fc'^^ft'.''^ ^Ica; %. ndfa n ANATOMY, DESCRIPTIVE AND SURGICAL. BY HENRY GRAY, F.E.S, Fellow of the Royal College of Surgeons; Lecturer on Anatomy at St. George's Hospital Medical School. A NEW EDITION, THOROUGHLY REVISED BY AMERICAN AUTHORITIES, FROM the THIRTEENTH ENGLISH EDITION Edited by T. PICKERING PICK, F.R.C.S. LEA BROTHERS & CO., PHILADELPHIA AND NEW YORK. 1897. H\ y^ Y\D wots , r+eVvi i Entered according to Act of Congress, in the year 1897, by LEA BEOTHERS & CO., in the office of the Librarian of Congress at Washington. All rights reserved. Westcott & Thomson, Stereotype™ and Eleclrotypers, Philada. William J. Dornan, Printer, Philada. TO SIR BENJAMIN COLLINS BRODIE, BART., F.R.S., D.C.L., SERJEANT-SURGEON TO THE QUEEN, CORRESPONDING MEMBER OF THE INSTITUTE OF FRANCE, Ubxs Worft is H>eOtcate& IN ADMIRATION OF HIS GREAT TALENTS AND IN REMEMBRANCE OF MANY ACTS OF KINDNESS SHOWN TO THE AUTHOR FROM AN EARLY PERIOD OF HIS PROFESSIONAL CAREER. PUBLISHERS' NOTE TO THE NEW AMERICAN EDITION, In his masterpiece Henry Gray left undying evidence of his anatomical knowledge and of his comprehension of the best method of imparting it to other minds. After forty years its merits are only brightened by the numerous works which have endeavored to contest its supremacy. During that time it has had the benefit of the careful scrutiny of many leading anatomists of the English- speaking race. Anatomy is far from stationary, either in its facts or in improve- ments in the method of their presentation ; hence any work which would faith- fully reflect the existing position of the science must be revised at comparatively frequent intervals. Fortunately for students and practitioners, Gray's Anatomy enjoys a demand rendering such revision possible. An evidence of the unremitting attention bestowed on this book is afforded in the issue now presented. Its basis is found in the revision of 1896 by Pro- fessor J. Playfair McMurrich and Dr. B. B. Gallaudet. The new chapters on the Brain and the Abdominal Viscera by Dr. Gallaudet and Dr. F. J. Brockway, respectively, have been retained. The section on the Mouth and Teeth has been rewritten by Prof. H. H. Burchard, who has taken account of the latest advances in the highly specialized department which particularly concerns students and practitioners of Dentistry. The splendid illustrations in Gray have long been known as the most effective and intelligible presentations of anatomical structures ever produced. In the edition of 1896 this series was increased by the addition of one hundred and thirty-five new pictures. The total of seven hundred and seventy-two illus- trations stands unchanged in the new issue, but it includes a large number of new engravings, no expense having been spared to effect improvement wherever possible. The practical application of anatomical facts in medicine and surgery has always been a prominent feature of the work, and this distinctive character- istic has received especial care. In short, this edition is presented to the medical public with the con- fident expectation that it will be found worthy in every respect to main- tain the exalted position which the work has for so many years enjoyed as the most convenient and intelligible exposition of its subject. PREFACE TO THE THIRTEENTH ENGLISH EDITION. When Henry Gray published this work in 1858, he entitled it Anatomy, Descriptive and Surgical, and he introduced under each subdivision such observations on practical points of Surgery as shoAV the necessity of an accurate acquaintance with the anatomy of the part under examination. This was the first time that such an endeavor had been made by an English Anatomist. The Editor has endeavored to follow^ in the lines originally laid down by the Author, and has tried to keep before himself the fact that the work is intended for Students of Surgery rather than for the Scientific Anatomist. Not that the Editor would wish to disparage, for an instant, the study of Philosophical or Scientific Anatomy, but that he thought it right, con- sidering the class of students for whom the work is primarily intended, that he should be practical rather than abstract and theoretical. Accordingly, he has not altered in any way the original plan of the work, but has endeavored to render it more practical, and of more use to the student, who will hereafter have to apply his knowledge of Anatomy to his practice of Surgery, by intro- ducing a considerably increased amount of Surgical Anatomy, and by pointing out the bearings of Anatomy on the practice of Surgery. In addition to this, the whole work has undergone a careful revision, and in some minor details a rearrangement has been made. The Editor is deeply indebted to his friend Mr. Ross for much kind assist- ance in the preparation of this edition, and also for the help that he has rendered him in passing these pages through the press. To Dr. Leonard Remfry he is also much indebted for his kindness in revis- ing the section on the anatomy of the Female Organs of Generation. Several new illustrations have been added, principally from dissections in the Hunterian Museum of the Royal College of Surgeons. The Editor takes this opportunity of thanking Prosector Pearson for the kind interest he has dis- played and assistance he has rendered in the preparation of these drawings, which were taken from dissections made by this master in the art of dissecting. 8 CONTENTS. GENERAL ANATOMY. The Blood.................33 The Lymph and Chyle ...........37 The Animal Cell..............38 Epithelium................41 Connective Tissue..............44 Pigment................50 Cartilage..................51 White Fibro-cartilage..........52 Yellow or Reticular, Elastic Cartilage ... 53 Bone....................54 Development of Bone..........59 Muscular Tissue..............64 TJnstriped Muscle............6s Nervous Tissue...............69 The Brain...............73 The Nerves...............73 The Sympathetic Nerve.........75 PAGE Origin and Termination of Nerves .... 75 The Ganglia..............79 The Vascular System............80 The Arteries..............80 The Capillaries.............82 The Veins...............84 The Lymphatics............85 The Lymphatic Glands.........87 The Skin and its Appendages....... 89 The Nails................92 The Hair................93 The Sebaceous Glands..........94 The Sudoriferous Glands ........95 Serous Membranes..............96 Synovial Membranes............96 Mucous Membranes.............97 Secreting Glands..............98 DEVELOPMENT. Growth and Development of the Body . . 100 The Ovum.................100 Fecundation of............101 Segmentation of............102 Division of Blastodermic Membrane.....104 First Rudiments of the Embryo.......107 The Amnion................Ill The Chorion................112 The Belly-stalk..............113 The Decidua................114 The Placenta...............115 Development of the Embryo Proper.....115 The Spine...............115 The Ribs and Sternum.........117 The Cranium and Face.........117 The Nervous Centres ..........120 The Nerves..............122 The Eye................122 The Ear................124 The Nose...............125 The Skin, Glands, and Soft Parts .... 125 The Limbs ..............125 The Muscles..............126 The Blood-vascular System.........126 Vitelline Circulation..........126 Placental Circulation..........127 The Alimentary Canal and its Appendages . . 132 The Respiratory Organs..........134 The Urinary Organs............135 The Generative Organs...........137 Male Organs..............137 Female Organs.............137 External Organs...........139 Chronological Tables of the Development of the Foetus ..............141 DESCRIPTIVE AND SURGICAL ANATOMY. OSTEOLOGY.—THE SKELETON. The Skeleton...............143 Number of the Bones ...........143 Form of Bones...............143 The Spine. General Characters of a Vertebra......144 Characters of the Cervical Vertebrae.....145 Atlas...................146 Axis...................147 Vertebra Prominens............148 Characters of the Dorsal Vertebrae......149 Peculiar Dorsal Vertebras..........151 Characters of the Lumbar Vertebrae.....151 Structure of the Vertebrae.........152 Development of the Vertebrae........152 " Atlas .........153 " " Axis..........154 " '• Seventh Cervical ... 154 " " Lumbar Vertebrae . . ■ 154 Progress of Ossification in the Spine.....154 Sacrum..................155 Coccyx.................159 Of the Spine in general.......... Surface Form of Spine......... Surgical Anatomy of Spine........ The Skull. Bones of the Cranium.......... Occipital Bone........... Parietal Bones............ Frontal Bone............ Temporal Bones........... Sphenoid Bone............ Ethmoid Bone .......... Development of the Cranium..... The Fontanelles........... Wormian Bones......... Congenital Fissures and Gaps..... Bones of the Face: Nasal Bones............. Superior Maxillary Bones....... Changes produced in Upper Jaw by Age Lachrymal Bones.......... Malar Bones............. 160 162 162 164 164 168 170 173 180 185 187 188 L88 188 189 189 195 195 196 9 10 CONTEXTS. PAGE Palate Bones..............197 Inferior Turbinated Bones.......200 Vomer ................201 Lower Jaw ..............201 Changes produced in the Lower Jaw by Age.................204 Sutures of the Skull............206 Vertex of the Skull............208 Base of the Skull, Internal Surface .... 208 Anterior Fossa............20? Middle Fossa..............210 Posterior Fossa.............211 Base of Skull, External Surface.......211 Lateral Region of the Skull........214 Temporal Fossa..............215 Mastoid Portion..............216 Zygomatic Fossa..............216 Spheno-maxillary Fossa...........216 Anterior Region of the Skull........217 Orbits...................217 Nasal Fossae................219 Surface Form of Skull..........222 Surgical Anatomy of Skull.........224 Os Hyoides ................227 The Thorax. The Sternum...............228 The Ribs.................232 Peculiar Ribs..............234 Costal Cartilages..............236 Surface Form of Chest...........236 Surgical Anatomy of Chest.........237 The Upper Extremity. The Shoulder and Pelvic Girdles......238 The Clavicle................23rt Surface Form.............241 Surgical Anatomy...........241 The Scapula................242 Surface Form.............247 Surgical Anatomy...........247 The Humerus...............248 Surface Form.............253 Surgical Anatomy...........253 The Forearm...............254 The Ulna.................254 Surface Form.............259 The Radius................259 Surface Form.............261 Surgical Anatomy of Bones of Forearm . 261 The Hand................262 The Carpus................262 Bones of the Upper Row........262 Bones of the Lower Row........266 The Metacarpus.............267 Peculiar Characters of the Metacarpal Bones . 268 Phalanges.................270 Surface Form of Bones of Hand.....270 Surgical Anatomy of Bones of Hand . . 271 Development of the Bones of the Hand . . . 271 The Lower Extremity. The Hip..................272 Os Innominatum..............272 Ilium.................272 Ischium................272 Os Pubis................277 Development of the Os Innominatum .... 278 The Pelvis.................279 Differences between the Male and Female Pelvis................282 Surface Form of Bones of Pelvis.....283 Surgical Anatomy of Bones of Pelvis . . 283 The Femur or Thigh-Bone.........284 Surface Form.............290 Surgical Anatomy...........290 The Leg..................291 Patella..................291 Surface Form.............292 Surgical Anatomy...........292 Tibia...................293 Surface Form............296 Fibula...................297 Surface Form............299 Surgical Anatomy of Bones of Leg • . 299 The Foot...............299 Tarsus................299 Os Calcis.................299 Astragalus.................303 Cuboid ... .............303 Navicular................304 Cuneiform.................305 Metatarsal Bones..............306 Phalanges...............308 Development of the Bones of the Foot . . . 308 Construction of the Foot as a whole . . . 309 Surface Form of Foot.........310 Surgical Anatomy of Foot........311 Sesamoid Bones . .............312 THE ARTICULATIONS. Structures composing the Joints.......313 Articular Lamella of Bone.......313 Ligaments..............313 Synovial Membrane..........313 Bursas.................314 Synovia...............314 Forms of Articulation: Synarthrosis..............314 Amphiarthrosis.............315 Diarthrosis...............315 Movements of Joints............316 Articulations of the Trunk. Articulations of the Vertebral Column .... 319 " Atlas with the Axis . . . 323 " Spine with the Cranium . 325 " Atlas with the Occipital Bone.........325 Articulation of the Axis with the Occipital Bone 326 Surgical Anatomy of Articulations of the Spine. 327 Temporo-maxillary Articulation.......327 Surface Form.............330 Surgical Anatomy ... ......330 Articulations of the Ribs with the Vertebrae: Costo-vertebral.............330 Costo-transverse............331 Articulations of the Cartilages of the Ribs with the Sternum and Ensiform Cartilage .... 334 Interchondral Articulations.........334 Ligaments of the Sternum ........336 Articulation of the Pelvis with the Spine . . . 336 Articulations of the Pelvis : Articulation of the Sacrum and Ilium . . 336 Ligament between the Sacrum and Ischium 337 Articulation of the Sacrum and Coccyx . 339 Articulation of the Pubes........339 Articulations of the Upper Extremity. Sterno-clavicular..............340 Surface Form.............342 Surgical Anatomy............342 Acromioclavicular.............342 Surface Form.............344 Surgical Anatomy...........344 Proper Ligaments of the Scapula......344 Shoulder-joint...............345 Surface Form.............343 Surgical Anatomy...........343 Elbow-joint................349 Surface Form.............352 Surgical Anatomy...........352 Radio-ulnar Articulations..........353 Surface Form.............353 Wrist-joint...............\ ' 353 Surface Form.............35- Surgical Anatomy...........357 CONTENTS. 11 PAGE Articulations of the Carpus.........357 of the first row of Carpal Bones. 357 of the second row of Carpal Bones 358 of the two rows of Carpal Bones. 358 Carpo-metacarpal Articulations.......359 of the Metacarpal Bone of Thumb and Trapezium.............359 of the four inner Metacarpal Bones and Carpus..............360 Articulations of the Metacarpal Bones .... 361 Metacarpophalangeal Articulations.....361 Surface Form.............362 Articulations of the Phalanges.......362 Articulations of the Lower Extremity. Hip-joint.................362 Surface form..............366 Surgical Anatomy...........366 Knee-joint.................368 Surface Form.............374 Surgical Anatomy...........374 Articulations between the Tibia and Fibula . 376 page Ankle-joint................377 Surface Form.............379 Surgical Anatomy...........379 Articulations of the Tarsus.........380 of the Os Calcis and Astragalus. 380 of the Os Calcis and Cuboid . . 381 of the Os Calcis and Navicular . 382 Surgical Anatomy......382 of the Astragalus and Navicular. 382 of the Navicular and Cuneiform. 383 of the Navicular and Cuboid . . 383 of the Cuneiform with each other 383 of the External Cuneiform and Cuboid...........384 Torso-metatarsal Articulations.......384 Articulations of the Metatarsal Bones .... 385 Synovial Membranes in Tarsal and Metatarsal Joints .... .........385 Metatarsophalangeal Articulations......386 Articulations of the Phalanges.......387 Surface Form.............387 MUSCLES AND FASCIA. General Description of Muscle.......388 Tendons......389 Aponeuroses .... 389 " Fascia.......389 Muscles and Fascia of the Cranium and Face. Subdivision into Groups...........390 Cranial Region. Dissection.................391 Occipito-frontalis..............392 Auricular Region. Dissection.................. 393 Attrahens Aurem.............393 Attollens Aurem..............394 Retrahens Aurem.............394 Actions..................394 Palpebral Region. Dissection.................394 Orbicularis Palpebrarum..........394 Corrugator Supercilii............395 Tensor Tarsi................395 Actions.................395 Orbital Region. Dissection................ 396 Levator Palpebrae.............396 Rectus Superior, Inferior, Internal, and Ex- ternal Recti.............397 Superior Oblique..............397 Inferior Oblique..............397 Actions..................398 Surgical Anatomy.............398 Nasal Region. Pyramidalis Nasi..............398 Levator Labii Superioris Alaeque Nasi .... 399 Dilatator Naris, Anterior and Posterior . . . 399 Compressor Nasi....... ......399 Compressor Narium Minor.........399 Depressor Alae Nasi.............399 Actions.................399 Superior Maxillary Region. Levator Labii Superioris (Proprius).....400 Levator Anguli Oris............400 Zygomaticus, Major and Minor.......400 Actions..................400 Inferior Maxillary Region. Dissection.................400 Levator Labii Inferioris...........400 Depressor Labii Inferioris..........401 Depressor Anguli Oris...........401 Actinns..................401 Intermaxillary Region. Dissection............ Orbicularis Oris......... Buccinator............ Risorius............. Actions............. Temporo-Maxillary Region. Masseteric Fascia ......... Masseter.............. Temporal Fascia.......... Dissection............ Temporal . . .......... Pterygo-Maxillary Region. Dissection................ External Pterygoid............ Internal Pterygoid.......... . Actions................. Surface Form of Muscles of Head and Face Muscles and Fascia of the Neck. Subdivision into Groups.......... Superficial Region. Dissection............... Superficial Cervical Fascia........ Platysma Myoides............ Surgical Anatomy............ Actions................. Deep Cervical Fascia ... ....... Sterno-mastoid......... Boundaries of the Triangles of the Neck . Actions................. Surface Form............ Surgical Anatomy............ Infra-hyoid Region. Dissection . . Sterno-hyoid . Stern o-thyroid Thyro-hyoid . Omo-hyoid . . Actions . . . Supra-hyoid Region. Dissection............ Digastric............. Stylo-hyoid........... Stylo-hyoid Ligament...... Mylo-hyoid.......... Genio-hyoid.......... Actions............. 401 401 402 402 402 403 403 403 403 403 404 404 405 405 406 406 407 407 407 407 407 407 409 409 410 411 411 411 411 411 411 412 413 413 413 413 414 414 414 414 Lingual Region. Dissection.................415 12 CONTENTS. PAGE tTt'iiio-hyo-glossus............-415 Hyo-glossus...............41(1 Chrondro-glossus............416 Stvlo-glossus..............416 Palatoglossus..............416 Muscular Substance of Tongue ......416 Superior Lingualis............417 Transverse Lingualis.....,......41,-i Vertical Lingualis.............418 Inferior Lingualis.............418 Surgical Anatomy.............418 Actions..................418 Pharyngeal Region. Dissection.................419 Inferior Constrictor.............419 Middle Constrictor.............420 Superior Constrictor............420 Stylo-pharyngeus.............420 Actions..................420 Palatal Region. Dissection................421 Levator Palati...............421 Tensor Palati.............. 422 Palatine Aponeurosis............422 Azygos Uvulae...............422 Palato-glossus...............422 Palato-pharyngeus.............422 Salpingo-pharyngeus . . " ■........423 Actions..................423 Surgical Anatomy.............423 Vertebral Region (Anterior). Rectus Capitis Anticus Major........424 Rectus Capitis Anticus Minor........424 Rectus Capitis Lateralis..........425 I,minus Colli................425 Vertebral Region {Lateral). Scalenus Anticus..............425 Scalenus Medius..............425 Scalenus Posticus..............426 Actions..................426 Surface Form of Muscles of Neck......427 Muscles and Fascia of the Trunk. Subdivision into Groups..........427 The Back. Subdivision into Layers...........427 First Layer. Dissection.................428 Superficial and Deep Fasciae.........428 Trapezius.................428 Ligamentum Nucha?............430 Latissimus Dorsi...............430 Second Layer. Dissection.................431 Levator Anguli Scapulae..........431 Rhomboideus Minor............431 Rhomboideus Major............431 Actions..................432 Third Layer. Dissection.................432 Serrntus Posticus Superior.........432 Serratus Posticus Inferior..........432 Vertebral Aponeurosis...........433 Lumbar Fascia...............433 Splenius..................433 Splenius Capitis..............433 Splenius Colli...............433 Actions..................434 Fourth Layer. Dissection.................434 Erector Spinas...............434 Ilio-costalis...............434 Musculus Accessorius ad Ilio-costalem . . . . 436 Cervicalis Ascendens............436 PAOH Longissimus Dorsi.............'36 Transversalis Colli............436 Trachelo-mastoid ............. 436 Spinalis Dorsi...............436 Spinalis Colli...............4;|^ Complexus.................43^ Biventer Cervicis.............. 43 < Fifth Layer. Dissection .'................437 Semispinalis Dorsi............437 Semispinalis Colli.............437 Multifidus Spines..............438 Rotatores Spinas..............438 Supraspinales...............438 Interspinals................438 Extensor Coccygis.............438 Intertransversales.............438 Rectus Capitis Posticus Major........439 Rectus Capitis Posticus Minor........439 Obliquus Capitis Inferior..........439 Obliquus Capitis Superior..........439 Suboccipital Triangle............439 Actions..................440 Surface Form of Muscles of Back......440 The Thorax. Intercostal Fasciae.............441 Intercostal Muscles ............441 External and Internal Intercostals.....442 Infracostales (subcostales).........442 Triangularis Sterni............442 Levatores Costarum............442 Actions .................443 Muscles of Inspiration and Expiration . . . 444 Diaphragmatic Region. Diaphragm................444 Actions..................446 The Abdomen. Dissection ................447 Superficial Fascia.............447 External or Descending Oblique......448 External Abdominal Ring.........449 The Intercolumnar Fibres.........450 The Intercolumnar Fascia.........450 Poupart's Ligament............450 Gimbernat's Ligament...........450 Triangular Ligament............451 Internal or Ascending Oblique.......451 Cremaster.................452 Transversalis...... ........453 Rectus...................453 Pyramidalis................455 Linea Alba...............455 Lineae Semiluuares, Lineae Transversae . . . 456 Actions..................456 Fascia Transversalis............456 Internal Abdominal Ring..........456 Inguinal Canal...............457 The Deep Crural Arch...........457 Surface Form of Muscles of Abdomen .... 457 Deep Muscles of the Abdomen. Quadratus Lumborum...........453 Actions................ 453 Muscles of the Pelvic Outlet and Perinxinn. Corrugator Cutis Ani............453 External Sphincter Ani........ 45^ Internal Sphincter Ani.........\ ' 459 Levator Ani............ ^n Coccygeus ...........\ \ ^gQ Superficial Perineal Fascia ....... 460 Central Tendinous Point.......[ 459 Transversus Perinaei ■........, 461 Accelerator Urinae.......... ! ! 461 Erector Penis............... 462 Triangular Ligament...........' 453 Compressor Urethrae........ [ 464 CONTENTS. 13 Muscles of the Perinieum in the Female, page Transversus Perinaei............164 Sphincter Vaginae.............464 Erector Clitoridis.............465 Triangular Ligament...........465 Compressor Urethrae....... ... 465 Muscles and Fascle of the Uppe* Extremity. Subdivision into Groups..........465 Dissection of Pectoral Region and Axilla . 466 Fasciae of the Thorax...........466 The Shoulder. Anterior Thoracic Region. Pectoralis Major.............. 467 Costo-coracoid Membrane . . .......468 Pectoralis Minor..............469 Subclavius.........■ . . .... 469 Actions................ 470 Lateral Thoracic Region. Serratus Magnus.......... . 470 Actions......... .... 471 Superficial Fascia...... .... 471 Acromial Region. Deep Fascia................471 Deltoid..................471 Actions.............. ■ 172 Surgical Anatomy.............472 Anterior Scapular Region. Subscapular Fascia .............. 472 Subscapularis............. 472 Actions..................473 Posterior Scapular Region. Dissection.................i~3 Supraspinous Fascia............473 Supraspinatus...............473 Infraspinous Fascia.............473 Infraspinatus.............. 473 Teres Minor................474 Teres Major................474 Actions.................. 475 The Arm. Anterior Humeral Region. Dissection.................475 Deep Fascia of Arm............175 Coraco-brachialis..............476 Biceps..................476 Brachialis Anticus.............477 Actions..................477 Posterior Humeral Region. Triceps..................477 Subanconeus................478 Actions .................478 Surgical Anatomy.............478 The Forearm. Dissection.................478 Deep Fascia of Forearm..........478 Anterior Brachial Region, Superficial Layer. Pronator Radii Teres............479 Flexor Carpi Radialis............ 479 Palmaris Longus..............480 Flexor Carpi Ulnaris............480 Flexor Digitorum Sublimis.........480 Deep Layer. Dissection.................481 Flexor Profundus Digitorum ........ 481 Flexor Longus Pollicis...........482 Pronator Quadratus............483 Actions..................483 Radial Region. page Dissection.................483 Supinator Longus....... . . 483 Extensor Carpi Radialis Longior . ... 484 Extensor Carpi Radialis Brevior.....484 Posterior Brachial Region, Superficial Layer. Extensor Communis Digitorum ,......485 Extensor Minimi Digiti..........485 Extensor Carpi Ulnaris...........486 Anconeus.................486 Deep Layer. Supinator Brevis..............486 Extensor Ossis Metacarpi Pollicis......486 Extensor Brevis Pollicis..........488 Extensor Longus Pollicis..........488 Extensor Indicis..............4S8 Actions..................488 Surgical Anatomy.............489 The Hand. Dissection.................489 Anterior Annular Ligament......... 489 Synovial Membranes of the Flexor Tendons at the Wrist..............489 Posterior Annular Ligament........490 Deep Palmar Fascia............490 Superficial Transverse Ligament of the Fingers................492 Radial Group...............492 Abductor Pollicis............492 Opponens Pollicis...........492 Flexor Brevis Pollicis.........492 Adductor Obliquus Pollicis.......493 Adductor Transversus Pollicis...... 493 Actions................494 Ulnar Group................494 Palmaris Brevis............494 Abductor Minimi Digiti.........494 Flexor Brevis Minimi Digiti......494 Opponens Minimi Digiti........495 Actions................496 Middle Palmar Group...........496 Lumbricales..............496 Interossei Dorsales...........496 Interossei Palmares..........496 Actions................497 Surface form of Muscles of Upper Extremity . 497 Surgical Anatomy of the Muscles of the Upper Extremity. Fractures of the Clavicle..........499 " Acromion Process.....499 " Coracoid Process......500 " Humerus.........500 " Olecranon.........501 " " Radius..........501 Ulna...........502 " Radius and Ulna......502 " Lower end of Radius .... 502 Muscles and Fasciae of the Lower Extremity. Subdivision into Groups..........502 Iliac Region. Dissection.................503 Iliac Fascia................503 Psoas Magnus...............504 Psoas Parvus.................504 Iliacus...................504 Actions...................505 Surgical Anatomy.............505 The Thigh. Anterior Femoral Region. Dissection.................505 Superficial Fascia.............506 Deep Fascia (Fascia Lata)..........506 Saphenous Opening.............507 Iliac and Pubic portions of Fascia Lata . . . 508 Tensor Vaginae Femoris..........508 14 CONTENTS. PAGE Sartorius.................508 Quadriceps Extensor............509 Rectus Feinoris..............509 Vastus Externus..............509 Vastus Internus and Crureus........510 Subcrureus................510 Actions..................510 Surgical Anatomy.............511 Internal Femoral Region. Dissection............. ... 511 Gracilis..................511 Pectineus.................511 Adductor Longus..............512 Adductor Brevis..............512 Adductor Magnus.............513 Actions..................513 Surgical Anatomy.............513 The Hip. Gluteal Region. Dissection . ................514 Gluteus Maximus.............514 Gluteus Medius..............515 Gluteus Minimus.............516 Pyriformis.................516 Obturator Membrane............516 Obturator Internus............516 Genielli..................517 Gemellus Superior.............517 Gemellus Inferior.............517 Quadratus Femoris.............517 Obturator Externus............518 Actions..................518 Posterior Femoral Region. Dissection.................518 Biceps...................518 Semitendinosus..............519 Semimembranosus.............519 Actions..................519 Surgical Anatomy of Hamstring Tendons . . 520 The Leg. Dissection of Front of Leg.........520 Deep Fascia of the Leg...........520 Anterior Tibio-fibular Region. Tibialis Anticus..............521 Extensor Proprius Hallucis.........521 Extensor Longus Digitorum.........521 Peroneus Tertius..............522 Actions..................522 Posterior Tibio-fibular Region, Superficial Layer. Dissection.................522 Gastrocnemius...............522 PAGE Salens...................323 Tendo Achillis...............§23 Plantaris................._';-^ Actions...................y~±- Deep Layer. Deep Transverse Fascia of Leg..... Popliteus............... Flexor Longus Hallucis......... Flexor Longus Digitorum........ Tibialis Posticus............ Actions................ 524 524 Fibular Region. Peroneus Longus............. Peroneus Brevis............. Actions................. Surgical Anatomy of Tendons around Ankle 526 526 527 527 527 528 The Foot. Anterior Annular Ligament.........528 Internal Annular Ligament.........528 External Annular Ligament........529 Plantar Fascia...............529 Dorsal Region. Extensor Brevis Digitorum....... ......530 Plantar Region. Subdivision into Groups..........530 Subdivision into Layers..........530 First Layer...........530 Dissection...............530 Abductor hallucis...........530 Flexor brevis digitorum........530 Fibrous Sheaths of Flexor Tendons . . . 531 Abductor Minimi Digiti........531 Second Layer..........532 Flexor Accessorius...........532 Lumbricales..............532 Third Layer..........532 Flexor Brevis Hallucis.........532 Adductor Obliquus Hallucis......533 Flexor Brevis Minimi Digiti......533 Adductor Transversus Hallucis.....533 Fourth Layer..........534 Interossei...............534 Surface Form of Muscles of Lower Extremity 535 Surgical Anatomy of the Muscles of the Lower Extremity. Fracture of the Neck of the Femur.....537 the Femur below Trochanter Minor 537 the Femur above the Condyles . 538 the Patella...........538 the Tibia............538 the Fibula, with Dislocation of the Foot outward.........538 THE ARTERIES. General Anatomy. Subdivision into Pulmonary and Systemic . . 539 Distribution of—Where found........539 Mode of Division—Anastomoses.......539 Pulmonary Artery..........540 the aorta. Divisions.................541 Ascending Aorta..............541 Coronary Arteries.............542 Arch of Aorta...............543 Peculiarities................543 Surgical Anatomy.............544 Branches.................545 Peculiarities of Branches..........545 Arteria Innominata. Relations................. 545 Peculiarities................546 Surgical Anatomy.............546 Common Carotid Arteries. Course and Relations............547 Peculiarities................549 Surface Marking..............549 Surgical Anatomy.............549 External Carotid Artery. Course and Relations............551 Surface Marking..............551 Surgical Anatomy.............55^ Branches.................55^ Superior Thyroid Artery. Course and Relations............552 Branches.............. " 552 Surgical Anatomy.............552 Lingual Artery. Course and Relations............553 Branches.................553 Surgical Anatomy.............553 CONTENTS. 15 Facial Artery. page Course and Relations............554 Branches.................555 Peculiarities................556 Surgical Anatomy.............556 Occipital Artery. Course and Relations............ 556 Branches................. 557 Posterior Auricular Artery. Course and Relations............ 557 Branches.................557 Ascending Pharyngeal Artery. Course and Relations............558 Branches.................558 Surgical Anatomy.............559 Temporal Artery. Course and Relations............ 559 Branches.................559 Surgical Anatomy.............559 Internal Maxillary Artery. Course and Relations ...........559 Peculiarities................559 Branches from First Portion........560 " " Second Portion.......561 " Third Portion........562 Surgical Anatomy of the Triangles of the Neck. Anterior Triangular Space. Inferior Carotid Triangle..........563 Superior Carotid Triangle..........564 Submaxillary Triangle...........564 Posterior Triangular Space. Occipital Triangle.............565 Subclavian Triangle............565 Internal Carotid Artery. Cervical Portion..............566 Petrous Portion..............566 Cavernous Portion.............566 Cerebral Portion..............566 Peculiarities................567 Surgical Anatomy.............568 Branches.................°68 Ophthalmic Artery............568 Cerebral Branches of Internal Carotid . . . 570 The Blood-vessels of the Brain.......573 Arteries of Upper Extremity. Subclavian Arteries. First Part of Right Subclavian Artery .... 577 First Part of Left Subclavian Artery .... 577 Second Part of Subclavian Artery......578 Third Part of Subclavian Artery......578 Peculiarities................579 Surface Marking..............579 Surgical Anatomy.............579 Branches . . . . ■............581 Vertebral Artery.............581 Basilar Artery.............. 583 Circle of Willis..............584 Thyroid Axis..............584 Inferior Thyroid.............584 Suprascapular Artery...........585 Transversalis Colli............585 Internal Mammary............586 Superior Intercostal...........587 The Axilla..............587 Surgical Anatomy of the Axilla.......587 Axillary Artery. First Portion................589 Second Portion...............590 Third Portion...............590 Peculiarities.......... ....."-90 page Surface Marking..............591 Surgical Anatomy.............591 Branches.................592 Brachial Artery. Relations.................593 Bend of the Elbow.............593 Peculiarities of Brachial Artery.......594 Surface Form...............595 Surgical Anatomy.............595 Branches.................596 Radial Artery. Relations.................597 Deep Palmar Arch.............598 Peculiarities................598 Surface Marking..............598 Surgical Anatomy.............598 Branches.................599 Ulnar Artery. Relations.................601 Peculiarities of Ulnar Artery........601 Surface Marking . . . . ,.........602 Surgical Anatomy.............602 Branches.................602 Superficial Palmar Arch..........604 Arteries of the Trunk. Descending Aorta...........605 Thoracic Aorta. Course and Relations............605 Surgical Anatomy.............606 Branches.................606 Abdominal Aorta. Course and Relations............608 Surface Marking..............609 Surgical Anatomy.............609 Branches.................610 Cceliac Axis...............610 Gastric Artery..............611 Hepatic Artery.............611 Splenic Artery..............611 Superior Mesenteric Artery........612 Inferior Mesenteric Artery........614 Suprarenal Arteries ...........615 Renal Arteries..............616 Spermatic Arteries............616 Ovarian Arteries............. 616 Phrenic Arteries.............616 Lumbar Arteries.............617 Middle Sacral Artery...........617 Luschka's Gland.............617 Common Iliac Arteries. Course and Relations............618 Branches.................618 Peculiarities................618 Surface Marking..............619 Surgical Anatomy.............619 Internal Iliac Artery. Course and Relations............620 Peculiarities................621 Surgical Anatomy.............621 Branches.................622 Vesical Arteries............. 622 Haemorrhoidal Arteries..........622 Uterine Arteries............. 622 Vaginal Arteries.............622 Obturator Artery............. 622 Peculiarities...............623 Internal Pudic Artery..........623 In the Male..............623 Peculiarities..............624 Surgical Anatomy...........624 Branches...............625 In the Female.............625 Sciatic Artery..............626 Lumbar Artery.............626 16 CONTENTS PAGE Lateral Sacral Artery..........627 Gluteal Artery . . .'...........627 Surface Marking of Branches of Internal Iliac . 627 Surgical Anatomy of Branches of Internal Iliac...................628 External Iliac Artery. Course and Relations............628 Surgical Anatomy.......... . 628 Deep Epigastric Artery........ . . 629 Deep Circumflex Iliac Artery.......629 Arteries of the Lower Extremity. Femoral Artery. Course and Relations............630 Scarpa's Triangle..............630 Hunter's Canal...............630 Common Femoral.............631 Superficial Femoral............632 Peculiarities...............633 Surface Marking............. 633 Surgical Anatomy............633 Branches................635 Deep Femoral...............635 Branches.......,....., . . 636 Popliteal Space............, 637 Popliteal Artery. Course and Relations........ . 638 Peculiarities................ 638 PAGE Surface Marking ............-|;^ Surgical Anatomy...... j^ 3ranches . . . . •............"**■' Anterior Tibial Artery. Course and Relations........ .641 Peculiarities........... • 642 Surface Marking......... ... 642 Surgical Anatomy........ ... 642 Branches ........ ■ 642 Dorsalis Pedis Artery. Course and Relations............643 Peculiarities................643 Surface Marking........ .....643 Surgical Anatomy.............643 Branches.................644 Posterior Tibial Artery. Course and Relations............645 Peculiarities................645 Surface Marking..............645 Surgical Anatomy.............645 Branches.................646 Peroneal Artery. Course and Relations............646 Peculiarities................646 Plantar Arteries..............647 Surface Marking............. 648 Surgical Anatomy............648 THE VEINS. General Anatomy. Subdivision into Pulmonary, Systemic, and Portal.................. Anastomoses of Veins............ Superficial Veins.............. Deep Veins, Venae Comites......... Sinuses.................. Pulmonary Veins........... Systemic Veins............. Veins of the Head and Neck. Frontal Vein ............... Facial Vein................ Surgical Anatomy............ Temporal Vein............... Internal Maxillary Vein.......... Temporo-maxillary Vein.......... Posterior Auricular Vein.......... Occipital Vein............... Veins of the Neck. External Jugular Vein..... Surgical Anatomy...... Posterior External Jugular Vein Anterior Jugular Vein..... Internal Jugular Vein..... Surgical Anatomy...... Lingual Vein......... Pharyngeal Vein........ Thyroid Veins......... Vertebral Veins . . .... Veins of the Diploe ...... Cerebral Veins. Superficial Cerebral Veins . . . . Deep Cerebral Veins...... Cerebellar Veins........ Sinuses of the Dura Mater. Superior Longitudinal Sinus..... Inferior Longitudinal, Straight Sinuses Lateral Sinus ............. Occipital Sinuses.........., Cavernous Sinuses.......... Surgical Anatomy......... 649 649 649 649 650 650 650 651 652 652 652 652 653 653 653 653 653 654 654 654 655 654 654 654 655 655 656 657 657 657 658 6.58 659 659 659 Circular Sinus............... 660 Superior Petrosal Sinus........... 660 Inferior Petrosal Sinus......... 660 Transverse Sinuses.............661 Emissary Veins..............661 Veins of the Upper Extremity and Thorax. Superficial Veins..............662 Deep Veins............ ... 662 Axillary Vein.........., .... 664 Surgical Anatomy............665 Subclavian Vein..............665 Innominate Veins.............665 Peculiarities of..............665 Internal Mammary Veins..........666 Inferior Thyroid Veins...........666 Superior Intercostal Veins.........666 Superior Vena Cava............667 Azygos Veins...............667 Bronchial Veins..............668 Spinal Veins...............668 Veins of the Lower Extremity—Abdomen and Pelvis. Internal Saphenous Vein..........670 External Saphenous Vein..........670 Popliteal Vein...............671 Femoral Vein............... 672 Deep Epigastric Veins...........672 Deep Circumflex Iliac Veins........672 Internal Iliac Vein.............672 Internal Pudic Veins............672 Common Iliac Veins.....•......672 Peculiarities...............673 Inferior Vena Cava.............673 Peculiarities...............674 Lumbar Veins...............674 Spermatic Veins..............674 Surgical Anatomy............674 Ovarian Veins...............674 Renal and Suprarenal Veins........675 Phrenic Veins...............675 Hepatic Veins...............675 CONTENTS. 17 Portal System of Veins. page Superior Mesenteric Vein..........675 Splenic Vein................675 Inferior Mesenteric Vein..........675 Gastric Veins...............676 PAGE Portal Vein................677 Cardiac Veins..............677 Coronary Sinus............677 THE LYMPHATICS. General Anatomy. Subdivision into Deep and Superficial Lymphatic or Conglobate Glands . . Thoracic Duct........• Right Lymphatic Duct....... Lymphatics of Head, Face, and Neck. Lymphatic Glands of Head....... Lymphatics of the Head...... Superficial Lymphatics of the Face • • Deep Lymphatics of the Face...... Lymphatics of the Cranium...... Lymphatic Glands of the Neck..... Superficial Cervical Glands....... Deep Cervical Glands.......... Superficial and Deep Cervical Lymphatics Surgical Anatomy........... Lymphatics of the Upper Extremity. Superficial Lymphatic Glands....... Deep Lymphatic Glands......... Axillary Glands.............. Surgical Anatomy.......... Superficial Lymphatics of Upper Extremity . Deep Lymphatics of Upper Extremity . . . . Lymphatics of the Lower Extremity. Superficial Inguinal Glands......... Surgical Anatomy............. Deep Lymphatic Glands......... Anterior Tibial Gland........... Popliteal Glands.............. Deep Inguinal Glands.......... Gluteal and Ischiatic Glands....... Superficial Lymphatics of Lower Extremity Internal Group........... External Group.......... Deep Lymphatics of Lower Extremity . Lymphatics of Pelvis and Abdomen. Lymphatic Glands of Pelvis....... External Iliac Glands.......... Internal Iliac Glands........... Sacral Glands.............. 679 679 680 680 681 681 682 682 682 683 683 683 684 684 684 684 684 684 685 686 686 686 686 686 686 686 686 686 686 687 687 687 687 688 Lumbar Glands.............688 Superficial Lymphatics of Wall of Abdomen . 689 " " of Gluteal Region . . 689 " " of Scrotum and Peri- naeum......689 of Penis.....689 " " of Labia, Nymphae, and Clitoris ... 689 Deep Lymphatics of Pelvis and Abdomen . . 689 Lymphatics of Bladder...........689 of Rectum..........689 of Uterus...........689 of Testicle...........690 of Kidney...........690 of Liver...........690 Lymphatic Glands of Stomach......690 Lymphatics of Stomach..........690 Lymphatic Glands of Spleen........690 Lymphatics of Spleen..........690 Lymphatic System of the Intestine. Lymphatic Glands of Small Intestines (Mesen- teric Glands)..............691 Lymphatic Glands of Large Intestine .... 691 Lymphatics of Small Intestines (Lacteals) . . 691 " of Large Intestine.......691 Lymphatics of Thorax. Lymphatic Glands of Thorax........691 Intercostal Glands...........691 Internal Mammary Glands.......691 Anterior Mediastinal Glands......691 Posterior Mediastinal Glands......691 Superior Lymphatics on Front of Thorax . . 691 Deep Lymphatics of Thorax........691 Intercostal Lymphatics........691 Internal Mammary Lymphatics.....692 Lymphatics of Diaphragm.........692 Bronchial Glands.............692 Lymphatics of Lung...........692 Cardiac Lymphatics............692 Thymic Lymphatics............692 Thyroid Lymphatics............692 Lymphatics of OZsophagus.........692 NERVOUS SYSTEM. General Anatomy. Subdivision into Cerebro-spinal Axis, Ganglia, and Nerves ..... ........ The Spinal Cord and its Membranes. Dissection................ Membranes of the Cord.......... Dura Mater.............. Arachnoid............... Pia Mater............... Ligamentum Denticulatum....... Spinal Cord................ Fissures of Cord............ Columns of Cord............ Structure of the Cord......... Commissure of the Cord........ Minute Anatomy of the Cord........ Neuroglia............... White Substance............ Collateral Fibres........... Gray Substance ... ........ 693 693 693 693 694 695 695 695 696 697 697 697 698 698 698 700 701 The Brain and its Membranes. Membranes of the Brain....... 702 Dura Mater. Structure.................703 Arteries, Veins..............703 Nerves.......*........703 Glandulae Pacchioni............703 Processes of the DuraMater........704 Falx Cerebri..............704 Tentorium Cerebelli..........704 Falx Cerebelli.............704 The Arachnoid Membrane. Subarachnoid Space ...........705 Cerebro-Spinal Fluid............705 The Pia Mater...............705 The Brain. Subdivision into Cerebrum, Cerebellum, Pons Varolii, Medulla Oblongata........706 Weight of Brain..............706 Medulla Oblongata. Surface..................709 Pyramids.................709 Olive or Olivary Body...........710 18 CONTENTS. page Funiculus Gracilis.............711 Funiculus Cuneatus............711 Funiculus of Rolando...........711 Restiform Bodies.............712 External Arciform Fibres .........712 Internal Structure.............712 White Matter...............714 Funiculus of Rolando...........714 Funiculus Cuneatus............715 Funiculus Gracilis............715 Gray Matter of the Anterior and Lateral Areas 715 Gray Matter of the Posterior Area.....715 Nuclei...................715 Nuclei in Relation to Floor of the Fourth Ven- tricle ..................716 Nucleus of the Spinal Accessory Nerve . . . 716 Nuclei of the Vagus and Glossopharyngeal Nerves.................716 Nuclei of the Auditory Nerve........716 White Matter.............716 Pyramid................716 Olivary Body.............717 Fibres in the Grooves...........717 Restiform Body............. 717 Fibres of Formatio Reticularis.....718 Longitudinal Fibres of the Formatio Reticu- laris...................718 Posterior Longitudinal Bundle.......718 Ascending Root of the Fifth Nerve.....718 Funiculus Solitarius............718 Transverse and Dorso-ventral Fibres .... 718 External Arciform Fibres........718 Internal or Deep Arciform Fibres.....719 Raphe..................719 The Pons Varolii. Ventral Surface..............720 Dorsal Surface...............720 Relations of the Cerebellar Peduncles to Each Other.................720 Deep Portion of the Pons..........720 Trapezium..............721 Septum or Raphe..............721 Gray Matter of the Pons..........721 Nuclei Pontis.............721 Gray Matter of the Formatio Reticularis . . 721 Superior Olivary Nucleus..........722 Nuclei of the Auditory Nerve.......722 Nucleus of the Facial Nerve........722 Nucleus of the Sixth Nerve........722 Nuclei of the Fifth Nerve.........722 Floor of the Fourth Ventricle.......723 Tela Choroidea Inferior Lingula ....... Choroid Plexuses The Cerebellum. Weight of the Cerebellum......... Main Lobes of the Cerebellum...... Notches of the Cerebellum......... Worm................... Hemispheres. . . . •............ Lobules of Superior Worm....... Lobules of Inferior Worm........ Structure of Each Lobule........ Lingula and Fraenula............ Lobulus Centralis and Alae ... . . . Tuber Valvulae and Postero-inferior Lobules . Pyramid and Digastric Lobules..... Uvula and Amygdalae........... Nodulus and Flocculi............ Peduncles of the Cerebellum....... Inferior Medullary Velum......... Tent and Lateral Recess.......... Superior Medullary Velum......... Arbor Vitfe........... . . . Fibres of the Peduncles.......... Fibrae Propriae of the Cerebellum . . . . Fourth Ventricle............. Boundaries of the Fourth Ventricle..... Roof of Lower Portion of Fourth Ventricle Lateral Recess; Tela Choroidea Inferior . Lateral Recess.............. 725 725 726 727 727 728 728 728 729 729 730 731 The Mid-Braix. Main Divisions.......... Crustse...... ...... Fibres of the Crusta....... Substantia Nigra ........ Tegmeutium........... Corpora or Tubercula Quadrigemiua Aqueduct of Sylvius....... Central Gray Matter ... Superior Surface of Mid-brain . ■ Posterior Perforated Lamina . • Subthalamic Region....... paub 739 740 740 741 741 742 742 742 743 744 744 745 745 745 732 733 734 734 734 734 735 737 738 73* 739 The Inter-Brain. Optic Thalamus..............'Jz Structure of the Optic Thalamus......74/ Third Ventricle........ • • • 'Jf Posterior Commissure..........'48 Pineal Gland..............' *° Structure.................J49 Epithelial Roof...............'J^> Velum Interpositum..........' 4J Tela Choroidea Superior'..........750 Posterior Perforated Lamina......730 Corpora Albicantia...........7>0 Tuber Cinereum ..........750 Pituitary Body............731 Lamina Cinerea............751 Anterior Boundary...........751 Choroid Plexuses............751 Openings...............^'~ Optic Tracts...............7.>2 The Hemispheres. General Considerations and Development. Frontal Lobes...............753 Parietal Lobes...............753 Fornix.........•........753 Anterior Commissure............753 Corpus Callosum..............753 Septum Lucidum..............754 Occipital Lobe............754 Temporal Lobe............754 The Lateral Ventricles, and Structures in Connection therewith. ........756 ........757 ........758 758 758 759 760 760 760 762 762 763 763 763 765 765 766 766 738 768 769 770 770 771 771 Corpus Callosum.............. Central Cavity or Body........... Anterior Cornu.............. Posterior Cornu or Digital Cavity...... Middle or Descending Cornu........ Corpus Striatum.............. Internal Capsule.............. Taenia Semicircularis............ Fornix................. Anterior Commissure............ Septum Lucidum.............. Fifth Ventricle.............. Hippocampus major or Cornu Ammonis . Corpus Fimbriatum.......... Eminentia Collaterals or Pes Accessorius Fascia Dentata............... Choroid Plexuses.............. Choroid Plexus of the Body of the Ventricle Epithelial Floor of the Body of the Ventricle Epithelial Inner Wall of Descending Cornu . Choroid Plexus of Descending Cornu Structure of Choroid Plexus Transverse Fissure......... Surface Aspect of the Hemispheres .'.''.[ Surface of Each Hemisphere...... Gyri or Convolutions....... Structure of the Convolutions . . . . . External Lobes and Fissures of the Hemi- sphere ............. Fissure of Sylvius . . . . . .'..'.'.'. Fissure of Rolando....... CONTENTS. 19 PAGE Parietooccipital Fissure........774 Frontal Lobe..............775 Parietal Lobe.............776 Occipital Lobe.............777 Temporal Lobe.............777 Central Lobe or Island of Reil.....778 Mesial Lobes and Fissures of the Hemisphere . 778 Calloso-marginal Fissure........778 Parietooccipital Fissure....... 779 Calcarine Fissure............779 Collateral Fissure...........779 Dentate or Hippocampal Fissure.....779 Lobes or Convolutions Seen on the In- ternal Surface of the Hemisphere . . . 779 Gyrus Fornicatus......... 779 Marginal Convolution.........780 Quadrate Lobe.............780 Cuneate or Occipital Lobule.......780 Iufracalcariue.............780 Fourth Temporal Convolution.....781 Hippocampal Convolution........781 Uncinate Gyrus.............781 Olfactory Lobe...............782 Anterior Olfaetory Lobule.......782 Posterior Olfactory Lobule or Anterior Perforated Space...........784 Olfactory Roots..............784 Under Surface or " Base " of the Encephalon 784 Longitudinal Fissure.........784 Interpeduncular Space...........784 Structure of the Hemisphere........785 Projection or Peduncular Fibres .... 785 Transverse or Commissural Fibres . . . 786 Association-fibres Connecting Different Struct- ures in the Same Hemisphere.......786 Gray Matter of the Cortex......786 Weight of the Encephalon.........789 Cerebral Localization and Topography . . . . 789 Longitudinal Fissure........... 790 Fissure of Sylvius............790 Fissure of Rolando.............790 The Cranial Nerves. Enumeration................792 Olfactory Nerve..............792 Surgical Anatomy...........793 Optic Nerve................793 Tracts................793 Commissure..............793 Surgical Anatomy..........794 Motor Oculi Nerve .... ......794 Surgical Anatomy..........795 Pathetic Nerve...............796 Surgical Anatomy...........796 Trifacial Nerve..............796 Gasserian Ganglion...........797 Ophthalmic Nerve...........797 Lachrymal and Frontal Branches .... 798 Nasal Branches............798 Ophthalmic Ganglion..........799 Superior Maxillary Nerve........801 Spheno-palatine Ganglion........803 Inferior Maxillary Nerve........805 Auriculotemporal Branch.......806 Lingual Branch...........807 Inferior Dental Branch.........807 Otic Ganglion.............807 Submaxillary Ganglion........808 Surgical Anatomy of Fifth Nerve.....809 Abducens Nerve..... ........810 Relations of the Orbital Nerves in the Cavern- ous Sinus..............810 Eolations, etc. in the Sphenoidal Fissure . . . 810 " in the Orbit............810 Surgical Anatomy...........811 Facial Nerve................811 Branches of Facial Nerve........812 Surgical Anatomy...........815 Auditory Nerve..............815 Surgical Anatomy...........816 Glossopharyngeal Nerve..........816 2 page Pneumogastric (Vagus) Nerve .......819 Surgical Anatomy...........822 Spinal Accessory Nerve...........823 Surgical Anatomy...........823 Hypoglossal Nerve.............823 Surgical Anatomy...........825 The Spinal Nerves. Roots of the Spinal Nerves.........826 Origin of Anterior Roots........826 " of Posterior Roots........826 Ganglia of the Spinal Nerves........827 Posterior Divisions of the Spinal Nerves . . . 827 Anterior Divisions of the Spinal Nerves . . . 827 Cervical Nerves. Roots of the Cervical Nerves........828 Posterior Divisions of the Cervical Nerves . . 828 Anterior Divisions of the Cervical Nerves . . 830 The Cervical Plexus. Superficial Branches of the Cervical Plexus . 831 Deep Branches of the Cervical Plexus .... 832 The Brachial Plexus. Branches above the Clavicle. Posterior Thoracic.............837 Suprascapular............837 Branches below the Clavicle. Anterior Thoracic.............838 Subscapular Nerves ........... 838 Circumflex Nerve.............839 Musculocutaneous Nerve..........839 Internal Cutaneous Nerve.........839 Lesser Internal Cutaneous Nerve......840 Mediau Nerve...............840 Ulnar Nerve................841 Musculo-spiral Nerve............842 Radial Nerve.............844 Posterior Interosseous Nerve......844 Surgical Anatomy of Brachial Plexus .... 844 Dorsal Nerves. Roots of the Dorsal Nerves.........845 Posterior Divisions of the Dorsal Nerves . . . 845 Anterior Divisions of the Dorsal Nerves . . . 846 First Dorsal Nerve.............846 Upper Dorsal Nerves............846 Lower Dorsal Nerves............848 Last Dorsal Nerve.............848 Surgical Anatomy...........848 The Lumbar Nerves. Root of Lumbar Nerves...........849 Posterior Divisions of Lumbar Nerves . . . . 849 Anterior Divisions of Lumbar Nerves .... 850 The Lumbar Plexus. Branches of Lumbar Plexus........850 Ilio-hypogastric Nerve..........851 Ilio-inguinal Nerve.............851 Genito-crural Nerve............852 External Cutaneous Nerve........853 Obturator Nerve.............854 Accessory Obturator Nerve.........854 Anterior Crural Nerve...........855 Branches of Anterior Crural........855 Middle Cutaneous...........855 Internal Cutaneous...........855 Long Saphenous............856 Muscular and Articular Branches .... 856 The Sacral and Coccygeal Nerves. Roots of, origin of............857 Posterior Divisions of Sacral Nerves.....857 Coccygeal Nerve.............858. Anterior Divisions of Sacral Nerves.....H58 The Sacral Plexus. Superior Gluteal Nerve...........861 Inferior Gluteal Nerve...........861 20 CONTENTS. page Perforating Cutaneous Nerve........861 Pudic Nerve ...............861 Small Sciatic Nerve............862 Creat Sciatic Nerve............862 Internal Popliteal Nerve..........863 Posterior Tibial Nerve.........•. . 863 Plantar Nerves...............863 External Popliteal or Peroneal Nerve .... 864 Anterior Tibial Nerve...........865 Musculo-cutaneous Nerve..........865 Surgical Anatomy of Lumbar and Sacral Plexus 860 The Sympathetic Nerve. Subdivision of, into Parts..........867 Branches of the Ganglia, General Description of....................867 Cervical Portion of the Gangliated Cord..................869 Superior Cervical Ganglion..........869 Carotid Plexus...............869 Cavernous Plexus............ 869 Middle Cervical Ganglion...........872 Inferior Cervical Ganglion..........872 Thoracic Part of the Gangliated Cord . 872 Great Splanchnic Nerve..........873 Lesser Splanchnic Nerve..........873 Smallest Splanchnic Nerve ' ' , ' ' *-!* Lumbar Portion ok the Gangliated Cord 873 Pelvic Portion of the G\n<;liated Cord 874 The Great Plexuses of the Sympathetic. Cardiac Plexuses..............8r4 (ireat Cardiac Plexus . . ....... 8rl Superficial Cardiac Plexus.........HJ4 Coronarv Plexuses.............874 Solar Plexus.............. ■ 875 Phrenic Plexus..............S7._> Suprarenal Plexus.............87.j Renal Plexus............. ■ 87o Spermatic Plexus.............875 Ovarian Plexus...............876 Cceliac Plexus..............876 Superior Mesenteric Plexus........877 Aortic Plexus.......... • 87* Inferior Mesenteric Plexus.........877 Hypogastric Plexus.............877 Pelvic Plexus........... 878 Inferior Haemorrhoidal Plexus.......878 Vesical Plexus...............878 Prostatic Plexus..............878 Vaginal Plexus...............878 Uterine Plexus...............878 ORGANS OF Tongue. Structure of................879 Papillae of.................880 Glands of................882 Lymphoid Follicles........... 882 Fibrous Septum of.............882 Hyo-glossal Membrane...........882 | Meibomian Glands Arteries and Nerves of...........882 Conjunctiva Muscles of................882 " Nerves of.................883 Surgical Anatomy of...........883 SENSE. ■Appendages of the Eye. Eyebrows........... Eyelids............ Eyelashes .......... Structure of the Evelids . . . Tarsal Plates.....'...... Carunculae Lachrymales 907 907 907 907 908 908 908 909 Nose. Cartilages of................885 Muscles of.................8S(J Skin....................886 Front of Eve Mucous Membrane.............886 Surgical Anatomy Arteries, Veins, and Nerves.........886 Lachrymal Apparatus. Lachrymal Gland........ Canals........ " Sac.......... Nasal Duct, Nasal Fossse. Mucous Membrane of............887 Superior, Middle, and Inferior Meatuses . . . 887 Arteries, Veins, and Nerves of Nasal Fossse . 889 Surgical Anatomy of Nose and Nasal Fossae . 889 Eye. Situation, Form of.............890 Capsule of Tenon.............890 Tunics of, sclerotic............891 Cornea..................892 Choroid..................894 Ciliary Processes..............895 Iris....................896 Membrana Pupillaris...........898 Ciliary Muscle...............898 Retina...................898 Structure of Retina.............898 Structure of Retina at Yellow Spot.....902 Arteria Centralis Retinae..........902 Humors of the Eye. Aqueous Humor.............903 Anterior Chamber...........903 Posterior Chamber...........903 Vitreous Body...............903 Crystalline Lens and its Capsule......904 Changes Produced in the Lens by Age ... 904 Suspensorv Ligament of Lens........905 Canal of Petit..............905 Vessels of the Globe of the Eye.......905 Nerves of Eyeball.............905 Surgical Anatomy of Eye..........905 Ear. External Ear. Pinna, or Auricle........... Structure of Auricle.......... Ligaments of the Pinna........ Muscles of the Pinna.......... Arteries, Veins, and Nerves of the Pinna Auditory Canal............ Surface Form............. 909 910 910 911 911 911 912 912 913 913 914 914 915 Middle Ear, or Tympanum. Cavity of Tympanum....... Eustachian Tube.......... Membrani Tympani........ Structure of......... Ossicles of the Tympanum .... Ligaments of the Ossicula..... Muscles of the Tympanum .... Mucous Membrane of Tympanum Arteries of Tympanum....... Veins and Nerves of Tympanum . . ... 916 .... 917 .... 918 ... 918 .... 918 . . 919 . . 920 . . 920 . 920 ... 920 Internal Ear, or Labyrinth. Vestibule................921 Semicircular Canals: Superior Semicircular Canal ... . 922 Posterior Semicircular Canal . . 922 External Semicircular Canal 922 Cochlea: Central Axis of, or Modiolus......923 Spiral Canal of.............o,o;j Seala Tympani, Scala Vestibuli, and Scala Media..................924 CONTENTS. 21 PAGE The. Organ of Corti.............924 Perilymph................926 Membranous Labyrinth...........926 Utricle and Saccule.............926 Membranous Semicircular Canals......927 Endolymph................927 PAGE Otoliths..................927 Vessels of the Labyrinth..........927 Auditory Nerve, Vestibular Nerve.....927 Cochlear Nerve...............928 Surgical Anatomy.............928 THE ORGANS OF DIGESTION. Subdivisions of the Alimentary Canal The Mouth............. The Lips.............. The Cheeks............ The Gums ........... The Teeth. General Characters of......... Permanent Teeth........... Incisors............... Canine.........'...... Bicuspids............. Molars................ Temporary, or Milk Teeth...... Structure of the Teeth........ Ivory or Dentine........... Enamel.............. Cortical Substance.......... Development of the Teeth..... " of the Permanent Teeth Eruption of the Teeth........ The Palate. Hard Palate................ Soft Palate................. Uvula, Pillars of the Soft Palate...... Mucous Membrane, Aponeurosis, and Muscles of Soft Palate.............. The Tonsils. Arteries................. Veins and Nerves of Tonsils ........ 930 930 930 931 931 932 932 932 933 933 933 935 935 935 937 938 938 942 942 944 944 944 944 945 945 Parietal Peritoneum........... Anterior Wall . ............. Upper Wall . . ............ Inferior Wall..... ........ Visceral Peritoneum.......... Lesser Sac or Bursa Omentalis..... Recessus Peritonei or Retroperitoneal Fossa Duodenal Fossa............. Fossa Intersigmoidea.......... Pericaecal Fossae............. The Stomach. Form and Size........ Position and Relations .... Relations in Detail...... Alterations in Position .... Structure.......... Mucous Membrane...... Vessels and Nerves of Stomach Surgical Anatomy..... The Salivary Glands. Parotid Gland. Situation and Relations......... Stenson's Duct............. Surface Form............. Vessels and Nerves of Parotid Gland . . The Submaxillary Gland. Situation and Relations........ Wharton's Duct........... Vessels and Nerves of Submaxillary Gland The Sublingual Gland. Situation and Relations......... Vessels and Nerves of.......... Structure of Salivary Glands...... Surface Form of Mouth......... 945 946 947 947 947 947 947 948 948 948 949 The Pharynx and OZsophagus. Situation and Relations ... .... Structure of Pharynx......... Surgical Anatomy........... Relations of Oesophagus........ Structure............... Vessels ............... Nerves of............... Surgical Anatomy........... 951 951 952 952 953 953 954 954 Small Intestine. Duodenum.............. Course of Adult Duodenum...... Peritoneal Relations of Duodenum . . Ligaments of Duodenum....... Relations of Duodenum....... Jejunum and Ileum......... Structure of Small Intestine..... Mucous Membrane.......... Valvulae Conniventes......... Villi................. Structure of Villi.......... Follicles............... Duodenal Glands.......... Solitary Glands.............. Peyer's Glands............... Vessels and Nerves of Small Intestine . . . . Large Intestine. Structure................. Vessels and Nerves............. Caecum............ . . • . . . Vermiform Appendix............ Ileo-colic, Ueo-caecal Valve or Valvula Bau- hini................... Colon................... Ascending............... Transverse ............. Descending.............. Sigmoid..... ......... Relations of Large Intestine........ Rectum.................. Structure of Rectum........... Vessels and Nerves of Rectum....... Relations of Rectum............ Surface Form.............. Surgical Anatomy............. 986 986 986 986 988 993 994 994 996 997 999 1001 1003 1004 1004 1006 1007 1007 1008 1009 1011 1014 1014 1020 1020 1021 1021 1022 1023 1024 1024 1025 1025 1026 1028 1029 1030 1032 Liver. The Abdomen. Boundaries. Apertures of Regions . . 957 959 959 The Peritoneum. Omentum Mesentery Ligament 979 979 979 Volume..... Weight..... Surfaces .... Fissures .... Longitudinal Lobes...... Right . . . Left . . . Quadrate Caudate . . Spigelian . 1033 1035 1035 1035 1035 1036 1036 1038 1040 1041 1043 1045 1045 1047 1047 1049 1051 1051 1052 1052 1052 1052 1052 1052 CONTEN7S. PAGE Ligaments and Peritoneal Relations.....1053 Peritoneal Lines..............1054 Relations................1055 Fixation of Liver.............1056 Vessels of Liver.............1057 Nerves of Liver..............1058 Structure of Liver.............1059 Microscopic Appearance of Liver......1059 Hepatic Cells...............1060 Hepatic Artery..............1060 Portal Vein................1060 Excretorv Apparatus of Liver.......1063 Hepatic Duct...............1063 Gall-Bladder. Relations of Gall-bladder..........1064 Vessels and Nerves of Gall-bladder.....1064 Cystic Duct................1064 Ductus Choledochus............1064 Structure.................1065 Surface Form of Liver...........1065 Surgical Anatomy of Liver.........1065 Pancreas. page Dissection.................JI^Z Color..................j £i Volume..................[ g< Head................... < Bodv and Tail...............]l™ Relations in Detail.............j ^ Vessels and Nerves............ j ';- Surface Form ..........\cr^ Surgical Anatomy . .....l{)i,} Spleen. Form and Relations............1°74 Fixation and Peritoneal Relations......1076 Vessels and Nerves.............107^ Lymphatic Vessels.............10<* Structure................1Q77 Fibro-elastic Coat.............1078 Proper Substance.............1078 Surface Form of Spleen.......... 1081 Surgical Anatomy of Spleen........1081 THE THORAX. Cavity of.................1083 Upper Opening...............1083 LowerOpening...............1083 The Pericardium. Structure.................1084 Fibrous Layer..............1084 Serous Layer...............1085 Arteries of Pericardium ... ... 1085 Nerves of Pericardium...........1085 Vestigial Fold of Pericardium.......1085 Surgical Anatomy.............1086 The Heart. Position........,.........1086 Size...................1087 Subdivision into Four Cavities.......1087 Circulation of Blood in Adult........1087 Auriculo-ventricular and Ventricular Grooves 1087 The Right Auricle. Sinus...................1088 Appendix................1088 Openings.................1088 Valves...................1089 Relics of Foetal Structure ........1089 Musculi Pectinati.............1089 The Right Ventricle. Infundibulum...............1089 Openings.................1090 Tricuspid Valve..............1090 Chordae Tendineae and Columnae Carneae . . . 1090 Semilunar.................1090 The Left Auricle. Sinus...................1091 Appendix.................1091 Openings.................1091 Musculi Pectinati....... ... 1092 The Left Ventricle. Openings .................1092 Mitral and Semilunar Valves.......1093 Endocardium...............1094 Structure of Heart. Fibrous Rings...............1094 Muscular Structure.............1094 Muscular Structure of Auricles.......1094 Muscular Structure of Ventricles......1094 Vessels and Nerves of Heart........1095 Surface Marking of Heart........1096 Peculiarities in Vascular System of Foetus . . 1096 Foramen Ovale, Eustachian Valve......1096 Ductus Arteriosus.............1097 Umbilical or Hypogastric Arteries .... 1097 Fcetal Circulation.............1097 Changes in Vascular System at Birth .... 1099 ORGANS OF VOICE AND RESPIRATION' The Larynx. Cartilages of the Larynx..........1100 Thyroid Cartilage...........1100 Cricoid Cartilage............1101 Arytenoid Cartilages, Cartilages of Santo- riui and Wrisberg..........1102 Epiglottis...............1102 Ligaments of the Larynx......... 1102 Ligaments Connecting the Thyroid Cartilage with the Os Hyoides......... 1103 Ligaments Connecting the Thyroid Cartilage with the Cricoid............. 1103 Ligaments Connecting the Arytenoid Carti- lages to the Cricoid............1103 Ligaments of the Epiglottis........1103 Superior Aperture of the Larynx......1103 Cavitv of the Larvnx........... 1104 Rima Glottidis...............1104 False Vocal Cords.............1105 True Vocal Cords.............iiQ5 Ventricle of Larynx, Sacculus Laryngis . . . 1105 Muscles of Larynx............. 1105 Crico-thyroid.............1195 Crico-arytenoideus posticus...... n05 Crico-arytenoideus lateralis.......]1(k; Arytenoideus.............110H Thyro-arytenoideus..........hqq Muscles of the Epiglottis........[ ' i iq? Thyro-epiglottideus........[ \ iiq7 Aryteno-epiglottideus, superior . . . . . 1107 inferior.....1107 Actions of Muscles of Larynx.......1107 Mucous Membrane of Larynx...... . ! 1107 Glands, Vessels, and Nerves of Larynx . '. '. 1198 CONTENTS. 23 PAGE The Trachea. Relations................ . 1108 Bronchi..................1108 Structure of Trachea............1110 Cartilages.................1110 Fibrous Membrane.............1111 Muscular Fibres.............1111 Mucous Membrane.............1111 Glands...................1111 Vessels and Nerves.............1111 Surface Form...............1111 Surgical Anatomy of Laryngo-tracheal Region 1111 The Pleura. Reflections................1113 Vessels and Nerves.............1114 Surgical Anatomy............1114 Hie Mediastina. Superior Mediastinum..........1115 Anterior Mediastinum...........1116 Middle Mediastinum............1116 Posterior Mediastinum...........1116 The Lungs. Surfaces..................1117 Borders and Lobes.............1117 Root of Lung...............1118 Weight, Color, and Properties of Substance of Lung..................1118 Structure of Lung............1118 Serous Coat and Subserous Areolar Tissue . 1118 Parenchyma and Lobules of Lung.....1118 Bronchi, Arrangement of, in Substance of Lung.................1119 Structure of Smaller Bronchial Tubes .... 1119 The Air-cells................1119 Pulmonary Artery.............1119 Pulmonary Capillaries and Veins......1119 Bronchial Arteries and Veins . ......1120 Lymphatics and Nerves of Lung......1120 Surface Form of Lungs...........1120 Surgical Anatomy.............1122 The Thyroid Gland. Surface and Relations.........1123 Structure.................H23 Vessels and Nerves.............1124 Surgical Anatomy.............1124 The Thymus Gland. Relations................1124 Structure........ ■'......1125 Vessels and Nerves........... 1126 THE URINARY ORGANS. The Kidneys. Relations..................1127 Dimensions, Weight............1127 General Structure.............1128 Cortical Substance.............1129 Medullary Substance............1129 Minute Structure.............1129 Malpighian Bodies ............1129 " Tufts.............1129 Capsule............1129 Tubuli Uriniferi, Course..........1130 " Structure........ 1132 Renal Blood-vessels............1133 Renal Veins................1134 Venae Rectae................1134 Nerves .................. 1134 Lymphatics................1135 Surface Form...............1135 Surgical Anatomy.............1135 The Ureters. Situation.................1136 Calices..................1136 Course ..................1136 Relations..................1136 Structure.................1136 The Suprarenal Capsules. Relations.................1137 Structure ................. 1137 Vessels and Nerves.............1139 The Pelvis. Boundaries................1139 Contents..................1139 The Bladder. Shape, Position, Relations..........1139 Subdivisions..............1140 Urachus................1140 Ligaments...............1142 Structure.................1143 Interior of Bladder.............1144 Vessels and Nerves.............1144 Surface Form...............1144 Surgical Anatomy........ .... 1145 Male Urethra. Divisions.................1146 Structure.................1147 Surgical Anatomy.............1147 MALE GENERATIVE ORGANS. Prostate Gland............: . . 1148 Structure...............1149 Vessels and Nerves...........1149 Surgical Anatomy...........1149 Cowper's Glands..............1150 Structure...............1150 The Penis. Root....................1150 Glaus Penis................1150 Bodv...................1150 Structure of Penis ............1151 Corpora Cavernosa.............1151 Structure.................1151 Arteries of the Penis............1152 Corpus Spongiosum.............1152 The Bulb.................1152 Structure of Corpus Spongiosum.......1153 Lymphatics of the Penis..........1153 Nerves of the Penis............1153 Surgical Anatomy.............1153 The Testes and their Coverings. Scrotum..................1153 Coverings of the Testis...........1154 Vessels and Nerves of the Coverings of the Testis..................H55 The Spermatic Card. Its Composition.............1155 Relations of, in Inguinal Canal.......1155 Arteries of the Cord...........1155 Veins of the Cord............1155 Lymphatics and Nerves of the Cord.....1155 Surgical Anatomy.............1155 The Testes. Form and Situation........... 1156 Size and Weight..............1156 Coverings.................1156 Tunica Vaginalis . . .........1156 Tunica Albuginea...........1157 24 CONTENTS. Mediastinum Testis Tunica Vasculosa . . Structure of the Testis . Lobulus of the Testis Tubuli Seminiferi . . . Arrangement in Lobuli . in Mediastinum Testis in Epididymis . . . Vas Deferens, Course, Relations . . Structure.......... Vas Aberrans..........- Surgical Anatomv........ PAGE 1157 1157 1157 1158 1158 PAGE 1160 1160 Vesicuhr Seminalcs ........ Form and Size.............1160 Relations.............. ' ,j(;(| Structure............. ' 1](i() Ejaculatory Ducts.............(J1 1158 Structure .............. 1158 Vessels and Nerves.......... 1158 ' Surgical Anatomy.......... jj£j ; Descent of the Testes. 1159 Gubernaculum Testis............"61 1159 I Canal of Nuck...............110^ 1161 1161 FEMALE GENERATIVE ORGANS. Mons Veneris, Labia Majora........1163 " " Labia Minora........1164 Clitoris..................1164 Meatus Urinarius.............1165 Hymen, Glands of Bartholin........1165 Female Urethra........... 1167 Female Rectum...... . 1167 Vagina. Relations.................1167 Structure ................. 1167 Ilerus. Situation, Form, Dimensions........1168 Fundus, Body, and Cervix.........1168 Ligaments................ . 1170 Cavity of the Uterus............1171 Cavity of the Cervix............1171 Structure.................1171 Vessels and Nerves.............1173 Its Form, Size, and Situation in the Foetus . . 1173 at Puberty...........1173 Its Form, Size, etc. during Menstruation . . . 1173 " during Pregnancy ........1173 after Parturition.........1173 in Old Age............1174 Appendages of the Uterus. Fallopian Tubes..............1174 Structure................1174 Ovaries..................1175 Structure...............1175 Graafian Follicles...........1176 Discharge of the Ovum...........1177 Ligament of the Ovary ..........1177 Round Ligaments.............1177 Vessels and Nerves of Appendages.....1178 Mammary Glands. Situation and Size.............1178 Nipple . .,................1179 Structure of Mamma............1179 Vessels and Nerves.............. 1279 SURGICAL ANATOMY OF HERNIA. INGUINAL HERNIA. Coverings of Inguinal Hernia. Dissection . . ..............1180 Superficial Fascia..............1180 Superficial Vessels and Nerves........1180 Deep Layer of Superficial Fascia.......1181 Aponeurosis of External Oblique......1181 External Abdominal Ring..........1182 Pillars of the Ring.............1182 Intercolumnar Fibres............1182 Fascia............1182 Poupart's Ligament............1183 Gimbernat's Ligament...........1183 Triangular Ligament............1183 Internal Oblique Muscle..........1184 Cremaster.................1184 Transversalis Muscle............1184 Spermatic Canal..............1185 Fascia Transversalis............1185 Internal Abdominal Ring..........1186 Subperitoneal Areolar Tissue........1186 Deep Epigastric Artery...........1186 Peritoneum................H86 Oblique Inguinal Hernia. Course and Coverings of Oblique Hernia . . . 1187 Seat of Stricture..............H88 Scrotal Hernia...............H89 Bubonocele................usq Congenital Hernia.............H89 Infantile and Encysted Hernia.......1189 Hernia into the Funicular Process.....1189 Direct Inguinal Hernia. Course and Coverings of the Hernia . . . .1190 Seat of Stricture..............H90 Incomplete Direct Hernia.........ll<»i Comparative Frequency of Oblique and Direct Hernia.................H91 Division of Stricture in Inguinal Hernia . . 1191 1195 FEMORAL HERNIA. Dissection.................1191 j Crural Arch.............. Superficial Fascia.............1191 Gimbernat's Ligament......... " JJljg Cutaneous Vessels.............1191! Crural Sheath............' \ jjgg Internal Saphenous Vein..........1191 j Deep Crural Arch..........' ' jjy-. Superficial Inguinal Glands ........1193 Crural Canal............. 1197 Cutaneous Nerves.............1193 Femoral or Crural Ring....... . . 1198 Deep Layer of Superficial Fascia......1193 Position of Parts around the Ring . . . . 1198 Cribriform Fascia..............1193 Septum Crurale.........° ' iiqo Fascia Lata................1193 Descent of Femoral Hernia ....... ' hqq Iliac Portion...............1193 Coverings of Femoral Hernia . . . . . ' 1199 Pubic Portion..............1194 Varieties of Femoral Hernia ..... ngg Saphenous Opening.............1194 Seat of Stricture.........\ \ .1200 CONTENTS. 25 SURGICAL ANATOMY OF PERINEUM AND ISCHIORECTAL REGION. Ischio-Rectal Region. PAGE Dissection of ...............1201 Boundaries of..............1201 Superficial Fascia............1201 Ischio-rectal Fossa.............1202 Position of Parts contained in .......1202 Male Perinaeum. Boundaries and Extent...........1202 Deep Layer of Superficial Fascia.....1203 Course taken by the Urine in Rupture of the Urethra ................1203 Muscles of the Perinaeum (Male) ......1203 Deep Perineal Fascia ...........1204 Superficial Layer...........1204 Deep Layer..............1205 Parts between the two Layers.......1205 Compressor Urethrae............1205 PAGE Cowper's Glands..............1205 Dorsal Vessels and Nerves.........1205 Artery of the Bulb ............1205 Position of the Viscera at Outlet of Pelvis . . 1206 Prostate Gland ..............1206 Surgical Anatomy of Lithotomy ...... 1207 Parts divided in the Operation.......1207 Parts to be avoided in the Operation .... 1207 Abnormal Course of Arteries in the Perinaeum 1207 Female Perinaeum. Superficial Fascia.............1207 Deep Fascia................1208 Compressor Urethrae............1208 Perineal Body .............1208 Pelvic Fascia...............1209 Obturator Fascia ...........1209 Recto-vesical Fascia . ........1210 INDEX .............. . 1211 1 ^>V_>\ lc ^ GENERAL ANATOMY. THE fluids of the body, which are intended for its nutrition, are the lymph, the chyle, and the blood. There are other fluids also which partially subserve the same purpose, as the saliva, the gastric juice, the bile, the intestinal secretion: and others which are purely excrementitious, as the urine. But there is no need to describe the rest in this place, since they are the secretions of special organs, and are described, as far as is judged necessary for the purposes of this work, in subsequent pages. We shall here speak first of the blood, and next of the lymph and chyle. THE BLOOD. The blood is a thickish, opaque fluid, of a bright-red or scarlet color when it flows from the arteries, of a dark-red or purple color when it flows from the veins. It is viscid, and has a somewhat clammy feeling; it is salt to the taste, and^has a peculiar faint odor. It has an alkaline" reaction. Its specific gravity at 60° F. is about 1.055, and its temperature is generally about 100° F., though varying slightly in different parts of the bodv. General Composition of the Blood.—When blood is drawn from the body and allowed to stand, it solidifies in the course of a very few minutes into a jelly-like mass which has the same appearance and volume as the fluid blood, and, like it, looks' quite uniform. Soon, however, drops of a transparent yellowish fluid begin to ooze out from the surface of this mass and to collect around it. Coincidently with this the clot begins to contract, so that, in the course of about twenty-four hours, the original mass of coagulated blood has become separated into two parts —a "'clot" or "coagulum," considerably smaller and firmer than the first-formed jelly-like mass, and a large quantity of yellowish fluid, the serum, in which the ° The clot thus formed consists of a solid, colorless material, called fibrin, and a larcre number of minute cells or corpuscles, called blood-corpuscles, which are entangled and enclosed in the fibrin. The fibrin is formed during the act of solidi- fication In the fluid blood in the living body there is a substance named fibrinogen, which when acted upon by a second material, also contained m the blood, and named a fibrin-ferment, forms a solid substance fibrin, lhis latter in its process of solidification encloses and entangles the blood-corpuscles, and thus the clot is formed. . Recent observations have shown that the presence of a trace of a calcium salt is a necessary condition for the transformation of fibrinogen into fibrin, lhe fibrin-ferment does not exist as such in the blood contained in the blood-vessels, but seems to result from the destruction of what are known as the white corpus- cles and the blood-plaques to be described later. These structures, more espe- cially the plaques, disintegrate very rapidly when blood is drawn from the body, liberatino- the ferment, and so producing coagulation, and lesions of the cells lining the interior of the blood-vessels seem also to give rise to ferment-produc- tion and the intra-vascular formation of fibrin. 34 GENEB. \L A N. 1 TO MY. We may now consider the constituents of the blood in another wav. If a drop of blood is placed in a thin layer on a glass slide and examined under the micro- scope, it will be seen to consist of a number of minute bodies or corpuscles floating in a clear fluid; and, on more minute examination, it will be found that these cor- puscles are principally of two kinds. The one, greatly preponderating over the other in point of numbers, is termed the colored corpuscle; the other, fewer in number and less conspicuous, is termed the colorless corpuscle. From this we learn that blood is a fluid holding a large number of corpuscles of two varieties in suspension. The fluid is named liquor sanguinis or plasma, and must not be con- fused with the serum spoken of above in connection with the coagulation of the blood. It is serum and something more, for it contains one at least of the elements or factors from which fibrin is formed. The relation of these various constituents of blood to each other will be easily understood by a reference to the subjoined plan: ^ , f Colored x r C orpuscles { (< n i j ( 1 Colorless vClot Blood--; f~u-\. ■ [ ( Jnbrm J ^Liquor Sanguinis < ( Serum The blood-corpuscles, blood-disks, blood-globules are, as before stated, of two kinds: the red or colored, and the white or colorless corpuscles. The relative proportion of the one to the other has been variously estimated and no doubt varies under different circumstances. Thus venesection, by withdrawing a large proportion of the red globules, and by favoring the absorption of lymphatic fluid into the blood, greatly increases the relative proportion of the wThite corpuscles. Klein states that in healthy human blood there appears to be one white corpuscle for 600-1200 red ones. The proportion of corpuscles, colored and colorless com- bined, to liquor sanguinis is in one hundred volumes of blood about thirty-six volumes of the former to sixtv-four of the latter. Colored corpuscles when examined under the microscope are seen to be circular disks, biconcave in profile, having a slight central depression, with a raised bor- der (Fig. 1, b). AVhen viewed with a moderate magnifying power, this central depression looks darker than the edge. When exam- ined singly by transmitted light, their color appears to be of a faint reddish-yellow when derived from arterial blood, and greenish-yellow in venous blood. It is to their aggregation that blood owes its red hue. Their size varies slightly even in the same drop of blood, but it may be stated that their average diameter is about fig. l.-Human"blood-corpus- ¥ToT of an incn> tlieir thickness about 12^00, or nearly bl%en\lTt£0™AehecTnfted one-quarter of their diameter. Besides these, especially in rouleaux, d. Rendered spner- in some anaemic and diseased conditions certain onr ical by water, e. Decolorized i r j n -, „ . ' wl" by the same. /. Blood-globules pUSCleS are IOUnd Ot a much Smaller Size, about one- shrunk by evaporation. third or half the gize of the ordinarY one Theg^ however, are very scarce in normal blood. The number of red corpuscles in the blood is enormous; between -4.000,000 and 5,000.000 are contained in a cubic- millimetre. Power states that the red corpuscles of an adult would present an aggregate surface of about 3000 square yards. Human blood-disks present no trace of a nucleus. They consist of two parts : a colorless envelope or investinp- membrane, which is composed largely of fatty material; and a colored fluid con tents, which is a solution of a substance named haemoglobin. Hcemoqlobin is proteid compound of a very complex constitution, the haemoglobin of the horse having the formula C^H^N^S.FeO^. It has a great affinity for oxygen and when removed from the body crystallizes readily under certain circumstances. It is readily soluble in water, and the addition of this fluid to a droD of bloori speedily dissolves out haemoglobin from the corpuscle. THE BLOOD. 35 If the web of a frog's foot is spread out and examined under the microscope, the blood is seen to flow in a continuous stream through the vessels, and the corpuscles show no tendency to adhere to each other or to the wall of the vessel. Doubtless the same is the case in the human body ; but when drawn and examined on a slide without reagents, the blood-globules often collect into heaps like rouleaux of coins (Fig. 1, c). During life the red corpuscles may be seen to change their shape under pres- sure so as to adapt themselves to some extent to the size of the vessel. They are also highly elastic, for they speedily recover their shape when the pressure is removed. They are soon influenced by the medium in which they are placed, and by the specific gravity of the medium. In water they swell up, lose their shape, and become globular; subsequently the haemoglobin becomes dissolved out, and the envelope can be barely distinguished as a faint, circular outline. Solu- tions of salt or sugar, denser than the serum, give them a stellate or crenated appearance; and the usual shape may be restored by diluting the solution to the proper point. The same crenated outline may be produced as the first effect of the passage of an electric shock; subsequently, if sufficiently strong, the shock ruptures the envelope. A solution of salt or sugar of the same specific gravity as serum merely separates the blood-globules mechanically without changing their shape. The white corpuscles (Fig. 2) are rather larger than the red in human blood, measuring from about yoW t0 2T$&"" markable property of undergoing |% %$*"""' ^. -|||§ '•"' "amoeboid" changes (Fig. 3). That ^ ** ...-.''^ #%. ® _.d, is to sav, they have the power of send- £MM&^ ^JP ^ ?5&t'\ »•& O' mg out finger-shaped or filamentous %^as6? %J 0$ *& gs| j&s processes of their own substance, by ||p -iV |3| ^" which they move and take up gran- FlG. 2.^. White corpuscles of human blood, d. Red ules from the surrounding substance. corpuscles. High power. In locomotion the corpuscle pushes out a process of its substance—% pseudcpodium, as it is called—and then shifts the rest of the body into it. In the same way, when any granule or particle comes in its way it wraps a pseudopodium round it, Fig. 3— Human colorless blood-corpuscle, showing its successive changes of outline within ten minutes when kept moist on a warm stage. (Schofield.) and then, withdrawing it, lodges the particle in its own substance. By means of these amoeboid properties they have the power of wandering or emigrating from the blood-vessels by penetrating their coats, and thus finding their way into the perivascular spaces. The white corpuscle may be taken as the type of a true animal cell. It has no limiting membrane, but consists of a mass of transparent albuminous substance, called protoplasm, containing one or more nuclei. These nuclei may assume varying shapes, being sometimes spherical, sometimes horseshoe-shaped, some- times moniliform, these various shapes being transition stages between the mono- nuclear and polynuclear corpuscles. The white corpuscles are very similar to, if not identical with, the corpuscles of lymph and chyle, and they also bear a strong resemblance to the cells found 3H GENERAL ANATOMY. in pus. From the fact that cells exactly like the colorless corpuscles are being constantly furnished to the blood by the lymphatic vessels and the chyle-ducts, and also from their varying proportions in different parts of the circulation and in different pathological conditions, the colorless corpuscles have been regarded —erroneously, however—as an earlier stage of the colored blood-disks, but the evidence in favor of this must be regarded as quite inconclusive. There can be no doubt that during embryonic life the red corpuscles are developed from mesoblastic cells in the vascular area of the blastoderm. They are at first nucleated and resemble white corpuscles, except in their color, and, like them, are possessed of amoeboid movements. They are succeeded by smaller, non-nucleated corpuscles, having all the characters of adult colored corpuscles, probablv formed by a conversion of the former into the latter. So that at birth the nucleated red corpuscles have disappeared. In after life an important source of the red corpuscles is the red marrow of bones, in which certain cells found in the marrow are converted into colored blood-corpuscles by the loss of their nuclei, and by their protoplasm.becoming tinged with yellow. It is probable, also, that the spleen may be a place for the formation of red corpuscles. This theory, which was formerly universally believed, and was then discarded for the hypothesis that the spleen was concerned in the destruction of the red corpuscles, has lately been revived by Bizzozero. The question must still be regarded as sub judice. The proportion of white corpuscles appears to vary considerably in different parts of the circulation, being much larger in the blood of the splenic vein and hepatic vein than in other parts of the body, while in the splenic artery they are very scanty. In addition to these corpuscles, a third variety is found in mammalian blood, and has been specially studied and described by Hayem, Bizzozero, and Osier. They are pale circular or oval disks, about one-quarter or one-third the size of the red blood-corpuscles, and apparently contain no nucleus. They have been named blood-plates or blood-plaques, and are supposed by Bizzozero to originate the fibrin- ferment, and to be especially concerned in the coagulation of the blood. The liquor sanguinis or plasma is the fluid part of the blood, and contains in solution various organic substances, such as fibrinogen, paraglobulin or serum globulin, and serum albumen, together with certain salts, sugar, fatty matter, and gases. Paraglobulin is probably contained partly in solution in the plasma, and partly in the colorless corpuscles, and can be obtained by diluting the liquor san- guinis with ten times its volume of ice-cold water, and then transmitting through it a stream of carbon dioxide. Fibrinogen may be obtained in the same way as paraglobulin, but the liquor sanguinis must be still further diluted and the current of carbon dioxide must pass for a much longer time. Fibrin may be obtained by whipping the blood, after it has been withdrawn from the body, w ith a bundle of twigs, to which the fibrin, as it coagulates, adheres. Fibrin may also be obtained by filtering the freshly-drawn blood of an animal whose corpuscles are large, care being taken to retard coagulation as long as possible. Under these circumstances the corpuscles are retained on the filter, and the liquor sanguinis, passing through, coagulates and separates into fibrin, free from corpuscles and serum. Fibrin, thus obtained, is a white or buff-colored substance, presenting a stringy appearance, and under the microscope exhibiting fibrillation. When exposed to the air for some time, it becomes hard, dry, brown, and brittle. It is a proteid compound, insoluble in hot or cold water, alcohol or ether. Under the influence of dilute hydrochloric acid it swells up, but does not dissolve • but when thus swollen it is easily dissolved by a solution of pepsin. If heated for considerable time in a solution of dilute hydrochloric acid, it gradually dissolves. ^ Serum is the fluid liquor sanguinis after the fibrin has been separated from it It is a straw-colored fluid having a specific gravity of 1.027, with an alkali reaction. Upon boiling it becomes solid, on account of the albumen which it contains. It contains also salts, fatty matters, sugar, and gases. LYMPH AND CHYLE. 37 Gases of the Blood.—When blood is exposed to the vacuum of an air-pump, about half its volume is given off in the form of gases. These are carbon dioxide, oxygen, and nitrogen. The relative quantities in 100 volumes of arterial and venous blood, at 0° C. and 1 m. pressure of mercury are shown in the accom- panying table: Oxygen. Carbon dioxide. Nitrogen. Arterial blood, 16 vols. 30 vols. 1 to 2 vols. Venous blood, 6 to 10 vols. 35 vols. 1 to 2 vols. Roughly stated, they are as follows: Carbon dioxide about two-thirds of the whole quantity of gas, oxygen rather less than one-third, nitrogen below one- tenth (Huxley). The greater quantity of the oxygen is in loose chemical com- bination with the haemoglobin of the blood-corpuscles, but some part is simply absorbed, just as it would be by water. The carbon dioxide is in a state of chem- ical combination with the salts of the serum, especially the sodium, with which it is combined partly as a carbonate and partly as a bicarbonate. The nitrogen is unimportant. It (or at least the greater part of it) is merely absorbed from the atmosphere under the pressure to which the blood is exposed, and can therefore be mechanically removed. Blood-crystals.—Haemoglobin, as stated above, when separated from the blood- corpuscles, readily undergoes crystallization. These crystals, named haemoglobin crystals, all belong, with the exception of those obtained from the squirrel, to the rhombic system. In human blood they are elongated prisms (Fig. 4, a). In the Fkj. 4.—Blood-crystals, a. Haemoglobin crystals from human blood, b. Hsemin crystals from blood treated with acetic acid. c. Haematoidin crystals from an old apoplectic clot. squirrel they are hexagonal plates. Other crystals may be obtained by mixing dried blood with an equal quantity of common salt, and boiling it with a few drops of glacial acetic acid. A drop of the mixture placed on the slide will show the crystals on cooling. These are named hcemin crystals, and consist of small acic- ular prisms (Fig. 4, b). Occasionally in old blood-clots a third form of crystal is found, the haematoidin crystal (Fig. 4, c). LYMPH AND CHYLE. Lymph is a transparent, colorless, or slightly yellow fluid, which is conveyed by a system of vessels, named lymphatics, into the blood. These vessels take their rise in nearly all parts of the body from the interstices of the connective tissue, and take up the fluid contained in these spaces and return it into the veins close to the heart, there to be mixed with the mass of the blood. The greater number of these lymphatics empty themselves into one main duct, the thoracic duct, which passes along the front of the spine and opens into one of the large veins at the root of the neck. The remainder empty themselves into a smaller duct, which terminates in the corresponding vein on the opposite side of the neck. Chyle is an opaque, milky-white fluid, absorbed by the villi of the small intestines from the food, and carried by a set of vessels similar to the lymphatics, named lacteals, to the commencement of the thoracic duct, where it is intermingled 38 GENERAL ANATOMY. with the lymph and poured into the circulation through the sani' channels. It must be borne in mind that these two sets of vessels, lvmphati- - :»nd lacteals, though differing in name, are identical in structure, and that the character of the fluid they convey is different only while digestion is going on. At other times the lacteals convey a transparent, nearly colorless fluid not to be distinguished from lymph. Both these sets of vessels, in their passage to the central duct, pass through certain small glandular bodies, termed lymphatic glands, where their contents perhaps undergo elaboration. Lymph, as its name implies, is a watery fluid. It closely resembles the liquor sanguinis, and contains about 5 per cent, of albumen and 1 per cent, of salts. When examined under the microscope, it is found to consist of a clear colorless fluid, in which are floating a number of corpuscles, lymph-corpuscles. These bodies are identical in structure, and not to be distinguished from the white blood- corpuscles previously described. They vary in number in different parts of the lymphatic vessels, and indeed are said by Kolliker to be absent in the smaller ones. They are always increased in number after the passage of the lymph through a lymphatic gland, and are said to be increased in size as the fluid ascends higher in the course of the circulation. Chyle is a milk-white fluid, which exactly resembles lymph in its physical and chemical properties, except that it has, in addition to the other constituents of lymph, an enormous amount of fatty granules, " the molecular basis of chyle," and it is to the presence of these molecules that chyle owes its milky color. Under the microscope it presents a number of corpuscles, named "chyle-corpuscles," which are indistinguishable from lymph-corpuscles or white blood-cells, and the molecular basis, consisting principally of fatty granules of extreme minuteness (Fig. 5, a), but also of a few small oil-globules. Lymph and chyle after their pas- sage through their respective glands, if withdrawn (^ from the body and allowed to stand, separate more @ (H ® " ^© or ^ess completely into a clear liquid, wThich is ~ ^ ^ /-£. identical with the serum of the blood, and a thin ^ (Mk ^ ® jelly-like clot, consisting of a fibrillated matrix in ::>^\ ^^ which lymph-corpuscles or chyle-corpuscles and 1$$0- ® v: d ® fatty molecules, as the case may be, are entangled. , . ^ If the contents of the thoracic duct are exam- t* (r\ ^ @ ... IP ined? especially after a meal, there may be found - ^ !| v^\ ^ v, in it corpuscles with a reddish tinge. These have {y or lymph- and chyle-corpuscles x - $&? . ^ - in process of transformation into blood-globules. fig. 5.-chyie from the lacteals. They frequently give to the surface of clotted chyle and lymph a pinkish hue. They must not be mistaken for mature blood-globules, which are sometimes found in lymph and chyle, and which are regarded by most observers as accidental—i. e. produced by the manipulations of the dissector. J THE ANIMAL CELL. All the tissues and organs of which the body is composed were originally developed from a microscopic body (the ovum), consisting of a soft gelatinous granular material enclosed in a membrane, and containing a vesicle or small spherical body, inside which are one or more solid spots (see Fig 73) ' This mav be regarded as a perfect cell. Moreover, all the solid tissues can be shown to con- sist largely of similar bodies, differing, it is true, in external form, but essentiallv similar to an ovum. These are also cells. ' In the higher organisms all such cells maybe defined as " nucleated masses of protoplasm of microscopic size." The two essentials, therefore, of an animal cell in the higher organisms are, the presence of a soft gelatinous granular material THE ANIMAL CELL. 39 similar to that found in the ovum, and which is usually styled protoplasm; and a small spherical body imbedded in it, and termed a nucleus; the remaining con- stituents of the ovum—viz. its limiting membrane and the solid spot contained in the nucleus, called the nucleolus—are not considered essential to the cell, and in fact many cells exist without them. Protoplasm (sarcode, blastema, germinal matter, or bioplasm) is a proteid com- pound. It also contains certain inorganic substances, as phosphorus and calcium, which latter appears to be essential to its life and function. It is of a semi-fluid, viscid consistence, and appears, sometimes, either as a hyaline substance, homo- geneous and clear, or as a granular substance, consisting of minute molecules imbedded in a transparent matrix. These molecules are regarded by some as adventitious material taken in from without, and often probably of a fatty nature, since they are frequently soluble in ether. In most cells, however, protoplasm shows a more definite structure, consisting of minute striae or fibrils arranged in a clear transparent matrix, or a honeycombed reticulum containing in its interstices a homogeneous substance. Protoplasm is insoluble in water, coagulates at 130° F., and has a great affinity for certain staining reagents, as logwood or carmine. The most striking characteristics of protoplasm are its vital properties of motion and nutrition. By motion is meant the powTer which protoplasm has of changing its shape and position by some internal power in itself, which enables it to thrust out from its main body an irregular process, into which the whole of the protoplasmic substance is gradually drawn, so that the mass comes to occupy a new position. This, on account of its resemblance to the movements observed in the Amoeba or Proteus animalcule, has been termed "amoeboid movement." Ciliary movement, or the vibration of hair-like processes from the surface of any structure, may also be regarded as a variety of the motion with which protoplasm is endowed. Nutrition is the power which protoplasm has of attracting to itself the materials of growth from surrounding matter. When any foreign particle comes in contact with the protoplasmic substance, it becomes incorporated in it by being enwrapped by one or more processes projected from the parent mass and enclosed by them. When thus taken up, it may remain in the substance of the protoplasm for some time without change, or may be assimilated by the protoplasm. The Nucleus is a minute body, imbedded in the protoplasm, and usually of a spherical or oval form, its size having little relation to the size of the cell. It is usually surrounded by a well-defined wall, the nuclear membrane, and its contents, known as the nuclear substance, are composed of a stroma or network and an inter- stitial substance, the relative amount of the two varying in different nuclei. The network appears to be continuous through the nuclear membrane with the proto- plasmic reticulum, from which it differs, however, in having strung along it bands of a substance which stains readily with certain dyes, and is therefore named chromatin. The chromatin differs chemically from ordinary protoplasm in con- taining nuclein, in its power of resisting the action of acids and alkalies, in its imbibing more intensely the stain of carmine, haematoxylin, etc., and in its remaining unstained by some reagents which color ordinary protoplasm ; as, for example, nitrate of silver. The process of reproduction of cells commences in the nucleus, and is usually described as being brought about by indirect or by direct division. Indirect division or karyokinesis (karyomitosis) has been observed in all the tissues—generative cells, epithelial tissue, connective tissue, muscular tissue, and nerve-tissue—and it is the typical method by which the division of cells takes place, although the process of reproduction of cells by direct division occurs not infrequently, especially in highly specialized cells. The process of reproduction by indirect division commences in the nucleus, the stroma of which undergoes complex changes, leading to the division of this body previous to the cleavage of the protoplasm of the cell. The changes consist briefly of the following: (1) At the commencement of the process the nuclear network is 4(1 GENERAL A NA TO MY. well developed, but shows only slight indications of activitv. (2) The chromatic fibrils, after rearranging themselves, become thicker, and probably combine in one long filament, which forms a loose convolution. This is called the glomerulus or skein (Fig. 6, b). At the same time a number of protoplasmic granules arrange themselves at two points in the cell-protoplasm opposite each other; these points are called the poles, and the line midway between them, and bisecting at right SIDE OR EQUATORIAL VIEW. END OR POLAR VIEW. SIDE OR EQUATORIAL VIEW. Fig. 6— Karyokinesis, or indirect cell-division. Diagram explaining the formation of tbp f.i,r,->m«.«„ „ * achromatic karyokinetic figures in epithelial cells. The radiating arrangement of nrntnniQ^ ■ i • also indicated, although it is in the ova of the lower animals that this appearance has been studied. All the figures are simplified for diagrammatic purposes, but represent stages whthnnn specially recognized in specimens properly stained. The longitudinal splitting of the filaments has not i ea y De sented. a. Resting nucleus, the nuclear network deeply stained, b. Glomerulus convolution n.£n-repre~ Rosette or wreath, d. Aster or monaster. >:. Diaster or daughter star. f. Daughter rneott^i skein, c. glomeruli or skeins, h. Daughter nuclei. (By Dr. S. Delepine.) 6 ius>eues. o. Daughter angles a line connecting the two, is called the equator. The ap-o-reo-atio f protoplasmic granules are termed the ceutrosomes, and they are surrounded b clear protoplasmic areas known as the archoplasm spheres. (3) The chromatic THE ANIMAL CELL. 41 filament becomes arranged in more or less distinct loops converging toward the two poles, resembling somewhat in appearance a rosette or wreath (Fig. 6, c). From the poles to the loops, fine threads, not staining like the others (achromatic), are seen bridging across the space left between the filament and the cell- protoplasm. These are known as the nuclear spindle. (4) The loops now become flattened so as to form a festooned ring or star at the equator of the nucleus. This is known as the single star, aster, monaster. The loops begin to break transversely at the equator (Fig. 6, d*), having sometimes previously broken at their polar ends. The nuclear spindle or achromatin is very distinct, as well as a radiating arrangement of protoplasmic granules toward the poles. It is at this stage, or sometimes after, that a longitudinal splitting of the filaments occurs, so that they become more numerous and more slender. (5) After breaking across at the equator, the chromatic filaments move toward the poles as if they were guided by the achromatic threads. These threads bridge across between the two receding stars, which are known as diaster or daughter stars. The pro- toplasm, with its radiating granules, begins to group itself around the two poles (Fig. 6, e). (6) The daughter stars have now reached the poles; the broken ends become united, so that each daughter chromatic filament becomes a single festooned filament, forming a rosette or wreath, the daughter rosettes or wreaths. There is now distinct evidence of cleavage in the protoplasm (Fig. 6, f). (7) By further irregular contraction the regular arrangement of the loops becomes lost, and the filament presents a convoluted appearance, constituting the daughter glomeruli or skeins (Fig. 6, g). The cleavage of the protoplasm is now complete except where the achromatic threads are found. (8) By further convolution and contraction the loops of the filament become fused together, and form again a network. The nuclear membrane which disappeared at the beginning of the karyokinesis is formed anew, and two daughter cells with nuclei are formed (Fig. 6, h). The remains of the achromatic threads bridge across the intercellular substance, but later usually disappear completely. In the reproduction of cells by direct division the process is brought about either by segmentation or by gemmation. In reproduction by segmentation or fission the nucleus first splits by becoming constricted in its centre, and thus assuming an hour-glass shape. This leads to a cleavage or division of the whole protoplasmic mass of the cell; and thus we find that two new cells have been formed, consisting of the same substance as the original one, and each containing a nucleus. These daughter cells are of course at first smaller than the original mother cell; but they grow, and the process may be repeated in them, so that multiplication may rapidly take place. In reproduction by gemmation a budding- off or separation of a portion of the nucleus and parent-cell takes place, and, becoming separated, forms a new organism. The cell-wall, which is not an essential constituent, and in fact is often absent, consists of a flexible, transparent, structureless or finely striated membrane, which is permeable to fluids. As far as is known, every animal cell is derived from a pre-existing cell. The death of cells is accomplished either by their mechanical detachment from the surface, preceded possibly by their bursting and discharg- ing their contents, or by various forms of degeneration—fatty, pigmentary, or calcareous. EPITHELIUM. All the surfaces of the body—the external surface of the skin, the internal surface of the digestive, respiratory, and genito-urinary tracts, the closed serous cavities, the inner coat of the vessels, and the ducts of all secreting and excreting glands—are covered by one or more layers of simple cells, called epithelium or epithelial cells. These cells are also present in the sensory and terminal parts of the organs of special sense, and in some other organs, as the pituitary and thyroid bodies. They serve various purposes, forming in some cases a protective layer, in others acting as an agent in secretion and excretion, and again in others being concerned in the elaboration of the organs of special sense. Thus, in the skin, 42 (i KNERAL ANA TOM Y. the main purpose served by the epithelium (here called the epidermis) is that of protection. As the surface is worn away by the agency of friction or change of temperature new cells are supplied, and thus the surface of the true skin and the vessels and nerves which it contains are defended from damage. In the gastro- intestinal mucous membrane and in the glands the epithelial cells appear to be the principal agents in separating the secretion from the blood or from the aliment- ary fluids. In other situations (as the nose, fauces, and respiratory passages) the chief office of the epithelial cells appears to be to maintain an equable tempera- ture by the moisture with which they keep the surface always slightly lubricated. In the serous cavities they also keep the opposed layers moist, and thus facilitate their movements on each other. Finally, in all internal parts they ensure a perfectly smooth surface. Of late years there has been a tendency on the part of many histologists to divide these several epithelial linings into two classes: into (1) epithelial tissue proper, consisting of nucleated protoplasmic cells, which form continuous masses on the skin and mucous surfaces and the linings of the ducts and alveoli of secreting and excreting glands ; and (2) endothelium, which is composed of a single layer of flattened transparent squamous cells, joined edge to edge in such a man- ner as to form a membrane of cells. This is found on the free surfaces of the serous membranes, as the lining membrane of the heart, blood-vessels, and lym- phatics ; on the surface of the brain and spinal cord, and in the anterior chamber of the eye. And, though the separation must be an artificial one, since every gradation of transition between the two classes may be observed, it would seem advisable for the purpose of description to employ it. 1. True epithelial tissue consists of one or more layers of cells, united together Fig. 7.—Epithelial cells from the oral cavity of man. Magnified 350 times < c. The same with two nuclei. ^»ige. b. Middle-sized. by an interstitial cement-substance, supported on a basement-membrane, and is naturally grouped into two classes, according as there is a single layer of cells (simple epithelium) or more than one (stratified epithelium). The various kinds of epithelium, whether arranged in a single layer or in more than one layer are usually spoken of as squamous or pavement, columnar, spheroidal or () GENERA I * I .V.l TOM )'. in addition to its occurrence in adipose tissue is also Avidely present in the body, as in the fat of the brain and liver and in the blood and chyle, etc. Fat-cells (Fig. 19) consist of a number of vesicles, varying in size, but of about the average diameter of jfa of an inch. They are formed of an exceedingly delicate protoplasmic membrane, filled Avith fatty matter, Avhich is liquid during life, but becomes solidilied after death. They are round or spherical Avhere they have not been subjected to pressure; •^^~r,..>,,^jp-^^ otherwise they assume a more or less ,J^^^, ^f'^^^X^^^^ angular outline. A nucleus is always ^f^^^i^^|^\^i- ^ present, and can be easily demonstrat- c^^^mM'ff^-^r^^W ^f^3^ ed hJ Gaining with hematoxylin; in 7\f_jOf VC": ~W^l^i&?sL d the natural condition it is so com- Xsfl ':--^f-^ C^X^^^^) f\ pressed by the contained oily matter ^^ri^'C^^f^f^^^Qj^ as t0 be scarcely recognizable. These ^Jgtj^f^^^ fat-cells are contained in clusters in —-C ~ ^m~ ^-r—- "—^- .cr the areolae of fine connective tissue, 3iinc septa, d. The ground-substance, containing wwv" kjvun,i,iu ,_o f numerous nucleated cells, some of which are more dis- spontaneously before the fat IS exam- tinctlv branched and flattened than others, and appear .1 , , J -, .-, therefore more spindle-shaped. med, and are seen under tne micro- scope in a crystalline form, as in Fig. 19, a. By boiling the tissue in ether or strong alcohol the fat may be extracted from the vesicle, Avhich is then seen empty and shrunken. Fat is said to be first detected in the human embryo about the fourteenth Aveek. The fat-cells are formed by the transformation of the protoplasmic con- nective-tissue corpuscles, into Avhich small globules of fat find their way, and increase until they distend the corpuscle into the thin mantle of protoplasm which forms the cell-wall, and in Avhich its nucleus is still to be seen (Fig. 20). PIGMENT. In various parts of the body pigment is found; most frequently in epithelial cells and in the cells of connective tissue. Pigmented epithelial cells are found forming the external layer of the retina (Fig. 21) and on the posterior surface of the iris. Pigment is also found in the epithelial cells of the deeper layers of the cuticle in some parts of the body—such as the areola of the nipple and in colored patches of skin, and especially in the skin of the colored races, and also in hair. It is also found in the epithelial cells of the olfactory region and of the membranous labyrinth of the ear. ^ceii^oTretiSI^" In tne connective-tissue cells pigment is frequently met Avith in the loAver vertebrates. In man it is found in the choroid coat of the eye, and in the iris of all but the light-blue eyes and the albino. It is also occasionally met with in the cells of retiform tissue and in the pia mater of the upper part of the spinal cord. These cells are characterized by their larger size and branched processes, which, as well as the body of the cells, are filled with granules. The pigment consists of dark-brown or black granules of very small size, closely packed together within the cells, but not invading the nucleus. Occasionally the pigment is yellow, and when occurring in the cells of the cuticle constitutes "freckles." CARTILAGE. 51 CARTILAGE. Cartilage is a non-vascular structure which is found in various parts of the body—in adult life chiefly in the joints, in the parietes of the thorax, and in various tubes, such as the air-passages, nostrils, and ears, which are to be kept permanently open. In the foetus at an early period the greater part of the skele- ton is cartilaginous. As this cartilage is afterward replaced by bone, it is called temporary, in contradistinction to that which remains unossified during the Avhole of life, and Avhich is called permanent. Cartilage is divided, according to its minute structure, into true or hyaline cartilage, fibrous or fibro-cartilage, and yellow or elastic or reticular cartilage. Besides these varieties met Avith in the adult human subject, there is a variety called cellular cartilage, which consists entirely, or almost entirely, of cells, united in some cases by a network of very fine fibres, in other cases apparently destitute of any intercellular substance. This is found in the external ear of rats, mice, and some other animals, and is present in the chorda dorsalis of the human embryo, but is not found in any other human structure. The various cartilages in the body are also classified, according to their function and position, into articular, interarticular, costal, and membraniform. Hyaline cartilage, which may be taken as the type of this tissue, consists of a gristly mass of a firm consistence, but of considerable elasticity and of a pearly- bluish color. Except where it coats the articular ends of bones, it is enveloped in a fibrous membrane, the perichondrium, from the vessels of which it imbibes its nutritive fluids, being itself destitute of blood-vessels; nor have any nerves been traced into it. Its intimate structure is very simple. If a thin slice is examined under the micro- scope, it will be found to consist of cells of a rounded or bluntly angular form, lying in groups of two or more in a granular or almost homogeneous matrix (Fig. 22). The cells, when arranged in groups of two or more, have generally a straight outline where they are in contact Avith each other, and in the rest of their cir- cumference are rounded. The cell-contents consist of clear translucent proto- plasm containing minute granules, and imbedded in this are one or two nuclei having usually a granular appearance, but occasionally being clear and occupied bv one or more nucleoli. The cells are imbedded in cavities m the matrix, called cartilage lacunce, which are lined by a distinct transparent membrane called the capsule. Each lacuna is generally occupied by a single cell but during the division of the cells it may contain two, four, or eight cartilage-cells. By boiling the cartilage for some hours and treating it with concentrated mineral acid, the capsule mav be freed from the matrix, and can then be demonstrated as a distinct vesicle containing the cells. By exposure to the action of an electric shock the cell assumes a jagged outline and shrinks away from the interior of the '^ The matrix is transparent and apparently without structure, or else presents a dimly granular appearance, like ground glass. Some observers have shown that the matrix of hyaline cartilage, and especially the articular variety, after pro onged maceration, can be broken up into fine fibrils. These fibrils are prob- ably of the same nature, chemically, as the white fibres of connective tissue. It ?s believed by some histologists that the matrix is permeated by a number of fine hannelsf which connect the lacuna with each other, and that these canals communicate with the lymphatics of the perichondrium, and thus the structure is permeated with a current of nutritious fluid. Fig. '22.—Human cartilage-cells, from the cricoid carti- lage. Magnified 350 times. 52 GENERAL ANATOMY. The articular cartilages, the temporary cartilages, and the costal cartilages are all of the hyaline variety. They present minute differences in the size and shape of their cells and in the arrangement of their matrix. In the articular cartilages, which sIioav no tendency to ossification, the matrix is finely granular under a high power; the cells and nuclei are small and are disposed parallel to the surface in the superficial part, Avhile nearer to the bone they become vertical. Articular cartilages have a tendency to split in a vertical direction, probably from some peculiarity in the intimate structure or arrangement of the component parts of the matrix. In disease this tendency to a fibrous splitting becomes very manifest. Articular cartilage is not covered by perichondrium, at least on its free surface, where it is exposed to friction, though a layer of connective tissue can be traced in the adult over a small part of its circumference continuous with that of the synovial membrane, and here the cartilage-cells are more or less branched and pass insensibly into the branched connective-tissue corpuscles of the synovial membrane. Articular cartilage forms a thin incrustation upon the joint-surfaces of the bones, and its elasticity enables it to break the force of any concussion, whilst its smoothness affords ease and freedom of movement. It varies in thickness accord- ing to the shape of the bone on Avhich it lies ; where this is convex the cartilage is thickest at the centre, where the greatest pressure is received; and the reArerse is the case on the concave surfaces of the bones. Articular cartilage appears to imbibe its nutriment partly from the vessels of the neighboring synovial mem- brane, partly from those of the bone upon Avhich it is implanted. Mr. Toynbee has shown that the minute vessels of the cancellous tissue as they approach the articular lamella dilate and form arches, and then return into the substance of the White fibro-cartilage consists of a mixture of white fibrous tissue and cartilag- inous tissue in various proportions; it is to the first of these two constituents that its flexibility and toughness are chiefly owing, and to the latter its elasticity ^ hen examined under the microscope it is found to be made up of fibrous con nective tissue arranged in bundles, with cartilage-cells between the bundles • these CARTILAGE. 53 to a certain extent resemble tendon-cells, but may be distinguished from them by being surrounded by an investing capsule and by their being less flattened (Fig. 24). The fibro-cartilages admit of nected to the surrounding ligaments. The synovial membrane of the joint is prolonged over them a short distance from their attached margins. They are found in the temporo-maxillary, sterno-clavicular, acromio-clavicular, Avrist and knee-joints. These cartilages are usually found in those joints which are most exposed to violent concussion and subject to frequent movement. Their use is —to maintain the apposition of the opposed surfaces in their various motions; to increase the depth of the articular surfaces and give ease to the gliding movement; to moderate the effects of great pressure and deaden the intensity of the shocks to which the parts may be subjected. Humphry has pointed out that these inter- articular fibro-cartilages serve an important purpose in increasing the variety of movements in a joint. Thus, in the knee-joint there are two kinds of motion, —viz. angular movement and rotation, although it is a hinge joint, in which, as a rule, only one \rariety of motion is permitted; the former movement taking place betAveen the condyles of the femur and the interarticular cartilage, the latter between the cartilage and the head of the tibia. So, also, in the temporo-maxil- lary joint, the upAvard and downward movement of opening and shutting the mouth takes place between the cartilage and the jaAv-bone, the grinding move- ment between the glenoid cavity and the cartilage, the latter moving Avith the jaAv-bone. The connecting fibro-cartilages are interposed betAveen the bony surfaces of those joints Avhich admit of only slight mobility, as betAveen the bodies of the ver- tebrge and between the pubic bones. They form disks, Avhich adhere closely to both of the opposed bones, and are composed of concentric rings of fibrous tissue, with cartilaginous laminae interposed, the former tissue predominating tOAvard the circumference, the latter toward the centre. The circumferential fibro-cartilages consist of a rim of fibro-cartilage, Avhich surrounds the margin of some of the articular cavities, as the cotyloid cavity of the hip and the glenoid cavity of the shoulder; they serve to deepen the articular surface and to protect the edges of the bone. The stratiform fibro-cartilages are those which form a thin coating to osseous grooves through which the tendons of certain muscles glide. Small masses of fibro-cartilage are also developed in the tendons of some muscles, where they glide over bones, as in the tendons of the peroneus longus and the tibialis posticus. Yellow, or reticular, elastic cartilage is found in the human body in the auricle of the external ear, the Eustachian tubes, the cornicula laryngis, and the epiglottis. It consists of cartilage-cells and a matrix, the latter being pervaded in every direction, except immediately around each cell, by a netAvork of yellow 54 G EN ERA L . \ NA TOM }'. elastic fibres, branching and anastomosing in all directions (Fig. 25). The fibres resemble those of yellow elastic tissue, both in appearance and in being unaffected by acetic acid; and according to Rollett their continuity Avith the elastic fibres of the neighboring tissue admits of being demonstrated. The distinguishing feature of cartilage as to its chemical composition is that it yields on boiling a substance called chondrin, very similar to gelatin, but differing from it in not being precipitated by tannin. According to Kiihne there is a small amount of gelatin in hyaline cartilage. Virchow believes that the semilunar disks in the knee- joint are wrongly denomi- nated cartilages, since they yield no chondrin on boil- Fig. 25.-Yellow cartilage, ear of horse. High power. ing 5 an(* n© appears to re- gard them as a modification of a tendinous structure, Avhich, however, agrees with the cartilages in the important particular of being non-vascular. Temporary cartilage and the process of its ossification will be described with Bone. BONE. Structure and Physical Properties of Bone.—Bone is one of the hardest struc- tures of the animal body ; it possesses also a certain degree of toughness and elasticity. Its color, in a fresh state, is of a pinkish white externally, and deep red Avithin. On examining a section of any bone, it is seen to be composed of two kinds of tissue, one of Avhich is dense and compact in texture, like ivory; the other consists of slender fibres and lamellae, which join to form a reticular struc- ture ; this, from its resemblance to lattice-work, is called cancellous. The com- pact tissue is always placed on the exterior of the bone; the cancellous is always internal. The relative quantity of these two kinds of tissue varies in different bones, and in different parts of the same bone, as strength or lightness is requisite. Close examination of the compact tissue shows it to be extremely porous, so that the difference in structure between it and the cancellous tissue depends merely upon the different amount of solid matter, and the size and number of spaces in each; the cavities being small in the compact tissue and the solid matter between them abundant, whilst in the cancellous tissue the spaces are large and the solid matter in smaller quantity. Bone during life is permeated by vessels and is enclosed in a fibrous membrane, the periosteum, by means of which many of these vessels reach the hard tissue. If the periosteum is stripped from the surface of the living bone, small bleeding points are seen, which mark the entrance of the periosteal vessels; and on section during life every part of the bone Avill be seen to exude blood from the minute vessels Avhich ramify in it. The interior of the bones of the limbs presents a cylindrical cavity filled with marrow and lined by a highly vascular areolar structure, called the medullary membrane or internal periosteum, Avhich, how- ever, is rather the areolar envelope of the cells of the marrow than a definite membrane. The periosteum adheres to the surface of the bones in nearly every part excepting at their cartilaginous extremities. Where strong tendons or ligaments BONE. 55 are attached to the bone, the periosteum is incorporated with them. It consists of tAvo layers closely united together, the outer one formed chiefly of connective tissue, containing occasionally a few fat-cells; the inner one, of elastic fibres of the finer kind, forming dense membranous networks, Avhich can be again separated into several layers. In young bones the periosteum is thick, and very vascular, and is intimately connected at either end of the bone with the epiphysial cartilage, but less closely with the shaft, from Avhich it is separated by a layer of soft blas- tema, containing a number of granular corpuscles or " osteoblasts," in Avhich ossification proceeds on the exterior of the young bone. Later in life the peri- osteum is thinner, less vascular, and the osteoblasts have become converted into an epithelial layer, Avhich is separated from the rest of the periosteum in many places by cleft-like spaces, Avhich are supposed to serve for the transmission of lymph. The periosteum serves as a nidus for the ramification of the vessels previous to their distribution in the bone; hence the liability of bone to exfolia- tion or necrosis, when denuded of this membrane by injury or disease. Fine nerves and lymphatics, which generally accompany the arteries, may also be demonstrated in the periosteum. The marrow not only fills up the cylindrical cavity in the shafts of the long bones, but also occupies the spaces of the cancellous tissue and extends into the larger bony canals (Haversian canals) Avhich contain the blood-vessels. It differs in composition in different bones. In the shafts of adult long bones the marroAV is of a yellow color, and contains, in 100 parts, 96 of fat, 1 of areolar tissue and vessels, and 3 of fluid, with extractive matter, and consists of a matrix of fibrous tissue, supporting numerous blood-vessels and cells, most of Avhich are fat-cells, but some few are "marrow-cells." In the flat and short bones, in the articular ends of the long bones, in the bodies of the vertebrae, in the cranial diploe, and in the sternum and ribs, it is of a red color, and contains, in 100 parts, 75 of water and 25 of solid matter, consisting of albumen, fibrin, extractive matter, salts, and a mere trace of fat. The red marrow consists of a small quantity of areolar tissue, blood-vessels, and numerous cells, some feAv of Avhich are fat-cells, but the great majority roundish nucleated cells, the true " marroAV-cells " of Kolliker. These marrow-cells resemble in appearance the white corpuscles of the blood, though they are larger and have a relatively larger nucleus and a clearer protoplasm, but, like them, possess amoeboid movements. Amongst them may be seen smaller cells (erythroblasts) Avhich possess a slightly pinkish hue ; and it has been held by Neumann that they are a transitional stage betA\een marrow-cells and red blood-corpuscles, while others believe them to be the direct descendants of the nucleated embryonic blood-cells (see p. 127), and to be transformed into blood- corpuscles by the loss of their nuclei. Giant-cells (myelo-plaques, osteoclasts), large, multinucleated, protoplasmic masses, are also to be found in both sorts of adult marrow, but more particularly in red marrow. They were believed by Kolliker to be concerned in the absorption of bone matrix, and hence the name Avhich he gave to them—osteoclasts. They excavate small shallow pits or cavities, which are named Howships lacunas, in Avhich they are found lying. Vessels of Bone.—The blood-vessels of bone are very numerous. Those of the compact tissue are derived from a close and dense network of vessels ramifying in the periosteum. From this membrane vessels pass into the minute orifices in the compact tissue, running through the canals which traverse its substance. The cancellous tissue is supplied in a similar way, but by a less numerous set of larger vessels, Avhich, perforating the outer compact tissue, are distributed to the cavities of the spongy portion of the bone. In the long bones numerous apertures may be seen at the ends near the articular surfaces, some of Avhich give passage to the arteries of the larger set of vessels referred to; but the most numerous and largest apertures are for the veins of the cancellous tissue, Avhich run separately from the arteries. The medullary canal in the shafts of the long bones is supplied by one large artery (or sometimes more), Avhich enters the bone at the nutrient foramen 56 GENERAL ANATOM)' (situated in most cases near the centre of the sliaft), and perforates obliquely the compact structure. The medullary or nutrient arterv, usually accompanied by one or tAvo veins, sends branches upAvard and doAvnAvard to supply the medullary membrane, Avhich lines the central cavity and the adjoining canals. The ramifica- tions of this vessel anastomose with the arteries both of the cancellous and com- pact tissues. In most of the flat, and in many of the short spongy bones, one or more large apertures are observed, Avhich transmit, to the central parts of the bone, vessels corresponding to the medullary arteries and veins. The veins emerge from the long bones in three places (Kolliker): (1) by one or tAvo large veins, which accompany the artery; (2) by numerous large and small veins at the artic- ular extremities; (3) by many small veins which arise in the compact substance. In the flat cranial bones the veins are large, very numerous, and run in tortuous canals in the diploic tissue, the sides of the canals being formed by a thin lamella of bone, perforated here and there for the passage of branches from the adjacent cancelli. The same condition is also found in all cancellous tissue, the veins being enclosed and supported by osseous structure and having exceedingly thin coats. When the bony structure is divided, the vessels remain patulous, and do not con- tract in the canals in Avhich they are contained. Hence the constant occurrence of purulent absorption after amputation in those cases Avhere the stump becomes inflamed and the cancellous tissue is infiltrated and bathed in pus. Lymphatic vessels, in addition to those found in the periosteum, have been traced by Cruikshank, into the substance of bone, and Klein describes them as running in the Haversian canals. Nerves are distributed freely to the periosteum, and accompany the nutrient arteries into the interior of the bone. They are said by Kolliker to be most numerous in the articular extremities of the long bones, in the vertebrae and the larger flat bones. Minute Anatomy.—The intimate structure of bone, which in all essential particulars is identical in the compact and cancellous tissue, is most easily studied in a transverse section from the compact Avail of one of the long bones after maceration, such as is shown in Fig. 26. If this is examined with a rather low power the bone will be seen to be mapped out into a number of circular districts, each one of Avhich consists of a central hole, surrounded by a number of concentric rings. These districts are termed Haversian systems; the central hole is an Haversian canal, and the rings around a're layers of bone-tissue arranged concentrically around the cen- tral canal, and termed lamella'. More- found that between these lamella, and therefore also arranged concentrically around the central canal are a number of little dark specks, the lacuna', and that these lacuna are connected with each other and with the central Haversian canal bv a number of fine dark lines which radiate like the spokes of a wheel and are called canaliculi. All these structures —the concentric lamella, the lacuna, and the canaliculi—may be seen in anv single Haversian system, forming a circular district round a central, Haversian canal. Between these circular systems, filling in the irregular intervals which are^ left between them, are other lamella, with their lacuna and canaliculi runnino- in ,P%,-. "**..§%fc Fig 26.—From a transverse section of the shaft of the humerus. Magnified 350 times, a. Haversian canals, b. Lacuna?, with their canaliculi in the lamellae of these canals, c. Lacunae of the interstitial lamella;. d. Others at the surface of the Haversian systems, with canaliculi given off from one side. over, on closer examination, it Avill be BONE. 57 various directions, but more or less curved (Fig. 27). These are termed interstitial lamella. Again, other lamella, for the most part found on the surface of the bone, are arranged concentrically to the circumference of bone, constituting, as it were, a single Haversian system of the whole bone, of which the medullary cavity would represent the Haversian canal. These latter lamella are termed circumferential, or by some authors primary or fundamental lamella, to distinguish them from those laid down around the axis of the Haversian canals, Avhich are then termed secondary or special lamella. The Haversian canals, seen as round holes in a transverse section of bone at or about the centre of each Haversian system, may be demonstrated to be true canals if a longitudinal section is made, as in Fig. 29. It will then be seen that these round holes are tubes cut across, which run parallel with the longitudinal Fig. 27.—Transverse section of compact tissue of bone. Magnified about 150 diameters. (Sharpey.) axis of the bone for a short distance, and then branch and communicate. They vary considerably in size, some being as large as ywo oi* an in(m ^n diameter; the average size being, however, about ^¥ of an inch. Near the medullary cavity the canals are larger than those near the surface of the bone. Each canal, as a rule, contains tAvo blood-vessels, a small artery and vein; the larger ones also con- tain a small quantity of delicate connective tissue, with branched cells, the pro- cesses of which communicate with the branched processes of certain bone-cells in the substance of the bone. Those canals near the surface of the bone open upon it by minute orifices, and those near the medullary cavity open in the same Avay into this space, so that the whole of the bone is permeated by a system of blood-vessels running through the bony canals in the centre of the Haversian systems. The lamellae are thin plates of bone-tissue encircling the central canal, and might be compared, for the sake of illustration, to a number of sheets of paper pasted one over another around a central hollow cylinder. After macerating a piece of bone in dilute mineral acid, these lamella may be stripped off in a longi- tudinal direction as thin films. If one of these is examined with a high power under the microscope it will be found to be composed of a finely reticular struc- ture, presenting the appearance of lattice-Avork made up of very slender, trans- parent fibres, decussating obliquely, and coalescing at the points of intersection so as to form an exceedingly delicate netAVork. In many places the various lamella may be seen to be held together by tapering fibres, which run obliquely through them, pinning or bolting them together. These fibres were first described by Sharpey, and were named by him perforating fibres. 58 G EN ERA L . 1NA TO MY. V,A Fig. 2S— Nucleated bone-cells and their processes, contained in the bone-lacunae and their canaliculi respectively. From a section through the vertebra of an adult mouse. (Klein and Noble Smith.) The lacuna' are situated betAveen the lamelhe. and consist of a number of oblong spaces. In an ordinary microscopic section, viewed by transmitted light, they appear as dark, oblong, opaque spots, and Avere formerly believed to be solid cells. Subsequently, when it was seen that the Haversian canals were channels which lodge the vessels of the part, and the canaliculi minute tubes by which the plasma of "the blood circulates through the tissue, it was taught that the lacuna were hollow spaces filled during life with the same fluid, and only lined (if lined at all) bv a delicate membrane. But this view appears also to be delusive. Examination of the structure of bone, Avhen recent, led Yirchow to believe that the lacuna are occupied during life Avith a nucleated cell, the processes from which pass doAvn the canal- iculi—a view Avhich is now universally received (Fig. 28). It is by means of these cells that the fluids necessary for nutrition are brought into contact with the ultimate tissue of bone. The canaliculi are exceedingly minute channels, which pass across the lamella and connect the lacuna Avith neighboring lacuna and also Avith the Haversian canal. From this central canal a number of the canaliculi are given off, Avhich radiate from it, and open into the first set of lacuna, arranged around the Haversian canal, betAveen the first and second lamella. From these lacuna a second set of canaliculi are given off, Avhich pass outward to the next series of lacuna, and so on until they reach the periphery of the Haver- sian system; here the canaliculi given off from the last series of lacuna do not communicate Avith the lacuna of neighboring Haversian systems, but after passing outAvard for a short distance form loops and return to their own lacuna. Thus every part of an Haversian system is supplied Avith nutrient fluids derived from the vessels in the Haversian canals and traversing the canaliculi and lacuna. The bone-cells are contained in the lacuna, Avhich, however, they do not com- pletely fill. They are flattened nucleated cells, Avhich Yirchow has shown are homologous Avith those of connective tissue. The cells are branched, and the branches, especially in young bones, pass into the canaliculi from the lacuna. If a longitudinal section is examined, as in Fig. 29, the structure is seen to be the same. The appearance of concentric rings is replaced by that of lamella or rows of lacuna, parallel to the course of the Haversian canals, and these canals appear like half-tubes instead of circular spaces. The tubes are seen to branch and communicate, so that each separate Haversian canal runs only a short distance. In other respects the structure has much the same appearance as in transverse sections. In sections of thin plates of bone (as in the Avails of the cells Avhich form the cancellous tissue) the Haversian canals are absent, and the canaliculi open into the spaces of the cancellous tissue (medullary spaces), which thus have the same func- tion as the Haversian canals in the more compact bone. Chemical Composition.—Bone consists of an animal and an earthy part inti- mately combined together. The animal part may be obtained by immersing the bone for a considerable time in dilute mineral acid, after which process the bone comes out exactly the same shape as before, but perfectly flexible, so that a long bone (one of the ribs for example) can easily be tied in a knot. If noAv a transverse section is made (Fig. 30), the same general arrangement of the Haversian canals, lamella, lacuna and canaliculi is seen, though not so plainly, as in the ordinary section. BONE. 59 The earthy part may be obtained separate by calcination, by which the animal matter is completely burned out. The bone Avill still retain its original form, but it will be Avhite and brittle, will have lost about one-third of its original weight, and will crumble down with the slightest force. The earthy matter confers *'f. *H* ^4^^1M^^|ii^^ on Done ^s hardness and rigidity, and the ^ll/ij hi** '0%%*\ ^^m animal matter its tenacity. &M ■ Fig. 29.—Section parallel to the surface from the shaft of the femur. Magnified 100 times, a. Haversian canals, b. Lacunae seen from the side. c. Others seen from the sur- face in lamellae which are cut horizontally. Fig. 30.—Section of bone after the removal of the earthy mat- ter by the action of acids. The animal base is often called cartilage, but differs from it in structure, in the fact that it is softer and more flexible, and that Avhen boiled with a high pressure it is almost entirely resolved into gelatin. The organic constituent of bone forms about one-third, or 33.3 per cent.; the inorganic matter, two-thirds, or 66.7 per cent.; as is seen in the subjoined analysis of Ber- zelius: Organic matter . Gelatin and blood-vessels . 33.30 f Phosphate of lime .... . 51.04 Inorganic j Carbonate of lime .... . 11.30 or j Fluoride of calcium | Phosphate of magnesia 2.00 Earthy matter . . 1.16 (_ Soda and chloride of sodium 1.20 100.00 Some chemists add to this about 1 per cent, of fat. Some difference exists in the proportion betAveen the two constituents of bone at different periods of life. In the child the animal matter predominates, Avhereas in aged people the bones contain a larger proportion of earthy matter, and the animal matter is deficient in quantity and quality. Hence in children it is not uncommon to find, after an injury to the bones, that they become bent or only partially broken, whereas in old people the bones are more brittle and fracture takes place more readily. Some of the diseases, also, to which bones are liable mainly depend on the disproportion betAveen the two constituents of bone. Thus in the disease called rickets, so common in the children of the poor, the bones become bent and curved, either from the superincumbent Aveight of the body, or under the action of certain muscles. This depends upon some defect of nutrition by which bone becomes deprived of its normal proportion of earthy matter, whilst the animal matter is of unhealthy quality. In the vertebra of a rickety subject Dr. Bostock found in 100 parts 79.75 animal and 20.25 earthy matter. Development of Bone.—In the foetal skeleton some bones, such as the long bones of the limbs, are cartilaginous; others, as the cranial bones, are membran- ous. Hence two kinds of ossification are described: the intracartilaginous and the intramembranous ; and to these a third is sometimes added, the subperiosteal; this, hoAvever, is the same as the second, only taking place under different cir- cumstances. (iO G EN ER AL A N. I T() M >'. Intracartilaginous Ossification.—Just before ossification begins the bone is entirely cartilaginous, and in a long bone, Avhich may be taken as an example, the process commences in the centre and proceeds toAvard the extremities, which for some time remain cartilaginous. Subsequently a similar process commences in one or more places in those extremities and gradually extends through it. The extremity does not, however, become joined to the shaft of the bone until groAvth has ceased, but remains separated by a layer of cartilaginous tissue termed epiphysial carti- lage. The first step in the ossifica- tion of the cartilage is that the cartilage-cells, at the point where ossification is commen- cing and which is termed a cen- tre of ossification, enlarge and arrange themselves in rows (Fig. 31). The matrix in which they are imbedded increases in quan- tity, so that the cells become further separated from each other. A deposit of calcareous material now takes place in this matrix, between the rows of cells, so that they become sepa- rated from each other by longi- tudinal columns of calcified matrix, presenting a granular and opaque appearance. Here and there the matrix betAveen two cells of the same row also becomes calcified, and thus we have transverse bars of calcified substance stretching across from one calcareous column to another. Thus Ave have lon- ,, i •■ • ,, .. , gitudinal groups of the cartilage- cells enclosed in oblong cavities, the walls of which are formed of calcified matrix. These cavities are called the primary areolae (Sharpey). At the same time that this process is going on in the centre of the cartilage of which the foetal bone consists, certain changes are taking place on its surface Ihis is covered by a very vascular membrane, the periosteum, on the inner surface of which—that is to say, on the surface in contact with the cartilage-are a number of cells called osteoblasts. By the agency of these cells a thin layer of bony tissue is being formed between the periosteum and the cartilage, bv the intramcm branous mode of ossification presently to be described. We have then in this first stage of ossification, two processes going on simultaneously: in the centre of the cartilage the formation of a number of oblong spaces, enclosed by calcified matnx and containing the cartilage-cells enlarged and arranged in groups and on the surface of the cartilage the formation of a layer of true membrane-bone The second stage consists in the prolongation into the cartilage of processes of thl deeper or osteogenetic layer of the periosteum (Fie ?y> ir\ Th« ULehbes 0I tne of blood-vessels and cells (osteoblasts). Thev exSvate uLJ^tV^V011^ formed bony layer by absorption, and pass through it into the deified matrix' (FiT 32). Wherever these processes come in contact with the calcified wall" of the Fig. 3L-Longitudinal section through the ossifying portion ol a long bone in the human embryo, a. Cartilaginous region b Region of calcified matrix. BONE. 61 primary areolae they absorb it, and thus cause a fusion of the original cavities and the formation of larger spaces, which are termed the secondary areolae (Sharpey) Fig. 33.—Part of a longitudinal section of the developing femur of a rabbit, a. Flat- tened cartilage-cells, b. Enlarged cartilage- cells, c. d. Newly-formed bone. e. Osteo- FIG. 32,-Section of fetal bone of cat. ir. Irruption of ^ / ^tf}^ ^A^o/kt the subperiosteal tissue. ». Fibrous layer of the perios- Shrunken carWag^ceU!■ ^ om Alias oj mis teum. o. Layer of osteoblasts, im. Subperiosteal bony tology, Klein ana moie omnu.) deposit. (From Quain's Anatomy, E. A. Schafer.) or medullary spaces (Miiller). In these secondary spaces the original cartilage- cells disappear, and their cavities become filled with embryonic marrow consisting of osteoblasts and vessels, and derived, at all events in part m the manner described above, from the osteogenetic layer of the periosteum (Fig oM). What becomes of the cartilage-cells is not finally determined. By most histologists they are believed to be converted, after division, into osteoblasts, and so assist in form- ing the embryonic marrow. Others, on the other hand, believe that they are simply absorbed and take no part in the formation of bone. Thus far then, we have got enlarged spaces (secondary areolae), the walls ot which are still formed by calcified cartilage-matrix, containing an embryonic marrow, derived from the processes sent in from the osteogenetic layer of the peri- osteum, and consisting of blood-vessels and round cells, osteoblasts (Fig. 33), some of which probably are derived from the division of the original cartilage-cells which have disappeared. The walls of these secondary areolae are at this time of only inconsiderable thickness, but they now become thickened by the deposition of lay- ers of new bone on their interior. This process takes place in the following manner: Some of the osteoblasts of the embryonic marrow after undergoing rapid division, arrange themselves as an epithelioid layer on the surface of the 62 G ENERA L . I NA TO MY. wall of the space (Fig. 84). This layer of osteoblasts forms a bony stratum, and thus the wall of the space becomes gradually covered with a layer of true osseous substance. On this a second layer of osteoblasts arrange them- selves, and in their turn form an os- seous layer. By the repetition of this process the original cavity becomes very much reduced in size, and at last only remains as a small circular hole in the centre, containing the remains of the embryonic marrow—that is, a blood-vessel and a feAV osteoblasts. This small cavity constitutes the Ha- Fig. 34.—Transverse section from the femur of a human embryo about eleven weeks old. a. A med- ullary sinus cut transversely; and b, another, long- itudinally, c. Osteoblasts, d. Newly-formed osseous substance of a lighter color, e. That of greater age. /. Lacunae with their cells, g. A cell stilt united to an osteoblast. Fig. 35.—Vertical section from the, edge of the ossifying portion of the diaphysis of a metatar- sal bone from a foetal calf. (After Muller.) a. Ground-mass of the cartilage, o. Of the bone. c. Newly-formed bone-cells in profile, more or less imbedded in intercellular substance, d. Medul- lary canal in process of formation, with vessels and medullary cells, e. f. Bone-cells on their broad aspect, g. Cartilage-capsules arranged in rows, and partly with shrunken cell-bodies. versian canal of the perfectly ossified bone. The successive layers of osseous matter Avhich have been laid down and which encircle this central canal, consti- tute the lamellae of Avhich, as we have seen, each Haversian system is made up. As the successive layers of osteoblasts form osseous tissue, certain of the osteo- blastic cells remain included betAveen the various bony layers. These continue persistent, and remain as the corpuscles of the future bone, the spaces enclosing them forming the lacune (Fig. 34). The mode of the formation of the canaliculi is not knoAvn. Such are the changes Avhich may be observed at one particular point, the centre of ossification. While they have been going on here a similar process has been proceeding in the same manner toAvard the end of the shaft, so that in the ossify- ing bone all the changes described above may be seen in different parts, from the true bone in the centre of the shaft to the hyaline cartilage at the extremities. The bone thus formed differs from the bone of the adult in being more spongy and less regularly lamellated. Thus far, then, Ave have followed the steps of a process by Avhich a solid bony mass is produced, having vessels running into it from the periosteum, Haversian BONE, 63 canals in which those vessels run, medullary spaces filled Avith foetal marrow, lacunae with their contained bone-cells, and canaliculi growing out of these lacunae. This process of ossification, however, is not the origin of the whole of the skeleton, for even in those bones in Avhich the ossification proceeds in a great measure from a single centre, situated in the cartilaginous shaft of a long bone, a considerable part of the original bone is formed by intramembranous ossification beneath the perichondrium or periosteum ; so that the girth of the bone is increased by bony deposit from the deeper layer of this membrane. The shaft of the bone is at first solid, but a tube is hollowed out in it by absorption around the vessels passing into it, Avhich becomes the medullary canal. This absorption is supposed to be brought about by large " giant-cells," which have long been recognized as a constituent of foetal marroAv, and Avhich are believed by Kolliker to have the power of absorbing or dissolving bone, and he has therefore named them "osteoclasts" (Fig. 33,/). They vary in shape and size, and are known by containing a large number of clear nuclei, sometimes as many as twenty. The occurrence of similar cells in some tumors of bones has led to such tumors being denominated "myeloid." As more and more bone is removed by this process of absorption from the interior of the bone to form the medullary canal, so more and more bone is deposited on the exterior from the periosteum, until at length the bone has attained the shape and size Avhich it is destined to retain during adult life. As the ossifi- cation of the cartilaginous shaft extends tOAvard the articular ends it carries with it, as it were, a layer of cartilage, or the cartilage grows as it ossifies, and thus the bone is increased' in length. During this period of growth the articular end, or epiphysis, remains for some time entirely cartilaginous ; then a bony centre appears in it, and it commences the same process of intracartilaginous ossification; but this process never extends to any great distance. The epiphyses remain separated from the shaft by a narroAV cartilaginous layer for a definite time. This layer ultimately ossifies, the distinction betAveen shaft and epiphysis is obliterated, and the bone assumes its completed form and shape. The same remarks also apply to the processes of bone which are separately ossified, such as the trochanters of the femur. The bones, having been formed, continue to grow until the body has acquired its full stature. They increase in length by ossification continuing to extend in the epiphysial cartilage, Avhich goes on growing in advance of the ossi- fying process. They increase in circumference by deposition of new bone, from the deeper layer of "the periosteum, on their external surface, and at the same time an absorption takes place from within, by which the medullary cavity is lncrcjiSGu.. The medullary spaces which characterize the cancellous tissue are produced by the absorption of the original foetal bone in the same way as the original medul- lary canal is formed. The distinction between the cancellous and compact tissue appears to depend essentially upon the extent to which this process of absorption has been carried; and we may perhaps remind the reader that in morbid states of the bone inflammatory absorption produces exactly the same change, and converts portions of bone naturally compact into cancellous tissue. Intramembranous Ossification.—The intramembranous ossification is that by which the bones of the vertex of the skull are entirely formed. In the bones Avhich are so developed no cartilaginous mould precedes the appearance of the bone-tissue. In the membrane which occupies the place of the future bone, a little network of bony spiculae is first noticed, radiating from the point of ossification When these rays of growing bone are examined by the microscope, they are found to consist of a network of fine clear fibres and granular cells with a ground- substance between. The fibres are termed osteogenic fibres, and soon become dark and granular from calcification, and as they calcify they are found to enclose the granular cells or " osteoblasts " (Fig. 36). The calcification not only involves the osteogenic fibres, but also the ground-substance of the tissue in which they 64 GENERAL A NA TOMY. Fig. 36.—Osteoblasts from the parietal bone of a human em- bryo thirteen weeks old. (After Gegenbauer.) a. Bony septa with the colls of the lacunae. 6. Layers of osteoblasts, c. The \i transition to bone-corpuscles. The latter in are contained. The cells at first lie upon the osteogenic fibres, so that they can be removed bv brushing the specimen with a hair-pencil, in order to render the fibres clear; but they grad- ually become involved in the ossifying matrix, and form the corpuscles of the future bone, the spaces in which they are enclosed constituting the la- cuine. As the tissue increases in thickness, vessels shoot into it, grooving for themselves spaces or channels, Avhich be- come the Haversian canals. Thus, the intramembranous and intracartilaginous processes of ossification are similar in their more essential features. The number of ossific cen- tres is different in different bones. In most of the short bones ossification commences by a single point in the centre, and proceeds toward the cir- cumference. In the long bones there is a central point of ossification for the shaft or diaphvsis; and one or more for each extremity, the epiphysis. That for the shaft is the first to appear. The union of the epiphyses Avith the shaft takes place in the reverse order to that in Avhich their ossification began, and appears to be regulated by the direction of the nutrient artery of the bone. Thus, the nutrient arteries of the bones of the arm and fore-arm are directed toAvard the elbow, and the epiphyses of the bones forming this joint become united to the shaft before those at the opposite extremity. In the lower limb, on the other hand, the nutrient arteries pass in a direction from the knee: that is, upAvard in the femur, downAvard in the tibia and fibula; and in them it is observed that the upper epiphysis of the femur, and the lower epiphysis of the tibia and fibula, become first united to the shaft. Where there is only one epiphysis, the medullary artery is directed toward that end of the bone Avhere there is no additional centre, as toward the acromial end of the clavicle, toAvard the distal end of the metacarpal bone of the thumb and great toe, and toAvard the proximal end of the other metacarpal and meta- tarsal bones. Besides these epiphyses for the articular ends, there are others for projecting parts or processes, Avhich are formed separately from the bulk of the bone. For an account of these the reader must be referred to the description of the individual bones in the sequel. A knoAvledge of the exact periods when the epiphyses become joined to the shaft is often of great importance in medico-legal inquiries. It also aids the sur- geon in the diagnosis of many of the injuries to which the joints are liable; for it not infrequently happens that, on the application of severe force to a joint, the epiphysis becomes separated from the shaft, and such injuries may be mistaken for fracture or dislocation. MUSCULAR TISSUE. The muscles are formed of bundles of reddish fibres, endoAved with the property of contractility. Two kinds of muscular tissue are found in the animal body__viz. that of voluntary or animal life, and that of involuntary or organic life. The muscles of animal life (striped muscles) are capable of being put in action and controlled by the will. They are composed of bundles of°fibres enclosed in a MUSCULAR TISSUE. 65 delicate web called the "perimysium," in contradistinction to^the sheath of areolar tissue which invests the entire muscle, the "epimysium." The bundles are termed "fasciculi;" they are prismatic in shape, of different sizes in different muscles, and for the most part placed parallel to one another, though they have a tendency to converge toward their tendinous attachments. Each fasciculus is made up of a bundle of fibres, which also run parallel with each other, and Avhich are separated from one another by a delicate connective tissue derived from the peri- mysium, and termed endomysium (Fig. 37). A muscular fibre may be said to consist of a soft contractile substance enclosed in a tubular sheath, named by BoAvman the sarcolemma. The fibres are cylindrical or prismatic in shape, and are of no great length, not extending, it is said, further than an inch and a half. They end either by blending with the tendon or aponeurosis, or else by becoming drawn out into a tapering extremity Avhich is connected to the neighboring fibre by means of the sarcolemma. Their breadth varies in man from ^tto to "giro °f an inch, the average of the majority being about -^-§. fig.37.—Transverse section from As a rule, the fibres do not divide or anastomose; f^^t^tt^pS^- but occasionally, especially in the tongue and facial ium^ ^Fascicuius^ c internal muscles, the fibres may be seen to divide into several branches. The precise mode in which the muscular fibre joins the tendon has been variously described by different observers. It may perhaps, be sufficient to say that the sarcolemma, or membranous investment of the muscular fibre, appears to become blended with the tissue of the tendon, and prolonged more or less into the tendon, so that the latter forms a kind of sheath around the fibre for a longer or shorter distance. When muscular fibres are attached to the skin or mucous membranes, their sarcolemma probably becomes continuous with the fibres of the areolar tissue. The sarcolemma, or tubular sheath of the fibre, is a transparent, elastic, and apparently homogeneous membrane of considerable toughness, so that it will some- times remain entire Avhen the included substance is ruptured (see *ig. On the internal surface of the sarcolemma in mammalia, and also in the substance ot the fibre in the lower animals, elongated nuclei are seen (Fig. 55), and in connec- tion with these a row of granules, apparently fatty, is sometimes observed. Upon examination of a muscular fibre by transmitted light under a sufficiently high power, it is found to be apparently marked by alternate light and dark bands or striae, which pass transversely, or somewhat obliquely, round the fibre (hig. 38). The dark and light bands are of nearly equal breadth, and alternate with great regu- larity Other striae pass longitudinally over the fibres, though they are less distinct than the former. This longitudinal striation gives the fibre the appearance of bein* made up of a bundle of fibrillar The muscular fibre can be broken up either in a Witudinal or transverse direction (Fig. 39). If hardened in alcohol, it can be broken up longitudinally, and forms the so-called fibnllae of which some suppose the fibre to be made up. Each fibril is marked by transverse stria?, and appears to consist of a single row of minute quadrangular particles, named "sarcous elements" by Bowman. A still further division, however is capable of being made, and each of these fibrillar may be divided into minute threads (Fig. 40 b, d). cTnsi ting of an alternate dark and light spot. After exposure to the action of dilute hydrochloric acid, the muscular fibre can be broken transversely (Fig. 39, B). It then forms disks or plates, consisting of the same quadrangular particles, attached by their lateral surfaces. Upon closer examination with a very high power the appearances become more complicated and are susceptible of various interpretations. The transverse Steiation which in Figs. 38 and 39 appears as a mere alternation of dark and light G6 GENERAL A NA TO MY. bands, is resolved into the appearance shoAvn in Fig. 40, which shows a series of broad dark bands, separated by a light band, Avhich is itself divided into tAvo by a dark streak. This streak is termed Krause's membrane ; it is continuous at each end Avith the sarcolemma investing the muscular fibre. Thus it may be said that the fibre is divided into a number of transverse compartments by this membrane. each compartment containing in the centre a dark plate Avith a bright border above and beloAv; that is to say, betAveen the dark central part and the membrane of Krause. A muscular fibre presents, then, the appearance of the folloAving layers in regular alternation: a dark layer, the transverse disk; a bright trans- parent layer, the lateral disk ; a dark line, the intermediate disk or membrane of Krause ; then another lateral disk, a transverse disk, and so on (Figs. 40 and 41). This appearance, following the observations of Rollett, is due to the mode of for- Fig. 38.—Two human muscular fibres. Magnified 350 times. In the one, the bundle of fibrillae (b) is torn, and the sarcolemma (a) is seen as an empty tube. Fig. 39.—Fragments of striped elementary fibres, showing a cleavage in opposite directions. Magnified 300 diameters, a. Longitudinal cleavage. The longi- tudinal and transverse lines are both seen. Some lon- gitudinal lines are darker and wider than the rest, and are not continuous from end to end. This results from partial separation of the fibrillae. c. Fibrillae separated from one another by violence at the broken end of the fibre, and marked by transverse lines equal in width to those on the fibre, c', c" represent two appearances com- monly presented by the separated single fibrillae (more highly magnified). At c' the borders and transverse lines are all perfectly rectilinear, and the included spaces per- fectly rectangular. At c" the borders are scalloped and the spaces bead-like. When most distinct and definite the fibrilla presents the former of these appearances. b. Transverse cleavage. The longitudinal lines are scarcely visible, a. Incomplete fracture following the opposite surfaces of a disk, which stretches across the interval, and retains the two fragments in connection. The edge and surfaces of this disk are seen to be minutely granular, the granules corresponding in size to the thickness of the disk and to the distance between the faint longitudinal lines, b. Another disk nearly detached. 6'. Detached disk, more highly magnified, showing the sarcous elements. mation of a muscular fibre, which is made up of tAvo principal parts: 1, fibrillae ; and 2, a hyaline or faintly granular substance, resembling protoplasm, and called sarcoplasm. The fibrillae are arranged in bundles called muscular columns or sar- costyles, and these again in larger groups, which, collected together, form the fibre. The fibrillae are surrounded by the sarcoplasm, Avhich surrounds also the columns and groups of columns, being in these latter situations greater in amount than between the fibrillae. So that on transverse section a muscular fibre is seen to be divided into a number of areas, called the areas of Cohnheim, more or less polyhedral in shape, and consisting of the columns of fibrillae surrounded by trans- parent sheaths of sarcoplasm. And these areas are collected into larger or smaller groups, which in the same manner are surrounded by transparent sarcoplasm. Each area of Cohnheim presents a granular appearance due to the cross-section of its constituent fibrillae, surrounded by a small amount of the hyaline sarcoplasm. The fibrillae extend throughout the Avhole length of, and are parallel to, the long axis of the muscular fibre. They present the folloAving appearances in regular alternation : (1) a dim prismatic or rod-shaped element, the sarcous element of Boivrnan • (2) a thin bridge, Avhich joins the sarcous element to (3) a dark granule. Then again MUSCULAR TISSUE. 67 another thin bridge joining the same granule to the next sarcous element, and so on. When these fibrillae are collected together into columns, and the columns into muscular fibres, the appearance mentioned above is produced. The sarcous ele- ments, Avhen arranged side by side and almost touching each other, with very little sarcoplasm between them, represent the transverse disk. The bridges, being much thinner than the sarcous element or the dark granules, have between each other a much larger amount of sarcoplasm, and this gives to this part the trans- parent appearance of the lateral disk. And, lastly, the granules joined edge to edo-e in a row present the appearance of a membrane, Avhich represents the inter- mediate disk. On the muscular fibre, immediately beneath the sarcolemma, the sarcoplasm FlG 4L—Part of a striped muscular fibre of the water-beetle, prepared with absolute alcohol Magnified 300 diameters. (Klein and Noble Smith.) a. Sarcolemma b. Membrane of Krause; owing to contrac- tion during hardening, the sarcolemma shows regular bulgings. At the side of . TOfliise's membrane is the transparent lat- Fig. 40.-Portion of a medium-sized human muscular prai disk Several nuclei of muscle-cor- fibre. Magnified nearly 800 diameters, b Separated bun- muscles are shown, and in them a minute dies of fibrils, equally magnified a. a Larger and 6 6 Kork smaller collections, c. Still smaller, d. d. The smallest which could be detached. becomes here and there collected into small, P.lfte^ke masses. They contain oval nuclei and are termed "muscle-corpuscles." Finally, in the centie ot eacn _ element a transparent lighter band can «™$™*%.^A ~ known as the median disk of Hensen, and is due to the substance oi the saicous ^"This foZ^m^Juiirfibre composes the whole of the voluntary musc.es a!l the muscles of the ear, those of the larnyx pharynx, tongue the upp„ h, b* o the cesonhagus, the heart, and the walls of the large veins at the pom wheie the> ojZ iX it. The fibres of the heart, however differ *Wr™*W ^sver of other striped muscles. They^are^mallei-by one-thirtb £ ^t'^W «tri-T> are bv no means so distinct. Ine nores aiemdueupu ~l gla'ce Is joined end to end (Fig. 42). Each cell contains .,clea,r ovJ ™de», Stuated near the centre of the cell. The extremities of the cdk have a t de„ , to branch or divide, the subdivisions.uniting vvith offsets f,on, othm .e^ thus rvrndnome- an anastomosis ot tne nores vr*g- ^-;- -*- . , i „„A teiwee'n the'Sdies of fibres is much less than in ordinary striped muscle, and no sarcolemma has been proved to exist. f The capillaries of striped muscle are very abundan , amiI foim a soit.* iect^ angular network, the branches of which run longitudinally in the endomysmm Keen the muscular fibres, and are joined at short intervals by transve e analtomosing "ranches. The larger vJcular channels, arteries and veins, aie 9939993 68 GENERA L A NA TOM 1'. Fig. 42.—Anastomosing muscular fibres of the heart seen in a longitu- dinal section. On the right the lim- its of the separate cells with their nuclei are exhibited somewhat dia- grammatically. found only in the perimysium, betAveen the muscular fasciculi. The smaller ves- sels present peculiar saccular dilatations, Avhich are supposed to act as receptacles for the blood during the contraction of the muscular fibres, Avhen it is pressed out from some of the capil- laries. Nerves are profusely distributed to striped muscle. The mode of their termination will be described on a subsequent page. The existence of lymphatic vessels in striped muscle has not been ascertained, though they have been found in tendons and in the sheath of the muscle. The unstriped muscle, or muscle of organic life, is found in the walls of the hollow viscera — viz. the loAver half of the oesophagus and the Avhole of the remainder of the gastro-intestinal tube ; in the trachea and bronchi, and the alveoli and infundibula of the lungs; in the gall-bladder and ductus communis choledochus; in the large ducts of the salivary and pancreatic glands; in the pelvis and calices of the kidney, the ureter, bladder, and urethra; in the female sexual organs—viz. the ovary, the Fallopian tubes, the uterus (enormously developed in preg- nancy), the vagina, the broad ligaments, and the erectile tissue of the clitoris; in the male sexual organs—viz. the dartos scroti, the vas deferens and epididymis, the vesicular seminales, the prostate gland, and the corpora cavernosa and corpus spongiosum; in the ducts of certain glands, as in Wharton's duct; in the capsule and trabeculae of the spleen; in the mucous membranes, forming the muscularis mucosae; in the skin, forming the arrectores pilorum, and also in the SAveat- glands; in the arteries, veins, and lymphatics; in the iris and the ciliary muscle. Plain or unstriped muscular fibre is made up of spindle-shaped cells, called contractile fibre-cells, collected into bundles and held together by a cement-sub- stance, in which are contained some connective-tissue corpuscles (Fig. 43). These bundles are further aggregated into larger bundles or flattened bands, and bound together by ordinary connective tissue. The contractile fibre-cells (Fig. 44) are elongated, spindle-shaped, nucleated cells of various lengths, averaging from -^ to -^ of an inch in length, and ^^ to -g-sVo °f an mc^ *n Dreadth. On transverse section they are more or less poly- hedral in shape, from mutual pressure. They present a faintly longitudinal stri- ated appearance, and consist of an elastic cell-Avail containing a central bundle of fibrillae, representing the contractile substance, and an oval or rod-like nucleus Avhich includes, Avithin a membrane, a fine network communicating at the poles of the nucleus Avith the contractile fibres (Klein). The adhesive interstitial sub- stance, Avhich connects the fibre-cells together, represents the endomvsium, or del- icate connective tissue Avhich binds the fibres of striped muscular tissue into fas- ciculi ; Avhile the tissue connecting the individual bundles together represents the perimysium. The unstriped muscle, as a rule, is not under the control of the Avill nor is the contraction rapid and involving the Avhole muscle, as is the case Avith the muscles of animal life. The membranes Avhich are composed of the unstriped muscle sIoavIv contract in a part of their extent, generally under the influence of a mechanical stimulus, as that of distension or of cold; and then the contracted part sIoavIv relaxes Avhile another portion of the membrane takes up the contrac- tion. This peculiarity of action is most strongly marked in the intestines con- stituting their vermicular motion. Chemical Composition of Muscle.—In chemical composition the muscular fibres of both forms consist mainly of a proteid substance—myosin—Avhich is classed as one of the globulins. It is readily converted by the action of dilute acids NERVOUS TISSUE. 69 into syntonin or acid-albumen, and by the action of dilute alkalies into alkali- albumen. Muscle, which is neutral or slightly alkaline in reaction Avhen at rest, Fig. 43.—Non-striated elementary fibres from the human colon, a. Treated with acetic acid, showing the corpuscles. 6. Fragment of a detached fibre, not touched with acid. is rendered acid, by contraction, from the development probably of sarcolactic acid. After death muscle also exhibits an acid reaction, but this appears to be due to post-mortem change. NERVOUS TISSUE. The nervous tissues of the body are comprised in two great systems—the cerebrospinal and the sympathetic; and each of these systems consist of a central organ, or series of central organs, and of nerves. The cerebrospinal system comprises the brain (including the medulla oblongata), the spinal cord, the cranial nerves, the spinal nerves, and the ganglia connected with both these classes of nerves. The sympathetic system consists of a double chain of ganglia, with the nerves Avhich go to and come from them. It is not directly connected Avith the brain or spinal cord, though it is so indirectly by means of its numerous communications with the cranial and spinal nerves. Both these nervous systems are composed of an aggregation of tissue-elements termed neurons, each of which consists of a nucleated cell whose protoplasm is prolonged into a varying number of processes, one of which is usually of consid- erable length and forms the essential part of a nerve-fibre. The cell-bodies have a tendency to be associated together in more or less definite masses, such as the spinal and sympathetic ganglia, the central portion of the spinal cord, the floor of the medulla oblongata, the cortex of the cerebellum and of the cerebral hemi- spheres, and the various ganglia distributed through the different parts of the brain. These masses present macroscopically a grayish appearance, which con- trasts strongly Avith the pure Avhite color usually shown by the nerve-fibres, so that it is customary to speak of the nervous system as composed of two substances, the gray matter and the white or fibrous matter. The nerve-fibres of the sympa- thetic system, however, usually lack the constituent which gives the ordinary fibres their white appearance, and they consequently have a grayish color. The gray substance is distinguished by its dark reddish-gray color and soft consistence. It is found in the brain, spinal cord, and various ganglia, inter- mingled with the fibrous nervous substance, and also in some of the nerves of special sense, and in gangliform enlargements which are found here and there in the course of certain cerebro-spinal nerves. It is composed, as its name implies, Fig. 44.—Muscular fibre-cells from human arteries. 1. From the popliteal artery, a. without; b. with acetic acid. 2. From a branch of the anterior tibial, a. Nuclei of the fibres. Magnified 350 times. 70 GENER. 1L A NA TO MY. Fig. 45.—Cell from the anterior horn of the gray matter of the spinal cord, a, Axis-cylinder process, b. Aggregation of pigment-granules. (From Obersteiner.) of cells, commonly called nerve-cells or ganglion-corpuscles, containing nuclei and nucleoli. The cells together with the blood-vessels in the gray nerve-substance, and the nerve-fibres and vessels in the Avhite nerve-substance, are imbedded in a peculiar ground-substance, named by Yirchow neuroglia, and consisting of large branched cells (Fig. 46, C), the branches passing in every direction among the nerve-tissue, thus holding it and binding it together. It is developed from the epi- blast, and contains neither the character- istic fibres nor cells of connective tissue, and therefore cannot be regarded as be- longing to the true connective tissues. Each nerve-cell consists of a finely gran- ular protoplasmic material, of a reddish or yellowish-brown color, Avhich occasionally presents patches of a deeper tint, caused by the aggregation of pigment-granules (Fig. 45). No distinct limiting membrane or cell-wall has been ascertained to exist. The nucleus is, as a rule, a large, Avell- defined, round, vesicular body, often pre- senting an intranuclear netAvork, and con- taining a nucleolus which is peculiarly clear and brilliant. The nerve-cells vary in shape and size; some are small, spher- ical or ovoid, with generally an even out- line, such as those found in the spinal ganglia ; others, again, are caudate or stel- late in shape, and are characterized by their large size and by their having one or more tail-like processes issuing from them, Avhich occasionally divide and sub- divide into numerous branches (Fig. 46, A). These are found in greatest number in the gray matter of the spinal cord. Still others are flask-shaped, as in the cortex of the cerebellum; or conical, as in the cerebral convo- lutions. For the most part nerve- cells have one or more processes, and they are distinguished by the number of these processes, as unipolar, bipolar, or multi- polar cells. These processes are very delicate and are direct con- tinuations of the protoplasm of the nerve-cell. The majority of the processes of a multipolar cell are exceedingly fine, and branch dendritically, spreading out among the adjacent nervous elements; these processes are termed the protoplasmic processes or dendrites. One of the pro- cesses, hoAvever, does not thus branch, but gives off from time to time lateral branches termed collaterals, and eventually form the axis-cylinder of a nerve-fibre; this is the axis-cylinder process. The white or fibrous nerve-substance or nerve-fibre is found universally in the ,r,¥,1?; 46-~:£en? of nervous system impregnated with silver (Golgis method). A. Cell from the cortex of the cerebral hemispheres (after van Gehuchten). a. Protoplasmic process b. Axis-cylinder process, c. Collaterals. B. T-shaped cell from spinal root ganglion (after van Gehuchten). C. Neuroglia- ceU from the white substance of the cerebellum (after K61- NERVOUS TISSUE. 71 nervous cords, and also constitutes a great part of the brain and spinal cord. The fibres of which it consists are of two kinds, the medullated or white fibres, and the non-medullated or gray fibres. The medullated fibres form the white part of the brain and spinal cord, and also the greater part of the cerebro-spinal nerves, and give to these structures their opaque, Avhite aspect. When perfectly fresh they appear to be homo- geneous ; but soon after removal from the body they present, Avhen exam- ined by transmitted light, a double outline or con- tour, as if consisting of two parts. The central portion is named the axis-cylinder of Purkinje; around this is a sort of sheath of fatty material, named the white substance of Schivann, Avhich gives to the fibre its double contour, and the whole is en- closed in a delicate membrane, the neurilemma,1 primitive sheath, or nucleated sheath of Schivann (Fig. 47). The axis-cylinder is the essential part of the nerve-fibre, and is always present; the other parts, the medullary sheath and the neurilemma, being occasionally absent, especially at the origin and termination of the nerve-fibre. It undergoes no interruption from its origin in the nerve-centre to its peripheral termination, and must be regarded as a direct prolongation of a nerve-cell. It con- stitutes about one-half or one-third of the nerve- fibre, the Avhite substance being greater in propor- tion in the nerves than in the central organs. It is perfectly transparent, and is therefore indistin- guishable in a perfectly fresh and natural state of the nerve. When examined under a high power it presents the appearance of longitudinal striation, as if composed of very fine, homogeneous fibrillae, held together in a faintly granular interstitial material. Occasionally at its termination the axis-cylinder of a fibre may be seen to break up into exceedingly fine fibrillae, confirming the vieAV of its fibrillar structure. These fibrillae have been termed the primitive fibrillae of Schultze. The axis-cvlinder is said to be enveloped in a very delicate, hyaline sheath, which separates it from the white matter of Schwann. The medullary sheath or white matter of Schwann is regarded as being a fatty matter in a fluid state, which insulates and protects the essential part of the nerve—the axis-cylinder. The white matter varies in thickness to a very considerable extent, in some forming a layer of extreme thinness, so as to be scarcely distinguishable, in others forming about one-half the nerve-tube. The size of the nerve-fibres, which varies from l to -tAtq- of an inch, depends mainly upon the amount of the white substance, though the axis-cylinder also varies in size within certain limits. The white matter of Schwann does not always form a continuous sheath to the axis-cylinder, but undergoes interruptions in its continuity at regular intervals, giving to the fibre the appearance of constriction at these points. These were first described by Ran- vier, and are knoAvn as the ncxles of Ranvier (Fig. 48). The por- tion of nerve-fibre betAveen t\vo nodes is called an internodal seg- ment. The neurilemma or prim- itive sheath is not interrupted at the nodes, but passes over them as a continuous membrane. Each i In older histological works the term "neurilemma » is used to designate the fibrous envelope of (he whole nerve, now called " perineurium." Fig. 47.—Human nerve-fibres. Mag- nified 350 times. Three of them are fine, one of which is varicose, one of mid- dling thickness, and with a simple con- tour ; and three thick, two of which are double-contoured, and one with gru- mous contents. pIG 48 —\ node of Ranvier of a medullated nerve-fibre, viewed" from'above, magnified about 750 diameters. The medul- larv sheath is discontinuous at the node, whereas the axis-cyl- inder passes from one segment into the other At the node the sheath of Schwann appears thickened. (Klein and Noble Smith .> 72 GENERAL A N1 TOMY. internodal segment contains an oval nucleus imbedded in the medullary sheath, and occasionally more than one nucleus may be seen in the same internode. Medullated nerve-fibres frequently present a beaded or varicose appearance: this is due to manipulation and pressure causing the oily matter to collect into drops, and in consequence of the extreme delicacy of the primitive sheath even .slight pressure will cause the transudation of the fatty matter, Avhich collects as drops of oil outside the membrane. This is, of course, promoted by the action of ether (Fig. 49). The neurilemma or primitive sheath (sometimes called the tubular membrane or sheath of Schwann) presents the appearance of a delicate, structureless membrane. Here and there beneath it, and situated in depressions in the white matter of SchAvann, are nuclei surrounded by a small amount of protoplasm. The nuclei are oval and someAvhat flattened, and bear a definite rela- tion to the nodes of Ranvier; one nucleus generally lying in the centre of each node, though in some feAv instances two nuclei may be found in the same node. The sheath of Schwann, it is to be noted, does not occur in the med- ullated fibres contained within the spinal cord and brain. Non-medullated Fibres.—Most of the nerves of the sympathetic system, and some of the cerebro- spinal (see especially the descrip- tion of the olfactory nerve), con- sist of another variety of nervous fibres, which are called the gray or gelatinous nerve-fibres—fibres of Remdk (Fig. 50). These con- sist of a bundle of finely striated fibrillae enclosed in a sheath. Nuclei may be detected at inter- vals in each fibre, situated between the axis-cylinder and the neurilemma. In external appearance the gelatinous nerves are semi-transparent and gray or yel- lowish-gray. The individual fibres vary in size, generally averaging about half the size of the medullated fibres; but, on the one hand, the primitive fibrillae formed by the breaking up of the cerebro-spinal fibres, as above mentioned, are of hardly appreciable thickness; Avhile, on the other hand, some of the gelatinous fibres (especially those on the olfactory bulb) are said to be three or four times as thick as those of the cerebro-spinal nerves. Chemical Composition.—The difference in the chemical composition of the white and gray matter is indicated by the following analyses by Petrowsky of the brain of the ox : Gray. White. Water........_._...............si. 60% 68.30% Solids (percentage composition): Proteids . . ."....................55.37 24.72 Lecithin......................17.24 9.90 (/holesterin and fat..................18.68 51.91 Cerebrin .......................0.53 9.55 Other organic compounds...............6.71 3.34 Salts........................1.45 0^57 Fig. 49.—Magnified 300 diam- eters, o. Nerve-fibre of the com- mon eel in water. The delicate line on its exterior indicates the neurilemma. The dark double- edged inner one is the white matter of Schwann, slight- ly wrinkled, b. The same in ether. Several oil-globules have coalesced in the interior, and others have accumulated around the exterior of the tube. The white matter has in part disappeared. Fig. 50.—A small ner- vous branch from the sym- pathetic of a mammal, a. Two dark-bordered nerve- tubes among a number of Remak's fibres, b. The proteids in the above analysis practically represent the protoplasm, Avhich NERVOUS TISSUE. 73 naturally is much greater in the gray than in the white matter. On the other hand, the cholesterin, fat, and cerebrin (the latter ill-defined nitrogenous compounds belonging to the group of glucosides) are probably important constituents of the medullary sheath. Another substance also occurring in the medullary sheath, though not determined separately in the above analysis, is neurokeratin, which forms a fibrous network througbout the sheath, and resembles keratin in its marked resistance to reagents. It probably makes up the greater part of the unidentified organic matter of the white substance in the above analysis, while in the gray substance the unidentified matter is probably largely composed of protagon, a phosphorized compound closely resembling lecithin, but differing from it by its insolubility in ether. The nervous structures are divided, as before mentioned, into two great sys- tems—viz. the cerebrospinal, comprising the brain and spinal cord, the nerves connected Avith these structures, and the ganglia situated on them; and the sym- pathetic, consisting of a double chain of ganglia and the nerves connected with them. All these structures require separate consideration. The brain or encephalon is that part of the cerebro-spinal system which is contained in the cavity of the skull. It is divided into several parts, for a description of Avhich reference must be made to the account of the structure of the brain in a subsequent portion of this work. In these parts the gray matter is found partly on the surface of the brain, forming the cortex of the cerebrum and of the cerebellum. Again, gray matter is found in the interior of the brain, collected into large and distinct masses or ganglionic bodies, such as the corpus striatum, optic thalamus, corpora quadrigemina, the olivary bodies, and the corpora dentata of the cerebellum, Finally, gray matter is found intermin- gled intimately Avith the white, but Avithout definite arrangement, as in the gray matter in the pons Varolii and the floor of the fourth ventricle. The white matter of the brain is divisible into three distinct classes of fibres. These are, in the first place, projection fibres, such as the fibres which connect the brain Avith the spinal cord; that is to say, those which are usually traced upward from the columns of the spinal cord, through the medulla oblongata into the encephalon, chiefly by means of the anterior pyramids, passing through the pons Yarolii and crura cerebri to the internal capsules of the corpora striata, and thence to the cerebral cortex, and by means of the restiform bodies into the cerebellum. The second class of white fibres in the brain are commissural, con- necting opposite sides of the brain, as, for instance, the fibres of the corpus callo- sum and the anterior commissure of the thalamencephalon. And the third class are the association fibres which connect different regions of the same side of any of the portions of the brain. The fibres of this last class are more especially developed in the cerebral hemispheres, Avhere they connect different areas of the cortex, as, for example, the cortical centre for sight in the occipital lobe with the motor centre for speech in the frontal lobe. The manner in which the gray and white matter are intermingled in the brain and spinal cord is very intricate, and can only be fully understood by a careful study of the details of its descriptive anatomy in the sequel. The further consid- eration of this subject will therefore be deferred until after the description of the various divisions of which the cerebro-spinal system is made up. The nerves are round or flattened cords, formed of the nerve-fibres already described. They are connected at one end with the cerebro-spinal centre or with the ganglia, and are distributed at the other end to the various textures of the body; they are subdivided into two great classes—the cerebro-spinal, which pro- ceed from the cerebro-spinal axis, and the sympathetic or ganglionic nerves, Avhich proceed from the ganglia of the sympathetic. The cerebro-spinal nerves consist of numerous nerve-fibres collected together and enclosed in a membranous sheath (Fig. 51). A small bundle of primitive fibres, enclosed in a tubular sheath, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or 74 G EN ERA L . 1 A\ 1 TOM )' Fig. 51.—Transverse section through a microscopic nerve, representing a compound nerve-bundle, sur- rounded by epineurium. Magnified 120 diameters. The medullated fibres are seen as circles with a cen- tral dot—viz. medullary sheath and axis-cylinder—in transverse section. They are imbedded in endoneur- ium, containing numerous nuclei, which belong to the connective-tissue cells of the latter. (Klein and Noble Smith.) p. Epineurium, consisting of lamina? of fibrous connective tissues, alternating with flattened nucleated connective-tissue cells. I. Lymph-space between epi- neurium and surface of nerve-bundle. fasciculi, which are bound together in a common membranous investment, and constitute the nerve. In structure the common mem- branous investment, or sheath of the Avhole nerve, Avhich is called the epi- neurium, as Avell as the septa given off from it, and Avhich separate the fas- ciculi, consists of connective tissue, composed of Avhite and yellow elastic fibres, the latter existing in great abundance. The tubular sheath of the funiculi, called the perineurium, consists of a fine, smooth, transparent membrane, Avhich may be easily sepa- rated, in the form of a tube, from the fibres it encloses; in structure it con- sists of connective tissue, Avhich has a distinctly lamellar arrangement, con- sisting of several lamellae, separated from each other by spaces containing lymph. The nerve-fibres are held together and supported within the funiculus by delicate connective tissue, called the endoneurium. It is con- tinuous Avith septa Avhich pass imvard from the innermost layer of the peri- neurium, and consists of a ground-sub- stance in Avhich are imbedded fine bun- dles of fibrous connective tissue Avhich run for the most part longitudinally. It serves to support the capillary vessels, Avhich are arranged so as to form a network Avith the elongated meshes. The cerebro-spinal nerves consist almost exclusively of the medullated nerve-fibres, the non-medullated existing in very small proportions. The blood-vessels supplying a nerve terminate in a minute capillary plexus, the vessels composing Avhich pierce the perineurium and run, for the most part, parallel Avith the fibres; they are connected together by short, transverse vessels, forming narroAv, oblong meshes, similar to the capillary system of muscle. Fine non-medullated nerve-fibres accompany these capillary A-essels, vaso-motor fibresy and break up into elementary fibrils, which form a network around the vessel. Horsley has also recently demonstrated certain medullated fibres as running in the epineurium and terminating in tactile corpuscles or end-bulbs of Krause, or in small, but perfect, Pacinian corpuscles. These nerve-fibres are termed nervi nervorum, and have been considered to have an important bearing upon certain neuralgic pains. The nerve-fibres, as far as is at present knoAvn, do not coalesce, but pursue an uninterrupted course from the centre to the periphery. In separating a nerve, hoAvever, into its component funiculi, it may be seen that they do not pursue a perfectly insulated course, but occasionally join at a very acute angle with other funiculi proceeding in the same direction; from this, branches are o-iven off to join again in like manner with other funiculi. It must be remembered hoAvever that in these communications the nerve-fibres do not coalesce, but merely pass into the sheath of the adjacent nerve, become intermixed with its nerve-fibres and again pass on, to become blended Avith the nerve-fibres in some adjoining funiculus. Nerves, in their course, subdivide into branches, and these frequently commu- nicate with branches of a neighboring nerve. In the subdivision of a nerve the filaments of which it is composed are continued from the trunk into the branches NERVOUS TISSUE. 75 and at their junction with the branches of neighboring nerves the filaments pass to become intermixed with those of the other nerves in their further progress; in no instance, however, have the separate nerve-fibres been shoAvn to inosculate. The communications Avhich take place betAveen two or more nerves form what is called a, plexus. Sometimes a plexus is formed by the primary branches of the trunks of the nerves—as the cervical, brachial, lumbar, and sacral plexuses—and occasionally by the terminal funiculi, as in the plexuses formed at the periphery of the body. In the formation of a plexus the component nerves divide, then join, and again subdivide in such a complex manner that the individual funiculi become interlaced most intricately; so that each branch leaving a plexus may contain filaments from each of the primary nervous trunks which form it. In the formation also of smaller plexuses at the periphery of the body there is a free interchange of the funiculi and primitive fibres. In each case, hoAvever, the individual filaments remain separate and distinct, and do not inosculate Avith one another. It is probable that through this interchange of fibres the different branches passing off from a plexus have a more extensive connection Avith the spinal cord than if they each had proceeded to be distributed without such connection with other nerves. Consequently the parts supplied by these nerves have more extended relations Avith the nervous centres; by this means, also, groups of muscles may be associated for combined action. The sympathetic nerves are constructed in the same manner as the cerebro- spinal nerves, but consist mainly of non-medullated fibres, collected into funiculi, and enclosed in a sheath of connective tissue*. There is, hoAvever, in these nerves a certain admixture of medullated fibres, and the amount varies in different nerves. Those branches of the sympathetic which present a Avell-marked gray color are composed more especially of non-medullated nerve-fibres, intermixed with a fewT medullated fibres; whilst those of a white color contain more of the latter fibres and a feAv of the former. Occasionally, the gray and white cords run together in a single nerve, without any intermixture, as in the branches of communication between the sympathetic ganglia and the spinal nerves, or in the communicating cords between the ganglia. These medullated fibres are derived from the central nervous system through the rami communicantes, which pass from the cerebro-spinal nerves to the various sympathetic ganglia. The nerve-fibres, both of the cerebro-spinal and sympathetic system, convey impressions of a twofold kind. The sensory nerves, called also centripetal or afferent nerves, transmit to the nervous centres impressions made upon the peripheral extremities of the nerves, and in this way the mind, through the medium of the brain, becomes conscious of external objects. The motor nerves, called also centrifugal or efferent nerves, transmit impressions from the nervous centres to the parts to Avhich the nerves are distributed, these impressions either exciting muscular contraction, or influencing the processes of nutrition, growth, and secretion. Origin and Termination of Nerves.—By the expression " the termination of nerve-fibres " is signified their connection with the nerve-centres, and Avith the parts they supply. The former are sometimes called their origin, or central termination ; the latter their peripheral termination. The origin in some cases is single—that is to say, the Avhole nerve emerges from the nervous centre by a single root; in other instances the nerve arises by tAvo or more roots, which come off from different parts of the nerve-centre, sometimes widely apart from each other, and it often happens, when a nerve arises in this way by two roots, that the functions of these two roots are different; as, for example, in the spinal nerves, each of Avhich arises by tAvo roots, the anterior of Avhich is motor and the posterior sensory. The point where the nerve root or roots emerge from the nervous centre is named the superficial or apparent origin, but the fibres of which the nerve consists can be traced for a certain distance into the nervous centre to some por- tion of the gray substance, which constitutes the deep or real origin of the nerve. 76 GENERAL ANATOMY. In the case of motor or efferent nerve-fibres the deep origin is in cells contained within the spinal cord or brain, the axis-cyliuder processes of these cells being prolonged to form the fibres. In the case of the sensory nerves the origin is somewhat different, inasmuch as they arise from the cells of ganglia situated externally to the central nervous system. The sensory fibres of a spinal nerve arise, for instance, from the cells of the ganglion of the posterior root: these cells give off a process which branches in a T-shaped manner (Fig. 4l>, I>), one of the limbs of the T extending peripherally, Avhile the other passes imvards and penetrates the spinal cord. In connection Avith the sensory cranial nerves, origins are described imbedded Avithin the substance of the brain ; these are not, hoAvever, the proper origins, but are groups of cells around Avhich the fibres, groAving inwards form the ganglion-cells, situated just outside the brain, end, and from Avhich new fibres arise, Avhich pass upwards in the substance of the brain. Peripheral Terminations of Nerves.—The manner in Avhich nerve-fibres ter- minate peripherally are several, and may be conveniently studied in the sensory and motor nerves respectively. Sensory nerves would appear to terminate either in minute primitive fibrillae or netAvorks of these ; or else in special terminal organs, Avhich have been termed peripheral end-organs, and of Avhich there are three principal varieties—viz. the end-bulbs of Krause, the tactile corpuscles of Wagner, and the Pacinian corpuscles. Termination in Fibrillae.—"When a medullated nerve-fibre approaches its termi- nation, the Avhite matter of SchAvann suddenly disappears, leaving only the axis- cylinder surrounded by the neurilemma, and Ave have noAV a non-medullated fibre. This undergoes repeated division, and after a time loses its neurilemma, and consists only of an axis-cylinder, which can be seen, in preparations stained Avith chloride of gold, to be made up of fine varicose fibrils. Finally, the axis- cylinder breaks up into its constituent primitive nerve-fibrillae, Avhich anastomose Avith one another, thus forming a netAvork, and often present regular varicosities. This network passes between the elements of the tissue to Avhich the nerves are distributed, Avhich is always epithelial, and the nerve-fibrils end in the interstitial substance betAveen the epithelial cells, or, as is believed by some, actually ter- minate within the cells as minute SAvellings close to the nucleus. In this A\ay nerve-fibres have been found to terminate in the epithelium of the skin and mucous membranes, and in the anterior epithelium of the cornea. The end-bulbs of Krause (Fig. 52) are minute oblong or cylindrical corpuscles, into the interior of Avhich the axis-cylinder of the nerve-fibre passes, and termi- nates in a coiled, plexiform mass or in a bulbous extremity. The corpuscle con- sists of a simple nucleated capsule, containing a soft, homogeneous core, in which the termination of the axis-cylinder is contained. The Avhite matter of ScliAvann ceases abruptly as the axis-cylinder enters the corpuscle, but the neurilemma is continued inward Avith the axis-cylinder, and forms an investment of the core, lining the interior of the capsule. The end-bulbs have been described as occurring in the conjunctiva (where, in man, they are spheroidal in shape), in the mucous membrane of the mouth, and in the cutis and mucous membrane of the penis, clitoris, and vagina, where they are termed genital corpuscles. The latter have a mulberry-like appearance, from being constricted by connective-tissue septa into from two to six knob-like masses. In the synovial membrane of certain joints (e. g. those of the fingers) rounded or oval end-bulbs have been found; these are designated articular end-bulbs. The tactile corpuscles (Fig 53). described by Wagner and Meissner, are oval- shaped bodies, made up of connective tissue, and consisting of a capsule and imperfect membranous septa, derived from it, which penetrate its interior ' The axis-cylinders, entering the capsule, pursue a convoluted course, supported'by the septa, and terminate in small globular or pyriform enlargements, near the inner surface of the capsule. These tactile corpuscles have been described as occurring in the papillae of the corium of the hand and foot, the front of the fore arm the NERVOUS TISSUE. 77 skin of the lips, and the mucous membrane of the tip of the tongue, the palpebral conjunctiva, and the skin of the nipple They are not found in all the papillae; Fig. 52.—End-bulb of Krause. a. Medul- lated nerve-fibre, b. Capsule of corpuscle. (From Klein's Elements of Histology.) Fig. 53.—Tactile papilla of the hand treated with acetic acid. Magnified 350 times, a. Side view of a papilla of the hand. a. Cortical layer, b. Tactile corpuscle.with transverse nuclei, c. Small nerve of the papilla, with neurilemma, d. Its two nervous fibres running with spiral coils around the tactile corpuscle, e. Apparent termination of one of these fibres, b. A tactile papilla seen from above, so as to show its transverse section, a. Cortical layer, b. Nerve-fibre, c. Outer layer of the tactile body, with nuclei, d. Clear interior substance. but from their existence in those parts in which the skin is highly sensitive, it is probable that they are specially concerned in the sense of touch, though their absence from the papillae of other tactile parts shows that they are not essential to tlllS SOUSG The Pacinian corpuscles1 (Fig. 54) are found in the human subject chiefly on the nerves of the palm of the hand and sole of the foot and in the genital organs of both sexes, lying in the subcutaneous tissue; but they have also been described as connected with the nerves of the joints, and in some other situations, as the mesentery of the cat and along the tibia of the rabbit. Each of these corpuscles is attached to and encloses the termination of a single nerve-fibre, lhe corpuscle, which is perfectly visible to the naked eye (and which can be most easily demon- strated in the mesentery of a cat), consists of a number of lamellae or capsules, arranged more or less concentrically around a central clear space, in which the nerve-fibre is contained. Each lamella is composed of bundles of fine connective- tissue fibres, and is lined on its inner surface by a single layer of nucleated endo- thelial cells. The central clear space, which is elongated or cylindrical in shape is filled with a transparent material, in the middle of which is the single medullated fibre, which traverses the space to near its distal extremity Here it terminates in a rounded knob or end, sometimes bifurcating previously, in which case each branch has a similar arrangement. Todd and Bowman have described minute arteries as entering by the sides of the nerves and forming capillary ^F m the intercapsular spaces, and even penetrating into the central space Other authors describe the artery as entering the corpuscle at the pole opposite to the nerve. ^Herbst has described a somewhat similar « nerve-ending " to the Pacinian cor- puscle, as being found in the mucous membrane of the tongue of the duck and in some other situations. It differs, however, from the Pacinian corpuscles, in being smaller, its capsules thinner and more closely approximated and especially in the fact that the axis-cylinder in the central clear space is coated with a con- tinuous row of nuclei. These bodies are known as the corpuscles of Herbst. Tactile corpuscles have been described by Grandry as occurring in the papillae of the beak and tongue of birds, and by Merkel as occurring in the papill* and 1 Often called in German anatomical Avorks " corpuscles of Vater." GENERA L . 1N, i TOM Y. epithelium of the skin of man and animals, especially in those parts of the skin devoid of hair. They consist of a capsule composed of a very delicate, nucleated membrane, and contain tAvo or more granular, someAvhat flattened cells, between which the med- ullated nerve-fibre, which enters the capsule by piercing its investing membrane, is supposed to terminate. The nerves supplying tendons have peculiar nerve-endings, and are especially numerous near the point where the tendon becomes muscular. In this situation spindle-shaped bodies are found, and are known as the organs of Golgi. They are apparently composed of several tendinous bundles fused into one, into which one or more nerve-fibres pass, and, dividing, spread out between the tendon- bundles. Nerve-fibres occasionally terminate in tendons as end-bulbs or as small Pacinian cor- puscles. In the organs of special sense the nerves seem to terminate in cells, which are modified epithe- lial cells, and have received the name of sensory or nerve-epithelium cells. In reality, hoAvever, the nerve-fibre is in these cases a process of the epi- thelial cell, and if folloAved centrally will be found to end by branching around a ganglion-cell. From this an axis-cylinder continues the path along which the stimulus travels toAvard the brain. These nerve-epithelium cells are to be regarded as specially modified neurons. Motor nerves are to be traced either into un- In the un- striped or involuntary muscles the nerves are de- rived from the sympathetic, and are composed mainly of the non-medullated fibres. Near their termination they divide into a number of branches, which communicate and form an intimate plexus. At the junction of the branches groups of ganglion-cells are situated. From these plexuses minute branches are given off, Avhich divide and break up into the ultimate fibrillae of which the nerve is composed. These fibrillae course between the involuntary muscle-cells, and, according to Elischer, terminate on the surface of the cell, opposite the nucleus, in a minute SAvelling. Arnold and Franken- hauser believed that these ultimate fibrillae penetrated the muscular cell and ended in the nucleus. More recent observation has, hoAvever, tended to disprove this. In the striped or voluntary muscle, the nerves supplying the muscular fibres are derived from the cerebro-spinal nerves, and are composed mainly of medullated fibres. The nerve, after entering the sheath of the muscle, breaks up into fibres, or bundles of fibres, which form plexuses, and gradually divide until, as a rule, a single nerve-fibre enters a single muscular fibre. Sometimes, hoAvever, if the muscular fibre is long, more than one nerve-fibre enters it. Within the muscular fibre the nerve terminates in a special expansion, called by Kiihne, who first accurately described them, motorial end-plates (Fig. 55).1 The nerve-fibre, on approaching the muscular fibre, suddenly loses its white matter of ScliAvann which abruptly terminates ; the neurilemma becomes continuous Avith the sarco- lemma of the muscle, and only the axis-cylinder enters the muscular fibre where it immediately spreads out, ramifying like the roots of a tree, immediately beneath 1 Thev had, however, previously been noticed, though not accurately described, by Doyere who named them " nerve-hillocks." J ' Fig. 54.—Pacinian corpuscle, with its system of capsules and central cavity. a. Arterial twig, ending in capillaries, which form loops in some of the inter- capsular spaces, and one penetrates to striped or Striped muscular fibres. the central capsule, b. The fibrous tissue ... . , ^ ,, of the stalk prolonged from the perineu- rium, n. Nerve-tube advancing to the central capsule, there losing its white matter, and stretching along the axis to the opposite end, where it is fixed by a tubercular enlargement. NERVOUS TISSUE. 79 the sarcolemma, and is imbedded in a layer of granular matter, containing a number of clear, oblong nuclei, the Avhole constituting an end-plate from which the contractile Avave of the muscular fibre is said to start. Fig. 55.—Muscular fibres of Lacerta viridis with the terminations of nerves, a. Seen in profile, p.p. The nerve end-plates, s-s. The base of the plate, consisting of a granular mass with nuclei, b. The same as seen in look- ing at a perfectly fresh fibre, the nervous ends being probably still excitable. (The forms of the variously- divided plate can hardly be represented in a Woodcut by sufficiently delicate and pale contours to reproduce correctly what is seen in nature.) c. The same as seen two hours after death from poisoning by curare. The Ganglia may be regarded as separate and independent nervous centres, of smaller size and less complex structure than the brain, connected with each other, with the cerebro-spinal axis, and with the nerves in various situations. They are found on the posterior root of each of the spinal nerves; on the posterior or sen- sory root of the fifth cranial nerve; on the facial and auditory nerves ; and on the glosso-pharyngeal and pneumogastric nerves. They are also found in a connected series along each side of the vertebral column, forming the trunk of the sympathetic; and on the branches of that nerve, generally in the plexuses or at the point of junction of two or more nerves Avith each other or with branches of the cerebro-spinal system. On section they are seen to consist of a reddish-gray substance, traversed by numerous Avhite nerve-fibres ; they vary considerably in form and size; the largest are found in the cavity of the abdomen; the smallest, not visible to the naked eye, exist in considerable numbers upon the nerves distributed to the different viscera. The ganglia are invested by a smooth and firm, closely-adhering, membranous envelope, consisting of dense areolar tissue; this sheath is continuous with the peri- neurium of the nerves, and sends nu- merous processes into the interior of the ganglion, which support the blood- vessels supplying its substance. In structure all ganglia are essen- tially similar (Fig. 56), consisting of the same structural elements as the other nervous centres—viz. a collection of nerve-cells and nerve-fibres. The nerve- or ganglion-cells in the ganglia of the spinal nerves are pyriform in shape, the Fig. 56.—Section through a microscopic ganglion. Magnified 300 diameters. (Klein and Noble Smith.) c. Capsule of the ganglion, n. Nerve-fibres passing out of the ganglion. The nerve-fibres which entered the gangtion are not represented. The nerve-fibres are ordinary medullated fibres, but the details of their structure are not shown, owing to the low magnifying power. The ganglion-cells are invested by special capsules, lined by a few nuclei, which are here repre- sented as if contained in the capsule. 80 G EN ERA L . 1NA TO M Y. smaller end being drawn out into a process Avhich bifurcates at its extremity in a T-like manner, the two limbs of the T forming the axis-cvlinder of the peripheral and central portions of a sensory nerve-fibre. In the'sympathetic ganglia the cells are multipolar, and give off a single unbranched axis-cylinder. Cells of this type are found in the ciliary, spheno-palatine, submaxillary, and otic ganglia attached to certain of the cranial nerves, and these may in consequence be con- sidered as the cranial portion of the sympathetic system. The ganglion-cells are usually enclosed in a transparent capsule with nuclei on its inner surface. The nerve-fibres on entering the ganglion lay aside their perineurium, which becomes continuous Avith the capsule. Some fibres run through the ganglion without being connected with the cells. THE VASCULAR SYSTEM. The Vascular System, exclusive of its central organ, the heart, is divided into four classes of vessels: the minute structure of Avhich we arteries, capillaries, veins, and lymphatics; the will noAv proceed briefly to describe, referring the reader to the body of the work for all that is necessary in the details of their ordinary anatomy. Structure of Arteries (Fig. 57).—The arteries a're composed of three coats: inter- nal or endothelial coat (tunica intima of Kolliker); middle muscular coat {tunica media); and external cellular coat (tunica adventitia). The two inner coats together are very easily separated from the external, as by the ordinary operation of tying a ligature on an artery. If a fine string be tied for- cibly upon an artery and then taken off, the external coat will be found undivided, but the internal coats are divided in the track of the ligature and can easily be fur- ther dissected from the outer coat. The inner coat can be separated from the middle by a little maceration, or it may be stripped off in small pieces; but, on account of its friability, it cannot be separated as a com- plete membrane. It is a fine, transparent, colorless structure Avhich is highly elastic, and is commonly corrugated into longitudi- nal wrinkles. The inner coat consists of— 1. A layer of pavement-epithelium, the cells of which are polygonal, oval, or fusiform, and have very distinct round or oval nuclei. This endothelium, as it is now generally called, is brought into view most distinctlv by staining with nitrate of silver. 2. A subepithelial layer, consisting of delicate . connective tissue with branched cells lying e interspaces of the tissue. 3. An elastic or fenestrated layer, which con- sists of an elastic membrane containing a network of elastic fibres, having prin- cipally a longitudinal direction and in which, under the microscope, small elon- gated apertures or perforations may be seen, giving it a fenestrated appearance by Henle the fenestrated membrane. This membrane ^s ot the inner coat, and can be separated into several some of which present the appearance of a network of longitudinal elastic Fig. 57.—Transverse section through a small artery and vein of the mucous membrane of the epiglottis of a child. Magnified about 350 diame- ters. (Klein and Noble Smith.) a. Arterv, show- ing the nucleated endothelium, e, which lines it: the vessel being contracted, the endothelial cells appear very thick. Underneath the endothelium is the wavy elastic intima. The chief part of the wall of the vessel is occupied by the circular mus- cle-coat m: the staff-shaped nuclei of the muscle- cells are well seen. Outside this is a, part of the adventitia. This is composed of bundles of con- nective-tissue fibres, shown in section, with the nuclei of the connective-tissue corpuscles. The adventitia gradually merges into the sur- rounding connective tissue, v. Vein showing a thin endothelial membrane, e, raised acciden- tally from the intima, which on account of its delicacy is seen as a mere line on the media to. This latter is composed of a few circular un- striped muscle-cells, a. The adventitia, simi- lar in structure to that of an artery. th( It Avas therefore called forms the chief thickne iavei THE VASCULAR SYSTEM. 81 fibres, and others present a more membranous character, marked by pale lines having a longitudinal direction. In arteries of less than a line in diameter the subepithelial layer consists of a single layer of stellate cells, and the connective tissue is only largely developed in the large-sized vessels. The fenestrated mem- brane in microscopic arteries is a very thin layer, but in the larger arteries, and especially in the aorta, it has a very considerable thickness. The middle coat (tunica media) is distinguished from the inner by its color and by the transverse arrangement of its fibres, in contradistinction to the longi- tudinal direction of those of the inner coat. It consists of two varieties of struc- ture, yellow elastic tissue and muscular tissue, Avhich are present in varying quan- tities in different vessels, according to their size, the former tissue preponderating in the larger vessels and the latter in the smaller ones. In the largest arteries this coat is of great thickness, of a yelloAV color, and highly elastic; it diminishes in thickness and becomes redder in color as the arteries become smaller, and finally becomes very thin and disappears. In small arteries this coat is purely muscular, consisting of muscle fibre-cells (Fig. 44) united to form lamellae which vary in number according to the size of the artery; the very small arteries having only a single layer, and those not larger than one-tenth of a line in diameter three or four layers. In arteries of medium size (Fig. 58) this coat becomes thicker in proportion S*V \' 'Iff! U' . b fa I to the size of the vessel; its layers of muscular tissue are more numerous and inter- mixed with numerous fine elastic fibres Avhich unite to form broad-meshed networks. In the larger vessels, as the femoral, superior mesenteric, cceliac axis, external iliac, brachial and popliteal arte- ries, the elastic fibres unite to form lamellae, which alter- nate with the layers of mus- cular fibre. In the largest arteries the muscular tissue is only slightly developed and forms about one-third or one- fourth of the whole substance of the middle coat; this is especially the case in the aorta and trunk of the pul- monary artery, in Avhich the individual cells of the mus- _ cular layer are imperfectly formed, while in the carotid, axillary, iliac, and sub- clavian arteries the muscular layer of the middle coat is more developed, lhe elastic lamellae are well marked, may amount to fifty or sixty in number and alternate regularly with the layers of muscular tissue. They are most distinct and arranged with greatest regularity in the abdominal aorta, innominate artery, and common carotid. In the larger arteries bundles of white connective-tissue fibres have also been found in small quantity in the middle coat. The external coat (tunica adventitia) consists mainly of fine and closely felted bundles of white connective tissue, but also contains elastic fibres m all but the smallest arteries. The elastic tissue is much more abundant next the tunica media and it is sometimes described as forming here betAveen the adventitia and media a special laver, the tunica elastica externa of Henle. This aver is most marked in arteries' of medium size. In the largest vessels the external coat is relatively thin; but in small arteries it is as thick or thicker than the middle coat. 7 6 Fig. 5S.—An artery from the mesentery of a child, .062'" and 6, vein 067'" in diameter, treated with acetic acid and magnified 350 times V Tunica adventitia, with elongated ™clei. £ Juclei of the contractile fibre-cells of the tunica media, seen partly from the surface, partly apparent in transverse section, y. Nuclei of the en- dothelial cells. 5. Elastic longitudinal fibrous coat. 82 G EN ERA L . 1 NA TO MY. In the smaller arteries it consists of a single layer of white connective tissue and elastic fibres; while in the smallest arteries, just above the capillaries, the elastic fibres are wanting, and the connective tissue, of Avhich the coat is composed, becomes more homogeneous the nearer it approaches the capillaries, and is gradually reduced to a thin membranous envelope Avhich finally disappears. Some arteries have extremely thin coats in proportion to their size; this is especially the case in those situated in the cavity of the cranium and spinal canal, the difference depending on the greater thinness of the external and middle coats. The arteries, in their distribution throughout the body, are included in a thin fibro-areolar investment, which forms what is called their sheath. In the limbs this is usually formed by a prolongation of the deep fascia; in the upper part of the thigh it consists of a continuation downward of the transversalis and iliac fasciae of the abdomen; in the neck, of a prolongation of the deep cervical fascia. The included vessel is loosely connected Avith its sheath by a delicate areolar tissue; and the sheath usually encloses the accompanying veins, and sometimes a nerve. Some arteries, as those in the cranium, are not included in sheaths. All the larger arteries are supplied with blood-vessels like the other organs of the body; they are called the vasa vasorum. These nutrient vessels arise from a branch of the artery or from a neighboring vessel, at some considerable distance from the point at which they are distributed; they ramify in the loose areolar tissue connecting the artery with its sheath, and are distributed to the external coat, but do not, in man, penetrate the other coats; though in some of the larger mammals some few vessels have been traced into the middle coat. Minute veins serve to return the blood from these vessels; they empty themselves into the venae comites in connection with the artery. Lymphatic vessels and lymphatic spaces are also present in the outer coat. Arteries are also supplied Avith nerves, which are derived chiefly from the sym- pathetic, but partly from the cerebro-spinal system. They form intricate plexuses upon the surfaces of the larger trunks, and run along the smaller branches as single filaments or bundles of filaments, Avhich twist around the vessel and unite with each other in a plexiform manner. The branches derived from these plexuses penetrate the external coat, and are principally distributed to the muscular tissue of the middle coat, and thus regulate, by causing the contraction and relaxation of this tissue, the amount of blood sent to any part. The Capillaries.—The smaller arterial branches (excepting those of the cavern- ous structure of the sexual organs, of the spleen, and in the uterine placenta) terminate in a network of vessels Avhich pervade nearly every tissue of the body. These vessels, from their minute size, are termed capillaries (capillus, a hair). They are interposed between the smallest branches of the arteries and the com- mencing veins, constituting a network, the branches of which maintain the same diameter throughout; the meshes of the network being more uniform in shape and size than those formed by the anastomoses of the small arteries and veins. The diameter of the capillaries varies in the different tissues of the body, their usual size being about 3^-0 of an inch. The smallest are those of the brain and the mucous membranes of the intestines; and the largest those of the skin and the marrow of bone, where they are stated to be as large as -j^pr of an inch. The form of the capillary net varies in the different tissues, the meshes being generally rounded or elongated. The rounded form of mesh is most common, and prevails where there is a dense network, as in the lungs, in most glands' and mucous membranes, and in the cutis; here the meshes are more or less angular. sometimes nearly quadrangular or polygonal; more frequently irregular Elongated meshes are observed in the bundles of fibres composing muscles and nerves, the meshes being usually of a parallelogram form, the long axis of the mesh running parallel with the long axis of the nerve and fibre. Sometimes the capillaries have a looped arrangement; a single vessel projecting from the THE VASCULAR SYSTEM. 83 common network and returning after forming one or more loops, as in the papillae of the tongue and skin. The number of the capillaries, and the size of the meshes, determine the degree of vascularity of a part. The closest network and the smallest interspaces are found in the lungs and in the choroid coat of the eye. In these situations the interspaces are smaller than the capillary vessels them- selves. In the kidney, in the conjunctiva, and in the cutis the interspaces are from three to four times as large as the capillaries Avhich form them; and in the brain from eight to ten times as large as the capillaries in their long diameter, and from four to six times as large in their transverse diameter. In the adventitia of arteries the width of the meshes is ten times that of the capillary vessels. As a general rule, the more active the function of the organ, the closer is its capillary net and the larger its supply of blood ; the network being very narrow in all growing parts, in the glands, and in the mucous membranes; wider in bones and ligaments, Avhich are comparatively inactive; and nearly altogether absent in tendons, in Avhich very little organic change occurs after their formation. Structure.—The walls of the capillaries consist of a fine, transparent, endothelial layer, composed of cells joined edge to edge by an interstitial cement-substance, and continuous with the endothelial cells Avhich line the arteries and veins. When stained with nitrate of silver the edges which bound the endothelial cells are brought into view (Fig. 59). These cells are of large size and of an irregular polyg- onal or lanceolate shape, each containing an oval nucleus which may be brought into view by carmine or haematoxylin. BetAveen their edges, at various points of their meeting, roundish dark spots are sometimes seen, Avhich have been described as Fig. 59.—Capillaries from the Fig. 60.—Finest vessels on the arterial side. From the human mesentery of a guinea-pig after treat- brain. Magnified 300 times. 1. Smallest artery. 2. Transition ment with solution of nitrate of sil- vessel. 3. Coarser capillaries. 4. Finer capillaries, a. Structure- ver. a. Cells. 6. Their nuclei. less membrane still with come nuclei, representative of the tunica adventitia. b. Nuclei of the muscular fibre-cells, c. nuclei within the small artery, perhaps appertaining to an endothelium, d. Nuclei in the transition vessels. stomata, though they are closed by intercellular substance. They have been believed to be the situation through which the white corpuscles of the blood, when migrating through the blood-vessels, emerge; but this view, though probable, is not universally accepted. In many situations a delicate sheath or envelope of branched nucleated connec- 84 GENERAL ANATOMY. tive-tissue cells is found around the simple capillary tube, particularly in the larger ones, and in places such as the lymphatic glands Avhere the capillaries are supported by a retiform connective tissue. In the largest capillaries (Avhich ought, perhaps, to be described rather as the smallest arteries) there is, outside the endothelial layer, a muscular layer, consisting of contractile fibre-cells, arranged transversely, as in the tunica media of the larger arteries (Fig. 60). The veins, like the arteries, are composed of three coats—internal, middle, and external; and these coats are, with the necessary modifications, analogous to the coats of the arteries; the internal being the endothelial, the"middle the muscular, and the external the connective or areolar. The main difference between the veins and the arteries is the comparative weakness of the middle coat of the former, and to this it is due that the veins do not stand open Avhen divided, as the arteries do, and that they are passive rather than active organs of the circulation. In the veins immediately above the capillaries the three coats are hardly to be distinguished. The endothelium is supported on an outer membrane separable into two layers, the outer of Avhich is the thicker, and consists of a delicate, nucleated membrane (adventitia), while the inner is composed of a netAvork of longitudinal elastic fibres (media). In the veins next above these in size (one-fifth of a line, according to Kolliker) a muscular layer and a layer of circular fibres can be traced, forming the middle coat, Avhile the elastic and connective elements of the outer coat become more distinctly perceptible. In the middle-sized veins the typical structure of these vessels becomes clear. The endothelium is of the same character as in the arteries, but its cells are more oval, less fusiform. It is supported by a connective-tissue layer, consisting of a delicate netAvork of branched cells, and external to this is a layer of longitudinal elastic fibres, but seldom any appearance of a fenestrated membrane. This constitutes the internal co^t. The middle coat is composed of a thick layer of connective tissue Avith elastic fibres, intermixed, in some veins, with a transverse layer of muscular fibres. The white fibrous element is in considerable excess, and the elastic fibres are in much smaller proportion in the veins than in the arteries. The outer coat consists of areolar tissue, as in the arteries, Avith longitudinal elastic fibres. In the largest veins the outer coat is from tAvo to five times thicker than the middle coat, and contains a large number of longitudinal muscular fibres. This is most distinct in the inferior vena cava, and at the termination of this vein in the heart, in the trunks of the hepatic veins, in all the large trunks of the vena port:e, in the splenic, superior mesenteric, external iliac, renal, and azygos veins. In the renal and portal veins it extends through the Avhole thickness of the outer coat, but in the other veins mentioned a layer of connective and elastic tissue is found external to the muscular fibres. All the large veins Avhich open into the heart are covered for a short distance Avith a laver of striped muscular tissue continued on to them from the heart. Muscular tissue is Avanting in the veins—(1) of the maternal part of the placenta; (2) in the venous sinuses of the dura mater and the veins of the pia mater of the brain and spinal cord: (3) in the veins of the retina; (4) in the veins of the cancellous tissue of bones ; (5) in the venous spaces of the corpora cavernosa. The veins of the above- mentioned parts consist of an internal endothelial lining supported on one or more layers of areolar tissue. The internal and external jugular veins and the subclavian vein are said to contain either no muscular fibres at all, or at all events onlv a slight amount in their micldle coat. Most veins are provided Avith valves, Avhich serve to prevent the reflux of the blood. They are formed by a reduplication of the inner coat, strengthened by connective tissue and elastic fibres, and are covered on both surfaces Avith endo- thelium, the arrangement of Avhich differs on the two surfaces. On the surface of the valve next the wall of the vein the cells are arranged transverselv; whilst on the other surface, over Avhich the current of blood flows, the cells are'arranged vertically in the direction of the current. Their form is semilunar. They are THE VASCULAR SYSTEM. 85 attached by their convex edge to the wall of the vein; the concave margin is free, directed in the course of the venous current, and lies in close apposition with the wall of the vein as long as the current of blood takes its natural course; if, how- ever, any regurgitation takes place, the valves become distended, their opposed edges are brought into contact, and the current is intercepted. Most commonly two such valves are found placed opposite one another, more especially in the smaller veins or in the larger trunks at the point where they are joined by smaller branches; occasionally there are three and sometimes only one. The Avail of the vein on the cardiac side of the point of attachment of each segment of the valve is expanded into a pouch or sinus, which gives to the vessel, when injected or dis- tended Avith blood, a knotted appearance. The valves are very numerous in the veins of the extremities, especially of the lower extremities, these vessels having to conduct the blood against the force of gravity. They are absent in the very small veins—i. e. those less than -fa of an inch in diameter; also in the venae cavae, the hepatic veins, portal vein and its branches, the renal, uterine, and ovarian veins. A feAv valves are found in the spermatic veins, and one also at their point of junction Avith the renal vein and inferior vena cavra in both sexes. The cerebral and spinal veins, the veins of the cancellated tissue of bone, the pulmonary veins, and the umbilical vein and its branches, are also destitute of valves. They are occasionally found, feAv in number, in the venae azygos and intercostal veins. The veins are supplied with nutrient vessels, vasa vasorum, like the arteries. Nerves also are distrib- uted to them in the same manner as to the arteries, but in much less abundance. The lymphatic vessels, including in this term the lacteal vessels, Avhich are identical in structure Avith them, are composed of three coats. The internal is an endothelial and elastic coat. It is thin, trans- parent, slightly elastic, and ruptures sooner than the other coats. It is composed of a layer of elongated epithelial cells with serrated margins, by which the adjacent cells are dovetailed into one another. These are supported on a single layer of longitudinal elastic fibres. The middle coat is composed of smooth mus- cular and fine elastic fibres, disposed in a transverse direction. The external, or fibro-areolar, coat con- sists of filaments of connective tissue, intermixed with Fig. 62.—1. Endothelium from the under surface of the centrum tendineurn of the rabbit, a. Stomata. 2. Endo- thelium of the mediastinum of the dog. a. Stomata. 3. Section through the pleura of the same animal. 6. Free orifices of short lateral passages of the lymph-canals. (Copied from Ludwig, Schweigger-Seydel, and Dyb- kowsky.) abc Fig. 61.—Transverse section through the coats of the thoracic duct of man. Magnified 30 times, a. Endothelium, striated lamellae, and inner elastic coat. &. Longitudinal connective tissue of the middle coat. c. Transverse muscles of the same. d. Tunica adven- titia, with e, the longitudinal muscular fibres. smooth muscular fibres, longitudinally or obliquely disposed. It forms a protective covering to the other coats, and serves to connect the vessel with the neighboring structures. The above description applies only to the larger lymphatics; in the smaller vessels there is no muscular or elastic coat, and their structure consists only of a connective-tissue coat, lined by endothelium. The thoracic duct (Fig. 61) is a somewhat more complex structure than the other lymphatics; it presents a distinct subepithelial layer of branched corpuscles, similar to that found in the arteries, and in the middle coat is a layer of connective tissue with its fibres *<) GENERAL ANATOMY. arranged longitudinally. The lymphatics are supplied by nutrient vessels, which are distributed to their outer and middle coats; but no nerves have at present been traced into them. The lvmphatics are very generally provided Avith valves, Avhich assist mate- rially in effecting the circulation of the fluid they contain. These valves are formed of a thin layer of fibrous tissue, lined on both surfaces by endothelium. Their form is semilunar; they are attached by their convex edge to the sides of the vessel, the concave edge being free and directed along the course of the con- tained current. Usually tAvo such valves, of equal size, are found opposite one another; but occasionally exceptions occur, especially at or near the anastomoses of lymphatic vessels. Thus, one valve may be of very rudimentary size and the other increased in proportion. The valves in the lymphatic vessels are placed at much shorter intervals than in the veins. They are most numerous near the lymphatic glands, and they are found more frequently in the lymphatics of the neck and upper extremity than in the lower. The Avail of the lymphatics immediately above the point of attach- ment of each segment of a valve is expanded into a pouch or sinus, Avhich gives to these vessels, Avhen distended, the knotted or beaded appearance Avhich they present. Valves are wanting in the vessels composing the plexiform network in which the lymphatics usually originate on the surface of the body. Origin of Lymphatics.—The finest visible lymphatic vessels (lymphatic capil- laries) form a plexiform netAvork in the tissues and organs, and they consist of a single layer of endothelial plates, Avith more or less sinuous margins. These ves- sels commence in an intercommunicating system of clefts or spaces in the connec- tive tissue of the different organs, Avhich have no complete endothelial lining. They have been named the rootlets of the lymphatics, and are identical Avith the spaces in Avhich the connective-tissue corpuscles are contained. This then is properly regarded as one method of their commencement, when the lymphatic vessels are apparently continuous Avith spaces in the connective tissue, and Klein has described and figured a direct communication between these spaces and the lymphatic vessel.1 But the lymphatics have also other modes of origin, for the intestinal lacteals commence by closed extremities, though some observers believe that the closed extremity is continuous Avith a minute network contained in the substance of the villus, through Avhich the lacteal is connected Avith the epithelial cells covering it. Again, it seems now to be conclusively proved that the serous membranes present stomata or openings betAveen the epithelial cells (Fig. 62) by Avhich there is an open communication Avith the lymphatic system, and through which the lymph is thought to be pumped by the ultimate dilatation and contraction of the serous surface, due to the movements of respiration and circulation,2 so that the serous and synovial sacs may be regarded, in a certain sense, as large lymph-caArities or sinuses. Yon Recklinghausen was the first to observe the passage of milk and other colored fluids through these stomata on the peritoneal surface of the central tendon of the diaphragm. Again, in most glandular structures the lymphatic capillaries have a lacunar origin. Here they begin in irregular clefts or spaces in the tissue of the part; occupying the penetrating connective tissue and surrounding the lacunae or tubules of the gland, and in many places separating the capillary netAvork from the alveolus or tubule, so that the interchange betAveen the blood and the secreting cells of the part must be carried on through this lvmph- space or lacuna. Closely allied to this is the mode of origin of lymphatics in perivascular and perineural spaces. Sometimes a minute artery may be seen to be ensheathed for a certain distance by a lymphatic capillary vessel, Avhich is often many times wider than a blood-capillary. These are known as perivascular lvmphatics. 1 Atlas of Histology, pi. viii. fig. xiv. •The resemblance between lymph and serum led Hewson long ago to regard the serous cavities as sacs into which the lymphatics open. Kecent microscopic discoveries confirm this opinion in a very interesting manner. v THE VASCULAR SYSTEM. 87 Terminations of Lymphatics.—The lymphatics, including the lacteals, discharge their contents into the veins at tAvo points ; namely, at the angles of junction of the subclavian and internal jugular veins: on the left side by means of the thoracic duct, and on the right side by the right lymphatic duct. (See description of lymphatics on a subsequent page.) Lymphatic glands (conglobate glands) are small oval or bean-shaped bodies, situated in the course of lymphatic and lacteal vessels, so that the lymph and chyle pass through them on their way to the blood. They generally present on one side a slight depression—the hilum—through Avhich the blood-vessels enter and leave the interior. The efferent lymphatic vessel also emerges from the gland at this spot, AA'hile the afferent vessels enter the organ at different parts of the periphery. On section (Fig. 63), a lymphatic gland displays two different struc- tures: an external, of lighter color—the cortical; and an internal, darker—the medullary. The cortical structure does not form a complete investment, but is deficient at the hilum, Avhere the medullary portion reaches the surface of the gland; so that the efferent vessel is derived directly from the medullary structure, Avhile the afferent vessels empty themselves into the cortical substance. Lymphatic glands consist of (1) a fibrous envelope, or capsule, from which a frameAvork of processes (trabecular) proceed inward, dividing the gland into open spaces (alveoli) freely communicating Avith each other; (2) a quantity of adenoid tissue occupying these spaces without completely filling them; (3) a free supply of blood-vessels, Avhich are supported on the trabeculae; and (4) the afferent and efferent vessels. Little is knoAvn of the nerves, though Kolliker describes some fine nervous filaments passing into the hilum. The capsule is composed of a layer of connective tissue, and from its internal surface are given off a number of membranous septa or lamellae, consisting, in man, of connective tissue, Avith a small admixture of muscular fibre-cells; but in many of the loAver animals composed almost entirely of involuntary muscular fibre. They pass inward, radiating toward the centre of the gland, for a certain distance; that is to say, for about one-third or one-fourth of the space between the circum- ference and the centre of the gland. They thus divide the outer part of its interior into a number of oval compart- ments or alveoli (Fig. 63). This is the cortical portion of the gland. After having penetrated into the gland for some distance, these septa break up into a number of smaller trabeculae, which form flattened bands or cords, interlacing Avith each other in all directions, forming in the central part of the organ a num- ber of intercommunicating spaces, also called alveoli. This is the medullary portion of the gland, and the spaces or alveoli in it not only freely communicate with each other, but also Avith the alveoli of the cortical portion. In these alveoli or spaces (Fig. 64) is contained the proper gland-substance or lymphoid tissue. The gland-pulp does not, Iioav- ever, completely fill the alveolar spaces, but leaves, betAveen its outer margin and the trabeculae forming the alveoli a channel or space of uniform width through- out. This is termed the lymph-path or lymph-sinus (Fig. 66). Running across it are a number of trabeculae of retiform connective tissue, the fibres of Avhich are, for the most part, covered by ramified cells. This tissue appears to serve the purpose of maintaining the gland-pulp in the centre of the space in its proper position. Fig. 63.—Section of small lymphatic gland, half- diagrammatically given, with the course of the lymph, o. The envelope, b. Septa between the fol- licles or alveoli of the cortical part. c. System of septa of the medullary portion, down to the hilum. d. The follicles, e. Lymph-tubes of the medullary mass. /. Different lvmphatic streams which sur- round the follicles, arid flow through the interstices of the medullary portion, g. Confluence of these passing through the efferent vessel, h, at the hilum. GENERA L A NA TOMY. On account of the peculiar arrangement of the framework of the organ, the Fig. 65.—From the medullary substance of an inguinal gland of the ox. (After His.) a. Lymph- tube, with its complicated system of vessels, o. t v, ♦ ■ n„„/i „fth0 a™ Retinacula stretched between the tube and the Fig. 64.-Follicle from a lymphatic gland of the dog, ™£ Portion of another lymph-tube. d. in vertical section, a. Reticular sustentacular substance %eV™- c- ™rllon OI auouie y v of the more external portion, 6, of the more internal, and *-w>- c, of the most external and most finely webbed part on the surface of the follicle, d. Origin of a large lymph-tube. e. Of a smaller one. /.Capsule, g. Septa, h. Vasafferens. i. Investing space of the follicle, with its retinacula. k. One of the divisions of the septa. 1,1. Attachment of the lymph-tubes to the septa. gland-pulp in the cortical portion is disposed in the form of nodules, and in the medullary part in the form of 6 rounded cords. It consists of ordinary lymphoid tissue, be- ing made up of a delicate re- ticulum of retiform tissue, Avhich is continuous Avith that in the lymph-paths, but mark- ed off from it by a closer retic- ulation ; in its meshes are closely packed lymph-corpus- cles, traversed by a dense plexus of capillary blood-ves- sels. The afferent vessels, as above stated, enter at all parts of the periphery of the gland, and after branching and form- ing a dense plexus in the sub- stance of the capsule, open into the lvmph-sinuses of the cortical part. In doing this they lose all their coats except their endothelial lining, which is continuous with a layer of similar cells lining the lymph-paths. In like manner the efferent vessel commences from the lymph-smuses of the medullary portion. The stream of lymph carried to the gland by the afferent vessel thus passes through the plexus in the capsule to the lymph-paths of the cortical portion, Avhere it is exposed to the action of the gland-pulp; flowing through these, it enters the paths or sinuses of the medullary portion, and finally emerges from the hilum by means of the efferent vessel. The stream of lymph in its passage through the lymph-sinuses is much retarded by the presence of the reticulum. Hence morphological elements, either normal or Fig. 66.—Section of lymphatic gland tissue Small artery in substance of same. c. Lymph-paths. corpuscles, e. Capillary plexus. Trabeculae. d. Lymph- THE SKIN AND ITS APPENDAGES. 89 morbid, are easily arrested and deposited in the sinuses. This is a matter of con- siderable importance in connection Avith the subject of poisoned wounds and the absorption of the poison by the lymphatic system, since by this means septic organisms carried along the lymphatic vessels may be arrested in the lymph-sinuses of the gland tissue, and thus be prevented from entering the general circulation. The arteries of the gland enter at the hilum, and either pass at once to the gland- pulp, to break up into a capillary plexus, or else run along the trabeculae, partly to supply them and partly running across the lymph-paths to assist in forming the capillary plexus of the gland-pulp. This plexus traverses the lymphoid tissue, but does not pass into the lymph-sinuses. From it the veins commence, and emerge from the organ at the same place as that at Avhich the artery enters. THE SKIN AND ITS APPENDAGES. The skin (Fig. 67) is the principal seat of the sense of touch, and may be regarded as a covering for the protection of the deeper tissues; it is also an im- portant excretory and absorbing organ. It consists principally of a layer of vascular connective tissue, named the derma, corium, or cutis vera, and an external covering of epithelium, termed the epidermis or cuticle. On the surface of the former layer Fig. 67.—A sectional view of the skin (magnified). are the sensitive papillae; and Avithin, or imbedded beneath it, are certain organs Avith special functions—namely, the sweat-glands, hair-follicles, and sebaceous glands. The epidermis or cuticle (scarf-skin, Fig. 68) is an epithelial structure belong- ing to the class of stratified epithelium. It is accurately moulded on the papillary layer of the derma. It forms a defensive covering to the surface of the true skin, and limits the evaporation of watery vapor from its free surface. It varies in thickness in different parts. In some situations, as in the palms of the hands and soles of the feet, it is thick, hard, and horny in texture. This may be partly due !>0 GENERAL ANATOMY. to the fact that these parts are exposed to intermittent pressure, but that this not the only cause is proved bv the fact that the condition exists to a very consi erable extent at birth. The more superficial layer of cells, called the horny lay Fig. 68—Microscopic section of skin, showing the epidermis and derma; a hair in its follicle : the erector pili muscle: sebaceous and sudoriferous glands. (stratum corneum), may be separated by maceration from the deeper layers, Avhich are called the rete mucosum, and Avhich consist of several layers of differently shaped cells. The free surface of the epidermis is marked by a network of linear furrows of variable size, marking out the surface into a number of spaces of polyg- onal or lozenge-shaped form. Some of these furroAvs are large, as opposite the flexures of the joints, and correspond to the folds in the derma produced by their movements. In other situations, as upon the back of the hand, they are exceed- ingly fine, and intersect one another at various angles; upon the palmar surface of the hand and fingers and upon the sole of the foot these lines are very distinct and are disposed in curves. They depend upon the large size and peculiar arrange- ment of the papillae upon Avhich the epidermis is placed. The deep surface of the epidermis is accurately moulded upon the papillary layer of the derma, each papilla being invested by its epidermic sheath; so that Avhen this layer is removed by maceration, it presents on its under surface a number of pits or depressions corre- sponding to the elevations in the papillae, as Avell as the ridges left in the interA^als between them. Fine tubular prolongations are continued from this layer into the ducts of the sudoriferous and sebaceous glands. In structure, the epidermis consists of several layers of epithelial cells agglu- tinated together and having a laminated arrangement. These several layers may be described as composed of four different strata from within outAvard: (1) The rete Malpighii, composed of several layers of epithelial cells, of Avhich the deepest layer is elongated in figure and placed perpendicularly on the surface of the corium, their loAver ends being denticulate, to fit into corresponding denticula- tions of the true skin; Avhile the succeeding laminae consist of cells of a more rounded or polyhedral form, the contents of Avhich are soft, opaque, granular, and soluble in acetic acid. They are often marked on their surfaces Avith ridges and furroAvs, and are covered with numerous fibrils, Avhich connect the surfaces of the cells : these are known as prickle cells (see page 43). (2) Immediately superficial to these is a single layer of flattened, spindle-shaped cells, the granular layer, which contain granules that become deeply stained in haematoxylin, and are composed of a substance termed eleidin. They are supposed to be cells in a transitional stage between the protoplasmic cells of the rete Malpighii and the horny cells of the superficial layers. (3) Above this layer the cells become indis- tinct, and appear, in sections, to form a homogeneous or dimly striated mem- brane composed of closely-packed scales, in which traces of a flattened nucleus THE SKIN AND ITS APPENDAGES. 91 may be found. It is called the stratum lucidum. (4) As these cells suc- cessively approach the surface by the development of fresh layers from beneath, they assume a flattened form from the evaporation of their fluid contents, and consist of many layers of horny epithelial scales in which no nucleus is discernible, forming the stratum corneum. These cells apparently become changed in their chemical composition, as they are now unaffected by acetic acid. The deepest layer of the rete Malpighii is separated from the papillae by an apparently homogeneous basement membrane, Avhich is most distinctly brought into view in specimens prepared with chloride of gold. This, according to Klein, is merely the deepest portion of the epithelium, and is "made up of the basis of the individual cells, which have undergone a chemical and morphological altera- tion." The black color of the skin in the negro and the tawny color among some of the white races is due to the presence of pigment in the cells of the cuticle. This pigment is more especially distinct in the cells of the deeper layer or rete mucosum, and is similar to that found in the cells of the pigmentary layer of the retina. As the cells approach the surface and desiccate, the color becomes partially lost. The derma, corium, or cutis vera, is tough, flexible, and highly elastic, in order to defend the parts beneath from violence. It varies in thickness, from a quarter of a line to a line and a half, in differ- ent parts of the body. Thus it is very thick in the palms of the hands and soles of the feet; thicker on the posterior aspect of the body than the front, and on the outer than the inner side of the limbs. In the eyelids, scrotum, and penis it is exceedingly thin and delicate. The skin generally is thicker in the male than in the female, and in the adult than in the child. The corium consists of fibrous connective tissue, Avith a large admixture of elastic fibres and numerous blood-vessels, lymphatics, and nerves. The fibro- areolar tissue forms the framework of the cutis, and is differently arranged in different parts, so that it is usual to describe it as consisting of tAvo layers: the deeper or reticular layer, and the superficial or papillary layer. Unstriped muscular fibres are found in the superficial layers of the corium, wherever hairs are found; and in the subcutaneous areolar tissue of the scrotum, penis, labia majora of the female, and the nipples. In the latter situation the fibres are arranged in bands, closely reticulated and disposed in superimposed laminae. The reticular layer consists of strong interlacing fibrous bands, composed chiefly of the Avhite variety of fibrous tissue, but containing, also, some fibres of the yellow elastic tissue, which vary in amount in different parts, and connective- tissue corpuscles, Avhich are often to be found flattened against the Avhite fibrous tissue-bundles. Toward the attached surface the fasciculi are large and coarse, and the areolae which are left by their interlacement are large, and occupied by adipose tissue and sweat-glands. Below this the elements of the skin become gradually blended with the subcutaneous areolar tissue, which, except in a few situations, contains fat. ToAvard the free surface the fasciculi are much finer, and their mode of interlacing close and intricate. The papillary layer is situated upon the free surface of the reticular layer ; it con- sists of numerous small, highly sensitive, or vascular eminences, the papillae, which rise perpendicularly from its surface. The papillae are conical-shaped eminences, having a round or blunted extremity,occasionally divided into two or more parts and connected by a thin base with the free surface of the corium. Their average length is about y^q of an inch, and they measure at their base -%\-$ of an inch in diameter. On the general surface of the body, more especially in those parts Avhich are endoAved with slight sensibility, they are few in number, short, exceedingly minute, and irregularly scattered over the surface; but in some situations, as upon the palmar surface of the hands and fingers, upon the plantar surface of the feet and toes, and around the nipple, they are long, of large size, closely aggregated together, and arranged in parallel curved lines, forming the elevated ridges seen on the free surface of the epidermis. In these ridges the larger papillae are arranged in a 92 GENERAL ANATOMY. double r(rw, Avith smaller papillae betAveen them; and these toavs are subdivided into small square-shaped spaces by short transverse furrows, regularly disposed; in the centre of each of these transverse furroAvs is the minute orifice of the duct of a sweat-gland. No papillae exist in the grooves betAveen the ridges. In structure the papillae consist of very small and closely interlacing bundles of finely fibrillated tissue, Avith a feAv elastic fibres. The majority of the papillae con- tain loops of blood-vessels, and these are knoAvn as the vascular papillae in contra- distinction to others Avhich usually possess no blood-vessels, but contain tactile cor- puscles. These tactile papillae are most numerous in the derma of the palm of the hand and of the sole of the foot, but occur also in smaller numbers on the back of the hand and foot, on the flexor surface of the forearm, and on the nipple. The arteries supplying the skin form a netAvork in the subcutaneous tissue, from Avhich branches are given off to supply the SAveat-glands, the hair-follicles, and the fat. Other branches are given off which form a plexus immediately beneath the corium ; from this fine capillary vessels pass into the papillae, forming, in the smaller papillae, a single capillary loop, but in the larger a more or less convoluted vessel. There are numerous lymphatics supplied to the skin Avhich form tAvo networks, superficial and deep, communicating with each other and Avith those of the subcutaneous tissue by oblique branches. They originate in the cell- spaces of the tissue. The nerves of the skin terminate partly in the epidermis and partly in the cutis vera. The former form a dense plexus in the superficial layer of the corium, Avhich extends horizontally and gives off numerous fibrils; these are prolonged into the epidermis, and terminate betAveen the cells, either in bulbous extremities or in a netAvork ; or, according to some observers, in the deep epithelial cells them- selves. The latter terminate in end-bulbs, touch-corpuscles, or Pacinian bodies in the manner already described; and, in addition to these, a considerable number of fibrils are distributed to the hair-follicles, Avhich are said to entwine the follicle in a circular manner. Other nerve-fibres are supplied to the plain muscular tissues of the hair-muscles (arrectores pili) and to the muscular coat of the blood-vessels. These are probably non-medullated fibres. The appendages of the skin are the nails, the hairs, the sudoriferous and sebaceous glands, and their ducts. The nails and hairs are peculiar modifications of the epidermis, consisting essentially of the same cellular structure as that tissue. The nails are flattened, elastic structures of a horny texture, placed upon the dorsal surface of the terminal phalanges of the fingers and toes. Each nail is convex on its outer surface, concave within, and is implanted by a portion, called the root, into a groove in the skin; the exposed portion is called the body, and the anterior extremity the free edge. The nail has a very firm adhesion to the cutis, being accurately moulded upon its surface, as the epidermis is in other parts. The part of the cutis beneath the body and root of the nail is called the matrix, because it is the part from Avhich the nail is produced. Corresponding to the body of the nail, the matrix is thick, and covered Avith large, highly vascular papillae, arranged in longitudinal roAvs, the color of which is seen through the transparent tissue. Behind this, near the root of the nail, the papillae are small, less vascular, and have no regular arrangement, and here the tissue of the nail is somewhat more opaque; hence this portion is of a Avhiter color, and is called the lunula on account of its shape. The cuticle, as it passes forward on the dorsal surface of the finger or toe, is attached to the surface of the nail, a little in advance of its root; at the extremity of the finger it is connected Avith the under surface of the nail a little behind its free edge. The cuticle and horny substance of the nail (both epidermic structures) are thus directly continuous with each other. The nails, in structure, consist of cells having a laminated arrangement, and these are essentially similar to those composing the epidermis. The deepest layer of cells, which lie in contact with the papillae of the matrix, are of elongated form, arranged perpendicularly to the THE SKIN AND ITS APPENDAGES. 93 surface; those which succeed them are of a rounded or polygonal form, the more superficial ones becoming broad, thin, and flattened, and so closely compacted as to make the limits of each cell very indistinct. It is by the successive growth of new cells at the root and under surface of the body of the nail that it advances forward and maintains a due thickness, Avhilst, at the same time, the growth of the nail in the proper direction is secured. As these cells in their turn become displaced by the growth of new cells, they assume a flattened form, their nuclei become indistinct, and they finally become closely compacted together into a firm, dense, horny texture. In chemical com- position the nails resemble epidermis. According to Mulder, they contain a somewhat larger proportion of carbon and sulphur. The hairs are peculiar modifications of the epidermis, and consist essentially of the same structure as that membrane. They are found on nearly every part of the surface of the body, excepting the palms of the hands, soles of the feet, and the penis. They vary much in length, thickness, and color in different parts of the body and in different races of mankind. In some parts, as in the skin of the eyelids, they are so short as not to project beyond the follicles containing them; in other parts, as upon the scalp, they are of considerable length: again, in other parts, as the eyelashes, the hairs of the pubic region, and the male Avhiskers and beard, they are remarkable for their thickness. The hairs generally present a cylindrical or more or less flattened form and a reniform outline upon transverse section. A hair consists of a root, the part implanted in the skin ; the shaft or stem, the portion projecting from its surface; and the point. The root of the hair presents at its extremity a bulbous enlargement, which is A\hiter in color and softer in texture than the shaft, and is lodged in a follicular involution of the epidermis called the hair-follicle. When the hair is of consider- able length the follicle extends into the subcutaneous areolar tissue. The hair- follicle commences on the surface of the skin with a funnel-shaped opening, and passes inward in an oblique direction to become dilated at its deep extremity, to correspond with the bulbous condition of the hair which it contains. It has opening into it, near its free ex- tremity, the orifices of the ducts of one or more seba- ceous glands (Fig. 68). At the bottom of each hair- follicle is a small conical vascular, eminence or papilla, similar in every respect to those found upon the sur- face of the skin ; it is continuous with the dermic layer of the follicle, is highly vascular and supplied with nervous fibrils; this is the part through which mate- rial is supplied for the production and constant growth of the hair. In structure the hair-follicle consists of two coats—an outer or dermic, and an inner or epidermic. The outer or dermic coat is formed mainly of fibrous tissue; it is continuous with the corium, is highly vascular, and supplied by numerous minute nervous filaments. It consists of three layers (Fig. 69). The most internal, next the cuticular lining of the follicle, consists of a hyaline basement-membrane, having a glassy, transparent appearance, Avhich is well marked in the larger hair-follicles, but is not very distinct in the follicles of minute hairs. It is continuous with the basement-membrane of the surface of the corium. External to this is a layer of spindle-shaped cells, arranged in a circular manner around the follicle and imbedded in a somewhat fibrous matrix, but reaching only as high as the entrance of the ducts of the sebaceous glands. Externally is a thick layer of Fig. 69.—Transverse section of hair-follicle. 1. Dermic coat of follicle. 2. Epidermic coat or root-sheath, a. Outer layer of dermic coat, with blood-vessels. 6,6. Vessels cut across, c. Middle layer, d. Inner or hyaline layer. e. Outer root-sheath. /, g. Inner root-sheath, h. Cuticle of root- sheath, i. Hair. (From Quain's Anatomy, Biesiadecki.) 94 GENERAL ANATOMY connective tissue, arranged in longitudinal bundles, in Avhich are contained the blood-vessels and nerves. The inner or epidermic layer is closely adherent to the root of the hair, so that when the hair is plucked from its follicle this layer most commonly adheres to it and forms what is called the root-sheath. It consists of tAvo strata, named respectively the outer and inner root-sheath; the former of these corresponds with the Malpighian laver of the epidermis, and resembles it in the rounded form and soft character of its cells ; at the bottom of the hair-follicle these cells become con- tinuous with those of the root of the hair. The inner root-sheath consists of a delicate cuticle next the hair; then of one or tAvo layers of horny, flattened, nucleated cells, known as Huxley's layer ; and finally of a single layer of non- nucleated, horny, flattened cells, called Henle s layer. The hair-follicle contains the root of the hair, which terminates in a bulbous extremity, and is excavated so as to exactly fit the papilla from Avhich it grows. The bulb is composed of polyhedral epithelial cells, which as they pass upward into the root of the hair become elongated and spindle-shaped, except some in the centre which remain polyhedral. Some of these latter cells contain pigment- granules, Avhich give rise to the color of the hair. It occasionally happens that these pigment-granules completely fill the cells in the centre of the bulb, which gives rise to the dark tract of pigment often found, of greater or less length, in the axis of the hair. The shaft of the hair consists of a central pith or medulla, the fibrous part of the hair, and the cortex externally. The medulla occupies the centre of the shaft and ceases toAvard the point of the hair. It is usually Avanting in the fine hairs covering the surface of the body, and commonly in those of the head. It is more opaque and deeper colored Avhen viewed by transmitted light than the fibrous part; but when viewed by reflected light it is Avhite. It is composed of roAvs of poly- hedral cells, Avhich contain air-bubbles. The fibrous portion of the hair consti- tutes the chief part of the shaft; its cells are elongated and unite to form flattened fusiform fibres. BetAveen the fibres are found minute spaces Avhich contain either pigment-granules in dark hair or minute air-bubbles in Avhite hair. In addition to this there is also a diffused pigment contained in the fibres. The cells which form the cortex of the hair consist of a single layer which surrounds those of the fibrous part; they are converted into thin, flat scales, having an imbricated arrangement. Connected Avith the hair-follicles are minute bundles of involuntary muscular fibres, termed arrectores pili. They arise from the superficial la}Ter of the corium, and are inserted into the outer surface of the hair-follicle, below the entrance of the duct of the sebaceous gland. They are placed on the side toward Avhich the hair slopes, and by their action elevate the hair (Fig. 68). The sebaceous glands are small, sacculated, glandular organs, lodged in the substance of the corium. They are found in most parts of the skin, but are most abundant in the scalp and face: they are also very numerous around the apertures of the anus, nose, mouth, and external ear; but are Avanting in the palms of the hands and soles of the feet. Each gland consists of a single duct, more or less capacious, Avhich terminates in a cluster of small secreting pouches or saccules. The sacculi connected Avith each duct vary, as a rule, in numbers from tAvo to five, but, in some instances, may be as many as twenty. They are composed of a transparent, colorless membrane, enclosing a number of cells. Of these the outer layer or marginal cells are small, polyhedral, epithelial cells, continuous Avith the lining cells of the duct. The remainder of the sac is filled Avith larger cells, con- taining fat, except in the centre, where the cells have become broken up, leaving a cavity containing the debris of cells and a mass of fatty matter, Avhich consti- tutes the sebaceous secretion. The orifices of the ducts open most frequently into the hair-follicles, but occasionally upon the general surface. On the nose and face the glands are of large size, distinctly lobulated, and often become much enlarged THE SKIN AND ITS APPENDAGES. 95 from the accumulation of pent-up secretion. The largest sebaceous glands are those found in the eyelids—the Meibomian glands. The sudoriferous or sweat glands are the organs by which a large portion of the aqueous and gaseous materials are excreted by the skin. They are found in almost every part of this structure, and are situated in small pits in the deep parts of the corium, or, more frequently, in the subcutaneous areolar tissue, surrounded by a quantity of adipose tissue. They are small, lobular, reddish bodies, consist- ing of a single convoluted tube, from which the efferent duct proceeds upward through the corium and cuticle, becomes someAvhat dilated at its extremity, and opens on the surface of the cuticle by an oblique valve-like aperture. The efferent duct, as it passes through the epidermis, presents a spiral arrangement, being tAvisted like a corkscreAV, in those parts where the epidermis is thick; where, how- ever, it is thin, the spiral arrangement does not exist. In the superficial layers of the corium the duct is straight, but in the deeper layers it is convoluted or even twisted. The spiral course of these ducts is especially distinct in the thick cuticle of the palm of the hand and sole of the foot. The size of the glands varies. They are especially large in those regions where the amount of perspiration is great, as in the axillae, Avhere they form a thin, mammillated layer of a reddish color, which corresponds exactly to the situation of the hair in this region; they are large also in the groin. Their number varies. They are most numerous on the palm of the hand, presenting, according to Krause, 2800 orifices on a square inch of the integument, and are rather less numerous on the sole of the foot. In both of these situations the orifices of the ducts are exceedingly regular, and cor- respond to the small transverse grooves which intersect the ridges of the papillae. In other situations they are more irregularly scattered, but in nearly equal num- bers, o\rer parts including the same extent of surface. In the neck and back they are least numerous, their number amounting to 417 on the square inch (Krause). Their total number is estimated by the same writer at 2,381,248, and, supposing the aperture of each gland to represent a surface of -^ of a line in diameter, he calculates that the whole of these glands would present an evaporating surface of about eight square inches. Each gland consists of a single tube intricately con- voluted, terminating at one end by a blind extremity, and opening at the other end upon the surface of the skin. In the larger glands this single duct usually divides and subdivides dichotomously ; the smaller ducts ultimately terminating in short caecal pouches, rarely anastomosing. The Avail of the duct is thick, the width of the canal rarely exceeding one-third of its diameter. The tube, both in the gland and Avhere it forms the excre- tory duct, consists of tAvo layers—an outer, formed by fine areolar tissue, and an inner layer of epithelium. The external or fibro-cellular coat is thin, continuous with the superficial layer of the corium, and extends only as high as the surface of the true skin. The epithelial lining in the distal part of the coiled tube of the gland proper consists of a single layer of cubical epithelium, supported on a basement membrane, and beneath it, between the epithelium and the fibro-cellular coat, there is a layer of what are usually regarded as plain mus- cular fibres, arranged longitudinally. In the duct and the proximal part of the coiled tube of the gland proper there are t\vo or more layers of polyhedral cells, lined on their internal surface—i. e cate membrane or cuticle, and on their outer surface by a limiting membrana Fig. 70.—Coiled tube of a sweat-gland cut in vari- ous directions, o. Longitudinal section of the proxi- mal part of the coiled tube. 6. Transverse section of the same. c. Longitudinal section of the distal part of the coiled tube. d. Transverse section of the same. (From Klein and Noble Smith's Atlas of Histology.) . next the lumen of the tube—by a deli- 96 GENERAL ANATOMY propria, but there are no muscular fibres. The epithelium is continuous with the epidermis and Avith the delicate internal cuticle, Avhich is all that is present in the epidermic portion of the tube. When the cuticle is carefully removed from the surface of the cutis, these convoluted tubes of epithelium may be drawn out and form short, thread-like processes on its under surface. The contents of the smaller sweat-glands are quite fluid; but in the larger glands the contents are semi-fluid and opaque, and contain a number of colored granules and cells which appear analogous to epithelial cells. SEROUS MEMBRANES. The serous membranes form shut sacs and may be regarded as lymph-sacs, from which lymphatic vessels arise by stomata or openings between the epithelial cells (see page 86). The sac consists of one portion which is applied to the walls of the cavity which it lines—the parietal portion ; and another reflected over the surface of the organ or organs contained in the cavity—the visceral portion. Sometimes the sac is arranged quite simply, as the tunica vaginalis testis; at others with numerous involutions or recesses, as the peritoneum, in Avhich, nevertheless, the membrane can always be traced continuously around the whole circumference. The sac is completely closed, so that no communication exists between the serous cavity and the parts in its neighborhood. An apparent exception exists in the peritoneum of the female; for the Fallopian tube opens freely into the peritoneal cavity in the dead subject, so that a bristle can be passed from the one into the other. But this communication is closed during life, except at the moment of the passage of the ovum out of the ovary into the tube, as is proved by the fact that no inter- change of fluids ever takes place between the two cavities in dropsy of the perito- neum or in accumulation of fluid in the Fallopian tubes.1 The serous membrane is often supported by a firm, fibrous layer, as is the case with the pericardium, and such membranes are sometimes spoken of as " fibro-serous." The various serous membranes are the peritoneum, lining the cavity of the abdomen; the two pleurae and the pericardium, lining the lungs and heart respec- tively ; and the tunicae vaginales, surrounding each testicle in the scrotum.2 Serous membranes are thin, transparent, glistening structures, lined on their inner surface by a single layer of polygonal or pavement endothelial cells, supported on a matrix of fibrous connective tissue, with networks of fine elastic fibres, in which is contained numerous capillaries and lymphatics. On the surface of the endothelium betAveen the cells numerous apertures or interruptions are to be seen. Some of these are stomata, surrounded by a ring of cubical epithelium (see Fig. 12), and communicating Avith a lymphatic capillary (see p. 86); others (pseudosto- mata) are mere interruptions in the epithelial layer, and are occupied by pro- cesses of the branched connective-tissue corpuscle of the subjacent tissue or by accumulations of the intercellular cement-substance. The secretion of these membranes is, in most cases, only sufficient in quantity to moisten the surface, but not to furnish any appreciable quantity of fluid. When a small quantity can be collected, it appears to resemble in many respects the lymph, and like that fluid coagulates spontaneously ; but when secreted in large quantities, as in dropsy, it is a watery fluid, which gives a precipitate of albumen on boiling. SYNOVIAL MEMBRANES. Synovial membranes, like serous membranes, are connective-tissue membranes placed between two movable tissues, so as to diminish friction, as between the two articular ends of the bones forming a movable joint; between a tendon and a tJJhA com.muni>catt!on betwfn .the "terine cavity and the peritoneal sac is not only apparent in the dead subject, but is an anatomica fact which is established by the continuity of its epithelium with that covering the uterus, Fallopian tubes, and fimbriae. epunenum 2 The arachnoid membrane, lining the brain and spinal cord was formerly regarded as a serous membrane but is now no longer classed with them, as it differs from them in structure, and doesnot form a shut sac as do the other serous membranes. MUCOUS MEMBRANE. 97 bone, Avhere the former glides over the latter ; and between the skin and various subcutaneous bony prominences. The synovial membranes are composed essentially of connective tissue, con- taining numerous vessels and nerves. It was formerly supposed that these mem- branes were analogous in structure to the serous membranes, and consisted of a layer of flattened cells on a basement-membrane. No such cells, however, exist, and the only ones found on the surface are irregularly branched connective-tissue corpuscles, similar to those found throughout the tissue. Here and there these cells are collected in patches and present the appearance of epi- thelium, but do not possess the true characters of an endothelial layer. They are surrounded and held together by an albuminous ground-substance. A further description of the synovial membranes w ill be found in the descriptive anatomy of the joints. MUCOUS MEMBRANE. Mucous membranes line all those passages by Avhich the internal parts com- municate Avith the exterior, and are continuous with the skin at the various orifices of the surface of the body. They are soft and velvety, and very vascular, and their surface is coated over by their secretion, mucus, Avhich is of a tenacious con- sistence, and serves to protect them from the foreign substances introduced into the body with Avhich they are brought in contact. They are described as lining the two tracts—the gastro-pulmonary and the genito-urinary; and all, or almost all, mucous membranes may be classed as belonging to and continuous Avith the one or the other of these tracts. The external surfaces of these membranes are attached to the parts which they line by means of connective tissue, Avhich is sometimes very abundant, forming a loose and lax bed, so as to allow considerable movement of the opposed surfaces on each other. It is then termed the submucous tissue. At other times it is exceedingly scanty, and the membrane is closely connected to the tissue beneath; sometimes, for example, to muscle, as in the tongue; sometimes to cartilage, as in the larynx; and sometimes to bone, as in the nasal fossae and sinuses of the skull. In structure a mucous membrane is composed of corium and epithelium. The epithelium is of various forms, including the squamous, columnar, and ciliated, and is often arranged in several layers (see Fig. 11). This epithelial layer is supported by the corium, which is analogous to the derma of the skin, and con- sists of connective tissue, either simply areolar or containing a greater or less quantity of lymphoid tissue. This tissue is usually covered on its external surface bv a transparent structureless basement-membrane, and internally merges into the submucous areolar tissue. It is only in some situations that the basement-mem- brane can be demonstrated. The corium is an exceedingly vascular membrane, containing a dense network of capillaries, Avhich lie immediately beneath the epithelium, and are derived from small arteries in the submucous tissue. The fibro-vascular layer of the corium contains, besides the areolar tissue and vessels, unstriped muscle-cells, which form in many situations a definite layer, called the muscularis mucosae. These are situated in the deepest part of the mem- brane, and are plentifully supplied with nerves. Other nerves pass to the epi- thelium and terminate between the cells. Lymphatic vessels are found in great abundance, commencing either by caecal extremities or in netAvorks, and com- municating with plexuses in the submucous tissue. Imbedded in the mucous membrane are found numerous glands, and project- ing from it are processes (villi and papillae) analogous to the papillae of the skin. These glands and processes, however, exist only at certain parts, and it will be more convenient to defer their description to the sequel, Avhere the parts are described as they occur. 7 98 GENERA L A N1 TOM Y. SECRETING GLANDS. The secreting glands are organs Avhose cells manufacture a secretion of a more or less definite composition, the material for the secretion being primarily selected from the blood. The essential parts, therefore, of a secreting gland are cells, Avhich have the poAver of extracting from the blood certain matters, and in some cases converting them into new chemical compounds; and blood- vessels, by Avhich the blood is brought into close relationship Avith these cells. The general arrangement in all secreting structures—that is to say, not only in secreting glands, but also in secreting membranes—is that the cells are arranged on one surface of an extravascular basement-membrane, which supports them, and a minute plexus of capillary vessels ramifies on the other surface of the membrane. The cells then extract from the blood certain constituents Avhich pass through the membrane into the cells, Avhere they are prepared and elaborated. The basement-membrane does not, however, always exist, and any free surface Avould appear to ansAver the same purpose in some cases. By the various modifications of this secreting surface the different glands are formed. This is generally effected by an invagination of the membrane in different ways, the object being to increase the extent of secreting surface Avithin a given bulk. In the simplest form a single invagination takes place, constituting a simple gland; this may be either in the form of an open tube (Fig. 71, a), or the Avails SECRETING GLANDS. 99 the primary one, as in Fig. 71, D and e, the gland is then termed a compound one. These secondary invaginations may assume either a saccular or tabular form, and so constitute the two subdivisions—the compound saccularor racemose gland, and the compound tubular. The racemose gland in its simplest form consists of a primary invagination which forms a sort of duct, upon the extremity of Avhich are found a number of secondary invaginations called saccules or alveoli, as in Brun- ner's glands (Fig. 71, d). But, again, in other instances, the duct, instead of being simple, may divide into branches, and these again into other branches, and so on ; each ultimate ramification terminating in a dilated cluster of saccules, and thus Ave may have the secreting surface almost indefinitely extended, as in the salivary glands (Fig. 71, e). In the compound tubular glands the division of the pri- mary duct takes place in the same way as in the racemose glands, but the branches retain their tubular form, and do not terminate in saccular recesses, but become greatly lengthened out (Fig. 71, f). The best example of this form of gland is to be found in the kidney. All these varieties of glands are produced by a more or less complicated invagination of a secreting membrane, and they are all identical in structure; that is to say, the saccules or tubes, as the case may be, are lined with cells, generally spheroidal or columnar in figure, and on their outer surface is an intimate plexus of capillary vessels. The secretion, Avhatever it may be, is eliminated by the cells from the blood, and is poured into the saccule or tube, and so finds it way out through the primary invagination on to the free surface of the secreting membrane. In addition, however, to these glands, Avhich are formed by an invagination of the secreting membrane, there are some few others Avhich are formed by an evagination or protrusion of the same structure, as in the vascular fringes of synovial membranes. This form of secreting structure is not nearly so frequently met with. ORIGIN AND DEVELOPMENT OF THE BODY. THE Avhole body is developed out of the ovum (Fig. 72) Avhen fertilized by the spermatozoon, the ovum being merely a simple nucleated cell. All the complicated changes by Avhich the various intricate organs of the Avhole body are formed from one simple cell may be reduced to two general processes—viz. the segmentation or cleavage of cells, and their differentiation. The former process consists in the splitting of the nucleus and its surrounding protoplasm, Avhereby the original cell is represented by tAvo. The differentiation of cells is a term used to describe that unknoAvn power or tendency impressed on cells Avhich, to all methods of examination noAV known, seem absolutely identical, whereby they grow into different forms; so that (to take the first instance which occurs in the growth of the embryo) the indifferent cells of the vascular area are differentiated, some of them into blood-globules, others into the solid tissue which forms the blood-vessels. The extreme complexity of the process of develop- Zona pellucida. Yolk.. Germinal vesicle. Germinal Discus prolig. Fig. 72.—Ovum of the sow. Fig. 73.—Human ovum from a mid- dle-sized follicle. Magnified 350 times. a. Vitelline membrane or zona pellucida. 6. External border of the yolk and internal border of the vitelline mem- brane, c. Germinal vesicle and germi- nal spot. ment renders it at all times difficult to describe it intelligibly, and still more so in a work like this, where adequate space and illustration can hardly be afforded, having respect to the main purpose of the work. I can only hope to render the leading features of the pro- cess tolerably plain, and must refer the reader Avho wishes to follow the various changes more minutely to the special works on the subject, and especially the works of Minot and Hertwig. Many of the statements which are accepted in human embryology are made only on the strength of observations on the lower animals, many stages in the development of the human embryo being yet unknown to us. The ovum is a small spheroidal body situated in immature Graafian vesicles near their centre, but in the mature ones in contact with the membrana granulosal at that part of the vesicle which projects from the surface of the ovary. The cells of the membrana granulosa are accumulated round the ovum in greater number than at any other part of the vesicle, forming a kind of granular zone, the discus proliqerus. The human ovum (Fig. 73) is extremely minute, measuring from -A^ to^ of an inch in diameter. It is a cell consisting externally of a transparent envelope the zona pellucida or vitelline membrane. Within this, and in close contact with it. is the cell-protoplasm containing granules of yolk or vitclius ; imbedded in the 100 ' See the description of the ovary at a future page. FERTILIZATION OF OVUM. 101 substance of the yolk is a small vesicular body, the germinal vesicle (vesicle of Pur- kinje), the nucleus of the cell; and this contains as its nucleolus a small spot, the macula germinativa, or germinal spot of Wagner. The zona pellucida, or vitelline membrane, is a thick, colorless, transparent mem- brane, which appears under the microscope as a radially striated membrane, bounded externally and internally by a dark outline. The striae are believed to be minute pores, and are regarded as the channels by which nutritive particles are admitted into the interior of the ovum, and possibly the way by which the spermatozoa gain access into the interior of the ovum, after the rupture of the Graafian follicle. The presence of these striae has given to the zona pellucida the name of zona radiata, or striated membrane of the ovum. The yolk consists of granules or globules of various sizes imbedded in a finely reticulated matrix of protoplasm. The smaller granules resemble pigment; the larger granules, Avhich are in the greatest number at the periphery, resemble fat- globules. In the human ovum the number of granules is comparatively small. Before and immediately after fertilization the cell protoplasm shoAvs distinct movements of contraction and expansion. The germinal vesicle consists of a fine, transparent, structureless membrane containing a clear matrix, in which are occasionally found a few granules. It is about t^-q of an inch in diameter, and in immature ova lies nearly in the centre of the yolk; but as the ovum becomes developed it approaches the surface and enlarges somewmat. The germinal spot occupies that part of the periphery of the germinal vesicle which is nearest to the periphery of the ovum. It is opaque, of a yelloAV color, and finely granular in structure, measuring from -$^q-$ to 2410() of an inch. The phenomena attending the discharge of the ova from the Graafian vesicles, since they belong as much or more to the ordinary function of the ovary than to the general subject of the growth of the body, are described Avith the anatomy of the ovaries on a subsequent page. Either before its escape from the Graafian follicle or immediately after, the ovum undergoes a peculiar change, which results in the formation of one or more peculiar bodies, the polar globules of Robin, and also of another body, which is named the "female pronucleus." The manner in which these bodies are developed from the germinal vesicle is briefly as follows: Usually before the rupture of the Graafian follicle, but after the ovum has become mature or ripe, a portion of the germinal vesicle with a small amount of surrounding protoplasm is protruded outside the yolk, but still remains Avithin the vitelline membrane; this forms a small globular mass and constitutes the first polar globule. After a time, generally not till the ovum has entered the tube, a second protrusion of a portion of the germinal vesicle takes place, and forms a second polar globule. We have thus about three-quarters of the germinal vesicle extruded from the yolk and about one-quarter remaining behind, and at the ejection of each of these bodies a visible shrinking of the yolk takes place. The portion of the germinal vesicle which remains behind recedes from the surface toward the centre of the yolk and assumes a-spherical form, and is now termed the " female pronucleus." All these changes, it must be understood, occur at each expulsion of an ovum, and are quite independent of fecundation. The first changes in the ovum which take place at the time of conception appear to be as follows: A spermatozoon penetrates the ovum, and comes into contact with the portion of the germinal vesicle remaining in the ovum. It seems as if this normally occurs in the Fallopian tube,1 but it is possible that it sometimes occurs before the ovum has entered the tube, or after it has passed through the tube and reached the cavity of the uterus; abnormally it may even 1 Many physiologists, as Bischoff and Dr. M. Barry, taught that the ovum is fecundated in the ovary but the reasoning of Dr. Allen Thomson appears very cogent in proving that the usual spot at which the spermatozoa meet the ovum is in the tube, down which it slowly travels to the uterus, in its course becoming surrounded by an albuminous envelope derived from the walls of the tube. 102 DEVELOPMENT. take place in the peritoneal cavity. The spermatozoon becomes buried in the yolk, the tail disappears, and the head, Avhich is really the nucleus of the sperma- tozoon, constitutes the '' male pronucleus." This gradually approaches the female pronucleus, Avhich by this time is situated in the centre of the ovum. As soon as thev come into contact they fuse into one, and thus fecundation is effected (Fig. 7-t).1 Fig. 74.—Fertilization of the ovum of an echinoderm. s. Spermatozoon, m. pr. Male pronucleus. /. pr. Fe- male pronucleus. 1. Accession of a spermatozoon to the periphery of the vitellus. 2. Its penetration. 3. Trans- formation of the head of the spermatozoon into the male pronucleus. 4, 5. Blending of the male and female pronuclei. (From Quain's Anatomy, Selenka.) The first result of the fertilization of the ovum is its cleavage or multiplica- tion, it being first cleft into two masses, the germinal vesicle having previously ,, FlS,v7o~Flrst staSes °f segmentation of a mammalian ovum; semi-diagrammatic. (From a drawing bv Allen Thomson.) 2. p. Zona pellucida, p. gl. Polar globules, u. Upper cell. I. Lower cell a Division into two spheres. 6. stage of four spheres, c Eight spheres, the upper cells partially enclosing the lower cells d.e. Succeeding stages of segmentation, showing the more rapid division of the upper cells and the enclosure of the lower cells by them. rr "-UBUC split up into two nuclei; so that it now consists of two separate masses of proto- plasm, each containing a nucleus, situated within the original vitelline membrane, 1 If }hf ^udent refers to the development of degenerative organs, he will find that the ovum of the female and the spermatozoon of the male are derived from fundamentally the same structures, and therefore their fusion is the union of two elements of very similar morpholou X. fourth to the seventh. The articular processes are oblique : the superior are of an oval form, flattened, and directed backward and upward; the inferior forward and downward. The transverse processes are short, directed downward, outward, and forward, bifid at their extremity, and marked by a groove along their upper surface, Avhich runs doAvmvard and outAvard from the superior intervertebral notch, and serves for the transmission of one of the cervical nerves. I hey are situated in front of the articular processes and on the outer side of the pedicles. The transverse processes are pierced at their base by a foramen, for the transmis- sion of the vertebral artery, vein, and plexus of nerves. Each process is formed by tAvo roots: the anterior root, sometimes called the costal process, arises from the side of the body, and is the homologue of the rib in the dorsal region of the spine ; the posterior root springs from the junction of the pedicle with the lamina, and corresponds with the transverse process in the dorsal region. It is by the Anterior tubercle of trans- verse process Foramen for vertebral artery. Posterior tubercle of transverse process. Transverse process. ,-Superior articular process. Inferior articular process. process. Fig. 109.—Cervical vertebra. junction of the two that the foramen for the vertebral vessels is formed. The extremity of each of these roots forms the anterior and posterior tubercles of the transverse processes.1 The peculiar vertebrae in the cervical region are the first, or Atlas ; the second, or Axis ; and the seventh, or Vertebra prominens. The great modifications in the form of the atlas and axis are designed to admit of the nodding and rotatory movements of the head. The Atlas (Fig. 110) is so named from supporting the globe of the head. The chief peculiarities of this bone are that it has neither body nor spinous process. The body is detached from the rest of the bone, and forms the odontoid process of the second vertebra; Avhile the parts corresponding to the pedicles join in front to form the anterior arch. The atlas consists of an anterior arch, a posterior arch, and two lateral masses. The anterior arch forms about one-fifth of the bone: its anterior surface is convex, and presents about its centre a tubercle, for the attach- ment of the Longus colli muscle; posteriorly it is concave, and marked bv a smooth, oval or circular facet, for articulation with the odontoid process of the axis. The upper and lower borders give attachment to the anterior occipito- atlantal and the anterior atlanto-axial ligaments, which connect it with the occipital bone above and the axis beloAv. The posterior arch forms about tAvo-fifths of the circumference of the bone; it terminates behind in a tubercle, which is the rudi- ment of a spinous process, and gives origin to the Rectus capitis posticus minor. The diminutive size of this process prevents any interference in the movements betAveen it and the cranium. The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior occipito-atlantal liga- 'The anterior tubercle of the transverse process of the sixth cervical vertebra is of large size, and is sometimes known as "Chassaignac's" or the "carotid tubercle." It is in close relation with the carotid artery, which lies in front and a little external to il so that, as was first pointed out by rhnssaignac, the vessel can with ease be compiessed igainst it. CER VIC A L VER TEBRjE. 147 ment, while in front, immediately behind each superior articular process, is a groove, sometimes converted into a foramen by a delicate bony spiculum Avhich arches backAvard from the posterior extremity of the superior articular process. These grooves represent the superior intervertebral notches, and are peculiar from being situated behind the articular processes, instead of in front of them, as in the other vertebrae. They serve for the transmission of the vertebral artery, which, ascending through the foramen in the transverse process, Avinds round the lateral mass in a direction backward and imvard. They also transmit the suboc- cipital nerve. On the under surface of the posterior arch, in the same situation, are tAvo other grooves, placed behind the lateral masses, and representing the infe- rior intervertebral notches of other vertebrae. They are much less marked than the superior. The loAver border also gives attachment to the posterior atlanto- axial ligament, Avhich connects it with the axis. The lateral masses are the most bulky and solid parts of the atlas, in order to support the weight of the head; they present tAvo articulating processes above, and tAvo below. The two superior are of large size, oval, concave, and approach each other in front, but diverge behind; they are directed upward, imvard, and a little backAvard, forming a kind of cup for the condyles of the occipital bone, and are admirably adapted to the nodding movements of the head. Not unfrequently they are partially subdivided by a more or less deep indentation Avhich encroaches upon each lateral margin. The inferior articular processes are circular in form, flattened or slightly concave, and directed doAvmvard and inward, articulating Avith the axis, and permitting the rotatory movements. Just beloAv the inner margin of each superior articular surface is a small tubercle, for the attachment of the transverse ligament, which, stretching across the ring of the atlas, divides it into tAvo unequal parts; the anterior or smaller segment receiving the odontoid process of the axis, the posterior allowing the transmission of the spinal cord and its membranes. This part of the spinal canal is of considerable size, to afford space for the spinal cord; and hence lateral displacement of the atlas may occur without compression of this structure. The transverse processes are of large size, project directly outAvard from the lateral masses, and serve for the attachment of special muscles Avhich assist in rotating the head. They are long, not bifid, and perforated at their base bv a canal for the vertebral artery, Avhich is directed from below, upward and backward. The Axis (Fig. Ill) is so named from forming the pivot upon Avhich the first vertebra, carrying the head, rotates. The most distinctive character of this bone is the strong,^ prominent process, tooth-like in form (hence the name odontoid), Avhich rises perpendicularly from the upper surface of the body. The body is of a triangular form, deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and fore part of the adjacent vertebra. It presents in front a median longitudinal ridge, separating tAvo lateral depressions for the attach- 14S THE SKEL E TON. ment of the Longus colli muscle of either side. The odontoid process presents tAvo articulating surfaces: one in front, of an oval form, for articulation with the Odontoid process. Rough surface for check ligaments.- Articular surface for transverse ligament. Spinous process. -1 %i;l Articular surface for atlas. Body. f%JJ Transverse process. Inferior articular process. Fig. ill.—Second cervical vertebra, or axis. atlas ; another behind, for the transverse ligament—the latter frequently encroach- ing on the sides of the process. The apex is pointed, and gives attachment to one fasciculus of the odontoid ligament (ligamentum suspensorium). BeloAv the apex the process is somewhat enlarged, and presents on either side a rough impression for the attachment of the lateral fasciculi of the odontoid or check ligaments, which connect it to the occipital bone ; the base of the process, where it is attached to the body, is constricted, so as to prevent displacement from the transverse ligament, which binds it in this Body. nterior root. situation to the anterior arch of the atlas. Sometimes, hoAvever, this process does become dis- placed, especially in children, in whom the ligaments are more relaxed: instant death is the result of this accident. The pedicles are broad and strong, especially their anterior extrem- ities, which coalesce with the sides of the body and the root of the odontoid process. The lam- inae are thick and strong, and the spinal foramen large, but smaller tban that of the atlas. The trans- verse processes are very small, not bifid, and perforated by the vertebral foramen, or foramen for the vertebral artery, Avhich is directed obliquely upAvard and outAvard. The superior articular surfaces are round, slightly convex, directed upward and outward, and are peculiar in being supported on the body, pedicles, and transverse processes. The inferior articular surfaces have the same direction as those of the other cervical vertebrae. The superior intervertebral notches are very shallow, and lie behind the articular processes; the inferior in front of them, as in the other cervical vertebra?. The spinous process is of large size, very strong, deeply channelled on its under surface, and presents a bifid, tubercular extremity for the attachment of muscles Avhich serve to rotate the head upon the spine. Seventh Cervical (Fig. 112).—The most distinctive character of this vertebra is Spinous process. Fig. 112.—Seventh cervical vertebra, or vertebra prominens. DORSAL VERTEBRAE. 149 the existence of a very long and prominent spinous process; hence the name "vertebra prominens." This process is thick, nearly horizontal in direction, not bifurcated, and has attached to it the ligamentum nuchae. The transverse process is usually of large size, especially its posterior root; its upper surface has usually a shallow groove, and it seldom presents more than a trace of bifurcation at its extremity. The vertebral foramen is sometimes as large as in the other cervical vertebrae, but is usually smaller on one or both sides, and sometimes wanting. On the left side it occasionally gives passage to the vertebral artery; more frequently the vertebral vein traverses it on both sides ; but the usual arrangement is for both artery and vein to pass in front of the transverse process, and not through the foramen Characters of the Dorsal Vertebrae. The Dorsal Vertebrae are intermediate in size between those in the cervical and those in the lumbar region, and increase in size from above doAvnAvard, the upper Fig. 113.—A dorsal vertebra. vertebrae in this segment of the spine being much smaller than those in the lower part of the region. The dorsal vertebrae may be at once recognized by the pres- ence on the sides of the body of one or more facets or half-facets for the heads of the ribs. The bodies of the dorsal vertebrae resemble those in the cervical and lumbar regions at the respective ends of this portion of the spine; but in the middle of the dorsal region their form is very characteristic, being heart-shaped, and as broad in the antero-posterior as in the lateral direction. They are thicker behind than in front, flat above and beloAv, convex and prominent in front, deeply concave behind, slightly constricted in front and at the sides, and marked on each side, near the root of the pedicle, by two demi-facets, one above, the other below. These are covered Avith cartilage in the recent state, and, Avhen articulated with the adjoin- ing vertebrae, form, with the intervening fibro-cartilage, oval surfaces for the reception of the heads of the corresponding ribs. The pedicles are directed back- ward, and the inferior intervertebral notches are of large size, and deeper than in any other region of the spine. The laminae are broad, thick, and imbricated— that is to say, overlapping one another like tiles on a roof. The spinal foramen is small, and of a circular form. The spinous processes are long, triangular in form (bavonet-shaped), directed obliquely dowmvard, and terminate in a tubercular extremity. They overlap one another from the fifth to the eighth, but are less ].-,() THE SKELETON. oblique in direction above and below. The articular processes are flat, nearly vertical in direction, and project from the upper and lower part of the pedicles; Fig. 114.—Peculiar dorsal vertebrae. the superior being directed backward and slightly outAvard and upAvard, the inferior forAvard and a little imvard and doAvnward. The transverse processes arise from the same parts of the arch as the posterior roots of the transverse processes in the neck, and are situated behind the articular processes and pedicles; they are thick, strong, and of great length, directed obliquely backward and outward, presenting a clubbed extremity, Avhich is tipped on its anterior part by a small concave surface, for articulation Avith the tubercle of a rib. Besides the articular facet for the rib, three indistinct tubercles may be seen rising from the transverse processes, one at the upper border, one at the loAver border, and one externally. In man they are comparatively of small size, and serve only for the attachment of muscles. But in some animals they attain considerable magnitude, either for 07 LUMBAR VERTEBRAE. 151 the purpose of more closely connecting the segments of this portion of the spine or for muscular and ligamentous attachment. (See beloAv, twelfth dorsal vertebra.) The peculiar dorsal vertebrae are the first, ninth, tenth, eleventh, and twelfth (Fig. 114). The First Dorsal Vertebra presents, on each side of the body, a single entire articular facet for the head of the first rib and a half facet for the upper half of the second. The upper surface of the body is like that of a cervical vertebra, being broad transversely, concave, and lipped on each side. The articular sur- faces are oblique, and the spinous process thick, long, and almost horizontal. The Ninth Dorsal has no demi-facet beloAv. In some subjects, however, the ninth has two demi-facets on each side, then the tenth has a demi-facet at the upper part; none below. The Tenth Dorsal has (except in the cases just mentioned) an entire articular facet on each side above, Avhich is partly placed on the outer surface of the pedicle. It has no demi-facet below. In the Eleventh Dorsal the body approaches in its form and size to the lumbar. The articular facets for the heads of the ribs, one on each side, are of large size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebra than in any other part of the dorsal region. The spinous process is short, nearly horizontal in direction, and presents a slight tendency to bifurcation at its extremity. The transverse processes are very short, tubercular at their extremities, and have no articular facets for the tubercles of the ribs. The Twelfth Dorsal has the same general characters as the eleventh, but may be distinguished from it by the inferior articular processes being convex and turned outward, like those"of the lumbar vertebrae; by the general form of the body, lamime, and spinous process, approaching to that of the lumbar vertebrae; and by the transverse processes being shorter, and marked by three elevations, the superior, inferior, and external tubercles, which correspond to the mammillary, accessory, and transverse processes of the lumbar vertebrae. Traces of similar elevations are usually to be found upon the other dorsal vertebrae (vide ut supra). Characters of the Lumbar Vertebrae. The Lumbar Vertebrae (Fig. 115) are the largest segments of the vertebral column, and can at once be distinguished by the absence of the foramen in the Fig. 115.—Lumbar vertebra. transverse process, the characteristic point of the cervical vertebrae, and by the absence of any articulating facet on the side of the body, the distinguishing mark of the dorsal vertebrae. The body is large, and has a greater diameter from side to side than from before backward, slightly thicker in front than behind, flattened or slightly concave above and below, concave behind, and deeply constricted in front and at the sides, 15-2 THE SKELETON. presenting prominent margins, Avhich afford a broad basis for the support of the superincumbent Aveight. The pedicles are very strong, directed backward from the upper part of the bodies; consequently, the inferior intervertebral notches are of considerable depth. The laminae are broad, short, and strong, and the spinal foramen triangular, larger than in the dorsal, smaller than in the cervical, region. The spinous processes are thick and broad, someAvhat quadrilateral, horizontal in direction, thicker beloAv than above, and terminating by a rough, uneven border. The superior articular processes are concave, and look backward and imvard; the inferior, convex, look fonvard and outAvard; the former are separated by a much wider interval than the latter, embracing the loAver articulating processes of the vertebra above. The transverse processes are long, slender, directed trans- versely outward in the upper three lumbar vertebrae, slanting a little upAvard in the loAver tAvo. They are situated in front of the articular processes, instead of behind them as in the dorsal vertebrae, and are homologous with the ribs. Of the three tubercles noticed in connection Avith the transverse processes of the tAvelfth dorsal vertebra, the superior ones become connected in this region Avith the back part of the superior articular processes, and have received the name of mammillary processes; the inferior are represented by a small process pointing doAvmvard, situated at the back part of the base of the transverse process, and called the accessory processes: these are the true transverse processes, which are rudimental in this region of the spine ; the external ones are the so-called transverse processes, the homologue of the rib, and hence sometimes called costal processes. Although in man these are comparatively small, in some animals they attain considerable size, and serve to lock the vertebrae more closely together. The Fifth Lumbar vertebra is characterized by having the body much thicker in front than behind, which accords with the prominence of the sacro-vertebral articulation; by the smaller size of its spinous process; by the wide interval betAveen the inferior articulating processes ; and by the greater size and thickness of its transverse processes. Structure of the Vertebrae.—The structure of a vertebra differs in different parts. The body is composed of light, spongy, eancellous tissue, having a thin coating of compact tissue on its external surface perforated by numerous orifices, some of large size, for the passage of vessels; its interior is traversed by one or tAvo large canals, for the reception of veins, which converge toward a single large, irregular aperture or several small apertures at the posterior part of the body of each bone. The arch and processes projecting from it have, on the contrary, an exceedingly thick covering of compact tissue. Development.—Each vertebra is formed of four primary cartilaginous portions (Fig. lit!), one for each lamina and its processes, and two for the body. Ossifica- tion commences in the laminae about the sixth Aveek of foetal life, in the situation wmere the transverse processes afterward project, the ossific granules shooting backAvard to the spine, forward into the pedicles, and outAvard into the transverse and articular processes. Ossification in the body commences in the middle of the cartilage about the eighth Aveek by two closely approximated centres, which speedily coalesce to form one central ossific point. According to some authors, ossifica- tion commences in the laminae only in the upper vertebrae—i. e. in the cervical and upper dorsal. The first ossific points in the lower vertebrae are those which are to form the body, the osseous centres for the laminae appearing at a subsequent period. At birth these three pieces are perfectly separate. During the first year the laminae become united behind by a portion of cartilage in Avhich the spinous process is ultimately formed, and thus the arch is completed. About the third year the body is joined to the arch on each side, in such a manner that the body is formed from the three original centres of ossification, the amount contributed by the ped- icles increasing in extent from below upward. Thus the bodies of the sacral vertebrae are formed almost entirely from the central nuclei; the bodies of the lumbar are formed laterally and behind by the pedicles; in the dorsal region the pedicles advance as far forAvard as the articular depressions for the head of the LUMBAR VERTEBRAE. 153 ribs, forming these cavities of reception; and in the neck the lateral portions of the bodies are formed entirely by the advance of the pedicles. Before puberty By 4 primary centres. ! ' '• f',S, ---—— ,1 for under surface of body, 21 years. Fig. 117. 1 for each trans- verse process, 16 years. [sometimes 1) for spinous process (16 years). Fig. 118. 1 for anterior arch (1st year), not constant. ' 1 for each lateral mass Fig. 119.—Atlas. }bef, 'ore birth. By 6 centres. -S for odontoid process /jjj£\ 16th month). ^££i l-^^y'* j~ lfor each lateral mass. 1 for body (6th month, Fig. 120.—Axis. 2 additional centres. no other changes occur, excepting a gradual increase in the groAvth of these primary centres; the upper and under surfaces of the bodies and the ends of the transverse and spinous processes being tipped Avith cartilage, in Avhich ossific granules are not as yet deposited. At sixteen years (Fig. 118), four secondary centres appear, one for the tip of each transverse process, and two (sometimes united into one) for the end of the spinous process. At twenty-one years (Fig. 117), a thin circular epiphysial plate of bone is formed in the layer of cartilage situated on the upper and under sur- faces of the body, the former being Bv s centres. the thicker of the two. All these become joined, and the bone is com- pletely formed between the twenty- fifth and thirtieth year of life. Exceptions to this mode of de- velopment occur in the first, second, and seventh cervical, and in the vertebrae of the lumbar region. The Atlas (Fig. 119).—The num- ber of centres of ossification of the atlas is very variable. It may be developed from two, three, four, or five centres. The most frequent ar- rangement is by three centres. Two of these are destined for the two lateral or neural masses, the ossifica- tion of Avhich commences about the seventh Aveek near the articular pro- cesses, and extend backward; these portions of bone are separated from one another behind, at birth, by a narroAv inter\ral filled in Avith carti- lage. Between the second and third years they unite either directly or through the medium of a separate centre developed in the cartilage in the middle line. The anterior arch, at birth, is altogether cartilaginous, and in this a sepa- rate nucleus appears about the end of the first year after birth, and, extending laterally, joins the neural processes in front of the pedicles. Sometimes there are two nuclei developed in the cartilage, one on either side of the median line, Avhich join to form a single mass. And occasionally there is no separate centre, but the for tubercles on superior articular process. Fig. 121.—Lumbar vertebra. 154 THE SKELETON. anterior arch is formed by the gradual extension forward and ultimate junction of the tAvo neural processes. The Axis (Fig. 120) is developed by six centres. The body and arch of this bone are formed in the same manner as the corresponding parts in the other ver- tebne : one centre (or tAvo, which speedily coalesce) for the loAver part of the body, and one for each lamina. The odontoid process consists originally of an extension upAvard of the cartilaginous mass in which the loAver part of the body is formed. At about the sixth month of foetal life tAvo osseous nuclei make their appearance in the base of this process: they are placed laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval between the cleft and the summit of the process is formed by a Avedge-shaped piece of cartilage, the base of the process being separated from the body by a cartilaginous interval, which gradually becomes ossified at its circumference, but remains cartilaginous in its centre until advanced age.1 Finally, as Humphry has demonstrated, the apex of the odontoid process has a separate nucleus, Avhich appears in the second year and joins about tbe tAvelfth year. In addition to these there is a secondary centre for a thin epiphysial plate on the under surface of the body of the bone. The Seventh Cervical.—The anterior or costal part of the transverse process of the seventh cervical is developed from a separate osseous centre at about the sixth month of foetal life, and joins the body and posterior division of the trans- verse process betAveen the fifth and sixth years. Sometimes this process continues as a separate piece, and, becoming lengthened outward, constitutes what is known as a cervical rib. The Lumbar Vertebrae (Fig. 121) have two additional centres (besides those peculiar to the vertebrae generally) for the mammillary tubercles, Avhich project from the back part of the superior articular processes. The transverse process of the first lumbar is sometimes developed as a separate piece, Avhich may remain permanently unconnected with the remaining portion of the bone, thus forming a lumbar rib—a peculiarity which is rarely met with. Progress of Ossification in the Spine generally.—Ossification of the laminae of the vertebrae commences at the upper part of the spine, and proceeds gradually doAvnward. Ossification of the bodies, on the other hand, commences a little below the centre of the spinal column (about the ninth or tenth dorsal vertebra), and extends both upward and dowmvard. Although, however, the ossific nuclei make their first appearance in the lower dorsal vertebrae, the lumbar and first sacral are those in which these nuclei are largest at birth. Attachment of Muscles.—To the Atlas are attached nine pairs: the Longus colli, Rectus capitis anticus minor, Rectus lateralis, Obliquus capitis superior and inferior, Splenius colli, Levator anguli scapulae, First Intertransverse, and Rectus capitis posticus minor. To the Axis are attached eleven pairs: the Longus colli, Levator anguli scapulae, Splenius colli, Scalenus medius, Transversalis colli, Intertransversales, Obliquus capitis inferior, Rectus capitis posticus major, Semispinalis colli, Mul- tifidus spinae, Interspinales. To the remaining vertebrae, generally, are attached thirty-five pairs and a sin- gle muscle: anteriorly, the Rectus capitis anticus major, Longus colli, Scalenus anticus medius and posticus, Psoas magnus and parvus, Quadratus lumbo- rum, Diaphragm, Obliquus abdominis internus, and Transversalis abdominis— posteriorly, the Trapezius, Latissimus dorsi, Levator anguli scapulae, Rhomboideus major and minor, Serratus posticus superior and inferior, Splenius, Erector spinae, Ilio-costalis, Longissimus dorsi, Spinalis dorsi, Cervicalis ascendens, Transversalis colli, Trachelo-mastoid, Complexus, Biventer cervicis, Semispinalis dorsi and colli, Multifidus spinae, Rotatores spinae, Interspinales, Supraspinales, Intertransversales, Levatores costarum. 1 See Cunningham, Journ. Anat., vol. xx. p. 238. SACRAL AND COCCYGEAL VERTEBRAE. 155 Sacral and Coccygeal Vertebrae. The Sacral and Coccygeal Vertebrae consist, at an early period of life, of nine separate pieces, Avhich are united in the adult so as to form two bones, five enter- ing into the formation of the sacrum, four into that of the coccyx. Occasionally, the coccyx consists of five bones.1 The Sacrum (sacer, sacred) is a large, triangular bone (Fig. 122), situated at the lower part of the vertebral column, and at the upper and back part of the pelvic Fig. 122.—Sacrum, anterior surface. cavity, where it is inserted like a wedge betAveen the tAvo innominate bones; its upper part or base articulating Avith the last lumbar vertebra;, its apex Avith the coccyx. The sacrum is curved upon itself, and placed very obliquely, its upper extremity projecting forward, and forming, Avith the last lumbar vertebra, a very prominent angle, called the promontory or sacro-vertebral angle; Avhilst its central part is directed backward, so as to give increased capacity to the pelvic cavity. It presents for examination an anterior and posterior surface, tAvo lateral surfaces, a base, an apex, and a central canal. The Anterior Surface is concave from above dowmvard, and slightly so from side to side. In the middle are seen four transverse ridges, indicating the original division of the bone into five separate pieces. The portions of bone intervening betAveen the ridges correspond to the bodies of the vertebrae. The body of the first segment is of large size, and in form resembles that of a lumbar vertebra; the succeeding ones diminish in size from above doAvmvard, are flattened from before backAvard, and curved so as to accommodate themselves to the form of the sacrum, being concave in front, convex behind. At each end of the ridges above mentioned are seen the anterior sacral foramina, analogous to the intervertebral foramina, 1 Sir George Humphry describes this as the usual composition of the coccvx.—On the Skeleton. p. 456. 15(1 THE SKELETON. four in number on each side, someAvhat rounded in form, diminishing in size from above doAvmvard, and directed out- ward and forward; they transmit the anterior branches of the sacral nerves. External to these foramina is the lateral mass, consisting at an early period of life of separate segments; these become blended, in the adult, with the bodies, Avith each other, and Avith the posterior transverse processes. Each lateral mass is traversed by four broad, shallow grooves, which lodge the anterior sacral nerves as they pass outAvard, the grooves being separated by prominent ridges of bone, Avhich give attachment to the slips of the Pyriformis muscle. If a vertical section is made through the centre of the bone (Fig. 123), the bodies are seen to be united at their cir- cumference by bone, a wide interval being left centrally, Avhich, in the recent state, is filled by intervertebral substance. In some bones this union is more complete between the lower segments than betAveen the upper ones. The Posterior Surface (Fig. 124) is convex and much narrower than the anterior. In the middle line are three or four tubercles, which represent the rudimentary spinous processes of the sac- ral vertebrae. Of these tubercles, the first is usually prominent, and perfectly distinct from the rest; the second and third are either separate or united into a tubercular ridge, which diminishes in size from above downward ; the fourth usually, and the fifth always, remaining un- developed. External to the spinous processes on each side are the lamince, broad and Avell marked in the first three pieces; sometimes the fourth, and generally the fifth, being undeveloped: in this situation the loAver end of the sacral canal is exposed, and is liable to be opened in the sloughing of bed-sores. External to the laminae is a linear series of indistinct tubercles representing the articular processes ; the upper pair are large, well developed, and correspond in shape and direction to the superior articulating processes of a lumbar vertebra; the second and third are small; the fourth and fifth (usually blended together) are situated on each side of the sacral canal: they are called the sacral cornua, and articulate with the cornua of the coccyx. External to the articular processes are the four posterior sacral foramina ; they are smaller in size and less regular in form than the anterior, and transmit the posterior branches of the sacral nerves. On the outer side of the posterior sacral foramina is a series of tubercles, the rudiment- ary transverse processes of the sacral vertebras. The first pair of transverse tubercles are large, very distinct, and correspond Avith each superior lateral angle of the bone; the second, small in size, enter into the formation of the sacro-iliac articulation; the third give attachment to the oblique fasciculi of the posterior sacro-iliac ligaments; and the fourth and fifth to the great sacro-sciatic ligaments. The interspace betAveen the spinous and transverse processes on the back of the sacrum presents a Avide, shallow concavity, called the sacral groove: it is continuous above with the vertebral groove, and lodges the origin of the Erector spinae. » Fig. 123.—Vertical section of the sacrum. SACRAL AND COCCYGEAL VERTEBRAE. 157 The Lateral Surface, broad above, becomes narrowed into a thin edge below. Its upper half presents in front a broad, ear-shaped surface for articulation Avith the ilium. This is called the auricular surface, and in the fresh state is coated with fibro-cartilage. It is bounded posteriorly by deep and uneven impressions, for the attachment of the posterior sacro-iliac ligaments. The lower half is thin and sharp, and ends in a prominence, the inferior lateral angle ; the border gives attachment to the greater and lesser sacro-sciatic ligaments, and to some fibres of the Gluteus maximus; beloAv the angle is a deep notch, Avhich is converted into a foramen by the transverse process of the upper piece of the coccyx, and transmits the anterior division of the fifth sacral nerve. The Base of the sacrum, Avhich is broad and expanded, is directed upAvard and forward. In the middle is seen a large oval articular surface, which is connected with the under surface of the body of the last lumbar vertebra by a fibre-carti- laginous disk. It is bounded behind by the large, triangular orifice of the sacral canal. The orifice is formed behind by the laminae and spinous process of the first sacral vertebra: the superior articular processes project from it on each side; they are oval, concave, directed backAvard and inward, like the superior articular processes of a lumbar vertebra; and in front of each articular process is an inter- vertebral notch, Avhich forms the lower half of the last intervertebral foramen. Lastly, on each side of the large oval articular surface is a broad and flat triangular surface of bone, Avhich extends outward, supports the Psoas magnus muscle and lumbo-sacral cord, and is continuous on each side with the iliac fossa. This is called the ala of the sacrum, and gives attachment to a few of the fibres of the Iliacus muscle. The Apex, directed downward and forward, presents a small, oval, concave surface for articulation with the coccyx. The Spinal Canal runs throughout the greater part of the bone; it is large 15S THE SKEL ETON. and triangular in form above, small and flattened, from before backward, below. In this situation its posterior Avail is incomplete, from the non-development of the laminae and spinous processes. It lodges the sacral nerves, and is perforated by the anterior and posterior sacral foramina, through Avhich these pass out. Structure.—It consists of much loose, spongy tissue Avithin, invested externally by a thin layer of compact tissue. Differences in the Sacrum of the Male and Female.—The sacrum in the female is usually wider than in the male ; the loAver half forms a greater angle Avith the upper, the upper half of the bone being nearly straight, the loAver half pre- senting the greatest amount of curvature. The bone is also directed more obliquely backAvard, Avhich increases the size of the pelvic cavity; but the sacro-vertebral angle projects less. In the male the curvature is more evenly distributed over the Avhole length of the bone, and is altogether greater than in the female. Peculiarities of the Sacrum.—This bone, in some cases, consists of six pieces; occasionally, the number is reduced to four. Sometimes the bodies of the first and second segments are not joined or the laminae and spinous processes have not coalesced. Occasionally the upper pair of transverse tubercles are not joined to the rest of the bone on one or both sides ; and, lastly, the sacral canal may be open for nearly the lower half of the bone, in consequence of the imperfect development of the laminae and spinous processes. The sacrum, also, varies considerably with respect to its degree of curvature. From the examination of a large number of skeletons it Avould appear that in one set of cases the anterior surface of this bone Avas nearly straight, the curvature, Avhich Avas very slight, affecting only its loAver end. In another set of eases the bone Avas curved throughout its whole length, but especially toAvard its middle. In a third set the degree of curvature Avas less marked, and affected especially the lower third of the bone. Development (Fig. 125).—The sacrum, formed by the union of five vertebrae, has thirty-five centres of ossification. The bodies of the sacral vertebrae have each three ossific centres: one for the central part, and one for the epiphysial plates on its upper and under surface. Occasionally the primary centres for the bodies of the first and second piece of the sacrum are double. The arch of each sacral vertebra is developed by two centres, one for each lamina. These unite with each other behind, and subsequently join the body. The lateral masses have six additional centres, two for each of the first three vertebrae. These centres make their appearance above and to the outer side of the anterior sacral foramina (Fig. 125), and are developed into separate segments Two epiphysial laminx for each lateral surface.* Fig. 125.—Development of the sacrum. Fig. 126. (Fig. 126); they are subsequently blended with each other, and with the bodies and transverse processes to form the lateral mass. Lastly, each lateral surface of the sacrum is developed by two epiphysial plates (Fig. 127): one for the auricular surface, and one for the remaining part of the thin lateral edge of the bone. THE COCCYX. 159 Cor mi' Period of Development.—At about the eighth or ninth Aveek of foetal life ossi- fication of the central part of the bodies of the first three vertebrae commences, and at a someAvhat later period that of the last two. Between the sixth and eighth months ossification of the laminae takes place; and at about the same period the characteristic osseous tubercles for the first three sacral vertebrae make their appearance. The period at Avhich the arch becomes completed by the junction of the lamiiue Avith the bodies in front and Avith each other behind varies in different segments. The junction betAveen the laminae and the bodies takes place first in the loAver vertebrae as early as the second year, but is not effected in the upper- most until the fifth or sixth year. About the sixteenth year the epiphyses for the upper and under surfaces of the bodies are formed, and betAveen the eighteenth and tAventieth years those for each lateral surface of the sacrum make their appearance. The bodies of the sacral vertebrae are, during early life, separated from each other by intervertebral disks. But about the eighteenth year the two loAvest segments become joined together by ossification extending through the disk. This process gradually extends upAvard until all the segments become united, and the bone is completely formed from the twenty-fifth to the thirtieth year of life. Articulations.—"With four bones: the last lumbar vertebra, coccyx, and the tAvo ossa innominata. Attachment of Muscles.—To eight pairs: in front, the Pyriformis and Coccvg- eus, and a portion of the Iliacus to the base of the bone; behind, the Gluteus maximus, Latissimus dorsi, Multifidus spinae, and Erector spinae, and sometimes the Extensor coccygis. The Coccyx. The Coccyx (xoxxo^, cuckoo), so called from having been compared to a cuc- koo's beak (Fig. 128), is usually formed of four small segments of bone, the most rudimentary parts of the vertebral column. In each of the first three segments may be traced a rudi- mentary body, articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone, Avithout distinct processes. All the segments are destitute of pedicles, laminae, and spinous processes, and, consequently, of intervertebral foramina and spinal canal. The first segment is the largest: it resembles the loAvermost sacral vertebra, and often exists as a separate piece; the last three, diminishing in size from above doAvmvard, are usually blended together so as to form a single bone. The gradual diminution in the size of the pieces gives this bone a triangular form, the base of the triangle joining the end of the sacrum. It presents for examination an anterior and posterior sur- face, tAvo borders, a base, and an apex. The anterior surface is slightly concave, and marked with three transverse grooves, indicating the points of junction of the different pieces. It has attached to it the anterior sacro-coccygeal ligament and Levator ani muscle, and supports the loAver end of the rectum. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface ; and presents on each side a lineal row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. Of these, the supe- rior pair are large, and are called the cornua of the coccyx; they project upward, and articulate Avith the cornua of the sacrum, the junction between these two bones completing the fifth posterior sacral foramen for the transmission of the pos- terior division of the fifth sacral nerve. The lateral borders are thin, and present a Anterior surface. Posterior surface. Fig. 128.—Coccvx. 160 THE SKELETON 1st lumbal Fig. 129.—Lateral view of the spine. series of small eminences, Avhich represent the transverse processes of the coccygeal vertebra?. Of these, the first on each side is the largest, flattened from before backAvard. and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the fifth anterior sacral foramen for the transmission of the anterior division of the fifth sacral nerve ; the others diminish in size from above doAvmvard, and are often Avanting. The borders of the coccyx are narrow, and give attachment on each side to the sacro-sciatic ligaments, to the Coccygeus muscle in front of the ligaments, and to the Gluteus maximus behind them. The base. presents an oval surface for articulation with the sacrum. The apex is rounded, and has attached to it the tendon of the external Sphincter muscle. It is occasionally bifid, and sometimes deflected to one or other side. Development.—The coccyx is developed hy four centres, one for each piece. Occa- sionally one of the first three pieces of this bone is developed by tAvo centres, placed side by side. The ossific nuclei make their ap- pearance in the following order: in the first segment, at birth; in the second piece, at from five to ten years; in the third, from ten to fifteen years; in the fourth, from fif- teen to tAventy years. As age advances these various segments become united in the fol- loAving order: the first two pieces join; then the third and fourth; and, lastly, the bone is completed by the union of the second and third. At a late period of life, especially in females, the coccyx often becomes joined to the end of the sacrum. Articulation.—With the sacrum. Attachment of Muscles.—To four pairs and one single muscle: on either side, the Coccygeus; behind, the Gluteus maximus and Extensor coccygis, when present; at the apex, the Sphincter ani; and in front, the Levator ani. The Spine in General. The Spinal Column, formed by the junc- tion of the vertebrae, is situated in the median line, at the posterior part of the trunk ; its average length is about tAvo feet two or three inches, measuring along the curved anterior surface of the column. Of this length the cervical part measures about five, the dorsal about eleven, the lumbar about seven inches, and the sacrum and coccyx the remainder. The female spine is about one inch less than the male. THE SPINE IN GENERAL. 161 VieAved in front, it presents tAvo pyramids joined together at their bases, the upper one being formed by all the vertebrae from the second cervical to the last lumbar, the lower one by the sacrum and coccyx. When examined more closely, the upper pyramid is seen to be formed of three smaller pyramids. The upper- most of these consists of the six loAver cervical vertebrae, its apex being formed by the axis or second cervical, its base by the first dorsal. The second pyramid, Avhich is inverted, is formed by the four upper dorsal vertebrae, the base being at the first dorsal, the smaller end at the fourth. The third pyramid commences at the fourth dorsal, and gradually increases in size to the fifth lumbar. VieAved laterally (Fig. 129), the spinal column presents several curves, Avhich correspond to the different regions of the column, and are called cervical, dorsal, lumbar, and pelvic. The cervical curve commences at the apex of the odontoid process, and terminates at the middle of the second dorsal vertebra; it is convex in front, and is the least marked of all the curves. The dorsal curve, Avhich is concave forAvard, commences at the middle of the second, and terminates at the middle of the tAvelfth dorsal. Its most prominent point behind corresponds to the spine of the seventh dorsal vertebra. The lumbar curve commences at the middle of the last dorsal vertebra, and terminates at the sacro-vertebral angle. It is convex anteriorly; the convexity of the loAver three vertebrae being much greater than that of the upper ones. The pelvic curve commences at the sacro- vertebral articulation and terminates at the point of the coccyx. It is concave anteriorly. The dorsal and pelvic curves are the primary curves, and begin to be formed at an early period of foetal life, and are due to the shape of the bodies of the vertebrae. The cerArical and lumbar curves are compensatory or secondary, and are developed after birth in order to maintain the erect position. They are due mainly to the shape of the intervertebral disks. The spine has also a slight lateral curvature, the convexity of Avhich is directed toward the right side. This is most probably produced, as Bichat first explained, chiefly by muscular action, most persons using the right arm in prefer- ence to the left, especially in making long-continued efforts, Avhen the body is curved to the right side. In support of this explanation it has been found by Be'clard that in one or tAvo individuals Avho Avere left-handed the lateral curvature Avas directed to the left side. The spinal column presents for examination an anterior, a posterior, and tAvo lateral surfaces; a base, summit, and spinal canal. The anterior surface presents the bodies of the vertebrae separated in the recent state by the intervertebral disks. The bodies are broad in the cervical region, narrow in the upper part of the dorsal, and broadest in the lumbar region. The Avhole of this surface is convex transversely, concave from above downward in the dorsal region, and convex in the same direction in the cervical and lumbar regions. The posterior surface presents in the median line the spinous processes. These are short, horizontal, Avith bifid extremities, in the cervical region. In the dorsal region they are directed obliquely above, assume almost a vertical direction in the middle, and are horizontal beloAv, as are also the spines of the lumbar Aertebrae. They are separated by considerable intervals in the loins, by narrower intervals in the neck, and are closely approximated in the middle of the dorsal region. Occasionally one of these processes deviates a little from the median line—a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the spine. On either side of the spinous processes, extending the whole length of the column, is the vertebral groove formed by the laminae in the cervical and lumbar regions, Avhere it is shalloAv, and by the laminae and transverse processes in the dorsal region, where it is deep and broad. In the recent state these grooves lodge the deep muscles of the back. External to the vertebral grooves are the articular processes, and still more externally the transverse process. In the dorsal region the latter processes stand backward, on n 1(52 THE SKELETON. a plane considerably posterior to the same processes in the cervical and lumbar regions. In the cervical region the transverse processes are placed in front of the articular processes and on the outer side of the pedicles, between the interver- tebral foramina. In the dorsal region they are posterior to the pedicles, interver- tebral foramina, and articular processes. In the lumbar they are placed also in front of the articular processes, but behind the intervertebral foramina. The lateral surfaces are separated from the posterior by the articular processes in the cervical and lumbar regions, and by the transverse processes in the dorsal. These surfaces present in front the sides of the bodies of the vertebra1, marked in the dorsal region by the facets for articulation with the heads of the ribs. More posteriorly are the' intervertebral foramina, formed by the juxtaposition of the intervertebral notches, oval in shape, smallest in the cervical and upper part of the dorsal regions, and gradually increasing in size to the last lumbar. They are situated between the transverse processes in the neck, and in front of them in the back and loins, and transmit the spinal nerves. The base of that portion of the vertebral column formed by the tAventy-four movable vertebra? is formed by the under surface of the body of the fifth lumbar vertebra; and the summit by the upper surface of the atlas. The vertebral or spinal canal follows the different curves of the spine; it is largest in those regions in Avhich the spine enjoys the greatest freedom of move- ment, as in the neck and loins, Avhere it is Avide and triangular; and narroAv and rounded in the back, Avhere motion is more limited. Surface Form.—The only part of the vertebral column which lies closely under the skin, and so directly influences surface form, is the apices of the spinous processes. These are always listinguishabie at the bottom of a median furrow, which, more or less evident, runs down the mesial line of the back from the external occipital protuberance above to the middle of the sacrum below. In the neck the furrow is broad, and terminates below in a conspicuous projec- tion, which is caused by the spinous process of the seventh cervical vertebra (vertebra promi- nens). Above this the spinous process of the sixth cervical vertebra may sometimes be seen; the other cervical spines are sunken, and are not visible, though the spine of the axis can be felt, and generally also the spines of the third, fourth, and fifth cervical vertebrae. In the dorsal region the furrow is shallow, and during stooping disappears, and then the spinous pro- cesses become more or less visible. The markings produced by these spines are small and close together. In the lumbar region the furrow is deep, and the situation of the lumbar spines is frequently indicated by little pits or depressions, especially if the muscles in the loins are well developed and the spine incurved. They are much larger and farther apart than in the dorsal region. In the sacral region the furrow is shallower, presenting a flattened area which terminates below at the most prominent part of the posterior surface of the sacrum, formed by the spinous process of the third sacral vertebra. At the bottom of the furrow may be felt the irregular posterior surface of the bone. Below this, in the deep groove leading to the anus, the coccyx may be felt. The only other portions of the vertebral column which can be felt from the surface are the transverse processes of three of the cervical vertebrae—viz. the first, the sixth, and the seventh. The transverse process of the atlas can be felt as a rounded nodule of bone just below and in front of the apex of the mastoid process, along the anterior border of the sterno-mastoid. The transverse process of the sixth cervical vertebra is of surgical importance. If deep pressure be made in the neck in the course of the carotid artery, opposite the cricoid cartilage, the prominent anterior tubercle of the transverse process of the sixth cervical vertebra can be felt. This has been named Chassaignacs tubercle, and against it the carotid artery may be most conveniently compressed by the finger. The transverse process of the seventh cervical vertebra can also often be felt. Occasionally the anterior root, or costal process, is large and segmented off, forming a cervical rib. Surgical Anatomy.— Occasionally the coalescence of the laminae is not completed, and con- sequently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal membranes (dura mater and arachnoid), and sometimes of the spinal cord itself, takes place, constituting the disease known a,s spina bifida. This disease is most common in the lumbo-sacral region, on account of the fact, previously stated, that the closure of the arches takes place gradually from above downward ; but it may occur in the dorsal or cervical region, or the arches throughout the whole length of the canal may remain unapproximated. In some rare cases, in consequence of the non-coalescence of the two primary centres from which the body is formed, a similar condition may occur in front of the canal, the bodies of the vertebrae being found cleft and the tumor projecting into the thorax, abdomen, or pelvis, between the lateral halves of the bodies affected. The construction of the spinal column of a number of pieces, securely connected together and enjoying only a slight degree of movement between any two individual pieces, though per- THE SKULL. 163 mitting of a very considerable range of movement as a whole, allows a sufficient degree of mobility without any material diminution of strength. The many joints of which the spine is composed, together with the very varied movements to which it is subjected, render it liable to sprains; but so cfosely are the individual vertebras articulated that these sprains are rarely or ever severe, and any amount of violence sufficiently great to produce tearing of the ligaments would tend rather to cause a dislocation or fracture. The further safety of the column and its less liability to injury is provided for by its disposition in curves, instead of in one straight line. For it is an elastic column, and must first bend before it breaks: under these circumstances, being made up of three curves, it represents three columns, and greater force is required to pro- duce bending of a short column than of a longer one that is equal to it in breadth and material. Again, the safety of the column is provided for by the interposition of the intervertebral disk between the bodies of the vertebrae, which act as admirable buffers in counteracting the effects of violent jars or shocks. Fracture-dislocation of the spine may be caused by direct or indirect violence, or by a combination of the two, as when a person, falling from a height, strikes against some prominence and is doubled over it. The fractures from indirect violence are the more com- mon, and here the bodies of the vertebrae are compressed, whilst the arches are torn asunder ; whilst in fractures from direct violence the arches are compressed and the bodies of the ATertebrae separated from each other. It will therefore be seen that in both classes of injury the spinal marrow is the part least likely to be injured, and may escape damage even where there has been considerable lesion of the bony framework. For, as Mr. Jacobson states, "being lodged in the centre of the column, it occupies neutral ground in respect to forces which might cause fracture. For it is a laAv in mechanics that Avhen a beam, as of timber, is exposed to breakage and the force does not exceed the limits of the strength of the material, one division resists compression, another laceration of the particles, while the third, between the two, is in a negative condition."1 Applying this principle to the spine, it will be seen that, whether the fracture^dislocation be pro- duced by direct violence or indirect, one segment, either the anterior or posterior, will be exposed to compression, the other to laceration, and the intermediate part, where the cord is situated, will be in a neutral state. When a fracture-dislocation is produced by indirect violence the dis- placement is almost always the same, the upper segment being driven forward on the lower, so that the cord is compressed between the body of the vertebra below and the arch of the vertebra above. The parts of the spine most liable to be injured are (1) the dorsi-lumbar region, for this part is near the middle of the column, and there is therefore a greater amount of leverage, and more- over the portion above is comparatively fixed, and the vertebrae which form it, though much smaller, have nevertheless to bear almost as great a weight as those below; (2) the cervico-dorsal region, because here the flexible cervical portion of the spine joins the more fixed dorsal region ; and (3) the alto-axoid region, because it enjoys an extensive range of movement, and, being near the skull, is influenced by violence applied to the head. In fracture-dislocation it has been proposed to trephine the spine and remove portions of the laminae and spinous processes. The operation can only be of use when the paralysis is due to the pressure of bone or the effusion of blood, and not to cases, which are by far the most common, Avhere the cord is crushed to a pulp. And even in those cases where the cord is compressed by bone the portion of displaced bone which presses on the cord is generally the body of the vertebra below, and is therefore inaccess- ible to operation. The operative proceeding is one of great severity, involving an extensive and deep wound and great risk of septic meningitis, and, as the advantages to be derived from it are exceedingly problematical and confined to a very few cases, it is not often resorted to.^ Trephin- ing has also been resorted to in some cases of paraplegia due to Pott's disease of the spine. Here the paralysis is due to the pressure of inflammatory products, and where this is new scar- tissue, formed by the organization of granulation tissue, its removal has been attended with a very considerable amount of success. THE SKULL. The Skull, or superior expansion of the vertebral column, has been described as if composed of four vertebrae, the elementary parts of which are specially modified in form and size, and almost immovably connected, for the reception of the brain and special organs of the senses, these vertebrae are the occipital, parietal, frontal, and nasal. Descriptive anatomists, hoAvever, divide the skull into two parts, the Cranium and the Face. The Cranium (xpduoc, a helmet) is composed of eight bones—viz. the occipital, two parietal, frontal, two temporal, sphenoid, and ethmoid. The Face is composed of fourteen bones—viz. the two nasal, two superior maxillary, two lachrymal, two malar, two palate, two inferior turbinated, vomer, and inferior maxillary. The ossiculi auditus, the teeth, and Wormian bones are not included in this enumeration. 1 Holmes's System of Surgery, vol. i. p. 529, 1883. 164 THE SKELETON. Skull, 22 bones < Cranium, 8 bones . { Face, 14 bones . . < Occipital. Two Parietal. Frontal. Tavo Temporal. Sphenoid. Ethmoid. Tavo Nasal. Two Superior Maxillary. Tavo Lachrymal. Two Malar. Tavo Palate. Two Inferior Turbinated. Vomer. Inferior Maxillary. THE CRANIUM. The Occipital Bone. * The Occipital Bone (ob, caput, against the head) is situated at the back part SUPERIOR CONSTRICTOR of Pharynx. fasi/iur it roc. Fig. 130.—Occipital bone. Outer surface. and base of the cranium, is trapezoid in form (Fig. 130), curved upon itself, and presents for examination two surfaces, four borders, and four angles. The external surface is convex. MidAvay betAveen the summit of the bone and the posterior margin of the foramen magnum is a prominent tubercle, the external occipital protuberance, for the attachment of the Ligamentum nuchae; and, descending from it as far as the foramen, a vertical ridge, the external occipital crest. This tubercle and crest vary in prominence in different skulls. Passing outward from the occipital protuberance is a semicircular ridge on each side, the THE CRANIUM. 165 superior curved line. Above this line there is often a second less distinctly marked ridge, called the highest curved line (linea suprema); to it the epicranial aponeurosis is attached. The bone betAveen these two lines is smoother and denser than the rest of the surface. Running parallel with these from the middle of the crest is another semicircular ridge on each side, the inferior curved lines. The surface of the bone above the superior curved lines is rough and porous, and in the recent state is covered by the Occipito-frontalis muscle, while the ridges, as well as the surface of the bone betAveen them, serve for the attachment of numerous muscles. The superior curved line gives attachment internally to the Trapezius, externally to the muscular origin of the Occipito-frontalis, and to the Sterno-cleido-mastoid to the extent shown in Fig. 130; the depressions between the curved lines to the Complexus internally, the Splenius capitis and Obliquus capitis superior exter- nally. The inferior curved line and the depressions below it afford insertion to the Rectus capitis posticus, major and minor. The foramen magnum is a large, oval aperture, its long diameter extending from before backAvard. It transmits the medulla oblongata and its membranes, the spinal accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries,' and the occipito-axial ligaments. Its back part is wide for the transmis- sion of the medulla, and the corresponding margin rough for the attachment of the dura.mater enclosing it; the fore part is narroAver, being encroached upon by the condyles; it has projecting toward it, from beloAv, the odontoid process, and its margins are smooth and bevelled internally to support the medulla oblongata. On each side of the foramen magnum are the condyles, for articulation Avith the atlas ; they are convex, oblong, or reniform in shape, and directed doAvnward and out- ward ; they converge in front, and encroach slightly upon the anterior segment of the foramen. On the inner border of each condyle is a rough tubercle for the attachment of the ligaments (check) which connect this bone with the odontoid process of the axis; whilst external to them is a rough tubercular, prominence, the transverse or jugular process (the representative of the transverse process of a vertebra), channelled in front by a deep notch, which forms part of the jugular foramen or foramen lacerum posterius. The under surface of this process presents an eminence Avhich represents the paramastoid process of some mammals. The eminence is occasionally large, and extends as Ioav as the transverse process of the atlas. This surface affords attachment to the Rectus capitis lateralis muscle and to the lateral occipito-atlantal ligament; its upper or cerebral surface presents a deep groove Avhich lodges part of the lateral sinus, whilst its external surface is marked by a quadrilateral rough facet, covered Avith cartilage in the fresh state, and articulating Avith a similar surface on the petrous portion of the temporal bone. On the outer side of each condyle, near its fore part, is a foramen, the anterior con- dyloid; it is directed doAvmvard, outAvard, and forAvard, and transmits the hypo- glossal nerve, and' occasionally a meningeal branch of the ascending pharyngeal artery. This foramen is sometimes double. Behind each condyle is a fossa,1 some- times perforated at the bottom by a foramen, the posterior condyloid, for the trans- mission of a vein to the lateral sinus. In front of the foramen magnum is a strong quadrilateral plate of bone, the basilar process, Avider behind than in front; its under surface, Avhich is rough, presenting in the median line a tubercular ridge, the pharyngeal spine, for the attachment of the tendinous raphe and Superior constrictor of the pharynx ; and on each side of it rough depressions for the attachment of the Rectus capitis anticus, major and minor. The Internal or Cerebral Surface (Fig. 131) is deeply concave. The posterior or occipital part is divided by a crucial ridge into four fossae. The tAvo superior fossae receive the occipital lobes of the cerebrum, and present slight eminences and depressions corresponding to their convolutions. The two inferior, Avhich receive the hemispheres of the cerebellum, are larger than the former, and com- 1 This fossa presents many variations in size. .It is usually shallow, and the foramen small; occa- sionally wanting on one or both sides. Sometimes both fossa and foramen are large, but confined to one side only; more rarely, the fossa and foramen are very large on both sides. lb() THE SKELETON. paratively smooth ; both are marked by slight grooves for the lodgment of arteries. At the point of meeting of the four divisions of the crucial ridge is an eminence, the internal occipital protuberance. It nearly corresponds to that on the outer surface, and is perforated by one or more large vascular foramina. From this eminence the superior division of the crucial ridge runs upAvard to the superior ano-le of the bone ; it presents a deep groove for the superior longitudinal sinus. the margins of Avhich give attachment to the falx cerebri. The inferior division, the internal occipital crest, runs to the posterior margin of the foramen magnum, Superior angle. Inferior angle. Fig. 131.—Occipital bone. Inner surface on the edge of Avhich it becomes gradually lost; this ridge, which is bifurcated below, serves for the attachment of the falx cerebelli. It is usually marked by a single groove, Avhich commences at the. back part of the foramen" magnum and lodges the occipital sinus. Occasionally the groove is double where tAvo sinuses exist. The transverse grooves pass outAvard to the lateral angles; they are deeply channelled, for the lodgment of the lateral sinuses, their prominent margins afford- ing attachment to the tentorium cerebelli.1 At the point of meeting of these grooves is a depression, the torcular Ilerophili.2 placed a little to one or the other side of the internal occipital protuberance. More anteriorly is the foramen mag- num, and on each side of it, but nearer its anterior than its posterior \ art, the 1 Usually one of the transverse grooves is deeper and broader than the other; occasionally both grooves are of equal depth and breadth, or both equally indistinct. The broader of the two transverse grooves is nearly always continuous Avith the vertical groove for the superior longitudinal sinus. 2 The columns of blood coming in diflerent directions were supposed to he pressed together at this point (torcular, a wine-press). THE CRANIUM. 167 internal openings of the anterior condyloid foramina; the internal openings of the posterior condyloid foramina are a little external and posterior to them, protected by a small arch of bone. At this part of the internal surface there is a very deep groove in Avhich the posterior condyloid foramen, Avhen it exists, has its termina- tion. This groove is continuous, in the complete skull, Avith the transverse groove on the posterior part of the bone, and lodges the end of the same sinus, the lateral. In front of the foramen magnum is the basilar process, presenting a shallow depression, the basilar groove, Avhich slopes from behind, upAvard and forward, and supports the medulla oblongata and part of the pons Varolii, and on each side of the basilar process is a narrow channel, Avhich, Avhen united Avith a similar channel on the petrous portion of the temporal bone, forms a groove which lodges the inferior petrosal sinus. Angles.—The superior angle is received into the interval betAveen the posterior superior angles of the two parietal bones : it corresponds Avith that part of the skull in the foetus Avhich is called the posterior fontanelle. The inferior angle is represented by the square-shaped surface of the basilar process. At an early period of life a layer of cartilage separates this part of the bone from the sphenoid, but in the adult the union betAveen them is osseous. The lateral angles corre- spond to the outer ends of the transverse grooves, and are received into the interval between the posterior inferior angles of the parietal and the mastoid portion of the temporal. Borders.—The superior border extends on each side from the superior to the lateral angle, is deeply serrated for articulation with the parietal bone, and forms, by this union, the lambdoid suture. The inferior border extends from the lateral to the inferior angle; its upper half is rough, and articulates Avith the mastoid por- tion of the temporal, forming the masto-occipital suture ; the inferior half articu- lates with the petrous portion of the temporal, forming the petro-occipital suture; these tAvo portions are separated from one another by the jugular process. In front of this process is a deep notch, which, with a similar one on the petrous por- tion of the temporal, forms the foramen lacerum posterius or jugular foramen. This notch is occasionally subdivided into tAvo parts by a small process of bone, and it generally presents an aperture at its upper part, the internal opening of the posterior condyloid foramen. Structure.—The occipital bone consists of two compact laminae, called the outer and inner tables, having between them the diploic tissue; this bone is espe- cially thick at the ridges, protuberances, condyles, and internal part of the basilar process ; whilst at the bottom of the fossae, especially the inferior, it is thin, semi- transparent, and destitute of diploe. Development. (Fig. 132).—At birth the bone consists of four distinct pai'ts : a tabular or expanded portion, which lies behind the foramen magnum ; two con- dylar parts, which form the sides of the foramen; and a basilar part, which lies in front of the foramen. The number of nuclei for the tabular part vary. As a rule, there are four, but there may be only one (Blandin) or as many as eight (Meckel). They ap- pear about the eighth Aveek of foetal life, and soon unite to form a single piece, Avhich is, however, fissured in the direction indicated in the plate. The basilar and tAvo condyloid por- tions are each developed from a single nucleus, which appears a lit- tle later. The upper portion of the tabular surface—that is to say. the portion above the transverse fissure —is developed from membrane; the rest of the bone is developed from cartilage. At birth the k pieces separate. M-4 for occipital ^ portion. 1 for each condyloid ■, £* portion. =, ——1 for basilar portion. J -i Fig. 132.—Development of occipital bone. By seven centres, 168 THE SKELETON. At about the fourth year the tabular and the two condyloid pieces join, and about the sixth year the bone consists of a single piece. At a later period, between the eighteenth and twenty-fifth years, the occipital and sphenoid become united, form- ing a single bone. .. , Articulations.—With six bones: two parietal, two temporal, sphenoid, and L ''Attachment of Muscles.—To twelve pairs : to the superior curved line are attached the Occipito-frontalis, Trapezius, and Sterno-cleido-mastoid lo the space between the curved lines, the Complexus,1 Splenius capitis, and Obliquus capitis superior; to the inferior curved line, and the space between it and the foramen magnum, the Rectus capitis posticus, major and minor; to the transverse process, the Rectus capitis lateralis ; and to the basilar process, the Rectus capitis anticus, major and minor, and Superior constrictor of the pharynx. The Parietal Bones. The Parietal Bones (paries, a wall) form, by their union, the sides and roof of the skull. Each bone is of an irregular quadrilateral form, and presents for examination two surfaces, four borders, and four angles. Surfaces.—The external surface (Fig. 133) is convex, smooth, and marked about its centre by an eminence called the parietal eminence, which indicates the point Fig. 133.—Left parietal bone. External surface. where ossification commenced. Crossing the middle of the bone in an arched direction are tAvo Avell-marked curved lines or ridges, of which the lower is the more distinct and is termed the temporal ridge; it marks the upper attachment of the temporal muscle and follows a semicircular course across the bone. The upper ridge is less marked, and pursues a similar course across the bone, but about two- 1 To these the Biventer cervicis should be added, if it is regarded as a separate muscle. THE PARIETAL BONES. 169 fifths of an inch above the temporal ridge ; it marks the attachment of the temporal fascia. Above these ridges the surface of the bone is rough and porous, and covered by the aponeurosis of the Occipito-frontalis; betAveen them the bone is smoother and more polished than the rest; beloAv them the bone forms part of the temporal fossa, and affords attachment to the temporal muscle. At the back part of the superior border, close to the sagittal suture, is a small foramen, the parietal foramen, which transmits a vein to the superior longitudinal sinus, and sometimes a small branch of the occipital artery. Its existence is not constant, and its size varies considerably. The internal surface (Fig. 134), concave, presents eminences and depressions for lodging the convolutions of the cerebrum and numerous furrows for the rami- fications of the meningeal arteries; the latter run upward and backward from the Fig. 134.—Left parietal bone. Internal surface. anterior inferior angle and from the central and posterior part of the loAver border of the bone. Along the upper margin is part of a shallow groove, Avhich, when joined to the opposite parietal, forms a channel for the superior longitudinal sinus, the elevated edges of Avhich afford attachment to the falx cerebri. I\ear the groove are seen several depressions, especially in the skulls of old persons; they lodge the Pacchionian bodies. The internal opening of the parietal foramen is also seen when that aperture exists. Borders.—The superior, the longest and thickest, is dentated to articulate Avith its fellow of the opposite side, forming the sagittal suture. The inferior is divided into three parts : of these, the anterior is thin and pointed, bevelled at the expense of the outer surface, and overlapped by the tip of the great Aving of the sphenoid; the middle portion is arched, bevelled at the expense of the outer surface, and overlapped by the squamous portion of the temporal; the posterior portion is thick and serrated for articulation Avith the mastoid portion of the temporal. The anterior border, deeply serrated, is bevelled at the expense of the outer surface above and of the inner below; it articulates with the frontal bone, forming the 170 THE SKELETON. coronal suture. The posterior border, deeply denticulated, articulates Avith the occipital, forming the lambdoid suture. Angles.—The anterior superior angle, thin and pointed, corresponds Avith that portion of the skull Avhich in the betas is membranous and is called the anterior fontanelle. The anterior inferior angle is thin and lengthened, being received in the interval betAveen the great Aving of the sphenoid and the frontal. Its inner surface is marked bv a deep groove, sometimes a canal, for the anterior branch of the middle meningeal artery. The posterior sujwrior angle corresponds Avith the junction of the sagittal and lambdoid sutures. In the foetus this part of the skull is membranous, and is called the posterior fontanelle. The posterior inferior angle articulates Avith the mastoid portion of the temporal bone, and generally presents on its inner surface a broad, shalloAv groove for lodging part of the lateral sinus. Development.—The parietal bone is formed in membrane, being developed by one centre, Avhich corresponds with the parietal eminence, and makes its first appearance about the seventh or eighth Aveek of foetal life. Ossification gradually extends from the centre to the circumference of the bone: the angles are conse- quently the parts last formed, and it is in their situation that the fontanelles exist previous to the completion of the groAvth of the bone. Articulations.—With five bones: the opposite parietal, the occipital, frontal, temporal, and sphenoid. Attachment of Muscles.—One only, the Temporal. The Frontal Bone. The Frontal Bone (frons, the forehead) resembles a cockle-shell in form, and consists of two portions—a vertical or frontal portion situated at the anterior part Nasal I spine. Fig. 135.—Frontal bone. Outer surface. of the cranium, forming the forehead; and a horizontal or orbito-nasal portioi which enters into the formation of the roof of the orbits and nasal fossae. THE FRONTAL BONE. 171 Vertical Portion.—External Surface (Fig. 135).—In the median line, traversing the bone from the upper to the lower part, is occasionally seen a slightly-elevated ridge, and in young subjects a suture, which represents the line of union of the two lateral halves of Avhich the bone consists at an early period of life; in the adult this suture is usually obliterated and the bone forms one piece; traces of the obliterated suture are, however, generally perceptible at the lower part. On either side of this ridge, a little below the centre of the bone, is a rounded eminence, the frontal eminence. These eminences vary in size in different individuals, and are occasionally unsymmetrical in the same subject. They are especially prominent in cases of Avell-marked cerebral development. The \vhole surface of the bone above this part is smooth, and covered by the aponeurosis of the Occipito-frontalis muscle. Below the frontal eminence, and separated from it by a slight groove, is the superciliary ridge, broad internally, where it is continuous Avith the nasal eminence, but less distinct as it arches outAvard. These ridges are caused by the projection outAvard of the frontal sinuses,1 and give attachment to the Orbicularis palpebrarum and Corrugator supercilii. BetAveen the tAvo superciliary ridges is a smooth surface, the glabella or nasal eminence. Beneath the superciliary ridge is the supraorbital arch, a curved and prominent margin, which forms the upper boundary of the orbit, and separates the vertical from the horizontal portion of the bone. The outer part of the arch is sharp and prominent, affording to the eye, in that situation, considerable protection from injury; the inner part is less promi- nent. At the junction of the internal and middle third of this arch is a notch, sometimes converted into foramen by a bony process, and called the supraorbital notch or foramen. It transmits the supraorbital artery, vein, and nerve. A small aperture is seen in the upper part of the notch, which transmits a vein from the diploe to join the supraorbital vein. The supraorbital arch terminates externally in the external angular process and internally in the internal angular process. The external angular process is strong, prominent, and articulates Avith the malar bone; running upward and backAvard from it are tAvo Avell-marked lines, Avhich, commencing together from the external angular process, soon diverge from each other and run in a cur\red direction across the bone. The lower one, the temporal ridge, gives attachment to the Temporal muscle, the upper one to the temporal fascia. Beneath them is a slight concavity that forms the anterior part of the temporal fossa and gives origin to the Temporal muscle. The internal angular processes are less marked than the external, and articulate with the lachrymal bones. BetAveen the internal angular processes is a rough, uneven interval, the nasal notch, Avhich articulates in the middle line Avith the nasal bone, and on either side Avith the nasal process of the superior maxillary bone. From the concavity of this notch projects a process, the nasal process, which extends beneath the nasal bones and nasal processes of the superior maxillary bones and supports the bridge of the nose. On the under surface of this is a long pointed process, the nasal spine, and on either side a small grooved surface enters into the formation of the roof of the nasal fossa. The nasal spine forms part of the septum of the nose, articulating in front Avith the nasal bones and behind with the perpendicular plate of the ethmoid. Internal Surface (Fig. 13b').—Along the middle line is a \rertical groove, the edges of Avhich unite beloAv to form a ridge, the frontal crest; the groove lodges the superior longitudinal sinus, Avhilst its margins afford attachment to the falx cerebri. The crest terminates beloAv at a small notch which is converted into a foramen by articulation Avith the ethmoid. It is called the foramen ccecum, and varies in size in different subjects: it is sometimes partially or completely impervious, lodges a process of the falx cerebri, and Avhen open transmits a vein 1 Some confusion is occasioned to students commencing the study of anatomy by the name "sinuses" having been given to two perfectly different kinds of spaces connected with the skull. It may be as well, therefore, to state here, at the outset, that the "sinuses" in the interior of the cranium which produce the grooves on the inner surface of the bones are Arenous channels along which the blood runs in its passage back from the brain, Avhile the "sinuses" external to the cranial cavitv (the frontal, sphenoidal, ethmoidal, and maxillary) are hollow spaces in the bones themselves which communicate with the nostrils, and contain air. 172 THE SKEL E T<) X, from the lining membrane of the nose to the superior longitudinal smus. On either side of the irroove the bone is deeply concave, presenting eminences and depressions for the convolutions of the brain, and numerous small furrows for lod