal condition the upper teeth form a larger arch than the lower. The upper incisors and canines close in front of the lower ; occasionally they fall upon, but rarely fall behind them. The labial tubercles of the bicuspids and molars of the lower jaw are received in the depressions between the labial and lingual tubercles of the upper set of teeth; hence the labial tubercles of the upper over- lap the corresponding tubercles in the lower teeth. In consequence of the difference in width of the crowns of the upper and lower incisors, it happens that in closure of the mouth each tooth impinges upon two teeth. The milk teeth.—These are smaller in number and size than the teeth of the permanent set. The formula is:— 2 12 I - C -«*-== 20. 2 12 108 THE SKELETON. The temporary teeth are smaller than their successors; the enamel of the crown terminates in a thick edge; and the tubercles on the crowns of the molars are less regular and pronounced. The incisors are similar to those of the permanent set, but the canines have shorter and broader crowns than their successors. THE MORPHOLOGY OF THE SKULL. In Man the skull during development passes through three stages. At first the brain vesicles are enclosed in a sac of indifferent tissue which ultimately becomes tough and fibrous. This, the membranous cranium, is represented in the adult by the dura mater. Gradually the sides and base of the membranous cranium become cartilaginous ; in due course osseous tissue appears in the membranous tracts, and later in the cartilage. Eventually an osseous box is formed, consisting of membrane-bones and cartilage-bones intricately interwoven. Fig. i 00.—The Chondro-Cranium. Nasal cartilages. Ethmoid cartilage. Crista galli. Orbito-sphenoid. Optic foramen. Foramen rotundum. Foramen ovale. Ali sphenoid. Hiatus fallopii. Internal auditory meatus. Jugular foramen. Periotic capsule. Aqueductus vestibuli Floccular fossa. Anterior condyloid foramen. [Condyles. Mastoid foramen, Occipital cartilage. Membrane A study of the skull in the chondral stage is very instructive. It consists of two parts ; (i) the skull proper; and (2) the appendicular elements. The skull proper consists of three regions:— The basi-cranial or notochordal region, which ultimately gives rise to the chief parts of the occipital bone. Anterior to this is the trabecular region, from which the sphenoid is subsequently developed. The most anterior portion is the ethmo-vomerine region, from which the nasal sep- tum and its associated cartilages arise. Wedged in on each side between the basi-cranial and trabecular regions is the complicated periotic capsule. The appendicular elements of the cranium are a number of cartilaginous rods, which undergo a remarkable metamorphosis, and, in the adult, are represented by the ear- bones, the styloid process, and the hyoid. The chondro-cranium at the third month presents the following parts: Seen from above, the cartilage extends from the cranial base to a spot midway between the base and the vertex, shading off indefinitely on the dura mater. The conspicuous oval masses on each side are the periotic cartilages, in which the floccular fossae are conspicu- ous objects. Each periotic cartilage is joined to the sphenoid by a strip, termed the sphenotic cartilage, which usually persists in the adult skull. At this date the cartilage for the orbito-sphenoid (the so-called lesser wing) is co-extensive with the ali-sphenoid, and forms part of the lateral wall of the skull. The snout-like appearance of the anterior part of the skull is caused by the fronto-nasal plate. On each side of the ethmo-vome- MORPHOLOGY OF THE SKULL. 109 rine plate near its anterior termination there are two small concave pieces of cartilage for Jacobson’s organ. They are sometimes referred to as the ploughshare cartilages, owing to their shape. These rods of cartilage are named, from before backward, the mandibular, hyoid, and thyroid bars. They may with care be easily dissected in the foetus between the third and fourth months. Their metamorphosis is as follows :— The two extremities of the mandibular bar ossify; the distal end ultimately forms that portion of the mandible adjacent to the symphysis; the proximal end ossifies as the malleus. The intermediate portion disappears; the only vestige which remains is a band of fibrous tissue, the sphenoid-mandibular ligament, extending from the spine of the sphenoid to the spine of the mandible. The hyoid bar fuses distally with the thyroid bar, and is represented by the hyoid bone. Its proximal end becomes the incus, tympano-hyal, and styloid process ; the intervening strip is represented in the adult by the stylo-hyoid ligament. The styloid process has two centres of ossification. A nucleus appears anterior to The Metamorphosis of the Branchial Bars. Fig. ioi.—The Cranium at Birth. the stylo-mastoid foramen, and is known as the tympano-hyal. At birth the true styloid process is cartilaginous. In the second year it ossifies, and subsequently becomes firmly ankylosed to the tympano-hyal. Occasionally the hyoid bar may ossify through- out. When this is the case the styloid process reaches to the hyoid and replaces the stylo-hyoid ligament. The stapes originates in a piece of cartilage which is traversed by the temporary stapedial artery. Its centres of ossification require investigation. The internal pterygoid plate arises in a piece of cartilage which represents the palato-quadrate of lower verte- brates. The internal pterygoid plate is an appendicular element engrafted on to the. sphenoid. In many mammals it is a separate bone throughout life. In the same way the styloid process is an appendicular element ankylosed to the petrosal and the tym- panic plate; in many mammals it remains separate throughout life. The Skull at Birth. The skull at birth presents, when compared with the adult skull, several important and interesting features. Its peculiarities may be considered under three headings: The peculiarities of the foetal skull as a whole ; the condition of individual bones; the remnants of the chondral skull. THE SKELETON. The general characters of the foetal skull.—The most striking features of the skull at birth are, its relatively large size in comparison with the body, and the predominance of the cerebral over the facial portion of the skull; the latter is, in fact, very small. The frontal and parietal eminences are large and conspicuous; the sutures are Fig. 102.—The Cranium at Birth. Fig. 103.—The Cranium at Birth in Sagittal Section. absent; the adjacent margins of the bones of the vault are separated by septa of fibrous tissue continuous with the dura mater internally and the pericranium externally ; hence it is difficult to separate the roof bones from the underlying dura mater, each bone being lodged as it were in a dense membranous sac. The bones of the vault consist of a single layer without any diploe, and their cranial surfaces present no digital impressions. Six MORPHOLOGY OF THE SKULL. membranous spaces exist, named fontanelles: two are median, named anterior and posterior; and two exist on each side, termed anterior and posterior lateral fontanelles. Each angle of the parietal bones is in relation with a fontanelle. The anterior fontanelle is lozenge-shaped, the posterior triangular. The lateral fontanelles are irregular in outline. Turning to the base of the skull, the most striking points are the absence of the mas- toid processes and the large angle which the pterygoid plates form with the skull base, whereas in the adult the angle is almost a right one. The base of the skull is relatively short, and the lower border of the mental symphysis is on a level with the occipital condyles. The facial skeleton is relatively small in consequence of the small size of the nasal fossae ; these are as wide as they are high, and are almost filled with the turbinals. The Peculiarities of Individual Bones at Birth, The occipital consists of four distinct parts : the basi-occipital, two ex-occipitals, and tht squamo-occipital; these four parts are united by hyaline cartilage. Compared with Fig. 104.—The Occipital at Birth. Interparietal portion (Develops in membrane) The interparietal and supra-occipital por- tions form the squa- mo-occipital of the adult. Supra-occipital portion. (Develops in cartilage.) Ex-occipital, FORAMEN MAGNUM Basi-occipital. the adult bone, the following are the most important points of distinction : There is no pharyngeal tubercle or jugular process ; the squamo-occipital presents two deep fissures separating the interparietal from the supraoccipital portion, and extending nearly as far inward as the occipital protuberance. The grooves for the lateral sinus are absent. The sphenoid in a macerated foetal skull falls into three pieces. The main portion consists of the united pre- and post-sphenoid with the orbito-sphenoids and lingulae. The pre-sphenoid is quite solid and connected with the ethmo-vomerine cartilage, and presents no traces of the air sinuses which occupy this part in the adult skull. The pre- sphenoid by its upper surface forms part of the anterior cranial fossa, from which it is subsequently excluded by the orbito-sphenoids. The optic foramina are large and tri- angular in shape. The lingulae stand out from the basi-sphenoid as two lateral buttresses, and the floor of the sella turcica presents the cranio-pharyngeal canal, which in a recent bone is occupied by fibrous tissue. The dorsum ephippii is yet cartilaginous. The ali- sphenoids with the pterygoid processes are separated from the rest of the bone by cartilage. The foramen rotundum is complete, but the future foramen ovale is merely a deep notch in its posterior border, and there is no foramen spinosum. The pterygoid processes are short, and each internal pterygoid plate presents a broad surface for articulation with the 112 THE SKELETON. lingulae. The Vidian canal is a groove between the internal pterygoid plate, the lingula, and greater wing. The temporal bone at birth consists of three parts (excluding the ear-bones) : the pe- trosal, squamosal, and tympanic. The petrosal presents a large and conspicuous floccu- lar fossa; the hiatus Fallopii is a shallow bay lodging the geniculate ganglion of the facial nerve. There is a relatively large mastoid antrum, but no mastoid process. The styloid process is unossified, but the tympano-hyal may be detected as a minute rounded nod- ule of bone near the stylo-mastoid foramen. The squamosal has a very shallow glenoid fossa and a relatively large post-glenoid Fig. 105.—The Sphenoid at Birth. Vidian canal. Lingula. tubercle. The posterior part of the inferior border is prolonged downward into an un- cinate process to close externally the mastoid antrum. The tympanic bone or annulus is a delicate horseshoe-shaped ossicle, attached by its anterior and posterior horns to the inferior border of the squamosal. The ear-bones are chiefly of interest from their size, for they are as large at birth as in the adult. The processus gracilis (Folian process) may be 2 cm. in length. The frontal consists of two bones separated by a median vertical (metopic) suture. The frontal eminence is very conspicuous, but the superciliary ridges and frontal sinuses are wanting. The nasal spine, which later becomes one of the most conspicuous features of this bone, is absent. There is no temporal ridge. Fig. 106.—The Temporal Bone at Birth Squamosal Tympanic, Petrosal. The parietal is simply a quadrilateral lamina of bone, concave on its inner and con- vex on the outer surface. The parietal eminence, which indicates the spot in which the ossification of the bone commenced, is large and conspicuous. The grooves for blood- sinuses, as in other cranial bones, are absent. Each angle of the parietal is in relation with a fontanelle. As in the adult, the anterior inferior angle of the bone is prolonged downward toward the ali-sphenoid. The ethmoid consists of two lateral portions separated by the still cartilaginous ethmo- vomerine plate. The ethmoid cells are represented by shallow depressions, and the uncinate process is undeveloped. MORPHOLOGY OF THE SKULL. The sphenoidal turbinals are two small triangular pieces of bone lying in the peri- chondrium on each side of the ethmo-vomerine plate near its junction with the pre- sphenoid. (Indicated by the * in Fig. 103.) The maxilla presents the following characters: The maxillo-premaxillary suture is visible on the palatine aspect of the bone. The alveolar border presents five sockets for teeth. The infraorbital foramen communicates with the floor of the orbit by a deep fissure ; this fissure sometimes persists in the adult. The antrum is a shallow groove. The mandible at birth consists of two halves united by fibrous tissue in the line of the future symphysis. Each half is a bony trough lodging teeth. The trough is divided by thin osseous partitions into five compartments : of these, the fifth is the largest, and is often subdivided by a ridge of bone. The floor is traversed by a furrow as far forward Fig. 107.—The Temporal Bone at Birth. [Outer view.) SQUAMOSAL Petro-squamous suture. Petrosal. Post-glenoid tubercle, Glaserian fissure, Stylo-mastoid foramen. Tympano-hyal. Tympanic fissure Carotid canal. as the fourth socket (that for the first milk molar), where it turns outward at the mental foramen. This furrow lodges the mandibular (inferior dental) nerve and artery, which enter by the mandibular foramen. The condyle is on a level with the mental extremity of the bone. The palate bones differ mainly from the adult bone in that the vertical and horizontal plates are of the same length; thus the nasal fossae in the foetus are as wide as they are high, whereas in the adult the height of each nasal fossa greatly exceeds the width. Concerning the remaining bones little need be said. The vomer is a delicate trough of bone for the reception of the inferior border of the ethmo-vomerine plate ; its inferior border, that which rests upon the palate, is broad, and the bone presents quite a different appearance to the adult vomer. The nasal bones are short but broad ; the malar and. Fig. 108.—Temporal Bone at Birth. (Inner view.) Hiatus fallopii. Floccular fossa. Aqueductus vestibuli. Internal auditory meatus. inferior turbinals are relatively very large; and the lachrymals are thin, frail, and deli- cate lamellae. The hyoid consists of its usual five parts. There is a median nucleus for the basi- hyal, and one on each side for the greater cornua (thyro-hyals). The lesser cornua are cartilaginous. Remnants of the cartilaginous cranium.—It has already been pointed out that at an early date the base of the skull and the face are represented by hyaline cartilage, which for the most part is replaced by bone before birth. Even at birth remnants of this primi- tive chondral skull are abundant. In the cranium, cartilaginous tracts exist between the various portions of the occipital bone, as well as at the line of junction of the occipital with the petrosal and sphenoid. The dorsum ephippii is entirely cartilaginous at birth,. 114 THE SKELETON. and the last portion of this cartilage disappears with the ankylosis of the basi-occipital and basi-sphenoid about the twenty-fifth year. A similar strip of cartilage lying between the jugular process and the jugular surface of the petrosal persists until late in life. A strip of cartilage unites the ali-sphenoids with the lingulae, and for at least a year after birth this cartilage is continuous with that which throughout life occupies the sphenotic (middle lacerated) foramen. A strip of cartilage exists along the posterior border of the orbito-sphenoid, and not infrequently extends outward to the pterion. In the adult skull it is replaced by ligamentous tissue. Fig. 109.—The Frontal at Birth. The ethmo-vomerine plate is entirely cartilaginous, and near the end of the nose sup- ports the lateral nasal cartilages, remnants of the fronto-nasal plate. The fate of the ethmo-vomerine plate is instructive. The upper part is ossified to form the mesethmoid ; the lower part atrophies from the pressure exerted by the vomer ; the tip remains as the triangular cartilage. The lateral snout-like extremities of the fronto-nasal plate persist as the lateral cartilages of the nose. Among the appendicular elements of the skull, the styloid process and a large por- tion of the hyoid are cartilaginous at birth. Fig. xio.—The Maxilla at Birth. Pre-maxillary portion Outer view. Inferior view. Inner view. The Nerve-foramina of the Skull. The various foramina and canals in the skull which give passage to nerves may be arranged in two groups, primary and secondary. Primary foramina indicate the spots where the nerves quit the general cavity of the dura mater, and as this membrane indi- cates the limit of the primitive cranium, a cranial nerve, in a morphological sense, becomes extra-cranial at the point where it pierces this membrane. In consequence of the complicated and extraordinary modifications the vertebrate skull has undergone, many nerves traverse, in the adult skull, bony tunnels and canals which are not repre- sented in the less complex skulls of low vertebrates such as sharks, rays, etc. To such foramina and canals the terms secondary or adventitious may be applied. MORPHOLOGY OF THE SKULL. Nerve-foramina are further interesting in that they occupy sutures, or indicate the points of union of two or more ossific centres. To this rule the foramen rotundum is the only exception in the human skull. The Primary Foramina. 1. Foramen magnum.—This is bounded by four distinct centres, the supra-, basi-, and two ex-occipitals. It transmits the spinal accessory nerve, the vertebral artery and its anterior and posterior spinal branches, the spinal cord and its membranes. 2. The anterior condyloid.—At birth this is a deep notch in the anterior extremity of the ex-occipital, and becomes a complete foramen when the basi- and ex-occipitals fuse. Occasionally it may be complete in the ex-occipital, but it indicates accurately the line of union of these two elements of the occipital bone. It transmits the hypoglossal nerve, the meningeal branch of the ascending pharyngeal artery, and its venae comites. 3. Jugular foramen.—This occupies the petro-occipital suture, and is formed by the basi- and ex-occipital in conjunction with the petrosal. It transmits the glosso-pha- ryngeal, pneumogastric, and spinal accessory nerves, a meningeal branch of the ascend- ing pharyngeal artery, and receives the lateral and inferior petrosal sinuses. 4. Auditory.—This marks the point of confluence of the groups of centres termed pro-otic and opisthotic. It transmits the facial and auditory nerves with the auditory twig of the basilar artery. 5. Trigeminal.—This is only a foramen when the dura mater is present in the skull. It is a notch at the apex of the petrosal converted into a foramen by the tentorium. The Fig. hi.—The Mandible at Birth. Outer view Inner view main trunk of the trigeminal nerve with the small motor root traverses it to enter the Meckelian cave. 6. Petro-sphenoidal.—This is a notch between the side of the dorsum ephippii and apex of the petrosal which becomes converted into a foramen by dura mater. Sometimes this ossifies, as in Fig. 96. 7. Optic.—This foramen is formed by the confluence of the orbito- and pre- sphe- noidal centres. It opens into the orbit and transmits the optic nerve and ophthalmic artery. Foramina transmitting the various subdivisions of the fifth nerve.—The primary foramen of exit for the trigeminal nerve is formed partly of bone and partly of mem- brane at the apex of the petrosal. The three divisions of the nerve issue through sec- ondary foramina. (a) The sphenoidal fissure is an elongated chink, bounded above by the orbital wing and below by the greater wing of the sphenoid, internally by the body of the sphenoid, and externally by the frontal. It opens into the orbit, and transmits the third, fourth, first (ophthalmic) division of the fifth, and sixth nerves, also the ophthalmic vein. (b) The foramen rotundum is the only exception to the rule relating to the formation of nerve foramina; it is probably a segment of the sphenoidal fissure. The foramen is really a canal running from the middle cranial fossa to the spheno-maxillary fossa, and transmits the second or maxillary division of the trigeminal. (c) Foramen ovale.—This at birth is a gap in the hinder border of the greater wing (ali-sphenoid) of the sphenoid, and is converted into a foramen by the petrosal; sub- The Secondary Nerve-foramina. 116 THE SKELETON. sequently it becomes complete in the sphenoid. It transmits the third (inferior maxillary) division of the trigeminal and the small or motor root, the small superficial petrosal nerve (which occasionally passes through a separate foramen), and the small meningeal artery with its venae comites. The ethmoidal canals.—These commence in the suture between the os planum and the frontal bone, and traverse the space between the upper surface of the lateral mass of the ethmoid and the horizontal plate of the frontal, to emerge on the cribriform plate; they are situated outside the dura mater. The anterior foramen transmits the nasal branch of the ophthalmic, which subsequently gains the nasal cavity by passing through the nasal slit (ethmoidal fissure) beside the crista galli. The infraorbital canal indicates the line of confluence of the maxillary and malar centres of the superior maxilla; occasionally it is completed by the malar; rarely it is incomplete above, and communicates by a narrow fissure with the orbit. It lodges the infraorbital nerve and artery. The spheno-malar foramen is situated in the suture between the malar and the greater wing of the sphenoid (ali-sphenoid): it transmits the temporal branch of the orbital nerve and a branch of the lachrymal artery. In the adult this foramen may be wholly confined to the malar bone. The malar canals traverse the malar bone, and indicate the line of confluence of the two chief centres for this bone. The malar twigs of the orbital nerve issue from them accompanied by arterial twigs. The spheno-palatine foramen is a deep groove between the orbital and sphenoidal processes of the palate bone, converted into a foramen by the sphenoidal turbinal. It is traversed by the naso-palatine nerve and artery as they enter the nasal from the spheno- maxillary fossa. Scarpa’s foramina are two minute openings in the meso-palatine suture where it is in relation with the anterior palatine fossa. They are traversed by the naso-palatine nerves. The pterygo-palatine foramen is situated between the sphenoidal process of the palate bone, the internal pterygoid plate of the sphenoid, and the sphenoidal turbinal. The pterygo-palatine nerve and artery pass through it. The Vidian canal is trumpet-shaped : the narrower end is situated in the sphenotic foramen ; the broader orifice opens on the posterior wall of the spheno-maxillary fossa. The canal is io mm. long ; in the foetal skull it is a chink between the base of the internal pterygoid plate, the ali-sphenoid, and the lingula of the sphenoid. The canal is traversed by the Vidian branch of the spheno palatine ganglion and the Vidian artery. The posterior palatine canal is a passage left between the maxilla, the vertical plate and tuberosity of the palate bone, and the internal pterygoid plate; it commences on the hard palate by the posterior palatine foramen. The descending palatine nerve and artery traverse this canal. Several foramina open from it. In the suture between the vertical plate of the palate bone and the maxilla, two small openings allow minute nerves to issue for the middle and inferior turbinals. In the fissures between the tuberosities of the palate and maxillae, and the pterygoid plates, the middle and external palatine nerves issue. These foramina are sometimes called accessory and external palatine canals. The mandibular or inferior dental canal runs between the dentary and splenial elements of the mandible. The posterior orifice of the canal is the mandibular (inferior dental) foramen; the anterior orifice, the mental foramen, indicates the line of union of the mento-Meckelian and dentary centres. The mandibular nerve and artery enter the canal at its posterior orifice; the mental foramen allows the mental nerve to escape from the canal accompanied by the mental artery. Foramina transmitting the facial nerve and its branches.—The main trunk of the facial enters the internal auditory meatus and traverses the Fallopian, canal. In the early embryo the nerve lies on the petrosal, and is not covered in with bone until the fifth month of foetal life. The terminal orifice, the stylo-mastoid foramen, is situated between the tympanic, tympano-hyal, and epiotic elements of the complex temporal bone. The “ iter chordae posterius ” is a chink between the squamosal and the tympanic elements, and allows the chorda tympani nerve to enter the tympanum. The fissure of exit for this nerve is the subdivision of the Glaserian fissure termed the canal of Huguier, or “ iter chordae anterius.” The Glaserian fissure lies between the tympanic plate and the squamosal. It transmits the tympanic branch of the internal maxillary artery, and lodges the slender process of the malleus. The spheno-maxillary fissure is situated between the posterior border of the orbital plate of the maxilla and a smooth ridge on the orbital surface of'the greater wing of the sphenoid. It transmits the superior maxillary division (second) of the fifth nerve. THE RIBS. 117 THE RIBS AND STERNUM. The Ribs.—These form a series of narrow flattened bones, twenty-four in number, arranged in twelve pairs, extending from the sides of the thoracic vertebrae toward the median line on the anterior aspect of the trunk. The first seven pairs are termed true ribs, because their anterior ends are connected by means of cartilage with the sides of the sternum. The lower five— false ribs—are subdivided into two sets: the eighth, ninth, and tenth are con- nected together by their costal cartilages; the eleventh and twelfth have their anterior extremities free, and are called in consequence floating ribs. Thus the first seven are vertebro-sternal; the eighth, ninth, and tenth are vertebro- chondral; the eleventh and twelfth, vertebral ribs. The ribs increase in length from the first to the seventh, and then decrease from this rib to the twelfth. In breadth they increase from behind forward ; the greatest breadth of a rib is at its junction with the costal cartilage. The two or three upper ribs form nearly a right angle with the spine, but the succeeding set curve obliquely downward. The obliquity is greatest at the ninth, and then decreases in the ribs below. Typical characters of a rib.—The seventh is regarded as the most typical rib. It presents a vertebral extremity or head; a narrow portion or neck ; a sternal end; and an intermediate portion, the shaft. The head has two facets divided by a horizontal crest. The crest is connected by an interosseous ligament with an intervertebral disc; the facets articulate with the demi-facets on the sides of the bodies of two vertebrae. As a rule, the lower facet is the larger, and articulates with the thoracic vertebra, to which the- rib corresponds in number. This is the primary facet, and is the one represented in those ribs which possess only a single facet on the rib-head. The anterior margin is lipped for the costo-vertebral (stellate) ligament. The neck is that portion of the rib extending from the head to the tubercle. The posterior surface of the neck is in relation with the transverse process of the lower vertebra with which the head articulates; it forms the anterior boundary of the costo-transverse foramen, and is rough where it gives attachment to the middle costo-vertebral ligament. The superior border of the neck is con- tinuous with the corresponding border of the shaft, and the point where the neck ends this border is produced so as to form a crest (crista colli superior) for the anterior costo-transverse ligament. The inferior border of the neck is continuous with the ridge of the subcostal groove. The difference in the relation of the neck to the upper and lower borders of the rib shaft is useful in determining to which side a rib belongs. The tubercle consists of an upper part, rough for the posterior costo-transverse (rhomboid) ligament, and a lower faceted portion for articulation with the tip of the transverse process. The tubercle projects below the lower edge of the rib to form a crest (crista colli inferior), marking the beginning of the subcostal groove. The shaft has two surfaces and two borders. It is strongly curved. At first the curve is in the same plane as the neck, but it quickly turns forward at a spot on the posterior surface of the shaft known as the angle, where it gives attach- ment to the sacro-lumbalis muscle and some of its subdivisions. The rib has also a second or upward curve beginning at the angle. These curves are expressed by describing the main curve as disposed around a vertical, and the second or upward curve around a transverse axis. When a rib, except the first and twelfth, is laid with its lower edge upon the table, the rib-head rises and the rib touches the table at two places, viz., at the sternal end, and in the neighborhood of the angle. The external surface of the rib is convex, and gives attachment to muscles. Near its anterior extremity it forms a somewhat abrupt curve, indicated by a ridge on the bone, which gives attachment to the serratus magnus muscle, and is some- times called the anterior angle. 118 THE SKELETON. The internal surface is concave and presents the subcostal groove near its inferior border. The groove is best marked near the angle, and lodges the inter- costal vessels and nerves. The ridge limiting the groove above is continuous with the inferior border of the neck of the rib ; it gives attachment to the internal inter- costal muscles. Fig. i 12—The Seventh Rib of the Left Side. {Seen from below.) Tubercle. Articular ■portion of tubercle. ■Neck. ■ Head. Subcostal Groove. Shaft. Sternal end for costal cartilage. The superior border is rounded, and affords attachment to the internal and extertial intercostal muscles. The inferior border commences abruptly near the angle and gives attachment to the external intercostal muscles. The sternal end of the shaft is cupped for the reception of the costal cartilage. THE RIBS. The seventh rib and its costal cartilage give attachment to the following muscles:— Internal intercostals (sixth and seventh). External intercostals (sixth and seventh). Levatores costarum (sixth and seventh). Infracostal (when present). Diaphragm. Trans versalis. External oblique abdominis. Rectus abdominis (costal cartilage). Triangularis sterni (costal cartilage). Pectoralis major (costal cartilage). Serratus magnus. Ilio-costalis, or sacro-lumbalis. Musculus accessorius. Longissimus dorsi. It gives attachment to the following ligaments :— Anterior costo-vertebral (stellate). Middle costo-vertebral (interosseous). Anterior costo-transverse. Posterior costo-transverse (rhomboid). Interosseous of rib-head. Fig. i 13.—First and Second Ribs. Tubercle. _ Neck. — Head.- Levator costae. Accessorius (insertion). Cervicalis ascendens (origin). Serratus posticus superior (insertion). Scalenus posticus, Levator costae and accessorius. Scalenus medius. Groove for subclavian artery. Scalenus anticus. Groove for subclavian vein. Ex. Intercostals - Serratus magnus .Third digitation of serratus magnus. External intercostals. Shaft. Blood-supply.—The ribs are very vascular and derive numerous branches from the intercostal arteries. The branches in the shaft run toward the rib-head. Those of the head and neck take a contrary direction, and run, as a rule, toward the shaft. In the neighborhood of the tuberosity the vessels seem to run in any direction. Peculiar ribs.—Several of the ribs differ in many particulars from this general description. They are the first, second, tenth, eleventh, and twelfth. The first rib is the broadest and most sharply curved. The head is small, and, as a rule, is furnished with only one articular facet. The tubercle is large and prominent, the neck narrow. The shaft is broad, has no angle, and is curved around a vertical axis only. The anterior surface presents two shallow grooves separated near the superior border by a rough surface (Lisfranc’s tubercle) 120 THE SKELETON. for the scalenus anticus muscle. The groove in front of this surface is for the subclavian vein, the groove behind it is for the subclavian artery. Between the groove for the artery and the tubercle there is a rough surface for the scalenus medius muscle; anterior to this rough surface and close beside the groove is an area from which the first digitation of the serratus magnus takes origin. I he under surface is smooth and lacks a groove. The inferior border is thick, and rounded for the internal and external intercostal muscles. The costal cartilage of this rib fuses with the manubrium of the sternum; occasionally the sternal extremity and costal cartilage of this rib are replaced by fibrous tissue. When a well-developed cervical rib is present, the head of the first may present two facets as in a typical rib. The first rib, with its costal cartilage, gives attachment to the following muscles:— Internal intercostal. External intercostal Levator costae. Scalenus anticus. Scalenus medius. Subclavius (costal cartilage). Sterno-hyoid (costal cartilage). Pectoralis major (costal cartilage Serratus magnus. Musculus accessorius. Fig. 114.—The Vertebral Ends of Tenth, Eleventh, and Twelfth Ribs. Angle. facet (Sometimes two facets are pres- ent.) X Single facet. (This rib has an angle, but no tuberosity and no neck.) XI Single facet. (This rib has neither tuber- osity, angle, nor neck.) XII Blood-supply.—This is derived mainly from the superior intercostal branch of the subclavian artery. The second rib, like the first, is strongly curved ; its posterior angle is faintly marked; and the shaft, like that of the first, can lie flat on the table. It has a prominent anterior angle for the serratus magnus. It gives attachment to the following muscles :— Internal intercostals (first and second). External intercostals (first and second). Levator costae. Pectoralis major (costal cartilage). Serratus magnus. Serratus posticus superior. Scalenus posticus. Musculus accessorius. Blood-supply.—Superior intercostal branch of the subclavian artery, and the first aortic intercostal. THE RIBS. 121 The tenth rib has usually a single facet on its head. Occasionally a second is present. When this is the case, the ninth thoracic vertebra is not exceptional, and presents two demi-facets. The eleventh rib has a single facet on the head. The angle is feebly marked, and the subcostal groove shallow. It lacks a neck and tubercle. The twelfth rib has a large head furnished with one facet. The shaft is narrow, and its length extremely variable. It may be as short as 3 cm., or attain a length of 20 cm. (8"). Epiphysis for the head. Appears at fifteen ; fuses at twenty-three. Fig. ii5.—Rib at Puberty. Epiphysis for tubercle. Appears at fifteen ; fuses at twenty-three. The cartilaginous shaft commences to ossify at the eighth week oi intra-uterine life. The twelfth rib gives attachment to the following muscles;— Internal intercostal. External intercostal. Levator costae. Diaphragm. Transversalis abdominis. External oblique. Internal oblique. Serratus posticus inferior. Musculus accessorius. Sacro-lumbalis or ilio-costalis. Erector spinse. Quadratus lumborum. The costal cartilages are bars of hyaline cartilage attached to the anterior extremities of the ribs; they represent unossified epiphyses. Like the shaft of a rib, each has an outer and inner surface; the outer surfaces give origin and insertion to large muscles; and the inner surfaces, from the second to the seventh inclusive, are in relation with the triangularis sterni. The upper and lower bor- ders serve for the attachment of the internal intercostal muscles. The upper seven cartilages, and occasionally the eighth, are connected with the sternum. The first fuses with the manubrium; the remaining six are received in small articular con- Latissimus dorsi 122 THE SKELETON. cavities, and retained by means of ligaments. The cartilages of the vertebro- chrondal ribs are united to each other and to the seventh costal cartilage by ligaments (sometimes by short vertical bars of cartilage), and those of the vertebral ribs end freely. The inner surfaces of the lower six afford attachment to the diaphragm and the transversalis muscle. The second, third, fourth, and fifth costal cartilages articulate with the sides of the sternum, at a spot corresponding to the junction of two sternebrae. The sixth and seventh (and eighth when this reaches the sternum) are arranged irregularly. As a rule the sixth lies in a recess in the side of the fifth sternebra; the seventh corresponds to the line of junction of the meso-and metasternum ; and the eighth articulates with the metasternum. (See Fig. 116.) Blood-supply.—The twigs for the costal cartilages are derived from the ter- minal twigs of the aortic intercostals, and from the internal mammary arteries. Development.—At the eighth week of intra-uterine life the ribs are cartila- ginous. About this date an earthy spot appears near the angle of each rib, and spreads with great rapidity along the shaft, and by the fourth month reaches as far as the costal cartilage; the proportion borne by the rib-shaft to the costal cartilage is about the same at this date as in adult life. Whilst the ribs are in a cartilaginous condition, eight of them reach the sternum; even after ossification has taken place, the costal cartilage of the eighth rib, in many instances, articulates with the sternum as late as the eighth month (Fig. 116). This relationship may persist through life, but usually the cartilage retrogresses, and is replaced by liga- mentous tissue. About the fifteenth year a secondary centre appears for the head of each rib, and a little later one makes its appearance for the tubercle, except in the tenth, eleventh, and twelfth ribs. The secondary centres fuse with the ribs about the twenty-third year. The costal cartilage stands in relation to the rib- shafts as unossified epiphyses; the rib-shaft increases in length mainly at its line of junction with the costal cartilage. Variations in the Number and Shape of the Ribs. The ribs may be increased in number by addition either at the cervical or lumbar end of the series, but it is extremely rare to find an additional rib or pair of ribs in both the cervical and lumbar region in the same subject. Cervical ribs are fairly common ; as a rule they are of small size and rarely extend more than a few millimetres beyond the extremity of the transverse process. Occasion- ally they exceed such insignificant proportions and reach as far as the sternum : between these two extremes many varieties occur. As a rule, the existence of a cervical rib is not detected until the skeleton is macerated ; hence, we know little of the correlated arrange- ment of soft parts. In one fortunate case Turner was able to make a thorough dissec- tion of a specimen in which a complete cervical rib existed. Its head articulated with the body of the seventh cervical veretebra and had a stellate ligament. The tubercle was well developed, and articulated with the transverse process. The costal cartilage blended with that of the first thoracic rib, and gave attachment to the costo-clavicular ligament. Between it and the first thoracic rib there was a well-marked intercostal space occupied by intercostal muscles. It received the attachment of the scalenus anticus and medius muscles, and it was crossed by the subclavian artery and vein. The nerves of the inter- costal space were supplied in part by the eighth cervical and first dorsal. The artery of the space was derived from the deep cervical, which, with the superior intercostal, arose from the root of the vertebral. The head of the first thoracic rib in this specimen articu- lated with the seventh cervical, as well as with the first thoracic vertebrae. An interesting fact is also recorded in the careful account of this specimen : There was no movable twelfth thoracic rib on the same side as this well-developed cervical rib, and the twelfth thoracic vertebra had mammillary and accessory processes, and a strong elongated costal process, and was in linear series with the lumbar transverse processes. Gruber and Turner, from a careful and elaborate study of this question, summarize the variations in the cervical rib thus: It may be very short and possess only a head, neck, and tubercle. When it extends beyond the transverse process, its shaft may end freely or join the first thoracic rib: this union may be effected either by bone, cartilage, or ligament. In very rare instances it may have a costal cartilage and join the manubrium of the sternum. Not infrequently a process, or eminence, exists on the first thoracic rib at the spot where it articulates with a cervical rib. Lumbar ribs are of less significance than cervical ribs and rarely attain a great THE STERNUM. 123 length. Their presence is easily accounted for, as they are the differentiated costal elements of the transverse processes. They are never so complete as in cervical ribs, and articulate only with the transverse processes ; the head never reaches as far as the body of the vertebra, and there is no neck or tubercle. An extra levator costa muscle is associated with a lumbar rib. Not the least interesting variation of a rib is that known as the bicipital rib. This condition is seen exclusively in connection with the first thoracic rib. The vertebral end consists of two limbs which lie in different transverse planes. These bicipital ribs have Fig. 116.—The Thorax at the Eighth Month. (On the left side eight cartilages reach the sternum.) been especially studied in whales and man. This abnormality is due to the fusion of two ribs, either of a cervical rib with the shaft of the first thoracic ; or the more common form, the fusion of the first and second true ribs. Among unusual variations of ribs should be mentioned the replacement of the costal cartilage and a portion of the rib-shaft by fibrous tissue, a process which occurs as a normal event, during development, in the eighth rib. Sometimes the shafts of two or more ribs may become united by small quadrilateral plates of bone extending across the intercostal spaces. The sternum is a thin flat bone situated in the anterior wall of the thorax. In the young subject it consists of six pieces, or sternebrae. Of these, the four middle fuse together to form the gladiolus (mesosternum); the superior remains distinct throughout life as the manubrium (pre-sternum) ; and the lower segment, also distinct until very advanced life, is the xiphoid (metasternum). The anterior surface of the adult sternum is convex, and gives origin to the pectoralis major muscle of each side ; near its superior angle the sterno-mastoid muscle arises. This surface is traversed by five lines, indicating the former segmentation of this bone. The posterior surface is concave, and traversed by five lines corresponding to those on the anterior surface. At the upper part it gives origin to the sterno- hyoid and sterno-thyroid muscles. The posterior surface of the lower four segments gives origin to the triangularis sterni. The xiphoid is usually perforated ; a branch of each internal mammary artery traverses the foramen ; and on each side of it a portion of the diaphragm is attached. Occasionally the xiphoid is bifid. The superior border presents the interclavicular notch, to which the fibres of the interclavicular ligament are attached ; this border terminates at each end in an articular notch for the sternal end of the clavicle. The margins of the notch give attachment to the sterno-clavicular ligaments. The lateral borders of the sternum present a series of depressions, which receive the sternal extremities of the costal cartilages of the first seven ribs, and occasionally that of the eighth (see Fig. 116). The borders intervening between these depressions or notches are in relation with the internal intercostal muscles. 124 THE SKELETON. In order to appreciate the nature of these notches, it is advantageous to study the sternum in a young subject. Each typical sternebra presents four angles ; each angle presents a demi-facet. Between each sternebra there is an inter-sterne- bral disc ; when two sternebrae are in position, each notch for a costal cartilage is Fig. i 17.—The Sternum. {Anterior view!) Interclavicular notch. Clavicular notch Sterno-mastoid, For first costal cartilage. Manubrium or Pre-sternum. Second. Pectoralis major. Third. - Gladiolus or mesosternum. Fourth.- Fifth.- Sixth.- Seventh.- Rectus abdominis. Aponeurosis of trans- versals and exter- nal oblique. Xiphoid or meta- sternum. Xiphoid foramen formed by a sternebra above and below with an intersternebral disc in the middle, thus repeating the relation of the rib-head to the vertebral centra. Later in life these fuse more or less together, except in the case of the first and second sterne- brse, which usually remain separate to the end of life. The first (pre-sternum) is THE STERNUM. the most modified of all the sternebrse, and differs from them in the fact that the costal cartilage of the first rib is continuous with it, and in the fact that it supports the clavicles. Occasionally a rounded pisiform bone is seen on each side, Fig. ii8.—The Sternum. {Posterior view.) Clavicular notch Sterno-hyoid, For first costal cartilage. Sterno-thyroid - Second. _ Third. - Fourth. Triangularis sterni Fifth. Sixth. Seventh. Diaphragm. immediately internal to the articular notch for the clavicle; these are the epi- sternal bones. The last sternebra, or xiphoid, is the least developed, and, though calcified in old age, rarely ossifies. Its tip is directly continuous with the linea alba, and the base gives slight attachment to the rectus abdominis muscle. 126 THE SKELETON. The following muscles are attached to the sternum : — Pectoralis major. Sterno-cleido mastoid. Internal intercostals. Rectus abdominis. Triangularis sterni. Transversalis. Diaphragm. Sterno-hyoid. Sterno-thyroid. Ligaments.—In addition to the ligaments proper to the costal cartilages, the following require enumeration : — Posterior sterno-clavicular. Interarticular fibro-cartilage. Interclavicular. Anterior sterno-clavicular. Linea alba. Blood-supply.—The arteries of the sternum are derived mainly from the internal mammary arteries by direct branches termed sternal; many twigs are furnished by the perforating branches of the internal mammary, and also from the terminal twigs of the aortic intercostals. Development.—The sternum results from the fusion of the ventral ends of Fig. 119.—Two Stages in the Formation of the Cartilaginous Sternum. {After Ruge. CLAVICLE the cartilaginous bars which in the early embryo represent the ribs. At first these bars fuse together laterally, and for some time the sternum is represented by two strips of cartilage separated by a median fissure. Very early this cap is bridged over anteriorly. Nine costal cartilages are in relation with the sternum at this stage. Gradually the lateral strips unite with each other to form the meso-sternum. The ninth costal cartilage divides: one part remains attached to the sternum and becomes the xiphoid, whilst the end still attached to the rib acquires a new attach- ment to the eighth cartilage. The ends, still adherent to the sternum, may re- main separate and give rise to a bifid metasternum (xiphoid); much more fre- quently they unite, leaving a small foramen. The eighth cartilage may retain its sternal attachment permanently. At first the sternum and costal cartilages are continuous ; a joint soon forms between the pre-sternum and metasternum. Gradually joints arise between the costal cartilages and the sternum (except in the case of the first). The division of the metasternum into sternebrae is a still later process, and arises during the process of ossification. Ossification.—The transformation of the sternum into bone is a slow and THE THORAX. 127 irregular process. The pre-sternum (manubrium) has a mesial nucleus about the sixth month of intra-uterine life ; later, several smaller accessory centres may appear. The mesosternum usually ossifies from seven centres. The second sternebra ossi- fies from a single median nucleus about the eighth month. Below this, three pairs of ossific nuclei appear, and they may remain long separate. Of these, two pairs for the third and fourth sternebrse are visible at birth. The pair for the fifth sternebra make their appearance toward the end of the first year. The various lateral centres unite in pairs, and at the sixth year the sternum consists of six sternebrse, the lowest (metasternum) being cartilaginous. Gradually the four pieces representing the mesosternum fuse with each other, and at twenty-five they form a single piece, but exhibit, even in advanced life, traces of their original separation. The metasternum is always imperfectly ossified, and does not ankylose with the mesosternum till after middle life. The pre-sternum and mesosternum rarely fuse. The dates given above for the various nuclei are merely approximations, for they are extremely variable, not only in appearing, but in their number. The same remark applies also to the age at which the various segments ankylose; hence the sternum affords very uncertain data as to age. Abnormalities of the Sternum.—The mode of development of the ster- num, as described above, is of importance in connection with some deviations to which it is occasionally subject. At an early period it consists of two lateral halves; in some rare instances these have failed to unite, and thus give rise to the anomaly of a completely cleft sternum. The union of the two halves may occur in the region of the manubrium, but fail below this point; in some instances the upper and lower segments have duly coalesced with the opposite side, but union has failed in the middle segments. The clefts resulting from these failures of coalescence are in many instances so small as not to be of any moment, and not even recognized until the skeleton has been prepared. In a few in- dividuals they have been so extensive as to allow the pulsation of the heart to be perceptible to the hand, and even to the eye, through the skin covering the defect in the bone. A common variation in the sternum is asymmetry of the costal cartilages. Instead of corresponding, the cartilages may articulate with the sternum in an alternating manner. The cause of this asymmetry is not very obvious. THE THORAX. The thorax is a bony basket of conical shape, formed by the thoracic vertebrae, the ribs with their costal cartilages, and the sternum. The thorax is compressed antero-posteriorly so that it measures less in the sagittal than in the transverse axis : it is also deeper posteriorly than anteriorly. Its posterior boundaries are formed by the thoracic vertebrae and the ribs as far outward as their angles; the backward curve of the libs produces on each side of the vertebrae a deep furrow, the costo- vertebral groove, in which the erector spina muscle and its subdivisions are lodged. This anterior boundary is formed by the sternum and costal cartilages. This surface is slightly convex, and has a slight inclination forward in its lower part. The lateral boundaries are formed by the ribs from their angles to the costal cartilages. The top of the thorax presents an elliptical aperture, the thoracic inlet, which measures, on an average, 12.5 cm. (5") transversely, and 6.2 cm. in its sagittal axis. 128 THE SKELETON. The lower opening of the thorax is very irregular, and forms two" curved lines ascending upward from the last rib to the lower border of the gladiolus Fig. 120.—The Thorax. (Front view.) (mesosternum). These two borders form the sub-costal angle, and the xiphoid (metasternum) projects into the middle of it. The intervals between the ribs are the intercostal spaces, and are eleven in number on each side. THE CLAVICLE. The clavicle is a rod of bone passing from the top of the sternum to the acro- mion process of the scapula. It presents two curves : an inner, with the convexity- directed forward ; and an outer, the smaller, with the convexity directed back- ward. The clavicle consists, for descriptive purposes, of an outer flattened and an inner prismatic portion. The outer third has two surfaces and two borders. The superior surface looks directly upward, and affords attachment to the trapezius muscle posteriorly, and the deltoid anteriorly; a small tract intervening between the muscles is sub- cutaneous. The inferior surface is rough, and at its most posterior part pre- sent the tuberosity of the clavicle; it overhangs the coracoid process and gives THE CLAVICLE. 129 attachment to the conoid ligament. From the tuberosity a ridge, the oblique line, runs outward and forward ; to it the trapezoid ligament is attached. The anterior border is thin ; presents often a small prominence, the deltoid tubercle, and gives origin to the deltoid muscle. The posterior border is thick and rounded ; to it the trapezius is inserted. The inner two-thirds is prismatic inform; it has three surfaces and three borders. Of these, the anterior surface is convex and presents near the sternal end a rough surface for the sternal portion of the pectoralis major, and a rough surface above for the sterno-cleido-mastoid. Near the middle of the shaft it is Fig. 121.—The Left Clavicle. {Superior surface.) Anterior. Deltoid. Pectoralis major. Outer or acromial end. Inner or sternal end. Trapezius. Posterior. Sterno-mastoid. smooth and covered by the thin platysma myoides; sometimes a small canal passes at right angles through this surface of the clavicle; it is traversed by a clavicular branch of the cervical plexus. The posterior surface is concave, and forms an arch over the brachial plexus and subclavian artery. The inferior surface com- mences externally as a groove for the subclavius, the floor of the groove being continuous with the inferior surface of the outer third of the clavicle, and fre- quently presents the orifice of the nutrient foramen. Internally, this groove becomes very narrow and runs on to the rough surface for the rhomboid liga- ment. On the sternal side of the rhomboid impression there is often a facet Fig. 122.—The Left Clavicle. {Inferior surface.) Posterior. Capsular ligament. Oblique line for trapezoid ligament. Tuberosity for conoid ligament. Rhomboid ligament and Sterno- hyoid. Sterno- thyroid. Subclavius. Facet for first costal cartilage. Sternal facet. Deltoid. Acromial facet. Anterior. Pectoralis major. where the clavicle plays on the first costal cartilage. Close beside this facet the sterno-hyoid finds an attachment, and occasionally the sterno-thyroid. Of the three borders, the superior separates the anterior and posterior surfaces; it is faintly- marked toward the sternal end ; externally, it becomes continuous with the pos- terior border of the outer third. The anterior border separates the anterior and inferior surfaces ; it is continuous with the anterior border of the flattened portion. The posterior border separates the inferior and posterior surfaces, and forms the posterior lip of the groove for the subclavius; it begins at the conoid tubercle, and ends at the rhomboid depression. The inner or sternal end of the clavicle is 130 THE SKELETON. broad and expanded ; it plays upon a fibro-cartilage interposed between it and the clavicular facet of the manubrium of the sternum, and its borders are rough for the attachment of the sterno-clavicular and interclavicular ligaments. The acromial, or outer end, presents a smooth articular facet, directed slightly downward for the acromion ; its edges, especially the superior, are rough for the acromio-clavicular ligaments. The following muscles are attached to the clavicle :— Sterno-cleido-mastoid. Pectoralis major. Platysma myoides. Subclavius. Deltoid. Trapezius. Sterno-hyoid. Sterno-thyroid (occasionally). Ligaments : — Interclavicular. Interarticular (sternal). Capsular (sterno-clavicular). Rhomboid or costo-clavicular. Capsular (acromio-clavicular). Interarticular (acromio-clavicular). Conoid. Trapezoid. Costo-coracoid membrane. Deep cervical fascia. Blood-supply.—The nutrient artery is a branch of the suprascapular; it enters the bone on the under surface of the shaft near the middle of the subclavian groove. It is directed toward the acromial end. The acromial end of the clavicle receives numerous branches from the acromio-thoracic artery, and twigs from the arteries in the muscles attached to it. Ossification.—The clavicle is ossified from two centres. The primary nucleus appears in the sixth week of embryonic life in the tissue immediately overlying the cartilaginous pre-coracoid bar (see p. 134). The clavicle begins as a membrane bone, but the ossification quickly extends into the underlying cartilage ; it is, therefore, a dermal splint engrafted on cartilage. About the seventeenth year a secondary nucleus appears at the sternal end. Consolidation is complete by the twentieth year. THE SCAPULA. The scapula is a large flat bone, triangular in shape, situated on the posterior aspect of the thorax, and resting on the ribs from the second to the seventh. Of its two surfaces the anterior is deeply concave, forming the subscapular fossa, which is marked by several ridges commencing at the posterior border of the bone and passing transversely ; these ridges divide this surface into several shallow grooves from which the subscapular muscle takes origin: the highest groove is the deepest. The outer third of this surface is smooth, and overlapped by subscapular muscle: the superior and inferior angles are somewhat triangular, and connected by a narrow ridge of bone along the posterior border. The ridge and its terminal surfaces serve for the insertion of the serratus magnus. The posterior surface, or dorsum, is generally convex ; it is unequally divided by a prominent lip of bone, the spine. The part above the spine is the supraspinous fossa, and lodges the supra-spinatus muscle. The hollow below the spine is the infraspinous fossa ; it is larger than the supraspinous fossa, and is limited inferiorly by a ridge which runs from the glenoid fossa backward to join the posterior border a short distance above the inferior angle. To this oblique ridge the stout aponeurosis is attached which separates the teres major and teres minor muscles from the infra-spinaius muscle. The infraspinatus arises from the inner two-thirds of the infraspinous fossa, and overlaps the outer third. The supra- and infra-spinous fossae communicate with each other round the outer end THE SCAPULA. of the spine; this part corresponds to the neck of the scapula, and the groove is the scapular notch ; it transmits the suprascapular nerve and artery from one fossa to another. The surface of bone below the oblique ridge presents two, and occasionally three, facets for muscles: the long narrow outer one is for the origin of the teres minor; this is crossed near its middle by a groove for the dorsal artery of the scapula. The second facet is broader, and gives attachment to the teres major muscle. In bones from a muscular subject the third facet, quite at the inferior angle, is for a few fibres of the latissimus dorsi. Fig. 123.—The Left Scapula. {Dorsal surface.) Coraco-acromial ligament. Pectoralis minor. , Umo-hyoid and the transverse ligament. Biceps.. Acromion process. Deltoid. Superior angle. Levator anguli scapulae. Supra- spinatus. Neck of scapida and scapular notch. Capsular lig. Glenoid fossa. Rhomboideus minor. Groove for dorsal artery of the scapula. ~ Teres minor.— Rhomboideus major., Axillary border.— Vertebral border. Teres major. — Inferior angle. Latissimus dorsi. The spine commences at the posterior border of the scapula by a broad triangular surface ; it then crosses the dorsal surface obliquely to the glenoid fossa, becoming more prominent as it passes outward till it reaches the neck of the scapula; from this point it forms the overhanging acromion process. The spine presents a superior surface which gives origin to the supra-spinatus muscle, and an inferior surface which affords origin to the infra-spinatus muscle. It has a prominent crest, which is continuous posteriorly with the vertebral border, and, at its commencement, is smooth for a bursa between it and the trapezius. The crest is subcutaneous, and presents two lips—a superior for the insertion of the 132 THE SKELETON. trapezius, and an inferior lip for the origin of the deltoid. The crest is continued into the acromion process. The acromion process forms the summit of the shoulder, and presents two surfaces, two borders, and a tip. The upper surface affords origin at its posterior part to a portion of the deltoid. The under surface is concave and smooth. Its inner border, a continuation of the superior lip of the crest, receives the trapezius, and presents near the tip a small articular facet for the outer end of the clavicle; the edges of the facet are rough for the acromio-clavicular ligaments. The outer border is continuous with the inferior lip of the crest, with which it forms an Serratus magnus. Fig. 124—The Left Scapula. {Ventralsurface.') Suprascapular notch. Conoid lig. Trapezoid ligament. Coraco-acromial ligament. Biceps and cora- co-brachialis. Clavicular facet. Biceps. Glenoid fossa. Capsule Triceps (middle or long head). Serratus magnus. angle; it gives origin to the deltoid. The tip of the acromion affords attachment to the coraco-acromial ligament. Of the three borders presented by the scapula, the external, or axillary, is the thickest, and extends from the posterior inferior angle to the lower margin of the glenoid cavity. Near its junction with the glenoid cavity there is a rough surface from which the long head of the triceps arises; below this is the groove for the dorsal artery of the scapula. The subscapularis muscle encroaches on this border from the anterior surface, and the teretes from the posterior aspect. The posterior, or vertebral, border, sometimes called the base, is the longest; it extends from the posterior superior to the posterior inferior angle. It THE SCAPULA. is very narrow, but affords attachment to three muscles: namely, the levator anguli scapula above the spine; the rhomboideus minor on a level with the spine; . and the rhomboideus major, through the intervention of a fibrous arch from the spine to the inferior angle. The superior border is the shortest and thinnest, ending externally in the coracoid process. At the base of the coracoid is the suprascapular notch, to the edges of which the transverse ligament is attached. Not infrequently the notch is replaced by a supra- scapular foramen. This notch or foramen transmits the suprascapular nerve, and occasionally the suprascapular artery, but as a rule the artery passes over the ligament. From the adjacent borders of the notch and from the ligament, the omo-hyoid takes origin. The anterior angle of the scapula is formed by the glenoid cavity. This cavity is shallow and pyriform, with its major axis vertical; the lower end is the broader ; the upper end or apex gives origin to the long tendon of the biceps. The margins are raised, and afford attachment to the glenoid ligament. In the recent state, the cavity is covered with hyaline cartilage, and forms an articular fossa for the head of the humerus. The margin is somewhat defective where it is overarched by the acromion. The circumference is rough for the attachment of the capsular ligament. Beyond this is a narrow, constricted portion, called the neck of the scapula. Projecting upward from the neck is the coracoid process, a prominence of bone anterior to, but parallel with, the acromion. The tip of the coracoid gives origin to the short tendon of the biceps, the coraco-brachialis muscle, and the costo- coracoid ligament. The superior surface affords attachment to the pectoralis minor muscle, and to the coraco-clavicular ligaments (conoid and trapezoid). The outer border has attached to it the coraco-acromial ligament. Muscles.—The following are attached to the scapula : — Supra-spinatus. Infra-spinatus. Subscapularis. Teres major. Teres minor. Omo-hyoid. Pectoralis minor. Serratus magnus. Latissimus dorsi. Trapezius. Rhomboideus major. Rhomboideus minor. Levator anguli scapulae. Biceps. Coraco-brachialis. Triceps (long head). Deltoid. Ligaments:— Conoid. Trapezoid. Costo-coracoid membrane. Costo-coracoid ligament. Capsular (acromio-clavicular). Coraco-acromial. Suprascapular (transverse). Capsular (shoulder-joint). Coraco-humeral. Gleno-humeral. Glenoid. Rhomboid loop. Spino-glenoid. Inferior transverse. Blood-supply.—The scapula is supplied by the following arteries: Twigs from the subscapular artery and from the subscapular branch of the suprascapular enter the bone on the anterior surface. The dorsal artery of the scapula dis- tributes branches in the infraspinous, whilst the suprascapular artery supplies the supraspinous fossa, the spine, the glenoid fossa, and sends branches into the infra- spinous fossa. The acromion is supplied by branches of the acromio-thoracic artery. Ossification.—The scapula is ossified from seven centres. Two may be con- sidered as primary, and the remainder as secondary nuclei. The centre for the body appears in a plate of cartilage near the neck of the scapula about the eighth week of intra-uterine life, and quickly forms a triangular plate of bone, from which the spine appears as a slight ridge about the middle of the third month. At birth the glenoid fossa and part of the scapular neck, the acromion, coracoid, and vertebral border are cartilaginous. During the first year a nucleus appears for the coracoid, and extends into the glenoid fossa, and along the upper border as far as the suprascapular notch. 134 THE SKELETON. During the fifteenth year the coracoid is ankylosed to the scapula, and the secondary centres appear. Two nuclei are deposited in the acromial cartilage, and fuse to form the acromion, and join the spine at the twentieth year. This union of the acromion and spine may be fibrous, hence the acromion is often found separate in macerated specimens. The cartilage along the vertebral border ossifies from two centres : one in the middle and one at the posterior inferior angle. A thin scale may occasionally be detected at the tip of the glenoid fossae. Morphology.—It is impossible to comprehend the significance of the scapu- lar nuclei without considering briefly the morphology of the shoulder (pectoral) girdle. In its most generalized form the shoulder girdle consists of cartilage, which is disposed in three parts. Of these, a dorsal segment represents the scapula and a ventral bar, reaching to the sternum, represents the coracoid. The meeting place Fig. 125.—Ossification of the Scapula. The scapula at the third year, showing the coracoid element. (.Anterior view.) The scapula at birth. (Anterior view.) of the coracoid and scapula is the glenoid fossa. Anterior to the coracoid there is a third piece, more or less parallel with the coracoid, named the pre-coracoid. The human shoulder girdle is modified from the type form, mainly in the suppression of the pre-coracoid, and, in part, of the coracoid. The suppression is brought about by the clavicle, which commences to ossify in the membrane overlying the pre-coracoid ; it then invades and replaces the cartilage. The scapular end of the coracoid ossifies and becomes the coracoid process of the scapula; the ventral end degenerates to form the costo-coracoid ligament, which lies in the free border of the membrane of that name. The dorsal cartilage ossifies and becomes the scapula ; the large tract of cartilage on the vertebral bor- der of the young scapula represents the large suprascapular cartilage of batrachians. The suprascapular notch indicates the line of union of scapular and coracoid elements. In the embryo the notch is bridged over with cartilage, which may ossify or become ligament. THE HUMERUS. THE HUMERUS. The humerus is the longest bone of the upper limb. Its upper extremity pre- sents a hemispherical surface covered with cartilage, and known as the head. The head articulates with the glenoid cavity of the scapula, and is directed upward, inward, and backward. Below the articular surface the bone is rough and con- stricted, constituting the anatomical neck. To the outer side of the head are two tuberosities, separated by the bicipital groove. The greater tuberosity is the higher and more posterior ; it is marked by three facets for muscles: an upper one for the supra-spinatus, a middle for the infraspinatus, and an inferior for the teres minor. The lesser tuberosity is the more prominent; it serves for the insertion of the subscapularis. The furrow between the tuberosities lodges the long tendon of the biceps, extends downward in the axis of the humeral shaft, and, gradually becoming shallower, ends near the junction of the upper and middle third of the shaft. The margins of this, the bicipital groove, are called lips, and afford attachment to muscles. The pectoralis major occupies the whole length of the outer lip. The inner lip receives, below, the teres major, and, above, the latissimus dorsi; the tendon of the latter muscle is also attached to the floor of the groove. Between the tuberosities, the transverse humeral ligament converts the groove into a canal. In addition to the long tendon of the biceps and its tube of synovial membrane, the groove transmits a branch of the anterior circumflex artery. The constriction immediately below the tuberosities is the surgical neck. The shaft is prismatic in its upper third, but flattened below. Three borders and three surfaces may be recognized. The anterior border commences at the greater tuberosity, as the anterior or outer lip of the bicipital groove, and, passing downward, skirts the radial side of the coronoid fossa, to become continuous with the ridge separating the capitellum and trochlea. The radial or outer border extends from the posterior border of the greater tuberosity to the radial condyle. This border is not well marked in the upper part of the shaft; near the middle it is interrupted by the musculo-spiral groove; the lower half is termed the external condylar ridge, and affords attachment to the supinator longus and extensor carpi radialis longior muscles, and the external intermuscular septum. The ulnar or internal border commences at the lesser tuberosity, as the inner lip of the bicipital groove, and extends downward to the ulnar (internal) condyle. Near its centre is a ridge for the insertion of the coraco-brachialis, and below this the foramen for the nutrient artery. The three borders considered above bound three surfaces. The external surface lies between the anterior and radial borders. Near its middle is a rough impression for the insertion of the deltoid;■ somewhat lower is the termination of the musculo-spiral groove. The internal surface lies between the anterior and ulnar borders. The lower halves of the internal and external surfaces afford origin to the brachialis anticus muscle. The internal surface usually presents, about 5 cm. (2") above the ulnar condyle, an elongated rough surface. This is the supracondyloid ridge ; it is occasionally replaced by a prominent spine of bone, the supracondyloid process (Fig. 128), from which a band of fibrous tissue extends to the ulnar condyle, forming a ring, transmitting the median nerve and the brachial artery. The nerve is not always accompanied by the artery; in some instances of high division of the brachial the foramen transmits the inter- osseous artery. The process gives origin to the pronator radii teres, and some- times affords insertion to a part of the coraco-brachialis. The posterior surface lies between the ulnar and radial borders. It is obliquely divided by the musculo-spiral groove. The surface above the groove serves for the origin of the external head ; the part below for the internal head of the triceps. The lower extremity of the humerus is flattened, and presents from the ulnar to the radial side the following parts: a prominent process, the ulnar (in- ternal) condyle, from which the pronator radii teres arises, and to the lower part of which the internal lateral ligament is attached. From this ligament the flexor 136 THE SKELETON. carpi radialis, palmaris longus, flexor sublimis digitorum, and flexor carpi ulnaris muscles arise. Posteriorly the condyle forms with the trochlea a groove traversed bv the ulnar nerve. External to the condyle there is the inferior articular surface, subdivided by a low ridge into the trochlea and the capitellum. The trochlea pIG. 126. The Left Humerus. [Anterior view.) Supraspinatus. Subscapularis, Latissimus dorsi Bicipital groove. Pectoralis major. Teres major. Coraco-brachialis, Deltoid JBrachialis anticus Supinator longus Extensor carpi radialis longior, Pronator radii teres, Extensor carpi radialis brevior. Extensor communis digitorum. Extensor minimi digiti. Extensor carpi ulnaris. Supinator brevis. Flexor carpi radialis. Palmaris longus. Flexor sublimis digitorum. Flexor carpi ulnaris. is, in shape, like the section of a pulley wheel; the ulnar extends much lower than the radial edge ; the articular surface is sharply indicated anteriorly and pos- teriorly. The trochlea fits into the greater sigmoid cavity of the ulna. Above the trochlea on the anterior surface is the rounded coronoid fossa, which receives THE HUMERUS. the coronoid process of the ulna when the forearm is flexed. On the posterior aspect there is the olecranon fossa, for the reception of the anterior edge of the olecranon in extension of the forearm. These fossae in most humeri are separated Fig. 127.—The Left Humerus. {Posterior view.) Capsular ligament, Infraspinatus Teres minor, Triceps (external head) Musculo-spiral groove, Triceps (internal head) Capsular ligament. Olecranon fossa. External condyle. Anconeus and external lateral liga- ment. ■Internal condyle. Groove for ulnar nerve. Flexor carpi ulnaris. by a thin translucent disc of bone, sometimes merely by fibrous tissue, so that in macerated bones a perforation, the supratrochlear foramen, exists. The radial head or capitellum is received by the depression on the summit of the radius ; it is limited to the anterior and lower surface of the humerus. Above, it terminates THE SKELETON. in a shallow fossa, which receives the edge of the radius in flexion. The ridge between the trochlea and the capitellum corresponds to the interval between the ulna and radius ; the shallow groove on the outer side of the ridge receives the inner margin of the head of the radius. External to the capitellum is the exter- Fig. 128.—The Left Humerus with a Supracondyloid Process and some Irregular Muscle Attachments. (Anterior view.) Lesser tuberosity. Subscapularis. Capsular ligament. Coraco-brachialis brevis (Rotator humeri). Bicipital groove. Head. - Greater tuberosity. “Transverse humeral ligament. Fourth head of biceps. Rough surface for deltoid Coraco-brachialis. Third head of biceps. Brachialis anticus. Coraco-brachialis.. Supracondyloid process. The external condylar ridge Pronator radii teres. Capsular ligament. Coronoid fossa. Internal condyle. Internal lateral ligament. Trochlea. ■Radial depression. •External condyle. Capitellum. nal or radial condyle. It is less prominent than the ulnar condyle, and gives attachment to the external lateral ligament of the elbow, and to a tendon from which five extensor muscles arise, viz., extensores carpi radialis brevior, digitorum communis, minimi digiti, carpi ulnaris, and the supinator brevis. On the posterior THE HUMERUS. aspect this condyle extends to the edge of the trochlea, and gives origin to the anconeus. Fig. 129.—Ossification of the Humerus. Unites with the shaft at the twentieth year. The upper epiphysis is formed by the union of the nucleus for the head, greater tuberosity, and that for the lesser tuberosity. These form a common epiphysis before uniting with the shaft. Shaft begins to ossify in the eighth week of intra-uterine life. Nucleus for the internal condyle appears at fifth; fuses at the eighteenth year. Nucleus for trochlea appears at the tenth year. Nucleus for external condyle ap- pears at fourteenth year. Nucleus for capitellum appears in the third year. The centres for the radial condyle, trochlea, and capitellum unite together and form an epiphysis which fuses with the shaft at the seventeenth year. Supraspinatus. Infraspinatus. Teres major. Teres minor. Subscapularis. Deltoid. Pectoralis major. Coraco-brachialis. Muscles.—The humerus affords attachment for the following muscles : — Latissimus dorsi. Biceps (occasionally). Brachialis anticus. Triceps. Pronator radii teres. Flexor carpi radialis. Palmaris longus. Flexor sublimis digitorum. Anconeus. Flexor carpi ulnaris. Supinator longus. Extensor carpi radialis longior. Extensor carpi radialis brevior. Extensor digitorum communis. Extensor minimi digiti. Extensor carpi ulnaris. Supinator brevis. 140 THE SKELETON. Ligaments.—To the upper extremity of the humerus the following ligaments are attached : — Capsular. Coraco-humeral. Gleno-humeral. Transverse humeral. To the lower extremity :— Internal lateral ligament External lateral ligament Anterior ligament Posterior ligament of the elbow joint. Arteries.—The blood-supply of the humerus is derived from the suprascapu- lar and the anterior and posterior circumflex arteries. Branches from these arteries enter the foramina which cluster around the circumference of the head and tuber- osities. At the top of the bicipital groove there is a large nutrient foramen, which transmits a branch from the anterior circumflex artery. The nutrient artery of the shaft is derived from a muscular branch of the brachial; it enters the bone near the middle of the inner border immediately below the insertion of the coraco- brachialis, and is directed to the distal end. The lower extremity is nourished by numerous twigs derived from the anastomotic, the superior and inferior pro- funda, and the recurrent branches of the radial, ulnar, and interosseous arteries. Ossification.—The humerus ossifies from one primary and six secondary nuclei. The centre for the shaft appears about the eighth week of intra-uterine Fig. 130.—The Head of the Humerus at the Sixth Year. {In section.) The centre for the head appears during the first year; it is sometimes present at birth. The centre for the greater tuberosity ap- pears in the third year. life, and extends very rapidly. At birth the bone presents two cartilaginous ex- tremities, which ossify in the following manner : A nucleus for the head appears early in the first year; it is not infrequently present at birth (Spencer). The nucleus for the greater tuberosity appears in the third year. In the fifth year a centre may be deposited for the lesser tuberosity, but this is not constant. The three nuclei coalesce to form a disc of bone, which unites with the shaft about the twentieth year. The inferior extremity ossifies from four centres: the centre for the capitellum appears in the third year, and those for the inner (ulnar) condyle, the trochlea, and external (radial) condyle at the fifth, tenth, and fourteenth year respectively. The nuclei for the capitellum, trochlea, and radial condyle coalesce before uniting with the shaft, which they do in the seventeenth year. The ulnar condyle joins the shaft somewhat later. A study of the upper end of the humeral shaft before its union with the epi- physis is of interest in relation to what is known as the neck of the humerus. The term neck is applied to three parts of this bone. The anatomical neck is the con- striction to which the capsular ligament is attached. This is accurately indicated by the constriction which lies internal to the tuberosities ; the upper extremity of the humeral shaft before its union with the epiphysis terminates in a low, three- sided pyramid, the surfaces of which are separated from each other by ridges. The inner of these three surfaces underlies the head of the bone, and the two outer THE ULNA. 141 surfaces underlie the tuberosities. The axis of the inner, isolated portion forms with the shaft an angle of 130° ; it constitutes the morphological neck of the hu- merus, and is of the same nature as the neck of the femur. The surgical neck is an indefinite area below the tuberosities where the bone is liable to fracture. THE ULNA. The ulna is the inner bone of the forearm: it lies parallel with, but is longer than, the radius. The upper extremity is the thickest and strongest part of the ulna, and is of irregular shape. The superior articular surface is called the greater sigmoid cavity, and receives the trochlea of the humerus; it is trans- versely constricted near its middle. The prominence above the constriction is termed the olecranon, the part below the coronoid process. Fig. 13i.—Upper End of Left Ulna. {Outer view.) Olecranon.- Greater sigmoid fossa. Orbicular ligament. Lesser sigmoid fossa. Oblique ligament. Supinator brevis. Flexor profundus digitorum. Interosseous membrane The olecranon process is the highest part of the ulna; to its upper surface the triceps is inserted, and the anterior margin of this surface affords attachment to the posterior ligament of the elbow. The anterior surface of the olecranon is articular, and forms the upper and back part of the greater sigmoid cavity, and its margins give attachment to ligaments. The posterior surface of this process is triangular, and separated from the skin merely by a bursa. On the inner side there is a tubercle for the origin of the flexor carpi ulnaris; and below this a fasciculus of the internal lateral ligament of the elbow is inserted. The coronoid process forms the lower lip of the greater sigmoid cavity : its 142 THE SKELETON. upper surface is articular and forms nearly a right angle with the olecranon portion. The anterior edge of the coronoid process is sometimes called the apex. The inferior aspect is rough for the insertion of the brachialis anticus muscle, and the lower outer angle has a tubercle to which the oblique ligament is attached. The inner edge has a smooth tubercle from which the flexor sublimis digitorum Fig. 132.—The Left Ulna and Radius. (Antero-inlernal view.) Capsular ligament Internal lateral ligament. Tubercle for the flexor sublimis digitorum. External lateral ligament. Brachialis anticus. Pronator radii teres (lesser head). Flexor longus pollicis (accessory head). ■Greater sigmoid fossa. Head of radius. Neck of radius. Lower limit of orbicular ligament. Oblique ligament. Bicipital tubercle. ■Oblique ligament. Supinator brevis. Flexor sublimis digitorum. Oblique line. ULNA- —Radius. Pronator radii teres. Interosseous membrane, Flexor longus pollicis. Flexor profundus digitorum Pronator quadratus Pronator quadratus. Anterior radio-ulnar ligament Internal lateral ligament Supinator longus. External lateral ligament. Interarticular fibro-cartilage. Capsular ligament. arises ; the ridge of bone immediately below this tubercle gives origin to the lesser head of the pronator radii teres, and below this again the rounded accessory bundle of the flexor longus pollicis arises. A triangular depressed surface, posterior to the sublimis tubercle, gives origin to the upper fibres of the flexor profundus digitorum. To the outer side of the rough surface for the brachialis anticus is a triangular space, the base of which is represented by the lesser sigmoid cavity, which receives the lateral articular THE ULNA. surface of the head of the radius; the anterior and posterior margins of this cavity afford attachment to the orbicular ligament. The rest of the triangle is depressed, and gives origin to the siipinator brevis. The shaft throughout the greater part of its extent is prismatic, but tapers toward the lower extremity, becoming thin and rounded in its lower third. It has three borders and three surfaces. Fig. 133.—The Left Ulna and Radius. {Postero-external view.) Triceps.- Capsular ligament.- Olecranon. Subcutaneous surface. Anconeus. Lower limit of orbicular ligament. Biceps. Supinator brevis. Extensor ossis metacarpi pollicis. An aponeurosis is attached to this bor- der from which the flexor and extensor carpi ulnaris and flexor profundus digitorum arise. Extensor primi internodii pollicis. Extensor secundi internodii pollicis. Radius. Ulna. Extensor indicis. Grooves for extensor ossis and extensor primi internodii pollicis. For extensor carpi radialis longior and brevior. Extensor secnndi internodii pollicis. . Extensor minimi digiti. . Extensor carpi ulnaris. .Internal lateral ligament. Extensor communis digitorum and extensor indicis. Capsule. Posterior radio-ulnar ligament. Of the three borders, the outer (or interosseous) is the most marked; it commences at the apex of the triangle from which the supinator brevis arises, becomes very prominent in the middle of the bone, but is indefinite near its termi- nation; the interosseous membrane is attached to it. The anterior border is directly continuous with the inner edge of the rough surface for the brachiaiis anticus, and terminates inferiorly in front of the styloid process ; throughout the 144 THE SKELETON. greater part of its extent it is rounded, and affords origin to the flexor p7'ofundus digitorum ; in its lower fourth it is rough and prominent for the pronator quad- ratus. The posterior border extends from the tubercle, near the tip of the olecranon, to the back part of the styloid process. The upper three-fourths gives attachment to an aponeurosis, from which the plexor and extensor carpi ulnaris and the flexor profundus digitorum muscles arise. Of the three surfaces, the anterior lies between the anterior and interos- seous borders; it is concave for the greater part of its extent. The upper three- fourths gives origin to the flexor profundus digitorum, the lower fourth to the pronator quadratus; the upper limit of the surface for the pronator is sometimes indicated by a transverse ridge. The internal surface is bounded by the an- terior and posterior borders. The upper three-fourths is occupied by the flexor pi'ofundus digitorum; the remainder is subcutaneous. The posterior surface lies between the interosseous and posterior borders. Its upper fourth is marked off by an oblique ridge running from the lesser sigmoid cavity to the posterior border. The surface above the line receives the insertion of the anconeus; from the line itself a few fibres of supuiator brevis arise. The surface below the oblique line is subdivided by a vertical ridge ; the portion lying between this ridge and the posterior border is in relation with the extensor carpi ulnaris. Between this line and the interosseous border the following muscles arise in order from above downward : extensor ossis metacarpi pollicis, the extensor secundi internodii pollicis, and the extensor indicis. The lower extremity of the ulna is of small size and consists of two parts, a head and styloid process, separated from each other, on the under surface, by a groove into which an interarticular cartilage is inserted. That part of the head adjacent to the groove is semilunar in shape and plays upon the interarticular cartilage which excludes it from the wrist-joint. The margin of the head is also semilunar, and is received into the sigmoid cavity of the radius. The styloid process projects from the inner and back part of the bone, and appears as a con- tinuation of the posterior border. To its extremity the internal lateral ligament is attached, and its posterior surface is grooved for the passage of the tendon of the extensor carpi ulnaris. Muscles.—The following are attached to the ulna:— Triceps. Anconeus. Brachialis anticus. Pronator quadratus. Flexor sublimis digitorum. Flexor profundus digitorum Flexor longus pollicis. Flexor carpi ulnaris. Extensor ossis metacarpi pollicis. Extensor secundi internodii pollicis. Extensor indicis. Pronator radii teres. Supinator brevis. Extensor carpi ulnaris. Ligaments :— Internal lateral of elbow. Anterior of elbow. Posterior of elbow. Orbicular. Oblique. Interosseous membrane. Anterior radio-ulnar. Posterior radio-ulnar. Internal lateral of wrist-joint. Interarticular fibro-cartilage. Blood-supply.—The nutrient vessel enters the shaft near the middle of the anterior surface ; it is derived from the anterior interosseous trunk, and is directed toward the proximal end. The upper extremity receives branches from the an- terior and posterior ulnar recurrent and from the interosseous recurrent. The lower end receives twigs from the anterior and posterior interosseous arteries. Ossification.—The ulna is ossified from three centres. The primary nucleus appears near the middle of the shaft in the eighth week of embryonic life. At birth the greater portion of the olecranon process is cartilaginous. During the fourth year a nucleus appears for the distal epiphysis. The cartilaginous olecranon is mainly ossified from the shaft, and in the course of the tenth year a scale-like epiphysis appears at its summit. This unites during the sixteenth year. The distal epiphysis consolidates about the eighteenth year. THE RADIUS. THE RADIUS. The radius is shorter than the ulna and lies parallel with it. The upper end, or head, is surmounted by a circular disc, of which the superior surface is depressed for the reception of the capitellum of the humerus, especially in flexion of the forearm. The margin of the head is also articular; it is deeper on the ulnar aspect, where it is received by the lesser sigmoid cavity of the ulna ; the rest Fig. 134.—Articular Facets on the Lower End of Left Radius and Ulna. Posterior. Radius. Ulna Styloid process of ulna. For scaphoid For semilunar, Head of ulna: it articu- lates with the interarticu- lar fibro-cartilage of the wrist-joint. Anterior. of the circumference is embraced by the orbicular ligament. Below the cartilage- covered surface of the bone there is a constricted portion, or neck, which is in relation by its outer side with the supinator brevis. Beneath the neck, on the anterior aspect of the bone, there is an oval eminence, the bicipital tuberosity, divided longitudinally into a rough posterior portion for the biceps tendon, and a smooth anterior surface in relation with the bursa which is situated between the tendon and the tuberosity. The radius has three borders and three surfaces. Of the three borders the Fig. 135.—Posterior View of the Lower End of the Radius and Ulna. Radius. Ulna. The broad groove on the ra- dius is for the tendons of ext. communis digitorum and extensor indicis. Extensor minimi digiti lies in the groove between the ra- dius and ulna. ■Extensor carpi ulnaris. Insertion of supinator longus. Ext. ossis metacarpi pollicis and Ext. primi internodii pollicis. Extensor carpi radialis longior and brevior. Tubercle for posterior annular ligament. Extensor secundi internodii pollicis. •Styloid process. Styloid process, interosseous is the best marked. Commencing at the posterior edge of the bicipital tuberosity, it extends as a sharp ridge until it approaches the distal extremity of the bone; it then divides to become continuous with the anterior and posterior margins of the sigmoid cavity. It affords attachment to the interosseous membrane. The anterior border starts from the bicipital tuberosity, crosses obliquely to the outer side of the bone, and descends to the anterior border of the styloid process. The upper third of this border is called the oblique line, and limits the insertion of thz. supinator brevis and the origin of the flexor longus pollicis, and affords attachment to the flexor sublimis digito/um. The 146 THE SKELETON. posterior border, commencing at the back of the neck of the radius, is very indistinct at first, but becomes more marked near the middle of the bone; it terminates at the back part of the styloid process. The anterior surface is bounded by the anterior and interosseous borders. The upper two-thirds is occupied by the flexor longus pollicis, and a little less than the lower third by the pronator quadratics. The external surface lies between the anterior and pos- terior borders. The upper third affords insertion to the supinator brevis; at its centre there is a rough, low, vertical ridge for the pronator radii teres ; below this, the bone is smooth and overlapped by the tendons of the extensores carpi radialis longior and brevior, and crossed by the extensor ossis metacarpi pollicis and Fig. 136.—Ossification of the Radius and Ulna Appears at the tenth year; fuses at the sixteenth year. Appears at the fifth year; fuses at the seventeenth year. Radius.- —Ulna Appears at the fourth year ; fuses at the eighteenth year. Appears at the second year; fuses at the twentieth year. extensor' primi internodii pollicis. The posterior surface lies between the interosseous and posterior borders. The upper third is covered by the supinator brevis; the middle third gives origin to the extensor ossis metacarpi and extensor primi internodii pollicis ; and the lower third is covered by tendons. The lower extremity of the radius is quadrilateral; its carpal surface is articular and divided by a ridge into an inner quadrilateral portion, concave for articulation with the semilunar bone; and an outer triangular portion, extending on to the styloid process: this is concave to receive the superior surface of the scaphoid bone. The inner side of the lower end presents the sigmoid cavity for the reception of the rounded margin of the head of the ulna. The anterior surface is a raised ridge to which the anterior ligament of the wrist-joint is THE CARPUS. 147 attached. The outer surface is represented by the styloid process ; to its base the supinator longus is inserted, and the tip serves for the attachment of the external lateral ligament of the wrist. It is also marked by a shallow furrow for the tendons of the extensor ossis metacarpi and extensorprimi internodiipollicis. The posterior surface is convex, and marked by two prominent ridges separating three furrows. The posterior annular ligament is attached to these ridges, to the styloid process, and to the inner margin, thus forming with the bone a series of tunnels. The outermost is broad, shallow, and frequently subdivided by a low ridge. The outer subdivision is for the extensor carpi radialis longior, the inner for the extensor carpi radialis brevior. The middle groove is narrow and deep for the tendon of the extensor secundv internodii pollicis. The innermost is shallow and transmits the extensor indicis and the extensor communis digitorum which overlies the indicis. When the radius and ulna are articulated, an additional groove is formed for the extensor minimi digiti. Muscles.—The following muscles are attached to the radius :— Biceps. Supinator brevis. Supinator longus. Pronator radii teres Pronator quadratus. Extensor ossis metacarpi pollicis. Extensor primi internodii pollicis. Flexor longus pollicis. Flexor sublimis digitorum. Ligaments:— Oblique ligament. Interosseous membrane. Anterior radio-ulnar, Posterior radio-ulnar. Posterior annular. External lateral of wrist. Interarticular fibro-cartilage of wrist. Anterior radio-carpal. Posterior radio-carpal. Blood-supply.—The nutrient artery is derived from the anterior interosseous trunk ; it enters the shaft near the middle of the anterior surface, and runs toward the proximal end of the bone. The head of the bone is supplied by the radial recurrent and interosseous recurrent arteries. The lower end is supplied by the anterior and posterior interosseous arteries and numerous twigs from the carpal arches. Ossification.—The radius is ossified by one primary and two secondary centres. The shaft begins to ossify at the eighth week of embryonic life. The nucleus for the lower end appears in the second year, whilst that for the upper end is deposited in the fifth year. The head ankyloses with the shaft at the seven- teenth year, but consolidation is delayed at the lower end until the twentieth year. THE HAND. The skeleton of the hand consists of three parts—the carpus, metacarpus, and phalanges. THE CARPUS. . The carpus contains eight bones, arranged in two rows, four bones in each row. Enumerated from the radial to the ulnar side, the bones of the proximal row are the scaphoid, semilunar, cuneiform, and pisiform ; those of the distal row, the trapezium, trapezoid, magnum, and unciform. This is the largest bone of the proximal row. Its superior surface is some- what triangular and convex for articulation with the lower end and styloid pro- cess of the radius. Its inferior surface has two facets: a large one for the tra- The Scaphoid. 148 THE SKELETON. pezium, and a small one for the trapezoid. The dorsal surface is occupied by a long, deep groove for ligaments. The palmar surface is rough and concave above; below, it has a prominent tuberosity for the attachment of the anterior annular ligament and the abductor pollicis muscle. The outer (radial) surface is rough for ligaments. The inner (ulnar) surface is occupied by two articular facets, of which the upper one is crescentic in shape for the semilunar bone, whilst the lower is deeply concave for the reception of the head of the magnum. Articulations.—With radius, trapezium, trapezoid, magnum, and semilunar. Fig. 137.—The Left Hand. {Dorsal surfaced) SEMILUNAR Extensor carpi radialis longior. Extensor carpi radialis brevior. Extensor carpi ul naris. Metacarpal Extensor primi internodiipollicis. Ext. secun- di inter- nodii pol- licis. First phalanx. - Extensor communis digitorum. - Second phalanx. - Extensor communis digitorum. Third, ungual, or terminal phalanx. «■ The Semilunar. The semilunar has a convex superior surface for articulation with the lower end of the radius and the fibro-cartilage of the wrist. Its inferior surface is deeply concave for the head of the magnum. The ulnar ridge of the inferior articular surface is faceted for the unciform. The outer (radial) surface has a narrow semilunar facet for the scaphoid, whilst the inner (ulnar) aspect of the bone presents a quadrilateral facet for the base of the cuneiform. The palmar and THE CARPUS. 149 dorsal surfaces are rough and non-articular. Of these, the palmar is usually the more extensive; in the remaining carpal bones the dorsal surface is the broader. Articulations.—With the radius, scaphoid, cuneiform, magnum, and unci- form . Fig. 138.—The Left Hand. (.Palmar surface.') Flexor brevis pollicis. Abductor pollicis. Flexor carpi ulnaris. Abductor minimi- digiti. Flexor brevis and opponens minimi' digiti. Flexor carpi ulnaris. Adductor pollicis. Opponens minimi digiti. — Opponens'pollicis. Occasional insertion into trapezium Extensor ossis metacarpi pollicis. Flexor carpi radialis. Interosseus primus volaris, Opponens pollicis Flexor brevis and abductor pollicis. Flexor brevis and adductor pollicis, Abductor and flexor brevis minimi digiti. Flexor longus pollicis. =—Flexor sublirais digitorum. Flexor profundus digitorum. The Cuneiform. The cuneiform (or pyramidal bone) rests by its base on the ulnar side of the semilunar; its apex is directed downward and to the ulnar side, and serves for the attachment of the internal lateral ligament of the wrist. The base presents a facet for the semilunar. The inferior surface has a sinuous articular surface for the unciform bone. The superior surface has a convex smooth portion, where it plays upon the interarticular cartilage which intervenes between it and the lower end of the ulna; the remainder of this surface is rough for ligaments. The palmar surface has a conspicuous facet for the pisiform bone, and the dorsal surface is rough for ligaments. Articulations.—Pisiform, semilunar, and unciform. 150 THE SKELETON. The Pisiform. The pisiform resembles closely a split pea. Its dorsal aspect, corresponding to the cut surface of the pea, articulates with the facet on the palmar surface of the cuneiform. The rest of this bone is rough for the anterior annular ligament and the tendon of the flexor carpi ulnaris. Fig. 139.—The Left Scaphoid. For semilunar. For radius For ligament For trapezoid For trapezium For magnum. Tuberosity Fig. 140.—The Left Semilunar. For cuneiform. For unciform. For magnum. The Trapezium. The trapezium is the first bone of the distal row; it is very irregular in shape. The inferior surface is saddle-shaped, and articulates with the base of the first metacarpal bone. The superior surface has a facet for the scaphoid. The in- ner (ulnar) surface has two facets ; the lower and smaller is for the base of the second metacarpal, the upper and larger for the trapezoid. The radial and dorsal surfaces are rough for ligaments. The palmar surface presents a Fig. 141.—The Left Cuneiform. For semilunar. For pisiform. For unciform. Fig. 142.—The Left Pisiform. For cuneiform prominent ridge, which has to its ulnar side a deep groove which transmits the tendon of the flexor carpi radialis. To the ridge of the trapezium the anterior annular ligament is attached. The palmar surface affords attachment to the ab- ductor, flexor ossis, flexor brevis, and sometimes a portion of the extensor ossis metacarpi pollicis. Articulations.—With the scaphoid, trapezoid, and the first and second meta- carpal bones. THE CARPUS. 151 The Trapezoid. The trapezoid is also very irregular in shape, and much smaller than the tra- pezium. It has a broad dorsal surface ; the narrow palmar surface gives origin to a few fibres of the inner head of the flexor brevis pollicis. The portion of bone between these surfaces is constricted and mapped out into articular facets; of these, the inferior is most conspicuous ; it is saddle-shaped for the base of the second metacarpal. The radial surface has a facet for the trapezium ; the ulnar surface is articular for the magnum ; and the superior surface has a facet for the scaphoid. Articulations.—With the trapezium, magnum, scaphoid, second metacarpal. The Magnum. The magnum is the largest carpal bone, and occupies the centre of the wrist. The superior surface is globular, and sometimes called the head. It is re- Fig. 143.—The Left Trapezium The ridge. For scaphoid. For trapezoid. For second metacarpal. Groove for flexor carpi radialis. For first metacarpal. Fig. 144.—The Left Trapezoid, Palmar surface, For trapezium For second metacarpal Fig. 145.—The Left Magnum. For semilunar, For scaphoid. For semilunar. For unciform. The Radial or Outer Side. The Ulnar or Inner Side. For trapezoid, For second metacarpal, For third metacarpal. For fourth metacarpal. ceived into the cup formed by the semilunar and scaphoid. The articular surface of the head extends some distance on to the dorsal aspect of the bone. The infe- rior surface has three facets. The middle is the largest for the base of the third metacarpal. The ulnar facet is for the fourth, and the small radial facet is for the second metacarpal. The outer (radial) surface articulates with the trapezoid, and presents above this small facet a deep groove for an interosseous ligament. The inner (ulnar) surface of the bone has a long articular surface for the unciform (sometimes the lower part of this surface forms a detached facet), but is rough near its anterior part for ligaments. The palmar surface is convex and rough, and affords origin to the inner head of the flexor brevis pollicis. The rough dorsal surface is broad, and has a deep concavity, which serves to make the head of the bone more prominent, and gives rise to the appearance of a neck. Articulations.—Trapezoid, unciform, semilunar, scaphoid, and second, third, and fourth metacarpals. THE SKELETON. The Unciform. The unciform is the most readily recognized of all the carpals, as its palmar surface presents a prominent hook-like process ; this, the unciform process, has its concavity directed toward the radial side, and forms part of the inner boundary of the passage for the flexor tendons ; to the apex of the process the anterior annular ligament gains an attachment. It also affords origin to .the flexor brevis minimi and opponens minimi digiti muscles. The dorsal surface is rough for ligaments. The inferior surface has two facets for the bases of fourth and fifth metacarpals. The superior surface forms the apex of a wedge, and is smooth and rounded for articulating with a narrow facet on the ulnar side of the semi- lunar. The ulnar surface is mainly articular in the cuneiform, whilst the radial surface is faceted for the magnum. Articulations.—With the cuneiform, semilunar, magnum, and the fourth and fifth metacarpals. The central is an occasional element of the carpus. It is situated on the dorsal aspect of the carpus, between the scaphoid, magnum, and trapezoid. This bone is a normal element of the carpus in many mammals, even in the orang and gibbon. It is represented in the carpus of the human embryo, but in most indi- viduals it undergoes suppression or coalesces with the scaphoid. Blood-supply.—The arterial twigs to the carpal bones are derived from the anterior and posterior carpal branches of the radial and ulnar arteries. A large branch from the anterior interosseous is also distributed to the carpus, and twigs are furnished to it from the posterior interosseous artery. Unciform process Fig. 146.—The Left Unciform Fifth metacarpal. Fourth metacarpal. Magnum. Ossification.—At birth the carpal elements are cartilaginous, and the nucleus for each bone appears in the following order: — Magnum, first year. Unciform, second year. Cuneiform, third year. Semilunar, fourth year. Trapezium, fifth year. Scaphoid, sixth year. Trapezoid, eighth year. Pisiform, twelfth year. THE METACARPUS. The metacarpus consists of five bones. Each metacarpal bone has a shaft, a rounded distal end termed the head, and a square-shaped proximal extremity named the base. The shaft is prismatic; two surfaces of the prism are lateral and the third dorsal. The lateral surfaces afford attachment to the interosseous muscles : on the palmar aspect of the shaft these surfaces approach each other, and for some distance are only separated by a prominent ridge. The dorsal surface is smooth and covered in the recent state by the tendons of the extensor muscles of the fingers. Near the base this surface is divided by a median ridge ; as this ridge passes to the distal end of the shaft, it divides and forms two ridges which terminate in a prominent tubercle on each side of the head of the bone. The smooth surface on each side of the median ridge on the dorsal aspect, near the base, is for a dorsal interosseous muscle. The base is quadrilateral; its palmar and dorsal surfaces are rough for ligaments; the upper end articulates with the carpus, and its lateral aspects have facets for adjacent metacarpals. The head THE METACARPUS. has a semilunar articular surface for the base of the first phalanx, and is more extensive on the palmar than the dorsal aspect. On its palmar surface the head is grooved for flexor tendons, each corner of the groove being surmounted by a tubercle. The sides of the head are compressed, and each side is occupied by a well-marked fossa. The several metacarpals present distinctive characters. The first is the most peculiar ; it is the shortest, and its shaft resembles that of a phalanx. It has a concave palmar surface, and the dorsal surface lacks the bifurcated ridge. The Fig. 147.—The First (Left) Metacarpal. Radial Side. Ulnar Side. For trapezium. Fig. 148.—The Second (Left) Metacarpal. Radial Side. Ulnar Side. For trapezoid. For trapezium For third metacarpal. For magnum. base has a saddle-shaped articular surface for the trapezium, and at its outer (radial) corner presents a tubercle for the insertion of the extensor ossis metacarpi pollicis. The head of the bone presents on its palmar aspect two shallow grooves for the sesamoids in the flexor brevis pollicis. Muscles:— Extensor ossis metacarpi pollicis. Opponens pollicis. First dorsal interosseous. Interosseus primus volaris. THE SKELETON. Blood-supply.—The nutrient vessel is derived from the princeps pollicis artery : it enters on the ulnar side and is directed toward the head of the bone. The Second Metacarpal is the longest, and is easily recognized by its large, irregular base. The dorsal surface affords attachment to the tendon of the extensor carpi radialis longior and a part of the extensor carpi radialis brevior; to the palmar surface the tendon of the flexor carpi radialis is inserted. The remaining surfaces present four articular facets. The end of the bone is occupied by a deep groove for the trapezoid ; the ulnar ridge of this concavity is smooth for the magnum, and is directly continuous with a long, narrow facet for the third metacarpal. The radial surface of the base has a small, somewhat quadrangular facet for the tra- pezium. Muscles:— Flexor carpi radialis. Extensor carpi radialis longior. Extensor carpi radialis brevior. First and second dorsal interosseous. First palmar interosseous. Flexor brevis pollicis. Fig. 149.—The Third (Left) Metacarpal Radial Side, Ulnar Side. For magnum. For fourth metacarpal. For second metacarpal Styloid process. Blood-supply.—The nutrient artery is derived from the first palmar inter- osseous. It enters on the ulnar side, and is directed toward the proximal end or base of the bone. The Third Metacarpal is easily recognized by the prominent styloid pro- cess which projects from the radial corner of the dorsal surface of the base. A little below this process the extensor carpi radialis brevior finds insertion. The carpal surface of the base is nearly plane for the magnum. The radial surface has a long, narrow facet for the second metacarpal. On the ulnar side, two rounded facets are usually seen for the fourth metacarpal. Not infrequently one of them is absent. Muscles : — Extensor carpi radialis brevior. Adductor pollicis. Second and third dorsal interosseous. Blood-supply.—The nutrient artery is derived from the interosseous: it enters, as a rule, on the radial side, and is directed toward the base. The Fourth Metacarpal has a very small base. By its carpal surface it ar- THE METACARPUS. 155 ticulates with the unciform. The radial surface has two rounded facets for the third metacarpal; there is a small facet for the magnum at the posterior radial corner. The ulnar side has a narrow articular surface for the fifth metacarpal. Muscles :— The third dorsal interosseous. The fourth dorsal interosseous. The third palmar interosseous. Blood-supply.—The nutrient artery is furnished by the second interosseous; it enters on the radial side of the shaft, and is directed toward the proximal end. Fig. 150.—The Fourth (Left) Metacarpal For un- ciform. Radial Side. Ulnar Side. For magnum. For third metacarpal. For magnum. For fifth metacarpal. Fig. 15i.—The Fifth (Left) Metacarpal. Radial Side. Ulnar Side. For the unciform. Fourth metacarpal The Fifth Metacarpal is readily distinguished. The carpal facet is convex for the unciform. The ulnar aspect of the base forms a rounded tubercle for the extensor carpi ulnaris, whilst the radial side has a semilunar facet for the fourth metacarpal bone. The radial border of the dorsal surface of the shaft often has a prominent lip for the fourth interosseous muscle. Muscles :— Flexor carpi ulnaris. Extensor carpi ulnaris. Fourth dorsal interosseous. Third palmar interosseous. Opponens minimi digiti. THE SKELETON. Blood-supply.—The nutrient artery is derived from the third interosseous. It enters the shaft on the radial side, and is directed toward the proximal end. Ossification.—Each metacarpal is ossified from two centres. The nucleus for the shaft appears about the eighth week of embryonic life. At birth the shafts are well ossified, but each end is capped by a piece of cartilage. In the case of the first metacarpal, a centre for the epiphysis appears at the proximal end in the course of the third year. The bases of the remaining metacarpals are ossified from the shaft, but an epiphysis forms for the head of each bone in the third year. The bones are usually consolidated by the twentieth year. In many cases the first metacarpal has two epiphyses, one at the base and an additional one at the head; the latter is never so large as in the other metacarpal bones. Fig. 152.—The Phalanges of the Third Digit of the Hand. (Dorsal vinv.) Thirdjterminal or ungual phalanx. Second phalanx First phalanx The third metacarpal occasionally has an additional nucleus for the prominent styloid process which constitutes such a distinguishing feature of this bone. The styloid process sometimes remains distinct, and is then known as the sty- loid bone. Occasionally it fuses with the trapezoid or magnum. THE PHALANGES. The phalanges are the bones of the fingers. They number in all fourteen : the thumb has two, the other fingers three each. Each phalanx has a shaft, which is broad and slightly concave on the palmar, rounded and smooth on the dorsal aspect. The sides of the palmar surface are raised where they give attachment to the sheaths of the flexor tendons. The THE HIP-BONE. bases of the phalanges of the first row present glenoid fossae which play upon the convex heads of the metacarpals. Their distal ends are surmounted by minia- ture condyles. The phalanges of the second row are shorter than those of the first row. Their bases present two shallow pits, separated by a ridge. The terminal, third, or ungual phalanges have an expanded shaft for the support of the nail. The bases are identical in shape with those of the second row. Ossification.—Each phalanx ossifies from two centres: one for the shaft, which is deposited between the eighth and tenth week; and a nucleus for the Fig. 153.—Ossification of the Metacarpals and Phalanges, Appears in the third year. Consolidates in the twentieth year. Appear in the third, and consolidate in the twentieth year. Appear between the third and fifth year. Consolidate in the eighteenth year. Epiphysis for base, Metacarpal of Thumb. Epiphysis for head. epiphysis at the proximal end, which appears between the third and fifth years. Consolidation begins at the seventeenth, and is complete by the eighteenth year. The ossification of the terminal phalanx is peculiar. Like the other phalanges it has a nucleus for the shaft and a secondary nucleus for the epiphysis ; but the centre for the shaft appears at the tip of the phalanx; whereas in the other phalanges the earthy matter is deposited in the middle of the shaft. THE HIP-BONE. The hip-bone (innominate bone) is of irregular shape, resembling somewhat the blade of a screw propeller. It consists of three parts, which, though separate in early life, are, in the adult, firmly ankylosed. The three parts meet together at the cotyloid cavity or acetabulum. They are named ilium, ischium, and pubes. The ilium is the upper expanded portion ; it articulates with the sacrum, and forms the upper two-fifths of the acetabulum. The ischium is the lowest part of the bone; it forms the posterior and inferior two-fifths of the acetabulum, and assists the pubes to form the obturator foramen. The pubes forms the anterior 158 THE SKELETON. one-fifth of the acetabulum, completes the obturator foramen, and stretches toward the median line to meet with the opposite pubes to form a symphysis. Each part requires separate consideration. The ilium has two surfaces; the external surface, or dorsum, is convex in its general contour. It is limited superiorly by the semicircular crest, and is crossed by the three gluteal ridges. The superior gluteal ridge commences at the crest about 5 cm. (2") from its posterior termination, and passes downward to the middle of the greater sciatic (ilio-sciatic) notch. The space included between this ridge and the crest gives origin to the gluteus maxitnus, and at its lower part to a few fibres of the pyriformis. The middle gluteal ridge extends from the crest 2.5 cm. (1") behind its anterior extremity, and passes across the dorsum to terminate near the posterior end of the superior gluteal ridge, at the greater sciatic notch. The surface of bone between this ridge and the crest is for the origin of the gluteus medius. The inferior gluteal ridge begins in the notch separating the anterior iliac spines, and terminates posteriorly in the middle of the greater sciatic notch. The space between the middle and inferior ridges gives origin to the gluteus minimus, except a small area adjacent to the anterior superior iliac spine for the tensor vagina femoris. The bone between the inferior gluteal ridge and the margin of the acetabulum affords attachment to the capsule of the hip-joint. Toward its anterior part there is a rough surface for the reflected tendon of the rectus. The internal surface of the ilium consists of an anterior concave portion, termed the iliac fossa; it lodges the iliacus muscle. The fossa is limited below by the ilio-pectineal line; this line receives, at its anterior part, the insertion of the psoas parvus. A small portion of the ilium extends below the ilio-pectineal line to meet the ischium. The surface posterior to the fossa is divided into an auricular surface for articulation with the lateral aspect of the upper portion of the sacrum, and a superior rough surface—the tuberosity—for the posterior sacro-iliac and ilio-lumbarligaments. The crest extends from the anterior supe- rior iliac to the posterior 3»pferior iliac spine. It is thickest at its extremities. The prominent edges, or lips, are for the attachment of muscles and fasciae. The outer lip affords attachment to the gluteal portion of the fascia lata. The external oblique is inserted into the anterior, and the latissimus dorsi arises from the posterior half of this lip of the crest. The anterior two-thirds of the inter- mediate space gives origin to the internal oblique. The inner lip, by its anterior three-fourths, gives attachment to the transversalis ; behind this is a small surface for the quadratus lumborum, and the remainder is occupied by the erector spina. The extreme inner margin of the lip serves for the attachment of the iliac fascia. The anterior border of the ilium extends from the anterior superior spine to the margin of the acetabulum. The anterior superior spine gives attachment to Poupart’s ligament and the sartorius which also arises from the upper half of the superior iliac notch. This notch is terminated inferiorly by the anterior inferior spine : it is smaller, less prominent than the superior, and gives origin to the straight head of the rectus femoris and the main limb of the ilio-femoral band of the capsule of the hip-joint. Beneath the inferior iliac spine is the in- ferior iliac notch ; it is broad, but shallow, and limited by an eminence, the ilio-pubal ridge, which indicates the line of ankylosis of the pubes and the ilium. A few fibres of the iliacus arise from this notch. The posterior border of the ilium presents above the posterior superior spine, which gives attachment to the greater sacro-sciatic ligament and the multi- fldus spina, and a portion of the oblique sacro-iliac ligament. Below this is a shallow notch terminating below in the posterior inferior spine, corresponding to the posterior border of the auricular surface. This spine receives a portion of the greater sacro-sciatic ligament. Below the spine the posterior border of the ilium forms the upper segment of the greater sciatic notch. The ischium consists of a thick solid body, a prominent tuberosity, and a ramus. The body is triangular; its outer surface forms the posterior and inferior sec- tion of the acetabulum. The inner surface forms part of the true pelvis, and THE HIP-BONE. 159 meets the ilium a little distance below the ilio-pectineal line. It also forms the floor, or non-articular portion, of the acetabulum, and meets the pubes anteriorly; the line of junction is frequently indicated in adult bones by a rough line extend- ing from the ilio-pubal ridge to the margin of the obturator foramen. The free border of this surface forms the posterior boundary of the obturator foramen. The inner surface of the ischium gives origin to the obturator mternus. The pos- Fig. 154.—The Left Hip-bone. {Internalsurface') Quadratus lumborum. Erector spinae. Transversalis and the iliac fascia. Tuberosity. Multifidus spinae. Anterior su- perior spine of ilium. , Auricular surface. Posterior in- ferior spine of ilium. Anterior infe- rior spine of ilium. Psoas minor. Obturator internus. Ilio-pubalridge. Coccygeus. Levator ani. Groove for obtu- rator nerve and vessels. Groove for pudic ves- sels and nerve. Great sacro- sciatic lig- ament. Tuberosity of ischium. Transversus perinei. /thyroid /foramen Symphysial surface. Levator ani. Junction of pubes Crus penis and Compressor Sub-pubic and ischium. Erector penis. urethra. ligament. terior surface of the ischium lies between the posterior rim of the acetabulum and the greater sciatic notch. Inferiorly this surface is limited by the obturator groove, which receives the posterior fleshy border of the obturator externus when the thigh is flexed. The capsule of the hip-joint is attached to the outer part of the posterior surface. The pyriformis, the greater and lesser sciatic nerves, the sciatic artery, and the nerve to the quadratus femoris, cross it. The inner border 160 THE SKELETON. assists the ilium to complete the greater sciatic notch, which is terminated in- teriorly by the prominent ischiatic spine, which gives attachment to the lesser sacro-sciatic ligament, the levator ani, and coccygeus. From the base of the spine, posteriorly, the gemellus superior arises; and the internal pudic vessels and nerve, with the nerve to the obturator internus, cross it. The recess below the ischiatic spine is the lesser sciatic notch ; in the recent state it is covered with cartil- Fig. 155.—The Left Hip-bone. [Posterior view.) Posterior limit of external oblique. Insertion of external oblique. Internal oblique. Latissimus dorsi. Crest of ilium, Tensor vaginae femoris. Superior glu teal1 ridge.j Sartorius. Gluteus'* maximus. Posterior superior iliac spine. Rectus femoris Pyriformis. Posterior inferior iliac spine. Inferior iliac notch. Articular portion of the cotyloid cavity. Greater sciatic (ilio- sciatic) notch. Ischium Capsule. Spine of ischium. Synovial membrane. Gemellus superior. Pectineal ridge. Lesser sciatic notch. Gemellus inferior. Pectineus. - Rectus ab- dominis. - Pyramidalis. ' Adductor “ longus. Adductor brevis. COTYLOIT) NOTcJn Obturator notch. T H Y R O I ID FORAMEN Semimembranosus. Quadratus femoris. Descending ramus _ of pubes. Gracilis. — Semitendinosus and biceps. Adductor magnus. Ramus of ischium. Obturator externus. age, and presents two, three, or four grooves for the tendinous under surface of the obturator internus muscle. The tuberosity is that portion of the ischium which supports the body in the sitting posture. It has an inner and an outer lip, and an intermediate space which presents two rough surfaces; of these, the upper and outer is for the origin of the semi-membranosus, and the lower and inner surface for the conjoint origin of the biceps and semitendinosus. Above the surface for the semimembranosus, the tuber- THE HIP-BONE. 161 osity gives origin to the gemellus inferior. Its inner edge, or lip, is prominent, and gives attachment to the falciform edge of the greater sacro-sciatic ligament. The surface of the tuberosity above this lip is in relation with the internal pudic vessels and nerves. The outer lip is occupied by the quadratus femoris muscle, and the surface adjacent to this is occupied by the adductor magnus. The surfaces thin away to a sharp margin, which forms part of the boundary of the obturator foramen. The ramus of the ischium is a continuation of the tuberosity running upward to join the descending ramus of the pubes, to complete the obturator foramen. The outer surface of the ramus gives origin to the adductor magnus and the obtu- rator externus. To its inner surface the crus penis is attached ; it also gives origin to the transversus perinei, the erector penis, and the obturator internus. The pubes consists of a body and two rami. The body, quadrilateral in shape, is continuous with the ramus of the ischium by means of a flattened process termed the descending ramus. The outer surface of the body gives origin to the adductor longus. The adductor brevis, the gracilis, and the obturator externus Fig. 156.—An Immature Innominate Bone, Showing a Cotyeoid Bone. The cotyloid bone arise from the outer surface of the body and descending ramus. A small portion of the adductor magnus also arises from the descending ramus. The posterior sur- face of the body and that of the descending ramus is continuous with the corres- ponding surface of the ramus of the ischium, and affords attachment to the levator ani and obturator internus. The posterior surface of the descending ramus gives origin to the compressor urethra and a part of the erector penis, the crus penis, and the obturator internus. The inner border is rough and covered with fibro-cartil- age, which unites it with the opposite bone to form the pubic symphysis. The outer border forms part of the obturator foramen. The inner border of the descending ramus forms with the ramus of the ischium the pubic arch. The upper surface or crest of the pubes is limited externally by the pubic spine, which gives attachment to the outer (inferior) pillar of the external ab- dominal ring and Poupart’s ligament. The inner extremity of the crest is the angle of the pubes. Between it and the spine the following structures are at- tached : the linea alba, the rectus abdominis, the pyramidalis, and the conjoined tendon. The horizontal ramus extends from the body of the pubes to the ilium, forming by its outer extremity the anterior one-fifth of the articular surface of the 162 THE SKELETON. acetabulum. Its line of junction with the ilium forms the ilio-pubal ridge. Stretching from this ridge to the pubic spine there is a raised edge continuing the ilio-pectineal line. The surface of bone in front of the line is the pectineal surface ; it gives origin to the pectineus muscle, and is limited below by the obturator crest, which extends from the pubic spine to the cotyloid notch. The under surface of the horizontal ramus forms the upper boundary of the obturator foramen, and presents a deep groove for the passage of the obturator vessels and nerve. The acetabulum is a circular depression in which the head of the femur is lodged. It consists of an articular and a non-articular portion. The articular portion is circumferential and horseshoe-shaped ; the deficiency is in the lower segment. The pubes forms one-fifth of the acetabulum, and the ischium two- fifths; the rest is formed by the ilium. In rare instances the pubes maybe excluded by a fourth element, the cotyloid bone. The non-articular portion is formed mainly by the ischium, and is continuous below with the margin of the obturator foramen. The articular portion presents an outer rim to which the cotyloid ligament is attached, and an inner margin to which the synovial membrane is connected which excludes the ligamentum teres from the synovial cavity. The opposite angles of the horseshoe-shaped margin which limit the cotyloid notch are united by the transverse ligament, and through the cotyloid foramen thus formed a nerve and vessel enter the joint. The obturator (thyroid) foramen is situated between the ischium and pubes. Its margins are thin, and serve for the attachment of the obturator membrane. At the upper and posterior angle it is deeply grooved for the passage of the obturator vessels and nerve. Muscles attached to the hip-bone are:— Gluteus maximus. Gluteus medius. Gluteus minimus. Tensor vaginae femoris. Rectus femoris. Obturator externus. Obturator internus. Latissimus dorsi. Internal oblique. External oblique. Transversalis. Erector spinae. Multifidus spinae. Quadratus lumborum. Iliacus. Psoas parvus. Quadratus femoris. Accelerator urinae (occasionally). Sartorius. Pectineus. Pyramidalis. Pyriformis. Gemellus superior. Gemellus inferior. Gracilis. Adductor magnus. Adductor longus. Adductor brevis. Levator ani. Coccygeus. Transversus perinei. Erector penis. Compressor urethrae. Biceps femoris. Semitendinosus. Semimembranosus. The ligaments attached to the hip-bone are:— Greater sacro-sciatic. Lesser sacro-sciatic. Ilio-lumbar. Anterior sacro-iliac. Posterior sacro-iliac. Capsular and its accessories. Cotyloid. Transverse. Round (ligamentum teres). Anterior pubic. Posterior pubic. Superior pubic. Subpubic. Triangular. Poupart’s. Blood-supply.—The ilium receives on its anterior surface twigs from the ilio-lumbar, deep circumflex iliac, and obturator arteries. On the dorsum, arteries enter it from the gluteal and sciatic trunks. The ischium is supplied by the obturator, internal, and external circumflex. The pubes receives twigs from the obturator, internal, and external circumflex, deep epigastric, and the pubic branches of the common femoral artery. THE HIP-BONE. 163 Development.—The cartilaginous representative of the hip-bone consists at first of an ilio-ischiatic and a pubic segment. These quickly fuse and form a continuous plate (Rosenberg). Early in the third month a nucleus appears above the acetabulum for the ilium, and one appears a little later below the cavity for the ischium. In the fourth month a nucleus is seen in the pubic portion of the cartilage. At birth these three nuclei are of considerable size, but surrounded by relatively wide tracts of cartilage. In the sixth year the Y-shaped piece of Fig. 157.—The Pelvis of a Fcetus at Birth, to Show the Three Portions of the Innominate Bones. The nucleus for the ilium appears early in the third month. The nucleus for the pubes appears about the end of the fourth month. The nucleus for the ischium ap- pears in the third month. Appears at fifteen. Unites at twenty. Fig. 158.—Hip-bone, Showing Secondary Centres, Appears at fifteen. Unites at twenty. The lines of union are usually obliterated by the sixteenth year. Appears at sixteen. Fuses at twenty. Appears at fifteen, Fuses at twenty. cartilage in the acetabulum ossifies, and, uniting with the three surrounding elements, causes their consolidation, usually about the sixteenth year. When this nucleus is large, it may remain separate until after the twentieth year. This is the acetabular nucleus, and is regarded by some morphologists as the represen- tative of the cotyloid or acetabular bone constantly present in a few mammals, and is of sufficient size to exclude the pubes from the cotyloid cavity. During the eighth year the rami of the ischium and pubes coalesce. About the fifteenth year 164 THE SKELETON. two secondary nuclei appear in the iliac cartilage to form the crest and the anterior inferior spine. An accessory nucleus appears for the ischial tuberosity, and subsequently one for the pubic crest. These fuse with the main bone about the twentieth year. The fibrous tissue connected with the pubic spine represents the epipubic bone of marsupial mammals. THE PEL VIS. The pelvis is composed of four bones: the two hip bones, the sacrum, and coccyx. The hip bones form the lateral and anterior boundaries, meeting each other to form the pubic symphysis; posteriorly they are separated by the sacrum. The hollow of the pelvis is divided into the false and true pelvic cavity. The false pelvis is that part of the cavity which lies above the ilio-pectineal lines; this part is in relation with the hypogastric and inguinal regions. The true pelvis is situated below the ilio-pectineal lines. The upper circum- ference, called also the inlet of the pelvis, is bounded anteriorly by the spine and Fig. 159.—The Pelvis {Male.) crest of the pubes, posteriorly by the base of the sacrum, and laterally by the ilio- pectineal lines. The inlet in normal pelves is cordate, being obtusely pointed in front; posteriorly it is encroached upon by the promontory of the sacrum. It has three principal diameters: of these, the antero-posterior, called the conjugate diameter, is measured from the sacro-vertebral angle to the symphysis. The tranverse diameter represents the greatest width of the pelvic cavity. The oblique is measured from the sacro-iliac synchondrosis to the ilio-pubal ridge. The cavity of the true pelvis is bounded in front by the symphysis pubis, behind by the sacrum and coccyx, and laterally by a smooth wall of bone formed in part by the ilium, in part by the ischium ; it corresponds to the acetabulum. The cavity is shallow in front, where it is formed by the pubes, and is deepest posteriorly. The lower circumference, or outlet, of the pelvis is very irregular, and THE FEMUR. encroached upon by three bony processes: the posterior process is the coccyx, and the two lateral processes the ischial tuberosities. They separate three notches. The anterior is the pubic arch, and is bounded on each side by the conjoined rami of the pubes and ischium on each side. The two remaining gaps correspond to the greater and lesser sciatic notches ; they are bounded by the ischium an- teriorly, the sacrum and coccyx posteriorly, and the ilium above. These are converted into foramina by the greater and lesser sacro-sciatic ligaments. The position of the pelvis.—In the erect position of the skeleton, the plane of the pelvic inlet forms an angle with the horizontal, which varies in individuals from 50° 10 6o°. The base of the sacrum in an average pelvis lies nearly 10 cm. (4") above the upper margin of the symphysis pubis. The axis of the pelvis.—This is an imaginary line drawn at right angles to the planes of the brim, cavity, and outlet, through their centres. The average measurements of the diameters of the pelvis in the three planes are given below (after Lusk) :— Diameters. At the brim. At the outlet. Conjugate, \ . 4X inches, inches. Transverse, “ “ Oblique 5 “ “ Sex differences.—In the male the pelvis is deeper, the ridges for muscles more marked, and the bones thicker, than in the female. In the male, the obturator foramen is described as vertically ovate, the pubic symphysis is deep, and the pubic arch small. In the female, the bones are thinner, lighter, and the iliac alae more expanded than in the male. The symphysis is narrow, the pubic arch wider, and the ischial tuberosities more expanded than in the male. The obturator foramen is described as triangular. The pelvic cavity is larger in most of its measurements. The sacrum is wider, less curved as a rule, and has a less projecting promontory than in the male. THE FEMUR. This bone is the largest and longest in the skeleton. The upper extremity is surmounted by a hemispherical cartilage-covered articular portion called the head, which is directed upward and inward, to be received in the acetabulum of the hip-bone. A little below the centre of the head is a small rough depression to which the ligamentum teres is attached. The head is connected to the shaft by the neck, a stout rectangular process of bone which forms with the femoral shaft, in the adult, an angle of 125°. Its anterior surface is in the same plane with the front aspect of the shaft, but it is marked off from it by a ridge to which the capsule of the hip-joint is attached. This ridge commences at the greater trochanter in a small prominence, the superior cervical tubercle, and extends obliquely downward to the inferior cervical tubercle, and, winding to the back of the femur, becomes continuous with the inner lip of the linea aspera. The whole of this ridge is called the spiral line, but the part between the cervical tubercles is often called the anterior intertrochanteric line. The superior and inferior tubercles receive the limbs of the ilio-femoral or Y-shaped thickening in the capsule of the hip-joint. The posterior surface of the neck is smooth and concave, its inner half is enclosed in the capsule of the hip-joint. The superior surface is narrow, and pitted with nutrient foramina: it runs downward to the greater trochanter. The inferior surface, concave in outline, terminates at the lesser trochanter. The trochanters are prominences which afford attachment to muscles which rotate the thigh; they are two in number, the greater and the lesser. Fig. 160.—The Left Femur. [Anterior view.) Greater trochanter. Pyriformis. Superior cervical tubercle Obturator internus. Gluteus minimus. Capsule of the hip-joint attached to the anterior intertrochan teric line. Vastus externus Lesser trochanter Psoas. Adductor tubercle, Adductor magnus External lateral ligament. Popliteus. 166 Internal condyle. External condyle, Fig. 161.—The Left Femur. [Posterior view.) Obturator internus. Ligamentum teres. Gluteus medius. Tubercle of the quadratus femoris. Capsule. Posterior intertrochanteric line. Psoas. Vastus externus. Gluteal ridge. Gluteus maximus Lesser trochanter. Iliacus. Pectineus. Adductor brevis. Adductor magnus, Outer lip of the linea aspera Biceps. Intervening space of the linea aspera. Adductor longus. Vastus internus. Inner lip of the linea aspera. Nutrient foramina. Biceps. External condylar line. For femoral artery. Internal condylar line. Adductor magnus. Plantaris, Gastrocnemius, Adductor tubercle. Gastrocnemius. Anterior crucial ligament, Intercondyloid notch Internal lateral ligament. External condyle. Internal condyle. Posterior crucial ligament, 167 168 THE SKELETON. The greater trochanter is quadrilateral, and surmounts the junction of the neck with the shaft. Of its two surfaces, the external is the broader ; it is bisected diagonally by a ridge running from the posterior superior to the anterior inferior angle. The gluteus medius is inserted into this ridge ; a bursa occasionally inter- poses between the tendon and the bone. The inner surface presents a deep pit, the trochanteric fossa, which receives the tendon of the obturator externus. The upper border, called the tip, gives attachment from before backward to the tendons of the obturator internus with the gemelli, and the pyriformis. The anterior border receives the gluteus minimus. The posterior border is thick, rounded, and continuous with the posterior intertrochanteric line, which runs downward to terminate at the lesser trochanter, a conical prominence on the posterior aspect of the femur to which the psoas is inserted. Running downward from the lesser trochanter to meet the spiral line is a slender ridge, to which the iliacus is inserted. The surface of bone slightly posterior to this ridge is occupied by the pectineus. This part of the femur presents several converging ridges, which will be most conveniently considered with the linea aspera. The shaft of the femur is cylindrical in shape, and presents, in the middle third of its posterior aspect, a prominent vertical ridge of bone, the linea aspera, for the origin and insertion of muscles. In the middle of the shaft the linea aspera presents an inner lip, an outer lip, and an intervening space. Toward the upper third of the shaft these three parts diverge: the outer lip becomes continuous with the gluteal ridge, and ends at the base of the greater trochanter. When very prominent the gluteal ridge is termed the third trochanter. It affords attach- ment to the gluteus maximus. The inner lip curves inward below the lesser trochanter, and becomes the spiral line. The middle portion of the linea aspera bifurcates, the inner portion as it runs on to the lesser trochanter receives the iliacus; the outer passes upward to the centre of the posterior intertrochanteric line; it receives the quadratus femoris, and is called the linea quadrati. The upper limit of this line is often indicated by a rounded tubercle. Toward the lower third-of the shaft, the inner and outer lips of the linea aspera diverge to become continuous with the condylar ridges. Several muscles are connected with the linea aspera. The vastus internus arises from the whole length of the inner lip, and the vastus exte?mus from the outer lip. The adductor magnus is inserted into the upper half of the outer lip, and the lower half of the inner lip. The adductor longus and brevis are inserted into the intervening space; the adductor longus takes rather more than the middle third, and overlaps the lower part of the adductor brevis, which takes rather more than the upper third. The outer lip in its lower two-thirds gives origin to the shorter head of the biceps. The condylar lines are two in number; the outer is continuous with the outer lip of the linea aspera and terminates interiorly on the outer edge of the external condyle. From the upper half of this line a part of the short head of the biceps arises. Near its termination the line expands to give origin to the plantaris and the outer head of th e gastrocnemius. The inner condylar line is not so prominent as the outer; it is continuous with the inner lip of the linea aspera, and terminates at the adductor tubercle. The adductor magnus is inserted into the whole length of the line and to the tubercle. Near the middle of the line there is an interruption where the femoral artery passes through the opening in the tendon of the adductor magnus. The inner head of the gastrocnemius arises from the femur immediately above the internal condyle. The space enclosed between these diverging lines forms part of the anterior boundary of the popliteal space, and is in close relation with the popliteal vessels. The shaft of the femur is overlapped on the inner side by the vastus internus, and on the outer side by the vastus externus. The greater part of the anterior surface of the femoral shaft affords origin to the crureus. The lower extremity presents two cartilage-covered condyles, separated by a deep notch. The external condyle is more prominent anteriorly and wider than its fellow. The internal is more prominent posteriorly, and narrower; it is also lotiger, to compensate for the obliquity of the shaft. When the femur is properly articulated, the inferior surfaces of the condyles are nearly on the same THE FEMUR. 169 plane, and almost parallel to come into contact with the articular surfaces on the head of the tibia. Posteriorly the condyles are separated by a deep pit or notch; anteriorly they are united by an articular surface, over which the patella glides. The inner surface of the internal condyle has, near its posterior border, a rough surface for the internal lateral ligament of the knee-joint; above this is the adductor tubercle. The surface of this condyle, which bounds the intercondy- loid notch, affords attachment, near the anterior border, to the posterior crucial ligament. The surface of the external condyle which bounds the notch gives Fig. 162.—The Femur at Birth. Appears early in the ninth month of intra-uterine life. attachment, at its posterior part, to the anterior crucial ligament. The outer surface of the external condyle presents near the lower and posterior margin a deep groove, which receives the tendon of the popliteus muscle when the leg is flexed. The groove is surmounted by a tubercle for the external lateral ligament of the knee. The patellar facet is trochlear in shape; its outer portion is more extensive than the inner, corresponding ta the disposition of the articular facets on the posterior surface of the patella. 170 THE SKELETON. Muscles attached to the femur:— Pyriformis. Obturator internus and gemelli Obturator externus. Pectineus. Quadratus femoris. Gluteus maxim us. Gluteus medius. Gluteus minimus. Psoas. Iliacus. Adductor brevis. Vastus internus. Adductor magnus. Adductor longus. Vastus externus. Crureus and subcrureus. Biceps. Gastrocnemius. Plantaris. Popliteus. Fig. 163.—The Left Femur at the Twentieth Year. (.Posterior view.) Appears in the first, and fuses in the twentieth year. Appears in the fourth, and unites in the nineteenth year. Appears in the fourteenth, and unites in the eighteenth year. Appears early in the ninth month of intra-uterine life, and unites at the twenty-first year. Ligaments : — Capsular of hip-joint. Ligamentum teres. Internal lateral of knee-joint. External lateral of knee-joint, Anterior crucial. Posterior crucial. Posterior, or Winslow’s. Blood-supply.—The head and neck of the femur receive branches from the sciatic, obturator, and circumflex arteries. The trochanter receives twigs from the circumflex arteries. The nutrient vessel for the shaft is derived from the second perforating; it enters near the middle of the linea aspera, and is directed toward THE PATELLA. 171 the head of the bone. The condyles are nourished by articular branches from the popliteal and the anastomotic of the femoral. Ossification.—The shaft of the femur begins to ossify in the seventh week of intra-uterine life. Early in the ninth month a nucleus appears for the condyles. During the first year the nucleus for the head of the bone is visible, and one for the greater trochanter in the fourth year. The centre for the lesser trochanter is visible about the thirteenth or fourteenth year. The lesser trochanter joins the shaft at the eighteenth, the greater trochanter at the nineteenth, the head about the twentieth, and the condyles at the twenty-first year. The neck of the femur is an apophysis, or outgrowth from the shaft. The line of fusion of the condyloid epiphysis lies below the adductor tubercle, so that the tubercle with the spaces from which the gastrocnemius and plantaris arise, belong to the shaft, and not to the epiphysis. The morphological relation of the patellar facet to the articular portions of the condyles is worth notice. In a few mammals, such as the ox, this facet remains separated from the condyles by a furrow of rough bone. In the human femur it is faintly marked off by a shallow groove in the cartilage, best seen in a recently opened knee-joint. Some anatomists attribute these grooves in the cartilage to the pressure of the semilunar fibro-cartilages. The angle which the neck of the femur forms with the shaft measures at birth, on an average, 160°. In the adult it varies from no° to 140°; hence the angle decreases greatly during the period of growth. When once growth is completed, the angle, as a rule, remains fixed. (Humphry.) THE PATELLA. The patella is a sesamoid bone, somewhat triangular in shape, situated in front of the knee-joint. Its anterior surface is slightly convex, and pitted with small open- Fig. 164.—The Left Patella Anterior surface External articular facet, Posterior surface. Internal .articular facet. Lateral facet for internal condyle. For the .patellar ligament, ings, which transmit nutrient vessels to the interior of the bone. This surface is subcutaneous ; a bursa intervenes between it and the skin. The posterior surface is concave, and in great part cartilage-covered, forming a compound articular surface for gliding upon the femoral condyles. A slightly marked vertical ridge divides this surface into an outer larger portion for the external condyle, and an inner portion for the internal condyle. A slender articular facet close to the inner edge is sometimes marked off by a faint vertical ridge ; this facet comes in contact 172 THE SKELETON. with the internal condyle in extreme flexion of the leg. The lower part of the bone is produced to a blunt point, which is embedded in the patellar ligament, especially on the posterior aspect. The upper two-thirds of the circumference receives directly the fibres of the vastus interims and externus, the crureus and rectus feinoris muscles. Blood-supply.—The patella receives twigs from the superficial branch of the anastomotica, anterior tibial recurrent, and the inferior articular of the popliteal. Ossification.—The cartilage for the patella appears in the fourth month of intra-uterine life. The ossific nucleus is visible in the third year. THE TIBIA. The tibia is the larger bone of the leg ; it is situated on the inner side of, and nearly parallel with, the fibula. The upper extremity, or head, consists of two lateral eminences, or tuberosities. The superior surfaces of the tuberosities receive the condyles of the femur, the articular surfaces being separated by a non- articular ridge, to which ligaments are attached. The internal articular surface is oval in shape and concave for the internal condyle of the femur. The external articular surface is smaller, somewhat circular in shape, and presents an almost plane surface for the external condyle. The peripheral portion of each articular surface is overlaid by a fibro-cartilage of semilunar shape, connected with the margins of the tuberosities by bands of fibrous tissue termed coronary ligaments. Each semilunar fibro-cartilage is attached firmly to the rough tract separating the articular surfaces. This intermediate space is broad and depressed in front, where it affords attachment to the anterior limb of the internal and external semilunar cartilages and the anterior crucial ligament. Standing upward from the middle of this surface is the spine of the tibia. The posterior aspect of the base of the spine affords attachment to the posterior limb of the external and internal semi- lunar fibro-cartilages, and limits a deep notch inclined toward the inner tuberosity; this notch gives origin to the posterior crucial ligament. Anteriorly, the two tuberosities are confluent, and form a somewhat flattened surface of triangular out- line : its apex forms the tubercle of the tibia. The ligamentum patellae is inserted into the lower part of the tubercle; the upper part is smooth and separated from the ligament by a bursa. Laterally the inner tuberosity is less prominent, though more extensive than the outer; near the posterior part of its circumfer- ence there is a deep horizontal groove for the central portion of the semimem- branosus tendon. The margins of this groove and the surface of bone below give attachment to the internal lateral ligament of the knee. At a corresponding point of the outer tuberosity there is a rounded articular facet for the head of the fibula; the circumference of the facet is rough for ligaments. The shaft is prismatic, and very thick near the head; toward the lower third it is thinner and tapering, and gradually expands toward the lower end. It has three borders; the anterior is very prominent, and known as the crest of the tibia : commencing on the outer edge of the tubercle, it runs downward and curves inward, to terminate at the anterior margin of the malleolus. This border gives attachment to the deep fascia of the leg. The internal border starts from the back of the internal tuberosity, and ends at the posterior margin of the malleolus. The internal lateral ligament is attached to its upper 7.5 cm. (3"), and the middle third gives origin to the solens. The interosseous border extends from the fibular facet on the outer tuberosity to the lower end of the bone ; toward its termination the border bifurcates to enclose a triangular space for the attachment of the interosseous ligament between the tibia and fibula. The part above the bifurcation is connected with the interosseous membrane. These borders limit three surfaces. The internal surface is bounded by the TIBIA AND FIBULA. 17 3 Fig. 165.—The Left Tibia and Fibula. [Anterior view.) Spine of tibia. Internal fibro-cartilage. Capsule, Anterior crucial ligament Inner tuberosity, External fibro-cartilage. Capsule. Outer tuberosity. Biceps and the anterior tibio-fibular ligament. External lateral ligament, Internal lateral ligament Ligamentum patellae (Quadriceps extensor). Gracilis. Sartorius. Semi-tendinosus. Extensor longus digitorum External surface of tibia. Tibialis anticus. Peroneus longus.' Peroneus brevis. Anterior border or crest of the tibia. Extensor longus digitorum. Peroneal surface of fibula. Internal surface of tibia. Extensor surface of fibula. Extensor proprius hallucis. Interosseous membrane. Fibula. Peroneus tertius. Subcutaneous portion. Anterior tibio-fibular ligament. Internal lateral ligament Capsule. Internal malleolus External malleolus. External lateral ligament (Anterior fasciculus). 174 THE SKELETON. Fig. i66.—The Left Tibia and Fibula. (.Posterior view.) Popliteal notch. External fibro-cartilage. Capsule. Posterior crucial ligament. Styloid process. Posterior tibio-fibular . ligament. Internal fibro-cartilage. Capsule. Semi-membranosus. Popliteus. Soleus Oblique line, Soleus. Tibialis posticus, Posterior surface of tibia. Flexor longus digitorum, Flexor longus hallucis, Flexor surface of fibula, Nutrient foramen Tibia. Fibula, Peroneus brevis, Posterior tibio-fibular ligament. Groove for flexor longus hallucis. External lateral ligament (posterior fasciculus). External lateral ligament (middle fasciculus). Groove for tibialis posticus and Flexor longus digitorum. Internal lateral ligament. Capsule. TIBIA AND FIBULA. 175 internal border and the crest \ it is broad above, where it receives the insertion of the sartorius, gracilis, and semitendinosus; the rest of the surface is convex and subcutaneous. The external surface lies between the crest of the tibia and the interosseous border. The upper two-thirds presents a hollow for the origin of the tibialis anticus; the rest of the surface is overlaid by the extensor tendons and the anterior tibial vessels. The posterior surface is limited by the interosseous ridge and the internal border. The upper part presents a rough oblique ridge, Fig. 167.—The Tibia and Fibula at the Sixteenth Year Appears at birth ; unites at twenty-one; but is some- times delayed to twenty- five. Appears at the fifth year; unites at twenty-two. Appears at second year; unites at the eighteenth year. Appears at the second year; unites at twenty. extending from the fibular facet on the outer tuberosity to the internal border, a little above the middle of the bone. This oblique ridge gives origin to the solens and attachment to the popliteal fascia ; the surface above is for the insertion of the popliteus. An indefinite vertical ridge commences near the middle of the oblique line, and marks off a semilunar space, limited externally by the interosseous border. This is for the tibialis posticus ; it extends as low as the junction of the middle and lower thirds. The portion of bone outside this vertical line is for the flexor longus digitorum. The lower third of the posterior surface is covered by flexor tendons. 176 THE SKELETON. The inferior extremity is somewhat quadrilateral, and resembles the distal end of the radius. Its inferior surface is articular for the upper surface of the astragalus and is continuous with the external surface of the malleolus, which articulates with the facet on the inner side of the astragalus. The outer surface has a triangular rough area for the lower end of the shaft of the fibula, its margins being rough for ligaments. The anterior border is slightly convex, and by its margin gives attachment to the anterior ligament of the ankle. The posterior surface has two grooves: the one which encroaches on the malleolus is for the tendons of tibialis posticus and flexor longus digitorum, and an outer shallow groove for the tendon of flexor longus hallucis. The inner surface is prolonged down- ward to form the malleolus; from its tip and margins the internal lateral (deltoid) ligament of the ankle joint arises. The inner surface of the malleolus is convex and subcutaneous; the outer, as already stated, has a facet for the inner surface of the astragalus. The tibia affords attachment to the following muscles : — Semimembranosus. Sartorius. Gracilis. Semitendinosus. Quadriceps extensor. Popliteus. Tensor vaginae femoris (indirectly). Tibialis posticus. Tibialis anticus. Soleus. Peroneus longus. Flexor longus digitorum. Extensor longus digitorum. Biceps femoris. Ligaments :— Anterior crucial. Posterior crucial. Internal lateral of the knee. Internal semilunar cartilage. External semilunar cartilage. Anterior tibio-fibular (inferior). Posterior tibio-fibular (inferior). Anterior of ankle. Anterior annular (vertical). Coronary. Anterior tibio-fibular (superior). Posterior tibio-fibular (superior). Ilio-tibial band. Interosseous membrane. Anterior annular (oblique). Internal annular. Internal lateral of ankle (deltoid). Posterior (of ankle). Transverse. Blood- supply.—The tibia is a very vascular bone. The nutrient artery for the shaft is furnished by the posterior tibial; it enters the bone near the interosseous border at the junction of the upper and middle thirds, and is directed downward. The head of the bone receives numerous branches from the inferior articular arteries of the popliteal, and the recurrent branches of the anterior and posterior tibial arteries. The lower extremity receives twigs from the posterior and anterior tibial, the anterior peroneal, and internal malleolar arteries. Ossification.—The centre for the shaft of the tibia appears in the eighth week of intra-uterine life. Toward the end of the ninth month, a small earthy nucleus appears in the cartilaginous head of the tibia. The nucleus for the lower extremity appears in the second year, and unites with the shaft at eighteen. The epiphysis for the head of the bone is one of the last to unite with its shaft; this event usually occurs about the twenty-first year, but may be delayed until twenty-five. The tubercle of the tibia is usually ossified from the epiphysis; occasionally it has an independent nucleus. THE FIBULA. 177 THE FIBULA. This is a long and slender bone, lying to the outer side of, and nearly parallel with the tibia ; the middle of the shaft is somewhat posterior to that of the tibia. The upper extremity, or head, is of irregular form, and presents an oblique facet on its inner aspect for articulation with the outer tuberosity of the tibia; the adjacent surfaces afford attachment to the superior tibio-fibular ligaments. The outer border of the head is prolonged into the styloid process, and gives attachment to the external lateral ligament of the knee ; the base of the process receives the biceps tendon. Near this point a portion of the peroneus longus arises; and posteriorly the head of the bone gives origin to the upper fibres of the soleus. The lower extremity, or external malleolus, is a thick pyramidal process of bone. Its inner surface presents anteriorly a triangular facet for articulation with the fibular facet on the outer side of the body of the astragalus. Posterior to this facet is the malleolar fossa, for the reception of the posterior fasciculus of the external lateral ligament of the ankle when the foot is extended. This fasciculus of the ligament arises from the margin of the fossa. Above the facet, the bone is rough for the inferior tibio-fibular ligaments. The outer surface is subcutaneous. The anterior surface gives attachment to the anterior fasciculus of the external lateral ligament of the ankle. The posterior surface has a shallow groove for the passage of the tendons of the peroneus longus and brevis. The tip of the malleolus gives attachment to the middle fasciculus of the external lateral ligament of the ankle. In the adult the fibular malleolus projects lower, and is more prominent than the tibial malleolus. The shaft is very variable in contour, and it is extremely difficult to find two fibulae alike. It has a well-marked anterior border, which, beginning in front of the head of the bone, divides in the lower third of the shaft, to enclose a tri- angular subcutaneous surface continuous with the outer surface of the malleolus. This border gives attachment to the anterior tibial fascia. The shaft on the outer side of this border is usually deeply concave for a part of its extent, and gives origin to the peroneus longus and brevis, and maybe called the peroneal (or outer) surface. Commencing at the head of the bone, in common with the anterior margin, and then gently diverging from it, is the ridge to which the inter- osseous ligament is attached. In the middle of the shaft the interosseous ridge is usually well-marked, and separated by 5 mm. from the anterior border. From the very narrow surface limited by these ridges, the extensor longus digitorum,pero- neus tertius and extensor longus hallucis arise. This is the extensor (or anterior) surface. The remainder of the shaft is the flexor (or posterior) surface, and possesses three subdivisions. One in the middle of its posterior aspect (in the midst of which is the orifice for the nutrient artery) gives origin to the flexor longus hallucis. This is limited above by the oblique line for the fibular origin of the soleus. Between these subdivisions and the interosseous ridge is the surface for the fibular origin of the tibialis posticus. The muscles arising from the fibula are :— Soleus. Tibialis posticus. Peroneus longus. Peroneus brevis. Peroneus tertius. Flexor longus hallucis. Extensor longus digitorum. Extensor proprius hallucis. The fibula affords insertion to the biceps. The following ligaments are connected with it:— External lateral of the knee. Anterior tibio-fibular. Posterior tibio-fibular. Interosseous membrane. External lateral ligament of knee. Transverse. Anterior tibio-fibular (inferior). Posterior tibio-fibular. External annular. Anterior annular (vertical). 178 THE SKELETON. Blood-supply.—The fibula receives the nutrient artery of its shaft from the peroneal branch of the posterior tibial. The head is nourished by branches from the inferior external articular branch of the popliteal artery, and the malleolus is supplied mainly by the peroneal, anterior peroneal, and external malleolar arteries. Development.—The shaft of the fibula commences to ossify in the eighth week of intra-uterine life. A nucleus appears for the lower in the second year, and one in the fifth year for the upper extremity. The lower extremity fuses with the shaft about twenty, but the upper one remains separate until the twenty-second year. The human fibula differs from all others in the excessive length of its malleolus ; in no other vertebrate does this process descend below the level of the tibial malleolus. In the majority of mammals the tibial descends to a lower level than the fibular malleolus. In the human embryo of the fourth month, the outer (fibu- lar) is very much smaller than the inner (tibial) malleolus. At the seventh month they are equal in length ; at birth, the fibular malleolus is the longer; and by the second year it assumes its adult proportion. (Gegenbaur.) The fibular is a vestigial bone in man, and survives mainly on account of the excessive development of its malleolus. This accounts for the fact that the lower epiphysis, though appearing first, unites with the shaft before the upper epiphysis. In birds, the head of the bone is large, and enters into the formation of the knee-joint, whilst the lower end atrophies. THE FOOT. The bones comprised in the skeleton of the foot are arranged in three groups:— tarsus, metatarsus, and phalanges. The tarsus consists of seven bones: The astragalus, os calcis or calcaneum, scaphoid, cuboid, and three cuneiform bones. THE ASTRAGALUS. This bone may, for descriptive purposes, be divided into a body, neck, and head. The body is quadrilateral. Its upper aspect resembles a segment of the wheel of a pulley ; hence it is called the trochlear surface. It is broader in front than behind, and articulates with the lower end of the tibia. The inferior surface is occupied by an elongated concave facet for articula- tion with the calcaneum. The internal surface presents a pyriform facet, broad in front, and con- tinuous with the trochlea : it articulates with the tibial malleolus. Below this facet, the inner surface is rough for the attachment of the deep fibres of the del- toid ligament. The external surface is almost entirely occupied by a triangular concave facet, broad above where it is continuous with the trochlea, for articulation with the fibular malleolus. The posterior surface is little more than a ridge of bone traversed obliquely by a deep groove, which receives the tendon of the flexor tongus hallucis muscle. Externally, this groove is limited by a prominent tubercle, which affords attachment to the posterior fasciculus of the external lateral liga- ment of the ankle. The neck is the constricted portion of the bone, and is continuous posteriorly with the body of the astragalus. Superiorly, the neck is rough, and has numerous foramina for blood-vessels. Inferiorly, it presents a deep groove, directed from behind forward and outward. When the astragalus is articulated with the calca- THE ASTRAGALUS. 179 neum, this furrow is converted into a canal in which is lodged the calcaneo- astragaloid (interosseous) ligament. The inner edge of this furrow is limited by Tendo-Achillis. Fig. 168.—The Left Foot. (.Dorsal surface.) Extensor brevis digi- torum. Peroneus brevis, Peroneus tertius. Metatarsus. First phalanx. Extensor brevis digijl torum. Second phalanx Third phalanx. Extensor longus hallu- cis. Extensor longus digitorum. an articular facet, which runs forward to become continuous with the facet on the head of the bone, and, like the articular surface of the sustentaculum tali of the calcaneum on which it glides, is sometimes divided. 180 THE SKELETON. The head of the astragalus is furnished anteriorly with an ovoid facet, which is received by the posterior surface of the scaphoid. On the inner and lower Fig. 169.—The Left P'oot. [Plantar surface.) Posterior surface of the cal caneum. Abductor minimi digiti. Abductor ossis metatarsi quinti. Abductor hallucis Flexor brevis digitorum. Accessorius (outer head) Accessorius (inner head). Tibialis posticus. Abductor ossis metatarsi quinti. Flexor brevis hallucis. Flexor brevis minimi digiti. Adductor hallucis. Third plantar inter- osseous. Second plantar inter- osseous. First plantar inter- osseous. Flexor brevis minimi digiti. Adductor brevis minimi digiti. Third plantar inter- ! osseous. Second plantar interosseous. ' i First plantar inter- 1 osseous. Tibialis anticus. Peroneus lor.gus. Abductor hallucis. Flexor brevis hallu- cis (inner portion). Flexor brevis hallu- cis (outer portion). Adductor hallucis. Transverse pedis. Flexor brevis digi- torum. Flexor longus digi torum. Flexorlongus hallucis. part, at the spot where the sustentacular facet becomes confluent with that on the head, there is a smaller facet separated by a ridge : this'plays upon the ealcaneo- scaphoid or spring ligament. THE ASTRAGALUS. 181 The os trigonum.—Occasionally the small portion of the astragalus posterior to the trochlear surface containing the groove which lodges the flexor longus hallucis tendon is separate from the rest of the astragalus, and is known as the os trigonum, or secondary astragalus (Fig. 171). Articulations.—The astragalus articulates with four bones, the tibia, fibula, scaphoid, and calcaneum ; and presents seven articular facets ; and when the facet for the sustentaculum tali is divided, as is so often the case, the articular surfaces Fig. 170.—The Left Astragalus. {Plantar view.') Groove for the flexor longus hallucis. For calcaneum Body.- Neck. - For the sustentaculum tali. For the calcaneo-astragaloid (or the spring) ligament. Head. - For scaphoid. Fig. i7i.—An Astragalus with the Os Trigonum, Os Trigonum. are increased to eight. Sometimes it presents a facet on the outer margin of its head for the cuboid, thus increasing the articular surfaces to nine. Ligaments :— Internal lateral ligament (deltoid). External lateral ligament. Astragalo-scaphoid. Calcaneo-astragaloid (interosseous). External calcaneo-astragaloid. Posterior calcaneo-astragaloid. Blood-supply.—The astragalus is supplied by the dorsalis pedis artery and its tarsal branch. 182 TILE SKELETON. Ossification.—The astragalus is ossified from one, occasionally from two, nuclei. The principal centre for this bone appears in the middle of the cartila- ginous astragalus at the seventh month of embryonic life. The additional centre is deposited in the posterior portion of the bone, and forms that part of the astragalus which, when it remains separate from the rest of the bone, is known as the os trigonum. At birth, the astragalus presents some important peculiarities in the disposition of the articular facet on the tibial side of the body, and in the obliquity of its neck. If, in the adult astragalus, a line be drawn through the middle of the trochlear surface parallel with its inner border, and a second line be drawn along the outer side of the neck of the bone so as to intersect the first, the angle formed by these two lines will express the obliquity of the neck of the bone. This in the adult varies greatly, but the average may be taken as io°. In the foetus at birth the angle averages 350, while in a young orang it measures 450. In the normal adult astragalus the articular surface on the tibial side is limited to the body of the bone. In the foetal astragalus it extends for some distance on to the neck, and sometimes reaches almost as far forward as the scaphoid facet on the head of the bone. This disposition of the inner malleolar facet is a charac- teristic feature of the astragalus in the chimpanzee and the orang. It is related to the inverted position of the foot which is found in the human embryo to near the period of birth, and is of interest to the surgeon in connection with some varieties of club-foot. (Shattock and Parker.) THE CALCANEUM. The calcaneum, or os calcis, is the largest tarsal bone. It is cuboidal in shape, and presents, for examination, six surfaces. The superior surface has in its middle a large, oval, convex, articular facet for the under aspect of the body of the astragalus ; behind the facet, the bone is rough and convex laterally. In front of the facet the bone presents a deep depres- sion, the floor of which is rough for the attachment of ligaments, especially the calcaneo-astragaloid, and the origin of the extensor brevis digitorum muscle; when the calcaneum and astragalus are articulated, this portion of the bone forms a floor to a cavity sometimes called the sinus pedis. Internally, this upper surface of the bone presents a well-marked lip, the sustentaculum tali, furnished with an elongated concave facet, occasionally divided into two, for articulation with the neck of the astragalus. The inferior surface is narrow and rough; it ends posteriorly in two tuber- cles : the inner is the larger and broader, the outer is narrower but prominent. The inner tubercle affords origin to the abductor hallucis, the flexor brevis digi- torum, and the abductor minimi digiti; the last muscle also arises from the inner tubercle, and the ridge of bone connecting the tubercles. The outer tubercle affords attachment to the abductor ossis metatarsi quinti. The rough surface in front of the tubercles gives attachment to the long plantar ligament (calcaneo- cuboid) and the outer head of the flexor accessorius. Near its anterior end this surface forms a rounded eminence, the anterior tubercle, from which (and the shallow groove in front) the short plantar (calcaneo-cuboid) ligament arises. The external surface is rough and slightly convex. Near the middle of this surface there is a small tubercle for the middle fasciculus of the external lateral ligament of the ankle joint. Anteriorly, we notice the two shallow peroneal grooves, separated by a tubercle, which is sometimes very prominent. The upper groove is for the tendon of the peroneus brevis, and the lower lodges the tendon of the peroneus longus. The inner surface is deeply concave, the hollow being increased by the over- hanging sustentaculum tali in front and above, and the prominent inner tuber- cle posteriorly. The under aspect of the sustentaculum is deeply grooved for the tendon of the flexor longus hallucis, whilst the hollow below receives the plantar vessels and nerves. Its lower border serves for the attachment of the inner head THE CALCANEUM. 183 of the flexor accessorius. The margin of the sustentaculum has attached to it a part of the deltoid ligament. The anterior surface is a concave articular facet for the posterior surface of the cuboid. Its outer and superior angle is somewhat prominent. The posterior surface is roughly rounded, and at the lower part serves for Fig. 172.—The Left Calcaneum. (Dorsal view.) Inner tubercle For astragalus, Interosseous groove. Peroneal tubercle. Facet for astragalus on the sustentaculum tali. the attachment of the tetido-Achillis. At its upper part it is smooth, and is in re- lation with a bursa. Articulations.—The calcaneum articulates with the cuboid, the astragalus, and with the os trigonum when it exists as a separate element. Fig. 173.—The Calcaneum at the Fifteenth Year, Showing the Epiphysis, Appears at the tenth, and unites at the sixteenth year. Muscles attached to the calcaneum Extensor brevis digitorum. Abductor hallucis. Flexor brevis digitorum. Abductor minimi digiti. Abductor ossis metatarsi quinti. Accessorius. Tendo-Achillis. Plantaris. And a slip from the tibialis posticus. 184 THE SKELETON. Ligaments :— Internal lateral of ankle. External lateral of ankle. Superior calcaneo-cuboid ligaments. Inferior calcaneo-cuboid ligaments. Internal annular. External annular. Anterior annular. Calcaneo-astragaloid (interosseous). External calcaneo-astragaloid. Posterior calcaneo-astragaloid. Superior calcaneo-scaphoid. Inferior calcaneo-scaphoid. Blood-supply.—The calcaneum is a vascular bone, and derives its blood from the posterior tibial, and the internal and external malleolar arteries. Ossification.—The primary nucleus for this bone is deposited in the sixth month of embryonic life. In the tenth year a nucleus appears for the epiphysis at the heel, and unites with the body of the bone at the sixteenth year. The inner and outer tubercles are formed by the epiphysis. This bone is situated on the outer side of the tarsus; its posterior surface is reniform in shape and articular for the anterior face of the calcaneum. The anterior surface is smaller, and divided by a low vertical ridge ; the inner facet is for the base of the fourth, the outer facet receives the base of the fifth meta- tarsal bone. The upper (dorsal) surface is rough and non-articular. The inferior (plantar) surface is divided by a prominent ridge, which limits a deep THE CUBOID. Fig. 174.—The Left Cuboid. (Inner view.) For external cuneiform For fourth metatarsal. For calcaneum Groove for tendon of the peron eus longus. furrow directed from without forward and inward. This, the peroneal groove, lodges the tendon of the peroneus longus. The corner of the ridge on the narrow outer (fibular) border of the bone is usually faceted for a sesamoid bone frequently found in the tendon of the peroneus longus. The margin of the ridge and the surface of bone behind it afford at- tachment to the long and short plantar (calcaneo-cuboid) ligaments. The flexor brevis hallucis muscle has a small attachment to this part of the cuboid. Fig. 175.—The Left Cuboid. {Inner view.) For external cuneiform. For calcaneum -For fourth metatarsal. For scaphoid (occasional) Groove for tendon of the peroneus longus. The internal surface presents near its middle and upper part an oval facet for articulation with the external cuneiform bone; behind this, a second facet for the scaphoid is frequently seen. Occasionally the two facets are confluent and form an elliptical surface. The remainder of the internal surface is rough, and has strong interosseous ligaments attached to it. Jutting from the inferior internal angle of the posterior surface is a process of THE SCAPHOID. 185 bone (calcanean process of cuboid), which projects beneath the sustentaculum •tali. This process occasionally terminates in a rounded facet, which plays on the head of the. astragalus external to the facet for the spring ligament. Articulations.—The cuboid articulates with the calcaneum ; the fourth and fifth metatarsal bones, frequently with the scaphoid, and occasionally with the astragalus. Muscles attached to the cuboid :— Tibialis posticus. Flexor brevis hallucis. Ligaments :— Superior calcaneo-cuboid. Interosseous and the cubo-scaphoid ligaments. Inferior calcaneo-cuboid. Ossification.—The cuboid is ossified from a single centre which appears a few days after birth. Occasionally the nucleus is visible as a minute earthy spot in the middle of the cartilage at birth. The scaphoid (navicular) bone receives in the hollow of its posterior sur- face the head of the astragalus. Anteriorly it is convex, and divided by two vertical ridges into three facets, for the internal, middle, and external cuneiform THE SCAPHOID. Fig. 176.—The Left Scaphoid. (Anterior view.) For middle cuneiform. Outer Border. For internal cuneiform Inner Border. T uberosity For external cuneiform. Fig. 177.—The Left Scaphoid, Showing a Facet for the Cuboid. ■ For middle cuneiform. - For external cuneiform. - For cuboid. For internal cuneiform Tuberosity. bones. Occasionally a fourth facet, extremely variable in size, is seen at the outer inferior angle for the cuboid. The upper (dorsal) surface is rough and broad ; the inferior (plantar) sur- face is nothing more than a ridge. The outer surface is rough for ligaments ; whilst the inner forms a large and prominent eminence, the scaphoid tuberos- ity, which affords an important attachment for the tibialis posticus tendon. Articulations.—With the head of the astragalus, with the three cuneiform bones, and frequently with the cuboid. Muscle attached to the scaphoid.—The tibialis posticus. Ligaments: — Dorsal, plantar, and interosseous cubo-scaphoid, Dorsal and plantar scapho-cuneiform. External and inferior calcaneo-scaphoid. Astragalo-scaphoid. 186 THE SKELETON. Ossification.—The nucleus for the scaphoid appears in the course of the fourth year. The tubercle of the scaphoid, into which the tibialis posticus acquires its main insertion, occasionally develops separately, and sometimes remains distinct from the rest of the bone. THE CUNEIFORM BONES. The cuneiform bones, three in number, are named from within outward— internal, middle, and external. They are wedge-shaped. The INTERNAL CUNEIFORM is distinguished by its large size, and from the fact that, when articulated, the base of the wedge is directed down- ward, and the sharp border upward. The posterior surface is concave and pyriform for articulating with the inner facet of the scaphoid. The anterior surface is a reniform articular facet for the base of the first meta- tarsal. The internal surface is rough, and presents an oblique groove for the Fig. 178.—The Left Internal Cuneiform. {Internal surface.) For first metatarsal Facet for the tendon of the tibialis anticus. Fig. 179-—I he Left Internal Cuneiform. [External surface^ For second metatarsal. For middle cuneiform. For scaphoid. tendon of the tibialis anticus: this groove is limited inferiorly by an oval facet into which a portion of the tendon is inserted. The external surface is concave and rough, except along the posterior and superior borders. Near the anterior extremity of the superior border there exists a distinct circular facet for the inner side of the base of the second metatarsal. In front of the facet a few fibres of the first dorsal interosseous muscle arise. The remaining sinuous articular facet is for the inner surface of the middle cuneiform. Articulations.—With the scaphoid, middle cuneiform, and the first and second metatarsals. Muscles.—Tibialis anticus and posticus, the peroneus longus, and first dorsal interosseous. Ossification.—A single nucleus, which appears in the course of the third year. 1 he MIDDLE CUNEIFORM, the smallest of the three, has its base directed upward and the sharp border downward. The posterior concave THE CUNEfFORM BONES. 187 surface is articular for the middle facet of the scaphoid. The anterior, somewhat narrower than the posterior surface, articulates with the base of the second meta- tarsal. The internal surface has a facet extending along its upper and posterior borders for the internal cuneiform. The external surface has a facet along the posterior border, and occasionally one at the anterior inferior angle for the external cuneiform. Articulations.—With the internal and external cuneiform bones, the scaphoid, and the second metatarsal. Ossification.—A single nucleus appears in the fourth year. Fig. 180.—The Left Middle Cuneiform. [Internal surface.) For internal cuneiform For second metatarsal. Fig. 181.—The Left Middle Cuneiform. [External surface.) For external cuneiform. For scaphoid. Occasional facet for external cuneiform Fig. 182.—The Left External Cuneiform. [Internal surfaced) For middle cuneiform For second metatarsal. The cir- cular facet at the inferior angle is for the middle cuneiform. For scaphoid Fig. 183.—The Left External Cuneiform. [External surface.) For fourth metatarsal. ■ For third metatarsal. • For cuboid. The EXTERNAL CUNEIFORM has its base directed upward, and its narrow border downward. The posterior surface is faceted for the scaphoid ; and the anterior, triangular in shape, articulates with the base of the third metatarsal. The internal surface has a large facet, extending along the posterior border, for the middle cuneiform; and on the anterior border, a narrow irregular facet for the outer border of the base of the second metatarsal; and occasionally a small facet at the anterior inferior angle for the middle cuneiform. The outer surface has a broad, distinctive facet, near its posterior superior angle, 188 THE SKELETON. for the cuboid; and at the anterior superior angle there is usually a facet for the inner side of the base of the fourth metatarsal. Articulations.—With the middle cuneiform, the scaphoid, the cuboid, and the second, third, and fourth metatarsals. Muscles.—The flexor brevis hallucis and a slip from the tibialis posticus. Ossification.—A single nucleus appears in the course of the first year. The three cuneiform bones rest posteriorly against the scaphoid ; and as they are of unequal length, the middle being the smallest, it follows that when the bones are placed in their natural positions a deep gap or recess is formed in front. Into this recess the base of the second metatarsal is received, thus explaining the small facets at the anterior superior angles of the internal and external cuneiforms. THE METATARSUS. The metatarsus consists of five bones, numbered one to five, beginning at the hallux. Each metatarsal presents a proximal portion termed the base, and a distal end or head. The shaft of each bone, with the exception of the first, is Fig. 184.—The First (Left) Metatarsal. Fibular Tibial or Inner Side. or Outer Side, Facet for internal cuneiform. For peroneus longus. Facet for second metatarsal (occasional). prismatic; the base of the prism is directed upward, and the narrow edge down- ward. The shaft tapers gradually from the base to the head and is slightly bowed, the concavity being on the plantar aspect. The base is prismatic : its terminal surface is faceted for articulation with the tarsus, and the adjacent borders of the base present small facets, in most cases for adjacent metatarsals. The head is semicircular, forming a convex articular surface for the base of the first phalanx. The compressed sides of the head present near their centres a depression surmounted by a prominent tubercle. The plantar surface is deeply grooved for the passage of flexor tendons. To the sides of the head the lateral ligaments of the metatarso-phalangeal joints are attached. The FIRST METATARSAL is the most modified; it is shorter, but much thicker than its fellows. The base presents a reniform, slightly concave facet for the internal cuneiform bone. On the outer (fibular) side of the base, near its lower angle, there is a tubercle into which the peroneus longus is inserted. A little above this, there is frequently a shallow but easily recognized facet, where it comes into contact with the base of the second metatarsal. THE METATARSUS. 189 The head of the bone has two deep grooves on the plantar surface for the sesamoids developed in the flexor brevis hallucis muscle. Muscles.—Peroneus longus ; tibialis anticus; first dorsal interosseous. Fig. 185.—The Second (Left) Metatarsal, TlBIAL OR Inner Side. Fibular or Outer Side. Facet for middle cuneiform. An occasional facet for the first metatarsal. Internal cuneiform i Facets for third / metatarsal. \ Facets for external f cuneiform. Fig. 186.—The Third (Left) Metatarsal, Facets for second me- tatarsal. Tibial or Inner Side FlBULAR OR Outer Side. Facet for external cuneiform.’ Facets for second me tatarsal. Facet for fourth meta- tarsal. Blood-supply.—The nutrient vessel enters the shaft on the fibular side, and is directed toward the head of the bone. The SECOND METATARSAL is the longest of the series. Its base is pro- longed backward to occupy the space between the internal and external cuneiform 190 THE SKELETON. bones; this leads to the formation of a small facet at the superior angle on the tibial side where it articulates with the internal cuneiform. It occasionally pre- sents a small facet for the first metatarsal. The outer (fibular) side of the base has two facets, each subdivided in well-marked bones. The dorsal facet is long Fig. 187.—The Fourth (Left) Metatarsal Facet for metatarsal. Tibial or Inner Side. Fibular or Outer Side. I Cuboid facet. Facet for'fnwtb metatarsal. Facet for external cuneiform. Facet for fifth metatarsal. Fig. 188.—The Fifth (Left) Metatarsal Tibial or Inner Side. Fibular or Outer Side. Cuboid facet. Fourth metatarsal Cuboid facet, Tuberosity. and narrow; the posterior section articulates with the external cuneiform; the anterior is for the third metatarsal. The lower facet is somewhat circular; its posterior section is for the external cuneiform, the anterior for the third metatar- sal. The terminal facet on the base is for the middle cuneiform : thus the second metatarsal articulates with three cuneiform bones. THE PHALANGES. 191 Muscles.—Adductor hallucis; first and second dorsal interosseous. Blood-supply.—The nutrient artery enters on the fibular side near the middle of the shaft, and is directed toward the base of the bone. The THIRD METATARSAL articulates by its base with the external cunei- form. It has on the inner (tibial) side two facets : one below the other for the second metatarsal, and a large facet on the fibular side for the fourth metatarsal. Muscles.—Adductor hallucis; first plantar; second and third dorsal inter- osseous. Blood-supply.—The nutrient artery enters on the inner (tibial) side of the shaft near its middle : it is directed toward the base. The FOURTH METATARSAL has a somewhat quadrilateral terminal facet for the cuboid bone. On its inner (tibial) side it has a large facet for the third metatarsal: the posterior part of this is occasionally marked off for the external cuneiform, but this is far from constant. When this cuneiform facet is present, the facet extends to the base of the bone. When absent, the surface is rough for ligament. The outer (fibular) side has a single facet for the fifth metatarsal. Muscles.—Adductor hallucis; second plantar interosseous ; third and fourth dorsal interosseous. Blood-supply.—The nutrient artery]of the shaft enters on the inner (tibial) side and runs toward the base. The FIFTH METATARSAL has on the fibular side of its base a large nipple- shaped tuberosity, to which the tendon of the peroneus brevis is inserted. Its oblique terminal facet articulates with the cuboid, and on the tibial side it has a large facet for the fourth metatarsal. The plantar aspect of the base has a shallow groove which lodges the abductor minimi digiti. Muscles :— Third plantar interosseous. Fourth dorsal interosseous. Peroneus brevis. Peroneus tertius. Abductor ossis metatarsi quinti. Flexor brevis minimi digiti. Blood-supply.—The nutrient artery enters on the tibial side of the shaft and runs toward the base. Ossification.—Each metatarsal ossifies from two centres. The primary nucleus for the diaphysis appears in the eighth week of embryonic life, in the middle of the cartilaginous metatarsal. At birth, each extremity is represented by cartilage, and that at the proximal end is ossified by extension from the primary nucleus, except in the case of the first metatarsal. For this, a nucleus appears in the third year. The distal ends of the four outer metatarsals are ossified by secondary nuclei which make their appearance about the third year. Very frequently an epiphysis is found at the distal end of the first metatarsal as well as at its base. The shafts and epiphyses consolidate at the twentieth year. The sesamoids belonging to the flexor brevis hallucis begin to ossify about the fifth year. THE PHALANGES. There are fourteen phalanges to each foot. The hallux has two, and the remaining toes three each. They are usually distinguished as first, second, and third. The last are sometimes called the ungual phalanges, because they support the nail. The phalanges of the first row have narrow, laterally compressed shafts, rounded on the dorsal and concave on the plantar aspects. The bases have deep glenoid fossae for the convex heads of the metatarsals with which they articulate ; whilst the heads have trochlear surfaces for the bases of the second phalanges. The phalanges of the second row are stunted, insignificant bones. Their shafts are flatter than those of the first row, besides being much shorter. The bases have two depressions, separated by a vertical ridge. The heads present trochlear surfaces for the ungual phalanges. 192 THE SKELETON. Fig. 189.—The Phalanges of the Middle Toe. Third, terminal, or ungual phalanx. Second phalanx. First phalanx. Fig. 190.—A Longitudinal Section of the Bones of the Lower Limb at Birth. The centre for the lower extremity of the femur _ appears early in the ninth month. The centre for the upper end of the tibia appears _ about a week before birth. Cartilage for the patella appears about the fourth month of intra-uterine life. 1 he centre for the scaphoid appears in the fourth year. lor the internal cuneiform appears in the third year. Metatarsal of hallux. The centre for the astra- galus appears in the. seventh month. The centre for the calca- neum appears in the' sixth month. First phalanx of hallux. Second phalanx of hallux. THE PHALANGES. The third, terminal, or ungual phalanges are easily recognized. The bases .articulate with the second phalanges ; the shafts are expanded to support the nails, and their palmar surfaces are rough where they come into relation with the pulp of the digit. The first phalanx of the hallux gives insertion to the following muscles :— Flexor brevis hallucis; abductor hallucis; transversus pedis; adductor hallucis; extensor brevis digitorum. The first phalanx of second toe : The first and second dorsal interosseous. The first phalanx of third toe : Third dorsal interosseous; first plantar interosseous. The centre for the epiphysis for the calcaneum appears at the tenth year; consoli- dates at the sixteenth year. Fig. i 91.—The Secondary Ossific Centres of the Foot. The centre for the epiphysis for the metatarsal of the hallux appears at the third year; consolidates at the twentieth year. The centres for the base of the terminal phalanges appear at the sixth year, and consoli- date at the eighteenth year. The’centres for the heads of the metatarsals appear at the third year, and consolidate at the twentieth year. The first phalanx of fourth toe: Second plantar interosseous; fourth dorsal interosseous. 1 he first phalanx of fifth toe: Third plantar interosseous; flexor brevis minimi digiti; and adductor minimi digiti. I he second phalanx of hallux: Flexor longus hallucis; extensor longus hallucis. The second phalanges of the remaining toes : Extensor longus digi- torum; flexor brevis digitorum. The third phalanges : Flexor longus digitorum ; extensor longus digitorum. Ossification.—Like the phalanges of the fingers, those of the toes ossify 194 THE SKELETON. from a primary and a secondary nucleus. The centres for the shaft appear during the eighth and tenth weeks of embryonic life; the secondary centres appear as thin, scale-like epiphyses at the proximal ends between the fourth and eighth years.* They consolidate earlier than the corresponding epiphyses in the fingers. The ungual phalanges, like those of the fingers, ossify from the distal ex- tremity. The average dates of ossification of the bones of the foot:— Calcaneum Sixth month. Epiphysis Tenth year. Astragalus Seventh month. Cuboid, At, or near, the ninth month. Scaphoid, Fourth or fifth year. Internal cuneiform, Third year. Middle cuneiform Fourth year. External cuneiform First year. Metatarsals Eighth to ninth week. Epiphyses, Third year; consolidate at the twentieth year. Phalanges Eighth to tenth week. Epiphyses Fourth to eighth year; consolidate about the eighteenth year. SECTION II. THE ARTICULATIONS. BY HENRY MORRIS, M.A., M.B.Lond., F. R.C.S.Eng. Surgeon to and Lecturer on Surgery, formerly Lecturer on Anatomy, at the Middlesex Hospital; late Examiner in Anatomy in the University of Durham; for the Conjoint Board of the Royal Colleges of Physicians and Surgeons : and for the Fellowship of the Royal College of Surgeons. The section devoted to the Articulations or Joints deals with the union of the various and dissimilar parts of the human skeleton. The following structures enter into the formation of joints. Bones constitute the basis of most joints. The articular ends are expanded, and are composed of cancellous tissue, surrounded by a dense and strong shell of compact tissue. This shell has no Haversian canals (the vessels of the cancellous tissue turn back and do not perforate it), or large lacunae, and no canaliculi, and are thus well adapted to bear pressure. The long bones articulate by their ends, the flat by their edges, and the short at various parts on their surfaces. The cartilage which covers the articular ends of the bones is called articular, and is of the hyaline variety. It is firmly implanted on the bone by one surface, while the other is smooth, polished, and free, thus reducing friction to a mini- mum, while its slight elasticity tends to break jars. It ends abruptly at the edge of the articulation, and is thickest over the areas of greatest pressure. Another form of cartilage, the white fibrous, is also found in joints :— (i) As interarticular cartilage in diarthrodial joints, viz., the knee, tem- poro-mandibular, sterno-clavicular, radio-carpal, and occasionally in the acromio- clavicular. It is interposed between the ends of the bones, partially or completely dividing the synovial cavity into two. It serves to adjust dissimilar bony surfaces, adding to the security of, while it increases the extent of motion at, the joint, and also acts as a buffer to break shocks. (ii) As circumferential or marginal fibro-cartilages, they serve to deepen the sockets for the reception of the heads of bones—e.g., the glenoid and cotyloid ligaments of the shoulder and knee. Another form of marginal plate is seen in the glenoid ligaments of the fingers and toes, which deepen the articulations of the phalanges and add to their security. (iii) As connecting fibro-cartilage. The more pliant and elastic is the more cellular form, and is found in the intervertebral discs; while the less yielding and more fibrous form is seen in the sacro-iliac and pubic articulations, where there is little or no movement. The ligaments which bind the bones together are strong bands of white, fibrous tissue, forming a more or less perfect capsule, round the articulation. They are pliant but inextensile, varying in shape, strength, and thickness according to the kind of articulation into which they enter. They are closely connected with 196 THE ARTICULATIONS. the periosteum of the bones they unite. In some cases—as the ligamenta subflava which unite parts not in contact—they are formed of yellow elastic tissue. The synovial membrane lines the interior of the fibrous ligaments, thus excluding them, as well as the cushions or pads of fatty tissue situate within and the tendons which perforate the fibrous capsule, from the articular cavity. It is a thin, delicate membrane, frequently forming folds and fringes which project into the cavity of the joint ; or, as in the knee, stretches across the cavity, forming a so called synovial ligament. In these folds are often pads of fatty tissue, which fill up interstices and form soft cushions between the contiguous bones. Some- times these fringes become villous and pedunculated, and cause pain in move- ments of the joints. They contain fibro-fatty tissue, with an isolated cartilage cell or two. The synovial membrane is well supplied with blood, especially near the margins of the articular cartilages and in the fringes. It secretes a thick, glairy fluid like white of egg, called synovia, which lubricates the joint. Another variety of synovial membrane is seen in the bursae, which are interposed between various moving surfaces. In some instances bursae in the neighborhood of a joint may communicate with the synovial cavity of that joint. THE VARIOUS KINDS OF ARTICULATIONS. There are three chief varieties of joints, viz., synarthrodial, or immovable; amphiarthrodial, or yielding; and diarthrodial, or movable joints. Synarthrosis is the term applied to all immovable joints in which the apposed surfaces or edges of the bones are in direct contact, as in the face bones, except the mandible, and all those of the skull ; or where bone and cartilage are in immediate union, as in the case of the first rib and the sternum, and the costal cartilages and the ribs. The unions of the bones of the skull and face are" usually called sutures, of which there are three chief varieties :— True sutures, where the edges of bones are firmly implanted into one an- other by means of projecting processes, as in the sagittal, lambdoid, and coronal sutures. False sutures, where the rough edges of the bones are in simple contact without interlocking, as in the intermaxillary suture; or where they overlap one another, as in the squamous suture. Grooved sutures, where the edge or plate of one bone is received into a cor- responding groove in the other, as in the rostrum of the sphenoid and vomer, or vomer and palatine processes of the maxillae, and the horizontal plates of the palate bones. Amphiarthrosis is the term applied to mixed joints which permit of slight movements, the opposed bony surfaces being firmly united by a plate or disc of fibro-cartilage. There is sometimes a partial synovial membrane. Examples are seen in the spine, sacro-iliac, and pubic joints. Diarthrosis is the term applied to all movable joints in which the bones have smooth cartilage-covered surfaces, lubricated by synovia, and bound together by more or less perfect capsules. This class is subdivided into the following varieties:— 1. Arthrodia.—A simple gliding joint formed by the apposition of two plane, or nearly plane, surfaces, which allow motion in one or more directions. The articular processes of the vertebrae, the joints of the carpus and tarsus, carpo- metacarpal, tarso-metatarsal, and intermetacarpal and intermetatarsal joints are good examples. 2. Ginglymus, or hinge-joint, where the ends of the bones are so adapted to each other as to allow motion in two directions, namely, flexion and extension ; the most perfect of them are the elbow and ankle. The knee has some gliding and rotatory motion, and is not a perfect hinge-joint, but ginglymo-arthrodial. MOVEMENTS OF JOINTS. 197 3. Enarthrodia, or ball-and-socket joint, where the enlarged head of one bone is received into a socket adapted to it on the other, as in the hip and shoulder joints. They are the most movable of all the joints, combining move- ments in all directions with axial rotation. 4. Trochoides, or pulley joints: this term is applied where either a pivot revolves in a ring, as in the superior radio-ulnar; or the ring revolves about a pivot, as in the central atlanto-axoidean joint. Table of the Various Classes of Joints. Class. Examples. I. Synarthrosis (a) True sutures Lambdoid, sagittal, coronal. (b) False sutures Internasal. Intermaxillary. Costo-chon- dral. (c) Grooved sutures Vomer and rostrum of sphenoid. II. Amphiarthrosis Bodies of vertebrae. Symphysis pubis, sacro-iliac, sacro-coccygeal. III. Diarthrosis. (a) Arthrodia Carpal, tarsal, carpo-metacarpal, tarso- metatarsal, intermetacarpal, and inter- metatarsal. Costotransverse. Inter- chondral (/. e., between costal cartilages). Sterno-clavicular, acromio-clavicular. Tibio-fibular. Lateral atlanto-axoidean ; and the joints between articular process- es of vertebrae. (b) Ginglymus, . . . - Elbow, ankle, wrist (double ginglymus). Metacarpo- and metatarso-phalangeal. Interphalangeal (c) Ginglymo-arthrodia, Temporo-mandibular. Occipito-atlantal. Knee. (d) Enarthrodia, Shoulder. Hip. (e) Trochoides, diarthrosis rota- toria, or lateral ginglymus. Central atlanto-axoidean. Superior and inferior radio-ulnar. THE VARIOUS MOVEMENTS OE JOINTS. The movements which may take place at a joint are either gliding, angular, rotatory, or circumductory. The gliding motion is the simplest, and is common to all diarthrodial joints: it consists of a simple sliding of the apposed surfaces of the bones upon one an- other, without angular or rotatory motion. It is the only kind of motion per- mitted in the carpal and tarsal joints, and in those between the articular processes of the vertebrae. The angular motion is more elaborate, and increases or diminishes the angle between different parts. There are four varieties, viz. : flexion and extension, which bend or straighten the various joints, and take place in a forward and back- ward direction (in a perfect hinge-joint this is the only motion permitted); and adduction and abduction, which, except in the case of the fingers and toes, signi- fies an approach to, or deviation from, the centre line of the body. In the case of the hand, the line to or from which adduction and abduction are made is drawn through the middle finger, while in the foot it is through the second toe. Rotation is the revolution of a bone about its own axis without much change of position. It is only seen in enarthrodial and trochoidal joints. The knee permits of slight rotation, also, in certain positions, which is a distinctive feature of this articulation. Circumduction is the movement compounded of the four angular movements 198 THE ARTICULATIONS. in quick succession, by which the moving bone describes a cone, the proximal end of the bone forming the apex, while the distal end describes the base of the cone. It is seen in the hip and shoulder, as well as in the carpo-metacarpal joint of the thumb, which thus approximates to the ball-and-socket joint. In some situations where a variety of motion is required, strength, security, and celerity are obtained by the combination of two or more joints, each allowing a different class of action, as in the case of the wrist, the ankle, and the head with the spine. Many of the long muscles, which pass over two or more joints, act on all, so tending to co-ordinate their movements and enabling them to be produced with the least expenditure of power. Muscles also act as elastic ligaments to the joints; and when acting as such are diffusers and combiners, not producers, of movement; the short muscles producing the movement, the long diffusing it, and thus allowing the short muscles to act on more than one joint. Muscles are so disposed at their attachments near the joints as never to strain the ligaments by tending to pull the bones apart, but, on the contrary, they add to the security of the joint by bracing the bones firmly together during their action. The articulations may be divided for convenience of description into those : 1. of the Skull; 2. of the Trunk; 3. of the Upper Limb, and 4. of the Lower Limb. THE ARTICULATIONS OF THE SKULL. The articulations of the skull comprise (1) the temporo-mandibular and (2) those between the skull and first two vertebrae : namely, (a) between the occiput and atlas; (b) between the atlas and axis; and (c) the ligaments which connect the occiput and axis. The union of the atlas and axis is described in this section because, firstly, there is often a direct communication between the synovial cavity of the trans- verse axoidean and the occipito-atlantal joints; secondly, the rotatory movements of the head take place around the odontoid process; and, thirdly, important ligaments from the odontoid process pass over the atlas to the occiput. Class.—Diarthrosis. (1) THE TEMPORO-MANDIBULAR ARTICULATION. Subdivision.—Ginglymo-Arthrodia. The parts entering into the formation of this joint are: the anterior portion of the glenoid fossa and glenoid ridge (eminentia articularis) of the temporal bone above, and the condyle of the lower jaw below. Both are covered with articular cartilage, which is also extended over the front of the glenoid ridge to facilitate the play of the interarticular cartilage. The ligaments which unite the bones are :— 1. Capsular. 2. Interarticular fibro-cartilage. 3. Spheno-mandibular. 4. Stylo-mandibular. The capsular ligament is often described as consisting of four portions, which are, however, continuous with one another around the articulation. 1. The anterior portion consists of a few stray fibres connected with the anterior margin of the fibro-cartilage, and attached below to the anterior edge of the condyle, and above to the front of the glenoid ridge. Some fibres of insertion of the external pterygoid pass between them to be inserted into the margin of the fibro-cartilage. 2. The posterior portion is attached above, just in front of the Glaserian fissure, and is inserted into the back of the jaw just below its neck. 3. The external portion or external lateral ligament (Fig. 192) is the strongest part of the capsule. It is broader above, where it is attached to the lower edge of the zygoma in nearly its whole length, as well as to the tubercle at TEMP OR O-MANDIB ULAR. 199 the point where the two roots of the zygoma meet. It is inclined downward and backward, to be inserted into the outer side of the neck of the condyle. Its fibres diminish in obliquity and strength from before backward, those coming from the tubercle being short and nearly straight. 4. The internal portion or short internal lateral ligament (Fig. 193) consists of well-defined fibres, having a broad attachment, above to the outer side of the alar spine of the sphenoid and inner edge of the glenoid fossa ; and below, a narrow insertion to the inner side of the neck of the condyle. Fatty and cellular tissue separate it from the spheno-mandibular ligament which is internal to it. The interarticular cartilage (Fig. 194) is an oval plate interposed between and adapted to the two articular surfaces. It is thinner at the centre than at the circumference, and is thicker behind where it covers the thin bone at the bottom of the glenoid fossa which separates it from the dura mater, than in front where it covers the glenoid ridge. Its inferior surface is concave and fits on to the condyle of the lower jaw; while its superior surface is concavo-convex from before back- Fig. 192.—External View of Temporo-mandibular Joint External por- tion of capsule. Stylo-mandibular ligament, ward, and is in contact with the articular surface of the temporal bone. It divides the joint into two separate synovial cavities, but is occasionally perforated in the centre, and thus allows them to communicate. It is connected to the capsular ligament at the margins, and has some fibres of the external pterygoid muscle inserted into its anterior margin. There are usually two synovial membranes (Fig. 194), the superior being the larger and looser, passing down from the margin of the articular surface above to the upper surface of the interarticular cartilage below ; the lower and smaller one passes from the interarticular cartilage above to the condyle of the jaw below, extending somewhat further down behind than in front. When the interarticular cartilage is perforated, the two sacs communicate. The spheno-mandibular ligament (long internal lateral) (Fig. 193) is a thin, loose band, situated some little distance from the joint. It is attached above to the alar spine of the sphenoid and contiguous part of the temporal bone, and is inserted into the mandibular spine of the lower jaw. It covers the upper end of the mylo-hyoid groove, and is here pierced by the mylo-hyoid nerve. Its origin 200 THE ARTICULATIONS. is a little internal to, and behind, but close to the origin of the short internal lateral ligament. It is separated from the joint and ramus of the jaw by the external pterygoid muscle, internal maxillary artery and vein, the mandibular nerve and artery, and the middle meningeal artery. It is really the fibrous remnant of a part of the mandibular (Meckelian) bar. Fig. 193.—Internal View of Temporo-mandibular Joint. Internal portion of capsule. Spheno-mandibu- lar ligament. Stylo-mandibular ligament. Stylo-hyoid ligament. Fig. 194.—Vertical Section through the Condyle of Jaw, to Show the Two Synovial Sacs and the Interarticular Fibro-cartilage. Interarticular fibro- cartilage. Section through condyle. Posterior portion of capsule. Spheno-mandibular ligament, Stylo-mandibular ligament The stylo-mandibular ligament (stylo-maxillary) (Figs. 192 and 193) is a process of the deep cervical fascia extending from near the tip of the styloid process to the angle and posterior border of the ramus of the jaw, between the masseter and internal pterygoid muscles. It separates the parotid from the submaxillary gland, and gives origin to some fibres of the stylo-glossus muscle. ATLAS WITH OCCIPUT 201 The arterial supply is derived from the temporal, middle meningeal, and ascending pharyngeal by its branches to the Eustachian tube. The nerves are derived from the masseteric and auriculo-temporal. Movements.—The chief movement of this joint is of (i) a ginglymoid or hinge character, accompanied by a slight gliding action, as in opening or shut- ting the mouth. In the opening movement the condyle turns like a hinge on the fibro-cartilage, while at the same time the fibro-cartilage, together with the con- dyle, glides forward so as to rise upon the eminentia articularis ; the fibro-cartilage reaching as far as the anterior edge of the eminence, which is coated with articular cartilage to receive it; but the condyle never reaches quite so far as the summit of the eminence. Should the condyle, however, by excessive movement (as in a convulsive yawn), glide over the summit, it slips into the zygomatic fossa, the. mandible is dislocated, and the posterior portion of the capsule is torn. In the shutting movement the condyle revolves back again, and the fibro-cartilage glides back, carrying the condyle with it. This combination of the hinge and gliding motions gives a tearing as well as a cutting action to the incisor teeth, without any extra muscular exertion. There is (ii) a horizontal gliding action in an antero-posterior direction, by which the lower teeth are thrust forward and drawn back again : this takes place almost entirely in the upper compartment, because of the closer connection of the fibro-cartilage to the condyle than to the squamosal bone, and also because of the insertion of the external pterygoid into both bone and cartilage. In these two sets of movements the joints of both sides are simultaneously and similarly engaged. The third form of movement is called (iii) the oblique rotatory, and is that by which the grinding and chewing actions are performed. It consists in a rota- tion of the condyle about the vertical axis of its neck in the lower compartment, while the cartilage glides obliquely forward and inward on one side, and backward and inward on the other, upon the articular surface of the squamosal bones, each side acting alternately. If the symphysis be simply moved from the centre to one side and back again, and not from side to side as in grinding, the condyle of that side moves round the vertical axis of its neck, and the opposite condyle and cartilage glide forward and inward upon the glenoid fossa. But in the ordinary grinding movement, one condyle advances and the other recedes, and then the first recedes while the other advances, slight rotation taking place in each joint meanwhile. (2) THE LIGAMENTS AND JOINTS BETWEEN THE SKULL AND SPINAL COLUMN, AND BETWEEN THE ATLAS AND AXIS. («) The Articulation of the Atlas with the Occiput. This articulation consists of a pair of joints symmetrically situated on either side of the middle line. The parts entering into their formation are the cup- shaped superior articular processes of the atlas, and the condyles of the occipital bone. They are united by the following ligaments :— Class.—Diarthrosis. S ubdivision.—Ginglymo-A rthrodia. 1. Anterior occipito-atlantal. 2. Posterior occipito-atlantal. 3. Two capsular. 4. Two anterior oblique. The anterior occipito-atlantal ligament (Fig. 195) is less than an inch (about 2 cm.)wide, and is composed of densely woven fibres, most of which radiate slightly outward as they ascend from the front surface and upper margin of the anterior arch of the atlas, to the anterior border of the foramen magnum; it is continuous laterally with the capsular ligaments, the fibres of which overlap its edges, and take an opposite direction inward and upward. The central fibres take a vertical course as they ascend from the anterior tubercle of the atlas to the pharyngeal tubercle on the occipital bone; they are thicker than the lateral fibres, 202 THE ARTICULATIONS. and are continuous below with the superficial part of the anterior atlanto-axoidean ligament, and through it with the anterior common ligament of the vertebral column. It. is in relation, in front, with the recti capitis antici minores; and behind, with the central odontoid or suspensory ligament. The posterior occipito-atlantal ligament (Fig. 196) is broader, more membranous, and not so strong as the anterior. It extends from the posterior surface and upper border of the posterior arch of the atlas to the posterior margin of the foramen magnum from condyle to condyle; being incomplete on either side for the passage of the vertebral artery into, and suboccipital nerve out of, the canal. It is somewhat thickened in the middle line by fibres, which pass from the posterior tubercle of the atlas to the lower end of the occipital crest. It is not Fig. 195.—Anterior View of the Upper End of the Spine. Continua- tion of the anterior common ligament of the vertebral column. Anterior occipito- atlantal ligament. Occipito- atlantal capsular ligament. The anterior oblique or lateral occipito- atlantal ligament. Atlanto-axoidean capsular ligament. _ Anterior atlanto- axoidean ligament. Body of axis. Short vertebral ligament. Capsular ligaments of articular processes between axis and the third, the third < and fourth, and the fourth and fifth cer- vical vertebrae. Anterior common ligament. tightly stretched between the bones, nor does it limit their movements; it corresponds with the position of the ligamenta subflava, but has no elastic tissue in its composition. It is in relation in front with the dura mater, which is firmly attached to it; and behind with the recti capitis postici minores, and enters into the floor of the suboccipital triangle. The capsular ligaments (Figs. 195, 196) are very distinct and strongly marked, except on the inner side, where they are thin and formed only of short membranous fibres. They are lax, and do not add much to the security of the joint. In front, the capsule descends upon the atlas, to be attached, some dis- tance below the articular margin, to the front surface of the lateral mass and to the base of the transverse process; these fibres take an oblique course upward and inward, overlapping the anterior occipito-atlantal. At the sides and behind, ATLAS WITH OCCIPUT. 203 the capsule is attached above to the margins of the occipital condyles; below, it skirts the inner edge of the foramen for the vertebral artery, and behind is attached to the prominent tubercle overhanging the groove for that vessel; these latter fibres are strengthened by a band running obliquely upward and inward to the posterior margin of the foramen magnum. The anterior oblique or lateral occipito-atlantal ligament (Fig. 195) is an accessory band which strengthens the capsule on the outer side. It is an oblique, thick band of fibres, sometimes quite separate and distinct from the rest, passing upward and inward from the upper surface of the transverse process beyond the costo-vertebral foramen to the jugular process of the occipital bone. Fig. 196.—Vertical Antero-posterior Section of Spinal Column through Median Line, Showing Ligaments. Ascending Left lateral odontoid ligament. portion of crucial lig- ament. Transverse ligament. Inner part of capsular ligament of occipito-atlantal joint. v Central odontoid ligament. Anterior occipito- atlantal ligament. Posterior occipito-atlantal ligament. Descending portion of cru- cial ligament. Posterior atlanto-axoidean ligament. Atlanto-odontoid synovial sac. Anterior atlanto- axoidean ligament Interspinous ligament Ligamentum subflavum. The synovial membrane of these joints occasionally communicates with the synovial sac between the odontoid process and the transverse ligament. The arterial supply is derived from twigs of the vertebral, and occasionally from twigs from the meningeal branches of the ascending pharyngeal. The nerve-supply comes from the anterior division of the suboccipital nerve. Movements.—By the symmetrical and bilateral arrangement of these joints, security and strength are gained at the expense of a very small amount of actual articular surface, the basis of support and the area of action being equal to the width between the most distant borders of the joint. 204 THE ARTICULATIONS. Almost the only movement permitted at these joints is of a ginglymoid character, producing flexion and extension upon a transverse axis drawn across the condyles at their slightly constricted parts. In flexion, the forehead and chin drop, and what is called the nodding move- ment is made ; in extension, the chin is thrown up and the forehead recedes. There is also a slight amount of gliding movement, either directly lateral, the outer edge of one condyle sinking a little within the outer edge of the socket, of the atlas, and that of the opposite condyle projecting to a corresponding degree. The head is thus tilted to one side, and it is even possible that the weight of the skull may be borne almost entirely on one joint, the articular surfaces of the other being thrown out of contact. Or the movement may be obliquely lateral, when the lower side of the head will be a trifle in advance of the elevated side. In this motion, which takes place on the antero-posterior axis, one condyle advances slightly and approaches the middle line, while the other recedes. There is no true rotation round a vertical axis possible between the occiput and atlas. These lateral movements are checked by the lateral odontoid ligaments and the outer part of the capsules ; extension is checked by the anterior occipito- atlantal and anterior oblique ligaments, and flexion by the posterior part of the capsule and cervico-basilar ligaments. 1. The Lateral Atlanto-axoidean Joints. (b) The Articulations Between the Atlas and Axis. Class.—Diarthrosis. Subdivision.—Arthrodia. Class.—Diarthrosis. Subdivision.— Trochoides. The bones that enter into the formation of the lateral joints are the inferior articular processes of the atlas and the superior of the axis ; the central joint is formed by the odontoid process articulating in front with the atlas, and behind with the transverse ligament. The ligaments which unite the axis and atlas are :— 2. The Central Atlanto-axoidean Joint. 1. The anterior atlanto-axoidean. 2. The posterior atlanto-axoidean. 5. The atlanto-odontoid capsular ligament. 3. Two capsular (for lateral joints). 4. The transverse ligament. The anterior atlanto-axoidean ligament (Figs. 195, 196) is a narrow but strong membrane filling up the interval between the lateral joints. It is attached, above to the front surface and lower border of the anterior arch of the atlas, and below to the transverse ridge on the front of the body of the axis. Its fibres are vertical, and are thickened in the median line by a dense band which is a con- tinuation upward of the anterior common ligament of the spine. This prolongation is fixed above to the anterior tubercle of the atlas, where it becomes continuous with the central part of the anterior occipito-atlantal (Fig. 195); it is sometimes separated by an interval from the deeper ligament, and is often described as the superficial atlanto-axoidean ligament. It is in relation with the longus colli muscle. The posterior atlanto-axoidean ligament (Fig. 195) is a deeper, but thinner and looser membrane than the anterior. It extends from the posterior root of the transverse process of one side to that of the other, projecting outward beyond the posterior part of the capsules which are connected with it. It is attached above to the posterior surface and lower edge of the posterior arch of the atlas, and below to the superior edge of the laminae of the axis on their dorsal aspect. It is denser and stronger in the median line, and has a layer of elastic tissue on its anterior surface like the ligamenta subflava, to which it corresponds in position. It is connected in front with the dura mater; behind, it is in rela- tion with the inferior oblique muscles, and is perforated at each side by the second cervical nerve. 1. The Lateral Atlanto-axoidean Joints are provided with short, liga- BETWEEN ATLAS AND AXIS. 205 mentous fibres, forming capsular ligaments (Fig. 195), which completely sur- round the lateral articular facets. Outside the canal, they are attached some, little distance from the articular margins, extending along the roots of the transverse processes of the axis nearly as far as the tips, but between the roots they skirt the inner edge of the costo-vertebral foramina. They are strengthened in front and behind by the atlanto-axoidean ligaments. Internally each capsule is thinner, and attached close to the articular margins, being strengthened behind by a strong band of slightly oblique fibres passing upward along the outer edge of the cervico- basilar ligament from the body of the axis to the lateral mass of the atlas behind the transverse ligament ; some of these fibres pass on, thickening and blending with the occipito-atlantal capsule, getting inserted into the margin of the foramen magnum. This band is sometimes called the accessory band (Fig. 199). There is a synovial sac for each joint. 2. The Central Atlanto-axoidean Joint, although usually described as one, is composed of two articulations, which are quite separate from one another: an anterior between the odontoid process and the arch of the atlas, and a poste- rior between the odontoid process and the transverse ligament. The transverse ligament (Figs. 196, 197, and 199) is one of the most im- portant structures in the body, for on its integrity our lives depend. It is a thick and very strong band, as dense and closely woven as fibro-cartilage, about a quarter of an inch (6 mm.) deep at the sides, and somewhat more in the middle Fig. 197.—Horizontal Section through the Lateral Masses of the Atlas and THE Top OF THE ODONTOID PROCESS. Atlanto-odontoid synovial sac. Atlanto - odontoid capsular ligament Transverse liga- ment. Posterior com- mon and cervico- basilar ligaments. Transverso-odon- toid synovial sac, Dura mater. line. Attached at each end to a tubercle on the inner side of the lateral mass of the atlas, it crosses the ring of this bone in a curved manner, so as to have the concavity forward ; thus dividing the ring into a smaller anterior portion for the odontoid process, and a larger posterior part for the spinal cord and its mem- branes, and the spinal accessory nerves. It is flattened from before backward, being smooth in front, and covered by synovial membrane to allow it to glide freely over the posterior facet of the odontoid process. Where it is attached to the atlas it is smooth and well rounded off to provide an easy floor of communi- cation between the transverso-odontoid and occipito-atlantal joints. To its posterior surface is added, in the middle line, a strong fasciculus of ver- tical fibres, passing upward from the root of the odontoid process to the basilar border of the foramen magnum on its cranial aspect. Some of these fibres are derived from the transverse portion. It gives the ligament a cruciform appear- ance; hence its name, the crucial ligament (Figs. 196, 199). The atlanto-odontoid capsular ligament (Fig. 197) is a tough, loose membrane, completely surrounding the apposed articular surfaces of the atlas and odontoid process. At the odontoid process it blends above with the front of the check and central occipito-odontoid ligaments, and arises also along the sides of the articular facet as far as the neck of the process; the fibres are thick, and blend with the capsules of the lateral joint. At the atlas they are attached to the non- articular part of the anterior arch in front of the tubercles for the transverse liga- 206 THE ARTICULATIONS. ment, blending, above and below the borders of the bone, with the anterior occipito-atlantal and atlanto-axoidean ligaments, as well as with the inner portion of the capsular ligaments. It holds the axis to the anterior arch of the atlas after all the other ligaments have been divided. The synovial membranes (Figs. 196, 197) are two in number: one for the joint between the odontoid process and atlas; and another (transverso-odon- toid) for that between the transverse ligament and the odontoid ; this last often com- municates with the occipito-atlantal. It is closed in by membranous tissue between the borders of the transverse ligament and the margin of the facet on the odontoid, and is separated from the front sac by the atlanto-odontoid capsular ligament. The arterial supply is from the vertebral artery, and the nerve-supply from the loop between the first and second cervical nerves. Movements.—The chief and characteristic movement at these joints is the Fig. 198.—The Superficial Layer of the Posterior Common Vertebral Ligament has BEEN REMOVED TO SHOW ITS DEEP OR SHORT FIBRES. THESE DEEP FIBRES FORM THE OCCIPITO-CERVICAL LIGAMENT. Occipito- cervical ligament, i. e., the deep stra- tum of the posterior common vertebral ligament. Atlanto- axoidean capsular ligament. Transverse process of atlas. rotation, in a nearly horizontal plane, of the collar formed by the atlas and trans- verse ligament, round the odontoid process as a pivot, which is extensive enough to allow of an all-round view without twisting the trunk. Partly on account of its ligamentous attachments, and partly on account of the shape of the articular surfaces, the cranium must be carried with the atlas in these movements. The rotation is checked by the ligaments passing from the axis to the occiput (check ligaments), and also by the atlanto-axoidean. Owing to the fact that the facets of both atlas and axis, which enter into the formation of the lateral atlanto- axoidean articulations, are convex from before backward, and have the articular cartilage thicker in the centre than at the circumference, the motion is not quite horizontal but slightly curvilinear. In the erect position, with the face looking directly forward, the most convex portions of the articular surfaces are alone in contact, there being a considerable interval between the edges; during rotation, therefore, the prominent portions of the condyles of the atlas descend upon those LIGAMENTS UNITING OCCIPUT AND AXIS. 207 of the axis, diminishing the space between the bones, slackening the ligaments, and thus increasing the amount of rotation, without sacrificing the security of the joint in the central position. Besides rotation, forward and backward movements and some lateral flexion are permitted between the atlas and axis, even to a greater extent than in most of the other vertebral joints. The following ligaments unite bones not in contact, and are to be seen from the interior of the canal after removing the posterior arches of axis and atlas and posterior ring of the foramen magnum :— (<:) The Ligaments Uniting the Occiput and Axis. 1. The occipito-cervical. 2. The crucial. 3. Two lateral odontoid or check. 4. The central odontoid or suspensory. Fig. 199.—Vertical Transverse Section of the Spinal Column and the Occipital Bone, to Show Ligaments. The cervico-basilar (1), though shown as a distinct stratum, is really the deeper part of the posterior common ligament (2). Vertical portion of crucial ligament. - Central odontoid . ligament. Lateral odontoid . ligaments. Transverse portion of crucial ligament. Accessory band of atlanto- axoidean capsules. Atlanto-axoidean joint. Cervico-basilar ligament Posterior common ligament. The occipito-cervical or cervico-basilar ligament (Figs. 197, 198, and 199) consists of a very strong band of fibres, connected below to the upper part of the body of the third vertebra and lower part of the body of the axis as far as the root of the odontoid process. It is narrow below, but widens out as it ascends to be fastened to the basilar groove of the occiput. Laterally, it is connected with the accessory fibres of the atlanto-axoidean capsule. It is really only the up- ward prolongation of the posterior common ligament, some of the fibres of which run on to the occipital bone without touching the axis, rise to two strata. It is in relation in front with the crucial ligament. The crucial ligament has been already described (see page 205). The lateral occipito-odontoid or check ligaments (Figs. 196 and 199) are two strong rounded cords, which extend from the sides of the apex of the odontoid process transversely outward to the inner edge of the anterior portion of the occipital condyles. They are to be seen immediately above the upper 208 THE ARTICULATIONS. border of the transverse ligament, which they cross obliquely owing to its for- ward curve at its attachments to the atlas. Some of their fibres occasionally run across the middle line from one check ligament to the other. At the odontoid process they are connected with the atlanto-odontoid capsule, and at the con- dyles they strengthen the occipito-atlantal capsular ligaments. The central odontoid or suspensory ligament (Figs. 196 and 199) con- sists of a slender band of fibres ascending from the summit of the odontoid process to the under surface of the occipital bone, close to the foramen magnum. It is best seen from the front, after removing the anterior occipito-atlantal ligament, or from behind by drawing aside the crucial ligament. The suspensory ligament is tightened by extension and relaxed by flexion or nodding; the lateral odontoids not only limit the rotatory movements of the head and atlas upon the axis, but by binding the occiput to the pivot, round which rotation occurs, they steady the head and prevent its undue lateral inclination upon the spine. By experiments, it has been proved that the head, when placed so that the orbits look a little upward, is poised upon the occipital condyles in a line drawn a little in front of their middle ; the amount of elevation varies slightly in different cases, but the balance is always to be obtained in the human body—it is one of the characteristics of the human figure. It serves to maintain the head erect without undue muscular effort, or a strong ligamentum nuchse and prominent dorsal spines such as are seen in the lower animals. Disturb this balance, and let the muscles cease to act, the head will either drop forward or backward according as the centre of the gravity is in front or behind the balance line. The ligaments which pass over the odontoid process to the occiput are not quite tight when the head is erect, and only become so when the head is flexed; if this were not so, no flexion would be allowed; thus, muscular action, and not ligamentous tension, is employed to steady the head in the erect position. It is through the combination of the joints of the atlas and axis, and occiput and atlas (consisting of two pairs of joints placed symmetrically on either side of the median line, while through the median line there passes a pivot, also with a pair of joints) that the head enjoys such freedom and celerity of action, remarkable strength, and almost absolute security against violence, which could only be obtained by a ball-and- socket joint; but the ordinary ball-and-socket joints are too prone to dislocations by even moderate twists to be reliable enough when the life of the individual depends on the perfection of the articulation ; hence the importance of this combination of joints. THE ARTICULATIONS OF THE TRUNK. These may be divided into the following sets: 1. Those of the vertebral column. (a) Union of the bodies. Union of the articular processes. 2. Vertebral column with the pelvis. 3. Pelvis. (a) Sacro-iliac synchondroses. (b) Sacro-coccygeal. (V) Intercoccygeal. (//) Symphysis pubis. 4. Ribs with the vertebral column. 5. The articulations at the front of the thorax. (a) Costal cartilages with the sternum. (b) Costal cartilages with the ribs. (c) Sternal. () The Sacro-coccygeal Articulation. The last piece of the sacrum and first piece of the coccyx enter into this union, and are bound together by the following ligaments : — Class.—Amphiarthrosis. Anterior sacro-coccygeal. Posterior sacro-coccygeal. Supracornual. Intertransverse. The intervertebral substance is a small oval disc, three-quarters of an inch (about 2 cm.) wide, and a little less from before backward, closely connected with the surrounding ligaments. It resembles the other discs in structure, but is softer and more jelly-like, though the laminae of the fibrous portion are well marked. The anterior sacro-coccygeal ligament is a prolongation of the glistening fibrous structure on the front of the sacrum. It is really the lower extremity of Intervertebral substance. 222 THE ARTICULATIONS. the anterior common ligament, which is thicker over this joint than over the cen- tral part of either of the bones. The posterior sacro-coccygeal ligament (Fig. 209) is a direct continua- tion of the posterior common ligament of the column, consisting of a narrow band of closely packed fibres, which become blended at the lower border of the first segment of the coccyx with the filum terminale and supracornual ligament. The supracornual ligament (Fig. 209) is the prolongation of the supra- spinous, which becomes inseparably blended with the aponeurosis of the erector sfince opposite the laminae of the third sacral vertebra, and is thus prolonged downward upon the back of the coccyx, passing over and roofing in the lower end of the spinal canal where the laminae are deficient. The median fibres (the supraspinous ligament) extend over the back of the coccyx to its tip, blend- ing with the posterior sacro-coccygeal ligament and filum terminale; the deeper Fig. 209.—Ligaments Connecting Sacrum and Coccyx Posteriorly Superficial part of the supraspinous ligament, turned up. Deep part of the supraspinous liga- ment, turned up. Intertransverse ligament. Lower end of the posterior com- mon ligament. Supracornual ligament connecting the cornua of the sacrum and coccyx,cut and turned down. fibres run across from the stunted laminae on one side to the next below on the opposite side, and from the sacral cornua on one side to the coccygeal on the opposite, some passing between the two cornua of the same side, and bridging the aperture through which the fifth sacral nerve passes. Its posterior surface gives origin to the gluteus maximus muscle. The intertransverse ligament (Fig. 209) is merely a quantity of fibrous tissue which passes from the transverse process of the coccyx to the lateral edge of the sacrum below its angle. It is connected with the sacro-sciatic ligaments at their attachments, and the fifth sacral nerve escapes behind it. It is perforated by twigs from the lateral sacral artery and the coccygeal nerve. The arterial supply is from the lateral sacral and sacro-median arteries. The nerves come from the fourth and fifth sacral and coccygeal nerves. The movements permitted at this joint are of a simple forward and back- THE SYMPHYSIS PUBIS. 223 ward, or hinge-like character. In the act of defecation, the bone is pushed back by the fecal mass, and, in parturition, by the foetus; but this backward movement is controlled by the upward and forward pull of the levator ani and coccygeus. The external sphincter also tends to pull it forward. (r) Intercoccygeal Joints. The several segments of. the coccyx are held together by the anterior and posterior common ligaments, which completely cover the bony nodules on their anterior and posterior aspects. Laterally, the sacro-sciatic ligaments, being attached to nearly the whole length of the coccyx, serve to connect them. Between the first and second pieces of the coccyx there is a very perfect am- phiarthrodial joint, with a well-marked intervertebral substance. (6a, meaning the muscles of the loins—is thick, rounded, and fusiform. Origin.—Inner part, by five processes which arise from (i) the sides of the intervertebral cartilages which intervene between the bodies of the last thoracic and the five lumbar vertebrae ; and (2) the adjacent part of the sides of the bodies of these vertebrae ; and between these processes from (3) tendinous arches which bridge over the sides of the bodies of these vertebrae. Outer part, from the lower border and the front of the transverse processes of all the lumbar vertebrae. Insertion.—The lower and back part of the lesser trochanter of the femur. Structure.—With the exception of the small tendinous arches which span the side of each of the four upper lumbar vertebrae from its upper to its lower bor- der, and which give passage to the lumbar vessels, the whole origin of the muscle is fleshy. The fibres pass downward and forward in penniform fashion, but with a slight convergence, to the inner side of the tendon, which, beginning in the interior of the muscle about the level of the crest of the ilium, becomes free upon its outer and posterior surface a short distance above Poupart’s ligament, while upon its inner surface it receives fibres down to its insertion. The muscle, having hitherto run in a downward, forward, and slightly outward direction, changes its course at Poupart’s ligament, and passes downward and backward to be attached to the lesser trochanter of the femur. In its passage along the brim of the pelvis and over the lower part of the iliac fossa, the tendon upon its anterior and outer aspect begins to receive the insertion of the iliacus muscle. Between the tendon and the capsule of the hip joint which is in close connection with it, is placed a bursa which frequently communicates through an opening in the capsule with the interior of the hip joint. Nerve-supply.—From the anterior primary branches of the second and third lumbar nerves by filaments which are given off from the lumbar plexus whilst it is passing through the muscle. Action.—The psoas is a powerful flexor of the thigh upon the pelvis, e.g., in walking, running, or going up stairs. The change in the direction of the tendon 366 THE MUSCLES. after crossing the horizontal ramus of the pubes makes its insertion nearly perpen- dicular to the axis of the femur. The psoas, therefore, acts with less mechanical disadvantage than is usual with the muscles of the limbs. It has been sometimes described as an external rotator of the hip ; and its insertion into the lesser tro- chanter at the inner side of the femur would appear to favor this view ; but a little consideration will show that, although it is attached on the inner side of the femur, yet, on account of the angle which the neck of the femur forms with its shaft, this point of attachment is really external to the axis about which the rota- tion of the femur takes place. It will follow, therefore, that any power of rotation exercised by this muscle will be rather internal than external. Fig. 286.—Psoas, Iliacus, and Quadratus Lumborum. Quadratus lurabo- _ rum. Intertransversalis anterior. Quadratus lumbo- rum. Psoas parvus. _ Iliacus. Psoas magnus Iliacus, Pyriformis. | Obturator externus. Psoas magnus. Acting from below, the psoas will flex the lower thoracic and the lumbar spine upon the pelvis and the pelvis upon the thigh, as when the body is raised from the reclining to the sitting position, or when the trunk is bent forward in rowing. Relations.—The front and inner surfaces are covered by the iliac fascia, which at the upper part of the muscle is thickened, and forms the ligamentum arcuatum internum of the diaphragm. In front lie also the peritoneum, the intestines, the renal vessels, the spermatic or ovarian vein, and the ureter. On the outer side is the iliacus muscle. In the interior of the muscle is the lumbar plexus, the nerves from which run for some distance in its substance. On the ILIA CVS. 367 inner side lies the external iliac artery; and behind is the vertebral column, the inner border of the quadratus lumborum, and the brim of the pelvis. In the thigh, after passing beneath Poupart’s ligament, it is covered by the femoral artery, the pectineus lies along its inner border, and the capsule of the hip joint lies behind it, together with the intervening bursa. Variations.—Sometimes the part of the psoas which arises from the lower lumbar vertebras forms a distinct muscle. Occasionally fibres from the psoas parvus join the psoas magnus. The iliacus—named from its attachment to the ilium—is a thick, triangular sheet. Origin.—(i) The upper surface of the ala of the sacrum ; (2) the front of the ilio-lumbar, lumbo-sacral, and anterior sacro-iliac ligaments; (3) the upper and outer half of the venter of the ilium; (4) the origin of the upper tendon of the rectus femoris and the ilio-femoral ligament near the anterior inferior spine of the ilium. Insertion.—(1) The outer surface of the tendon of the psoas, through which it is attached to the back of the lesser trochanter of the femur; (2) the upper and inner part of the shaft of the femur in a line about one inch long leading downward from the lesser trochanter. Structure.—Arising by fleshy fibres, the muscle converges in a fan-shape downward and inward, and its fibres enter the posterior and outer surface of the tendon of the psoas muscle from about two inches above Poupart’s ligament to its insertion. The lowest fibres are also continued, still fleshy, into their insertion on the inner part of the shaft of the femur. Nerve-supply.—From the lumbar plexus (through the second and third lumbar nerves) by the anterior crural nerve, which gives branches to its anterior surface about the middle of its inner border. Action.—Similar to that of the psoas, as a flexor of the thigh; and acting from the femur as a fixed point, it will draw forward and flex the pelvis upon the thigh. Relations.—The iliac fascia in front separates it from the peritoneum and intestines. The profunda femoris artery and several nerves from the lumbar plexus lie upon it. Behind, and to its inner side,- lies the psoas. After passing under Poupart’s ligament, it is crossed by the sartorius, and behind lie the rectus femoris and the capsule of the hip joint. 2. ILIACUS. Variations.—A small detached muscle occasionally arises from the anterior inferior spine, and is inserted into the lower part of the anterior intertrochanteric line, or the ilio- femoral ligament. Psoas Parvus. The psoas parvus—a small muscle, only occasionally present, named from its position in the loins and its small size—is fusiform and somewhat flattened. Origin.—The side of the intervertebral disc between the last thoracic and the first lumbar vertebra and the adjacent borders of the bodies of these vertebrae. Insertion.—The ilio-pectineal line. Structure.—Arising fleshy, the fibres converge and are inserted in a somewhat penni- form manner into the back and inner surface of a tendon which appears arbout two inches below the origin of the muscle upon its outer and anterior aspect, and becomes free about the level of the fifth lumbar vertebra. The tendon, a narrow fibrous band, lies upon the inner aspect of the psoas magnus on the brim of the pelvis, and expands at its lower extremity to be attached along the ilio-pectineal line and the pectineal eminence. Nerve-supply.—By small filaments from the first nerve of the lumbar plexus. Action.—To flex the pelvis upon the thorax ; or, taking the pelvis as a fixed point, it will flex the lower part of the thoracic spine as well as the lumbar spine upon the pelvis. It is a muscle which is well developed in some animals, having for its function the drawing forward of the lower part of the pelvis, accompanied by the arching of the lumbar spine which is seen when they are running swiftly. 368 THE MUSCLES. Relations.—In front, the iliac fascia, peritoneum, ligamentum arcuatum internum, intestines, renal vessels, ureter, external iliac vessels, etc. Behind and externally, the psoas magnus. Investing the abdominal portion of the ilio-psoas is a strong membrane, called the iliac fascia, which is attached to the crest of the ilium externally, and inter- nally to the posterior part of the ilio-pectineal line which forms the brim of the pelvis. Between these attachments it invests the front of the iliacus and psoas muscles. Above, it is continued upward as the covering of the latter muscle, at the sides of which it is attached to the transverse processes and bodies of the lumbar vertebrae, as well as to the intervertebral discs and the small tendinous arches which bridge the side of the bodies of these vertebrae. At the diaphragm it is thickened, and forms the ligamentum arcuatum internum ; near the tips of the transverse processes of the lumbar vertebrae it is attached to the anterior layer of the lumbar fascia (page 428). Below, it joins beneath the outer half of Poupart’s ligament with the transversalis fascia, but internal to this it passes downward into the thigh, forming with the transversalis fascia the sheath of the femoral vessels. Still further inward, it is continuous with the pubic portion of the fascia lata which invests the pectineus muscle, and it also sends backward a septum between the psoas and the pectineus which is attached to the ilio-pectineal eminence. 3. SARTORIUS. The sartorius—named somewhat erroneously from sartor, a tailor, because it has been supposed to be the muscle by which the cross-legged.sitting posture is produced—js a long, ribbon-shaped muscle, slightly fusiform at the two ends. Origin.—The anterior superior spine of the ilium and the adjacent part of the notch between this process and the anterior inferior spine. Insertion.—(i) The front part of the inner surface of the tibia, just internal to the tubercle ; (2) the upper part of the deep fascia covering the internal surface of the leg. Structure.—Arising by short, tendinous fibres, the fleshy fibres, which are the longest in the whole body, run parallel to one another inward and downward across the front of the thigh, and after reaching the inner surface of the thigh about the middle, the muscular band runs almost vertically downward to the back of the internal condyle of the femur. At this point the tendon of insertion makes its appearance as an aponeurosis which covers the deep aspect of the muscle and becomes free from fleshy fibres just below the knee joint, where it turns forward and covers the inner surface of the inner tuberosity of the tibia, being separated from it as well as from the tendons of the gracilis and semi-tendinosus by a large bursa. The upper border of this aponeurosis is thick and tendinous and is inserted directly into the bone. The lower part of the aponeurosis, which is of a much more membranous character, is continued downward and forward and blends with the deep fascia of the inner side of the leg, of which it is one of the chief constituents. Nerve-supply.—From the second, third, and fourth branches of the lumbar plexus, by filaments which are usually derived from the middle cutaneous branch of the anterior crural nerve as it pierces the muscle at the junction of its middle and upper thirds. Action.—(1) To flex the thigh, and at the same time rotate it slightly outward and abduct it. (2J To flex the knee, and when the knee is in the bent position it will also help in rotating the leg inward. (3) Being contained in the close-fitting sheath formed by the fascia lata and its deep processes, it will tend when it con- tracts to draw the soft parts upon the inner surface of the thigh forward, and so make tense the inner portion of the fascia lata. (4) Acting from below, it will flex the pelvis upon the thigh. Relations.—In front above lies the fascia lata; internally below lie the fascia lata and internal saphenous vein ; beneath lie the rectus femoris, iliacus, pectineus, SARTORIUS. 369 adductor longus and magnus, vastus internus, and the inner hamstring tendons, the femoral vessels, the anterior crural nerve and its internal saphenous and vastus internus branches. Fig. 287.—Muscles of the Front of the Thigh. Psoas. — Iliacus. — Gluteus medius. — Gluteus minimus. Pectineus. — — Tensor vaginae femoris. Adductor brevis. — Adductor longus. — — Sartorius. Gracilis. — — Rectus femoris. Adductor magnus. — Ilio-tibial band of fascia lata. Vastus externus. Vastus1 internus, Ligamentum patellae, Tendon of sartorius, Variations.—The sartorius is occasionally absent; it may also be divided longitudi- nally. It may have insertions into the fascia lata or the ligamentum patellae. A tendinous intersection sometimes crosses the muscle. THE MUSCLES. 4. PECTINEUS. The pectineus—named from pecten (= pubes) on account of its origin from that bone—is a quadrilateral sheet. Origin.—(1) The ilio-pectineal line between the spine of the pubes and the ilio-pubal eminence; (2) the surface in front of the inner end of this line, and (3) the deep surface of the pubic portion of the fascia lata close to its attachment to the ilio-pectineal line. Insertion.—The back of the femur in a vertical line about two inches long, beginning just behind the lesser trochanter. Structure.—The origin is by fleshy and tendinous fibres intermingled. The fibres then run parallel to one another by a tendinous insertion between the iliacus and the adductor brevis. The direction of the surfaces changes so that that which looks forward above is directed outward below. Nerve-supply.—From the lumbar plexus (through the third and fourth lum- bar nerves), by a branch of the anterior crural nerve, which, after passing behind the femoral artery and vein, enters the muscle about the middle of its external border. When there is an accessory obturator nerve, it passes over the brim of the pelvis to supply this muscle at the upper part of its anterior surface. Occa- sionally the muscle receives a branch upon its deep surface from the anterior di- vision of the obturator nerve. Action.—To flex and at the same time adduct the thigh; as, for example, in crossing the legs, when one thigh is brought forward and inward to place it in front of the other thigh. It is also a slight external rotator. Its predominant action is that of flexion, as is indicated by the fact that it receives the same nerve- supply as the sartorius and ilio-psoas. The tendency which it has to adduct during flexion is counteracted by the slight abduction produced by the sartorius. They will together produce a slight external rotation, as may be observed during the advance of the leg in walking. Relations.—In front, the pubic portion of the fascia lata, the femoral and profunda vessels, and at its insertion the psoas and iliacus muscles; behind, the adductor brevis, obturator externus, hip joint, and obturator nerve. Variations.—Sometimes a slight blending of the lower fibres of the pectineus with the adductor longus has been observed. THE GLUTEAL MUSCLES. These are arranged in three layers. First Layer. The first layer consists of two muscles—the gluteus maximus and the tensor vaginae femoris. 1. GLUTEUS MAXIMUS. The gluteus maximus (Figs. 291, 303)—named from its great size and from the region which it occupies (yXouTos = the buttock)—is a very thick and strong rhomboidal sheet. Origin.—(1) The posterior fifth of the outer lip of the crest of the ilium, and the outer surface of the ilium between the outer lip of the crest and the superior gluteal line; (2) the lumbar aponeurosis between the posterior superior spine of the ilium and the side of the sacrum; (3) the lateral portion of the posterior sur- face of the two last pieces of the sacrum ; (4) the side of the coccyx ; (5) the back of the great sacro-sciatic ligament; (6) in front of its attachment to the ilium a few of its fibres arise from the strong process of the fascia lata which invests the gluteus medius. GLUTEUS MAXIMUS. 3 71 Insertion.—(i) The upper part of the strong aponeurosis of the fascia lata, called the ilio-tibial band; (2) the gluteal ridge of the femur which leads from the lower border of the greater trochanter to the linea aspera; (3) the adjacent part of the tendinous origin of the vastus externus. Structure.—Its origin is almost entirely fleshy, a few tendinous fibres only being intermingled between the coarse bundles which run parallel to one another downward and outward to the aponeurosis of insertion. The upper half of this aponeurosis passes over the outer surface of the great trochanter to be attached to the upper part of the ilio-tibial band. Lower down the insertion consists of short tendinous fibres, which are not only attached to the rough process of the bone but to the adjacent tendon of the vastus externus, while the more superficial fibres still pass on to be attached to the fascia lata. The whole muscle forms a parallel- ogram of which the upper and lower parallel sides are formed by the origin and insertion which run in oblique lines downward and inward, while the outer and inner borders of the muscle running downward and outward form the other two sides of the parallelogram. This muscle is especially remarkable for the large size of the fasciculi in which its fleshy fibres are arranged, and which give the muscle its peculiarly coarse appearance. There are two well-marked bursae in connection with the deep surface of this muscle : the one covering the tuberosity of the ischium, which is partly covered by the muscle and partly projects from the middle of its lower border in such a way that when the thigh is extended it intervenes between the muscle and the prominence of bone, and when the thigh is flexed it lies between the tuberosity of the ischium and the subcutaneous fat. The second is a large, often multilocular cavity which separates the outer surface of the great trochanter from the aponeu- rosis of insertion of the upper part of the muscle. A small bursa is also occasion- ally found between the lower part of the muscle and the tendon of the vastus externus. Nerve-supply.—From the sacral plexus (through the fifth lumbar and the first and second sacral nerves), by means of the inferior gluteal branches of the small sciatic nerve which enter the deep surface of the muscle close to its inferior and internal border. Action.—To extend the hip joint. The upper part of the muscle, passing over the great trochanter, is placed at a considerable distance from the axis of movement which passes through the centre of the hip joint. A similar object is obtained by the insertion of the lower fibres of the muscle at some distance down the back of the femur. The whole muscle, therefore, is able to act as an extensor of the hip joint with much less mechanical disadvantage than is usual in the body. The gluteus maximus is not used in the movements of extension which require but little muscular power, such as those which draw the thigh backward in walking; for this purpose the contraction of the hamstring muscles at the back of the thigh is alone employed. Where, however, a greater effort is required, as in ascending a hill or in running and leaping, the gluteus maximus acts with great power. It has some influence as an external rotator. With respect to abduction and adduction, the action of the muscle is neutral. Acting alone, its upper fibres will assist in the former, and its lower fibres in the latter movement. By means of the ilio-tibial band it makes tense the outer portion of the fascia lata and is able to exert some force in the extension of the knee, especially when that movement is nearly completed. Taking its fixed point from below, the gluteus maximus is a powerful extensor of the pelvis and in some degree of the lower part of the spine, e.g., in rising from the stooping position or where the trunk in a sitting posture is drawn forcibly backward, as in the action of rowing. The influence which it has upon the back by means of its attachment to the lumbar aponeurosis is shown by the great pain which is felt in rising from the stooping position when there is any inflammation of the fasciae in this region, as in lumbago. Relations.—Behind, the thick adipose tissue of the buttock and the fold which forms its lower limit, and numerous cutaneous nerves; in front, the gluteus medius, pyriformis, gemelli and obturator interims, quadratus femoris, adductor magnus, biceps, semi-tendinosus and semi-membranosus, the gluteal, sciatic, and THE MUSCLES. pudic vessels, the great and small sciatic, the pudic and internal obturator nerves the two sacro-sciatic ligaments, the tuber ischii, and greater trochanter. Variations.—These are rare. Occasionally a bilaminar arrangement has been observed. 2. TENSOR VAGINAE FEMORIS. The tensor vaginae femoris (Figs. 287, 303)—named from its function of making tight the fascia lata, or sheath of the thigh (= vagina femoris)—is an elongated, four-sided sheet. Origin.—(1) The front of the outer lip of the crest of the ilium; (2) the upper part of the notch between the anterior superior and the anterior inferior spines of the ilium; (3) the inner surface of the fascia lata, by which it is closely invested. Insertion.—The fascia lata about one-fourth of the way down the outer side of the thigh. Structure.—The muscle consists of parallel fleshy fibres which arise by a short tendinous sheet, pass obliquely downward, outward, and backward, and are inserted between two layers of the upper part of the strong aponeurosis of the fascia lata on the outside of the thigh called the ilio-tibial band, which also gives attach- ment to the majority of the fibres of the gluteus maximus. The two muscles meet by their adjacent borders a little below the upper part of the greater trochanter at an angle of about 6o°. As they pass upward, the two divisions of the fascia lata form a strong sheath for the muscle. Nerve-supply.—Through the fourth and fifth lumbar nerves, and the first sacral, by the terminal branch of the superior gluteal nerve which enters the muscle about the middle of its deep surface near its posterior border. Action.—To abduct and rotate inward the thigh, and, taking its fixed point from below, to support the pelvis and to rotate the other side of it forward. Acting with the gluteus maximus, it will draw upward the ilio-tibial band, the obliquity of its fibres enabling it to counteract the tendency of that muscle to draw the band backward. The chief consequence of this traction upon the ilio-tibial band will be to assist in the latter part of the extension of the leg, by the drawing upward of the external tuberosity of the tibia. Relations.—Superficially, the fascia lata and the origin of the sartorius; deeply, the deeper layer of the fascia lata, the gluteus medius, the upper part of the rectus femoris and the vastus externus, with some of the branches of the external circumflex artery. Second Layer. The second layer consists of one muscle— GLUTEUS MEDIUS. The gluteus medius (Fig. 288)—named from its size and position, which are intermediate between those of the great and small gluteal muscles—is a strong, triangular sheet. Origin.—(1) The anterior four-fifths of the outer lip of the crest of the ilium ; (2) the outer surface of the ilium, bordered above by the middle portion of the outer lip of the crest of the ilium, and in the posterior fifth by the superior gluteal line, below by the middle gluteal line; (3) the strong process of the fascia lata which invests the outer surface of the muscle and separates it behind from the gluteus maximus; (4) the intermuscular septum which intervenes between it and the gluteus minimus just below the anterior superior spine of the ilium. Insertion.—The well-marked oblique impression extending from the posterior superior to the anterior inferior angle on the outer surface of the greater trochanter. Structure.—Arising by fleshy and tendinous fibres intermingled, the muscle GLUTEUS MEDIUS—GLUTEUS MINIMUS. 373 converges fanwise upon both surfaces of a strong, flat tendon which is visible rather higher up on the deep than the outer surface of the muscle. The front part of the muscle is stronger, and it gradually decreases in thickness toward its pos- terior edge. A bursa is contained between the deep portion of the tendon and the triangular space that lies in front of the impression upon the outer surface of the greater trochanter. Nerve-supply.—From the fourth and fifth lumbar nerves, and the first sacral nerve by branches of the superior gluteal nerve which enter the deep surface of the muscle near the middle of its posterior border. Action.—To abduct the hip joint. It will also by its thicker and stronger anterior fibres rotate the thigh inward. Its posterior fibres, on the other hand, which are not so strong, will tend slightly to rotate the thigh outward. Acting from below, it tends to support the pelvis upon the femur and to approximate the crest of the ilium to the great trochanter. This is by far the most important and frequent of its actions. In walking, if it were not for the powerful contraction of the gluteus medius and its associated muscles, the gluteus minimus and the tensor vaginae femoris, the pelvis would not be held firm upon the upper part of the thigh when one leg is upon the ground and the other is being advanced in the forward step. In fast walking the rotatory action of the muscle comes into play, for not only does the gluteus medius of the limb which is resting upon the ground support the pelvis by drawing downward the crest of the ilium, but, by drawing backward the front portion of that crest, it throws forward the opposite side of the pelvis and increases the length of the stride. Relations.—Superficially, the fascia lata, gluteus maximus, and tensor vaginae femoris; deeply, the gluteus minimus, superior gluteal vessels and nerve, and the great trochanter. Variations.—Sometimes a partially distinct bundle of fibres is inserted into the front of the upper border of the greater trochanter. A slip may be given from the lower border to the pyriformis. Third Layer. The third layer consists of one muscle—the gluteus minimus—which is con- tinuous with the external rotators which form the next group. GLUTEUS MINIMUS. The gluteus minimus (Fig. 290)—named from its position and smaller size—is a thick, triangular sheet. Origin.—(1) The outer surface of the ilium between the middle and inferior gluteal lines ; (2) a fibrous septum which intervenes between its fibres and those of the gluteus medius below the anterior superior spine ; (3) the front of the capsule of the hip joint. Insertion.—The well-marked vertical impression which forms the anterior border of the greater trochanter. Structure.—From the fleshy origin the fibres converge fanwise upon the deep surface of the tendon which makes its appearance about half-way down the muscle upon the front part of its outer surface and covers the whole of the outer surface of the muscle from this point down to its insertion. By its anterior border this muscle is closely blended with the anterior border of the gluteus medius and with some of the ligaments of the hip joint. Like the preceding muscle, it is also much thicker and stronger in front. Nerve-supply.—From the same sources as the preceding by the superior gluteal nerve, which distributes filaments to the middle of its outer surface near its posterior border. Action.—The same as the preceding: viz., to abduct and rotate inwrard the hip joint; and when it takes its fixed point from below, as is most usually the 374 THE MUSCLES. case, to flex the pelvis laterally and at the same time to rotate the other side forward. Relations.—Superficially, the gluteus medius, the superior gluteal vessels and nerve; deeply, the capsule of the hip joint and posterior head of the rectus femoris. Variations.—The front part of the muscle may be separate from the rest. It occa- sionally sends slips to the adjacent muscles. THE EXTERNAL ROTATORS OF THE THIGH. This group consists of six somewhat short muscles, which run transversely from the pelvic bones to the femur, and which follow immediately after the lower fibres of the gluteus minimus—viz., the pyriformis, the obturator internus with the two gemelli, the quadratus femoris, and the obturator externus. 1. PYRIFORMIS. The pyriformis—named from its pear shape (pints == pear)—is a thick, trian- gular sheet. Origin.—(i) The side of the front of the sacrum between the first, second, third, and fourth foramina; (2) the deep surface of the great sacro-sciatic ligament; (3) the posterior border of the innominate bone at the upper part of the great sacro-sciatic notch. Insertion.—A small facet upon the inner aspect of the anterior part of the upper border of the greater trochanter. Structure.—The greater part of the muscle arises by three fleshy slips on the ridges of bone between, and external to, the anterior sacral foramina. From this origin, which receives accessory slips of small size from the great sacro-sciatic ligament and the upper portion of the great sacro-sciatic notch, the fibres converge as they pass transversely outward and somewhat backward through the great sacro-sciatic foramen. The tendon is first visible upon the deep aspect of the muscle, and it becomes free near the posterior border of the greater trochanter. Shortly before its insertion it is closely blended with the tendon of the obturator internus muscle. Nerve-supply.—From the sacral plexus by small branches which pass from the second sacral nerve into the anterior surface of the muscle near its origin. Action.—To rotate the thigh outward. When the thigh is fixed, it will rotate the pelvis so that the face is turned to the opposite side; if the thigh be flexed, the pyriformis will abduct it. Relations.—In front, the sacral plexus and rectum, the back of the hip joint, and some of the branches of the internal iliac artery; behind, the gluteus maximus; above, the gluteus medius and minimus, the superior gluteal vessels and nerve; below, the coccygeus, the lesser sacro-sciatic ligament and gemellus superior, the sciatic and pudic vessels, and most of the branches from the sacral plexus. Variations.—The pyriformis may be absent. It is often divided by a part of the great sciatic nerve into two muscles, and sometimes into three. It may be more or less blended with the gluteus medius or minimus above, and the superior gemellus below. 2, 3, and 4. OBTURATOR INTERNUS AND GEMELLI. The obturator internus and gemelli form really a single muscle, the greater part of which arises inside the pelvis; while the gemelli form two accessory slips which join it from the margin of that cavity. The obturator internus—named from the fact that it arises from the mem- OBTURATOR INTERNUS AND GEMELLI. 375 brane which closes up the obturator foramen, and from its position within the pelvis—is a somewhat triangular sheet, or rather, perhaps, it should be described as the sector of a circle, for its origin within the pelvis is bounded by a curved line like a part of the circumference of'a circle. Fig. 288.—The External Rotators and the Hamstring Muscles. Gluteus medius. Gemellus superior. Pyriformis Gemellus inferior. Quadratus femoris. Obturator internus. Gluteus maximus Adductor magnus. Gracilis. Vastus externus. Biceps Semi-tendinosus. Semi-membranosus. Short head of biceps, Crureus, Plantaris, Sartorius. Semi-tendinosus. Gastrocnemius, Origin.—The whole of the interior of that part of the pelvis which is formed by the innominate bone: viz., (i) The back of the body and descending ramus of the os pubis, and of the ascending ramus of the ischium; (2) the whole of the 376 THE MUSCLES. inner surface of the obturator membrane; (3) the broad surface of bone behind the foramen, corresponding to the acetabulum on the exterior; (4) the outer surface of the pelvic and obturator fasciae. These extend from the ilio-pectineal line above to the great sacro-sciatic foramen behind, and to the spine and tuber- osity of the ischium below. Insertion.—The inner aspect of the upper border of the greater trochanter at the point where it unites with the upper border of the neck of the femur. Structure.—The muscle arises fleshy from the whole of the interior of the pouch-like cavity formed by the pelvic and obturator fasciae internally and the wall of the pelvis externally, which opens backward and downward at the lesser sacro-sciatic foramen. From this extensive origin the fibres converge downward and backward upon a broad, tendinous expansion which begins about one inch above the lesser sacro-sciatic foramen upon the outer surface of the muscle. This expansion is corrugated into four or five folds, which are separated from the cartilaginous lining of the lesser sacro-sciatic notch by a bursal cavity which allows of the smooth play of the tendon upon the bone. This cartilage presents corresponding grooves for the folds of the tendon. After passing through this foramen the tendon changes its course, and is directed transversely outward and forward to its insertion. The fleshy fibres extend upon the inner, which has now become its posterior surface for about half the distance from the notch to the facet upon the greater trochanter. For a short distance before its insertion it is intimately connected with the tendon of the pyriformis. Nerve-supply—From the first and second sacral nerves of the sacral plexus by a special nerve which, after passing through the lesser sacro-sciatic notch, is distributed to the muscle, entering its inner surface near its upper border and close to the lesser sacro-sciatic foramen. The gemellus superior—named from gemellus = a twin, because it is the upper of the two twin muscles which nearly surround the tendon of the obturator internus at its point of emergence from the pelvis—is a somewhat triangular sheet curved upon itself to embrace the rounded tendon of the obturator internus. Origin.—(1) The outer surface of the spine of the ischium; (2) the upper half of the outer edge of the lesser sacro-sciatic notch. Insertion.—The upper border and the anterior surface of the obturator internus tendon, about one inch from its insertion. Structure.—Arising fleshy from the bone at the margin of the lesser sacro- sciatic foramen, the muscular fibres converge slightly and form a sheet which is curved upon itself so as to fit round the upper border and anterior aspect of the obturator internus tendon, with which, after a course of about two inches in length, it blends. Nerve-supply.—The first and second nerves of the sacral plexus by a small special branch which enters the muscle at the upper part of its anterior surface near its origin. The gemellus inferior—the lower of these twin muscles—is also triangular in shape, but is somewhat broader and stouter than its fellow. Origin.—(1) The upper part of the inner border of the tuber ischii, and (2) the lower half of the outer edge of the lesser sacro-sciatic notch. Insertion.—The lower border and anterior surface of the tendon of the obturator internus, about one inch from its attachment to the greater trochanter. Structure.—Its fibres, arising fleshy from the lower half of the outer border of the lesser sacro-sciatic notch, converge and form a sheet which wraps round the lower part of the anterior surface of the tendon of the obturator internus. The two gemelli therefore together form an envelope which embraces the whole of the tendon of the obturator internus after its emergence from the pelvis, with the exception of a part of its posterior surface. Nerve-supply.—From the sacral plexus (through the fifth lumbar and first sacral nerves), by filaments from the special nerve to this muscle and the quadratus femoris, which enter the upper part of its anterior surface near its origin. Action.—The obturator internus with its two satellites, the gemelli, powerfully rotates the femur outward. It should be observed that, although the fibres are QUADRATUS FEMORIS. 377 mostly directed backward and downward within the pelvis, the action of the muscle is really determined by the outward and slightly forward direction of the tendon outside the pelvis ; and the notch upon the bone plays the part of a pulley in changing the direction of the force. Besides its action as an external rotator, the muscle will be able to assist abduc- tion when the thigh is bent through a right angle. Relations.—The obturator internus in the pelvis is in contact externally with the innominate bone and obturator membrane ; above, with the obturator artery and nerve; internally, with the pelvic and obturator fasciae, the levator ani, the pelvic viscera, and the pudic vessels and nerve. Outside the pelvis the tendon of the obturator internus, with the gemelli, is in contact, in front with the capsule of the hip joint and the tendon of the obturator externus; behind, with the gluteus maximus, great sacro-sciatic ligament, the sciatic vessels and nerves; above, with the pyriformis and the structures which come out of the pelvis below it; below, with the quadratus femoris and a branch of the internal circumflex artery. Variations.—One or other of the gemelli may be absent, but more frequently the upper one. An accessory slip to the obturator internus has been observed coming from the third piece of the sacrum. 5. QUADRATUS FEMORIS. The quadratus femoris—named from its square shape and its insertion into the femur—is a four-sided sheet. Origin.—The upper part of the outer border of the tuber ischii. Insertion.—The vertical ridge which begins just above the middle of the posterior intertrochanteric line of the femur, and is called the “ linea quadrati.” Structure.—Its fibres are fleshy and run parallel to one another almost hori- zontally outward and slightly forward. Nerve-supply.—From the sacral plexus (through the fifth lumbar and first sacral nerve) by a special branch which, after furnishing filaments to the inferior gemellus, enters the muscle near the upper part of its anterior surface close to its origin. Action.—It approximates the posterior border of the great trochanter to the tuber ischii, and so assists powerfully in the external rotation of the femur. Relations.—Behind, the gluteus maximus and the two sciatic nerves; in front, the obturator externus and the termination of the internal circumflex artery. Above is the inferior gemellus, and below the adductor magnus. Variations.—This muscle is not unfrequently absent. 6. OBTURATOR EXTERNUS. The obturator externus is a strong external rotator of the thigh, but it is also an adductor, and on account of its nerve-supply and position it is better described in that group of muscles. THE ADDUCTORS. The adductor muscles form a distinct group on the inner side of the thigh, and are all supplied by the obturator nerve with the exception of a small part of the adductor magnus. They consist of the adductor longus, adductor brevis, adductor magnus, gracilis, and] obturator externus. 378 THE MUSCLES. i. ADDUCTOR LONGUS. The adductor longus—so named from its action and its length compared with that of its immediate neighbor—is a thick, triangular sheet. Fig. 289.—The Deep Muscles of the Front of the Thigh. Rectus tendon Obturator externus, Gluteus medius. Gluteus minimus. Adductor longus, Adductor magnus Adductor brevis. Adductor longus, Vastus internus Vastus externus. Vastus internus. Rectus femoris Biceps. Ligamentum patellae Ilio-tibial band Origin.—A rounded impression on the front of the body ot the os pubis immediately below the crest and angle. Insertion.—(i) The lower two-thirds of the inner lip of the linea aspera (in ADDUCTOR LONG US. 379 the middle third of the thigh), and (2) the adjacent internal intermuscular septum. Structure.—Arising by a strong, rounded tendon, which extends about two inches downward upon the inner border of the muscle, the fleshy fibres diverge in a fan-shaped expansion, and are inserted by short, tendinous fibres which blend behind with those of the adductor brevis and adductor magnus. Fig. 290.—The Deep Muscles of the Back of the Thigh. Gluteus minimus. Obturator externus Obturator internus. Gluteus maximus. Adductor magnus. Vastus externus. Short head of biceps. Crureus, Vastus internus, Tendon of biceps Nerve-supply.—From the third and fourth nerves of the lumbar plexus, by branches from the anterior division of the obturator nerve which enter the muscle on the upper part of its posterior surface rather below its middle. Action.—To adduct and flex the femur, and at the same time to rotate it outward. 380 THE MUSCLES. Relations.—In front, the fascia lata, sartorius, vastus interims and femoral vessels ; behind, the adductor brevis and magnus, the profunda vessels, and obturator nerve ; its upper border touches the pectineus. Variations.—The adductor longus may arise by two heads, the outer being attached to the crest of the pubes, and separate from the ordinary head, which arises below the angle. Occasionally the muscle is divided by the passage of vessels into an upper and a lower portion. The adductor brevis—named from its action and its size as compared with the preceding muscle—is a thick, quadrilateral sheet. Origin.—The body and the descending ramus of the os pubis, below, and somewhat external to, the origin of the adductor longus. Insertion.—The inner lip of the linea aspera in its upper half, extending from just below the lesser trochanter to about the middle of the back of the femur. Structure.—Arising by short tendinous fibres, the muscle diverges into a fan- shaped fleshy expansion, which ends in short tendinous fibres blending with those of the adductor longus and adductor magnus. Nerve-supply.—From the third and fourth nerves of the lumbar plexus by the superficial branch of the obturator nerve, which sends filaments to the ante- rior surface of the muscle near the lower part of its upper border. Sometimes, however, it derives its nerve-supply from the deeper division of the obturator nerve, and, in that case, the nerves enter the muscle from behind. Action.—Like the preceding, it is an adductor and rotator outward of the femur, but it will not assist so powerfully in flexion. Relations.—In front, the pectineus, adductor longus, the profunda vessels, and superficial branch of the obturator nerve ; behind, the obturator externus and adductor magnus, and the deep branch of the obturator nerve. 2. ADDUCTOR BREVIS. Variations.—It is sometimes divided into an upper and a lower portion. Occasion- ally it joins above with the obturator externus. 3. ADDUCTOR MAGNUS. The adductor magnus—named from its action and its great size—is a thick, fan-shaped sheet, forming a right-angled triangle, the right angle of which is con- tained between the side corresponding to the insertion of the muscle at the back of the femur and the side formed by the free upper border of the muscle. Origin.—(i) The lower part of the outer border of the tuber ischii; (2) the outer surface of the ascending ramus of the ischium near its inner border ; (3) the front of the outer surface of the descending ramus of the pubes. Insertion.—(1) The back of the femur, in a line beginning at the lower extremity of the linea quadrati, and extending along the inner border of the gluteal ridge and the middle of the linea aspera down to its bifurcation ; (2) the adductor tubercle on the upper and posterior part of the internal condyle ; (3) the lower part of the internal intermuscular septum. Structure.—Its origin and insertion are by short tendinous fibres, with the exception of the insertion of the bundle of fibres which passes from the tuber ischii to the adductor tubercle. These arise by a long tendon above, and again become tendinous three or four inches above the knee joint, so as to form a long and con- spicuous tendon on the lower part of the inner border of the muscle. Between this part of the insertion of the muscle and the linea aspera, the fibres are attached to the back of the internal intermuscular septum and to a tendinous arch which allows of the passage of the femoral artery and vein from Hunter’s canal into the upper part of the popliteal space. Between the origin and insertion the fibres diverge ; the anterior fibres of origin passing horizontally outward to their inser- tion into the upper part of the back of the femur, while the fibres which arise behind pass vertically downward between the tuber ischii and the internal con- . ADD UCTOR MA GNUS— GRA CIL1S. 381 dyle. Moreover, the muscle is twisted upon itself so that the surface w'hich above looks inward and rather backward is directed forward below. A deep longitudinal groove is thus formed upon the upper part of the back of the muscle, in which lie the hamstring muscles and the great sciatic nerve. The upper part of the muscle, which arises in front, and is inserted into the inner border of the gluteal ridge, forms a triangular sheet, usually separate from the rest, and sometimes described as a distinct muscle, the adductor minimus. In addition to the opening for the femoral vessels, the muscle is pierced close to the bone by the perforating arteries and the terminal branch of the profunda femoris. Upon its anterior surface it receives a membranous expansion from the vastus internus, which passes inward beneath the sartorius to the adductor longus and magnus, forming the anterior wall of a sort of tunnel wdiich contains the femoral vessels in the middle third of the thigh, and is called Hunter’s canal. N erve-supply.—Chiefly from the third and fourth nerves of the lumbar plexus by the deep division of the obturator nerve wrhich supplies the muscle upon the outer part of its anterior surface. The lower fibres of the muscle, however, are supplied upon their posterior surface by the great sciatic nerve, a branch of the sacral plexus. Action.—This muscle is the most powerful of the adductors. The upper three-fourths of its fibres will also rotate outward the femur, while that part of the muscle which arises from the tuber ischii and is inserted into the inner condyle will tend slightly to rotate the thigh inward, and will at the same time extend as wTell as adduct the thigh. Duchenne suggests that this is the part of the muscle which equestrians should especially develop. Otherwise the adduction of the thighs in gripping the saddle is apt to throw out the toes, which is ungainly, and, if the rider have spurs on, may lead to unpleasant consequences. Relations.—In front lie the adductor brevis and longus, and lower down the vastus internus. Behind are the hamstring muscles, the gluteus maximus, and the great sciatic nerve. At its upper border are the quadratus femoris and obturator externus. Along its inner border lie the gracilis and part of the sartorius. Variations.—The posterior part of the muscle may form a distinct slip. Accessory bundles from the semi-membranosus or biceps may join the lower tendon. The upper border of the muscle may be blended with the quadratus femoris. The gracilis—named from its form {gracilis = slender)—is long and ribbon- shaped. Origin.—The inner edge of the anterior surface of the body and descending ramus of the os pubis from about the middle of the symphysis to the junction of the rami of the pubes and ischium. Insertion.—The inner surface of the tibia below its inner tuberosity, between the insertions of the sartorius and the semi-tendinosus. Structure—Arising by a broad and thin aponeurosis, the muscular fibres pass down the inner surface of the thigh almost parallel to one another, but with a slight convergence, so that the muscle, in descending, increases in thickness as it diminishes in breadth. About two inches above the inner condyle it becomes a rounded, flattened tendon. This runs behind the inner condyle, and, after form- ing one of the two hamstring tendons, which can be easily felt at the inner border of the popliteal space, it passes forward to be inserted in a slightly expanded form below the inner tuberosity. A few fibres pass from its lower border to the deep fascia of the leg. Nerve-supply.—From the third and fourth nerves of the lumbar plexus by a branch from the superficial division of the obturator nerve which enters the deep surface of the muscle above its middle. Action.—To adduct the thigh and flex the knee. When the knee is flexed, it will help in rotating the leg inward. 4. GRACILIS. 382 THE MUSCLES. Relations.—It lies superficially in its whole course under cover of the fascia lata. Upon its deep surface lie the adductor brevis and magnus, and lower down the semi-membranosus muscle. It has in front of it the sartorius muscle, which overlaps it slightly at the lower part of the thigh, and behind it is the tendon of the semi-tendinosus. The internal lateral ligament of the knee and a large bursa lie beneath its tendon. 5. OBTURATOR EXTERNUS. The obturator externus (Figs. 286, 289, 290)—named from its attachment to the obturator membrane upon its outer surface—is a triangular sheet. Origin.—(1) The inner half of the anterior surface of the obturator mem- brane ; (2) the descending ramus of the os pubis immediately internal to the foramen ; (3) the ascending ramus of the ischium internal to the foramen. Insertion.—The digital fossa upon the inner surface of the great trochanter. Structure.—It is a fan-shaped, triangular muscle, which arises fleshy from the adjacent surfaces of bone and membrane, in a curve which is convex forward and inward. From this wide origin the fibres converge outward, and end below the acetabulum in a rounded tendon which passes behind and in close contact with the capsule of the joint to its insertion in the digital fossa. Not unfrequently a small portion of the muscle is separated at its upper border from the rest by one or both of the divisions of the obturator nerve. Nerve-supply.—From the third and fourth nerves of the lumbar plexus by the deep division of the obturator nerve which distributes filaments to the deep surface of the muscle as it is passing through it. Action.—To adduct and rotate outward the thigh. Relations.—Behind, the obturator vessels, and at its insertion the quadratus femoris; in front, the psoas muscle, the pectineus, and adductor brevis; above, the obturator nerve, one or both branches of which perforate it, and more exter- nally the capsule of the hip joint. THE HAMSTRING MUSCLES. The hamstring muscles form a group at the back of the thigh, separated by intermuscular septa from the vastus externus on the outer, and the adductor magnus on the inner side. They consist of the biceps, semi-tendinosus, and semi- membranosus, and are supplied by the great sciatic nerve. Like the gluteus maximus their action is to extend the hip. 1. BICEPS FEMORIS. The flexor biceps femoris (Figs. 288, 290)—named from its two heads— consists of two parts: the longer head being somewhat fusiform, and the shorter a triangular sheet. Origin.—The long head from (1) the internal and posterior facet at the back of the tuber ischii by a tendon common to it and the semi-tendinosus; (2) the lower part of the great sacro-sciatic ligament. The short head from (1) the outer lip of the linea aspera from a point just above the middle of the bone down to the bifurcation ; (2) the upper two-thirds of the outer division of the linea aspera; (3) the external intermuscular septum. Insertion.—(1) A fossa below and in front of the styloid process of the head of the fibula; (2) the deep fascia covering the peronei muscles; (3) the outer tuberosity of the tibia. Structure.—The origin of the long head is by a short tendon which is con- tinued down to the middle of the thigh by a septum which divides this muscle from the semi-tendinosus. From this tendon and the outer surface of the septum the muscular fibres arise in penniform fashion and form a fusiform belly, which BICEPS EE MOP IS—SEMI- TENDINOSUS. 383 receives at the junction of the middle and lower thirds of the thigh the thick sheet of muscular fibres derived from the short outer head. The tendon commences upon the posterior outer surface of the muscle near its outer border, about the middle of the thigh. At the back of the external condyle the fleshy fibres cease. The rounded tendon here widens into a thick aponeurosis, which embraces the anterior portion of the external lateral ligament at the point of its insertion into the outer and anterior facet of the head of the fibula. Between this tendon and the external lateral ligament is a bursa. From the borders of the tendon at this point a thinner aponeurosis is given off to the outer tuberosity of the tibia in front and the deep fascia of the leg behind. Nerve-supply.—From the first, second, and third nerves of the sacral plexus by the great sciatic nerve which sends branches to the anterior and inner surfaces of the muscle about the middle of the thigh. The short head of the biceps receives its supply from the external popliteal nerve. Action.—To extend the hip and flex the knee. Its shorter head flexes the knee only. When the knee is flexed, both heads will unite in rotating the leg outward. When the knee is extended, the long head will have a slight influence in rotating the hip outward; Acting from below, the long head will assist in raising the body from the stooping position. Relations.—Behind, the plantaris, the outer head of the gastrocnemius, gluteus maximus, fascia iata, and the small sciatic nerve. In front, the tendon of the semi-membranosus, the adductor magnus, and the great sciatic nerve. Upon its inner border lie the semi-tendinosus, semi-membranosus, and the external popliteal nerve. Beneath the lower tendon is a bursa which separates it from the external lateral ligament of the knee joint. Variations.—The short head of the biceps may be absent. Accessory heads may be derived from the tuber ischii, the upper part of the linea aspera, the fascia lata, or the inner surface of the tendon of insertion of the gluteus maximus. It may send a slip to the gastrocnemius. 2. SEMI-TENDINOSUS. The semi-tendinosus (Fig. 288)—named from the long tendon which forms the lower half of the muscle—is fusiform and somewhat flattened. Origin.—By a tendon which is common to it and the preceding muscle, from the internal and posterior of the facets at the back of the tuber ischii. Insertion.—(1) The upper part of the inner surface of the tibia below and behind the insertion of the gracilis ; (2) the deep fascia of the inner side of the leg. Structure.—The rounded and somewhat flattened tendon of about two inches in length is succeeded by a fusiform mass of muscular fibres, which end just below the middle of the thigh in a flattened cylindrical tendon. This runs directly down- ward along the inner side of the popliteal space, where it can easily be felt be- neath the skin, behind and external to the tendon of the gracilis, in company with which it passes downward and forward behind the internal condyle to its insertion below the inner tuberosity. From the lower border of the flattened tendon an aponeurosis passes downward to the deep fascia of the leg. The fleshy part of the muscle is crossed about its middle by a thin tendinous intersection running down- ward and outward. Nerve-supply.—From the first, second, and third nerves of the sacral plexus by means of branches from the great sciatic nerve which enter the outer part of the deep surface of the muscle two or three inches below the tuber ischii. Action.—To extend the hip and flex the knee, and when the knee is flexed to rotate the leg inward. Acting from below, it lifts up the body from the stooping position. Relations.—Behind, the gluteus maximus and fascia lata ; on its outer side the biceps; in front, the semi-membranosus, adductor magnus, and near the knee the gracilis, sartorius, and the inner head of the gastrocnemius. The large bursa 384 THE MUSCLES beneath the sartorius tendon also wraps round the upper part of the tendon of the semi-tendinosus, and separates it from the internal lateral ligament of the knee joint. 3. SEMI-MEMBRANOSUS. The semi-membranosus (Fig. 288)—named from the broad, membrane-like aponeurosis which forms the upper third of the muscle—is strong, flattened, and fusiform. Origin.—The anterior and outer of the facets upon the back of the tuber ischii. Insertion.—(1) The lower part of the posterior extremity of the groove upon the back and inner side of the inner tuberosity of the tibia ; (2) by a band of fibres which pass upward and outward to the upper and back part of the external condyle of the femur, and blend with the posterior ligament of the knee joint; (3) by a broad expansion which, passing downward and outward from its insertion into the inner tuberosity to the oblique line at the back of the tibia, forms the aponeurosis which invests the posterior surface of the popliteus; (4) a few fibres pass downward and forward from the lower border of its tibial insertion to blend with the internal lateral ligament. Structure.—The upper part of the muscle consists of a strong, flat tendon, about three-quarters of an inch broad, which extends along the outer border of the muscle to the middle of the thigh. The tendon of insertion is not quite so broad but much thicker, and reaches up on the inner border of the muscle also as high as the middle of the thigh. Between these two tendons the muscular fibres, which are comparatively short, pass downward and inward, beginning upon the upper tendon about four inches below the tuber ischii, and ending upon the lower tendon close to the upper part of the inner condyle. The muscle has therefore a very distinctly penniform arrangement, but it is peculiar in this respect that the fleshy fibres are at each extremity attached to the tendon, and are not, as is usually the case, at one extremity attached to the bone. It is also unusual for a muscle to have so long a tendon at its proximal end. One effect of this arrangement is to allow of the free action of the long head of the biceps which crosses over this part of the semi-membranosus. Otherwise the swelling of the fibres of the biceps during contraction would have pressed upon and interfered with the action of the semi-membranosus, which usually contracts at the same time. Nerve-supply.—From the first, second, and third nerves of the sacral plexns by the great sciatic nerve which sends branches to the deep surface of the muscle about the middle of the thigh. Action.—To strongly extend the hip and to flex the knee. When the knee is flexed it will also assist in the internal rotation of the leg, but with less mechanical advantage than the semi-tendinosus and gracilis, as its line of action is so near to the axis of movement. Like most penniform muscles, the semi-membranosus is very powerful, as is shown by the thickness of its tendons. This strength is necessitated by the fact that its line of action is so much nearer to the axis of movement both in flexion and rotation inward of the knee. Like the other muscles which arise from the tuber ischii, it will co-operate powerfully in raising the body from the stooping position, this prominence of bone forming the short arm of the lever by which the trunk is raised. This group of muscles affords a good example of the peculiar action obtained by long muscles passing over two joints. If all three muscles were to remain passive, like so many ligaments, it is obvious that on flexion of the hip joint by means of the ilio-psoas and other muscles, the hamstrings would ensure the simultaneous flexion of the knee ; or, again, on extension of the knee by the action of the powerful muscles of the front of the thigh, the hamstrings would produce a corresponding extension of the hip joint. Seeing, however, that these hamstrings are not passive, but that they contract powerfully at the same time in many of these movements, it follows that in flexion of the hip in such movements as those of running, the knee is at the same time flexed with increased rapidity; QUADRICEPS EXTENSOR FEMORIS. 385 and again, when the knees are extended by the powerful contraction of the quadriceps muscle, the simultaneous action of the hamstring muscles will produce a still more rapid elevation of the trunk. Relations of the semi-membranosus.—Behind, the gluteus maximus, biceps, and semi-tendinosus; in front, the adductor magnus, posterior ligament of knee, and the popliteus. Along its outer border lies the great sciatic nerve, and just before its insertion the inner head of the gastrocnemius hooks round this border, being separated from it by a bursa which communicates with the knee joint. There is also usually a small bursa between its tendon and the back of the inner tuberosity of the tibia. Variations.—The semi-membranosus has occasionally been deficient, or only repre- sented by a thin musculo-tendinous band. It has also been found double. ANTERIOR MUSCLES OF THE THIGH. This group consists of the sartorius and the quadriceps extensor femoris. 1. SARTORIUS. This muscle has already been described. 2. QUADRICEPS EXTENSOR FEMORIS. The quadriceps extensor femoris (Figs. 287, 289), as its name implies, consists of four heads. Of these, one, the rectus, arises from the innominate bone; and the three others, the vastus externus, vastus internus, and crureus, from the femur; while the common tendon is inserted into the upper border and sides of the patella. (a) Rectus Femoris. The rectus femoris—named from its long, straight course—is strong, fusi- form, and flattened from before backward ; it arises by an anterior and posterior head. Origin.—Anterior head, from the front of the anterior inferior spine of the ilium ; posterior head, from the upper surface of the rim of the acetabulum just external to the attachment of the capsular ligament. Insertion.—The front of the upper border of the patella. Structure.—This muscle consists of two strong tendinous expansions joined by fleshy fibres. The upper expansion is formed above by the union of the two tendinous heads in a small arch, which is intimately connected with the capsule of the hip joint. From this arch the tendinous expansion descends upon the front of the muscle as far as the middle of the thigh, getting thinner and narrower as it descends. The tendon of insertion begins upon the back of the muscle also about the middle of the thigh, and soon expands into a broad aponeurosis which covers the back of the muscle at its lower end; about three inches above the patella, it becomes free of muscular fibres, and forms a strong tendinous band which is inserted into the upper border of the patella. The fleshy fibres pass from the back and sides of the upper expansion to the front and sides of the tendon of insertion. Seen from the front, these fleshy fibres appear to diverge on both sides from the upper expansion, and, after passing round the border of the muscle, they converge upon the tendon of insertion so as to give the muscle a bipenniform appearance. Nerve-supply.—From the lumbar plexus (through the second, third, and fourth lumbar nerves), by the anterior crural nerve which sends filaments to the posterior aspect of the muscle in the upper half of its course. Action.—To assist in the powerful extension of the knee by the quadriceps. It will also help in flexion of the hip ; and it will be a powerful agent in pre- 386 THE MUSCLES. venting dislocation of the head of the femur. When the hip joint is flexed, the muscle will act chiefly from its posterior head ; but when the hip is extended, the anterior head of the muscle will act with more power. Relations.—In front lie the sartorius, tensor vaginse femoris, and the fascia lata; behind, it lies on the hip joint and the crureus muscle; upon its inner border above is the iliacus; and outside it lie the gluteus medius and minimus. (<$) Vastus Externus. The vastus externus—named from its great size and its position upon the outer surface of the thigh—is a thick, rhomboidal sheet. Origin.—(i) The upper half of the anterior intertrochanteric line and the front of the upper part of the femur along the anterior border of the great trochanter; (2) a horizontal line which forms the lower border of the great trochanter ; (3) the outer lip of the gluteal ridge ; (4) the upper half of the outer lip of the linea aspera and the adjacent portion of the shaft of the femur for about one-sixth of an inch; (5) the external intermuscular septum in the neighborhood of its attachment to the linea aspera. Insertion.—(1) The outer half of the upper border of the patella, behind the preceding tendon, with which it also blends ; (2) the upper third of the outer border of the patella ; (3) by an aponeurosis which is inserted partly into the front of the external tuberosity of the tibia, partly into the deep fascia of the leg. Structure.—Arising partly directly from the bone, and partly by a strong apo- neurosis which covers the outer surface of the muscle in its upper two-thirds, the fleshy fibres run parallel to one another downward, forward, and inward, at the same time curving slightly as they pass over the rounded mass formed by the crureus muscle. The aponeurosis of insertion lies upon the inner surface of the muscle and receives fleshy fibres to within one inch of its insertion into the patella and its blending with the other tendons of the quadriceps muscle. Upon its anterior surface it unites with the tendon of the rectus muscle, and upon its posterior surface is received a part of the insertion of the crureus. Nerve-supply.—From the anterior crural (through the second, third, and fourth lumbar nerves), by several branches which enter the internal surface of the muscle in the upper third of the thigh. Action and relations.—These will be considered with those of the two follow- ing muscles. (V, d) Vastus Internus and Crureus. The vastus interims and crureus are so closely blended that it is better to describe their origins together before mentioning the way in which they may be separated. They have received their names, the former from its size and position ; the latter from its intimate connection with the whole of the front of the thigh bone, the term ‘crus’ being often used synonymously with the femur. The blended muscle is a somewhat fusiform sheet which is so curved laterally as to form a cylinder embracing the whole of the front and sides of the shaft of the femur. Origin.—(i) The outer lip of the lower half of the linea aspera and its external bifurcation, together with the adjacent external intermuscular septum; (2) the lower part of the anterior intertrochanteric line and the spiral line of the femur; (3) the inner lip of the whole length of the linea aspera and its internal bifurcation, together with the adjacent part of the internal intermuscular septum, and the front of the tendon of the adductor magnus; (4) the greater part of the front and sides of the femur within the limits formed by the three preceding attach- ments and the origin of the vastus externus. Insertion.—(1) The posterior aspect of the upper border of the patella ; (2) the upper half of the inner border of the patella ; (3) by a strong aponeurosis into the front of the inner tuberosity of the tibia and into the adjacent deep fascia of the leg. Structure.—The fibres of this large muscle arise fleshy from the surface of the VASTUS INTERNUS—CRUREUS. 387 femur and converge, from the outer side downward, forward, and inward ; from the front directly downward ; from the inner side downward, forward, and out- ward, upon the back and sides of a strong aponeurosis which covers the front of the muscle from about the middle of the thigh downward. The fibres which arise from the tendon of the adductor magnus and the adjacent intermuscular septum form the lowest part of the thick, muscular belly of the vastus internus, and are directed almost transversely outward to get to their insertion upon the inner border of the patella. The substance of the muscle is arranged in layers which wrap round the front and sides of the femur; and between the attachment of these layers to the bone, longitudinal strips of bone may be found upon dissection without any muscular attachment. The deepest of these layers in the lower fourth of the thigh forms a separate sheet of muscular fibre, sometimes called the subcrureus, which is inserted into the upper reflexion of the synovial membrane of the knee joint. Beneath this muscle is the bursa underneath the quadriceps, which in the adult communicates with the upper part of the knee joint. A somewhat arbitrary division may be made between the vastus internus and crureus by dissecting at the lower third of the thigh in a line with the inner border of the patella. With a few touches of the scalpel a longitudinal separation may be made clear, which extends upward to the lower part of the anterior inter- trochanteric line. The part of the muscle external to this line is the crureus, and the part internal the vastus internus. The ligamentum patellae maybe looked upon as the common tendon of the quadriceps. It is a band of fibrous tissue about an inch broad by one-quarter of an inch thick, and two or three inches in length, which is attached above to the apex and to the lower part of the posterior surface of the patella; and, after passing downward and very slightly outward, it is inserted into the anterior surface of the tubercle of the tibia. Attached to its sides are strong aponeuroses by which the lower fibres of the vastus externus and vastus internus and the ilio- tibial band are inserted into the tuberosities of the tibia, and which blend on their deep surface with the lower part of the capsule of the knee joint. Nerve-supply.—Numerous branches from the anterior crural are distributed to the upper half of the front of the crureus muscle and to the inner surface of the vastus internus at the junction of the middle and lower thirds of the thigh, the nerve to the vastus internus being a large and conspicuous branch which lies close to the outer side of the femoral artery in the upper part of Hunter’s canal. Action.—The vastus externus, crureus, and vastus internus, together with the rectus femoris, extend powerfully the knee. Their intermediate insertion into the sesamoid bone formed by the patella serves to lift from the line of the tibia the ligamentum patellae, which may be looked upon as the lower part of their common tendon. The enormous power of the whole of this combination of muscles is necessitated partly by the fact that the whole of the weight of the body has to be raised by it, and partly by the great mechanical disadvantage which results from the short arm of the lever upon which the tendon acts, and the obliquity of its insertion. On account of the direction of the femur, which is downward and inward, the tendency of the quadriceps is to draw the patella outward at the same time as upward. This is in some degree counteracted by the position and direction of the vastus internus. The great mass of the fibres of this part of the quadriceps arise in the lower part of the thigh, and are directed so transversely outward toward the inner border of the patella, that when they contract they tend to draw the patella inward as well as upward, and so the combined result and action of the various divisions of the quadriceps is to draw the patella more directly upward. If it were not for this arrangement, the contraction of the quadriceps would have a strong tendency to produce outward dislocation of the knee-cap. Relations of vastus externus, crureus, and vastus internus.—In front lie the fascia lata, tensor vaginae femoris, rectus femoris, and sartorius. To the inner side lie the femoral vessels and anterior crural nerve. On the outer side are the gluteus minimus and maximus. Behind are the biceps on the outer side of the femur, and the adductor longus and magnus on the inner side. 388 THE MUSCLES. Variations.—These are few in number. An accessory head to the. rectus from the anterior superior spine of the ilium has been described, and occasionally the outer head is absent. THE DEEP FASCIA OF THE LEG AND ANNULAR LIGAMENTS. The deep fascia of the leg is continuous above with the fascia lata of the thigh, and receives important additions from the tendons of the biceps, sartorius, gracilis, and semi-tendinosus. It is also attached to the lower part of the outer and inner tuberosities of the tibia and to the head of the fibula. At the back of the knee it is strengthened by transverse fibres which serve to bind together the muscles which form the boundaries of the popliteal space; the external saphenous vein also perforates it about the centre of the space. It is very thick and strong at the upper and outer part of the front of the leg; but behind, where it covers the muscles of the calf, the fascia becomes much thinner. The internal surface of the tibia is not covered by this fascia, which blends with the periosteum covering its anterior and inner borders throughout their whole length. It is also attached to the borders of the fibula by two strong intermuscular septa which form the anterior and posterior walls of a compartment containing the long and short peronei. In the lower third of the leg it is attached to the borders of the sub- cutaneous surface of the fibula. In the neighborhood of the ankle the deep fascia is thickened by the addition of numerous transverse fibres, and forms the annular ligaments. The anterior annular ligament (Fig. 298) consists of two parts, an upper and a lower. The upper part is a strong band of transverse fibres just above the ankle joint, which extends from the anterior border of the tibia to the anterior border of the subcutaneous surface of the fibula. Behind it there is a separate synovial sheath for the tendon of the tibialis anticus. The lower part of the anterior annular ligament arises from the upper surface and outer border of the great process of the calcaneum in two bands, a superficial and a deep, which, passing transversely inward, unite after a course of about an inch, and thus form a loop in which are contained the tendons of the extensor longus digitorum and the peroneus tertius, together with part of the origin of the extensor brevis digitorum. From the inner extremity of this loop two bands of fibres of varying distinctness proceed : one passes upward and inward to join with the front border of the internal malleolus; the other, which is usually the weaker, more directly inward over the scaphoid bone to join with the inner border of the plantar fascia. Beneath this inner portion of the lower part of the anterior annular ligament the tendons of the extensor proprius hallucis and tibialis anticus are contained in separate synovial sheaths. The external annular ligament passes from the posterior border of the external malleolus to the outer border of the tuberosity of the calcaneum and to the posterior part of the junction of the lower and outer surfaces of the calcaneum. It is continuous above with the deep fascia covering the calf muscles and the peronei; and also with the sheet of fascia which separates the two superficial from the two deep layers of muscles at the bark of the leg. Its deep surface is attached to the peroneal tubercle on the outer side of the calcaneum. The internal annular ligament extends from the posterior border of the internal malleolus to the inner border of the tuberosity of the calcaneum. It is also continuous above with the deep fascia of the leg and with the sheet of fascia which intervenes between the soleus and the deeper sheets of muscle at the back of the leg. GASTR O CNEMIUS. MUSCLES OF THE BACK OF THE LEG. The muscles in this region are arranged in two layers above, in four below. The first layer consists of the gastrocnemius and plantaris. First Layer. The gastrocnemius—named from yaariip = the belly, and xvjjpr) = the calf, because it forms the enlargement of that part of the leg—is double-headed, each head consisting of a fusiform muscle, the lower part of which blends with its fellow so as to form a common tendon of insertion. It forms the femoral origin of the great triceps surae muscle. Origin.—Outer head: a well-marked impression upon the upper and posterior part of the outer surface of the external condyle and the adjacent part of the posterior surface of the femur just above the external condyle. Inner head: an oval impression placed transversely across the posterior surface of the femur above the internal condyle, and reaching inward to the back of the adductor tubercle. Insertion.—By the tendo-Achillis (so named from the legend that the heel, into which this tendon is inserted, was the only vulnerable part of the hero Achilles) into the lower part of the posterior surface of the calcaneum. Structure.—The two heads arise by short, strong tendons; that of the inner is the stronger and thicker. These tendons converge downward toward one another, and are succeeded by large, fleshy expansions which unite at the upper part of the middle third of the leg. Near this point the tendon of insertion begins as an intermuscular septum between the two bellies of the muscle. This becomes thicker and stronger, and expands into a broad aponeurosis which covers the anterior surface of the united muscle. Just below the middle of the leg the fleshy fibres terminate upon the back of this aponeurosis in two curves, the convexity of which is downward, that of the inner portion of the muscle descending about half an inch lower than the outer. The strong aponeurosis becomes narrower and at the same time thicker, and after receiving the fibres of the soleus muscle is known by the name of the tendo-Achillis. Nerve-supply.—From the internal popliteal branch of the great sciatic nerve, which sends sural branches to the adjacent portions of the anterior surfaces of the two heads, in the upper third of the leg. Action.—Its action will be described with that of the soleus, which forms a part of the same muscle. Relations.—Behind, the deep fascia, the external saphenous vein and nerve, and the communicans fibularis nerve. Between the two heads above is the plan- taris muscle. In front lie the knee joint, the tendon of the semi-membranosus, the popliteus, the plantaris tendon, the soleus, the popliteal vessels, and internal popliteal nerve. On the outer side, above, are the biceps tendon, and external popliteal nerve ; on the inner side, above, are the tendons of the semi-tendinosus, gracilis, sartorius, and adductor magnus. A bursa lies beneath its inner head, separates it from the tendon of the semi-membranosus, and communicates with the knee joint. i. GASTROCNEMIUS. Variations.—The most common variation is the addition of a third head from the posterior surface of the lower end of the femur. This may cross, or even run between, the popliteal vessels. THE MUSCLES. Fig. 291.—Superficial Muscles of the Back of the Thigh and Leg. Gluteus medius. Aponeurosis of gluteus maximus. Gluteus maximus Semi-membranosus. Biceps. — Semi-tendinosus. Vastus externus. — Gracilis. Tendon of semi-membranosus. Sartorius. Plantaris. _ Gastrocnemius. — Soleus. — Flexor longus digitorum, Peroneus longus. Tendo-Achillis, PLANTARIS—POPLITE US. 391 2. PLANTARIS. The plantaris—named from its occasional attachment to the fascia covering the sole of the foot (= p/anta)—is a fusiform, somewhat flattened muscle with a very long ribbon-shaped tendon. Origin.—(1) The lower two inches of the outer bifurcation of the linea aspera together with the posterior surface of the femur immediately below that ridge, and (2) the adjacent part of the posterior ligament of the knee joint. Insertion.—The inner side of the lower portion of the posterior surface of the calcaneum ; sometimes, however, it blends with the inner border of the tendo- Achillis, and sometimes it is continued into the inner division of the plantar fascia. Structure.—Arising fleshy, the fibres of this small muscle have a somewhat penniform arrangement and converge upon the thin tendon, which appears first on the inner side of the muscle, and soon becoming free runs downward and slightly inward across the calf between the gastrocnemius and the soleus. In the lower third of the leg it lies along the inner border of the tendo-Achillis, with which it is sometimes blended. Nerve-supply.—From the internal popliteal branch of the great sciatic nerve by a small filament which enters the deep aspect of the muscle near the upper part of its inner border. Action.—This vestigial muscle is a feeble extensor of the ankle and flexor of the knee joiift. By its attachment to the posterior ligament of the knee joint it will tend to draw backward that ligament during flexion of the knee, and so prevent its being caught between the articular surfaces. Relations.—Behind lie the fascia of the popliteal space, the biceps, the gastrocnemius, and the external popliteal nerve; in front are the popliteal vessels and internal popliteal nerve, the popliteus muscle and the soleus. Variations.—In addition to the above-mentioned variations in the point of insertion, this muscle may sometimes be double at its origin, and it is not infrequently deficient. Second Layer. The second layer is formed above by the popliteus, which is covered behind by the aponeurosis derived from the semi-membranosus ; and below by the soleus, which is the lower head of the great triceps surge muscle. 1. POPLITEUS. The popliteus (Fig. 292)—named from its position on the floor of the ham (= poples)—is a triangular sheet. Origin.—The bottom of the anterior portion of a horizontal groove on the lower part of the outer surface of the external condyle of the femur; also by a small slip from the posterior ligament of the knee joint. Insertion.—(1) The back of the tibia from below the attachment of the pos- terior ligament of the knee joint to the oblique line; (2) the fascia derived from the tendon of the semi-membranosus, which covers the posterior surface of the muscle. Structure.—Arising by a somewhat flattened cylindrical tendon which passes at first backward and slightly downward within the knee joint, grooving the pos- terior border of the external semilunar cartilage; it then escapes from the capsule of the knee joint, receiving a small slip from the posterior ligament, and imme- diately expands into a fan-shaped muscle which forms a thick sheet, covering the upper fourth of the back of the tibia, and is inserted by fleshy fibres into the pouch formed by the bone in front and the aponeurosis derived from the semi-mem- branosus behind. The tendon of origin is surrounded by synovial membrane, 392 THE MUSCLES. which is reflected upon it about half an inch beyond the opening, through which it emerges from the posterior ligament of the knee joint. Nerve-supply.—From the sacral plexus by the internal popliteal division of the great sciatic nerve, which sends a special branch round the lower border of the muscle to distribute itself to the lower part of its deep or anterior surface. Action.—To flex the knee, which it will do but feebly on account of the obliquity of its direction and its proximity to the axis of the joint. When the knee is flexed it will act as an internal rotator of the leg. In this position the tendon of origin lies wholly in the groove for its reception upon the outer surface of the external condyle. It is possible that the attachment of the tendon of origin to the posterior ligament of the knee may enable the muscle when it contracts to draw backward the ligament, and so prevent the synovial membrane upon its anterior aspect from being nipped between the articular surfaces. Relations.—Behind, the aponeurosis of the semi-membranosus, the gastroc- nemius, plantaris, and the popliteal vessels, nerves, and glands. In front, the knee joint. Superficial to the tendon of origin is the external lateral ligament of the knee. Variations.—A second head of origin has been seen from a sesamoid bone in the oucer tendon of the gastrocnemius. 2. SOLEUS. The soleus—named from solea, the Latin for a sole-fish, because of the resemblance of the muscle to this flat fish—is a thick, fusiform sheet. Origin.—(i) The oblique line of the tibia and the inner border of its posterior surface, from the lower end of the oblique line to a little below the middle of the leg; (2) the back of the head and the upper third of the outer border of the posterior or flexor surface of the fibula and the adjacent external intermuscular septum; (3) a tendinous arch which stretches across the interval between the upper part of the back of the tibia and fibula. Insertion.—By a strong aponeurosis which blends with the anterior surface of the tendon of the gastrocnemius, and forms the tendo-Achillis. Structure.—The muscle arises partly by fleshy fibres and partly by a strong aponeurosis, which lies in front of the fleshy fibres, and is especially noticeable in the neighborhood of its tibial attachment. From the tibia and fibula the fibres pass in a bipenniform arrangement downward and toward the middle line, and after a very short course, not exceeding two inches in length, they blend with the tendon of insertion which begins near the upper part of the origin of the muscles, and in cross-sections of the muscle resembles in shape the letter T; one part of it forming a broad aponeurosis upon the posterior surface of the muscle, the other part a strong tendinous septum which passes forward from the middle of the broad aponeurosis above mentioned, so as to separate the fleshy fibres into two portions. About the junction of the middle and lower thirds of the leg, the tendon of insertion joins by its posterior aspect with that of the gastrocnemius muscle, but upon its anterior aspect and sides it receives fleshy fibres nearly as far down as the back of the ankle joint. The tendo-Achillis is a strong rounded band of tendon about five-eighths of an inch from side to side, and three- eighths of an inch from before backward; it is narrowest at the level of the ankle joint, and expands slightly before it is inserted into the lower part of the posterior surface of the calcaneum. A bursa intervenes between the tendon and the smooth upper part of the posterior surface of this bone. Nerve-supply.—From the internal popliteal division of the great sciatic nerve by sural branches which enter the upper half of the muscle upon the posterior surface ; and lower down by a branch from the posterior tibial nerve, which enters the anterior surface of the muscle. Action.—The chief action of the combined gastrocnemius and soleus is to extend the ankle joint. It is an extremely powerful muscle, as it acts with considerable mechanical disadvantage. The lever by means of which it acts may be best described SOLEUS—FLEXOR LONGUS DIGITORUM. 393 as one of the first order; the lever being that part of the foot which lies between the heel and the heads of the metatarsal bones, the ankle being the fulcrum ; a pressure equal to the weight of the body being exerted by the ground at the anterior extremity of the lever ; and the arm, at the end of which the muscle acts, being the comparatively short distance between the back of the heel and the centre of tlte ankle joint. When the ankle joint has been completely extended, this muscle will tend to adduct slightly the foot, and to invert the sole, this movement being carried out in the joint between the astragalus and calcaneum. Besides extending the ankle, the gastrocnemius will assist in flexing the knee joint. The chief object, however, which appears to be gained by the femoral attachment of this muscle is the addition to the rapidity of extension of the foot. Like some of the other long muscles which pass over two joints, the gastrocnemius, if it were an inextensible ligament, would cause extension of the ankle as soon as the knee was straightened by means of the great quadriceps muscle. Seeing, however, that during the contraction of the quadriceps the gastrocnemius is at the same time acting, it follows that the rapidity and amount of the extension of the ankle joint is almost doubled. By these means we obtain that rapid and powerful contraction which gives the spring to the body in leaping and running. We may see also how enormously strong the tendo- Achillis must be, as it has not only to bear the contraction of the gastrocnemius and soleus, but the additional strain thrown upon it by the simultaneous action of the quadriceps extensor of the knee. The soleus will assist in the extension of the ankle, and will even be able to perform this movement somewhat feebly by itself, when in extreme flexion of the knee joint the gastrocnemius is so relaxed as to be almost powerless. It is much stronger than the gastrocnemius, as may be inferred from the enormous number of short fibres by which it is formed. At the same time, however, as it only passes over the ankle and calcaneo-astragaloid joints, the range of its movements is very short. Variations.—A second soleus is sometimes formed beneath the normal muscle, and more or less separate from it. It is usually inserted into the calcaneum or internal annular ligament. Third Layer. The third layer is separated from the superficial layers by an aponeurosis called the deep tibial fascia. This is attached to the inner border of the tibia internally, and externally to the outer border of the flexor surface of the fibula, and the posterior of the two external intermuscular septa. It is thin above, but below it is strengthened by transverse fibres, and becomes much thicker. At the ankle it blends with the deep fascia of the leg and the external and internal annular ligaments. The third layer consists of two muscles—the flexor longus digitorum and the flexor longus hallucis. X. FLEXOR LONGUS DIGITORUM. The flexor longus digitorum—named from its being the longer of the two flexors of the toes—is a fusiform sheet. Origin.—(i) The inner part of the posterior surface of the tibia, beginning with the lower half of the oblique line, and ending about three inches above the inner ankle; (2) the front of the deep fascia which covers the sheet; (3) a thin inter- muscular septum which intervenes between this muscle and the tibialis posticus. Insertion.—The under surface of the base of the ungual phalanx of each of the four outer toes. Structure.—Arising fleshy from the tibia and adjacent fasciae, the fibres pass in a penniform manner into the front and outer side of a tendon which, beginning about the middle of the leg, gradually becomes thicker and stronger, and receives its last fleshy fibres about two inches above the ankle joint. It then passes beneath the internal annular ligament in a compartment posterior and external to that for 394 THE MUSCLES. the tibialis posticus. Thence it runs downward, forward, and outward beneath the first layer of the sole muscles, and, after having received fleshy fibres from the Fig. 292.—The Deep Muscles of the Back of the Leg, Plantaris. Outer head of gastrocnemius. Inner head of gastrocnemius Biceps Tendon of semi-membranosus. Popliteus, Tibialis posticus. Peroneus longus. Flexor longus digitorum Flexor longus hallucis Peroneus brevis Tibialis posticus, Tendo-Achillis, accessorius pedis and a small tendinous slip from the tendon of the flexor longus hallucis, divides, about half-way between the tuberosity of the calcaneum and the FLEXOR LONGUS HALLUCLS. 395 heads of the metatarsal bones, into four tendons. These enter the thecae of the four outer toes, and each tendon passes through the splitting of the tendon of the flexor brevis digitorum to its insertion upon the under surface of the base of the third phalanx. The lumbricales arise from its tendons in the sole of the foot. Nerve-supply.—From the posterior tibial nerve by branches which enter the superficial aspect of the muscle near its outer border, about the middle of the leg. Action.—To flex the last phalanges of the four outer toes ; it will then help to flex the second and first phalanges and the medio-tarsal joint of the foot. It will also help slightly in the extension of the ankle joint. In flexing the medio-tarsal joint, it will tend to preserve the arch of the instep. Relations.—Superficially, in the leg the soleus, posterior tibial vessels and nerve ; in the foot, the abductor hallucis and flexor brevis digitorum. Deeply, lie the tibialis posticus in the leg, and in the foot the tendon of the flexor longus hallucis, the accessorius, and the muscles which form the third layer of the sole of the foot. Variations.—An accessory head sometimes arises in the leg from the fibula, the tibia, or the deep fascia of the-leg ; it may join the rest of the muscle in the leg, or in the sole. Some of the tendons to the toes maybe wanting ; more often they are increased in num- ber and supply the deficiencies of the flexor brevis digitorum, and especially by sending slips to the little toe. The flexor longus hallucis—named from its action upon the great toe (hallux) and its length—is a strong fusiform sheet. Origin.—The lower two-thirds of the postero-internal (or flexor) surface of the fibula external to the oblique line; (2) the intermuscular septa between it and the tibialis posticus in front, and the peronei outside ; (3) the deep fascia covering its posterior surface; (4) the lowest portion of the interosseous membrane. Insertion.—(1) The under surface of the base of the last phalanx of the great toe ; (2) by a small slip into that part of the flexor longus digitorum tendon which is distributed to the second and third toes. Structure.—The muscle arises by fleshy fibres which pass with abipenniform arrangement into the tendon. This tendon appears first just below the middle of the leg at the back of the muscle near its inner border. The fleshy fibres are inserted into it as far as the ankle joint, and just above this point the tendon passes through the groove at the outer part of the back of the lower end of the tibia. The tendon then grooves the back of the astragalus, and afterward the under sur- face of the sustentaculum tali, where it lies external to the tendon of the flexor longus digitorum. From this point it passes forward in the second layer of the muscles of the sole, lying above and crossing the tendon of the flexor longus digi- torum, to which it gives a small slip. It then crosses beneath the inner head of the flexor brevis hallucis, lies in the groove between the sesamoid bones of that muscle, and is finally inserted into the base of the last phalanx. Nerve-supply.—From the posterior tibial nerve by branches which enter the muscle in the upper part of its posterior surface near its inner border. Action.—This muscle, which is much more powerful than the flexor longus digitorum, is a strong flexor of the last phalanx of the great toe, and is of great importance in walking, as it presses the great toe firmly against the ground. The ungual phalanx of the great toe is the last part of the foot to leave the ground when the step is completed ; and until this is the case the flexor longus hallucis is strongly contracted. It will also help to flex the first phalanx of the great toe upon its metatarsal bone, and it will act upon the joints which intervene between the first metatarsal bone and the astragalus; and, finally, it will assist in the exten- sion of the ankle joint. Relations.—Superficially, in the leg, it is covered by the soleus, and in the foot by the abductor hallucis, the flexor longus digitorum, the external plantar vessels and nerve ; on its outer side are the peronei; on its deep aspect in the leg lie the tibialis posticus and the peroneal vessels; and after passing over the back 2. FLEXOR LONGUS HALLUCIS. 396 THE MUSCLES. of the ankle and other joints, it lies upon the inner head of the flexor brevis hallucis. Variations.—An accessory portion of the muscle may be inserted into the susten- taculum tali or the inner surface of the calcaneum. The slip to the flexor longus digitorum tendon may vary in the number of toes to which it is distributed. Fourth Layer. The fourth layer consists of one muscle—the tibialis posticus. The tibialis posticus—named from its position in the back part of the leg and its origin from the tibia—is a thick fusiform sheet. Origin.—(i) The whole of the back of the interosseous ligament with the exception of the lowest portion ; (2) the posterior surface of the tibia close to the interosseous line, from the upper end of the oblique line to the junction of the middle and lower thirds of the shaft ; (3) the antero-internal (or inner part of the flexor) surface of the fibula at the back of the interosseous ridge to within an inch or two of the ankle ; (4) the intermuscular septa which intervene between it and the muscles of the third layer, viz., the flexor longus hallucis and the flexor longus digitorum ; and (5) a small portion of the deep fascia covering the back of the third layer. Insertion.—(1) The tuberosity of the scaphoid bone; (2) by several smaller offsets into the front of the lower surface of the sustentaculum tali and the under surface of all the other tarsal bones with the exception of the astragalus, and (3) the under surface of the bases of the second, third, and fourth metatarsal bones. Structure.—A strong bipenniform muscle, the central tendon of which, lying upon the middle of the back of the muscle, begins about the middle of the leg, and passes downward and inward upon the back of the muscle, receiving its last fleshy fibres about an inch above the ankle. Having passed inward beneath the tendon of the flexor longus digitorum, it enters the innermost groove on-the back of the internal malleolus, and is contained in a synovial sheath which accompanies it to its insertion upon the scaphoid bone. From this insertion strong fibrous bands radiate backward, outward, and forward to the tarsal and metatarsal bones, being intimately blended with the ligaments by which these bones are held together. This muscle, which is very strong, is contained, so to speak, in a four-sided prismatic case formed in the front by the interosseous membrane; at the sides, by the opposing surfaces of the tibia and fibula; and behind, at a distance of nearly half an inch from the interosseous membrane, by the intermuscular septa which separate the muscle from the flexor longus hallucis and the flexor longus digitorum. Just above its insertion into the tuberosity of the scaphoid bone, the tendon often contains a sesamoid bone. Nerve-supply.—From the posterior tibial, which sends branches forward to the back of the muscle in the upper third of the leg. Action.—(1) To adduct the front of the foot; (2) to invert the sole; (3) to extend the ankle—the last of these movements is somewhat limited ; (4) to support the longitudinal arch of the foot—firstly, by drawing backward the lower part of the scaphoid, and so preventing the descent of the head of the astragalus between the scaphoid and calcaneum, and secondly by its traction upon the other tarsal bones upon which the secondary offsets of its tendon are inserted. Relations.—Superficially, the soleus and third layer of muscles of the leg, the posterior tibial and peroneal vessels and the posterior tibial nerve above ; the tendon of the flexor longus digitorum and the abductor hallucis below ; deeply, the ankle joint and inferior calcaneo-scaphoid ligament. The anterior tibial vessels pass through a notch at the upper extremity of the muscle, between its tibial and fibular origins. TIBIALIS POSTICUS. FASCIA AND MUSCLES OF SOLE OF FOOT. 397 THE FASCIA AND MUSCLES OF THE SOLE OF THE FOOT. The plantar fascia is, like the corresponding fascia in the palm, very strong, and is divided into three parts. The central part, which is the strongest, arises from the under surface of the calcaneum at the back of the tubercles. It is tri- angular in shape and expands forward to its attachment at the base of the toes, where it splits into five divisions. Each division forms an arch over the tendons Fig. 293.—First Layer of the Muscles of the Sole. Abductor minimi digiti Flexor brevis digitorum. Abductor hallucis. Flexor brevis minimi digiti Flexor longus hallucis. Flexor brevis hallucis. Tendon of flexorlongus digitorum. First lumbricalis. Tendon of adductor hallucis entering the toe, and is continuous with the ligamentum vaginale of the theca. The sides of the arch pass upward to be attached to the deep transverse ligament which connects the heads of the metatarsal bones and to the lateral ligaments of the metatarso-phalangeal joints. The under surface of the fascia is attached to the deep surface of the skin by small, fibrous bands which form the walls of com- partments containing pellets of fat. These fibrous connections give firmness to the skin of the sole and prevent it from being moved about upon the subjacent fascia. The borders of the central portion of the plantar fascia are continued upward into the sole by the intei'nal and external intermuscular septa, which are 398 THE MUSCLES. attached above to the fibrous structures on the under surface of the tarsal bones. The inner portion, which is the thinnest division of the plantar fascia, is attached behind to the inner border of the great tubercle of the calcaneum and to the lower border of the internal annular ligament. It is inserted in front upon the inner side of the base of the first phalanx of the great toe, and above it becomes con- tinuous with the deep fascia covering the instep. The external portion is very thick, and arises from the outer border of the lesser tubercle of the calcaneum and the lower border of the external annular ligament. It terminates in front in the base of the first phalanx of the little toe, and at its inner border it blends with the central portion of the plantar fascia, where it is joined by the external inter- muscular septum, and upon its outer border it is closely connected with the base of the fifth metatarsal bone, and it is continuous with the deep fascia covering the instep. In the web between the toes some thin transverse fibres are found, the super- ficial transverse ligament of the toes. They bridge over part of the interval between the five slips into which the front part of the central division of the plantar fascia breaks up. The muscles and tendons in the sole of the foot are divided into four layers. The first layer consists of three muscles, which correspond in their position to the three compartments formed by the planter fascia and the two intermuscular septa, viz., the abductor hallucis, the flexor brevis digitorum, the abductor minimi digiti. First Layer. i. ABDUCTOR HALLUCIS. The abductor hallucis—named from its action upon the great toe—is a thick, triangular sheet, with a broad origin behind, which is divided into two heads. Origin.—Outer head: (i) The front and inner surfaces of the inner or greater tubercle on the under surface of the calcaneum ; (2) the deep surface of the inner portion of the plantar fascia; (3) the intermuscular septum which separates it from the flexor brevis digitorum. Inner head: (1) The deep aspect of the lower border of the internal annular ligament; (2) the under surface of the attach- ment of the tendon of the tibialis posticus to the tuberosity of the scaphoid bone and the adjacent prolongations of this tendon. Insertion.—The inner part of the lower surface of the base of the first phalanx of the great toe and the inner side of the internal sesamoid bone. Occa- sionally, also, the inner border of the expansion of the extensor proprius hallucis on the back of the first phalanx. Structure.—The outer head arises in close connection with the flexor brevis digitorum by short tendinous fibres, soon succeeded by a divergent fleshy bundle which is joined about two inches from its origin by the fleshy sheet formed by the inner head. The tendon to which these fleshy fibres converge appears first upon the inner and lower aspect of the muscle, and receives fleshy fibres nearly to its insertion, which is closely blended with that of the inner portion of the flexor brevis hallucis. The deep surface of the muscle arises from a fibrous arch attached on the one side to the septum between it and the flexor brevis digitorum ; on the other side to the tibialis posticus tendon and the fibrous tissue covering the under surface of the tarsal bones along the inner border of the foot. Through this arch pass the plantar vessels and nerves. Nerve-supply.—The internal plantar division of the posterior tibial nerve, by filaments which enter the deep surface of the middle of the muscle. Action.—(1) To flex the first phalanx upon the metatarsal bone ; (2) to abduct from the middle line of the foot the first phalanx of the great toe. Relations.—Superficially, the internal division of the plantar fascia; upon its outer border, the flexor brevis digitorum; deeply, the tendons of the tibialis ABDUCTOR MINIMI DIGIII. 399 anticus, tibialis posticus,* flexor longus digitorum, flexor longus hallucis, the plantar vessels and nerves. Variations.— A third head is occasionally derived from the deep surface of the skin upon the inner border of the foot, or from the long plantar ligament. The muscle may give a slip to the second toe. 2. FLEXOR BREVIS DIGITORUM. The flexor brevis digitorum pedis, or flexor perforatus—named from its being the shorter of the flexors of the four outer toes—is a triangular sheet, divided in front into four processes corresponding to the tendons of the toes. Origin.—(1) The outer part of the front of the lower surface of the great tubercle of the calcaneum; (2) the deep surface of the back part of the central portion of the plantar fascia; (3) the back part of the intermuscular septa on either side. Insertion.—The sides of the middle phalanx of each of the four outer toes upon its plantar aspect. Structure.—Arising tendinous by a pointed process from the under surface of the great tubercle, the fleshy fibres extend in a fan-shaped sheet, which, about half- way between the origin and the heads of the metatarsal bones, divides into four fleshy processes which soon become tendinous. The tendons are arranged in a similar manner to those of the flexor sublimis digitorum in the hand. After splitting beneath the first phalanx of the toe, the two halves of the tendon pass round the sides of the flexor longus digitorum tendon, and about the level of the base of the second phalanx they unite by their adjacent margins, and again diverge to be attached to the sides of the plantar surface of the second phalanx. Nerve-supply.—From the internal plantar division of the posterior tibial, by branches which enter the back of the deep aspect of the muscle near its inner border. Action.—This muscle, which is comparatively feeble, will flex the second phalanges of the toes, and in combination with the flexor longus digitorum it will assist in walking, by pressing the under surface of the phalanges of the toes against the ground. After it has flexed the second phalanges, it will act in a similar manner upon the metatarso-phalangeal and medio-tarsal joints. Relations.—Superficially, the plantar fascia; on either side, the other muscles of the first layer of the sole; deeply, the tendon of the flexor longus digitorum and the lumbricales, the accessorius muscle, and the external plantar vessels and nerve. Variations.—The part of the muscle which belongs to the little toe is often absent, and its place may be supplied by a small perforated slip from the tendon of the flexor longus digitorum. The abductor minimi digiti (pedis)—named from its action upon the fifth and smallest toe—is a thick, triangular sheet, partly muscular and partly aponeu- rotic. Origin.—(i) The outer side and the under surface of the front of the lesser tubercle of the calcaneum and the adjacent portion of the under surface of that bone in front of the great tubercle; (2) the upper surface of the back part of the outer division of the plantar fascia; (3) the outer surface of the back part of the external intermuscular septum ; (4) the long plantar ligament and other liga- mentous structures lying upon the outer border of the sole, and more especially an aponeurotic band which runs from the outer side of the lesser tubercle of the calcaneum to the outer side of the base of the fifth metatarsal bone, and of the base of the first phalanx of the fifth toe. Insertion.—(1) The outer part of the under surface of the base of the first phalanx of the little toe; (2) usually also the outer part of the under surface of 3. ABDUCTOR MINIMI DIGITI. 400 THE MUSCLES. the base of the fifth metatarsal bones; (3) the outer edge of the fourth tendon of the extensor longus digitorum upon the back of the first phalanx of the little toe. Structure.—The muscle, which is at first encased in the aponeuroses, from which as well as from the bone it takes origin, converges from both sides upon a tendon which is first visible on its under surface at the front of the calcaneum. A small portion of its outer part is now inserted into the tubercle of the fifth metatarsal bone, internal to the strong aponeurotic band which is also here attached. From this point the tendon of insertion is free on its inner side, but receives fleshy fibres still from the continuation of the aponeurotic band just men- tioned, until it is inserted into the base of the first phalanx. Nerve-supply.—From the external plantar division of the posterior tibial nerve, by filaments which enter the back part of the deep surface of the muscle near its inner border. Action.—(1) To abduct the first phalanx of the little toe from the middle line ; (2) to flex the metatarso-phalangeal joint of the little toe. The usual action of the muscle will be a combination of these two movements. Relations.—Superficially, the plantar fascia, the flexor brevis digitorum, and even a small portion of the abductor hallucis. Deeply, the accessorius, flexor brevis minimi digiti, long plantar ligament, and peroneus longus tendon. Variations.—The muscular slip attached to the base of the fifth metatarsal bone is often so distinct as to form a separate muscle, the abductor ossis metatarsi quiniti. Second Layer. The second layer consists of the flexor accessorius muscle, the four lumbricales, and the tendons of the flexor longus hallucis and the flexor longus digitorum. 1. FLEXOR ACCESSORIUS DIGITORUM PEDIS. The flexor accessorius digitorum pedis—named from its accessory or supplementary action in assisting the flexion of the toes by the flexor longus digitorum—is a double-headed quadrilateral sheet. Origin.—Inner head : The whole of the concave inner surface of the calca- neum below the groove for the flexor longus hallucis. Outer head : (i) The junction of the lower and outer surfaces of the calca- neum in front of the lesser tubercle; (2) the under surface of the back part of the long plantar ligament. Insertion.—The upper surface and outer border of the flexor longus digitorum tendon about midway between the tubercles of the calcaneum and the heads of the metatarsal bones. Structure.—Its inner head consists of fleshy fibres which converge from their origin in a somewhat fan-shaped sheet, and are joined shortly before their insertion into the tendon by the outer head, which consists of a pointed tendinous origin, from which the fleshy fibres form a somewhat smaller fan-shaped sheet which blends with that from the inner head, to be inserted by fleshy fibres upon the upper surface and outer border of the flexor longus digitorum, at its point of division into the tendons for the four outer toes. Nerve-supply.—From the external plantar division of the posterior tibial nerve, by branches which enter the under surface of the muscle near its origin. Action.—To help in the flexion of the last phalanges of the four outer toes, and at the same time to draw the toes somewhat outward. On account of the oblique direction of the tendons of the flexor longus digitorum in the foot, they would tend in flexing the toes to draw them at the same time inward. This tendency will be somewhat neutralized by the simultaneous contraction of the a.ccessorius. The accessorius will also be able to flex the toes when, on account of the extension of the ankle joint, the muscular fibres of the flexor longus digit- orum are so relaxed as to be incapable of action. THE FOUR LUMBRICALES. 401 Relations.—Superficially, the tendons of the flexor longus digitorum and flexor longus hallucis, with the external plantar vessels and nerve; deeply, the flexor brevis hallucis and long plantar ligament. Variations.—An additional head may arise above the ankle from the flexor longus digitorum, flexor longus hallucis, or soleus. Sometimes the outer head is wanting, and occasionally the whole muscle is absent. The distribution of its fibres to the tendons of the long flexor is very variable. It may send fibres to the tendon of the flexor longus hallucis. Fig. 294.—Second Layer of the Muscles of the Sole. Flexor brevis digitorum. Origin of abductor minimi digiti, Abductor hallucis. Part of abductor minimi digiti Accessorius, Flexor longus digitorum Flexor longus hallucis. Flexor brevis minimi digiti, Flexor brevis hallucis. Abductor minimi digiti. Adductor hallucis. Lumbricales. Abductor hallucis, Tendon of flexor brevis digitorum The four lumbricales—named from their shape {lumbricus=an earthworm) —are, like those in the palm, four small fusiform muscles. Origin.—The first, from the inner border of the innermost tendon of the flexor longus digitorum, from the point of division of the main tendon for about an inch forward; the other three, from the adjacent surfaces of the tendons of the first and second, the second and third, and the third and fourth tendons of the flexor longus digitorum on their plantar aspect. Insertion.—The inner border of the expansion of the extensor longus digito- rum tendon upon the back of the first phalanx of each of the four outer toes. Structure.—The origin of the muscle is entirely fleshy. It ends in a small 2. THE FOUR LUMBRICALES. 402 THE MUSCLES. rounded tendon a short distance above the web of the toes. This tendon runs forward and upward upon the inner side of its toe, above the superficial transverse ligament of the toes and beneath the deep transverse ligament of the metatarsus, to the side of the expansion of the extensor tendon. Nerve-supply.—The two inner are supplied by the internal plantar division of the posterior tibial nerve, by filaments which enter the back part of the lower surface of each muscle near its inner border ; the two outer, by the external plantar nerve, by filaments which enter the deep part of each muscle near its outer border. Action.—(1) To flex the first phalanx of the toe ; (2) to straighten the sec- ond and third phalanges. (3) The first will abduct the second toe from the axis passing through it, which is looked upon as the middle line of the foot. The three others will adduct. The lumbricales will be able to act upon the first phalanges, even when the second and third have been flexed by means of their special flexors. The chief advantage derived from the simultaneous extension of the two terminal phalanges and the flexion of the first phalanx is the application of the whole length of the toe to the ground in walking ; otherwise there would be a strong tendency to the flexion of the phalanges of the toes, which would prevent the proper application of the soft plantar aspect of the ungual phalanx to the ground. Relations.—Superficially, the flexor brevis digitorum. Deeply, the flexor longus digitorum tendons, the transversalis pedis, and the interossei. Third Layer. The third layer consists of four muscles—the flexor brevis hallucis, the adductor hallucis, the transversus pedis, and the flexor brevis minimi digiti. 1. FLEXOR BREVIS HALLUCIS. The flexor brevis hallucis, or flexor brevis pollicis pedis—named from its action, and its size in comparison with the other flexor of the great toe—is a thick triangular sheet with a forked insertion. Origin.—(i) The plantar ligaments and the continuations of the tibialis posticus tendon in the middle of the sole; (2) the inner part of the under surface of the cuboid bone. Insertion.—The inner and outer borders of the plantar aspect of the base of the first phalanx of the great toe. Structure.—Arising fibrous by a pointed process in the middle of the sole, the fibres diverge as they pass forward and slightly inward, and form two fleshy bundles of equal size, which are succeeded by short tendons. In each tendon is contained a sesamoid bone of ovoid shape about three-eighths of an inch in the long antero-posterior diameter, and a quarter of an inch from side to side, with a cartilaginous articular facet upon the upper surface which plays upon the lower surface of the condyles of the first metatarsal bone. At their insertion into the inner and outer part of the lower border of the base of the first phalanx, they are blended with the tendons of the abductor and the adductor hallucis. Nerve-supply.—From the internal plantar division of the posterior tibial nerve, by filaments which enter the undersurface of the muscle near the middle of its inner border. Action.—To flex and slightly adduct the first phalanx of the great toe. The sesamoid bones give a slight obliquity to its insertion, and so enable it to act with more power; at the same time they form a groove in which the strong tendon of the flexor longus hallucis plays. They also form a somewhat elastic support when the weight is placed upon the ball of the foot. Relations.—Superficially, the abductor hallucis, the tendon of the flexor longus hallucis, and the inner tendons of the flexor longus digitorum with the ADDUCTOR HALLUCIS. 403 lumbricales; deeply, the interossei and the termination of the external plantar vessels and nerve. Variations,—A small slip is occasionally given to the first phalanx of the second toe. 2. ADDUCTOR HALLUCIS. The adductor hallucis—named from its action upon the great toe—is a triangular sheet, the apex of which is directed forward and inward. Fig. 295.—Third Layer of the Muscles of the Sole. Part of abductor minimi digiti. Flexor longus hallucis. Flexor longus digitorum. Tibialis posticus. Flexor brevis minimi digiti Flexor brevis hallucis. Adductor hallucis, Transversus pedis, Origin.—(i) The continuation forward of the long plantar ligament which forms the sheath of the peroneus longus tendon ; (2) the under surface of the bases of the second, third, and fourth metatarsal bones. Insertion.—The outer part of the under surface of the base of the first phalanx of the great toe. Structure.—Arising by short tendinous fibres, the muscle converges in bipenniform fashion upon a short tendon, which blends with that of the flexor brevis hallucis and the outer sesamoid bone internally, and the transversus pedis externally. Nerve-supply.—From the external plantar division of the posterior tibial 404 THE MUSCLES. nerve by filaments which enter the upper surface of the muscle upon its outer border near its origin. Action.—(1) To adduct the first phalanx of the great toe toward the middle line of the foot; (2) to flex the first phalanx. Usually it will act during walking in combination with the flexor brevis hallucis and abductor hallucis, and the three muscles contracting together will produce direct flexion of the first phalanx, so that when the weight of the body rests upon the front part of the foot the second phalanx is pressed firmly against the ground by the action of the flexor longus hallucis, while the first phalanx is acted upon in the same manner by the combina- tion of these three short muscles. As Duchenne has pointed out, the abductor and adductor will have an important function in adjusting the pressure when the step has to be made upon uneven ground. Thus, in walking upon a slope the adductor hallucis of the one foot will direct the pressure downward and slightly outward, while the abductor of the other foot will direct the pressure downward and slightly inward. Relations.—Superficially, the flexor longus digitorum tendons and their lumbricales ; deeply, the interossei with the external plantar vessels and nerve; at the sides, the flexor brevis hallucis and transversus pedis. Variations.—The adductor hallucis sometimes sends a slip to the first phalanx of the second toe. 3. TRANSVERSUS PEDIS. The transversus pedis—named from the direction of its fibres—is a small muscle consisting of three or four fusiform bundles lying side by side, and uniting in a single tendon. Origin.—(1) The plantar ligaments of the three outer metatarso-phalangeal joints; (2) the under surface of the adjacent deep transverse metatarsal ligaments. Insertion.—The outer side of the base of the first phalanx of the great toe. Structure.—The fleshy fibres form a series of small bundles which converge slightly as they pass inward and slightly forward, and after uniting terminate in a short tendinous insertion which is closely blended with the outer surface of the tendon of the adductor hallucis. N erve-supply.—From the external plantar division of the posterior tibial nerve by filaments which pass to the upper part of the posterior edge of the muscle. Action.—(1) To adduct the first phalanx of the great toe ; (2) to draw together the heads of the metatarsal bones after they have been separated by the pressure of the weight of the body during the tread. Relations.—Superficially, the flexor longus digitorum tendons and lumbri- cales; deeply, the interossei. Variations.—Some or all of the bundles may be absent; most frequently the outer- most one. Occasionally fibres join the muscle from the fascia covering the interossei below the lower border of the adductor hallucis, so that the two muscles are more or less blended. The flexor brevis minimi pedis digiti—named from its action, upon the little toe—is small, flattened, and fusiform. Origin.—(i) The under surface of the base of the fifth metatarsal bone; (2) the adjacent part of the sheath of the peroneus longus tendon. Insertion.—(1) The outer part of the under surface of the base of the first phalanx of the little toe ; (2) the outer part of the front of the under surface of the fifth metatarsal bone. Structure.—Arising tendinous, the fleshy fibres run forward and a little out- ward td their short tendon of insertion, which is closely blended with that of the abductor minimi digiti. A few of the deeper fibres end in the metatarsal bone. Nerve-supply.—From the external plantar nerve by a branch which enters the under surface of the muscle. 4. FLEXOR BREVIS MINIMI DIGITI. INTEROSSEI. 405 Action.—To flex and slightly abduct the first phalanx of the little toe. Relations.—Superficially, the flexor longus digitorum and abductor minimi digiti; deeply, the interossei of the outermost interspace. Variations.—The insertion upon the metatarsal bone may form a separate muscle, the opponens digiti pedis quinti, or it may be entirely absent. Fig. 296.—Fourth Layer of the Muscles of the Sole, Peroneus longus. Plantar interossei Dorsal interossei. Fourth Layer. The fourth layer consists of the seven interosseous muscles INTEROSSEI. The interossei—named from their position between the metatarsal bones— are, like those of the hand, seven in number, three being plantar and four dorsal. The plantar are small and narrow fusiform bundles; the dorsal are bipenniform and of a somewhat broader fusiform shape than the plantar. The interossei of the foot differ from those of the hand in the fact that they adduct and abduct with respect to a longitudinal axis through the line of the second toe; whereas in the hand the median line passes through the middle finger. 406 THE MUSCLES. The plantar interossei.—Origin.—(i) The inner and lower surface of the three outer metatarsal bones; (2) the adjacent part of the sheath of the peroneus longus tendon. Insertion.—(1) The inner side of the bases of the first phalanges of the three outer toes; (2) the inner border of the expansions of the long extensor tendons on the back of the first phalanges of the same toes. The dorsal interossei arise from the adjacent surfaces of the metatarsal bones bounding each interosseous space. The first dorsal interosseous, however, differs somewhat in its internal head, which is from the base only of the first meta- tarsal bone and the adjacent outer surface of the internal cuneiform bone. Insertion.—-The first dorsal interosseous is inserted into: (1) the inner side of the base of the first phalanx of the second toe ; (2) the inner edge of the apo- neurosis of the extensor tendon upon the back of the first phalanx. The second, third, and fourth are inserted respectively into : (1) the outer side of the bases of the first phalanges of the second, third, and fourth toes; (2) the outer border of the extensor tendons upon the backs of the same phalanges. Structure.—The plantar interossei are penniform muscles consisting of fleshy fibres which run forward to the outer side of a tendon which begins about the middle of the space and becomes free opposite the heads of the metatarsal bones. The dorsal interossei are bipenniform, and consist of fleshy fibres which con- verge from both sides of the space upon a central tendon which begins about the middle of the interosseous space and becomes free opposite the heads of the meta- tarsal bones. The tendons of both sets of muscles before their insertion lie above the deep transverse metatarsal ligament which separates them from the tendons of the lumbricales. On the back of the foot the dorsal interossei are alone visible; in the sole of the foot both sets are seen. Nerve-supply.—From the external plantar nerve by filaments which enter the plantar aspect of the muscles, somewhat behind the middle of the interosseous space. Action.—The common action of all the interossei is (1) to flex the first phalanges of the four outer toes; (2) to extend the second and third phalanges. In these, two movements they are assisted by the lumbricales. In walking, this movement is of great importance as it keeps the toes straight when the weight of the body rests upon the front part of the foot. When these movements are paralyzed, the action of the long and short flexor of the toes is to curl them up, and the ends of the toes will be subjected to considerable pressure, which may set up inflammation to the beds of the nails. The special action of the plantar interossei is to adduct the first phalanges of the three outer toes; and of the dorsal interossei to abduct the second, third, and fourth toes from the middle line of the second toe. As the second toe can be abducted from its own middle line in two directions, it of course requires two abductors. Relations.—On the plantar surface both sets of interossei are in contact with the muscles of the third layer, and with the external plantar vessels and nerve; on the dorsal surface the dorsal interossei are covered by the tendons of the extensor longus and brevis digitorum. The dorsalis pedis and other perforating arteries pass through the back of the interosseous spaces between the double origins of the dorsal interossei. TIBIALIS ANTICUS—EXTENSOR PROPRIUS HALLUCIS. 407 MUSCLES OF THE FRONT OF THE LEG. Between the anterior border of the tibia and the anterior of the two external intermuscular septa, are placed four muscles: the tibialis anticus, the extensor proprius hallucis, the extensor longus digitorum, and the peroneus tertius. The tibialis anticus—named from its attachment to the tibia and its position in the front of the leg—is fusiform and somewhat flattened, with a long terminal tendon. Origin.—(i) Part of the under surface of the outer tuberosity of the tibia; (2) the outer surface of the upper two-thirds of the tibia ; (3) the adjacent part of the anterior surface of the interosseous membrane; (4) the posterior surface of the upper part of the deep fascia of the leg; (5) an intermuscular septum which separates it from the extensor longus digitorum in the upper third of the leg. Insertion.—The lower part of the front of the inner surface of the internal cuneiform bone and the adjacent part of the base of the first metatarsal bone. Structure.—A strong penniform muscle the fibres of which, arising fleshy from the bone and from the strong fascite, pass forward and most of them some- what outward to be attached to the deep surface and outer border of a tendon, which, beginning below the middle of the leg, becomes free of fleshy fibres two or three inches above the ankle joint; and, after passing first beneath the upper portion of the anterior annular ligament, then partly under and partly over the lower portion, expands slightly to be inserted upon the inner margin of the foot. In passing over the instep it turns upon itself so that its anterior surface becomes below internal. Nerve-supply.—From the anterior tibial division of the external popliteal nerve by branches which enter the upper third of the muscle upon the outer part of its deep aspect. Action.—(1) To flex the ankle joint; (2) to draw upward the inner border of the foot and so invert the sole ; (3) to adduct the front portion of the foot. The first of these movements will be performed chiefly in the ankle joint; the second and third in the medio-tarsal and calcaneo-astragaloid joints. This muscle is of great importance in walking, as it lifts up the anterior part of the foot and so enables the toes to clear the ground when the leg is swinging forward to begin another step. Relations.—Superficially, the deep fascia; on the outer side, the extensor longus digitorum and extensor proprius hallucis with the anterior tibial vessels and nerve; deeply, the interosseous membrane and tibia, and in the upper part of the leg the anterior tibial vessels. The tendon lies in a special synovial sheath beneath the two portions of the anterior annular ligament, and upon the ankle joint and inner bones of the tarsus. A small bursa separates the tendon from the upper part of the inner surface of the internal cuneiform bone. 1. TIBIALIS ANTICUS. Variations.—A small tendon is sometimes sent to the head of the first metatarsal bone, the base of the first phalanx of the great toe, or to the fascia covering the instep. 2. EXTENSOR PROPRIUS HALLUCIS. The extensor proprius hallucis—named from its being the special extensor belonging to the great toe {proprius— peculiar to)—is a somewhat triangular sheet. Origin.—(i) The middle two-fourths of the anterior (or extensor) surface of the fibula external to the attachment of the interosseous membrane; (2) the adjacent portion of the anterior surface of the interosseous membrane. Insertion.—(1) The ligamentous structures at the back and sides of the first 408 THE MUSCLES. metatarso-phalangeal joint; (2) the dorsal aspect of the base of the second phalanx of the great toe. Fig. 297.—The Muscles of the Front of the Leg. Ligamentum patellae, Gastrocnemius, Peroneus longus Tibialis anticus. Soleus. Peroneus tertius. Extensor longus digitorum. Extensor proprius hallucis, Peroneus tertius. Extensor brevis digitorum Dorsal interossei Structure.—Arising by fleshy fibres from the bone and interosseous mem- brane, the muscle is inserted in a penniform manner into a tendon which appears EXTENSOR LONGUS DIGITORUM. 409 about the middle of the leg upon its inner and front aspect, and becomes clear of muscular fibres about the level of the ankle joint. The tendon now passes beneath the upper part of the anterior annular ligament, and is then included in a special sheath beneath the lower part of the same ligament. Opposite the first metatarso-phalangeal joint it gives off from its sides and under surface bands of connective tissue which unite partly with the two lateral ligaments, especially the internal one, and partly with the periosteum upon the sides of the first phalanx. The rest of the tendon is flattened out and fits closely to the dorsal aspect of the first phalanx; it is finally attached to the second phalanx in a transverse line which crosses the upper surface of its base. Nerve-supply.—From the anterior tibial by filaments which enter the inner and deeper aspect of the muscle about the middle of the leg. Action.—(1) To extend the first phalanx of the great toe; (2) slightly to extend the second phalanx, but this movement is chiefly performed by the small muscles of the sole of the foot, which give off expansions to be attached to the borders of the tendon at the sides of the first phalanx ; (3) to flex the ankle, and at the same time it will slightly adduct the front of the foot and invert the sole. When the muscle contracts strongly it will hyper-extend the first phalanx, and at the same time flexion of the second phalanx will be produced by the resistance of the flexor longus hallucis tendon. Relations in the leg.—Superficially, the deep fascia, the tibialis anticus, and the extensor longus digitorum; internally, the tibialis anticus ; externally, the extensor longus digitorum ; deeply, the interosseous membrane, the tibia, and the anterior tibial vessels and nerve. The tendon lies beneath the two portions of the anterior annular ligament, and after crossing the anterior tibial artery near the ankle-joint it runs to its insertion with the dorsalis pedis and the innermost tendon of the extensor brevis digitorum on its outer side. Variations.—The muscle is occasionally divided, and a smaller external portion joins the first tendon of the extensor brevis digitorum, or is inserted separately into the head of the first metatarsal bone or the base of the first phalanx. 3. EXTENSOR LONGUS DIGITORUM. The extensor longus digitorum—named from its length and its action upon the toes—is fusiform and somewhat flattened, with a four-divided tendon. Origin.—(i) The outer part of the under surface of the external tuberosity of the tibia ; (2) the upper three-fourths of the anterior or extensor surface of the fibula; (3) the outer border of the anterior surface of the interosseous membrane in its upper third ; (4) the posterior surface of the deep fascia of the leg; (5) the intermuscular septa which separate it from the upper part of the tibialis anticus and from the long and short peronei. Insertion.—The three phalanges and the metatarso-phalangeal joints of each of the four outer toes. Structure.—This is a penniform muscle, and its fibres arise fleshy from the bones and the fasciae, and pass forward and inward to the back and outer side of the long tendon of insertion. This begins about the middle of the leg, and becomes free from fleshy fibres about the level of the ankle-joint; it passes behind the upper part of the anterior annular ligament, but not in a special synovial sheath ; then beneath the lower part of the anterior annular ligament in a special synovial sheath with the peroneus tertius. At this point it divides into four ten- dons, which diverge upon the back of the foot to the bases of the four outer toes. Each tendon first gives off some strong fibres, which blend with the lateral ligaments of the metatarso-phalangeal articulation, and with the periosteum along the borders of the first phalanx. It then forms a broad expansion covering the back of the first phalanx, and divides into three parts : the central part is inserted into the dorsal aspect of the base of the second phalanx ; and the two lateral parts pass forward with a slight convergence upon the back of the second phalanx to be inserted into the dorsal aspect of the base of the third phalanx. 410 THE MUSCLES. Nerve-supply.—From the anterior tibial by filaments which enter the deep aspect of the muscle in its upper third. Action.—(1) To extend the first phalanges of the four outer toes. It has some influence upon the second and third phalanges, but the distal part of its tendon,is acted upon chiefly by the short muscles in the sole of the foot, which are attached to the border of the expansion upon the first phalanx. When the muscle contracts to its fullest amount the first phalanges are extended, while the second and third phalanges are somewhat flexed by the long and short flexors. (2) To flex the ankle joint. (3) Slightly to abduct and evert the front part of the foot. Relations.—Superficially, the deep fascia of the leg and the anterior annular ligaments ; on its inner side, the tibialis anticusand extensor proprius hallucis, the anterior tibial vessels and nerve with their continuations in the foot. Externally, the intermuscular septum which separates it from the peroneus longus and brevis, the musculo cutaneous nerve, and, lower down, the peroneus tertius. Behind, the fibula and interosseous membrane with the anterior tibial nerve above ; below, the ankle joint, tarsal and metatarsal bones, and the extensor brevis digitorum. Variations.—The muscle may be divided nearly up to its origin. It may give off slips to the extensor proprius hallucis, extensor brevis digitorum, or one of the interossei. Sometimes, also, it has an insertion into some of the metatarsal bones. The peroneus tertius—named from the fibula, and called tertius because it is the third of the muscles which pass from the fibula to the metatarsus —is a small triangular sheet which is closely blended with the preceding muscle. Origin.—(i) The lower fourth of the anterior (or extensor) surface of the fibula; (2) the front of the interosseous membrane for an inch or two above the ankle joint ; (3) the external intermuscular septum and the deep fascia of the leg. Insertion.—The upper part of the base of the fifth metatarsal bone. Structure.—Arising fleshy, the muscular fibres pass downward and inward in penniform fashion to a tendon which appears on the inner border of its anterior surface. It becomes free from fleshy fibres at the level of the ankle joint, and after passing beneath the upper part of the anterior annular ligament, is included with the extensor longus digitorum in a special synovial sheath beneath the lower part of the ligament, and finally diverges from it to be inserted into the inner part of the upper surface of the base of the fifth metatarsal bone. Nerve-supply.—Unlike the other peronei, which are supplied with the mus- culo-cutaneous nerve, it receives filaments from the anterior tibial which enter the inner and deep aspect of the muscle in the upper part of its course. Action.—(1) To flex the ankle joint; (2) to abduct the anterior part of the foot; (3) slightly to elevate the outer border of the foot and so to produce eversion of the sole. Relations.—Superficially, the anterior annular ligament and branches of the musculo-cutaneous nerve; on the inner side, the extensor longus digitorum, of which it is really a subdivision ; on the outer side, the peroneus brevis; deeply, the ankle and outer tarsal joints with the extensor brevis digitorum. 4. PERONEUS TERTIUS. Variations.—The peroneus tertius is often closely blended with the extensor longus digitorum. It is sometimes wanting, and replaced by a slip of tendon from the extensor longus digitorum. Occasionally it sends slips of tendon to the expansion of the extensor longus digitorum on the first phalanx of the two outer toes, or to the fourth dorsal interosseous. EXTENSOR ERE VIS DIGITORUM. 411 MUSCLE ON THE DORSUM OF THE FOOT. This consists of the four bellies of one muscle—the extensor brevis digitorum. EXTENSOR BREVIS DIGITORUM. The extensor brevis digitorum—named from its being the shorter of the two muscles which extend the toes—is a triangular sheet which breaks up in front into four small divisions. Fig. 298.—The Muscles of the Dorsum of the Foot. Extensor longus digitorum. Peroneus brevis. Tibialis anticus. Extensor brevis digitorum. Extensor proprius hallucis. Peroneus tertius. Flexor brevis minimi digiti. Dorsal interossei Origin.—(i) The outer part of the upper surface of the great process of the calcaneum ; (2) the interior of the loop of fascia which forms the outer part of the lower anterior annular ligament. Insertion.—By four tendons into the four inner toes; the innermost is attached to the outer border of the upper surface of the first phalanx of the great 412 THE MUSCLES. toe near its base ; the three other tendons to the outer border of the tendons of the extensor longus digitorum just in front of the bases of the first phalanges. Structure.—Arising superficially by fleshy, and on the deep surface by short tendinous fibres, the muscle diverges inward and forward, and soon divides into four fleshy bellies, of which that to the great toe is the largest and most separate. Each portion has a bipenniform arrangement, with its central tendon upon the dorsal surface, and becoming free opposite the middle of the metatarsus. Nerve-supply.—From the anterior tibial nerve by small filaments which enter the deep surface of the muscle near its inner border as it crosses the cuboid and external cuneiform bones. Action.—(1) To extend the four inner toes. In the case of the outer toes the two last phalanges will be chiefly extended, and the obliquity of its insertion, by causing it to draw the toes somewhat outward at the same time that it extends them, will enable it to correct the opposite tendency of the long extensor. (2) The innermost tendon will act as an adductor of the first phalanx of the great toe. Relations.—Superficially, the tendons of the extensor longus digitorum and peroneus tertius; deeply, the tarsal and tarso-metatarsal joints; and, in the case of the tendon to the great toe, the dorsalis pedis vessels and the termination of the anterior tibia! nerve. Variations.—The number of tendons may be diminished or increased. Sometimes a tendon is given to the little toe. Accessory bundles may be derived from some of the tarsal or metatarsal bones, and slips have been found running to the dorsal interossei; and also a small slip between the first and second bellies, going to the inner side of the second toe or its metatarsal bone. MUSCLES ON THE OUTER SIDE OF THE LEG. Consists of two muscles—the peroneus longus and brevis—situated upon the outer side of the fibula in a compartment of quadrilateral section, bounded inter- nally by the fibula, in front and behind by intermuscular septa, and externally by the deep fascia of the leg. 1. PERONEUS LONGUS. The peroneus longus (Figs. 292, 296)—named from its being the longer of the two fibular muscles—is long and fusiform. - Origin.—(1) The outer tuberosity of the tibia by a few fibres ; (2) the front of the head of the fibula; (3) the upper two-thirds of the outer (or peroneal) sur- face of the fibula, occupying the whole of this surface above, and the posterior half of it below; (4) the inner surface of the deep fascia of the leg, and the opposed surfaces of the two external intermuscular septa. Insertion.—(1) The lower part of the outer surface of the base of the first metatarsal bone; (2) the lower part of the outer surface of the internal cuneiform bone close to its articulation with the first metatarsal bone. Structure.—This is a strong penniform muscle, the short fleshy fibres of which pass downward, and for the most part forward, to be inserted into the tendon which, beginning about three inches below the head of the fibula, runs along the front of the outer surface of the muscle, and becomes free in the lower third of the leg. It then passes behind the outer ankle, beneath the external annular ligament, in a special sheath with the tendon of the peroneus brevis, which lies in front of it. On the outer surface of the calcaneum it runs forward and downward in a special compartment of the external annular ligament below the companion tendon. At the outer border of the foot it again changes its direction, and passes obliquely inward and forward across the sole of the foot, in a canal formed by the long PERONEUS LONGUS—PERONEUS ERE VIS. 413 plantar ligament beneath, and by the groove in the cuboid bone above, to its insertion near the inner side of the sole. In the upper two-thirds of the leg the peroneus longus almost entirely conceals from view the peroneus brevis, which lies beneath and slightly anterior to it. The synovial tube which it enters at the outer ankle is common to it and the peroneus brevis, and bifurcates to accompany the two tendons where they are separated by the peroneal tubercle of the os calcis. A second sheath envelops the tendon in the sole, and where the tendon enters this canal it often contains a sesamoid bone which plays upon the front of the ridge of the cuboid bone. Nerve-supply.—From the musculo-cutaneous branch of the external pop- liteal nerve by filaments which enter the deep and posterior aspect of the muscle in its upper third. Action.—(1) To extend the ankle joint; (2) to abduct the anterior part of the foot; (3) to depress the inner border of the foot, and so to evert the sole; (4) by drawing backward and outward the base of the first metatarsal bone, it tends to render more concave the antero-posterior and transverse arches of the foot. In the former action it assists the tibialis posticus. In walking, it will act with the gastrocnemius and soleus in lifting the heel from the ground, and its tendency to evert the sole and abduct the foot will counteract the opposite tendency of the muscles attached to the tendo-Achillis. Moreover, the tendency of this latter set of muscles is to press the outer part of the ball of the toes firmly upon the ground. On the other hand, the influence of the peroneus longus in extending the foot is especially exerted upon the ball of the great toe. Bv the combined action of all these extensors of the ankle the whole of the ball of the foot is pressed evenly upon the ground and firmness of tread secured. Relations.—Superficially, the deep fascia, the external annular ligament; and in the sole the abductor minimi digiti, the adductor hallucis, and long plantar ligament; in front, the peroneus brevis, the extensor longus digitorum, and the musculo-cutaneous nerve; behind, the soleus and flexor longus hallucis; deeply, the external popliteal nerve which occupies a fibrous canal below the head of the fibula, the ankle-joint, calcaneum, cuboid, and the bases of the second and third metatarsal bones. Variations.—Sometimes a second peroneus arises between the peroneus longus and brevis, and sends its tendon to join that of the peroneus longus. A slip may be given to the external annular ligament. The insertion of the muscle may extend to the bases of the adjacent metatarsal bones. 2. PERONEUS BREVIS. The peroneus brevis (Figs. 292, 298)—named from its being the shorter of the two fibular muscles—is also a triangular sheet. Origin.—(1) The lower two-thirds of the outer (or peroneal) surface of the fibula; (2) the deep fascia of the leg and the intermuscular septa in front and behind. Insertion.—(1) The outer part of the base of the fifth metatarsal bone; (2) the outer border of the expansion of the tendon of the extensor longus digitorum upon the first phalanx of the little toe. Structure.—This is also a penniform muscle. The short fibres pass obliquely forward and inward to the tendon which runs along the outer surface of the muscle close to its anterior border. It becomes free from fleshy fibres just above the external malleolus where it passes beneath the external annular ligament in the same sheath with the peroneus longus tendon, and after changing its direction runs forward and somewhat downward upon the outer surface of the calcaneum and above the peroneal tubercle. Nerve-supply.—The musculo-cutaneous branch of the popliteal nerve by filaments which enter the deep aspect of the muscle about the middle of the leg. Action.—(1) Slightly to extend the ankle; (2) to abduct the anterior part of the foot; (3) slightly to elevate the outer border of the foot and so evert the sole. 414 THE MUSCLES. Relations.—Superficially, the peroneus longus, deep fascia of the leg and external annular ligament; in front, the extensor longus digitorum and peroneus tertius; behind, the peroneus longus and flexor longus hallucis ; deeply, the ankle joint, calcaneum, and cuboid bones. Variations.—The small slip which the tendon sends on to the expansion upon the little toe may be wanting, or it may be inserted into the first or even the second phalanx. This slip may be entirely separate, so as to form a fourth peroneus. THE MUSCLES OF THE THORAX. These consist of six muscles, or sets of muscles, which are attached chiefly to the ribs, their cartilages, and the sternum, viz., the external and internal intercostals, the levatores costarum, the triangularis sterni, infracostales (or subcostales), and diaphragm. The intercostal muscles—named from their position—are long narrow sheets of short oblique muscular fibres which occupy the intercostal spaces. The fibres of the outer sheet run downward and forward, and those of the inner down- ward and backward ; and the two sheets are the upper continuations of the obliquus externus and internus of the abdominal wall. Intercostal Muscles. i. THE EXTERNAL INTERCOSTALS. The external intercostals, which are stronger than the internal, are eleven in number, and fill the space between the ribs from the tubercle to the tip. In the higher spaces, however, they do not come quite so far forward as below. Above, the lower attachment barely reaches the tip of the rib ; while below, the upper attachment reaches the tip, and the lower is upon the cartilage. Origin.—The lower or outer border of all the ribs except the last, from tubercle to anterior extremity. Insertion.—The outer aspect of the upper border of all the ribs but the first from a little in front of the tubercle to the tip, or in the lower ribs for a short distance upon the cartilage. Structure.—Composed of obliquely directed parallel bundles of fleshy fibre, with a short tendinous origin, and with a slight admixture of fibrous tissue. The posterior are more oblique than the anterior fibres. The sheet formed by these fibres is thickest behind, and becomes gradually thinner forward. Between the cartilages it is succeeded by a thin membrane, the external intercostal fascia, which is composed of fibres running with the same slope as those of the muscle. Nerve-supply.—The intercostal nerves as they run forward give numerous filaments to the inner surface of the sheets. Action.—See later. Relations.—Superficially, the pectoralis major and minor, the serratus magnus, the external oblique, the latissimus dorsi, the trapezius, rhomboidei, the serrati postici, the continuation upward of the erector spinae, and the levatores costarum ; deeply, the internal intercostals and infracostales, the intercostal vessels and nerves. THE EXTERNAL INTERCOSTALS. 415 Fig. 299.—The External Intercostals and Levatores Costarum. Complex us. Obliquus superior. Rectus capitis posticus minor. Rectus capitis posticus major, Obliquus inferior, Multifidus spinae, Semispinalis colli Seventh cervical vertebra, Cervicalis ascendens Longissimus dorsi Semispinalis dorsi Multifidus spinae Levator costae, Twelfth thoracic vertebra, Longissimus dorsi. Ilio-costalis, Multifidus spinae Obliquus internus, Lumbar fascia, Ilio-costalis, Fifth lumbar vertebra, Multifidus spinae 416 THE MUSCLES. 2. THE INTERNAL INTERCOSTALS. The internal intercostals are eleven in number, and fill the space from the angles of the ribs to the anterior extremity of the cartilages. The fibres, which are shorter and not quite so oblique as those of the outer sheet, are directed down- ward and backward. Origin.—The upper border of the subcostal groove of the eleven upper ribs from the angle forward, and the continuation of this border upon the cartilages. Insertion.—The inner aspect of the upper border of the eleven lower ribs and cartilages. Structure.—The sheets are thicker in front. There is less fibrous tissue Fig. 300.—The Intercostal Muscles. External intercostals. External intercostals. Internal intercostals. Infracostales. Internal intercostals. mixed with the fleshy fibres than in the outer sheet. In the upper and lower spaces the fleshy fibres are continued a little further back than the angles. The rest of the space behind the thin posterior border of the sheet is filled by a thin membrane composed of fibres running in the same direction, and is called the internal intercostal fascia. Nerve-supply.—Branches from the intercostal nerves, which are supplied to its outer surface or are given off where the nerves are concealed in the interior of the muscle. Action.—See below. Relations.—Superficially, the external intercostal muscles, and the inter- THE INTERNAL INTERCOSTALS. costal arteries and nerves; deeply, the triangularis sterni, infracostales, and the pleura. The action of the intercostal muscles generally is to approximate the ribs to each other, and they are chiefly used in inspiration. The obliquity of their fibres enables them with a small contraction to produce a greater approximation than if they ran perpendicularly between the ribs (page 304). Moreover, if the fibres were all directed, like those of the outer sheet, downward and forward, there would be a tendency for the lower ribs to be drawn backward as well as upward in inspiration ; and if, on the other hand, all the fibres were directed downward and backward like those of the inner sheet, the tendency would be for the lower ribs to be drawn forward as well as upward in inspiration. The combined action of the two sets produces the direct elevation of the ribs, the forward pull of the inner sheet being counteracted by the backward pull of the outer sheet. If the external intercostals were carried forward as far as the sternum, they would tend to take the sternum as a fixed point and to depress the front extremities of the ribs. A similar result would follow the continuation backward of the internal inter- costals to the vertebral column. It will be also noticed that the front part of the external, and the back part of the internal intercostal sheets are thin and weak, so as to diminish this tendency toward an expiratory movement. It has been urged that both sets of intercostals cannot approximate the ribs, as in inspiration some of the intercostal spaces are seen to open out and become wider. To this it may be replied that, whatever happens in some of the spaces, it is certain that the gen- eral tendency is that of approximation of the ribs and diminution of the intervals between them, as after a full inspiration the last rib is nearer to the first rib. Moreover, it does not always follow that because a muscle is lengthening it may not be acting (cf. such cases as that of the long head of the triceps when it is used in extending the elbow during the elevation of the arm). If, when most of the ribs are being approximated, it should happen that some of the spaces are found to be widened, the action of the muscle in these widened spaces will probably be to prevent a greater separation, and by steadying the lower ribs to enable the mus- cles which descend from them to act. When the lowest rib is fixed by the quadratus lumborum and other muscles, it is probable that the intercostals, at any rate those of the lower spaces, by approximating the lower ribs to the last rib, may act as muscles of expiration. The following are some of the arguments which may be adduced in support of the view that both sets of intercostals act together, and also that their action is usually inspiratory. 1. The advantage already mentioned, from their oblique decussation enabling them to approximate the ribs more completely and at the same time to elevate them directly when they act in combination (cf. the action of the external and internal oblique in approximating the last rib to the crest of the ilium). 2. Muscles supplied by the same nerve are rarely antagonistic. 3. In long-standing paralysis of the intercostals the sternum is depressed, the chest flattened, and kept in a permanent condition of exaggerated expiration. 4. Galvanism of the intercostals produces expansion of the chest. In Du- chenne’s experiment he found that when he galvanized so slightly as only to affect the external intercostals, the inspiratory movement was small; but when he gal- vanized so strongly as to affect the nerve, and through the nerve the internal intercostals—as was known by the contraction of muscular fibre being felt between the cartilages of the ribs, in which situation the only fleshy fibres are those of the inner set—a strong inspiratory movement was produced. From the peculiar shape of the ribs and the mode of their articulation, their elevation is accompanied by a rotation of the arcs formed by them upon their chords so that their planes from a sloping attain an almost horizontal position. Hence the widening of the chest during inspiration, in addition to the increase of movement from before backward due to the elevation’of the tips of the ribs. 418 THE MUSCLES. 3. LEVATORES COSTARUM. The levatores costarum (Fig. 299)—named from their action, as elevators of the ribs—are twelve triangular sheets, which cover the back part of the inter- costal spaces, and are continuous with the fibres of the external intercostal muscles. Origin.—The tips of the transverse processes of the last cervical, and all the thoracic vertebrae except the last. Insertion.—The outer surface of the ribs from the tubercle to the angle. Structure.—Arising by short tendinous fibres, the muscle expands in a fan shape, and is attached to the next rib below. Frequently fibres pass over one rib and are inserted upon the next but one. Nerve-supply.—The intercostal nerves which send branches to their deep surfaces. Fig. 301.—The Muscles attached to the Back of the Sternum. Stern o-hyoid. Sterno-thyroid. Triangula- ris sterni. Sternal origin of diaphragm Costal origin of - diaphragm Triangula- ris sterni. Transversalis abdominis. Action.—To elevate the ribs in inspiration. Relations.—Superficially, the outer upward continuations of the erector spime; deeply, the external intercostals, which are continuous with the outer border of the muscles. 4. TRIANGULARIS STERNI. As the external and -internal oblique muscles of the abdomen are represented by the external and internal intercostals in the thorax, so also the transversalis abdominis has its counterpart in the thin stratum of muscular fibre at the sides of the sternum called the triangularis sterni, and the still thinner expansion behind of the infracostales. INFRA COSTALES—DIAPHRA GM. 419 The triangularis sterni—named from its shape and its connection with the sternum—is a thin, musculo-membranous, triangular sheet, with the apex below and directed internally, while the serrated base is external. Origin.—(i) The side of the lower third of the back of the sternum; (2) the upper and lateral part of the back of the ensiform cartilage; (3) the back of the inner ends of the fifth, sixth, and seventh costal cartilages. Insertion.—The outer end of the back and lower border of the cartilages of the second or third to the sixth ribs, and occasionally the tip of the ribs also. Structure.—The muscle is membranous at its origin and insertion, and it contains many bands of fibrous tissue. Its fibres diverge fanwise, the lower ones being horizontal, and in serial continuation with the upper digitations of the trans- versus abdominis, while its higher fibres run obliquely upward and outward. Nerve-supply.—The upper intercostals, which send filaments to its anterior aspect. Action.—To depress the anterior extremities of the ribs to which it is attached, and so to help in expiration. Relations.—In front, the internal intercostals, cartilages of the ribs, and internal mammary vessels; behind, the pleura and pericardium. 5. INFRACOSTALES. The infracostales -or subcostales—named from their position beneath the ribs—form a thin musculo-membranous sheet lining the back of the thorax external to the tubercles of the ribs; broader and better developed below, becoming narrower and thinner above. Frequently it consists of only a few bundles of fibres which can be distinguished from the internal intercostals by the fact that they are not confined to one intercostal space. Origin.—The lower part of the inner surface of the ribs near their angles. Insertion.—The upper part of the inner surface of the ribs, each bundle of fibres usually passing over one rib to be inserted upon the next higher. Structure.—The fibres arise tendinous, run upward and outward, and have tendinous insertions. The higher fibres run more vertically. The lower approach nearer to the vertebral column, arising from the ribs just external to their tubercles. Nerve-supply.—The intercostal nerves, which enter their outer surface. Action.—To depress the ribs and assist in expiration. Relations.—Externally, the external and internal intercostal muscles; inter- nally, the parietal layer of the pleura, which is separated from them by a thin aponeurosis, sometimes called the endothoracic fascia. 6. THE DIAPHRAGM. The diaphragm—named from its function as the dtAypaypa, or partition wall between the thorax and abdomen—is a dome-shaped musculo-membranous sheet of a kidney-shaped outline when seen from above, and consists of a pair of muscles with a lateral origin and a central aponeurotic insertion, resembling the two transversales abdominis, which unite in the linea alba so as also to form a single dome-shaped biventral muscle. Origin.—By three portions :— i. Anterior or sternal portion.—The lower border and back of the ensi- form cartilage, and the adjacent part of the back of the anterior aponeurosis of the transversalis abdominis. 2. Lateral or costal portion.—The lower border and inner surface of the cartilages of the six lower ribs, and sometimes also from the adjacent part of the ribs. 3. Posterior or vertebral portion.—(i) The ligamentum arcuatum externum, a fibrous thickening of the anterior layer of the lumbar fascia, which stretches from the tip of the transverse process of the second lumbar vertebra to 420 THE MUSCLES. the tip of the last rib; (2) the ligamentum arcuatum internum—a fibrous thickening of the iliac fascia, which arches over the upper part of the psoas from the side of the body of the second lumbar vertebra to the tip of it's transverse process ; (3) the crus of the diaphragm—a strong vertical band, fleshy externally, tendinous internally—arising on the right side from the front of the bodies of the first to the third or fourth lumbar vertebrge, from the intervening vertebral discs, and the anterior common ligament; on the left side, from the bodies of the first to the second or third vertebrae only, as well as the discs and anterior common ligament. Insertion.—The front, sides, and back, of the central tendon. Structure.—The fibres, arising fleshy from their extensive origin, pass at first vertically upward, and then arch inward to be attached to the borders of the cen- tral tendon. The sternal fibres are the shortest, and they are often separated from the costal portion by a small triangular interval filled with areolar tissue, and giving passage to the superior epigastric vessels. The costal origin forms a series Fig. 302.—Diaphragm. Sternal ‘origin. Middle divi- sion of ten- don. Opening for vena cava inferior. Right division of tendon. _ CEsophagus. -Left division of tendon. - Costal origin. I Ligamentum £ arcuatum internum. | Left crus. Ligamentum arcuatum externum. _ Transverse process of sec- ond lumbar vertebra. - Fourth lumbar vertebra. Aorta. Right crus. Psoas parvus. Psoas. Transversalis abdominis. Quadratus lumborum. of teeth which do not correspond accurately with the number of ribs, some rib cartilages having two teeth attached to them. They interdigitate with the serra- tions of the transversalis abdominis (Fig. 301). The aponeurotic fibres which form the inner portion of the two crura, after arching in front of the abdominal aorta, are continued by fleshy fibres which decussate, and so changing sides form a loop round the oesophagus before joining the central aponeurosis. The central tendon, or aponeurosis, forms the summit of the dome, and is of a similar outline to the diaphragm, being kidney-shaped, with the concavity behind. It approaches nearer the back than the front of the thorax. There is a slight notching of its outline in front, which divides it into three parts, so that it has somewhat of a trefoil shape, the right leaflet being the largest, and the left the smallest. Its fibres run in many directions. The diaphragm contains three large foramina, for the passage of the vena cava inferior, oesophagus, and aorta. Foramina.—Close to the posterior border of the central tendon at the junction THE ABDOMINAL PARIETES. 421 of the right and middle leaflet is a quadrilateral opening with rounded angles, the foramen for the vena cava inferior, the outer coat of which vessel is blended with its fibrous edges. The oesophageal opening is oval, with the long diameter directed forward. It is surrounded by fleshy fibres, and lies to the left of the middle line, opposite the body of the tenth thoracic vertebra. Through it passes the oesopha- gus, with the left vagus nerve in front, and the right behind ; also a few small oesophageal branches from the thoracic aorta, on their way to join some small oeso- phageal branches from the gastric artery. The aortic opening, formed by the union of the crura, is fibrous and of oval shape. It is situated in front of the twelfth thoracic vertebra, and is completed behind by the anterior common liga- ment. Through it pass the aorta, the vena azygos major, and the thoracic duct. In the crura on either side are small openings which allow of the passage of the great splanchnic nerves, and the left crus is usually perforated also by the vena azygos minor. Nerve-supply.—The two phrenic nerves, chiefly derived from the cervical plexus of each side through the fourth cervical nerves, break up close to the dia- phragm into many filaments, which penetrate the muscular structure near the anterior border of the central tendon, and are distributed to the under surface of the muscle. Sympathetic filaments are also given to it from the plexuses which accompany the phrenic arteries. Action.—To deepen the chest from above downward, and so produce a move- ment of inspiration. The central tendon, which is closely connected by means of the pericardium with the deep fascia of the neck, is but little depressed; but the arched fleshy fibres all around flatten, and so increase greatly the capacity of the sides of the thoracic cavity. At the same time the abdominal viscera are driven downward, and as the front part of the parietes is the most yielding, they are also displaced forward, so as to cause a greater prominence of this part of the abdomen. In the expulsive efforts of defecation and parturition, after the diaphragm has first contracted in a deep inspiration, and the glottis has been closed so as to prevent the escape of air from the chest, the abdominal muscles are able to contract with full effect upon the viscera, which have been pressed down by the previous descent of the diaphragm. The lower six ribs are slightly elevated by the diaphragm, and the hypochon- dria somewhat dilated, this latter movement being due to the forward and outward pressure of the depressed viscera. Relations.—Above lie the pleurae and pericardium, the heart and the lungs. Below are the peritoneum, the liver with its ligaments, the stomach, the spleen, pancreas, kidneys, and suprarenal capsules. The dome-shaped upper convex surface rises higher upon the right than the left side. On the right side, being raised by the liver, it reaches to the level of the junction of the fifth costal carti- lage with the sternum, and on the left side only to the level of the junction of the sixth costal cartilage. Variations.—The oesophageal opening has been found in the right crus, instead of being surrounded by decussating fibres from both crura. The sternal portion of the muscle is not infrequently absent. THE ABDOMINAL PARIETES. The superficial fascia the walls of the abdomen is continuous with that of the thorax and lower limbs, and is usually divided into two layers. The first layer is well provided with fat, which in many individuals attains to a considerable thickness, especially in the lower part of the anterior wall. The second or deep layer (Scarpa’s fascia) is of a more membranous character and contains a quantity of elastic fibres. Near the groin it is separated from the 422 THE MUSCLES. more superficial layer by blood-vessels and lymphatic glands. Upon its deeper surface it is loosely connected with the deep fascia which invests the external oblique muscle ; but it is closely blended with the linea alba, the fibrous structures in front of the pubic bones, the fascia lata immediately below Poupart’s ligament, and the crest of the ilium. Both layers are continued downward upon the external genital organs. In the male they lose their fat and blend with the suspensory ligament of the penis, the fascia covering that organ, and the dartos and septum of the scrotum. In the female they are continuous with the superficial fascia of the vulva. THE ABDOMINAL MUSCLES. The muscular portion of the abdominal wall forms a lozenge-shaped figure of which the vertical diagonal extends from the ensiform process to the symphysis pubis, while the transverse encircles the abdomen from tip to tip of the transverse processes of the third lumbar vertebra. The boundaries of this muscular wall are formed, above, by the costal carti- lages of the six lower ribs ; behind, by the tips of the transverse processes of the lumbar vertebrae ; below, by the crests of the ilia and the pubes. More accurately, each lateral half may be looked upon as a four-sided figure of which the upper boundary slopes backward and downward ; the lower, backward and upward ; while the long anterior boundary and short posterior boundary are vertical and parallel. The muscles contained in the parietes may be divided into vertical and transverse. The former, three in number, are situated two in front and one behind ; while the latter, also three in number, pass transversely, or with some obliquity, between the anterior and posterior boundaries of the space. The two lateral halves unite in front in a strong fibrous band called the linea alba, which stretches from the tip of the ensiform cartilage to the upper part of the symphysis pubis. It is partly formed by vertical fibres stretching between these two points, but chiefly by the interlacement of the transverse and oblique bands of fibrous tissue which pass between the aponeuroses of the muscles upon either side. In its lower two-fifths it is not more than one-eighth of an inch broad ; in its upper three-fifths it is broader, usually not less than a quarter of an inch in width, but in some bodies it may be stretched to a much greater extent. At the junction of the lower two-fifths and upper three-fifths is the small fibrous ring of the umbilicus through which pass the remnants of the foetal vessels. Anterior Vertical Muscles. These are two in number—the pyramidalis and rectus abdominis. The pyramidalis (Fig. 266)—named somewhat fancifully from its triangular shape—is a fan-shaped sheet of muscular fibre forming a right-angled triangle, of which the shortest side corresponds to the origin, and the other side containing the right angle to the linea alba. Origin.—(1) The front of the pubic crest ; and the fibrous structures which cover the front of the body of the os pubis and its symphysis. Insertion.—The linea alba at a point about half-way between the pubes and the umbilicus. Structure.—Arising by a short tendinous sheet, the fleshy fibres converge as they pass upward. Those nearer to the middle line ascend vertically, while those i. PYRAMIDALIS. PYRAMIDA LIS—RECTUS ABDOMINIS. 423 which arise near the pubic spine pass obliquely upward and inward to the ten- dinous insertion of the muscle into the linea alba three or four inches above the symphysis pubis, Nerve-supply.—From the eleventh and twelfth thoracic nerves and from the ilio-hypogastric branch of the lumbar plexus, through their terminal filaments which enter the deep surface of the muscle. Action.—By its contraction it pulls upon the linea alba and so upon the lower end of the ensiform cartilage. It will therefore assist the rectus in flexion of the thorax upon the pelvis, or of the pelvis upon the thorax. It can also help feebly to compress the abdominal viscera. Relations. — Superficially, the aponeuroses of the transverse abdominal muscles; deeply, the rectus abdominis, from which it is separated by a thin fibrous lamella. Variations.—The height to which this muscle extends is variable. It may be absent on one or both sides ; or it may be double. The rectus abdominis (Fig. 266)—named from its straight direction—is a strong ribbon-shaped muscle running vertically on either side of the linea alba from the pubes to the ensiform and adjacent costal cartilages. Origin.—By two tendons: (1) the larger or outer head from the whole of the crest of the pubes; (2) the inner head crosses the middle line of the body, and arises from the fibrous structures lying in front of the symphysis. Insertion.—(1) The anterior surface of the tip of the fifth rib ; (2) the front of the costal cartilages of the fifth, sixth, and seventh ribs; sometimes, also, (3) the deep posterior surface of the ensiform cartilage near its outer border. Structure.—The inner head arises tendinous from the other side of the mid- dle line, decussating with its fellow; the outer and stronger head arises by a shorter tendon, and is soon joined by the inner head. About an inch above the pubes a fleshy mass is formed, which expands as it ascends into a broad sheet, which below the umbilicus lies close to its fellow of the opposite side. Above, the two muscles are separated by an interval of at least a quarter of an inch. The insertion, which is by short tendinous fibres, is three or four times the width of the origin. The muscle is also curved considerably forward to correspond with the convexity of the front wall of the abdomen. At certain intervals transverse bands of fibrous tissue extend in an irregular zigzag manner across the muscle, especially upon its anterior surface. These are called thelineae transversae, and the transverse depressions which they produce are usually to be seen and felt through the skin. They are generally three or four in number on either side. One is situated opposite the umbilicus ; the second opposite the tip of the ensiform cartilage; the third half-way between these points ; and a fourth is sometimes present which extends incompletely across the muscle at some distance below the umbilicus. They are firmly connected with the anterior layer of the strong sheath of the muscle, which will afterward be described. They do not extend through the whole thickness of the muscle, being deficient behind. Nerve-supply.—From the terminal filaments of the anterior branches of the six lower thoracic nerves which enter the muscle on its posterior surface near the outer border ; and from the ilio-hypogastric branch of the lumbar plexus. Action.—(1) By the tendency of the curved bands of the muscle to become straight during contraction, all the viscera contained in its concavity are com- pressed. It will, therefore, help in defecation, micturition, and parturition ; also in expiration, and especially in strong expiratory efforts, such as coughing and sneezing. (2) By drawing down the ensiform cartilage and the anterior extremi- ties of the middle ribs it flexes the thorax upon the pelvis, and at the same time acts as a flexor of the thoracic and lumbar portions of the spine. Acting less strongly, it fixes the sternum, so that the sterno-mastoids by their contraction may flex the head, e. g., in rising from the recumbent position. (3) Taking its fixed 2. RECTUS ABDOMINIS. 424 THE MUSCLES. point from above, it will draw upward the pubic portion of the pelvis, and so flex the pelvis upon the thorax, as when the lower part of the body is drawn up toward the chest in climbing. The lineae transversae, which are the remnants of the septa which divide the muscular structure at intervals in the lower vertebrates, and which in the croco- dile form the abdominal ribs, have had various uses assigned to them. In the first place they will tend to keep the muscular fibres in their proper place, and prevent them from being separated so as to allow of ventral hernia. Secondly, they will enable the muscle to act not only upon the points of bone which form its direct attachment, but, by means of their connection with the sheath of the muscle and the aponeuroses of which it is formed, they will in some measure diffuse the action of the muscle over the lower ribs and the crest of the ilium. Thirdly, they will enable one part of the muscle to act independently, as, for example, when the lower part exercises some pressure upon the bladder in micturition. Fourthly, they prevent extensive separation when the muscle is injured. On account of the severe strain to which the muscle is exposed, it is sometimes ruptured. If the muscular fibres extended without interruption from the pubes to the ensiform car- tilage, such a rupture would occasion a much wider separation, and consequently much greater disablement than is now found to be the case. Relations.—Superficially, the front layer of its sheath above, and below the pyramidalis; deeply, it is separated from the transversalis fascia and peritoneum in the greater part of its course by the posterior layer of its sheath ; in its lower fourth it is in contact with the transversalis fascia; and above, it lies on the cartilages of the fifth to the ninth ribs, and covers the intercostal muscles which lie between them. Variations.—The rectus may be inserted as high as the fourth or even the third rib. A lateral rectus is sometimes found between the external and internal oblique muscles, extending from the tenth rib to the iliac crest. This group consists of three muscles—the obliquus externus, the obliquus internus, and the transversalis—which lie in successive strata in the abdominal wall. Transverse and Oblique Muscles. The obliquus externus abdominis—named from its position and direction —is a broad curved sheet, partly muscle and partly aponeurosis, of an irregular quadrilateral shape. Origin.—The outer surface of the eight lower ribs about their middle by a series of nearly horizontal lines which, after crossing each rib obliquely downward and backward, extend for a short distance along its lower border. Insertion.—(i) By a strong aponeurosis along the whole of the linea alba ; (2) the front of the os pubis close to the symphysis ; (3) the spine of the pubes and the adjacent part of the ilio-pectineal line ; (4) the deep fascia of the thigh in a thickened band which stretches from the spine of the pubes to the anterior superior spine of the ilium; (5) the anterior half of the outer lip of the crest of the ilium ; (6) at the lower part of the linea alba some of the fibres (the triangular fascial) stretch across the middle line, and are inserted into the front of the crest of the pubes and the inner part of the ilio-pectineal line of the other side. Structure.—At their origin the muscular fibres form a series of teeth which interdigitate in the upper part of the muscle with the serratus magnus, and in the lower with the latissimus dorsi. The general direction of the origin is an oblique line somewhat curved upon itself so as to be convex upward and backward. Above and below, the origin is nearer to the anterior extremity of the ribs. From this origin the fleshy fibres pass downward and forward, and at the same time diverge famvise, at first lying upon the ribs and their cartilages, and then without any 1. OBLIQUUS EXTERNUS. OBLIQUUS EXTERNUS. 425 Fig. 303.—External Oblique and Ilio-tibial Band. Pectoralis major. Origin of pectoralis major from aponeuro- sis of obliquus externus. Trapezius. Serratus, magnus. Latissimus dorsi. Obliquus externus, Linea semilunaris. Tensor j vaginae femoris. ■Gluteus maximus. Ilio-tibial band. .Tendon of biceps. 426 THE MUSCLES. bony support as part of the muscular wall of the abdomen. The change from fleshy to tendinous fibres takes place at some distance from the outer border of the rectus muscle, in such a way that the fleshy mass terminates rather abruptly in a right angle situated in the iliac region of the abdomen. This angle is formed in front by a vertical line, which passes downward from the tip of the ninth costal cartilage; and below by a horizontal line passing forward from a point upon the crest of the ilium an inch or two behind the anterior superior spine. This abrupt limitation of the muscular fibres gives rise to a projection which is distinctly visible through the skin in a muscular subject. The aponeurosis thus formed blends in nearly the whole of its extent with that of the adjacent muscle, the obliquus inter- nus, and in the middle line it unites at the linea alba with that of the opposite side. Above, it extends upward as high as the insertion of the rectus muscle, of which it forms part of the sheath, and in this locality it gives origin to a part of the pectoralis major. At the lower end of the linea alba the portion which, crossing the middle line, is inserted into the crest of the pubes and the ilio-pecti- neal line of the other side, is known by the name of the triangular fascia. The insertion into the pubic bone of the same side is interrupted by an interval corresponding to the crest of the pubes, and forms the external abdominal ring. From the spine of the pubes to the anterior superior spine of the ilium, the aponeurosis forms a thickened band slightly convex downward, which blends with the fascia lata, and is called Poupart’s ligament. The rest of the insertion into the outer lip of the crest of the ilium is by short tendinous fibres. The insertion of the lower edge of the aponeurosis is also carried backward and outward from the spine of the pubes along the inner part of the ilio-pectineal line by a horizontal triangle of fascia called Gimbernat’s ligament. This liga- ment is attached to the lower end of Poupart’s ligament in front, and it presents a concave surface upward, upon which lie the structures which emerge through the external abdominal ring. The external abdominal ring (Fig. 285) is an obliquely directed slit in the aponeurosis of the obliquus externus, which transmits the spermatic cord in the male, and the round ligament of the uterus in the female. The slit is formed by the divergence of the obliquely directed fibres of the aponeurosis. Those above, which form the inner pillar, as it is called, of the ring, run downward and inward to be attached to the front of the symphysis pubis; those below, which form the external pillar of the ring, form a thin edge at first, but thicken just before their attachment to the spine of the pubes and the inner ex- tremity of the ilio-pectineal line, for at this point the external pillar is identical with Poupart’s ligament. Upon the surface of the obliquus externus, close to the external abdominal ring, the oblique fibres of the aponeurosis are fastened together by some transversely directed fibres, the intercolumnar fibres, which run upward and inward from Poupart’s ligament, limiting and rounding off the upper and outer end of the external abdominal ring. A thin membrane, the intercolumnar fascia, is prolonged from the edges of this opening over the spermatic cord and round ligament, of which it forms the external envelope. Nerve-supply.—From the anterior branches of the lower thoracic nerves and from the ilio-hypogastricand ilio-inguinal nerves which come from the highest nerve of the lumbar plexus, by means of numerous filaments which, passing through the internal oblique, enter the muscle on its deep surface. Action.—(1) The curved muscular fibres in their contraction tend to become straight and so compress the viscera which lie in their concavity ; they act in defecation, micturition, parturition, and all expiratory efforts ; (2) the two obliqui externi acting together will draw upward the front part of the pelvis, and so flex it upon the thorax; (3) the muscle of one side, acting alone or in conjunction with the internal oblique of the opposite side, will rotate the pelvis and the lower part of the body to the same side ; (4) it will tend by its posterior fibres to draw the crest of the ilium upward toward the lower ribs, and will thus act as a lateral flexor of the pelvis upon the thorax; (5) acting from below, the muscles of the two sides will draw the thorax downward and forward and flex the lumbar and lower part of the thoracic spine ; (6) it will rotate the thorax upon the pelvis so as to turn the OBLIQUUS INTERNUS. 427 thorax and the upper part of the body to the opposite side ; (7) the posterior fibres will flex the thorax laterally. Relations.—Superficially, the integuments, and for a short space behind the latissimus dorsi; deeply, the lower ribs, their cartilages, the intercostal muscles between them, and the internal oblique ; and below, the spermatic cord or round ligament in the inguinal canal. , Variations.—The obliquus externus may rise from more or fewer ribs. Occasionally a deeper plane is separated from the rest of the muscle. In one case the anterior part of the aponeurosis was observed to be wanting. 2. OBLIQUUS INTERNUS. The obliquus internus abdominis (Fig. 266)—named from its relation to the preceding muscle and the direction of its fibres—is an irregular quadrilateral curved sheet, partly fleshy and partly aponeurotic. Origin.—(1) The outer half of Poupart’s ligament; (2) the anterior two- thirds of the space intervening between the inner and outer lips of the crest of the ilium; (3) the outer and posterior aspect of the aponeurosis of the transversalis abdominis (which aponeurosis is also called the lumbar fascia). Insertion.—(1) For about one inch into the inner extremity of the ilio- pectineal line; (2) the anterior border of the crest of the pubes; (3) the whole length of the linea alba; (4) the lower borders of the cartilages of the last three ribs. Structure.—Arising by fleshy and short tendinous fibres intermingled, a fleshy sheet is soon formed, the fibres of which diverge ; the anterior passing for- ward and downward, the middle forward and upward, and the posterior directly upward to their insertion, which is by means of a broad aponeurosis. At the front of the lower intercostal spaces the fibres run parallel to, and in the same plane with, the internal intercostals. The position of the change from fleshy to aponeurotic fibres may be indicated by two lines at right angles to one another; one passing upward and a little outward from the middle of Poupart’s ligament, the other horizontally forward below the tip of the last rib, and near the edges of the lower rib cartilages. The aponeurosis is blended with that of the external oblique, and in its upper three-fourths it divides into an anterior and a posterior plane which together form the sheath of the rectus muscle. In the lower fourth of the abdomen the whole of the aponeurosis passes in front of this muscle. The line of division of the aponeurosis of the internal oblique is indicated on the surface of the abdomen by a furrow called the linea semilunaris, which lies between the fleshy part of the muscle and the outer border of the rectus muscle, and forms a curve, concave inward, which extends from the cartilage of the eighth rib above to the vicinity of the pubes below. The plica semilunaris, or fold of Douglas, on the other hand, is the name given to the lower edge of the posterior sheath of the rectus, when that muscle pierces the aponeuroses so as to lie behind all of them in the lower fourth of its course. The lowest portion of the aponeurosis of insertion of the obliquus internus is closely blended with that of the transversalis abdominis, and is called the conjoint tendon. Nerve-supply.—From the anterior primary branches of the lower thoracic nerves, and from the first nerve of the lumbar plexus by means of the ilio-inguinal and ilio-hypogastric nerves. The main branches of these nerves run forward between this muscle and the transversalis abdominis, and give off their filaments to the internal surface of the muscle; some also are distributed to the muscle by the branches which perforate it in order to supply the external oblique. Action.—(1) The fibres of the muscle being curved tend to flatten upon their contraction and so to compress the viscera contained within their concavity; they will therefore help in defecation, micturition, parturition, and all expiratory efforts. (2) It will also assist expiration by drawing the lower ribs downward. (3) When both muscles act together they flex the thorax upon the pelvis. They 428 THE MUSCLES. will also flex the lumbar and lower thoracic spine. (4) When the muscle of one side acts alone, or in conjunction with the obliquus externus of the other side, it will rotate the thorax to its own side. (5) The posterior fibres of the muscle will draw down the side of the thorax ; it will therefore be a lateral flexor of the thorax and of the lumbar and lower dorsal spine. (6) Acting from the thorax, this muscle will flex the pelvis, rotate it to the opposite side, and by means of its pos- terior fibres it will act as a lateral flexor of the pelvis. Relations.—Superficially, the external oblique and latissimus dorsi; deeply, the transversalis abdominis. Its lower margin lies for a short distance in front of the inguinal canal, containing the spermatic cord in the male, and the round liga- ment in the female. The conjoined tendon lies internally beneath these struc- tures. The aponeurosis of the internal oblique is also in relation with the rectus muscle, of which it forms the sheath in the upper three-fourths of its extent. Variations.—Sometimes the muscle is crossed close to its insertion upon the ribs by tendinous insertions, which probably represent ribs. Cremaster. The cremaster (Fig. 285)—named from its action as a suspender of the testicle (zpe[ia