A MANUAL OF Normal Histology AND Organography BY CHARLES HILL, PH.D., M.D. 1 |U PROFESSOR OF HISTOLOGY AND EMBRYOLOGY, CHICAGO VETERINARY COLLEGE ; FORMERLY ASSISTANT PROFESSOR OF HISTOLOGY AND EM- BRYOLOGY AT THE NORTHWESTERN UNIVERSITY MEDICAL SCHOOL, CHICAGO Third Edition, Thoroughly Revised PHILADELPHIA AND LONDON W. B. SAUNDERS COMPANY 19 J 4 Copyright, 1906, by W. B. Saunders Company. Revised, reprinted, and recopyrighted January, 1909. Reprinted September, 1910. Revised, reprinted, and recopyrighted July, 1914 Copyright, 1914, by W. B. Saunders Company PRINTED IN AMERICA PRESS OF W. B. SAUNDERS COMPANY PHILADELPHIA PREFACE TO THIRD EDITION. In the present edition valuable suggestions were tendered the author by those instructors who have used the text in their classes, and for these sug- gestions grateful acknowledgment is here recorded. Each chapter has been carefully revised, and wher- ever necessary the topics have been elaborated to bring them in accord with the most recent advances in this particular science. The most significant changes will be observed in the topics dealing with Heredity and Sex, Glands, Blood, and Eymph. The new text on the stomach in ruminants and that on the hoof of the horse present such interest- ing histological structures as to make unnecessary any further explanation of their appearance in this edition. The author is again grateful for the continued generous reception accorded this volume, and ac- knowledges his appreciation of many favors at the hands of the publishers. Charles Hill. Chicago, III., July, 1914. 9 PREFACE. This manual is written in the interest of element- ary students. The fundamental facts in histology have therefore been presented in as clear and concise a manner as possible, and theories advanced only to simplify the facts and aid the memory in their retention. The figures have been selected with considerable care and are intended to illus- trate the salient points of the text. They are to be studied as critically as the text, and to further facilitate such a study the descriptive terms are placed on the figures rather than in foot-notes. The oral cavity deserves more attention than is usually given this subject. Neglect of proper care of teeth is a common failing, and the cause may be traced directly to a lack of knowledge of their structure and function. This chapter has therefore been enlarged. The author is greatly indebted to Professor Frederick B. Noyes, of the Northwestern University Dental School, for con- tributing most excellent figures on this subject. His critical essays form the basis for the descriptive part of this chapter. The author believes most thoroughly in the laboratory method of study. He believes, too, that the laboratory work should precede the class- 11 12 PREFACE. room work, for which this manual is * written. Laboratory technique, however, is so extensive a subject that a laboratory text, or the teacher's personal outlines, should be used for this particular work. In conformity with this view, only the funda- mental principles of laboratory technique are out- lined in the text. Lastly, the subjects treated have been made funda- mental and brief, that the teacher in charge may supplement the chapters by collateral work as may fit the particular course offered. It is therefore a basis on which the instructor may build and com- plete his ideal elementary course in histology. Charles Hill. CONTENTS. Page. Introduction 17 Preparation of Material 17 CHAPTER I. Development 26 The Cell 37 CHAPTER II. Tissues 51 Epithelial Tissue 51 Supporting Tissue 66 Connective Tissue 68 Cartilage 76 Bone 79 Muscular Tissue 87 Nervous Tissue 96 CHAPTER HI. Circulatory System, Blood, Marrow, and Lymphatic Organs i io Heart no Arteries and Veins in Blood 118 Marrow 123 Lymphatic System 127 Thymus Gland 131 Spleen 133 CHAPTER IV Digestive System 138 Mouth 138 Teeth 145 Tongue 174 Pharynx 182 Esophagus 184 Stomach 186 Small Intestine 196 Large Intestine 202 13 14 CONTENTS. Page. CHAPTER V. Digestive Glands 209 Salivary Glands 209 Pancreas 214 Liver 218 CHAPTER VI. Organs of Respiration 233 Larynx 233 Thyroid Gland 237 Parathyroids 240 Trachea and Bronchi 241 Lung 244 CHAPTER VIL The Urinary Organs 255 Suprarenal Glands 255 Kidneys 259 Ureters 271 Urinary Bladder 273 CHAPTER VIII. Reproductive Organs in Male 277 Testicles 277 Penis 290 Prostate Gland 296 CHAPTER IX. Reproductive Organs in the Female 299 Ovaries 299 Fallopian Tubes 311 Uterus 3r5 Pregnancy 325 Mammary Gland 330 CHAPTER X. The Skin 335 Hairs 341 Nails 347 Glands of skin 354 CONTENTS. 15 Page. CHAPTER XI. Peripheral Nerve Terminations 359 Motor Nerve Endings 359 Sensory Nerve Endings 361 CHAPTER XII. Spinal Cord 369 CHAPTER XIII. The Brain 382 Medulla 384 Summary of Tracts, their Origin and Terminations 392 Pons 392 Cerebellum 396 Cerebral Cortex 401 Neuroglia 404 Blood-vessels of Central Nervous System 407 CHAPTER XIV. The Eye 409 Tunica Externa 412 Tunica Media 416 Tunica Interna 419 Refracting Media 426 Blood-vessels 428 CHAPTER XV. Organ of Hearing 435 Development of Labyrinth 449 CHAPTER XVI. Olfactory Organ 451 CHAPTER XVII. Laboratory Directions 454 Preparation of Elastic Fibers 456 Standard Fixing Solutions 462 Standard Stains 465 Index 469 A MANUAL OF NORMAL HISTOLOGY AND ORGANOGRAPHY. INTRODUCTION. I. Spreads.-Thin spreads or smears are made upon cover glasses or on glass slides. The specimens are then studied, stained or unstained, but always in some liquid medium. They may be fixed and mounted permanently by treating the preparations just as if they were sections. Blood, marrow, nerve cells from brain or cord, and scrapings from organs, as the liver, may be prepared in this way. II. Teasing.-Muscle, tendon and nerve fibers are easily prepared in this way. The teasing, or spread- ing, may be done in water and glycerin, or small pieces may be dehydrated with alcohol and then teased in oil, or even in balsam, thus making a per- manent mount. Alcohol and oil harden the tissues, and satisfactory teasing is therefore more difficult. PREPARATION OF MATERIAL. 17 18 NORMAL HISTOLOGY AND ORGANOGRAPHY. III. Dissociation or Maceration of Tissue Ele- ments- i. Alcohol, 25 per cent.; time, twenty-four or forty-eight hours. 2. Strong acids, as hydrochloric or nitric; time, twenty-four hours. 3. Caustic potash, 25 per cent.; time, ten to thirty minutes. To obtain columnar and goblet cells of the intestine, remove several inches of the colon, clean carefully by passing water through it, and then distend the piece with 25 per cent, alcohol, ligating both ends. Next day open the bowel and make light scrapings from the mucous surface and place these in a vial containing equal parts of alcohol (50 per cent.) and glycerin. Shake the vial and the cells will dis- seminate throughout the fluid. The 25 per cent, alcohol dissolves the cement that holds these epi- thelial cells together. If desired, a little stain may be added to the glycerin preparation. The epithelium of the bladder may be obtained in the same manner, by distending the organ with 25 per cent, alcohol; also, the ciliated cells of the trachea, although in this case no distention is possible. All these cells come away very easily, and the scraping must be carefully done. Tubules of the kidney are readily obtained by treating small pieces with acid. In twenty-four hours, remove the pieces to equal parts of alcohol and glycerin, and shake. A drop of this will show all forms of tubules and glomeruli. The former are practically equivalent to epithelial casts, clinically so important in urinary analysis. PREPARATION OF MATERIAL. 19 The caustic potash reaction is more rapid. Pieces of tissue may be treated with this on the glass slide and examined in the fluid. Care must be observed that the alkali does not get on the lens of the micro- scope. IV. To Prepare Tissue for Sectioning in Celloidin or Paraffin. i. Fixing and Hardening. - Fixing consists in rapidly killing the cell and preserving its constitu- ents, nucleus and cytoplasm, before disintegration can take place. Most fixing agents coagulate the protoplasm and cell contents. (a) Heat.-Cover-glass preparations may be fixed by heating them in an oven or over a gas flame to ioo° or even 1500 C. (6) Fluids. (1) Acids-osmic, 1%; chromic, 1%; ni- tric, 10%; etc. (2) Salts-mercuric chloride saturated, potassium bichromate, 3%; etc. (3) Alcohol, 95%, or absolute. (4) Formalin, 5%. Acids and salts may be used separately as above, but as a rule different combinations are used, formulae of which are given on another page. (c) Precautions. (1) Fix living tissues, if possible. (2) Fix small pieces, so that fluids may readily penetrate. (3) Heat hastens the penetration. (4) Change as often as the fluid becomes cloudy. 20 NORMAL HISTOLOGY AND ORGANOGRAPHY. (5) Use a large quanitity of fluid (50 to 100 times the volume of the tissue). 2. Washing. (a) Water.-If there is a chemical change between the fixing agent and the tissue, use water. This is most frequently the case. The specimens should be very thoroughly washed, preferably in running water, for twenty-four hours or more. (6) Alcohol.-When alcohol is indicated, use the grades 50%, 70%, 95%, and leave in 80%. When- ever picric acid forms a part of the fixing agent, alcohol wash must be used. 3. Dehydrating. (a) We dehydrate to preserve the tissue from action of bacteria. (6) In order that imbedding fluids, which do not mix with water, may penetrate the tissue. Alcohol, the grades ending with absolute alcohol, is always the agent used. 4. Imbedding with Celloidin, Evaporation Method. (a) A bsolute A Icohol and Ether, Equal Parts.-After thorough dehydration in absolute alcohol, the tissue is transferred to absolute alcohol and ether, equal parts, where it is left for twenty-four hours. (6) Thin celloidin, 4%, made by dissolving cel- loidin shreds in equal parts of absolute alcohol and ether. The tissue may be left any length of time in thin celloidin, the longer the better. (c) Thick celloidin, 10%; time, twenty-four hours or longer. 5. Mounting on Block and Evaporation of Ether. (a) Cover surface, of perfectly dry block, with thin celloidin. PREPARATION OF MATERIAL. 21 (b) Remove the tissue from thick celloidin and place upon block, in the proper position for cutting. This is called orienting. A piece like a nerve may have to be supported with needles, and these re- moved later. (c) Add thick celloidin, from time to time, and open any air bubble that may appear. Leave the speci- men in air until the ether has evaporated so that the celloidin does not feel sticky to the touch. The usual time will be ten to twenty minutes. W) Transfer to Chloroform Vapor.-Pour a little chloroform over the bottom of a dish. Set the blocks in this so that the liquid does not reach the tissue. Cover tightly and leave for thirty minutes. (e) Transfer to chloroform liquid by immersing the tissue. Time, thirty minutes. (/) Transfer to 80% alcohol, where blocks may be left permanently. 6. Imbedding with Paraffin or Fusion Method. (a) Intermediate Stage.-The tissue is taken out of absolute alcohol, where it has been thoroughly dehydrated, and is then treated with some fluid that is miscible on the one hand with absolute alcohol, and on the other with paraffin. Liquids used are- (i) Chloroform. (2) Cedar-wood oil. (3) Turpentine. (4) Xylol. Tissues left in oils become brittle. From one to two hours are usually sufficient, depending upon the size of the piece to be imbedded. Chloroform will harden the tissue to a less degree than the other fluids. 22 NORMAL HISTOLOGY AND ORGANOGRAPHY. (6) Melted Paraffin.-The melting-point of paraf- fin should vary according to the room temperature where the sections will be cut. The following table gives the relation of melting-point of paraffin to this temperature: Paraffin melting-point. Room temperature. 45° C . ... 15° to 17° C. or 60° to 65° F. 48° C 22° C. or 70° F. 55° C . . . . 24° C. or 75° F. Tissues are left in melted paraffin from two to six hours. (c) Solidification of paraffin may be accomplished by means of- (i) Watch glasses. (2) Metallic frames. (3) Paper trays. (4) Tea-lead trays. The paraffin is poured into these trays, and the tissue quickly transferred to it. The piece is then oriented, and as soon as the paraffin has cooled enough to form a crust, the whole block is placed in cold water, where the paraffin is quickly cooled so as to avoid crystallization. The block is then ready to be cut in sections. A. Advantages of Celloidin Imbedding. 1. No heat is necessary. 2. Large sections may be cut, because penetration is more complete than is the case with paraffin. 3. Unnecessary to remove celloidin to stain; sections are therefore easily handled. PREPARATION OF MATERIAL. 23 B. Disadvantages oj Celloidin Sections. i. Slow process-at least three days. 2. No thin sections. 3. Celloidin may take the stain, particu- larly with saffranin. 4. Serial sections difficult to make. 5. More expensive. C. Advantages of Paraffin Imbedding. 1. Accommodates very small objects. 2. Thinner sections may be cut. 3. Rapid process. 4. Cheaper than celloidin method. D. Disadvantages of Paraffin Imbedding. 1. Must use heat, which is injurious to tissues. 2. Must remove paraffin to stain sections, and the latter therefore tear easily. 3. Proper room temperature necessary when sections are cut, in order to conform to melting-point of paraf- fin. 7. Cutting Sections.-Use the whole edge of the knife in cutting celloidin sections, and keep the knife wet with 70% alcohol. When cutting paraf- fin sections, the knife is placed at right angle to the block. Always trim away superfluous paraffin. 8. Staining celloidin sections. 1. Alcohol, 95%. 2. Water. 3. Hematoxylin, ten minutes. 24 NORMAL HISTOLOGY AND ORGANOGRAPHY. 4- Water. 5. Acid alcohol, HC1 0.5 to 1%; leave the sections in this until all stain is washed out of the celloidin. 6. Water. 7. Eosin, 0.5% solution, one to three minutes. 8. Alcohol, 35%. 9. Alcohol, 95%. 10. Xylol creosote (beechwood creosote, 20 parts; xylol, 80 parts). 11. Mount in Canada balsam and cover. The sections must become perfectly transparent in the xylol creosote. If they are cloudy or milky, water is present; and the sections must be returned to alcohol, 95%, and the process repeated. Sections that curl should be flattened out when lifted out of 95% alcohol, because in this the sections are soft. In xylol or in water the sections are hard. 9. Staining Paraffin Sections.-Since the paraffin has to be removed the sections first have to be fixed to the glass slide or cover glass. (1) Spread fixative on slide. Albumin fixative consists of egg albumin and glycerin, equal parts. A very thin spread is all that is necessary. Schaellin- baum fixative consists of clove oil 4 parts and thin celloidin 1 part. A thicker spread of this is used. (2) Place section upon slide and heat gently. (3) Xylol or turpentine to remove the paraffin. (4) Absolute alcohol to remove the oil. (5) Alcohol, 95%. Stain on the slide, or immerse the whole slide in PREPARATION OF MATERIAL. 25 the stain, following directions as for celloidin sec- tions. Stain in bulk before imbedding in paraffin when- ever this is possible, as then the sections may be mounted from xylol directly into balsam. An excellant way to get sections smooth is to float them on warm water-not so warm as to melt the paraffin -and then lift them out upon the glass slide. Decant surplus water and put away for twenty-four hours to dry. Next day remove paraffin with xylol and stain according to above directions. Review of Preparing Tissues. i. Fixing and hardening 2. Washing. 3. Dehydrating. 4. Imbedding in celloidin. 5. Mounting on block and evaporation of ether. 6. Imbedding in paraffin. 7. Cutting sections. 8. Staining celloidin sections. 9. Staining paraffin sections. CHAPTER I. DEVELOPMENT. The human body is composed of related structural units that may be grouped in a series of gradually increasing complexity. The simplest structural unit is the cell, which is defined as a spacially limited mass of protoplasm capable under certain conditions of assimilation, growth, and reproduction. It is a microscopic unit and forms the physical basis of life. The next grade of units is a tissue, which consists of a complex of similarly differentiated cells and their derivatives. Embryonic tissues are mostly cellular, while in some tissues of the adult body, such as bone and cartilage, the cell products predominate. The next higher grade of units is an organ, which struc- turally consists of a complex of tissues forming a body with a definite internal structure and external form. Lastly, the highest structural unit is a system, such as the nervous system, digestive system, respi- ratory system, a series of which, collectively, make up the human body. Histology is the branch of science that treats of cells and their derivatives. These cells, in the adult, are modified according to their intrinsic qualities, en- vironment, function, and varied experiences, which enable us to classify them and ultimately place them in a few elementary groups. The ovum, or starting-point of every individual, is a cell. Human embryology comprises its intra- 26 development. 27 uterine development. Ontogeny is a broader term, which includes not only embryology, but the develop- mental history of an individual up to old age or the senile condition. There is another form of develop- ment, much slower, but just as certain as ontogeny. This affects not only the individual, but, collectively, every member of the animal group. In the study of races there is ample evidence that structural changes Fig. I.--Formation of the polar bodies in the ova of Asterias fa- cialis (Hertwig): ps, polar spindle; pb', first polar body; pb", second polar body; n, nucleus returning to condition of rest. have slowly but gradually taken place. This broader developmental history, or history of a race, is known as phylogeny. It is closely interwoven with the ontogenetic development, so much so, that the latter in large part repeats the former, or one's phylogenetic history is repeated in the ontogeny. In development, therefore, the phylogenetic or intrinsic qualities of a cell are important factors. These factors constitute heredity. There is further 28 NORMAL HISTOLOGY AND ORGANOGRAPHY evidence that these factors are lodged in the chro- matin of the cell nucleus. Environment is the other great factor that brings about a structural modification. It is between environment on the one hand, and heredity on the other, that a specialization and differentiation of cells, tissues, and organs is produced. A cell is a spacially limited mass of protoplasm which, under certain conditions, will assimilate, grow, and reproduce itself. A tissue is a complex of simi- larly differentiated cells and their derivatives. An organ is a complex of tissues, forming a body with a definite internal structure and external form. Fig. 2.-Portions of the ova of Asterias glacialis, showing the ap- proach and fusion of the spermatozoon with the ovum (Hertwig): a, fertilizing male element; b, elevation of protoplasm of egg; b', b", stages of fusion of the head of the spermatozoon with the ovum. Ovulation and Maturation.-The ova develop in the ovaries and are differentiated very early during embryonic life. The estimated number of ova in each ovary is 35,000. It is a remarkable phenomenon that for many years these units show no attempt at development or cell division. At the age of puberty one or more of these cells pass periodically from the ovaries, approximately every twenty-eight days in the DEVELOPMENT. 29 non-pregnant woman. This process is known as ovulation, and continues up to the time of the meno- pause, which appears generally at the age of forty-five. As soon as the ovum is liberated from the ovary, a mitotic divis- ion of the nucleus takes place, and the ovum extrudes or pro- duces what is called the first polar body. This is a form of bud- ding, the polar body receiving one-half the original nucleus of the ovum. Without delay, a second division of the nucleus in the ovum takes place, and a second polar body is produced. This is also an equal division of the nucleus, but this time there is a reduction of one-half the number of chro- mosomes, and may be promS. Male Pronucleus. Female pronucleus. Segmen- tation nucleus. Fig. 3.-A, fertilized ovum of echinus (Hertwig): the male and the female pronucleus are approaching; in B they have almost fused; C, ovum of echinus after completion of fertilization (Hertwig). 30 NORMAL, HISTOLOGY AND ORGANOGRAPHY. called a reduction mitosis, as distinguished from all preceding and all succeeding divisions, which are called somatic mitosis. The significance of this re- duction has led to many theories. During the process the nucleus loses its membrane, is much re- duced in size, and is now known as the female pro- nucleus. All these preliminary changes are known as maturation of the ovum. Without fertilization, further development of the ovum does not seem possi- ble in higher forms, and the cell is invariably lost. Fertilization.-By this is meant the union of a spermatozoon with the ovum, or, more technically, the union of a male and a female pronucleus. This Fig. 4.- Diagram of the division of the frog's egg (Hertwig)'. A, stage of the first division. B, stage of the third division. The four segments of the second stage of division are beginning to be divi- ded by an equatorial furrow into eight segments; p, pigmented surface of the egg at the animal pole; pr, the part of the egg which is richer in protoplasm; d, the part which is richer in deutoplasm; sp, nuclear spindle. union takes place in the upper part of the oviduct. Maturation always precedes fertilization. If a spermatozoon enters the ovum before the polar bodies are extruded, the spermatozoon remains inert within the cell until maturation is completed. The ovum, thus reinforced, enters upon an aggressive development. 31 growth, a phenomenon quite in contrast with its preceding history. Segmentation or Cleavage.-Following fertilization -Minimal bole. 1/eye to. ti ve jjole. Fig. 5.- Cleavage in egg of frog, 1 to 16 cell stage. Fig. 6.- Blastula of triton taeniatus: jh, segmentation cavity; rz, mar- ginal zone; dz, cells with abundant yolk (Hertwig). the ovum multiplies rapidly by mitosis. The union of male and female nuclei restores the reduced num- ber of chromosomes, which remain constant and even 32 NORMAL HISTOLOGY AND ORGANOGRAPHY. in number for every succeeding division. By re- peated divisions, a spherical mass of cells is produced, known as the morula stage. Blastula.-The spherical mass quickly develops into a hollow sphere, lined by a single layer of cells, and is then a blastula. The cavity of the blastula is the segmentation cavity. Gastrula.-A more vigorous growth seems to take place at one point of the blastula, producing lateral pressure and an invagination at that place so as to form a two-layered cup-like structure-in Segmentation cavity. Ectoderm. Entoderm. Ceelenter on. Blastula. Blastopore gaslrula. Fig. 7.-Sections through a blastula and a gastrula of amphioxus some eggs a blastoderm-known as the gastrula. The gastrulae vary considerably according to the different forms of cleavage. It is an established fact that all metazoa pass through the morula, blastula, and gastrula stages, respectively, in the course of their development. The cup-like cavity of the gastrula is known as the archenieron or coelenteron, and is destined to develop into the alimentary canal. The pore or external opening of the coelenteron is called the blastopore. The gastrula has two layers of cells: an outer, the PLATE I. i, 2, 3, Diagrams illustrating the segmentation of the mammalian ovum (Allen Thomson, after von Beneden). 4, Diagram illustrating the relation of the primary layers of the blastoderm, the segmentation- cavity of this stage corresponding with the archenteron of amphioxus (Bonnet). ELATE 1. Outer cell. Outer cells Zona pellucida Outer cell- f mass. Polar bodies ' Inner cell- mass. inner cell.' Polar bodies. Inner cell _ Outer cells. - Inner cells. Inner cells. Outer cells. Inner cells Segmentation cavity- Inner cells. Outer cells. Thickened "ectoderm. .Ectoderm. Remains of outer cell-mass. {Cells of Rauber.) Ecto- derm. Entoderm. Segmentation cavity. Entoderm. Outer cells. Zona ' pellucida. DEVELOPMENT. 33 ectoderm, and an inner, the entoderm. The cells of the entoderm are much larger than the cells of the ectoderm and there is thus a structural difference. In cleavage that results in a two-layered blastoderm the term hypoderm is used, which is thus morpho- logically equivalent to the entoderm,. The two-layered gastrula is rapidly invaded by a third layer of cells, the mesoderm, which develops between the first two layers and ultimately fills that Fig. 8.- Sagittal section through an egg of triton (after the end of gastrulation): ak, outer germ-layer; ik, inner germ-layer; dz, yolk- cells; dl and vl, dorsal and ventral lips of the coelenteron; ud, coelen- teron; d, vitelline plug; mk, middle germ-layer (Hertwig). cavity. This cavity, which is the segmentation cavity of the blastula, permanently disappears. The origin of the mesoderm has long been a con- tested question. The favored theory seems to be that for higher forms, at least, it develops from the hypoderm. The mesoderm, although at first a solid mass of cells, is an invaginated fold in which a cavity soon appears, having an inner layer of cells that affiliates closely 34 NORMAL HISTOLOGY AND ORGANOGRAPHY. with the hypoderm cells, and an outer layer that ap- plies itself to the ectoderm. The hypoderm with its mesoderm layer is known as the splanchno pleure, while the ectoderm and its mesoderm is the so- Neural groove. Somite. Somatopleure. Splanchno- pleure. Entoderm, Notocord. Fig. 9.- Transverse section of chick embryo 22 hours old. matopleure. The new cavity thus produced is the coelom, or body cavity, and is destined to become the pleural and peritoneal cavities. The mesoderm on Axial zone. f Neural canal. Lateral zone. Somite. . Cavity ■within somite. Lateral plates for body- walls. Parietal mesoderm. Lateral plates for gut-tract. Pleuro- peritoneal cavity. \Chorda. .Gut entoderm. Primitive aortce. Middle plate. Fig. 10.- Transverse section of a sheep embryo, 17J days (Bonnet). Vitelline vein. each side of the neural canal becomes symmetrically blocked by means of a longitudinal fold and many transverse folds; thus many segments or joints are DEVELOPMENT. 35 produced, known as myotomes or mesoblastic somites. From these develop bone, voluntary muscle, and the dermis of the skin. While these progressive changes are going on in the mesoderm, a longitudinal dorsal groove develops in the ectoderm. By a median fusion of the margins of the groove, it is transformed into a longitudinal canal, the neural canal, which develops into the brain and spinal cord. Fig. ii.-Rabbit embryo of the ninth day, seen from the dorsal side (after Koiliker). The stem-zone (stz) and the parietal zone (pz) are to be distinguished. In the former 8 pairs of primitive segments have been established at the side of the chorda and neural tube; ap, area pellucida; rf, medullary groove; vh, fore-brain; ab, eye-vesicle; mh, mid-brain; hh, hind-brain; uw, primitive segment; stz, stem-zone; pz, parietal zone; h, heart; ph, pericardial part of the body cavity; vd, margin of the entrance to the head-gut (y orders Darmpforte), seen through the overlying structures; a), amniotic fold ; vo, vena ompha- lomesenterica. This brief embryonic growth has been productive in specialization and differentiation of cells. In no case will the cells of one germ layer reproduce, re- place, or function for the cells of any of the other layers. As derivatives of these three germ layers we 36 NORMAL HISTOLOGY AND ORGANOGRAPHY. are able to give the following table (Minot, "Em- bryology," 1903)- A. Ectoderm. i. Epidermis. (a) epidermal appen- dages. (b) lens of eye. 2. Epithelium of (a) cornea. (b) olfactory cham- ber. (c) auditory organ. (d) mouth (oral glands), (enamel organ), (hypophysis). (e) anus. (/■) chorion (fetal placenta). (.g) amnion. 3. Nervous system. (a) brain (optic nerve), (retina). (i) spinal cord. (c) ganglia. (d) neuraxons. B. Mesoderm. i. Mesothelium. (a) epithelium of per- itoneum, pericar- dium, pleura, uro- genital organs. (b) striated muscles. 2. Mesenchyma. (a) connective tissue, smooth muscle, pseudo - endothe- lium, fat-cells, pigment cells. (b) blood. (c) blood-vessels. (d) lymphatics. (^) spleen (/) supporting tis- sues, cartilage, bone. (.g) marrow. C. Entoderm. i. Notochord. 2. Epithelium of (a) digestive tract, esophagus, stom- ach, liver, pan- creas, small intes- tine, yolk-sack, large intestine, cecum, vermix, rectum, allantois (bladder). (i) pharynx, Eusta- chian tube, ton- sils, thymus, para- thyroids, thyroid. (c) respiratory tract, larynx, trachea, lungs. Vacuoles. Chromatin network. Spongioplasm. Linin network. Nuclear fluid. Hyaloplasm. Nuclear membrane. Nucleolus. Chromatin net-knot. Cell-membrane. Centrosome. Centrosphere. Exoplasm. Foreign inclosures. Metaplasm. Fig. 12.-Diagram of a cell (Bohm, Davidoff and Huber). DEVELOPMENT. 37 THE CELL. In 1838 Schleiden demonstrated a cellular basis for plants, and according to his conception these cells were minute compartments filled with a fluid sub- stance in each of which floated a nucleus. The fol- lowing year, 1839, Schwann showed that the animal body was likewise built up of cells resembling those described by Schleiden in plants. These observa- tions placed animals and plants on a common struc- tural basis and established the cell theory, now re- garded as one of the great biological discoveries of the eighteenth century. Von Mohl in 1846 recog- nized in these cells a viscid, semifluid, granular sub- stance which he named protoplasm. Meanwhile extensive observations by other scientists demon- strated the existence of cells without cell walls, all of which prepared the way for Max Schultze, who in 1861 showed conclusively the identity of protoplasm in all life, establishing the protoplasm theory, another great biological discovery of the eighteenth century. The conception of a cell, as postulated by Schleiden and Schwann, thus became modified, so that today this biological term stands for a nucleated mass of protoplasm which under certain conditions is capable of assimilation, growth, and reproduction. In some cells, as certain bacteria, no nucleus has been found; however, in animal tissues as a rule, the nucleus is con- stantly present and forms an essential part of the cell. Whenever the nucleus is lost or destroyed, the cell dies. Protoplasm.-Wherever we find protoplasm we find life, and wherever we find life we find protoplasm. Protoplasm is not life, but all agree it is the physical basis of life. Every particle of protoplasm has its 38 NORMAL HISTOLOGY AND ORGANOGRAPHY. origin in some antecedent protoplasm, and so on, in an unbroken series, all life is traced back to the earli- est primitive form of protoplasm. This protoplasm is a viscid, transparent, jelly-like substance. It is not a substance of uniform physical and chemical proper- ties, but a mixture of many organic compounds which in many ways resemble the proteid bodies or the albu- mins. It is insoluble in water, but absorbs water in variable quantities. The protoplasm of dry seeds may contain but three or four per cent, of water, while in parenchymatous or young growing tissues we may find ninety-five per cent, of water. The phenomenon of motion is common to all protoplasm. In plant protoplasm a streaming process is manifest, which shows considerable regularity as to the direction of the current within the cell. This motion, as well as physiological activities, is greatly modified by change in temperature, and its activities are also very sen- sitive to change in intensity of light and even to the different colors of light as well as to the actinic rays. It is therefore irritable in the highest degree. Cytoplasm is the name given to the protoplasm of the cell body or that which surrounds the nucleus. The cytoplasm exhibits (i) a fine reticulum of anas- tomosing or interlacing threads or plates of vary- ing complexity called spongioplasm or fibrillar mass. These threads are probably composed of small par- ticles or granules, named microsomes, that are in close touch with each other and arranged in rows. The other constituent of cytoplasm is (2) a fluid sub- stance lying between the meshes of the spongio- plastic reticulum, and has been called hyaloplasm, paraplasm, or cytolymph. Recent observations in- DEVELOPMENT. 39 dicate that the microsomes are primarily derived from the nucleus and constitute the more important vital parts of the cell. In some cells the microsomes are so placed as to give a foam-like structure to the cytoplasm rather than a reticular appearance. Again, the cytoplasm of certain cells has a homogeneous watery appearance devoid of any definite structure. There are therefore three theories as to the structure of protoplasm: i. That it is a fluid homogeneous substance. 2. That it consists of minute spherical globules, like an emulsion. 3. That it is a mass of interlacing fibrils, forming a complex reticulum. In many cells the protoplasm, at or near the sur- face, is quite dense, forming what is then called the ectosarc. The more vicsid central portion is the endosarc. In the cytoplasm, usually by the side of the nucleus, a small body may be found in most cells, called the centrosome. The centrosome is occasionally in the nucleus and but little larger than a microsome, being usually surrounded by a clear, radially striated area of protoplasm called the attraction sphere. The cen- trosome takes an active part in the multiplication of cells, but otherwise its function is problematic. The cell wall is to be regarded as a cell product. In plant tissues the cell wall is relatively thick and composed largely of cellulose. In animal tissues the cell wall is unusually thin, often difficult to demon- strate, and in many cases absent. Examples of the latter are amoebas, white blood corpuscles, nerve cells, and probably liver cells. 40 NORMAL HISTOLOGY AND ORGANOGRAPHY. Nucleus.-The nucleus is the second constituent of the cell and is a round or an oval protoplasmic body found floating in the cytoplasm. Its shape usually corresponds to the form of the cell, but oc- casionally C-shaped, ring-shaped, and even branched nuclei are found. Its position may be eccentric or at one end of the cell. It has more consistency than the cytoplasm, but is plastic and displays consider- able elasticity. Independent movement of the nu- cleus in the cytoplasm has often been observed. At the same time its relation to the cytoplasm is a most intimate one and many cytoplasmic particles doubt- less have their origin in the nucleus. The structure of the nuclear protoplasm is even more complex than that of the cytoplasm. A reticu- lum of coarse, thread-like texture is constantly present. This stains deeply and is therefore called chromatin. The chromatin threads, like the spongio- plasm of the cytoplasm, are made up of minute particles or granules compactly arranged in rows that cross and interlace, making nodal points here and there called nuclear net-knots. The chromatin is imbedded in or deposited on a less stainable reticu- lum called linin, and surrounding both chromatin and linin everywhere, and filling their meshes, is a semifluid substance that does not readily stain and is therefore called achromatin, nuclear sap, paralinin, or karyolymph. Imbedded in the achromatic substance are one or more spherical bodies called nucleoli. The nucleoli stain less heavily than the chromatin and may be dissolved by reagents that do not affect the chro- matin; therefore, they are composed of a substance DEVELOPMENT. 41 not identical with the latter. Their function is not known. The nucleus is usually enclosed in a thin nuclear membrane (amphipyrenin) not unlike chro- matin material. This membrane has perforations which allow a free communication between the achro- matic fluid of the nucleus and the cytolymph and establish a most intimate relation between nucleus and cytoplasm. Cell Inclusions.-Bodies of a solid nature, not pro- toplasmic, are common to many cells. These are pigments, oil, fat, crystals, glycogen, starch, chloro- phyl, etc., and are spoken of as cell inclusions. The last two are found almost exclusively in plant cells. By these inclusions the shape of the cell is often changed, and particularly the position of the nucleus. Fat gathers at one end of the cell, crowding the nu- cleus to the opposite extremity and displacing the cytoplasm to the periphery, mostly to that end of the cell occupied by the nucleus. Pigment may be in solution, more frequently in granules, and always in the cytoplasm, not in the nucleus. Vacu- oles are very common to most cells. These vary in number and size and are usually spherical cavities filled with fluid secreted by the protoplasm. The vacuoles contract, often with considerable regularity, and, as a rule, empty to the surface of the cell. Waste products are in this way eliminated from the body of the cell. The constituents of a typical cell may then be summarized as follows: i. Cytoplasm, the protoplasm that surrounds the nucleus, consisting of,- (a) Spongioplasm, a reticulum or fibrillar network; 42 NORMAL HISTOLOGY AND ORGANOGRAPHY. (6) Hyaloplasm, a fluid portion, also called cy- tolymph; (c) Cell membrane, often absent in animal cells. 2. Nucleo plasm or karyoplasm, the protoplasm of the nucleus,- (a) Nuclear membrane, frecpiently absent; (6) Chromatin, network that stains easily; Dispirem. Diaster. Resting nucleus. Mctakincsis. Diaster. Diastcr. Daughter cells. Monaster. Spirern. Fig. 13.-Mitotic division of cells in testis of salamander (Benda and Guenther). (c) Linin, closely applied to the chromatin, does not stain; dissolves in distilled water; (d) Nuclear sap, a fluid perhaps analogous to the hyaloplasm; (e) Nucleolus, spherical body that stains heavily; (/) Nuclear net knots, or karyosomes, false nuclei that are nodal points formed by interlacing chro- matin network; DEVELOPMENT.. 43 (g) Nuclear membrane, amphipyrennin; (A) Centrosome, a small spherical body often found in the cytoplasm near the nucleus. It is looked upon as the dynamic center in cell division. Mitosis or Karyokinesis.-Mitosis is indirect cell division, and refers to the changes manifest in the nucleus during such division. The process may be divided into four phases- i. Prophase. The first manifestation of mitosis appears in the centrosome. This little body is, therefore, looked upon as the dynamic center of the cell. The centrosome divides and each half passes to opposite poles of the nucleus. The chromatin network, which really consists of chromatin granules, is transformed into a skein of threads known as a spirem or mother skein. These threads break up into a definite number of segments known as chromo- somes. The chromosomes are even in number, and, for a given species, a constant number is always present. In the human cell there are sixteen chro- mosomes,-according to some, twenty-four. To- ward the close of this stage, each chromosome forms a loop and is finally arranged symmetrically around the equator of the nucleus, with the free ends of each loop turned away from the center. This symmetrical figure is known as monaster. During this stage the nuclear membrane usually disappears. The nucleolus also vanishes, just how is not clear. The net knots disappear with the formation of chromatin loops. During these changes the achromatic substance- linin and nuclear sap-has formed a central spindle 44 NORMAL HISTOLOGY AND ORGANOGRAPHY. with each apex directed toward a centrosome. This spindle consists of fine threads or lines directed toward the centrosomes. A like radiation becomes manifest in the cytoplasm, each line being directed toward, or from, one or the other centrosome. This radiation is absent from the protoplasm immediately surrounding each centrosome, forming a clear field called the attraction sphere. The lines that extend Fig. 14.- Diagram of mitosis. into the cytoplasm are known as polar rays. Those that form the spindle seem to be attached to the curved portions of the chromatin loops. 2. Metaphase.-This stage begins with the chro- matin loops arranged radially in the equatorial plane of the nucleus. The most important change in mitosis now takes place, in that each chromosome DEVELOPMENT. 45 loop divides lengthwise to form two daughter chromo- somes. This is an equal division, both qualitative and quantitative. The curved portion of each daughter loop passes along the rays of the achro- matic spindle and approaches one or the other cen- trosome. There are three theories as to the mech- anism involved: (i) It is affirmed that the threads of the spindle contract and pull each daughter loop toward its centrosome. (2) The rays or threads may elongate and push each loop toward the opposite centrosome. Accord- ing to this theory there should be twice as many lines or rays between the loops as there are spindle rays from each centrosome, an observation recorded by some investigators. (3) The centrosomes may be fermenting centers of chemical change, and the explanation, therefore, a chemical attraction or affinity. At the close of the metaphase the daughter loops arrange themselves respectively around each cen- trosome forming what is known as a diaster or daughter star. The free ends of these are turned away, and the curved portions of each are turned toward the centrosome. 3. Anaphase.-During this period the changes manifest in the prophase are reversed. The chro- matin loops are gradually transformed into twisted skeins of threads, called daughter skeins, which ultimately produce the normal chromatin reticulum. The nuclear membrane and nucleolus reappear. A constriction of the cytoplasm is manifest for the first 46 NORMAL HISTOLOGY AND ORGANOGRAPHY. time. This constriction appears in the plain passing between the daughter nuclei. 4. Telophase.-In this stage the cell divides com- pletely. Each daughter cell gradually assumes the normal condition of the parent cell from which it had its origin. The time required for complete division varies from one to several hours. A mitosis is the direct cell division and occurs sel- dom as a normal process. The nucleus merely con- stricts, without the formation of chromatin loops or filaments, thus producing two or more nuclei or nuclear fragments. The cytoplasm may not take part in this division, in which case polynucleated cells are formed; however, polynucleated cells may also arise from mitosis. Preceding the division the nucleolus, if present, may subdivide, while the centrosome does not seem to take any active part whatever. In the human body certain leucocytes have been described as dividing by amitosis, also polynucleated pavement cells of the bladder. De- generated cancer cells have been described as show- ing amitotic division, but whether a cause or a con- sequence of degeneration and disease can be argued with equal force. On the other hand, certain em- bryonic cells have been described as dividing by amitosis, which later take up the regular cell di- vision of amitosis, but these cases, if normal, must be regarded as very exceptional. Laws of Cell Cleavage.-(1) The cleavage plane is always equatorial to the nucleus. (2) The position of the nucleus depends on (a) the shape of the cell, and (6) on the distribution of food DEVELOPMENT. 47 material or secretions. If the cytoplasm is eccentric in the cell, the nucleus is associated with it. (3) When each plane of division is parallel to the preceding plane, a filament is produced. This is the law in some plants, as spirogyra, nostoc, etc. (4) When each plane is at right angle to the pre- ceding plane and in two dimensions, a surface of cells is formed, as simple epithelium. (5) When each plane is at right angle to the pre- ceding plane and in three dimensions, a volume or an organ is formed with three dimensions, as the morula stage in embryos. General Considerations.-The subject of cell divi- sion has given rise to much discussion. While we are unable to control mitosis, the following are factors that modify cell growth: 1. Trauma.-Following a cut or a bruise the ad- jacent cells are stimulated to rapid multiplication and the wound heals. 2. Heat.-There is a mean temperature for the maximum multiplication of cells which varies with the species. In man this mean temperature is blood heat, 98.6°. 3. Electricity.-By stimulating protoplasmic ac- tivity, electricity no doubt is a factor in influencing normal cell growth. Just how this is accomplished, and to what extent, is a much-disputed problem. 4. Light.-A very important factor in promoting multiplication, or decreasing it, or even destroying certain cells, as bacteria. The different rays of light have each a specific effect. 5. Nourishment.-Proper food is a stimulant. 48 NORMAL HISTOLOGY AND ORGANOGRAPHY. 6. Chemical.-Certain salt solutions, as sodium and potassium salts, have a stimulating effect. 7. Exercise.-Regular systematic exercise prompts a healthy growth. Massage acts in the same way. Pathological tumors are abnormal growths of nor- mal tissues. In many of these tumors the cells multiply rapidly by mitosis, resulting often in un- equal division of the chromosomes, or chromatin loops, but whether this is a cause or a consequence can be argued with equal force. We are unable to produce these tumors experimentally, and, unfor- tunately, we are often unable to stop their mul- tiplication of cells. The surface of a sphere increases as the square of its diameter, while the volume increases as the cube of the diameter. As the cells depend upon their surface area for the absorption of food and elimination of waste, and as the volume increases at a greater rate than the surface area, the reduction in size of a cell becomes a necessity. Much significance is attached to the fact that mitosis brings about an equal division of the chro- matin or chromosomes. If for any reason an un- equal division obtains, the cell becomes abnormal and a monstrosity, with death, follows. Experi- mentally this may be done with an egg cell, which, if anesthetized, allows more than one spermatozoon to enter, resulting in an unequal division of the female pronucleus and an abnormal development. That chromatin is the bearer of hereditary qualities is a postulate based upon the observation that mitosis DEVELOPMENT. 49 results in an equal division of the chromosomes. What these unrevealed biological units are is a matter of much controversy. Much work has been done in recent years on the individuality of the chromosomes, establishing the fact that they vary greatly in size, form, and con- stituents in one and the same cell. Some are long and some are short, thick and slender, greatly curved and nearly straight, stain dark or take only a slight stain; in short, we must now admit their personnel and postulate special cell function for each chromosome. Moreover, it is now practically established that certain spermatozoa, particularly in insects, have an odd chromosome, and that from eggs fertilized by this particular class males de- velop, whereas from fertilization by spermatozoa having an even number of chromosomes females are produced. In a species of insect, Lygoeus bicrucis, the males develop spermatozoa that have all the same number of chromosomes, but in one set there is present one large chromosome and in the other set there is present one small chromosome. If a spermatozoon with the small chromosome fertilizes the egg, a male develops, and if one with the large chromosome fertilizes it, then a female is formed. Sex chromosomes have now been recognized in a large number of males of different groups of ani- mals, and we can, therefore, safely affirm that the determination of sex rests, in most cases, with the intrinsic quality of the fertilizing spermatozoon. Morgan, therefore, concludes that "if these observa- 50 NORMAL HISTOLOGY AND ORGANOGRAPHY. tions are confirmed they show that in man, as in so many animals, an internal mechanism exists by which sex is determined. It is futile then to search for environmental changes that might determine sex." ("Heredity and Sex," page 248, Columbia University Press, 1913.) CHAPTER H. TISSUES. A tissue is a complex of similarly differentiated cells and their derivatives. In all embryonic tissues and some adult tissues the cell elements predominate, but in cartilage and bone and many connective tis- sues the cell products make up the bulk of the tissue. There are four kinds of elementary tissues,- (1) epithelial tissue; (2) Supporting tissue; (3) Muscular tissue; (4) Nerve tissue. Epithelium lines surfaces, external and internal, and forms the secreting cells of glands. (See table, page 36.) The cells of this tissue are derived from any one of the three germ layers. Blood and lymph vessels do not penetrate between the epithelial cells, but nerve fibers enter the deeper strata and end in minute varicosities that lie in contact with many of the cells. The cells have a regular form, a thin cell wall, and a distinct nucleus that is rich in chromatin and therefore stains easily with hematoxylin. They usually secrete a cement found between adjacent cells which serves the purpose of holding each cell firmly in place. The cell wall is usually smooth, but in certain places the lateral walls develop many short, minute processes (prickles) that meet like processes from adjacent cells, forming intercellular bridges, and be- tween the latter are found intercellular spaces filled with nourishing fluid for the individual cells. The I. EPITHELIAL TISSUE. 51 52 NORMAL HISTOLOGY AND ORGANOGRAPHY. cell rests upon a basement membrane that is usually considered to be made up of basal processes of the basal cells. The free surfaces of epithelial cells may develop cilia, which serve the purpose of sweeping away fluids or foreign bodies. In many instances a deli- cate lining called the cuticle covers the free ends. The cuticle is to be regarded as a cell product, and since in many cases a fine transverse striation can be seen, it seems probable that the cuticle is built from a large number of transverse rods cemented Fig. 15.-Epithelial cells from skin of frog. Surface view of external layer together. In columnar cells the nucleus is usually found at the basal end, thus being placed nearer the blood and lymph supply, the nourishing cell media. Epithelial tissue is classified as: (i) simple or (2) stratified. 1. Simple epithelium, consisting of a single layer of cells. (a) Simple squamous, flat single layer of cells, found in the alveoli of the lung and in Bowman's capsule of the kidney. TISSUES. 53 (6) Simple cuboidal, found forming the wall of most ducts, as the bile duct, pancreatic duct, portions of kidney tubules, and ducts of salivary glands. (c) Simple columnar, ciliated or non-ciliated. Fig. 16:-Squamous epithelial cells from the mouth. This is the most common form of simple epithelium. The alimentary canal, below the diaphragm, has simple columnar; also portions of the kidney tubules. Mu I 1<'. Fig. 17.- Simple columnar cells from intestine. Goblet cell. Simple ciliated is found in the oviduct, uterus, cen- tral canal of the spinal cord, and smaller bronchi. (d) Pseudo-stratified.-In this type all the cells rest on a common basement membrane, but the nuclei rest at different levels, which give the tissue the appearance of being stratified. Frequently this tissue is ciliated, as is the case in portions of the respiratory tract. 54 NORMAL HISTOLOGY AND ORGANOGRAPHY. 2. Stratified epithelium, consisting of several layers of epithelial cells. Fig. 18.- Ciliated epithelium from trachea. (a) Transitional, consisting of two or three layers of cells, found in the wall of the bladder, ureters, pelvis of kidney, and prostate portion of male urethra. In this case the surface layers of cells are Pavement cell. Pear shaped cell. Pavement cells. Interstitial cells. Fig. 19.- Epithelial cells from the bladder. flat, often polynuclcated and form a mosaic pattern upon the second layer, which is pear-shaped, with the broad ends forming depressions into the first layer of cells. The third layer consists of smaller, irregular, interstitial cells that fill the spaces between the pointed ends of the second row. TISSUES. 55 (6) Stratified Squamous.-In this case the super- ficial layers arc flat and the deeper ones cuboidal Pavement cell. Pear-shaped cell. Interstitial cell. Fig. 20.- Section of bladder epithelium. or columnar. This is the most extensive of the epithelial tissues. It forms the epidermis of the skin, the walls of the oral cavity and the esophagus, the epithelium of the conjunctiva, external auditory canal, va- gina, and the exter- nal sheath of hair follicles. The outer cells be- come horny and scale away quite regularly in thin lamellae. The deeper layers are ar- ranged to form papil- lae that interlock with connective tissue pa- pillae and thus not only anchor the epithelium to the subjacent tissue, but increase the absorbing surface by approximating a larger number of epithelial cells to the underlying blood and lymph capillaries. Corneum or horny layer. Stratum ' lucidum. ' Stratum granulosum. - Malpighian or germ- inal layer. Fig. 21.-Section of epidermis of skin from palm-surface of finger. 56 NORMAL HISTOLOGY AND ORGANOGRAPHY. (c) Stratified columnar, ciliated or non-ciliated This is found in the olfactory mucous membrane, the first part of many gland ducts, palpebral conjunc- tiva, portions of the male urethra, vas deferens, and portions of the larynx. General Considerations.-The epithelial cells are simpler and more embryonic than the cells of the other tissues. They are continually multiplying throughout life, to re- place the superficial layers that are con- stantly exfoliating from the surfaces. If any of these surfaces are injured, the cells marginal to the injury repair the loss by a gradual growth cover- ing the denuded sur- face. As a consequence of this mitotic activity, we find these cells fre- quently in pathological growths as epithelial growths or epithelioma. If the tumor is malignant it is a carcinoma or cancer. It is a remarkable fact that, in the adult, epithelium is able to produce cells only of its own kind,-i. e., squamous cells produce squamous epithelioma, and columnar cells columnar epithelioma. Epithelial tissue, however, is easily modified, as is evidenced by calloused hands, pro- duced by heavy labor, and the cornification of nails, hair, horns, and teeth. Fig. 22.-Section of stratified epithe- lium from esophagus. TISSUES. 57 Since the blood supply never penetrates epithelial layers, it is evident that the superficial layers of cells receive less nourishment and ultimately die, which, perhaps, accounts for the constant exfoliation. It is also evident that anything that will increase the blood supply will increase the nourishment, as fric- tion, massage, and hot applications. The nour- ishment, at best, is not very good, which explains the Epithelium of cornea. Substantia propria of cornea. Fig. 23.-Section showing corneal epithelium of the eye of pig. ease with which skin grafts are made. Epithelial cells will live for twenty-four hours or more in normal salt solutions, and will even multiply in favorable culture media. The nerve termination among the epithelial cells is an important relation which, in large part, controls their metabolism. A disturbed nervous system may impair or even cause a destruction of epithelial cells. 58 NORMAL HISTOLOGY AND ORGANOGRAPHY. Cilia are exclusively confined to epithelial cells. There are three theories to account for the motion of cilia: i. The contraction may be intrinsic in the wall of the cilium. This theory is supported by the fact that the cilium or flagellum of a spermatozoon will show motility when severed from the rest of the cell. 2. Contraction of the base where the cilia are attached. The cilia will continue to vibrate if a fragment of the cell protoplasm remains attached to them. 3. The cilia are supposed to be hollow tubes with walls of unequal elasticity. By forcing the proto- plasm rapidly into these tubes ciliary motion is produced. Pseudopodia are produced in this man- ner, and the morphological relation of pseudopodia and cilia is a close one. The one great physiological action of epithelium seems to be to secrete fluids. Consequently epithe- lium is found lining all cysts wherever the cyst is located,-in the ovary, the skin, or in connection with the alimentary tract. Conversely, a cyst may be formed wherever epithelium is found. Lastly, it is of the greatest importance that stu- dents should be able to recognize epithelial cells. The diagnostic points of this recognition are: 1. The oval or round distinct nucleus, usually rich in chromatin. 2. The regularity of the cells,-i. e., the cells of one class are alike, either squamous, or columnar, or ciliated. 3. They appear in compact layers or strata, not TISSUES. 59 loosely thrown together, and blood- and lymph- vessels are absent. 4. Presence of free nerve endings. While this is of no diagnostic microscopic value, it is physiologic- ally an important relation to bear in mind. In wounds and old sores the epithelial border is the most sensitive part and should be carefully manipu- lated to avoid inducing pain. Glands.-Much literature has been contributed the last years relative to the proper conception as to what constitutes a gland. The prevailing opin- ion seems to be that any structure which secretes or puts out a product that is not used directly in the metabolism of the body should be called a gland. If the fluid is a waste, the product is an excretion; if it has a utility, it is a secretion. Accordingly, mucous and synovial and serous membranes are glandular structures as well as the liver, the pan- creas, or the kidney. Furthermore, the simplest form of a gland is a single secreting cell situated apart by itself, and such unicellular glands are quite common in invertebrates and are represented in man by the goblet cells found in mucous membranes. Epithelial cells are the chief secreting cells of the body, and these cells, therefore, form the glandular tissue of all glands except the lympho-glandular, which is a connective-tissue production. The lymph glands thus constitute a class entirely by themselves as distinguished from all other forms, which may be called epithelial glands. As one of the important functions of lymph glands is to con- tribute white blood-corpuscles and thus scatter its 60 NORMAL HISTOLOGY AND ORGANOGRAPHY. own cells, they may also be called dehiscent or cyto- genic glands, a term applicable to the testes and ovaries, which are epithelial glands that perform a similar function by putting out their own cells in the form of spermatozoa and ovules. Numerous goblet cells are found in the simple epithelium lining the stomach and intestines, and are particularly abundant in the lower part of the bowel. These cells func- tion as glands and secrete mucus for the protection of the surface. In case of irritating media, such as undigested food or poisons, extensive mucus is poured out over the surface, thus protecting the delicate inner lining. In some cases of consti- pation this mucous secretion is impaired. Salts or drugs that increase the functional activity of these cells correct such complication. On the other hand, too extensive a secretion may be corrected by drugs, as opiates, that inhibit the physiological action of these cells. Constipation may be due to inertness of the musculature of the intestinal wall, in which case other remedies correcting this disturbance are indicated-massage, hydrotherapy, and drugs that act on the musculature. Physiologically, many gland cells are either mu- cous or serous. In mucous cells the mucus secretion collects at one extremity of the cell as a clear, glisten- Serous*gland. Fig. 24.- Skin and simple alveolar glands from the salamander. Mucous gland. TISSUES. 61 ing drop. The cytoplasm and nucleus are crowded to the opposite end. In serous cells the nucleus is more centrally placed, and the serous secretion is stored up as minute granules distributed through- out the cytoplasm, more especially in that por- tion of the cell lining the free surface. Some Crypt. Parietal cell. Chie} cell. Fig. 25.- Simple tubular gland from stomach. glands are mucous, some are serous, and some are mixed. Mucous Membrane.-A mucous membrane con- sists of a lining of epithelial cells, basement mem- brane, and membrane propria. The basement mem- brane is largely an elastic cellular secretion on which 62 NORMAL HISTOLOGY AND ORGANOGRAPHY. the epithelial cells rest, although at times flattened connective-tissue cells seem to enter into its forma- tion. The membrana propria is a connective-tissue production consisting of connective-tissue cells, fibers, and blood- and lymph-vessels. Mucous mem- Fig. 26.- Cells from different glands : a, Pancreas; b, submaxillary gland; c, liver. Demilune of Heidenhain. branes line cavities or tubes that communicate with the surface of the body, such as the alimentary canal, respiratory tract, and urogenital system. Serous Membrane.-A serous membrane has the same histo- logical elements as the mucous membrane. The epithelial lining is simple squafnous, and these cells secrete a serous fluid, more viscid and more of a lubricant than mucus. Serous membranes enclose cavities that do not com- municate with the surface of the body, as the pleural, pericardial, and peritoneal cavities and cavities of joints, forming in the latter case synovial membranes. Sheaths or bursae of tendons have serous membranes. Cell ready to secrete. Cell empty of secretion. Fig. 27.- Goblet or mucous cells from intes- tine. Tissues. 63 As to form, epithelial glands are classified as- i. Simple. (a) Simple tubular-gastric glands, sweat glands, and uterine glands. ^Lmple tubular. Corn^oic/td tubular. Compound alveolar alveolae Fig. 28.- Diagram of different forms of glands. (5) Simple alveolar-smallest sebaceous glands, and skin glands in amphib- ians. 2. Compound. (fl) Compound tubular-kidney, liver, testis. 64 NORMAL HISTOLOGY AND ORGANOGRAPHY. (6) Compound alveolar or racemose-sali- vary glands, mammary gland, lung, pancreas, sebaceous glands. Glands not included in this classification are uni- cellular glands and secreting membranes, which can- not be classified as to form. Lymph glands, which are of connective-tissue origin, and like the testis or ovary, may be called dehiscent or cy to genic glands. Follicular glands, such as the thyroid gland, and the ductless glands, producing internal secretions, such as the hypophysis cerebri, thyroid gland, suprarenal gland, areas of Langerhans of the pancreas, inter- stitial cells of the testis, and corpora lutea of the ovary. The thymus gland and spleen are lymphoid organs, and therefore to be classified among the lympho glandules. The object of any anatomical classification is to simplify and correlate structural facts. From the foregoing outline it is clear that glands, according to modern views, embrace such a complex of structures that any classification, either according to origin, or form, or tissues, or even function, does not accom- plish the end in view, namely, simplicity. The dif- ficulty met with is due to the fact that our con- ception of a gland rests largely with the physiolog- ical action of gland cells rather than with any com- mon intrinsic anatomical quality. Endothelium.-This term, introduced by His in 1865, is generally applied to the layer of cells that line closed cavities, such as peritoneal and pleural cavities, circulatory system, and cavities of joints. TISSUES. 65 These cells thus form the inner layer of serous mem- branes, and while structurally they bear a close re- semblance to epithelial cells, there is nevertheless an intrinsic difference made apparent by a comparison of pathological growths from these cells called endo- thelioma, and like growths from epithelial cells called epithelioma. Endothelioma are usually slower of growth, less malignant when malignancy exists, and have a tendency to form mucoid deposits. Endothe- lial cells are mononucleated, scaly, or of the pavement variety with wavy borders, and are held together with a cement substance that re- quires special staining tech- nique to demonstrate. They impart a transparent, smooth, glistening surface to the mem- brane which they clothe. Peritoneum and Pleura.- These are true serous mem- branes, the structure of which is described on page 62. Elas- tic fibers are particularly abundant in the membrana propria, giving strength to both peritoneum and pleura, so that these membranes are readily sewed in surgical cases. Physiologically these membranes are of the greatest importance: 1. It is claimed that the simple pavement epithe- lial cells of the peritoneum can produce a secre- tion that clots, and in this manner adhesions are Fig. 29.- Epithelium or endothelium from mesentery. Silver nitrate stain. 66 NORMAL HISTOLOGY AND ORGANOGRAPHY. quickly formed. This is of the greatest importance in preventing the spreading of an infection, as in peritonitis. 2. These cells act as phagocytes and feed upon bacteria in case of an infection. According to one view they can destroy living bacteria. A second theory is that they act as scavengers and remove only dead bacteria. Stomata and stigmata have been frequently de- scribed as minute openings in these membranes to facilitate the absorption of fluids. Stomata are said to have guard cells to regulate the size of the opening, and were supposed to be specially abundant in the peritoneal lining of the diaphragm. The exist- ence of stomata has lately been strenuously denied. The rapid absorption of peritoneal fluid is a well- established fact*. If stomata are absent the ab- sorption is purely one of osmosis or dialysis. It should be remembered that drainage is along lymphatic channels and therefore from the pelvis toward the thorax. II. SUPPORTING TISSUE. The embryonic connective tissue is largely cellular, but in the adult body the intercellular substance greatly predominates and gives the characteristics on which a classification is based. The cell elements are but slightly modified from the embryonic type, but the cell products or intercellular substance be- come modified to form bone, cartilage, or connective- tissue fibers. The difference here is relatively a dif- TISSUES. 67 ference in the degree of condensation of the inter- cellular substance, being either loosely arranged as in reticular connective tissue, or more compact as in tendons, or a greater degree of condensation as in cartilage, bone, and dentine. In all these types the cellular elements are morphologically very similar, which makes it possible for one form to develop into that of another; for instance, bone is produced from cartilage, or from fibrous connective tissues. The function of supporting tissue is largely a pas- sive one depending on its physical properties, and the amount of nourishment the cellular elements re- ceive is therefore a very variable quantity. Ten- dons, particularly, have a limited supply, perhaps because the cells form so small a part of these struc- tures. Nutrition is supplied from the lymph which penetrates the ground substance through clefts or minute channels placed in the intercellular material of the more condensed forms. In bone fine canals develop and anastomose to form a canalicular sys- tem, while in other forms, as mucous connective tis- sue and hyaline cartilage, the nourishing lymph seems to pass through the ground substance regard- less of lymph channels, as in these cases the latter have not been found. Blood vessels and capillaries ramify more or less freely through the matrix of supporting tissue, ex- cept in case of cartilage, where they are practically absent. Unlike epithelia, nerves may be abundant, but in no case do nerve fibers unite with the cellu- lar elements; however, special sensory nerve endings 68 NORMAL HISTOLOGY AND ORGANOGRAPHY. are frequently found, particularly in the connective- tissue elements. Fat in the human body is mostly found stored up in modified connective-tissue cells. This may occur wherever there is connective tissue, and fat cells must therefore be regarded as modified connec- tive-tissue cells. Likewise certain pigment cells and red blood corpuscles belong to this class. The supporting tissue is derived exclusively from the mesenchyma, a subdivision of the middle germ layer or mesoderm. It is divided into three classes- connective tissue, carti- lage, and bone. Fig. 30.-Connective-tissue cells from a chick embryo. Fig. 31.-Connective-tissue cells from Wharton's jelly of the umbilical cord. 1. Connective Tissue. The elements of this tissue consist of cells and cell products, in the form of connective-tissue fibers, which penetrate and give consistency and support to every organ in the body. i. Connective-tissue Cells. (a) Embryonic Connective-tissue Cells.-These are irregular, stellate cells found in embryos and in the umbilical cord. Those of the cord, with the matrix in which they are imbedded, form a soft, pulpy mass TISSUES. 69 known as Wharton's jelly, or mucous tissue. These cells are loosely associated in no definite order, their stellate processes interlace and sometimes appear to come in direct contact. Their nuclei are round, or oval, or elongated, forming what is known as the spindle-shaped and pointed nucleus, often resem- bling the cigar-shaped and rounded nucleus of a plain muscle cell. The nuclei are rich in chromatin, and therefore stain heavily with hematoxylin. Blood- and lymph-vessels mingle freely with these cells; in Fig. 32.-Two pigment cells from the dermis of a salamander. The pigment is in the cytoplasm. fact, this association is constant. The so-called granulation tissue in healing wounds consists of em- bryonic connective-tissue cells, always bleeds easily, because of its vascularity, and painless because of absence of nerve endings. (&) Pigment Cells.-These are connective-tissue cells in which pigment is stored in the cytoplasm, never in the nucleus. The cells are extensively branched, large and flat. In amphibians and rep- tiles they are abundant in the dermis of the skin, and enable the animal to change its color, as is the case with the tree toad and the chameleon. In the human 70 NORMAL HISTOLOGY AND ORGANOGRAPHY. body connective-tissue pigment cells are limited to the choroid coat and iris of the eye, to birth-moles, and to the piamater of the brain. The pigment may be of any color, the constituent being melanin, a coloring material probably derived from the blood. (c) Fat Cells.-These are connective-tissue cells with a large storage of fat. The fat occupies the center of the cell as a big drop which crowds the cytoplasm and nucleus to one side, closely pressed against the cell wall, which is unusually conspicuous. The cells are large and spherical. Since fat is dissolved by alcohol, these cells in sections are distorted, polyhe- dral, and appear more like irregular spaces than any- thing else. Normal fat is not to be confounded with pathological fat found in fatty degeneration of organs. In the latter case the fat appears as little droplets diffused through the cytoplasm of the dis- eased cells, and is pro- duced at the expense of protoplasm, a destructive process or katabolism. Normal fat is a constructive process or anabolism, and is therefore a storage of food or potential energy. Its production, physiologically, is not clearly understood. It may be produced from Fat. Cytoplasm. Nucleus. Fig. 34.-Normal fat cell. Fig. 33.-Pigment cells from the choroid coat of the eye. These cells are of connective- tissue origin. TISSUES. 71 a proteid diet, but its production is more easily prompted by a fatty diet and the carbohydrates. Cold prompts its production, as is clearly manifest in hibernating animals when the cold season ap- proaches, and the increased weight of animals, as a rule, during the winter season. Connective-tissue cell. Nucleus of fat cell. Fig- 35--Fat cells as they appear in sections treated with alcohol. Alcohol dissolves the fat. The usual stain for fat is osmic acid, in which fat acts as a reducing agent, precipitating black osmium. Any reducing agent will do this, as is made evident by the black color of the cork in a bottle containing osmic acid solution, fat being absent from cork. Other connective-tissue cells, as Plasma cells, Wan- dering cells, and Mast cells, are frequently described. These resemble normal constituents of blood and lymph to which they may belong. 2. Connective-tissue Products.-These products may be a jelly-like substance or fibers. Connective- tissue cells are always associated with these products. There are two theories as to the production of fibers. (a) The fibers may be processes of the cytoplasm that lose their cell connection. 72 NORMAL HISTOLOGY AND ORGANOGRAPHY. (6) The connective-tissue cells may secrete a homogeneous matrix, which later becomes striated, producing fibers in a manner as fibrin is formed in clotting blood. Connective tissue is classified according to its matrix into: i. Mucous Connective Tissue. -This consists largely of embry- onic connective-tissue cells and a jelly-like matrix or ground sub- stance which gives a reaction for mucus. It is found in the um- bilical cord, where it is known as Wharton's jelly, and in embry- onic tissue. 2. White Fibrous Connective Tissue.-This consists largely of white nonelastic fibers. The fibers are parallel to each other, not branched, and yield gela- Fig. 36. - Reticular tissue from a lymph gland. Tendon fibers. T endon cell. Fig. 37.-Teased tendon, showing fine wavy white fibers. Fig. 38.-Cross section of tendon. tin on boiling. The fibers swell up when treated with acetic acid. They are found in tendons, the apo- neuroses, and ligaments, the fascia of muscles, the dura mater, and the fibrous capsules of many organs. TISSUES. 73 3. Yellow Fibrous Connective Tissue.-The matrix in this consists of elastic fibers that are branched, and usually coarser than the white nonclastic fibers. They do not swell up when treated with acetic acid and yield elastin on boil- ing. Like the preceding, the fibers are frequently grouped into bundles with a limited supply of blood- vessels and connective- tissue cells. This tissue is found wherever elasticity is required, as in the ligamentuni nuchae and subflava, in the walls of Tendon fibers. T endon cell. Fig. 39.-Longitudinal section of tendon. Fig. 40.-a, Yellow elastic fibers from the teased ligamentum nuchas of the ox; b, Cross-section of a portion of the ligamentum nuchae of the ox. The elastic fibers are grouped in bundles with a few intervening connective-tissue cells. arteries, and in the membrana propria of the peri- toneum and pleura. 4. Reticular Connective Tissue.-This is a reticu- 74 NORMAL HISTOLOGY AND ORGANOGRAPHY. lum of interlacing fibrils and is found in adenoid tissue, lymph nodes, spleen, and membrana propria of mucous membranes. Also, to a limited extent, in bone marrow. 5. Areolar Connective Tissue.-This is really a mix- ture of interlacing bundles of white and yellow elastic fibers. It is found subcutaneously to the skin, to which it imparts elasticity. Areolar tissue is vascular and favors, therefore, a rapid spread of bacteria. Over bony prominences there is a limited supply of areolar tissue and the skin at these places has restricted mobility. It is at these points that the spread of an infection, such as erysipelas, is checked. General Considerations. -On account of the embry- onic condition of connec- tive-tissue cells these, like epithelial cells, are fre- quently met with in patho- logical tumors. If the tumor is malignant it is called a sarcoma, and is as fatal to life as carcinoma, or cancer. If the tumor is made up largely of fat cells, it is called a lipoma, and if the fibrous elements predominate it is a fibroma. The production of connective tissue is often nature's method of checking the spread of a disease. This tissue is produced as a wall in advance of a spreading infection, and if the bacteria are unable to penetrate this barrier, the disease soon becomes sclf- limiting. This accounts for the swollen infected Fig. 41.-Elastic fibers of the mesentery. TISSUES. 75 parts, and also for the redness, which is due to the extensive blood supply which is always associated with this tissue. Such a swollen tumor represents an induration and a congestion. In this manner a whole or a part of an organ may be affected. The connective-tissue fibers are absorbed with difficulty or not at all, and a permanent mark or scar remains as an evidence of the injury. In a healing wound, particularly if infected, these fibers are abundantly produced, and its redness is evidence of its extensive vascularity or blood supply. Later, these fibers con- tract, which occludes the blood, and then the color changes from a red to a white scar that no medical treatment can remove. Pigmentation is a most important subject. Pig- ment appears, as a rule, in the cytoplasm of cells, seldom between the cells. It is not confined to con- nective-tissue cells, but is common to epithelial cells, as the deep layer of the epidermis giving the color of races; is found in the retina cells, where it is always black, and in hair and nails. It appears in the cyto- plasm of muscle cells, particularly in old heart muscle,where it is found near the ends of the nuclei, and is nearly always present in nerve cells, giving a gray color to this tissue. Pigmentation is an ac- companiment of many diseases, particularly skin diseases. It is also produced under the influence of light, as freckles, that can only be removed by the normal exfoliation of the epithelium. The production of pigment seems to depend upon the blood. As blood is absent from epithelium there are two theories as to the manner in which the cells 76 NORMAL HISTOLOGY AND ORGANOGRAPHY. obtain it: (a) they may receive it directly from the blood, or (6) connective-tissue cells may elaborate it and deliver it secondarily to the epithelial cells. That the pigment is not intrinsic to epithelial cells is proved by the fact that colored skin grafted on a white man soon turns white, and white skin grafted on a colored person turns black. The fruitless at- tempts to change one's color are well known. A melanotic sarcoma is a pigmented connective- tissue tumor, very malignant, whose cells disseminate very rapidly throughout the body, producing every- where new tumors. These cells have their origin from normal pigmented connective-tissue cells, and therefore are supposed to come from birth-marks, or the choroid of the eye, or the piamater of the brain. The etiology of such tumors is unknown. Fortu- nately they are rare. The diagnostic points by which connective-tissue cells are known are: i. The easily stained round, or oval, or spindle-shaped nucleus. 2. The cells are loosely thrown together, not in compact layers or strata. 3. The stellate cells, although the proc- esses are often inconspicuous and not readily de- tected. 4. The tissue is vascular where cells are abundant. Cartilage is supporting tissue in which the inter- cellular substance predominates and yields chondrin upon boiling. The cartilage cells are typical con- nective-tissue cells, and occupy lenticular spaces in the matrix called lacuna. Cartilage is surrounded by a dense connective-tissue membrane called the 2. Cartilage. TISSUES. 77 perichondrium, in which smaller blood-vessels ramify. Blood- and lymph-vessels are absent from the carti- lage matrix, except rarely and in places where active growth or ossification is going on they may be present. According to the structure of the matrix, cartilage is classified as,- Perichondrium. Lacuna. Cartilage cell. Cartilage matrix. Fig. 42.-Section of hyaline cartilage from the trachea. 1. Hyaline Cartilage.-This is the simplest and most common form of cartilage. The matrix appears Matrix Cells. Lacuna. Fig. 43.-Two groups of cells from hyaline cartilage: A, Two cells found just beneath the perichondrium; B, Four cells found deeper in the cartilage matrix. to be a homogeneous substance, although many fine interlacing fibrils are present. The lacunae near the perichondrium have their long axis parallel to the 78 NORMAL HISTOLOGY AND ORGANOGRAPHY. surface, while deeper in the matrix the long axis is often at right angles to the surface. Each lacuna contains one or more cartilage cells. The cartilage surrounding lacunae usually stains differ- ently from the bal- ance of the matrix. This cartilage oc- curs as articular carti- lage of joints, at the end of ribs, and in the nose, the larynx, the trachea, and bronchi. 2. Elastic Carti- lage.-Elastic cartilage differs from the hyaline vari- ety in having typical interlacing, branched elastic fibers that form a dense network. This cartilage is found wherever elas- ticity is required, as in the external ear, the Eustachian tube, epi- glottis, part of ary- tenoid cartilages, and cartilages of Wrisberg and Santorini. 3. White Fibrous Cartilage.-In this va- riety the white fibers predominate. As a rule these fibers run parallel in bundles and do not branch. A granular matrix intervenes between the fibers. Fibrous cartilage is found in the intervertebral disc, in the sym- Cartilage cell. Elastic fibers. Fig. 44.-Section of elastic cartilage from epiglottis. White fibers. Cartilage cell. Fig. 45.- Section of white fibrocarti- lage from symphysis pubis. TISSUES. 79 physis pubis, and in the insertion of the round ligament. General Considerations.-Cartilage tumors are known as chondroma, and are common. Like cartilage they are of slow growth and therefore harmless. The absence of blood accounts, in large part for the inactivity of the cartilage cells, both in the normal and pathological condition. Further- more, cartilage cells are enclosed in the matrix in a manner that inhibit their multiplication. Cartilage therefore grows by apposition or acquisition, not by intussusception, like most tissues. Cartilage slowly ossifies with age. During this process loops of blood-vessels enter the matrix from the perichondrium, and lime salts are deposited ad- jacent to the cartilage cells. This process will be further described under bone development. The identification of cartilage is very easy, as the matrix has a marked affinity for many stains. 3. bone. Bone is the chief supporting tissue of the body, and consists of a calcified intercellular substance, mostly calcium phosphate, and connective-tissue cells, or bone cells. Organic substance constitutes one-third the weight, and inorganic substance two- thirds the weight of bone. The bone cells, some- times called bone corpuscles, are flattened stellate cells with many slender processes, and a well defined round or oval nucleus. Like cartilage cells they lie imbedded in lenticular spaces called lacunce. These lacunae, however, communicate with adjacent la- cunae by means of numerous capillary tubes called 80 NORMAL HISTOLOGY AND ORGANOGRAPHY. canaliculi, into which extend the slender cell proc' esses. Through these canaliculi the imprisoned cells receive their nourishment and give up their waste products. Haversian System.-This consists of a Haversian Canaliculi. Lacuna. ■ Nerve. Haversian canal. • Artery. ■ Vein. > Bone lamelice. Fig. 46:-Haversian system with only one lacuna sketched. canal, containing an artery, vein, and nerve, bone lamallae concentrically arranged around the canal, and from two to six rows of concentrically arranged cells with their lacunae and canaliculi. The canals average 0.05 mm. inch) in diameter. The canals, as a rule, run parallel with the shaft of the bone, but com- municate freely with each other. The blood penetrates as far as the Haversian canals but the lymph reaches each bone cell through the finer canaliculi. The nerve termi- nates in the wall of the blood-ves- sels and has no connection with the bone cells. Haversian systems occupy a central zone in a bony shaft. External and internal to this zone compact lamellae are present, arranged parallel to the surface. Fig. 47.-Bone cell or corpuscle. The cell occupies a lacuna. TISSUES. 81 Outer circumferen- tial lamella. Haversian or con- centric lamella. Haversian canal. Interstitial lamella. Inner circumferen- tial lamella. Fig. 48.- Segment of a transversely ground section from the shaft of a long bone, showing all the lamellar systems. Metacarpus of man (Bohm and Davidoff). 82 NORMAL HISTOLOGY AND ORGANOGRAPHY. In the circumferential lamellae canals, called Volk- mann's canals, convey blood-vessels to the Haver- sian canals. In the angular interstices, between the Haversian systems, lamellae and canaliculi are found arranged like those of the circumferential lamellae. The shafts of long bones contain a marrow cavity. At the ends the marrow cavity disappears, and the bony structure becomes spongy with many inter- stices and is then called cancellate bone. The middle of flat bones is made up of a like loose structure called diploe. Lacuna. Canaliculi. Haversian canal. Fig. 49.-Portion of a transversely ground disc from the shaft of a human femur (Bohm and Davidoff). Periosteum.-The periosteum is a dense, fibrous, connective-tissue membrane that covers the bone and is derived from the perichondrium of the carti- lage. It is composed of two layers, (a) an inner layer that contains many elastic fibers and osteo- blasts, or bone-forming cells, known as the osteo- genetic layer, and (&) an outer layer of coarse, white, fibrous bundles where numerous blood-vessels ramify and send branches to the Haversian canals. TISSUES. 83 The periosteum is anchored to the compact bone by means of bundles of fibers (Sharpens fibers') that pass concentrically or parallel to the Haversian systems. Blood Supply.-The compact bone is supplied with blood from the periosteum. Larger blood- vessels, called perforating vessels, pass directly through the bony shaft and supply the marrow. In removing bone, as a rib, the periosteum is not taken away, and because of the latter's vascularity and osteogenetic layer, the removed part regenerates. On the other hand, infected marrow and diseased bone may be removed from the inner surface until a mere shell remains of the once solid shaft. If all the infection is removed a regeneration follows. Development of Bone.-The development of bone is either intramembr anous or endochondral. In the latter a cartilage stage intervenes, otherwise the history in each case is the same. A synopsis of endochondral development is as follows: i. A solid shaft of hyaline cartilage, non-vascular and without any marrow cavity. 2. In the center of this shaft the cartilage cells enlarge, their lacunae enlarge and coalesce, particu- larly along lines extending toward the ends of the bone. The rosette produced by this excavation is called the primary areola of Sharpey. 3. Lime salts are deposited in the thin walls of these spaces, making calcified cartilage. 4. Osteogenetic cells and blood-vessels from the periosteum enter the cartilage spaces. The carti- lage cells disappear with this invasion and the ex- 84 NORMAL HISTOLOGY AND ORGANOGRAPHY. cavation, begun by the cartilage cells, is further en- larged by the bone cells. The excavated areas are now called the secondary areolce of Sharpey, the cavities having a rich blood supply quite in con- trast with the primary areolae. The marrow cavity Vesicular cartilage cells. Primary periosteal bone lamella. Periosteal bud. Periosteum. Unaltered hyaline cartilage. Fig. 50.-Longitudinal section through a long bone (phalanx) of a lizard embryo. The primary bone lamella originating from the periosteum is broken through by the periosteal bud. Connected with the bud is a periosteal blood-vessel containing red blood-corpuscles (Bohm and Davidoff). is excavated and the shaft becomes longitudinally porous. Endochondral bone, therefore, develops in cartilage, not from cartilage. 5. Osteogenetic cells attach themselves to the wall of these enlarged Haversian canals and become en- closed in lime deposits, forming thus the outer lam- ellae and outer row of bone cells of each Haversian TISSUES. 85 system. Cells with lamellae are added centripetally to this outer row and thus ultimately complete the Haversian system, leaving a small central canal contain- ing vessels and a nerve. Ossification begins in the center of the cartilage shaft and proceeds gradually toward each end, so that all the above changes occur at one and the same time. After birth these changes go on at the ends of the bone, so long as it keeps growing. During this period the bone is made thicker by deposits from the periosteum forming the circumferential lamellae of bony shafts. These lamellae q~c added without the inter- vention of a cartilage stage and therefore represent intra- membranous development. Regeneration of Bone.- The embryonic process of developing bone is repeated every time a broken bone heals. As a rule the carti- lage stage does not intervene. A synopsis of the healing process of a simple fracture is as follows: Fig. 51.- Longitudinal section through area of ossification from long bone of human embryo (Huber). 86 NORMAL HISTOLOGY AND ORGANOGRAPHY. i. Hemorrhage and clot. The fibrin of the clot tends to hold the broken ends in apposition. The parts are swollen and red, due to the influx of blood. 2. Organization of the clot. Connective-tissue cells and white corpuscles enter the clot, feed upon it and ultimately replace it, the connective-tissue cells meanwhile producing fibers. The organized clot is a more substantial fabric and more firmly holds the broken ends in apposition. 3. Osteogenetic cells enter the organized clot and deposit lime salts, producing a primary callus. The connective fibers shrink, pulling the broken ends firmly together, producing a sensation known as knitting of bone. The primary callus surrounds the bone, and may even fill the marrow cavity. 4. Haversian systems are formed, uniting the broken ends. These systems appear just as de- scribed under development of bone. 5. Primary callus is absorbed and marrow cavity excavated. Bone cells called osteoclasts are sup- posed to be active factors in this absorption. General Considerations.-Bone does not grow in the same sense as other tissues do. Any increase in size is due to apposition of bone lamellae upon those already formed. Accompanying and often pre- ceding bone production we usually find a destructive or excavating process. It is believed two classes of cells bring about these changes: (a) Osteoclasts that cause bone absorption, and (5) osteoblasts that en- gage in bone production. The latter are supposed to be particularly abundant in the osteogenetic layer of the periosteum. TISSUES. 87 Bone tumors are not uncommon and are called osteoma. They are of slow growth, usually as- sociated with bone, and harmless. On account of the great vascularity, a broken bone heals more rapidly than a broken tendon, or liga- ment, or a broken cartilage. An old bone is brittle and the healing process a slow one on account of the increase of earthy matter and a decrease of the organic. An infection beneath the periosteum is a felon. The periosteum is firmly attached to the bone by Sharpey's fibers and the pressure produced by an in- fection beneath it gives rise to extreme pain, which is instantly relieved by an incision. An inflam- mation in the bone is called an ostitis, while if it is located in the marrow cavity it is called an osteo- myelitis. Muscular tissue consists of elongated cellular ele- ments in which contraction takes place along the long axis of the cell. This contraction is intrinsic to the muscle cytoplasm, and of this the spongioplasm seems to be the active agent. The word sarcode and its derivatives is used in describing muscle proto- plasm. This word was introduced by Dujardin, in 1835, and was later replaced by the word protoplasm. 1. Smooth, Non-striated or Involuntary Muscle.- This is the simplest form of muscle tissue. The cells are mononucleated, elongated, or spindle-shaped, and vary in length from 40 to 200 /z. The nucleus occupies the center of the cell, is rich in chromatin, and oval, with blunt ends, or cigar-shaped. The HI. MUSCULAR TISSUE. 88 NORMAL HISTOLOGY AND ORGANOGRAPHY. cytoplasm is longitudinally striated, the striations being due to fibrils or sarcostyles, which are, structur- ally, probably analogous to the spongioplasm. Between the fibrils there is a homogeneous sub- stance, the sarcoplasm, which is analogous to the hyaloplasm. These cells are enclosed in a delicate cement layer usually not described as a cell wall. The ends overlap each other and are held together by a delicate cement substance. Nerve fibers from the sympathetic nervous system reach the muscle cells and terminate in small granules upon the mus- cle cytoplasm. Fig. 52.-a, Cell from smooth muscle of intestine; b, Cross section of smooth muscle of intestine. Smooth muscle is found in the wall of the tubes of the body, and invariably in thin layers, with one exception-the wall of the uterus-where the muscle may be an inch in thickness. Usually, too, this muscle is laid down as an internal circular layer with an externally applied and thinner longitudinal layer. Plain muscle is found in the wall of the ali- mentary tract, trachea and bronchi, bladder, ureter, uterus, Fallopian tubes, urethra, vas deferens, blood-vessels, lymph-vessels, large ducts of glands, TISSUES. 89 nipple, hair-follicles, Eustachian tube, spleen, pros- tate gland, ciliary muscles, and iris of the eye. 2. Cardiac Muscle.-The heart ontogenetically is a modified blood-vessel, and its muscle, therefore, has the same origin as smooth muscle. Heart- muscle cells are oval or brick-shaped and mono- nucleated, the oval nuclei occupying the center of Muscle nucleus. Connective-tissue cell. Fig. 53.- Longitudinal section of heart muscle fibers. the cell. Longitudinal fibrils and, in addition, a fine cross striation, are present in the cytoplasm, resembling the cross stri- ation of voluntary mus- cle. This cross striation is explained under Vol- untary Muscle, and therefore will not be given here. The cells are joined together, end to end, by delicate ce- ment lines and laterally may unite with adjacent cells by means of protoplas- mic processes. In the cytoplasm adjacent to the ends of the nuclei, normally fat is frequently present and Muscle nucleus. Connective- tissue cell. Fig. 54.- Cross section of heart muscle fibers. 90 NORMAL, HISTOLOGY AND ORGANOGRAPHY. also some pigment. The latter is more prominent in old hearts, to which it imparts a brown color. At present the exact structure of the heart muscle is a disputed question. In sections, many breaks or artifacts resemble the cement lines separating adjacent cells. The longitudinal fibrils are said to penetrate the cement and thus establish a con- tinuity of protoplasm between adjacent cells. The presence or absence of a cell wall, analogous to the sarcolemma of voluntary muscle, is also disputed. 3. Voluntary Muscle.-A voluntary muscle fiber is a multinucleated, greatly elongated cell, which may attain a length of 12 cm. (5 inches). These fibers are arranged parallel to each other and grouped into bundles, called fasciculi. Each fasciculus is Sarcolcmma. Sarcoslyles. Fig- 55--Voluntary muscle fiber. The sarcoplasm has broken, show- ing the smooth sarcolcmma. surrounded by connective-tissue cells and fibers in which many blood-vessels ramify. A finer fabric of connective tissue penetrates the fasciculus and gives support to the individual fibers. The connective tissue that enters a fasciculus is called the endo- mysium, and that which surrounds a fasciculus is called the perimysium. Fasciculi are grouped into coarser bundles and these collectively make up a muscle. The muscle is in turn enveloped in a firm connective-tissue layer called the epimysium. In gross anatomy the latter constitutes the deep fascia TISSUES. 91 of muscle. In tough meat the connective-tissue element is extensively developed and the fasciculi are large and coarse. Each muscle fiber has a delicate, transparent, smooth cell wall called the sarcolemma. The oval distinct nuclei lie immediately beneath the sarco- lemma in higher vertebrates, but in lower forms and in all embryos the nuclei lie deeper in the muscle protoplasm. These nuclei have the same structure as the nuclei of any other tissue, but the cytoplasm shows a distinct and regular cross and longitudinal striation, characteristic of only one other tissue- the cardiac muscle. The longitudinal striation is due to the presence of delicate fibrillae called sarcostyles, which is an- alogous to the spongio- plasm of other cells. A more homogeneous and fluid substance intervenes between the sarcostyles, called sarcoplasm, and is in turn analogous to the hyaloplasm of other cells. The sarcostyles are not uniformly or evenly dis- tributed in each muscle fiber, but are grouped into bundles. In cross sections the fiber has therefore a honeycomb structure, the minute areas being known as Cohnheim's fields. A single Cohnheim field represents the cut ends of a single bundle of fibrils or sarcostyles. The cross striation is intricate and therefore more difficult to explain. This striation consists of alter- Cohnheim's area, a bundle of sarcostyles. Sarcoplasm. M uscle nucleus. Sarcolemma. Fig. 56.- Cross section of three voluntary muscle fibers. 92 NORMAL HISTOLOGY AND ORGANOGRAPHY. nating light and dark bands. The dark bands are doubly refractive to light, or anisotropic, while the light bands are singly refractive, or isotropic. The dark bands represent a predominance of the sarco- style substance, and the light bands a predominance of the sarcoplasm. In the middle of the light band a dark line can be seen, known as Krause's membrane. In the middle of the dark band a light-colored line is present, known as Hensen's median disc. The latter disappears when a fiber contracts. Krause's membrane. Sarcomere. Sarcomere. Sarcous ele- ment. Hensen's me- dian disc. Sarcoplasm. Sarcostyles. Fig. 57.-Diagram of voluntary muscle fiber; A, Fiber relaxed; B, fiber contracted. These transverse markings are all due to the dis- tribution of the sarcoplasm and the regular con- strictions of the sarcostyles. The sarcostyles are not of uniform dimensions, but at regular intervals show dilatations alternating with constrictions. The dilatations appear at regular intervals and in the same transverse plane of the muscle fiber, thus giving rise to the dark band. Krause's membrane is not a membrane, but represents minute nodal points of the sarcostyles, placed in the same trans- TISSUES. 93 verse plane of the fiber and in the middle of the light band. The light band represents an abundance of sarcoplasm and it is in this sectional area that the sarcostyles suffer a constriction. As Hensen's me- dian disc is a light line in the middle of the dark band there must be a deep constriction, if not a complete constriction of the sarcostyles at this point. The whole muscle fiber between the two Krause's mem- branes is called a sarcomere, and con- sists of a median dark band and the proximal halves of the adjacent light bands. A single fibril or sarcostyle between two of Krause's mem- branes is called a sarcous element. It is believed that muscular contractil- ity is particularly a function of the sarcostyles and that the sarcoplasm serves more as a storage of energy or food. As to color there are two kinds of muscle, white and red. In white meat, as the muscle of the Muscle. Tendon. Fig. 58.-Part of a longitudinal sec- tion through the line of junction be- tween muscle and tendon. At the line where the tendon fibrils join the sarco- lemma (a), the nuclei of the muscle are very numerous. Sublimate preparation (Bohm and Davidoff). 94 NORMAL HISTOLOGY AND ORGANOGRAPHY. breast of a bird, the fibers have a poor supply of sarcoplasm and a predominance of sarcostyles. In red meat the fibers are rich in sarcoplasm and have a less supply of the sarcostyle protoplasm. In the myology of man both kinds of fibers are present. The white fibers are more powerful but have less endurance; that is, if held in tetanic contraction with no interval of rest they would tire quicker than the red fibers. The pectoral muscle of birds is powerful, but would soon tire but for the interval of rest that intervenes between the strokes of the wing; that is, during its upward movement. Fig. 59.-Three voluntary muscle fibers from an injected muscle, show- ing network of blood-capillaries. Blood Supply.-Blood-vessels follow the con- nective tissue of a muscle, and penetrate to the individual fibers where they break up into capil- laries. These vessels run, as a rule, parallel to the fibers, forming a network with anastomosing branches. They extend in a varicose manner between the fibers in such a way that when a muscle contracts they readily adjust themselves, without breaking. Nerve Supply. - Medullated nerve fibers accompany TISSUES. 95 the blood-vessels and terminate beneath the sarco- lemma in special end plates called muscle plates. These will be described under special nerve endings. Non-medullated or sympathetic nerve $bers also accompany blood-vessels, but they innervate the in- voluntary musculature of arteries and veins. Distribution.-Voluntary muscles are the skeletal muscles, and make up the bulk of the body. Striated fibers are present in the upper part of the esophagus, and also constitute the platysma muscle of the skin. Union with Tendon and Bone.-The muscle fibers terminate abruptly with tendon fibers. This is not a direct end-to-end union, but the tendon fibers fuse with the sarcolemma at an angle. In the same way the muscle fibers unite with the periosteum of the bone. At this point Sharpey's fibers are particularly abundant and firmly anchor the peri- osteum to the compact bone lamellae. General Considerations.-A muscle tumor is called a myoma. Tumors of plain muscle are common in the wall of the uterus. They are benign, of slow growth, and usually harmless. A tumor of striated muscle fibers is very rare. The tissue is highly specialized and the fibers therefore do not multiply readily. If a muscle is injured or cut the voluntary fibers regenerate partly from the cut end and partly from free muscle nuclei that are shed into the wound, but mostly by connective-tissue repair that leaves a permanent scar. The physiological action of plain muscle is slow, producing peristaltic contractions. That of volun- tary muscle is rapid, as in the wings of insects. 96 NORMAL, HISTOLOGY AND ORGANOGRAPHY. Voluntary muscles, while more powerful, tire easily. Plain muscle has a wonderful endurance. The pain produced by violent action of plain muscle is in direct proportion to the degree of contraction. Some examples are: the colicky pains of the intestine; labor pains; pains due to calculi in the ureter or bile duct; or the pain in appendicitis produced by con- traction of the plain muscle of the appendix. These pains have many things in common They may last for hours, they remit and recur with regularity, and they come in waves. An infection in a muscle, as a psoas abscess, bur- /Nucleus and nucleolus. Telodendria. Neurilemma. Medullary sheath. Axis cylinder. Node of Ranvier. Collateral. Dendrites. Fig. 60.-Diagram of a neuron. rows in the fascia,-that is, spreads along the con- nective-tissue septa, perimysium and endomysium. The quality of meat depends on the amount of con- nective tissue. In tough meat the fasciculi are coarse and perimysium abundant. In tender sir- loin the reverse prevails. Nervous tissue is most highly specialized of all tissues and consists of elements called neurons. A neuron is a nerve cell with all its processes. These cells vary greatly in size; usually they are large. IV. NERVOUS TISSUE. TISSUES. 97 They have one or more processes, no cell wall, and a distinct nucleus. The nucleus has a conspicuous nucleolus, a prominent nuclear membrane, but a small supply of chromatin. The cytoplasm is usually pigmented, the pigment being collected to one side of the cell. It is this pigment that gives nervous tissue a gray color wherever these cells are found. Fat and vacuoles are also usually found in the cytoplasm. The proc- esses of nerve cells are: Connective tissue. Fibrils of axial cord. Fibrils. M edullary sheath. Fig. 61.-Transverse section through the sciatic nerve of a frog. At a and b is a diagonal fissure between two Lantermann's segments; as a result, the medullary sheath here appears double (Bohm and Davidoff). i. Axis cylinder (Deiters' process, axon, neurite, or neuraxon), which is usually a long protoplasmic process that physiologically carries an impulse away from the cell. Collaterals are nerve processes that leave the axis cylinder at right angles. They are commonly found near the nerve cells, but may ap- pear at a node of Ranvier some distance away from the nerve cell. 98 NORMAL HISTOLOGY AND ORGANOGRAPHY. 2. Dendrites, which are usually short processes, very much branched, and physiologically carry an impulse toward the nerve cell. A collection of nerve cells constitutes a ganglion, while a nerve plexus is a reticulum or interlacing of nerve fibers. Nerve cells are classified, according to the number of their processes, into unipolar, bipolar, and multipolar. Nerve Cells.-i. Unipolar nerve cells.-These are nerve cells with but one process. If a nerve cell Nerve fibers. Pat cells. Artery and vein. Bipolar nerve cells. Fig. 62.- Section of spinal ganglion. has but one process that process must be an axis cylinder. If a nerve cell has many processes only one is an axis cylinder, the others are dendrites. Unipolar nerve cells are found in the olfactory mucous membrane. They are columnar or cylindrical and each gives rise to a basal process, the axis cylinder, which remains non-medullated and extends through the cribriform plate to enter the olfactory lobe of the cerebrum. This class of nerve cells is common in invertebrates. TISSUES. 99 2. Bipolar Nerve Cells.-Bipolar nerve cells have two processes,-one axis cylinder and one dendrite. Nerve cells of the spinal ganglia and ganglia of the Nerve fibers in cross section. , Nucleus of nerve cell. Nucleolus. Connective-tissue cells forming a capsule around the nerve cell. Fig. 63.-Two bipolar nerve cells from the spinal ganglion. cranial nerves belong to this class. These cells apparently are unipolar, but their embryology clearly shows the single process to be morphologically equivalent to two. In this particular case the long peripheral process carries an im- pulse to the cell, and this long process is therefore a dendrite. The short process that unites the ganglion with the central ner- vous system is the axis cylinder. These large bipolar cells are surrounded by a cap- sule of connective-tissue cells. The cells are large and the single compound process very soon divides into the two processes mentioned above. The cytoplasm Fig. 64.-Three ganglion cells from a spinal ganglion of a rabbit embryo. The cells are still bipolar. Their proc- esses come together in later stages, and finally form the T-shaped structure seen in the adult animal; chrome-silver method (Bohm and Davidoff). 100 NORMAL HISTOLOGY AND ORGANOGRAPHY. of these cells has a fibrillar structure, this striation having a close relation to the fibrillae of the axis cylinder. The spinal ganglia are situated on the posterior or sensory root of the spinal nerves and within the vertebral canal. The Gasserian, geniculate, audi- tory, jugular, and petrosal ganglia of the cranial nerves are morphologically equivalent structures. The nerve cells of all these ganglia are bipolar, with the exception of a few cells said to be multipolar. In addition to nerve cells, nerve fibers and connective-tissue elements make up the histology of these gan- glia. A liberal blood and lymph supply is always present. 3. Multipolar Nerve Cells.-■ These are nerve cells with many processes, only one of which is an axis cylinder. They constitute by far the bulk of nerve cells and are found in the brain and spinal cord and in ganglia along the sympa- thetic nervous system. The cells vary in size from 4 /z in the granular layer of the cerebellum to 150 /z, the largest nerve cells of the spinal cord. Chromatophile granules, vacuoles, fat, and a fibrillar structure is found associated with the cytoplasm. Large multipolar nerve cells, called cells of Purkinje, are found in the cerebellum and will be described with the histology of that organ. Nucleus. -<£an' glion cell with a process dividing at essL^from^a the™frogngbBdhm and Davidoff). TISSUES. 101 Nerve Fibers.-i. Medullated Fibers.-Medullated nerve fibers usually consist of three parts, (a) axis cylinder, (6) medullary sheath, (c) neurilemma. An axis cylinder is a cell process that carries an impulse away from the nerve cell. It is a slender cytoplasmic process and may be very long, as is the case with /^turaxis- .Dendrite Fig. 66.-Ganglion cell from the Gasserian ganglion of a rabbit; stained in methylene-blue (intra vitam) (Huber). the motor fibers that come from nerve cells in the anterior horn of the spinal cord and extend, without interruption, to muscles in the distal parts of the limbs. The axis cylinder presents a longitudinal striation, a fibrillar structure, that is supposed to be continuous with the cytoplasmic striation of the 102 NORMAL HISTOLOGY AND ORGANOGRAPHY. Dendrite. Neuraxis. Dendrite. 'Neuraxis. Fig. 67.-Motor neurons from the anterior horn of the spinal cord of a new-born cat; chrome-silver method (Huber). Telodendrum Dendrite. Cell-body. Neuraxis. Fig. 68.-A nerve cell with branched dendrites (Purkinje's cell), from the cerebellar cortex of a rabbit; chrome-silver method (Bohm and Davidoff). TISSUES. 103 cell body. The fibrils are imbedded in a fluid pro- toplasmic substance, the neuroplasm, and the whole surrounded by a delicate membrane, the exolemma. Implantation cone is an elevation that is sometimes Brush-like telodendrion. Main dendrite. Secondary dendrite. Basal dendrite. N euraxis with collaterals. Fig. 69.-Pyramidal cell from the cerebral cortex of man; chrome- silver method (Bohm and Davidoff). present at the junction of the axis cylinder and cell body. The medullary sheath (white sheath of Schwann) is a covering to the axis cylinder. This sheath never 104 NORMAL HISTOLOGY AND ORGANOGRAPHY. extends to the nerve cell but begins a little distance from it. It consists of fat and neurokeratin. The latter, on burning, gives an odor of burnt bone. It Ranvier's node. Axial cord. Medullary sheath. Nucleus. Ranvier's node. Fig. 70.-Medullated nerve fibers from a rabbit, varying in thick- ness and showing internodal segments of different lengths. In the fiber at the left the neurilemma has become slightly separated from the under- lying structures in the region of the nucleus (Bohm and Davidoff). is this sheath that gives the white color to nerves and the white matter of the brain. In osmic acid prep- arations, oblique fissures appear in the medullary sheath dividing it into sections known as Schmidt- TISSUES. 105 Lantermann segments. It is claimed by some that these are artifacts. Nodes of Ranvier are con- strictions of this sheath at regular intervals of 80 to 900 The smaller the fiber, the greater the distance between these nodes. Long fibers are slender, with long distance between the nodes; short fibers are coarse, with short distance between the nodes. Furthermore, in young fibers and at the distal por- tion of nerve fibers the nodes are relatively closer together. The neurilemma is a thin structureless membrane that surrounds the medullary sheath. An oval nucleus is present in this sheath, midway between the nodes of Ranvier. At each node the neurilemma is constricted and touches the axis cylinder, which in turn may be slightly thickened at this point and may give off a collateral. Medullated nerve fibers with a neurilemma are found in the cranial and spinal nerves. Medullated fibers without a neurilemma are found in the brain and spinal cord. The neurilemma gives great strength to the fibers. Its absence in the brain and cord accounts for the pulpy, soft nature of this tissue. 2. Non-medullated nerve fibers with a neurilemma, but without a medullary sheath, mingle with the medullated fibers. The sympathetic system con- Fibrils of axial cord. Neurilemma. Segment of Lantermann. Fig. 71.-Longitudinal section through a nerve fiber from the sciatic nerve of a frog (Bohm and Davidoff). 106 NORMAL HISTOLOGY AND ORGANOGRAPHY. sists largely of non-medullated fibers. Terminal branched endings of an axis cylinder, called neuro- podia, have neither medullary sheath nor neurilemma. The axis cylinder, just as it leaves its nerve cell, is likewise uncovered. Nerve Trunk.-The fibers that constitute a nerve are grouped into bundles called juniculi. Each funiculus is enclosed in a connective- tissue sheath, the perineurium, which sends septa, the endoneurium, in among the individual fibers. The whole nerve is enclosed in a firm con- nective-tissue sheath, the epineurium. Blood- and lymph-vessels accompany the connective-tissue elements and ramify through the nerve just as is the case in a muscle. Nerve cells with a long axis cylinder were classified by Golgi as Type I, and with a short axis cylinder as Type II. Golgi believed the former to be motor in function, and the latter sensory, a classification no longer tenable. Neuroglia tissue is a delicate sup- porting tissue of the brain and cord, consisting of cells with many fine in- terlacing branches, mossy cells, or spider cells. These cells develop from the ectoderm and are onto- genetically closely related to nerve cells. Their function is to give support, not to conduct nerve impulses. The great nerve center in the body is the cerebro- Nucleus. Fig. 72.-Re- mak's fibers (non-medullated fibers) from the pneumogas trie nerve of a rabbit (Bohm and Da- vidoff). TISSUES. 107 spinal system-brain and spinal cord. Next comes the sympathetic system, made up of ganglia and Epincurium. Perineurium. - Fat cells. Endoneurium. Funiculus. Nerve fibers in cross section. Artery and vein. Fig- 73--Cross section of nerve trunk. Neuraxis of peripheral sensory neuron. Spinal ganglion. • Dendrite of periph- eral sen- sory neu- ron. A nlerior horn of gray matter of spinal cord. ' Neuraxis of peripheral motor neuron. Nerve- trunk. Sympathetic ganglion. Neuraxis of sympathetic neuron. Fig. 74.- Diagram to show the composition of a peripheral nerve- trunk (Huber). mostly non-medullated nerve fibers that terminate in glands or smooth muscle. Lastly, the peripheral 108 NORMAL HISTOLOGY AND ORGANOGRAPHY. system,-nerve terminations formed in tissues and organs throughout the whole body. General Considerations.-Nerve cells are so highly specialized that their multiplication after birth is un- known. We never, therefore, find tumors of nerve cells. If a nerve cell is cut, the axis cylinder re- moved from the nerve cell dies while the end that is still attached to the cell regenerates and may Fig. 75.-Neurogliar cells: a, from spinal cord of embryo cat; b, from brain of adult cat; stained in chrome-silver (Bohm and Davidoff). restore the lost part. Surgeons unite the ends of a cut nerve so that the axis cylinder may develop along the old nerve trunk which becomes a path of least resistance. In amputations the cut nerve may grow into a tumor, called a neuroma. Such a tumor would con- sist of nerve fibers and the accompanying connective- tissue elements. Injury to nerve cells, such as TISSUES. 109 brain or ganglia, heal by production of connective tissue and accompanying scar. The function of the axis cylinder is to conduct a nerve impulse. Physiologically such an impulse travels away from the cell, but experimentally it may pass in the opposite direction, as is the case when a nerve is stimulated midway in its course. The axis cylinder being made up of fibrils, it follows that such a cylinder may conduct more than one impulse, which in turn reach different centers through dif- ferent collaterals. The function of the medullary sheath is to protect and nourish the axis cylinder. Experimentally the non-medullated nerve fibers will tire quicker than the medullated. The nodes of Ranvier are points where nourishment from the blood and lymph can reach the cylinder. It is affirmed by some that the endolemma is only a lymph space surrounding the axis cylinder. The neurilemma is protective in function and gives great strength to the fibers. With nerves that ter- minate in muscle fibers the neurilemma is continuous with the sarcolemma of the muscle. Proximally the neurilemma begins where the medullary sheath takes up, always a short distance from the nerve cell, which leaves the axis cylinder uncovered as it emerges from the cell. It is affirmed that the neuron represents the ele- mentary unit of nerve tissue, and that neurons are merely in contact with each other and not in proto- plasmic continuity. This idea constitutes the neuron theory. CHAPTER Hl. CIRCULATORY SYSTEM, BLOOD, MARROW, AND LYMPHATIC ORGANS. HEART. The heart is a muscular organ. Its wall consists of three layers, endocardium, myocardium, and epicardium. i. The endocardium is a serous membrane that covers the inner surface. Histologically it consists of two layers, an inner lining of simple squamous epithelial cells (endothelium or mesothelium), and an outer layer composed of connective-tissue fibers, connective-tissue cells, and smooth muscle cells. The endocardium is reflected over the heart valves where the smooth muscle is particularly abundant. 2. The myocardium is the middle layer and forms the mass of the heart wall. It consists of muscle tissue, the cardiac muscle already described (page 79). This muscle consists of many layers that course in different directions with connective-tissue elements intervening, in which branches of the coronary blood-vessels ramify. 3. The epicardium is the outer covering, a serous membrane, and histologically similar to the endo- cardium, with a greater deposit of fat. The epi- cardium is reflected to form the pericardium, the 110 CIRCULATORY SYSTEM. 111 epithelial cells secreting a serous fluid that acts as a lubricant. Arteries.-The arteries convey blood from the heart to the capillaries, and vary in size from the aorta, the largest, down to minute structures of mi- croscopic caliber. The walls of these vessels are composed of three layers: tunica intima, media, and adventitia. i. Tunica intima is the internal coat and is a very ARTERIES AND VEINS. Fig- 76.-Cross section of small artery and vein; A, artery; V, vein. thin, smooth, glassy membrane, often difficult to demonstrate in sections. This is again divided into three layers, the innermost being a layer of pavement endothelial cells, outside of which we find a delicate fibrous connective-tissue fabric, the sub- endothelium, anc utside of this again a layer of elas- tic fibers called the fenestrated membrane of Henle. The endothelial layer is made up of a single layer of flattened cells, held together by a cement substance and analogous to the endothelium of the peritoneum. 112 NORMAL, HISTOLOGY AND ORGANOGRAPHY. and pleura already described. These cells are plas- tic, loosely attached to the subendothelium, and form a slippery surface over which the arterial blood flows rapidly. Any damage to these cells results quickly in the formation of a small blood- clot at the point of injury, from which we infer that they play a most important physiological role in their relation to the blood stream. The subendo- thelium is made up of a delicate network of elastic fibers, enclosing a few connective-tissue cells, which allows the applied endothelium a limited amount of mobility. The fenestrated membrane of Henle (called the internal limited membrane of the media by some authors) consists of a coarser elastic network of heavier elastic fibers which when peeled away as a whole presents on the exposed surface a basket- work arrangement of its fibers with numerous in- tervening elongated apertures like so many windows, hence its name. This membrane in cross-section of arteries appears as a wavy or corrugated white line encircling the artery very near to its inner surface. 2. Tunica Media.-This is the middle layer of an artery, and makes up the bulk of its wall. In small arteries a considerable amount of smooth cir- cular muscle fibers is always present, while in the larger arteries circular elastic and non-elastic con- nective-tissue fibers make up its bulk. A sprinkling of connective-tissue cells may be seen, also a limited amount of longitudinal muscle and connective-tis- sue elements. A few blood capillaries and lymphatic spaces are present, which always connect with a CIRCULATORY SYSTEM. 113 coarser vascular system of the outer layer, never directly with the blood within the artery through the intima. Of course, nerve endings are found, which can only be demonstrated in specially pre- pared sections. 3. Tunica Adventitia.-This is the outer layer, Endothelium. Subendothelium. Fenestrated mem- brane oj Henle. • Media. Adventitia. Fat cells. Vasa vasorum. Fig. 77.-Cross section of aorta. and is made up of a loose arrangement of tissues, and, taken as a whole, is less definitely defined than the media. It varies in thickness according to the lo- cation of the artery, but, as a rule, it is not so wide as the media; while in the media the connective- tissue fibers are arranged in sheets which interlace with any muscle that may be present, in the adven- titia the fibers form diagonal bundles, mostly of the 114 NORMAL HISTOLOGY AND ORGANOGRAPHY. non-elastic kind, which mingle with the adjacent are- olar tissue with which arteries are nearly always as- sociated. These bundles often serve as support to organs, by which the latter are more firmly an- chored. From such a union between the vena cava and abdominal aorta to the liver this organ receives a substantial support. The kidneys and ovaries are organs that may be cited as benefiting greatly by such a connection. A considerable amount of fat is often present in the adventitia, also connective- tissue cells, nerves, a few smooth muscle fibers, lymphatics, and blood-vessels. The latter are called vasa vasorum, and play an important part in the nourishment of the arterial wall. The vasa vasorum are sub-branches derived usually from some small branch of an adjacent artery, but may come directly from a small branch of the same artery which is given off at a higher point. As stated before, large arteries have relatively a large amount of elastic fibers and a small amount of smooth muscle. The aorta has scarcely any muscle. In the small arteries the reverse is true. The wall of large arteries is relatively thinner than that of small ones. The reverse is true of the intima. In large arteries the adventitia is also relatively scant, while in the smaller ones the adventitia may be one- half to two-thirds the thickness of the media. On account of the rigid and elastic arterial wall these vessels are usually empty after death, contracted but retain their normal shape; while veins, on the other hand, collapse and usually contain a certain amount of blood. CIRCULATORY SYSTEM. 115 Veins.-These vessels convey the blood from the capillaries back to the heart. The progressive in- crease in size and the thickness of their walls is accompanied by a relative increase in blood pressure and rate of blood flow, yet nowhere is this equal to what obtains in the large arteries. Structurally we find the same layers in veins as in arteries, with the chief difference that the vein wall is much thinner. The endothelial layer of cells is supported by a very thin layer of delicate connective-tissue fibers, mostly non-elastic, while the fenestrated mem- brane of Henle is incomplete and usually difficult to demonstrate. The media, as in arteries, is the most prominent layer, but, unlike arteries, the non- elastic fibers prevail. Smooth muscle fibers, mostly circular, are often significant in this layer, while the other tissue elements are less conspicuous. The adventitia resembles more closely that found in arteries, with perhaps even less of the elastic ele- ments and more of the smooth muscle cells. Com- paring the different sizes of veins, we find an excess of elastic and muscular tissue in large veins. In the pulmonary vein the circular muscle fibers are well developed, while in the large cranial veins, such as the meningeal sinuses, muscle tissue is almost entirely absent. Veins, like arteries, therefore, show a structural variation, depending not only on size, but on location. It should be mentioned that in many superficial long veins, like those of the legs and neck, valves are present in the form of crescentic folds of the intima which function in overcoming the pressure of blood due to gravity. Those of the 116 NORMAL HISTOLOGY AND ORGANOGRAPHY. neck are so placed as to become functional when an animal lowers its head, as in the act of grazing. Summary of Arteries and Veins. I. Tunica intima. i. Endothelium, simple squamous epithelial cells. 2. Subendothelial layer. *(o) White connective-tissue fibers. (b) Connective-tissue cells. t(c) Elastic connective-tissue fibers. t3- Henle's fenestrated membrane (elastic internal limiting mem- brane). Interlacing basketwork of elastic fibers. II. Tunica media. fi. Smooth muscle, circular. f2. Elastic plates and fibers, longitudinal and circular. 3. Nerves. 4. Blood capillaries, difficult to demonstrate. *5. White connective fibers. 6. Connective-tissue cells. 7. Muscle fibers longitudinal, rare. III. Tunica adventitia. *1. White connective-tissue fibers, longitudinal and oblique. 2. Connective-tissue cells. t3- Elastic connective-tissue fibers, longitudinal (external limit- ing membrane). 4. Nerves. 5. Vasa vasorum (blood-vessels). 6. Lymphatic vessels and nodes. *7. Smooth muscle fibers. It should be remembered that structural difference in large and small arteries is in keeping with their function. In small arteries or arterioles, the involun- tary muscle is conspicuous, as it is the contraction of this muscle that regulates the blood supply to an organ. In large arteries, as the aorta, the muscle is * This tissue predominates in veins. tThis tissue predominates in arteries. CIRCULATORY SYSTEM. 117 unnecessary and is greatly reduced, while elastic ele- ments are unusually well developed. The muscle, too, is deficient in large veins situated deep in the body, as the vena cava. Many of the smaller and more superficial veins have valves, folds of the in- tima, so arranged as to equalize the gravity press- ure of the contained blood. Without these valves the thin-walled veins would become greatly distended. If for any cause the veins ex- pand so that the valves do not act, a permanent distention with engorgement of blood follows. The veins become distorted and are spoken of as varicose veins, a condition quite common to the long saphenous veins of the lower limbs. Capillaries. -These are the finer organic ramifications of the circulatory system, and unite arteries and veins. Histologically, the walls of capillaries consist of a single layer of flattened epithelial (endothelial or mesothelial) cells. The blood courses very slowly through these in- terlacing tubes. The white cells penetrate the walls and under certain conditions even the red corpuscles Endothelium. Subendothelium. Fenestrated mem- brane of Henle. Media. Adventitia. Fig. 78.- Cross section of small artery. Intima. Media. Adventitia. Vasa vasorum. Fig. 79.- Cross section of vein, 118 NORMAL HISTOLOGY AND ORGANOGRAPHY. may do so. According to some investigators, minute pores in the epithelial wall, called stigmata and sto- mata, allow this migration. Others deny the presence of these spores, in which case the blood elements escape by passing between two adjacent epithelial cells, after which this opening closes. The blood is derived from the mesoderm; it is a red fluid that consists of (i) a liquid portion, the plasma, and (2) solid constituents, the corpuscles. There are at least three classes of the latter, red corpuscles, 'white corpuscles, and platelets. 1. Red corpuscles (erythro- cytes) in the mammalia are non- nucleated, circular, biconcave discs. In all the other verte- brate groups and in all embryos they are nucleated oval and biconvex cells. Each corpuscle consists of a red coloring matter, hemoglobin, and a more substan-. tial fabric or reticulum, the stroma. The hemagiobin is the bearer of oxygen, is readily solu- ble in water, leaving the stroma or fabric, which is then known as a ghost corpuscle. The red corpuscles are soft and elastic and are covered by an oily film. In a fresh spread they adhere to each other by their concave surfaces forming rouleaux or "money- THE BLOOD. Flat view. Side view. Rouleau. Rouleau. Fig. 80.- Red blood- corpuscles from man. CIRCULATORY SYSTEM. 119 pile" rows. This is purely a physical phenomenon. As soon as the oily covering dissolves this combination disappears. The corpuscles are extremely susceptible to changes in the plasma. If water is added they will swell up and the hemoglobin begins to dissolve. With evaporation the corpuscles begin to shrink, forming minute processes and they are then said to be crenated. Evaporation of water produces an in- creased percentage of the salts in solution. This in turn ab- stracts water from the cor- puscles and the shrinking or crenated condition follows. It is estimated that the total amount of blood in man is one-thirteenth the weight of the body. The average normal male, therefore, has approximately 25,000,- 000,000,000 red corpuscles. The life period of a red , Fig. 81.- Crenated red blood-corpuscles from man. Fig. 82.-Red blood-corpuscle of frog; a, flat view; b, side view. corpuscle is not definitely known, but physiologists tell us it is probably from two to four weeks. Ac- 120 NORMAL HISTOLOGY AND ORGANOGRAPHY. cordingly the daily consumption and loss is enormous, and is equaled only by as constant and regular a production of new cells. Their number in man is 5,000,000 per cubic millimeter. The following table gives the size of the red blood- corpuscle in the different groups of animals: Man 7.2 to 7.8 p. Monkey 7.0 /x. Dog 7.5 /x. Cat 6.2 /x. Horse 5.6 /x. Guinea-pig . . 7.5 /x. Chick .... 12.1 by 7.2 {i. Duck .... 12.9 " 8.0 ft. Tortoise. .21.2 " 12.5/x. Snake. ...22.0 " 13.0/x. Frog 22.3 " 15.7/x. Newt . . . .30.7 " 19.0 [i. White Corpuscles.-These are colorless, nucleated, plastic, ameboid cells. Their number in man is from 7000 to 10,000 per cubic millimeter. They are variously classified according to the morphology of their nuclei, or the granules in the cytoplasm that Small mononuclear. Large mononuclear. Polymorphic Polynuclear. Eosinophile. Fig. 83.-White blood-corpuscles from man. take different stains, or as to their origin, or as to their function. For practical purposes they may be classified as: i. Lymphocytes size 8 to io microns... .22 per cent. 2. Large mononuclear leucocytes. " 10 to 15 " .... 4 " " 3. Polynucleated " 12 " ....74 " " (a) Mast cells 0.4 per cent. (b) Eosinophiles 2 to 4 " " (c) Neutrophiles 70 " " CIRCULATORY SYSTEM. 121 Lymphocytes are small, mononucleated, white cor- puscles, with a distinct staining nucleus and a very narrow border of cytoplasm. Amoeboid motion is, accordingly, much limited in this class. Large mononucleated leucocytes have a large vesic- ular and usually eccentric nucleus. Its chromatin occurs in scattered granules that stain less deeply with nuclear stains, while the finely granular cyto- plasm is usually abundant. These cells are gener- ally regarded as phagocytic in function. Polynuclear cells are only slightly larger than the red blood-corpuscles. The nuclei are often nodular, polymorphic; that is, are united by slender constric- tions, or are lobulated and of a variety of patterns. In a small number of these cells basophilic granules are found in the cytoplasm, which stains blue with basic stains. These are the mast cells. Another small group have eosin-staining granules, and these are the eosinophiles. The large bulk of polynucleated white corpuscles have cytoplasmic granules that take neither acid nor basic stains, and these are the neu- trophiles. They are the white corpuscles found abun- dantly in ordinary pus and the ones that produce a general leucocytosis in such infections. The percentage of these different cells and their total number per cubic millimeter is of the greatest clinical value in blood analysis. They are often called ijuandering cells, as they are able to pass through the capillary wall and migrate throughout the tissues and organs. The poly nucleated form is readily recognized by its multiple or fragmented nuclei. 3. Blood platelets are small, colorless, round, non- 122 NORMAL HISTOLOGY AND ORGANOGRAPHY. nucleated bodies about one-third the size of red blood-corpuscles. They are supposed to play an im- Fig. 84.- Ehrlich's leucocytic granules (from preparations of H. F. Muller): a, Acidophile or eosinophile granules, relatively large and regularly distributed; e, neutrophile granules; p, amphophile granules, few in number and irregularly distributed; y, mast cells witn granules of various sizes; 3, basophile granules; (a, o, and e, from the normal blood; y, from human leukemic blood; p, from the blood of guinea-pig) (Bohm and Davidoff). portant role in the coagulation of blood. As soon as blood is shed they disappear, unless special precaution is made to preserve them. They may be preserved by pricking the finger through a drop of osmic acid. Their number per cubic millimeter is from 200,000 to 600,000. Hemin Crystals (Teichman's crystals).-These come from the hemoglobin of the blood and when found are always a positive evidence of blood. The crystals can be obtained from clotted blood, no mat- ter how old the clot or stain is. Dry blood and salt, CIRCULATORY SYSTEM. 123 equal parts, are ground together on a glass slide, a few drops of glacial acetic acid are added and heat applied until gas-bubbles appear. The crystals are brown, rhombic, and easily recognized. Fig. 85.-Crystallized hemoglobin: a, b, Crystals from venous blood of man; c, from the blood of a cat; d, from the blood of a guinea-pig; e, from the blood of a hamster; f, from the blood of a squirrel (after Frey). MARROW. Bone marrow is either white or red. The white marrow occupies the shaft of the bone and is largely fat. The red is found in the ends of bones or can- cellated portions and is richly supplied with blood. 124 NORMAL, HISTOLOGY AND ORGANOGRAPHY. Histologically, we find in marrow all the con- stituents of blood and connective-tissue elements, fibers and cells. In addition, the following are some of the more characteristic cells of this tissue: i. H ematoblasts or Nucleated Red Blood-corpuscles. -These cells contain hemagiobin and a small round nucleus that stains heavily with hematoxylin. They are supposed to be the chief source of the red blood- corpuscle, in which case the nucleus must disappear either by disintegration or extrusion. 2. Marrow Cells or Myelocytes.-These are large cells with a rather large nucleus that stains lightly. 3. Eosinophiles.-These are destined to become the eosinophile of the blood. 4. Giant Cells (myeloplaxes or osteoclasts).- These are very large polynucleated cells, having from ten to twenty nuclei. Cells of this class are not numerous, but extremely large (30 to 100 (U). They may be found in the fetal liver or spleen, and are very char- acteristic of developing bone. They present a finely granular proto- plasm without any cell wall. The many nuclei are bunched about the center of the cell, and in this respect they differ from the giant cells found in tuberculosis foci, in which the nuclei are found near the periphery. They multiply by mitosis, and primarily are supposed to be derived from leucocytes by endogenous division of their nuclei. These remarkable cells have usually been re- garded as the active agents in bone absorption, but recently Wright has suggested that blood platelets Fig. 86. - Hemin, or Teischman's crys- t a 1 s from blood- stains of man. CIRCULATORY SYSTEM. 125 may be derived from their cytoplasm by a process of budding or by particles merely breaking away. General Considerations.-There is an old saying that "a person is as old as his blood." A truer ex- pression would be that he is as old as his blood- vessels. With age, or dissipation, the blood-vessels harden, due to depositions of connective-tissue ele- ments. This impairs the free circulation of blood and the body, as a whole, suffers. The hardened condition is spoken of as arteriosclerosis, or atheroma. Usually the in- tima suffers first by becoming much thickened. Later, a like disturbance takes place in the media and adventitia. As superficial scars remain permanently, and can not be eliminated, so there is no re- lief for this scar formation of the blood-vessels. Under this hardened condition a rupture of the smaller arteries is not uncommon, particularly those of the brain, as they have thinner walls. Such a disas- ter is apt to be fatal. An inflammation of the heart, as endocarditis, is apt to produce a deposit of connective tissue in the endocardium, which upon shrinking brings about defective valves, with leak- age of blood. This increases the work of the heart, and although that organ in an emergency can do Hematoblasts. Eosinophile. Marrow cell. Giant cell. Fig. 87.-Cellular elements of red marrow. 126 NORMAL HISTOLOGY AND ORGANOGRAPHY. twenty times its normal work, there is of course a limit to its power, and broken compensation sooner or later follows. The vasa vasorum, that carry blood to nourish the walls of both arteries and veins, are very important structures. The coronary vessels of the heart be- long to this class and their course is quite definitely known. Our knowledge of the rest is vague. They ramify through the adventitia and to a less extent Giant cell. Marrow cell. Hemaloblasl. Fai space. Fig. 88.-Section of red marrow. in the media. If a blood-clot forms within the ves- sel, loops from the vasa vasorum enter the clot and assist in its organization. The endothelial cells of the intima, according to one theory, are active agents in preserving the fluid condition of the blood; that is, inhibiting coagulation. If these cells are injured a clot of blood quickly forms upon the injured or denuded CIRCULATORY SYSTEM. 127 surface. Surgeons take advantage of this principle and twist or crush the ends of bleeding vessels to check a hemorrhage. The identification of blood-stains is often a medico- legal problem. The corpuscles of the blood pre- serve their integrity for a remarkably long period of time, so that in a water solution of even an old clot, Capsule. Trabecula. Germinal center. Lymph sinus Fig. 89.- Section of lymph node. the red blood-corpuscles are readily detected under the microscope. Hemin crystals is another evidence that the stain is blood. To identify the blood of man is practically impossible. Non-mammalian blood, as that of a bird, can usually be positively recognized by the nucleated red blood-corpuscles and their oval form. The practical value of this in criminal cases is apparent. LYMPHATIC SYSTEM, THYMUS, AND SPLEEN. i. Lymphatic Capillaries.-The walls of these capillaries consist of a single layer of flattened epithelial cells (mesothelial or endothelial). They 128 NORMAL HISTOLOGY AND ORGANOGRAPHY. therefore, histologically, resemble the blood-capil- laries. They are not so well defined but represent rather irregular cavities with numerous constrictions. These capillaries, according to one theory, form a closed system and open only into the larger vessels. Germ center. Mnosls. . Lymph-sinus. Medullary cord. Fig. 90.- From a human lymph gland. At a are seen the con- centrically arranged cells of the lymph nodules (fixation with Flem- ming's fluid) (Bohm and Davidofl). Another theory is that at their origin they communi- cate with intercellular spaces. 2. Lymphatic Vessels.-These accompany blood- vessels and have very thin walls. Ultimately they drain into the large thoracic lymph duct or the short right lymphatic duct; each finally opens into the venous system at the junction of the subclavian and jugular veins. The thoracic duct begins with the receptaculum chili, just below the diaphragm and a little to the right of the vertebra?, passes upward into the thorax to open into the venous system on the CIRCULATORY SYSTEM. 129 left side, as given above. The histology of the walls of these vessels resembles that of the veins. 3. Lymph Glands..-These represent adenoid tis- sue, and consist of (1) reticular connective tissue and (2) lymph cells. Lymph glands are found throughout the body in connection with lymph vessels, fat and connective tissue. They serve as filters to the lymph Epilh» Hum oj intestine. Gland. ■ Germ center. Submu- cosa. Fig. 91.- A solitary lymph nodule from the human colon. At a is seen the pronounced concentric arrangement of the lymph cells (Bohm and Davidoff). and contribute white corpuscles to the blood. Structurally, these nodes have a connective-tissue capsule, that sends filaments into the node, called trabeculae. Within these meshes lymph cells are densely packed around the periphery of secondary nodules, which in turn occupy the cortex of each node. The center of each nodule is known as the germ center or lymph pulp. The periphery of each secondary nodule, being densely packed with white lymph-corpuscles, takes a darker stain than the 130 NORMAL HISTOLOGY AND ORGANOGRAPHY. center. The space occupied by these white corpus- cles is called the lymph sinus. The cells of the sinus are in circulation while those of the germ center remain stationary. Lymph glands represent adenoid tissue and con- sist of two elements, (a) reticular connective tissue, with many elastic fibers, and (b) lymphoid cells. An inflammation of this tissue is therefore called adeni- tis. Blood-vessels and nerves ramify through this tissue. They enter at one point called the hilum. Lymph vessels connect with opposite points of the node, the efferent one passing out at the hilum. The Hilus.- Cortical 'substance ..Trabec- ula. Medul-^ lary | sub- stance. Fig. 92.- A small lobule from the thymus of child, with well- developed cortex, presenting a structure similar to that of the cortex of a lymph gland (Bohm and Davidoff). efferent quickly unites with a second node to which it becomes the afferent vessel. In this way the lymph nodes are united into chains, always accompanying blood-vessels and fascia. Solitary lymph nodes are found just beneath the epithelium of mucous membranes, particularly in the alimentary tract. They resemble secondary nodules of lymph nodes. In the lower part of the CIRCULATORY SYSTEM. 131 ileum they are collected into patches called agmi- nated lymph nodules or Peyer's patches. Hemolymph Glands.-These resemble the lymph nodes described above, except that the lymph sinus is filled with blood. When first discovered they were believed to be evidence of disease, but they are now looked upon as normal structures. They are most readily found in the fascia involving the thoracic aorta, and are particularly abundant in the sheep. Capsule. T rabecula. Cortex. Medulla. Corpuscle of Hassal. Fig. 93.- Section of lobule of thymus gland. THYMUS GLAND. The thymus gland is described in this place be- cause of its resemblance in the adult to a lymph organ. In the embryo it is an epithelial organ that develops from the hypoderm of the third and fourth visceral clefts. Lymphoid tissue invades this epithe- lium and reaches its highest development in a child two years old. After this age the lymphoid tissue is 132 NORMAL HISTOLOGY AND ORGANOGRAPHY. invaded by connective tissue and fat, so that at the age of puberty only a remnant of the original struc- ture remains. In the child the thymus is a paired, elongated, lobulated, ductless organ that lies partly in the neck and partly in the thorax upon the large blood- vessels. Structurally we recognize a capsule with trabecula, pulp and the corpuscles of Hassal. i. Capsule and Trabecula.-The capsule consists of dense connective tissue, mostly nonelastic fibers and cells. Processes or trabecula pass into the or- gan from the capsule and divide it up into distinct angular lobules. Fibers from the trabeculae enter the lobules where they interlace to form a supporting reticulum. 2. Pulp.-This consists of lymphoid cells that fill the intersticies of each lobule. The cells are more densely packed along the periphery of each lobule, so that an outer or cortical layer can be distin- guished from a central portion, the medulla. 3. Corpuscles of Hassal.- These are nests of epithelial cells that lie in the medulla and are remnants that show the epithelial origin of the or- gan. They stain red with eo- sin and are found in no other organ. It is affirmed that these epithelial cells continue to grow after birth and may be found late in life when only remnants of the thymus is present. Lymphoid cells. Epithelial cells. Fig. 94.-Corpuscle of Hassal surrounded by lym- phoid cells from the me- dulla. CIRCULATORY SYSTEM. 133 SPLEEN. The spleen is a blood-forming organ, very vas- cular, purple in color, and with a density slightly more than that of the liver. It varies greatly in size, the average being five inches long and three inches wide. Its surfaces touch the left kidney, the cardiac end of the stomach, and the left lower aspect of the diaphragm. Its long axis follows the direction of the tenth rib. It is practically covered by the Vein. Malpighian corpuscle. Trabecula. Capsule. Artery. Spleen pulp. Fig. 95.- Portion of section of human spleen. The figure gives a general view of the structure of the spleen (Sobotta). peritoneum. The structures to be recognized are capsule and trabecula, Malpighian corpuscles, and spleen pulp. i. Capsule and Trabecula.-The investing peri- toneum forms a serous coat with simple squamous 134 NORMAL HISTOLOGY AND ORGANOGRAPHY. epithelium and connective-tissue fibers. Subjacent to this the spleen is provided with a strong cap- sule consisting of elastic fibers, connective-tissue cells and involuntary muscle. The spleen is thus not only distensible but may pulsate. From the deep surface of the capsule processes or trabeculce of connective tissue and smooth muscle pass into the substance of the spleen. From the trabeculae finer branches pass to form a fine supporting fabric for the whole organ. Capsule. Trabecula. Malpighian body. Artery. Spleen pulp. Fig. 96.- Section of spleen. 2. Malpighian Corpuscles.-These are lymph pock- ets in the adventitia of the smaller arteries. The artery rarely passes through the center of the cor- puscle, but usually eccentric to or one side of it. The lymph corpuscle is liberally supplied with blood. 3. Spleen Pulp.-This constitutes the bulk of the spleen and fills the spaces between the trabeculae. The constituent corpuscles of the blood are present in this pulp and splenic cells. The latter are slightly CIRCULATORY SYSTEM. 135 larger than white blood-corpuscles, are mononu- cleated and contain pigment and frequently red blood-corpuscles. Blood Supply.-The splenic artery enters the hilum and its branches follow the trabeculae. Ultimately the smaller branches enter the spleen pulp. Beyond the Malpighian bodies the smaller arteries end in minute dilatations known as the ampullae of Thoma. Beyond these the blood flows directly into the meshes Larger fibers of a Malpighian body. Reticular fibril (G itterjas- ern). Fig. 97.- From the human spleen (chrome-silver method) (Bohm and Davidoff). of the spleen pulp with no other walls than the spleen cells. The veins begin in the same way as the arteries encl. The capillary veins pass directly to the trabeculae and ultimately unite at the hilus to form the splenic vein which drains into the portal. General Considerations.-The invasion of bacteria into the system is chiefly along the lymphatics. Each lymph node becomes a point of resistance, and 136 NORMAL HISTOLOGY AND ORGANOTHERAPY. usually enlarges many times the normal size, far in advance of the seat of infection. This is due to the absorption of the toxins. Thus the lymph nodes in the groin enlarge from an infection in the toe, those in the axilla from an infected finger, and those of the neck from a bad tooth. If these barriers break down the infection becomes systemic, a condition known in a general way as blood-poisoning. Capsule. Intralobular trabecula. Intralobular venous spaces. Intralobular vein. Ampulla of Thoma. Artery to one oj the ten com- partments. Intralobular artery. Spleen pulp cord. Interlobular vein. Interlobular trabecula. Intralobular vein. Intralobular trabecula. Malpighian corpuscle. Fig. 98.- Diagram of lobule of the spleen (Mall). The function of the thymus gland is not known. Since its structure resembles the tissue of a lymph node it is reasonable to suppose that it has a like function. Recently structural changes have been observed in this organ in epileptics, but whether these changes are a cause or a consequence of the dis- ease is not known. The lymphoid tissue of the spleen no doubt CIRCULATORY SYSTEM. 137 contributes to the supply of white blood-corpuscles. The broken-down red corpuscles found in this organ have led to the further idea that the spleen is a graveyard for the worn-out red corpuscles of the blood. Leucocytes are supposed to feed upon this detritus and then migrate to the liver, where it is elaborated into the bile pigment of that organ. Anything that causes an enlargement of the lymph nodes usually causes an enlargement of the spleen. Like these nodes the spleen is capable of enormous distention, due to the abundance of elastic con- nective-tissue fibers. This is particularly so in typhoid fever, where the spleen has been known to weigh fifteen or twenty pounds. On account of the rich blood supply an injury to the spleen causes severe hemorrhage, which the pulpy condition of the organ renders difficult to check, as a suture usually does not hold. In such accidents the whole spleen has been removed with- out fatal results. Extirpation of the spleen is also justified in certain diseases of that organ CHAPTER IV. DIGESTIVE SYSTEM. The digestive system consists of alimentary canal and accessory digestive glands. The Alimentary Canal.-This is a muscular tube extending through the body and measures about thirty feet in length. The following parts will be described: I. Mouth II. Pharynx. III. Esophagus. IV. Stomach. V. Small Intestine. i. Duodenum. 2. Jejunum. 3. Ileum. IV. Large Intestine. 1. Vermiform Appendix. 2. Cecum. 3. Colon. (a) Ascending. (&) Transverse. (c) Descending. (di) Sigmoid Flexure. 4. Rectum. The mouth is limited by the lips in front, and the cheeks laterally. The arched palate forms its roof THE MOUTH. 138 DIGESTIVE SYSTEM. 139 and the tongue is attached to the movable floor, while posteriorly it opens into the pharynx through the isthmus or jauces. This cavity is lined by a con- tinuous mucous membrane, consisting of stratified mucous epithelium placed on a tunica propria. In Sinus pracervicalis. Mandibular process of first visceral arch. Eye ■ Fig. 99.-Human embryo of about twenty-eight days (His): I-V, brain-vesicles; /\ /2, /3, /4, cephalic, cervical, dorsal, and lumbar flexures; ot, otic vesicle; ol, olfactory pit; mx, maxillary process; hl, H2, heart; I, ll, limbs; al s, allantoic stalk; ch, villous chorion. the submucosa is found connective-tissue elements in which the elastic fibers predominate; also con- nective-tissue cells, mucous and serous glands, nerves, and nerve endings, blood- and lymph-vessels. 140 NORMAL HISTOLOGY AND ORGANOGRAPHY. The mucous membrane is continuous with the skin at the outer border of the lips. At this border the horny layer of skin begins, otherwise the skin and this mucous membrane are similar structures. Morphologically, the mouth cavity is to be re- garded as a part of the outside surface of the body, which, embryologically, has been included by the development of neighboring parts. At the time the neural folds are closing dorsally to form the brain and cord there develops a series of paired, ventral, facial pits. These, enumerated from before back- wards, are: the lens of the eye, the nasal pit, the mouth, and gill clefts. The tissue between the latter are called visceral arches, while that one between the anterior gill cleft and the mouth cavity is the man- dibular arch. The latter is morphologically analogous to the visceral arches. In man the gill clefts all finally close permanently, but the ectodermal em- bryonic mouth cavity ultimately unites with the embryonic foregut, thus forming the jauces which lead to the pharynx. This final perforation be- tween the mouth cavity and the foregut is paired, in lower forms, which with other embryonic relations confirms the view that the mouth cavity morpho- logically represents a median fusion of two gill clefts. During this period of development the forebrain grows ventrally and the mandibular arch grows in the same direction. The space between these structures is the beginning of the mouth and the nose, and is called the stomodeum. At this time a rounded eleva- tion, from the base of the mandibular arch, grows for- ward along the base of the forebrain. This growth DIGESTIVE SYSTEM. 141 forms part of the maxillary arch, and finally most of the upper jaw. In this manner the stomodeum Nasal pit. Lateral protuberance. Globular protuberance. Maxillary arch. Mandibular arch. ■ Nasal process. -Nasal pit. 'Lacrimal canal. Maxillary arch. Mandibular arch. Stomodeum. Fig. 100.- Development of the face of the human embryo (His): A, Embryo of about twenty-nine days; B, embryo of about thirty-four days; C, embryo of about the eighth week; D, embryo at end of the second month. becomes divided into an olfactory region and the mouth cavity proper. The stomodeum at this stage 142 NORMAL HISTOLOGY AND ORGANOGRAPHY. is a deep pentagonal cavity. Its lower boundary is formed by the mandibular arch, while laterally are to be found the maxillary processes of each side. Its upper boundary is formed by an unpaired growth called the nasofrontal or nasal process (Fig. 100.) Situated on each side of the nasal process are the nasal pits. Each pit divides the nasofrontal process into a lateral external portion called the lateral frontal protuberance, which forms the outer boundary Ventricle of cerebrum. Third ventricle. Place from ivhich the hy- pophysis is developed. Fourth ventricle. Stomodeum. Heart. Foregut. Spinal cord. Notochord. • Fig. ioi.- Median section through the head of an embryo rabbit 6 mm. long (after Mihalkovics) of each nasal pit, and a median or central portion called the globular protuberance, which constitutes the inner boundary of each pit. The two lateral or side protuberances grow around the olfactory pits and form the alse of the nose, while the two central portions develop into the intermaxillary bone con- taining the incisor teeth and the center of the lip. By studying the text figures a correct idea of these DIGESTIVE SYSTEM. 143 relations is readily obtained. It will be seen that the line of contact between each lateral protuberance and maxillary process forms a groove, the naso-optic furrow or lacrimal groove, which later closes to form the lacrimal canal. The line of contact between each globular protuberance and the maxillary pro- cess is less close, and places each nasal pit in wide communication with the mouth. A failure of union in the latter case causes the deformity of harelip, Nasal pit. - Eye. Median triangular por- tion of palate. Dental ridge. Lateral portion of palate. Fig. 102.- Roof of the oral cavity of a human embryo with the fun- daments of the palatal processes (after His). which may be double or single, depending on whether both or only one side is involved. About the fortieth day, in the human embryo, the maxillary processes have grown so far toward the median plane that they have met and united with the lateral and also the median protuberances of the nasofrontal process. The nasal pits are thus sepa- rated externally from the oral fossa. With this union the arch of the upper jaw is complete, but the 144 NORMAL HISTOLOGY AND ORGANOGRAPHY. inclosed space is in one chamber, there being no separation between the mouth and nose cavities. The formation of a palate, however, effects a separa- tion between the two. The rudiments of the palate appear as shelf-like projections from the inner or oral surface of the upper jaw. A triangular piece grows backward from the globular protuberance of the nasofrontal process, which ultimately unites with horizontal or palatal plates from the maxillary arch. In the eighth week of embryonic life, union of the palatal plates begins at their anterior extremi- ties and proceeds backward. A deficiency in the union constitutes the deformity of clejt palate. Cleft palate is therefore, embryologically, a later development than harelip. Either may occur with- out the other, but they are usually found together. The cleft of the palate usually turns to one side, passing out between the cuspid and lateral incisor teeth. A double cleft palate is Y-shaped, the center piece in front containing the incisors, and representing the anterior triangular piece of the rudimentary palate, this piece having failed to unite with the lateral palatine plates. This deficiency may involve the hard or the soft palate, or it may affect both, and even produce a cleft or bifid uvula. The completion of the palate definitely separates the nasal chambers from the mouth, the only com- munication between the two being through the posterior nares. The permanent limitations of the mouth are thus established from a cavity that develops primarily as an ectodermal invagination. The ectoderm invests not only the mouth proper, DIGESTIVE SYSTEM. 145 but clothes at least the anterior portion of the adult pharynx. The tongue, however, is invested with en- toderm epithelium and so are the Eustachian tubes. Morphologica 1 ly, teeth are appendages of the skin, and are to be compared with such structures as hair and nails. They are thus a part of the exoskel- eton and their relation to the bones or the en- doskeleton is entirely a secondary process, for the purpose of strength and support. In many of the fishes the mouth generally is lined by simple cone- shaped teeth that serve the purpose of seizing and holding the ani- mal's prey. In man the additional function of masticating the food has greatly modified the form and structure of teeth. Dentition.-There are twenty deciduous or tem- porary teeth that erupt between the ages of six months and two and one-half years. In each jaw these are,-incisors 4, cuspids 2, molars 4, the dental TEETH. Fig. 103.- The palate and supe- rior dental arch (right side): i, Me- dian incisors; 2, lateral incisors; 3, canine; 4, first bicuspid; 5, second bicuspid; 6, first molar; 7, second molar; 8, wisdom-tooth; 9, mucous membrane of the hard palate con- tinuous behind with that of the soft palate; 10, the anteroposterior raphe of palate; n, pits on each side of the raphe perforated with the orifices of glands; 12, anterior rugosities of the mucous membrane (after Testut). Designation of the Follicles. Place of Origin of the Epithe- lial Cord. Period at which the Enamel-Or- gan First Appears Period at which the Dental Bulb Ap- pears. Time of the Appearance of the Fol- licular Wall. Closing of the Fol- licle and Rupture of the Cord. Periods at which the Dentine- cap First Appears. Periods at WHICH THE T EETH ARE Erupted. Periods at WHICH THE Teeth are Normally Shed. Inf. cent, in- • cis. 6th month. 7th year. Sup. cent, in- cis. . . . 10th month. 7% years. tition. Inf. lat. incis. Sup. lat. in- cis 16th week. 16th month. 20th month. 1 8th year. smporary den Inf. cuspids . Sup. cuspids, ist inf. mo- lars .... Epithelial lamina. From 7th to 8th week. 19th week. 10th week. ( Beginning < of the (4th month. . • 30th to the 32d month. 112th year. t- ist sup. mo- lars .... 2d inf. mo- lars .... 17th week. 24th month. 26th month. 28th month. 10th year. ioJ4 years nth year. 2d sup. mo- lars . . . 30th month. 11 % years. CHRONOLOGY OF THE DENTAL FOLLICLE IN MAN (Legros and Magitot). 146 ■ Int. cent, in- cis Sup. cent, in- cis Inf. lat. incis. Sup. lat. in- cis Cord of the corresponding temporary teeth. •I 7th year. 1 8% years. Inf. cuspids. Sup. cuspids. . About the 16th week. f 20th (. week. 21st week. 9th month. f ist month (after birth. ) II to 12 J years. Permanent dentition. ist inf. bi- ' cusp. . . . ist sup. bi- cusp. . . . 2d inf. bi- cusp. . . . 2d sup. bi- cusp. . •. . • ist inf. mo- ■ lars .... ist sup. mo- lars Cord of the corresponding temporary molars. Epithelial lamina. 15th week. 17th week. 18th week. 20th week. ( 6th month -< of fetal 1 life. ) 9 to 10 j years. y nth year. I From 5 to [ 6 years. 2d inf. mo- lars .... 2d sup. mo- lars .... . Cord of the ist permanent molars. 3d mo. after birth. | ist year. ist year. ist year. 3d year. ) From 12 to J 13 years. 3d inf. mo- ■ lars .... 3d sup. mo- lars .... Cord of the 2d permanent molars. J 3d year. f After the [ 6th year. After the 6th year. After the 6th year. 112th year. ) From 18 to J 25 years. 147 148 NORMAL HISTOLOGY AND ORGANOGRAPHY. formula for one side being,-I.f C.y M.| = 10. The second set, or permanent teeth, number thirty-two •Enamel. -Pulp cavity. ■Dentin- -Cementum. Fig. 104.- Scheme of a longitudinal section through a human tooth. In the enamel are seen the "lines of Retzius" (Bohm and Davidoff). PLATE II. Dissected Skulls Showing the Development of the Teeth (Noyes). ! Skull at nine months, central incisors just erupted, laterals not yet through the gum. The root of the central about half formed. The lower first and second temporary molars seen in their crypts. The crypt for the lower first permanent molar shown, but the developing tooth has dropped out of it. The upper temporary cuspid and first and second molars are seen in their crypts. Notice the straightness of the lower jaw. 2. Skull at one year. Two incisors in each jaw are erupted. The first molars are just starting. Notice the formation of the root of the lower temporary molars just beginning. Also notice the first permanent molar in its crvpt with half of the crown formed. 3. Skull in the second year. The temporary first molar and cuspid partly erupted. Notice the develonment of their roots. Notice the per- manent cuspid above and me first molar below in their crypts. 4. Skull in fourth year. Complete temporary dentition. Notice the upper central, lateral cuspid and bicuspid in their crypts; the lower incisors, cuspid, first bicuspid, and first permanent molar. 5. Skull in sixth year. Complete temporary dentition with the first permanent molar in place. The lower central incisors have just been lost and the permanent ones are just coming through the gum. The cuspids, bicuspids and second molar are seen in their crypts. 6. The left side of the same skull as No. ,5. Notice the extent to which the roots of the first permanent molar are developed. 7. Front view of the same skull as No. 6. Notice the position of the incisors and cuspids in their crypts. 8. Skull in seventh year. The toothless age. Upper incisors lost and the permanent ones not erupted. One lower incisor in place, first permanent molar in place, but the roots not fully formed. Crown of the second permanent molar seen in its crypt. PLATE IL PLATE HI. Dissected Skulls Showing the Development of the Teeth- Continued (Noyes). g. Skull in eleventh year. The incisors are in position, but the tem- porary molars and cuspids are still in position. The second permanent molar is through the bone but not through the gum. io. The left side of the same skull. On this side the lower tem- porary cuspid and first molar have been lost. Note the position of the upper cuspid in these pictures and the distance the root extends toward the orbit. The lateral on the left side is not of typical form, but is a 'peg tooth." ii. Skull in the thirteenth year. The lower second molar the only remaining temporary tooth. The second permanent molar is in place but the roots are not fully developed. The crypt for the third molar (wisdom tooth) is seen. 12. Skull of young adult. The upper centrals are broken. The second molars are fully developed and the third molar shows the crown fully formed in the crypt. 13. Skull of adult. This shows the full permanent dentition and the roots of the teeth. 14. Edentulous jaws. Notice the position of the mental foramen. Plate HI. digestive; system. 149 and in each jaw are divided into,-incisors 4, cus- pids 2, bicuspids 4, molars, 6, the dental formula for one side being,-I.f C.| B.f M.f = 16. Structure of Teeth.-The parts of a tooth are crown, neck, roots and pulp. Its calcareous wall consists of enamel, dentin, and cementuni. Enamel.-The enamel is the hardest tissue in the body and covers the exposed portion, or crown, of the teeth. Its function is to mechanically protect the tooth. This enamel is derived from the ecto- derm, while all bone tissues are products of the mesoderm. Bone, if injured, may regenerate and repair the defect. Enamel does not regenerate if injured, the defect being permanent, as the formative enamel tissue disappears before the eruption of the tooth. Chemically, it is composed of phosphates and carbonates of calcium and magnesium, a small amount of fluorides, water, and perhaps a very small amount of organic material. In consequence of the latter, enamel, unlike bone, is soluble in acids, leaving scarcely any residue. Enamel is composed of two structural elements,- (a) enamel rods or prisms (also called fibers), and (6) inter prismatic or cement substance, both of which are calcified. These elements have different properties, both chemical and physical. The interprismatic substance is more readily acted upon by acids, and it is therefore possible to etch enamel sections and produce a disassociation of the enamel rods. The interprismatic substance is not so strong as the rods, and in splitting or breaking the enamel the tissue usually separates along the cement lines; that is, 150 NORMAE HISTOLOGY AND ORGANOGRAPHY. these lines form paths of least resistance, a fact taken advantage of in operative dentistry. According to Noyes ("Dental Histology"), "the enamel rods, or prisms, are long, slender prismatic rods or fibers, five- or six-sided, pointed at both ends, and alternately expanded and constricted through- out their length. They are from 3.4 to 4.5 microns in diameter, some of them apparently reaching the entire distance from the surface of the dentin to the surface of the enamel, but, as the diameter of the rods is the same at their outer and inner ends, and as the crown surface is much greater than the surface of dentin cov- ered by enamel, there are many rods that do not extend through the entire thickness. These short rods end in tapering points be- tween the converging rods, which extend the entire distance. To ex- press this in terms of development, as the forma- tion of enamel begins at the surface of the dentin, the increasing area of crown surface requires more ameloblasts, and as new ameloblasts take their places in the layer the formation of new enamel rods begins between the rods which were previously forming. These short rods are most numerous over the marginal ridges and the points of the cusps." The rods are not perfectly smooth and even, but show alternately expansions and constrictions. Fig. 105.-a, Enamel rods in cross section; b, Enamel rods, longitudinal view. DIGESTIVE SYSTEM. 151 They are so arranged that the expansion of adjacent rods lie opposite each other; that is, the expansions do not interlock with the constrictions. The cement substance, therefore, has a reciprocal arrangement. Sections ground parallel to the rods show, therefore, dark and light lines, described as the striations oj the enamel, which arc caused by the difference in the refracting power of the prismatic and interprismatic substances. In a ground section across the rods, the tissue presents a mosaic pattern, which becomes more distinct if treated with acid. Fig. 106.- Transverse section of enamel (Noyes). Lines oj Retzius.-These lines or stratification bands begin at the tip of the dentin cusps and sweep around in larger and larger zones. They thus pass obliquely through the enamel and record the growth of the crown, as each line was at one time the surface of the enamel. They are to be regarded as traces of the strata caused by the periodic deposition of lime salts. According to Noyes, "the appearance of striation is the record in the fully formed tissue of the manner 152 NORMAL HISTOLOGY AND ORGANOGRAPHY. of growth, each dark stripe or expansion in a rod representing a globule of calcified material. The ameloblasts build up the rods by the addition of globule after globule, surrounding them with a cementing substance and completing the calcifi- cation of both. In this sense the striation of the enamel may be said to record the growth of the in- dividual rods." Direction of the En- amel Rods.-Upon the axial surface the rods are usually straight and parallel with each other, but upon the oc- clusal surface they change their direction by a series of sym- metrical curves, and often become much twisted and wound around each other, par- ticularly the inner ends. In operative dentistry it is found that the enamel upon the axial surface cleaves readily while the gnarled portion upon the occlusal surface tends to break away in chunks. Fig. no shows the general plan of the arrange- ment of the enamel rods in the formation of the crown. In the gingival half of the middle third the rods are horizontal. Their inclination, from this horizontal direction, gradually increases toward the Denlo- enamel margin. Enamel. Dentin. Lines of Retzius. Fig. 107.-Tip of an incisor, showing lines of stratification of the enamel (Noyes). DIGESTIVE SYSTEM. 153 root and toward the occlusal surface, so that at the apices of the latter surface the rods are placed vertical to a horizontal plane. Because of this plan Noyes divides all cavities, in dental work, into two classes: "i.-Those in which the enamel rods are in- Enamel. Enamel. Dento- enamel margin. Dent"- enamel margin. Dentin. Dentin. Fig. 108. - Straight enamel, showing dento-enamel junction (Noyes). Fig. ioq. - Gnarled enamel, showing dento-enamel junction (Noyes). dined toward the cavity, characteristic of the oc- clusal surfaces. " 2.-Those in which the enamel rods are inclined away from the cavity, characteristic of axial sur faces" (Fig. m). In preparing cavities on the axial surfaces the 154 NORMAL HISTOLOGY AND ORGANOGRAPHY. lateral walls should be beveled, as shown in the above figure. The historic requirements for strength in enamel walls are: 1. The enamel must be supported upon sound dentin. 2. The rods which form the cavo-surface angle must run uninterruptedly to the dentin. 3. They must be supported by short rods, with Enamel rods horizonlal.- Dentin. Dento-cnamcl margin. Enamel. Fig. no.- Drawing, showing the direction of the rods over the mesial marginal ridge of a bicuspid (Noyes). their inner ends resting on the dentin and their outer ends abutting upon the cavity wall, where they will be covered by the filling material. 4. That the cavo-surface angle be cut in such a way as not to expose the ends of the rods to fracture in condensing the filling material against them. "The first step in the preparation of an enamel wall is to determine the direction of the enamel rods by cleavage with a chisel or hatchet. Then the wall DIGESTIVE SYSTEM. 155 Rods inclined away from cavity. Dentin. Denlo-enamel margin. Rods inclined toward cavity. Enamel. Fig. in.- Illustrating the two classes of cavities (Noyes). ■Dentin. .Enamel- Fig. 112.- Labio-lingual section of superior lateral incisor, showing a pit cavity (Noyes). 156 NORMAL, HISTOLOGY AND ORGANOGRAPHY. must be smoothed or trimmed by a shaving motion of the chisel, increasing the inclination of the wall slightly. This is done so as to be sure and reach the rod directions and remove the portions of the tissue that has been splintered by the cleavage. Then the cavo-surface may or may not be trimmed, as the position demands" (Fig. m, Noyes). Enamel. Branching of the dentinal tubules. Dentinal tubules. Interglobular space. Fig. 113.- A portion of a ground tooth from man, showing enamel and dentin (Bohm and Davidoff). Grooves, fissures, pits and developmental lines are points of weakness and in operative work cavi- ties must be excavated so as to establish a strong margin, histologically, against which to pack the DIGESTIVE SYSTEM. 157 filling. The arrangement of the enamel rods must therefore be constantly borne in mind in the opera- tive repair of teeth. Dentin.-The dentin is the second layer of teeth, and not only makes up the mass of a tooth but de- termines its form; that is, the number of cusps and roots is moulded by the developmental process of the dentin. Its histologic form has much to do with the penetration of caries. Dentin, like bone, develops from the mesoderm, and consists of an organic, formative matrix impreg- nated with about 72 percent, of inorganic salts. On boiling it yields gelatin. Minute canals of dentinal tubules radiate from the central cavity of the tooth, which contains the formative organ or pulp. These tubules are from 1.1 to 2.3 microns in diameter and are separated from each other by a dentinal matrix of about 10 microns in diameter. In the crown the tubules branch but little, excepting close to the en- amel where they anastomose freely. In the crown they radiate in sweeping curves so as to open at right angles on the dentinal surface. This produces "s" or "f''-shaped curves known as primary curves. They also present many wavy curves known as secondary curves, which is really the result of an open spiral course taken by the tubules. In the body of the dentin a few small branches are given off at acute angles, but near the enamel junction the tu- bules fork and branch freely, forming an anasto- mosis that facilitates in the spreading of caries just beneath the enamel, the micro-organisms diffusing sideways and then penetrating the dentin in the direction of the tubes. 158 NORMAL HISTOLOGY AND ORGANOGRAPHY. In the root the tubules radiate directly to the ce- mentum, showing only the primary curves. Many fine branches pass in all directions from tubule to tubule. The dentin next to the cementum contains many small irregular spaces that connect with the dentinal tubules. They present a granular ap- pearance in ground sections, and are therefore called the granular layer of Tonies. These spaces are filled by the enlarged ends of the dentinal fibrils, which are cell processes of the odontoblasts, while the fibrils also fill the dentinal tubules. The layer of Tomes may some- times be found beneath the enamel, but is never well marked. The dento-enamel junction presents rounded projections. This scalloped appearance has given rise to the view that certain dentinal tubules pass for a short distance into the enamel. In ground sections, irregularly branched dentinal spaces arc often found at a uniform depth from the surface. These are the interglobular spaces of Czer- mak and represent areas of imperfectly developed dentin. Lastly, the sheaths of Neumann represent the inner wall of the dentinal tubules, and may be regarded as differentiated and more resistant ground substance. The formation of dentin continues for an indef- Fig. 114.- Section of den- tin at right angles to the tubules (Noyes). DIGESTIVE SYSTEM. 159 inite period after the eruption of a tooth. The proc- ess is one of apposition, thickening the dentin at the expense of the pulp. Finally this growth ceases. Irritation of the pulp, or the pulp of some tooth on the same side, may lead to the formation of second- ary dentin. The latter is an imperfect structure. The tubules are smaller and less numerous, while the matrix is less compact and shows a deficiency of Enamel. Dento-enamel margin. Dentin. Dentinal tubules. Fig. 115.- Section of dentin in the crown cut in length of the tubules (Noyes). inorganic salts. Several deposits of secondary dentin may thus be produced. The Pulp.-The pulp occupies the center of the tooth. It consists of connective-tissue cells, con- nective-tissue fibrils, a semifluid interfibrillar ground substance, nerve plexus largely non-medullated, blood and lymph vessels. We may recognize three kinds or layers of cells, the most important being the 160 NORMAL HISTOLOGY AND ORGANOGRAPHY. odontoblasts, forming the outer surface of the pulp next to the dentin. i. The odontoblasts form a continuous layer over the entire pulp surface, being everywhere in contact with the dentin. This layer has been called the Enamel pulp. Enamel cells. Odontoblasts. Fig. 116.-A portion of a cross section through a developing tooth (Bohm and Davidoff). The dentin is formed, but has become homo- geneous from calcification. Bleu de Lyon differentiates it into zones (a and b). At c is seen the intimate relationship of the odontoblasts to the tissue of the dental pulp. membrane eboris or the "membrane of ivory." The odontoblasts are mesoderm cells, columnar, some- times club-shaped, with basal nuclei and three kinds of processes, (i) Each cell has one to three long, slender, protoplasmic processes projecting into DIGESTIVE SYSTEM. 161 the dentinal tubules, and extending through the tubule to the outer surface of the dentin, where they completely fill the granular spaces already described as the granular layer of Tomes. It is generally believed that these processes may transmit im- pressions to the sensory nerves of the pulp. (2) Each odontoblast shows lateral processes, minute but blunt, that interlock with like processes from adjacent cells. (3) Usually a single process pro- jects from the basal end into the pulp. The odontoblasts are dentin-forming cells and superintend the formation and calcification of primary and secondary dentin. 2. The layer of Weil represents a layer of connec- tive-tissue cells forming a thin zone just beneath the odontoblasts. In thin sections this appears as a thin layer about half as thick as that of the odonto- blasts. 3. Underneath the layer of Weil the connective- tissue cells are numerous and closely packed. To- ward the center of the pulp they become loosely but uniformly scattered. The cells are small, have a single deep-staining nucleus, and the cytoplasm stretching out into slender processes in many direc- tions, forming stellate cells; or in two directions to form spindle cells. The connective-tissue fibrils of the pulp are similar to those of white fibrous connective tissue, sometimes resembling the reticular variety. The vascular con- dition of the pulp makes it an organ of nourishment for the dentin as well as the mature tooth. Cementum.-The cementuni covers the dentin in 162 NORMAL HISTOLOGY AND ORGANOGRAPHY. the root portion of a tooth. At the gingival margin it slightly overlaps the enamel. Near this margin it forms a thin layer, but becomes thicker toward the apex of the root and between the roots of the bi- cuspids and molars. The cementum consists of parallel lamellae of bone tissue that contain no Haversian canals. Small blood-vessels from the in- vesting peridental membrane penetrate the lamellae, while other small vessels from the pulp pass through Ctmenlum. Dentin. Fig. 117.- Cross section of human tooth, showing cement and dentin. At a are seen small interglobular spaces (Tomes' granular layer). the ccmentum in the opposite direction. Fibers from the investing peridental membrane find attach- ment in the cementum. These fibers resemble the fibers of Sharpey in bone. The ccmentum, there- fore, furnishes a medium of attachment by which the tooth is held in position. Ccmentum is constantly being produced by the apposition of new surface layers. In newly erupted DIGESTIVE SYSTEM. 163 teeth the cementum is thin and in teeth of old per- sons the cementum is thick. This continuous growth is necessary in order to establish attachment for new fibers of the peridental membrane and to con- form to the natural growth of the jaw. Between the lamellae, particularly in the apical portion of the root where the cementum is thick, numerous lacunae are present, resembling those of bone. Canaliculi radiate from these lacunae with less regularity, however, than in the case of bone. They may be confined to one side of a lacuna, usually the side toward the surface. Local thickenings of the cementum, called hyper- trophies, are common. These enlargements involve one or more of the lamellae and were formerly called exostoses, or cemcntostoses. Peridental Membrane.-This is an organic tissue that surrounds the root of teeth and occupies the space between the cementum and the bony wall of the alveoli. Its chief function is to anchor a tooth to the jaw and give support to the gingivus. Its chief constituent is white connective-tissue fibers in- terspersed with a variety of cells, blood-vessels, lymphatics and nerves. The fibrous tissue may be divided into two classes: coarse, radiating fibers that form the principal bulk and perform the principal function of anchorage, and a secondary fine variety that interlace with these and unite largely with the anastomosing blood-vessels of the tissue. The principal fibers connect, on the one hand, with the cementum which they enter in bun- dles to form the fibers of Sharpey, and on the other 164 NORMAL HISTOLOGY AND ORGANOGRAPHY. hand they unite with the periosteum of the bony alvoli and the subepithelial tissue of the gum. From the upper portion of the cementum these fibers pass horizontally, some of them directly to connect with the cementum of adjacent teeth and others to mingle with the connective tissue of the adjacent mucous membrane, thus giving a firm support to the Muscle Periosteum.*) Bone of alveolar- process. Peridental mem-, brane. .Cemenlum. Pulp. • Dentin. Fig. 118.- Transverse section of peridental membrane in alveolar portion (Noyes). gingivus, a condition which becomes of primary im- portance in the mastication of food. The fibrous mat of the gum is usually greater on the lingual side, where food is brought against the gingivus with con- siderable force. If a crown band is extended too far, or if deposits accumulate as in case of uncared-for DIGESTIVE SYSTEM. 165 teeth, these supporting fibers will be cut off and the gingivus drops down and no longer fills the inter- proximal space. In the alveolar portion the principal fibers not only spread out and radiate like a fan, but are in- clined downward from their attachment in the ce- mcntum to their anchorage in the bony wall of the alveolus. Some of these fibers are tangential to the cementum and thus support the tooth against a rotary strain. The principal fibers thus perform a physical function and firmly bind the tooth to the adjacent hard and soft tissues. At the alveolar border and at the apex of the root they are so ar- ranged as to support the tooth against lateral strain, while in the rest of the alveolar portion the tangential fibers are particularly numerous and sup- port the tooth against any rotary force which may result from the mastication of food. At the gingivus line the fibers blend with the submucosa and bind the gum closely to the neck of the tooth. At the apex of the root the secondary loose variety becomes continuous with the connective tissue of the tooth pulp. The cellular elements of the peridental membrane are the fibroblasts, cementoblasts, osteoblasts, osteo- clasts, and epithelial cells, which have been called the glands of the peridental membrane. All these cells are interposed between the bundles of supporting fibers already described. i. The fibroblasts are spindle-shaped connective- tissue cells arranged in radiating rows between the fibers. They are numerous in young teeth and 166 NORMAL HISTOLOGY AND ORGANOGRAPHY. the root. They produce the cementum and there- fore resemble the osteoblasts of bone. They have a single deep-staining nucleus and irregular processes that fit around and between the fibers and also ex- tend into the cementum. A cementoblast may be- come enclosed in the cementum and thus form a lacuna which it completely fills, thus making a Fibro- blast. Epilhe- liaLiords.z 'Cemento- blast. Cemcn- tum. • Dentin. Fig. 119.- Peridental membrane next to the cementum highly mag- nified (Noyes). relatively few in old teeth. The single nucleus stains deeply, being rich in chromatin. The cells are small and, as their name implies, their function is the pro- duction of fibers that give support to the tooth. 2. The cementoblasts are flat irregular cells that fit in and adjust themselves between the fibers so as to form a single layer everywhere over the surface of DIGESTIVE SYSTEM. 167 cement corpuscle analogous to a bone corpuscle. Such an inclusion is the exception in the life history of these cells. 3. The osteoblasts are also connective-tissue cells, but cover the bony wall of the alveoli. They lie between the fibers and their function is the pro- duction of bone which anchors the supporting fibers to the alveolar wall. These cells are analogous to the osteoblasts of bone. 4. The osteoclasts are large, bone-destroying, multinuclcated cells that are often called giant cells. They may also act upon and absorb the cementum and dentin. They are not constantly present in the peridental membrane but appear whenever cal- cified tissue is to be destroyed. They apply them- selves to the surface to be absorbed and by their physiological action excavate cavities in which they lie, known as Howship's lacuna. The latter may later fill in with new cementum or bone, thus leaving a permanent record of the process of absorption and repair. The absorption of the roots of deciduous teeth results from the physiological action of the osteoclasts. If for any cause, such as bacterial in- vasion, the osteoclasts fail to appear, the root of the deciduous tooth docs not absorb but remains as a permanent obstruction to the developing new tooth. 5. Epithelial cells, believed by some to be remains of the enamel organ, envelop the surface of the roots and are found in both young and old teeth. Their function is not known. They appear as cords of epithelial cells that anastomose freely to form an en- veloping network, which nowhere seems to unite 168 NORMAL, HISTOLOGY AND ORGANOGRAPHY. with the epithelium of the mucous membrane of the mouth. The structure of some of these cords re- sembles that of tubular glands, and Dr. Black has suggested that their function may be a glandular one. They not infrequently enter into the pathological conditions of the peridental membrane. Blood Supply.--Usually several small blood-vessels enter the foramina at the apex of the root and pass di- rectly to the pulp. Upon reaching the pulp these ves- sels anastomose freely, form- ing an extensive blood plexus. A capillary plexus with nar- row meshes has been de- scribed between the layer of odontoblasts and the dentin, but does not penetrate the latter. Both arteries and veins have very thin walls and may be easily ruptured. The pulp therefore bleeds very easily when exposed. No accompanying lymphatics have been described. The peridental membrane, being a connective-tissue layer, has a very rich blood supply. Vessels enter the membrane near the apex of the root, accompanying the nerve at that place; small arterioles penetrate laterally from the Haver- sian canals of the alveolar wall, and a third supply is derived from the mucous membrane of the gum, Fig. 120.- Showing the ar- rangement of epithelial cords or glands of the peridental membrane around the root of a central incisor (dia- gram by Dr. Black). DIGESTIVE SYSTEM. 169 vessels passing over the border of the alveolar proc- esses. This vascular condition is important, both in health and disease. Nerve Supply.-The tooth pulp is supplied with nerve fibers from the fifth cranial nerve. Medul- lated dendrites of sensory neurons enter the pulp cavity through the apical foramen of the root. All of them lose the medullary sheath, but do so at variable distances in the pulp. The varicose den- Odontoblasts. Odonto- blasts. Terminal nerve fiber. Terminal nerve fiber. Fig. 121.- Nerve termination in the pulp of a rabbit's molar, stained in methylene-blue (intra vitam): a, Odontoblasts seen in side view; b, a number of odontoblasts seen in end view, showing a termi- nal branch of a nerve fiber situated between the odontoblasts and the dentin (Huber). drites ultimately form a loose plexus immediately under the layer of odontoblasts and, therefore, practically at the periphery of the pulp. Small branches pass from this plexus to terminate between the odontoblast cells, or pass through the layer of odontoblasts, but in no case have they been traced into the dentin. The sensitive dentin is, therefore, due to an indirect irritation of these nerve endings, conveyed to the latter through the medium of the 170 NORMAL HISTOLOGY AND ORGANOGRAPHY. dentinal fibrils and the odontoblasts. The pulp is very sensitive to traumatic and chemical irritations, even when conveyed to it through the constituents of the dentin. It is especially sensitive to changes in temperature, heat or cold acting alike. It has no localized sensation of touch. Our knowledge of the nerve supply of the periden- tal membrane is not extensive. Both medullated and non-medullated fibers arc present, the latter being a part of the sympathetic nervous system, and accompany as well as innervate the small blood- vessels. The nerve fibers enter the peridental mem- brane in the same manner and from the same sources as the blood supply, which has already been de- scribed. Attachment of Teeth.-In considering the attach- ment of teeth it must be remembered that teeth arc not a part of the osseous system but are dermal appendages. The phylogenetic history of this sub- ject in vertebrates is very interesting. The de- scriptive literature is extensive and many classifi- cations of the different forms of attachment have been made. Tomes, in his "Dental Anatomy," classifies four forms of attachment: (i) by a fibrous membrane; (2) hinge-joint; (3) ankylosis; (4) in- sertion in a socket. The attachment by fibrous tissue is manifest in the scaly teeth of sharks. Each cone-shaped tooth has a flattened dermal plate. Calcified connective tissue is built into this plate, which it unites more or less fibrously to the submucous matrix of the mouth. Such teeth are practically dermal scales and have no DIGESTIVE SYSTEM. 171 direct attachment to the bony skeleton. The hinge-joint is merely a modification of the fibrous attachment, and is found in many fishes, reaching a high degree of development in the poison fangs of snakes. The hinge is composed of connective-tissue elements. In snakes the fang has a muscular at- tachment by which the reptile is able to erect the fang. By ankylosis is meant a direct calcified union with the bone of the jaw. Such teeth have no flattened base, but a calcified pulp which binds them firmly to the bony skeleton of the mouth. Ankylosis is confined to the teeth of certain fishes. The development of a socket is associ- ated with large teeth and a consequent strong attachment. The evolution of a socket is well represented phylogenetically in reptiles where Wiedcrshcim makes three classes: (i) pleurodont dentition (lacertilia), where "the teeth are situated upon a ledge on the inner side of the lower jaw, with which they become fused basally;" (2) acrodont dentition (chameleon,) where "they lie on the free upper border of the jaw;'' (3) thecodont dentition (crocodiles), where "they are lodged in alveoli.'' In man all the teeth are im- bedded in well-developed alveoli of the jaw-bones. Fig. 122.- Diagram illustrating the de vclopmcnt of a• socket, a, Pleurodint dentition; b, acrodont dentition; c, the- codont dentition. 172 NORMAL HISTOLOGY AND ORGANOGRAPHY. Here the function of the teeth is not only to seize and bite the food, but also to masticate it and test its quality. This change in function accounts for the heterodont dentition, which must have arisen by a modification of the simple homodont condition in which the teeth are all small, conical, and of the same size and shape. The primary arrangement of the teeth is such that those of one jaw do not usually correspond in position with those of the other, but rather with the interspaces between them. As a rule, the succession of teeth in man is nearly always reduced to two functional sets, the deciduous Dental ridge. Enamel organs. Dental ridge. Enamel organs. Neck. Denial ridge. Fig. 123.-Diagram illustrating the development of the enamel organ of three teeth. teeth and the permanent teeth. Traces of an earlier set have been found, which may be spoken of as a " predeciduous" dentition, and occasionally one or more teeth appear which replace corresponding permanent teeth, and thus indicate the possibility of an extra unrecorded set. An unlimited succession of teeth takes place in nearly all vertebrates, except with mammals. Development of Teeth.-The enamel of the tooth develops from the epithelium of the oral cavity. In the seventh week of fetal life the mucous epithelium covering the gums invaginates to form a dental groove. The ridge or shelf thus invaginated is called DIGESTIVE SYSTEM. 173 the dental ridge. Early in the third month this dental ridge pro- duces lateral proc- esses along its lin- gual side, one for each deciduous tooth. These epi- thelial processes or sacs are known as enamel organs and develop directly into the tooth enamel. A little later, during the third month, a second set of proc- esses comes from the lingual side of the dental ridge and in like manner forms the enamel organs of the permanent set of teeth. The origin of the dentin is closely associated with the enamel organs but comes from the con- nective tissue under- lying these organs. This connective tis- sue forms dental Epithelium. Enamel organ. Dental lamina. Enamel organ. Enamel cells. Dental lam- ina. Germ jor per- manent tooth. Enamel organ. Enamel cells. Odontoblasts. Germ jor per- manent tooth. Enamel. Enamel cells. Dentin. Odontoblasts. Pulp. Fig. 124.- Diagram illustrating the de- velopment of a tooth. 174 NORMAL HISTOLOGY AND ORGANOGRAPHY. papilla, which later become differentiated into the dentin and dental pulp. The developing papillae gradually become invested by the enamel organ and one by one erupt on the surface of the oral cavity either as deciduous or permanent teeth. It will be observed that the enamel organs are sac- like structures consisting of an outer and inner layer of epithelial cells. The inner layer envelops the dental papillae and is destined to form the enamel prisms. The outer layer becomes associated with an investing sheath of connective tissue, the dental sac, and serves as a temporary protection while the enamel is being formed. When the tooth erupts the outer lining of epithelial cells disappears. The tooth papillae arc thus all preformed at the time of birth. They remain latent and develop regularly into the different teeth according to the table on page 146. A serious illness of a child just before their eruption may affect their healthy growth by interfering with proper nutrition, and imperfect and pitted teeth result, which often ac- counts for an early decay. THE TONGUE. The tongue is a voluntary muscular organ that occupies the floor of the mouth. In lower verte- brates the tongue is a prehensile organ. In many fishes it is covered with teeth, its function being to capture and hold prey. In frogs and toads it is covered with mucous and peculiarly modified to capture insects. In reptiles it is often bifurcated, very motile, and used to frighten an enemy. In DIGESTIVE SYSTEM. 175 woodpeckers it is barbed and clearly a prehensile organ. In man, while the organ assists in taking Fig. 125.- Papillar surfaces of the tongue, with the fauces and tonsils: 1, 1, circumvallate papillae, in front of 2, the foramen cecum; 3, fungiform papillae; 4, filiform and conical papillae; 5, transverse and oblique rugae; 6, mucous glands at the base of the tongue and in the fauces; 7, tonsils; 8, part of the epiglottis; 9, median glosso-epi- glottidean fold (fraenum cpiglottidis) (from Sappey). food, its more important function is gustatory, the taste organs being located upon its surface. For 176 NORMAL HISTOLOGY AND ORGANOGRAPHY. description the tongue may be divided into body, base, inferior surface, and dorsum. Body.-This is chiefly made up of striped muscle which may be divided into intrinsic and extrinsic. A median septum divides it into two symmetrical lateral halves. Connective-tissue elements, nerves, the body of glands, and blood-vessels interlace freely with the muscle. The musculature is best studied in a beef's tongue that has been boiled, and is a subject that belongs to gross anatomy. In any section of the tongue, muscle fibers will be seen both in cross section and in longitudinal section. Base.-This is the posterior wide end of the tongue that is attached to the hyoid bone. It is covered with a smooth mucous membrane, beneath which is a rich supply of lymphoid tissue. The latter con- stitutes the lingual tonsil. Mucous glands are abun- dant. Inferior Surface.-This is covered with smooth mucous membrane on which open many mucous and serous glands. The surface is divided into two halves by a fibrous septum which passes to the floor of the mouth and is known as the lingual frenum. When this is abnormally short the person is said to be tongue-tied, and speech is impaired. The Dorsum.-This surface is convex both from before backward and from side to side. A median depression, or sulcus, divides it into lateral halves. The sulcus apex points backward to the foramen cecum just in front of the base. This cecum is a blind pocket that marks the origin of the middle portion of the thyroid gland, and is the remnant of DIGESTIVE SYSTEM. 177 the obliterated thyroid duct. The dorsal surface is studded with three sets of papillae, to be described in detail. Papillae.-1. Filiform Papillae.-These are not only the smallest but by far the most numerous, and give the tongue a velvety appearance. They are arranged in divergent rows that extend outward and forward from the median sulcus. Each papilla is conical, points backward, and is covered by a thick Fig. 126.-Section through two filiform papillae of tongue. layer of stratified, horny, squamous epithelium. The function of these papillae is purely prehensile. In carnivorous animals they give the tongue a rasp- like structure that serves effectually in cleaning bones. It is said that a tiger, in this way, can draw blood from a living hand. 2. Fungiform Papillae.-These are less numerous, larger, and supplied with blood, which gives them a 178 NORMAL HISTOLOGY AND ORGANOGRAPHY. red color. They are most numerous at the tip and margins of the tongue. Each is like an inverted cone and has a covering of eight or ten layers of squamous epithelial cells. Many of these papillae have taste buds in their lateral walls, analogous to those to be described in the third class of papillae- the circumvallate. A connective-tissue papilla oc- cupies the core of the fungiform. This core has a rich supply of blood-vessels which in fevers become congested with blood and give the dorsum a Fig. 127.-Section of fungiform papilla of tongue. speckled red color, spoken of as strawberry tongue. This is particularly the case in scarlet fever. 3. Circumvallate Papilla.-These are by far the largest and are found just in front of the foramen cecum. They are about ten in number and are ar- ranged in the form of a letter V, with the apex point- ing backward. They resemble the fungiform pa- pillae, only they are much larger. Each papilla is surrounded by a deep, narrow, circular trench or DIGESTIVE SYSTEM. 179 fossa, hence their name. The wall consists of strati- fied squamous epithelium and the core of connective tissue richly supplied with blood-vessels. From this core secondary connective-tissue papillae indent the under surface of the stratified epithelial wall. Taste Buds.-These are nests of epithelial cells that lie in the lateral walls of circumvallate and Epithe- lium. Taste buds Groove sur- rounding papilla. .Ebner's gland. Fig. 128.-Longitudinal section of a human circumvallate papilla (Bohm and Davidoff). many fungiform papillae, and are closely associated with the sense of taste. They resemble small acorns, and are made up of columnar cells so arranged as to form a central taste canal, which in turn opens by a pore into the circumvallate jossa. Two kinds of slender epithelial cells are present, (i) tegmental or 180 NORMAL HISTOLOGY AND ORGANOGRAPHY. cover cells, principally at the periphery of the bud, which support or ensheath (2) the gustatory or taste cells. The latter are smaller, more delicate and centrally placed, with the distal or free end bearing a small process that projects into the inner taste pore. The cells of the taste bud occupy the whole lateral wall; that is, the base of each cell rests upon the base- ment membrane next to the connective-tissue core and the distal end extends practically to the sulcus Taste buds. Fig. 129.-Two foliate papillas from tongue of rabbit. of the papilla. These taste buds, as a matter of pro- tection, develop in the lateral wall rather than in the exposed dorsal surface of each papilla. The nerve fibers of the gustatory nerve are not in protoplasmic continuity with the epithelial cells of the taste buds, as is the case with the sensory cells of the olfactory region. Nerve fibers enter the taste buds and terminate in varicosities that interlace and come in contact with the gustatory cells of each DIGESTIVE SYSTEM. 181 taste bud. It is evident that a food to be tasted must first be put into solution to pass into the sulcus and stimulate the delicate processes of the gustatory cells of taste buds. Foliate Papillae.-On each side of the rabbit's tongue, some distance back, can be seen a small oval patch, with diagonal grooves and ridges, resembling the side of a three-cornered file. These patches are the foliate papilla. In reality they are not papillae but alternating grooves and ridges. In transverse section, the lateral walls of the ridges will be found beset with taste buds resembling in detail those Surface pore. Fig. 130.-Section through taste bud. Fig. 131.-Cells from a taste bud: a, taste cells; b, supporting cells. described in the circumvallate papillae. The rabbit, therefore, to relish his clover, should roll the leaves over these lateral patches. Glands of the Tongue.-Small serous racemose glands are associated with the circumvallate pa- pillae into the fosses of which their ducts open. Glands are otherwise absent over the dorsum of the tongue. Over the other parts of the tongue both serous and mucous glands are abundantly present. Many of these are mixed serous and mucous glands. 182 NORMAL HISTOLOGY AND ORGANOGRAPHY. Blood Supply.-The arteries are the lingual, which branches to form (i) the dorsal lingual artery which anastomoses freely with the tonsillar branch of the facial, and (2) the ranine artery that passes along the under surface. The veins are the ranine and the dorsalis lingua that drain into the internal jugular. Nerves.-These are (1) the hypoglossal, the motor nerve; (2) the lingual, from the inferior maxillary of the fifth, which is accompanied by the chorda tympani of the seventh, or facial; (3) the glosso- pharyngeal, which supplies the taste buds; (4) the internal laryngeal. Many fibers of the sympathetic system mingle with these nerves. The pharynx is the common passage for both food and air. It is an expanded portion of the di- gestive tube five inches in length and with seven openings: one, the fauces from the mouth; two posterior nares; two Eustachian tubes; one to the trachea, and the orifice of the esophagus. The mucous membrane of the pharynx is lined with stratified squamous epithelium, except in the region of the posterior nares where the epithelium is ciliated. In the submucosa there is a generous supply of mucous and serous glands and lymphoid tissue. The latter is particularly abundant in the region of the posterior nares, forming in this location the pharyngeal tonsils or adenoids. In early youth the adenoids are prone to enlarge so as to obstruct normal breathing, a condition that justifies their removal. A rich supply of elastic longitudinal PHARYNX. DIGESTIVE SYSTEM. 183 connective-tissue fibers is also present in the sub- mucosa. The submucosa is therefore capable of being greatly distended, as is the case in throat in- fections, such as diphtheria, where the congestion is so great as to interfere with respiration. The diphtheria germs and toxins arc thus lifted up and walled off from the deeper structures and normal Epithelium. Cry pl. Lymphoid nodules Tonsillar sinus. Striated muscle. Fig. 132.-Section through the pharyngeal tonsil of man (Sobotta). blood supply. This is nature's method of eliminat- ing the disease, with the possible danger to the pa- tient of suffocation. External to the submucosa come several layers of striated muscle fibers forming the pharyngeal muscle, the description of which belongs to gross anatomy. Tonsil.-The tonsils are two oval lymphoid masses imbedded in the lateral walls of the pharynx, 184 NORMAL HISTOLOGY AND ORGANOGRAPHY. opposite the root of the tongue and between the anterior and posterior palatine arches. This lymph- oid tissue is covered with the oral mucous mem- brane, beset with many depressions or pits known as crypts. It is along these crypts that bacteria may enter the tonsil, producing an inflammation of that organ known as tonsillitis. Stratified epithelium. Muscularis mucosa. Mucous glands in the submucosa. Circular muscle layer. Longitudinal muscle layer. Fig- 133.-Cross section of the esophagus. Fibrous coal. ESOPHAGUS. The esophagus is the part of the alimentary canal that intervenes between the pharynx and the stom- ach, and is a very muscular tube about ten inches in length. Its upper end is opposite the lower bor- der of the crycoid cartilage and the sixth cervical vertebra. The lower end or cardiac orifice is oppo- DIGESTIVE SYSTEM. 185 site the eleventh dorsal vertebra. Two distinct constrictions are present, one at the beginning and one where it is crossed by the left bronchus. The normal distention at these points is about four- fifths inch. The wall of the esophagus may be divided into four coats: mucous, submucous, muscular, and fibrous. i. Mucous Layer.-This layer is thrown into many longitudinal folds and lined, as in the pharynx, with stratified epithelium. The tunica propria is well developed and may contain solitary lymph nodes. Tubular glands resembling those of the stomach are found in patches, particularly at the extremities of the esophagus. They are entirely confined to the mucosa and distinct from the mucous glands found in the submucosa. Their function is problematic. A muscularis mucosa is present in the esophagus just external to the tunica propria, con- sisting of longitudinally disposed smooth muscle cells. This layer becomes more prominent in the alimentary canal below the esophagus. 2. Submucosa.-This layer lies just external to the muscularis mucosa and consists of loose con- nective-tissue elements, blood and lymph vessels, nerves and the bodies of mucous glands. These glands are compound racemose and are particularly abundant in the lower part of the esophagus. The ducts pass through the muscular mucosa to open on the epithelial surface. They secrete mucus for the lubrication and protection of this surface. Not in- frequently the morning vomit of mucus in chronic 186 NORMAL HISTOLOGY AND ORGANOGRAPHY. gastritis comes from excessive secretion of these glands. The tissues of the submucosa are loosely held together, and sections, therefore, may tear along this layer. 3. Muscular Coat.-This consists of an inner cir- cular and an outer longitudinal layer, although the fibers of each often interlace. The longitudinal layer is particularly strong, often thicker than the circular. In the upper half many striated fibers are present that are continuous with the pharyngeal voluntary muscle. The control of these fibers en- ables the dog to return food to the mouth that has passed into the upper part of the esophagus. In the lower half, only smooth muscle fibers are present. The longitudinal layer passes on as the longitudinal layer of the stomach and intestine, while the circular becomes the diagonal fibers of the stomach and does not pass to the intestine. Connective-tissue ele- ments interlace and strengthen the whole muscu- lature. Foods and liquids are carried along this tube by peristaltic contraction of its muscles, and in this way cattle and horses can take nourishment without lifting their heads. 4. Fibrous Coat.-This consists of loose connec- tive-tissue elements, mostly white fibrous, binding the esophagus to adjacent structures. It is not well defined and often difficult to demonstrate as a distinct layer. The stomach varies greatly in form and position according to physiological conditions. For de- scriptive purposes it has two ends, cardiac and py- STOMACH. digestive system. 187 loric; two surfaces, dorsal and ventral; two curva- tures, greater and lesser; and two orifices, esophageal and pyloric. The most fixed point is the esophageal orifice, which is situated opposite the seventh left costal cartilage one inch from the sternal junction. The most movable portion is the pyloric end, which is situated one-half to one and one-half inches to the right of a median plane and a variable distance be- low the esophageal opening. The distance between 7Jnteru>rju.ijace Fig. 134.-Anterior outlines of stomach. (His' model.) the two orifices is about four inches. The full length of the stomach is about ten inches, and the greatest diameter four inches, with average capacity of one quart. These dimensions are subject to great variations. The stomach wall, like that of other parts of the food canal, is made up of four layers: mucosa, submu- cosa, muscular is, and serosa. 1. Mucosa.-The mucous surface is uneven, due 188 NORMAL HISTOLOGY AND ORGANOGRAPHY. to irregular folds. The surface is beset with minute pores or circular depressions, called crypts, into which the gastric glands open. As in other parts of the food canal this layer consists of epithelium, membrana propria, and muscularis mucosa. The epithelium is simple columnar with the nucleus near the bottom of the cell, leaving a clear proximal half Crypt. Gastric glands. Afuscularis mucosa. Submucosa. Circular muscle layer. Longitudinal muscle layer. Serous coat. to each cell that does not readily stain. The pits or crypts are lined by this same epithelium. The membrana propria has a rich supply of connective- tissue cells and extensive ramifications of blood and lymph capillaries. The muscularis mucosa is a thin muscle layer, external to the membrana propria, and consists of an inner layer of circular and an outer Fig. 135.-Cross section through the wall of a stomach. DIGESTIVE SYSTEM. 189 layer of longitudinal smooth muscle fibers. A liberal supply of connective tissue is associated with this muscle. This layer, therefore, offers resistance to an invasion of bacteria, while the muscular contrac- tion relieves pressure to the rich blood supply in the submucosa just external to it, and at the same time exerts pressure upon the gastric glands. Gastric Glands.- These are widely dis- tributed and per- haps the most impor- tant structures of the mucosa. They are simple tubular, except in the pyloric region, where many of them are branched. Usually several glands open into each crypt, the latter representing a circular pit-like evagination of the epithelial surface. The wall of each gland consists of simple epithelium and two kinds of cells are present: (i) chief cells, which are by far the most numerous; these are round or cuboid cells, with central nucleus that stains blue with hematoxylin; (2) parietal cells, which are less numerous, larger, and have a granular cytoplasm that takes the red eosin stain. They inter- Crypt. Parietal cell. Chie} cell. Fig. 136.-Simple tubular gland from stomach. 190 NORMAL HISTOLOGY AND ORGANOGRAPHY. vene with the chief cells but are placed at the pe- riphery of the glands, and communicate with the central lumen by means of a network of secreting ducts. They are most abundant in the cardiac end of the stomach and along the middle and inner third of each gland. These cells are supposed to have something to do with the se- cretion of hydrochloric acid. The cytoplasm of the chief cells contains granules of pepsinogen, which is converted into pepsin of the gastric juice. During fasting, these gran- ules accumulate, and during, or after, active secretion they become smaller and tend to disappear. The mucosa secretes a varying amount of mucus for the protec- tion of the delicate epithelial sur- face. Inmany formsof indigestion, and particularly in poison cases, the mucus secretion is very exten- sive and serves to keep the irrita- ting stomach contents away from the epithelial lining. The excess of mucus can be removed by stom- ach lavage. The chief difference between the pyloric and cardiac regions of the stomach is found in the mucosa, (i) The crypts in the cardiac end are shallow, while in the pyloric end the crypts frequently extend half way through the thickness of the mucosa. (2) The gastric glands Fig. 137.-A num- ber of fundus glands from the fundus of the stomach of young dog, stained after the chrome - silver method, showing the system of fine canals surrounding the pa- rietal cells and com- municating with the lumen of the glands (Huber). DIGESTIVE SYSTEM. 191 are longer than the crypts in the cardiac end; towards the pyloric end the glands become shorter, tortuous, and pressed closely against the muscu- laris mucosa. Many of the pyloric glands arc branched. (3) The parietal cells are numerous in Epithelium of esophagus. Cardiac gland Junction of esophagus ana stomach. Epithelium of stomach. Gastric crypt- Fig. 138.-From a section through the junction of the human esophagus and cardia (Bohm and Davidoff). the cardiac region and practically absent in the pyloric. The pyloric mucosa, in this way, conies to resemble that of the small intestine. In addition an occasional villus or Brunner's gland may be found in the pyloric end. 2. Submucosa.-The submucosa in all mucous membranes is highly vascular. Besides blood and lymph there is an abundant supply of connective- 192 NORMAL, HISTOLOGY AND ORGANOGRAPHY. tissue elements, largely elastic fibers, connective- tissue cells and fat cells. Nerve cells and nerve fibers, known as Meisner's plexus, are found here and in the submucosa through- out the alimentary canal. 3. Muscularis.- This consists of smooth muscle and may be divided into three layers: (a) an inner sheath where the fibers run ob- liquely; this sheath is continuous with the circular layer of the esophagus; (5) a middle circular layer which is con- tinued as the circu- lar layer of the in- testine ; (c) an outer longitudinal layer continuous with the longitudinal layer of both esophagus and intestine; nerve cells and nerve fibers form a plexus between the longitudinal and circular muscle of the whole alimentary tract, which is known as the plexus of Auerbach. 4. Serosa.-This consists of a thin layer of fibrous tissue covered by simple pavement epithelial cells Epithelium of fold be- tween gas- tric crypt. Gastric crypt. Pyloric gland. Mucosa. M uscularis mucosa Fig. 139.-From vertical section through human pylorus (Bohm and Davidoff). DIGESTIVE SYSTEM. 193 Chief cell. Lumen. Parietal ■ cell. Mucosa. Fig. 140.-Section through fundus of human stomach in a condition of hunger (Bohm and Davidoff) Lumen. Mucosa Chief cell. Parietal cell. Fig. 141.-Section through fundus of human stomach during digestion (Bohm and Davidoff). 194 NORMAC HISTOLOGY AND ORGANOGRAPHY. and bound down to the musculans by delicate fibrous septa. It is really a part of the peritoneum. The Stomach in Ruminants.-Ruminants (ox, sheep, goat, camel, llama) all have four compart- ments for the reception and maceration of food; rumen, reticulum, oma- sum, and abomasum. The first three are morphologically dis- tensions and modifica- tions of the lower end of the esophagus, while the abomasum alone corresponds to the stomach in other ani- mals and needs, there- fore, no further de- scription here. The Rumen is by far the largest compart- ment, reaching the enormous capacity of forty gallons in the ox. It is divided into four sac-like pouches by two muscular band-like girdles whose obvious func- tion is to contract on the contents and render assistance in the mechanical process of returning food for further mastication. Its mucous mem- brane is covered with pointed papillae 3 to 9 mm. in length, excepting where the muscular pillars are most prominent. Its epithelial lining is stratified, consisting of eight to twelve layers of cells, the Papilla. Stratified epi- thelium. Submucosa. Circular muscle. Longitudinal muscle. Serous coat. Fig. 141a.-Cross section through rumen of ox. DIGESTIVE SYSTEM. 195 inner ones being very scaly and presenting a fibrous- like structure. The submucosa is vascular, with a scattering of small mucous glands, but these form no digestive secretion. Strands of smooth muscle fibers extend into the core of each papilla of the mucosa, also a net-work of blood and lymph vessels. There are two smooth muscle layers, an inner cir- cular and an outer longitudinal, the inner layer being much the heavier. Tike the esophagus, these layers show a fine cross-striation, and there is no doubt but that these layers assist in the mechan- ical process of returning the food to the mouth for a more thorough mastication. The serosa is unusually heavy and easily detected in microscopic sections. The Reticulum is the second gastric reservoir and is the smallest compartment. Its mucous surface presents a honeycomb appearance when seen from the inside, hence its name. The muscular tunic is thin, otherwise the other layers are analogous to those found in the rumen. The Omasum, or third compartment, is only a little larger than the reticulum. The mucous mem- brane is extensively folded to form large leaves ex- tending the length of the organ. Between the large leaves are smaller leaves, and again a third and a fourth series, making altogether about 400 laminae of variable sizes. These leaves bear horny papillae, being large and pointed toward the reticu- lum end and small and warty toward the omasum end. These leaves are lined with eight to twelve layers of scaly, tesselated epithelial cells, forming a rough gritty surface. A liberal supply of smooth muscle is present in the center of each leaf, also a 196 NORMAL HISTOLOGY AND ORGANOGRAPHY. network of blood- and lymph-vessels. The physio- logical action of this muscle causes adjacent leaves to rub against each other, producing a trituration of the retained food. The muscular coat is fasciculated and thin and composed of two layers that pass in dif- ferent directions. The serosa presents nothing differ- ent from the general structure of the peritoneal lining. SMALL INTESTINE. The small intestine is about twenty-four feet long, and is divided into du- odenum, ten inches; jejunum and ileum,re- spectively, two-fifths and three-fifths of the remainder. About three feet from the lower end of the ileum Meckel's diverticu- lum may be present, representing the last embryonic closure of the intestine. The in- testine has the same number of layers as the stomach. The muscularis, however, consists of but two strata, an inner circu- lar and an outer lon- gitudinal. i. Mucosa.-The mucosa is lined by simple columnar epithelium in Villus. Artery. Vein. Crypt of Lieberkuhn. Muscularis mucosa. Submucosa. Circular in uscle layer. Longitudi- nal muscle layer. Serous coat. Fig. 142.-Section of small intestine with blood-vessels injected. DIGESTIVE SYSTEM. 197 which many goblet cells are present, particularly in the deeper folds. The membrana propria and muscularis mucosa are identical with those described in the stom- ach. The mucous surface of the small intestine ismuch increased by means of folds, of which there are three mechanisms: ■valvules conniventes, villi, and crypts of Lieberkuhn. (a) Valvulce Conni- ventes.-T h e s e are concentric, trans- verse, crescentic folds of the mucosa, that usually form two- thirds of a circle, although occasionally one forms an entire circle or even a spiral. These valves are two or three inches Fig. 143.-Portion of the wall of the small intestine, laid open to show the valvulae conniventes (Brinton). Fig. 144.-Mucous membrane of the jejunum, highly magnified (schematic): 1, 1, Intestinal villi; 2, 2, closed or solitary follicles; 3, 3, orifices of the follicles of Lieberkuhn (Testut) long, about one-third inch broad and one-eighth inch thick. The inner surface of the small intestine is thus thrown up in a series of shelves. This mechanism 198 NORMAL HISTOLOGY AND ORGANOGRAPHY. has an analogue in the typhlosole of the earthworm and the spiral valve of some fishes. (6) Villi.-These are tongue-like elevations of the mucosa one-thirtieth to one-fortieth inch in height, and barely visible to the naked eye. They are found on both sides of the valvulae conniventes and on the general surface of the mucosa. Collec- tively they give the surface a velvety appearance. The villi are most numerous in the upper part of the intestine, where they number fifty to eighty to the square inch. They are longer but more slender and less numerous in the ileum, where they number forty to sixty to the square inch. Their total num- Fig. 145.-a, Cross section of a villus; b, cross section of crypt of Lie- berkuhn. ber in the small intestine is estimated at 4,000,000. Each villus has a lining of simple columnar epithelium which covers a connective-tissue core. A few smooth muscle fibers enter this core from the muscularis mucosa. In addition there is a rich blood supply and a central lymphatic duct. The latter is a part of the lymphatic system of the intestine known as lacteals because of the milky lymph they contain after each meal. The villi de- velop as invaginations of the mucosa and are ex- clusively confined to the small intestine. digestive system. 199 (c) Crypts of Lieberkuhn.-These are sometimes spoken of as intestinal glands. They consist of pits or evaginated diverticula of the mucous epithelium that open as pores between the bases of the villi. The bottom of these crypts rests against the muscu- laris mucosa. Goblet cells are particularly numer- ous in the epithelial lining of their walls. Crypts Epithe- ■ lium of villus. •Central chyle-vessel of villus. Vein of ■ villus. Artery of. villus. •Chyle-vessel. Gland of Lieber- kuhn. Base of. villus. •Mucosa. -Muscularls mucosas. Artery. -Submucosa. Plexus of '* lymph-ves- sels. Circular mus- ' cular layer. Plexus of - lymph-ves- scls. * Vein. "Long. muse, layer with serous coat. Fig. 146.-Schematic transverse section of the human small intestine (after F. P. Mall). are also present in the large intestine and are analo- gous to the shorter crypts of the stomach into which the gastric glands open. Solitary Lymph Nodules.-These are simple nodes of lymph tissue situated just beneath the mucous epithelium. They are found along the whole ali- mentary tract and in all mucous membranes. 200 NORMAL HISTOLOGY AND ORGANOGRAPHY. Peyer's Patches, or Agminated Lymph Nodules.- These appear as oval elevations on the mucous sur- face and are collections of lymph nodules. They may be three inches long or less, and one-third to one-half inch broad. They number from thirty to forty, and are found in the ileum and always in the mucous surface op- posite the mesen- teric attachment, the long axis being parallel with that of the intestine. Their bodies usu- ally extend to the circular muscle layer and they therefore invade the submucosa. Villi are either stunted or altogeth- er absent over these patches. In early youth they are very prominent, while in middle life they be- gin to atrophy, and in old age they may entirely disappear. The patches are the seat of ulcerations, particu- larly in typhoid fever and tuberculosis. The latter form transverse ulcers as the bacteria of tuberculosis spread along the lymphatics which here are trans- verse to the intestine. The typhoid germ produces • Villus. Lymph follicle of ' a Peyer's patch. Circular muscle coat. Longitudi- nal muscle coat. Fig. 147.-Longitudinal section of ileum showing part of a Peyer's patch. • Serosa. DIGESTIVE SYSTEM. 201 an ulcer whose long axis is parallel to that of the intestine. Brunner's Glands.-These are branched tubular glands whose bodies are situated in the submucosa and whose ducts pass through the muscularis mucosa to open between or into the crypts of Lieberkuhn. They are confined to the duodenum, partic- uarly the upper part. Occasionally they may be found in the pyloric end of the stomach. The cells resemble those of the pyloric glands, being cylin- drical and finely granular. Brun- ner's glands are easily recognized, as they are the only glands that lie in the submucosa. 2. Submucosa.- The submucosa does not differ from the same layer already described in the wall of the stomach. 3. Muscularis.-The muscularis consists of an Villus Mucosa. Crypt of Lieber- kuhn. M uscularis mucosa. Glands of Brunner in the sub- mucosa. Circular muscle layer. Loneitudi- nal muscle layer. Serous coat. Fig. 148.-Longitudinal section of duodenum near pyloric end, showing glands of Brunner. 202 NORMAL HISTOLOGY AND ORGANOGRAPHY. inner circular and an outer longitudinal layer of smooth muscle. The inner circular is the heavier of the two and by its contraction produces many longi- tudinal folds in the mucosa. Smooth muscle, wher- ever found, is associated with connective-tissue elements, but the smooth muscle of the intestine has a less supply of this than the smooth muscle any other place in the body. 4. Serosa.-This layer is identical with the serosa de- scribed in the wall of the stomach. Tania coli. Saccula. Fig. 149.-Portion of large intestine. Appendices epiploica. LARGE INTESTINE. The average length of the large intestine is five feet. Its divisions are given on page 130. It is dis- tinguished from the small intestine by the following external features: tanice coli, saccula, and appendices epiploica. Tania Coli.-In the large intestine the longitudinal muscle is gathered into three bands or strips known as tseniae coli. Each band is about one-quarter inch wide and one foot shorter than the intestine to which it belongs. The large intestine, therefore, becomes sacculated-that is, it is divided by the three longitudinal muscle bands into three rows of sacculae. If the bands be dissected away the saccules DIGESTIVE SYSTEM. 203 disappear and the intestine becomes about one foot longer. Appendices epiploicce are small pedunculate proc- esses that project from the serous coat of the large intestine. The pouches are covered by the perito- neum and are usually distended with fat. These external features are the surgeon's guide in recogniz- ing the large intes- tine. Size is a less reliable factor. Structurally the large intestine has the same four lay- ers as the small in- testine. The three outer layers are identical. The mucosa presents a smooth surface with numerous mi- nute circular pits, the crypts of Lie- berkuhn. As villi are absent the mu- cosa resembles that of the stomach rather than that of the small intestine. The crypts of the stomach are shallow, while those of the intestine are deep and extend to the muscularis mucosa. Each crypt is lined by simple columnar epithelium. Goblet cells are very numerous in this epithelium. Mucosa. Crypt of Lieber- kuhn. Muscularis mucosa. Submucosa. M uscular layer, circular. Muscular layer, lon- gitudinal. Serous cov- ering. Fig. 150.-Cross section of large intes- tine, showing many goblet cells in epithe- lium. 204 NORMAL HISTOLOGY AND ORGANOGRAPHY. Vermiform Appendix.-The appendix, although very small, belongs to the large intestine. It is a worm-like tube about three inches long and one- quarter inch thick, although the length varies greatly. It is a blind tube that evaginates from Fig. 151. - Transverse section of human vermiform appendix. Observe the numerous lymph nodules. The clear spaces in the submu- cosa are adipose tissue (Sobotta). the lower end of the cecum. Lymph nodes are particularly abundant in the mucosa of the ap- pendix. The following taken from Cunningham's "Anat- omy" will be of interest to the student: "A vermi- form process is found only in man, the higher apes, digestive system. 205 and the wombat, although in certain rodents a somewhat similar arrangement exists. In carniv- orous animals the cecum is very slightly devel- oped; in herbivorous animals (with a simple stom- ach) it is, as a rule, extremely large. It has been suggested that the vermiform process in man is the degenerated remains of the herbivorous cecum, which has been replaced by the carnivorous. An- other and perhaps more probable view regards the appendix as a lymphoid organ, having the same functions as Peyer's patches and, like these, under- going degeneration after middle life" (Berry). In the different parts of the alimentary canal the mucosa shows a marked variation, as represented in the following table: Esophagus. Stratified epithelium. Mucous glands. Crypts absent. Villi absent. Valvulas absent. Stomach. Simple epithelium. Gastric glands. Crypts shallow. Villi absent. Valvula: absent. Small Intestine. Simple epithelium. Brunner's glands. Crypts of Lieber- kuhn. Villi present. Valvulae conniven- tes present. Large Intestine. Simple epithelium. Crypts. Crypts. Villi absent. Valvula: absent. Blood Supply of Stomach and Intestines.-The ar- teries of the stomach are all derived from the celiac axis, a branch of the aorta. The intestines are sup- plied by blood from the superior and inferior mesen- teric arteries, branches of the aorta. The arteries enter along the line of the mesenteric attachment and there form branches that pass transversely around the intestine to ultimately penetrate the longitudinal muscle layer. Between the two mus- cular coats branches are given off to supply the 206 NORMAL HISTOLOGY AND ORGANOGRAPHY. muscles themselves. The arteries then penetrate to the submucosa where an extensive blood plexus is formed. From this plexus branches pass through the muscularis mucosa and enter the mucosa. Here Epithelium of stomach. Region of the bodies of the gas- tric glands. M uscularis mucosce. Fig. 152.-Section through fundus of cat's stomach. The blood-vessels are injected (Bohm and Davidoff). they branch into a fine capillary network which in the small intestine penetrates to the core of the villi. Other branches from this plexus supply the inner portion of the circular muscle layer. The veins lie side by side with the arteries. Often two veins accompany one artery. The blood drains into the superior and inferior mesenteric veins; the inferior joins the splenic, and the latter unites with DIGESTIVE SYSTEM. 207 the superior to form the portal vein. This blood thus ultimately passes through the liver. Lymphatics of the Alimentary Canal.-The lym- phatics begin in the mucosa just beneath the epithe- lium. In the small intestine they begin with the cen- tral lymph vessel of a villus. These vessels form a network in the deeper portion of the mucosa and then pass through the muscularis mucosa to form Fig. 153.-A portion of the plexus of Auerbach from stomach of cat, stained with methylene-blue (intra vitam}, as seen under low mag- nification (Huber). an extensive loose plexus in the submucosa. Coarser lymphatic vessels lead from this plexus through the muscularis, where branches are received from a lymphatic plexus located between the two muscle coats. The solitary lymph nodes of the mucosa contain no lymphatics, but are encircled at their periphery 208 NORMAL HISTOLOGY AND ORGANOGRAPHY. by an extensive lymphatic network. The same is true of the lymph nodules in Peyer's patches. Nerve Supply of the Alimentary Canal.-The chief nerve supply of the alimentary tract consists of sym- pathetic neurons whose nerve cells form the centers of two plexuses, (i) that of Auerbach, situated between the two layers of the muscle coat, and (2) that of Meissner in the submucosa. The latter con- tains fewer ganglia and finer fibers. The numerous small sympathetic ganglia of each plexus are united by small bundles of non-medullated nerve fibers in which a few medullated nerve fibers are present. From these plexuses the nerve innervation extends to the glands and epithelial cells of the mucosa, and to the muscularis to end in small varicosities about the smooth muscle cells. While the nerve innervation is not under will con- trol it is capable of being stimulated by cerebro- spinal nerves. Medullated nerve fibers from this system have been traced to terminal end baskets surrounding cell bodies of many of the sympathetic neurons of these plexuse® CHAPTER V. DIGESTIVE GLANDS. SALIVARY GLANDS. i. Parotid Gland (serous gland).-This is a com- pound tubular gland, the largest of the salivary glands, situated in the parotid recess at the side of the head below and in front of the ear. It is a triangular mass that varies in weight from one-half ounce to one ounce or more. Its three surfaces are desig- nated as superficial, anterior and posterior. The gland is divided into lobes and lobules and inter- laced with connective-tissue elements from the parotid fascia that invests it. The parotid, or Stenson's duct, measures from one and one-half to two and one-half inches in length and one-eighth inch in diameter. It runs forward across the masseter muscle, passes around the anterior border of this muscle, pierces the buc- cinator, then forward a short distance to open on the inner surface of the cheek opposite the crown of the second upper molar. This duct is subject to injury in facial wounds or operations. The gland is an epithelial organ and consists of the excretory duct, interlobular, intralobular, and in- tercalated ducts, and the distal convoluted tubules or alveoli. The excretory duct (Stenson's) is lined by stratified epithelium near its end where it opens on 209 210 NORMAL HISTOLOGY AND ORGANOGRAPHY. the mucous surface of the cheek. The rest of the duct is lined by two layers of cubical epithelium, which is invested by a firm fibrous coat or tunica propria. The interlobular ducts lie between the Acini. Intralobu- lar duct. Connective tissue be tween lobules. Blood-ves- sel. Fig. 154.-Section through salivary gland of rabbit, with injected blood-vessels (Bohm and Davidoff). lobules and have much the same histology as the excretory duct, excepting the finer branches where the epithelium becomes simple cubical/ The intra- lobular ducts are found inside the lobules and have a simple layer of tall cylindrical cells whose cytoplasm DIGESTIVE GLANDS. 211 shows a distinct longitudinal striation. The inter- calated pieces, on the other hand, are clothed by a single layer of flat, slender, often spindle-shaped cells. The epithelial lining of the acini consists of typical serous-gland cells. This is a single layer of irregular columnar or cubical cells with nuclei situated near their basal portion. When at rest the cytoplasm is filled with zymogen granules which are used up and largely disappear during the process of secretion. Mumps is a specific disease of this gland, more technically known as parotitis. 2. Sublingual Gland (mucous gland).-This is really a collection of compound tubulo-alve- olar glands. It is an elongated flattened mass one and one-half to one and three-quarter inches in length, situ- ated in the floor of the mouth, one on each side of the median plane, and limited laterally by the ramus of the mandible. Its excretory ducts, from ten to twenty in number, open separately on the summit of papillae visible to the naked eye, which are situated just laterally to the base of the frenum of the tongue. The duct system of the gland is similar to that of the parotid, with the exception of the intercalated piece, which is absent. The alveoli are less tubular than those of the parotid and are lined by simple Intralobular duct. Intercalated duct. Alveolus. Fig. 155.-From the parotid gland of man. 212 NORMAL HISTOLOGY AND ORGANOGRAPHY. columnar epithelium with the nuclei situated at the base of the cells near the basement membrane. These are the chiej cells of the alveoli and they se- crete mucus, which is first stored up in the cyto- plasm in coarse granules known as 'mucigen. A second form of cells, less numerous, is found singly or in groups in the periph- ery of the alveoli and in close apposition to the basement membrane. On account of their shape and position they are called parietal cells, cres- cents of Gianuzzi, or demi- lunes of Heidenhain. They are finely granular, stain red with eosin, and are looked upon by some as secreting a serous fluid. There are three theories as to their use: (i) They may be considered as worn-out chief cells that have been crowded to the basement membrane after too active a secretion. (2) They may be considered as latent undeveloped cells ready to take the place of mucous cells that get lost in the process of active secretion. (3) They may be considered as normal active cells contributing constantly to the salivary secretion in a way that is at present unknown. Fig. 156.-Model of a small portion of a sublingual gland of man. The demilunes of Heid- enhain are more deeply shaded (Maziarski, " Anatomische Hefte," 1901). DIGESTIVE GLANDS. 213 3. Submaxillary Gland (mixed gland).-In man this gland is composed of tubules having a serous secretion and similar to those of the parotid gland, and tubules with alveolar enlargements like the sub- lingual gland that secrete mucus. Its histology, therefore, would be a repetition of what has already been described in the parotid and sublingual glands. The submaxillary gland is next in size to the pa- rotid, which it resembles in color and lobulation. It Parietal cell. Acinus. Parietal cell. Intralobular duct. Interlobular duct. big- x57--Section from the human submaxillary gland is placed against the inner surface of the angle of the lower jaw in close proximity to the parotid gland. It has a complete firm capsule derived from the cer- vical fascia. Connective-tissue elements from the capsule ramify between the lobes and lobules of the gland. The submaxillary, or Wharton's duct, is about two inches long, passes forward beneath the mylohyoid muscle, then along the inner side of the sublingual gland to open on the summit of a small papilla situ- 214 NORMAL HISTOLOGY AND ORGANOGRAPHY. ated in the floor of the mouth at the side of the fre- num of the tongue in close proximity to its fellow of the other side. The submaxillary gland of the rabbit is a serous gland; that of the dog and cat is mucous. The accessory salivary glands are numerous small glands of the mouth known according to their location as la- bial, palatine, and lingual. They are mostly glands with mucous secretions. Branched tubular glands with serous secretion occur in the tongue, their ducts opening into the depressions of the circumval- late papillae. Fig. 158.-A number of alveoli from the submaxillary gland of dog, stained in chrome-silver, showing some of the fine intercellular tubules (Huber). PANCREAS. The pancreas is a lobulated compound racemose gland analogous in its structure to the salivary- glands. It is situated transversely across the pos- terior wall of the abdomen, so deep in the body and so closely associated with other organs that but little is known of its diseases. Its length varies from six to eight inches, its breadth one and one-half inches and thickness from one-half to one inch. The right extremity, or head, rests in the concavity of digestive glands. 215 the duodenum and the other end touches the spleen. It lies behind the peritoneum and, unlike the salivary glands, it is not enclosed in a fibrous capsule, and is therefore looser and softer in its texture. The pancreas develops as two evaginations of the alimentary canal and embryologically, therefore, Outer zone of a secre- tory cell. Centro- acinal cell. Connec- tive tissue. Centro- acinal cell. Larger gland duct. Inter- mediate tubule. Inner granular zone of secretory cells. Fig. 159.-From section through human pancreas (sublimate) (Bohm and Davidoff). has two ducts. One of these, the pancreatic duct, or duct of Wirsung', opens jointly with the bile duct on the summit of an elevated papilla, situated at the inner side of the descending portion of the duodenum. This duct extends the length of the pancreas and receives in its course the short ducts from the various lobes composing the gland. 216 NORMAL HISTOLOGY AND ORGANOGRAPHY. The second duct, or duct of Santorini, loses its connection with the alimentary canal and comes to open into the duct of Wirsung. It is a very short tube, inferior in position and secondary in impor- tance. Histologically, the ducts are lined by a mucous membrane of simple columnar epithelial cells that are morphologically continuous and analogous with the epithelial cells of the intestine. This mucous Connective tissue. Centro-acinal cell. Secretory cell. Intermediate duct. Fig. 160. - Scheme showing relation of three adjoining alveoli to excretory duct, illustrating origin of centro-acinal cells (Bohm and Davidoff). membrane is ensheathed by a coat of connective- tissue elements, fibers and cells, all of which are associated with more or less fat. The acini resemble in form and size those of the salivary glands. The parietal cells are absent. The chief cells are columnar, the nucleus near the base of the cell, and the cytoplasm loaded with zymogen granules. During physiological activity these gran- ules are greatly reduced. In addition, centro-acinal digestive glands. 217 cells are present. These are smaller and flatter than the chief cells and occupy a central position of many acini. They represent an invagination of the neck of the acinus and are best understood by re- ferring to Fig. 160. Areas oj Langerhans.-These are oval cell masses that measure 0.2 to 0.3 mm. They are found in the lobules of the pancreas, always associated with the connective tissue but having no connection with the Pancreatic duct. Acinus. Centro-acinal cells. Blood capil- laries. Fig. 161.-Section from an injected pancreas of the dog. Connective tissue- Area of Langerhans. pancreatic tubules. The areas are surrounded by a rich supply of coarse capillary blood-vessels. The individual cells are epithelioid, smaller than those of the acini, and finely granular. In many respects they resemble the liver cells. It is believed that the secretions from these cells is absorbed by the blood and modifies the distribution and elimination of sugar. The areas thus have a compensatory rela- tion to the liver and may do in part the work of that organ. A marked disturbance in these areas has 218 NORMAL HISTOLOGY AND ORGANOGRAPHY. been observed in diabetes, but whether a cause or consequence is not known. LIVER. The liner is a large compound tubular gland whose terminal ducts anastomose. In this respect it differs from any other gland in the body. It develops as a ventral evagination of the intestinal wall and in close proximity to the origin of the pancreas, so that in the adult the ducts of these two organs have a Non-peritoneal surface. Imp. supra ren. (non-perit). Gastric sur- face. Tuber papil- lore. Imp. supra-rcn. T uber omen- tale. Imp. renalis. Imp. duodenalis. Impressio celica. Impressio pylorica. Fig. 162.-Posterior and inferior surfaces of the liver (Nancrede). common opening at the apex of a papilla, as already mentioned in the description of the pancreas. If an obstruction occurs at this opening, it is possible for the pent-up bile to invade the pancreas. The ven- tral liver diverticulum quickly bifurcates to form respectively the right and left lobes of the liver. By repeated divisions the bile system of the organ is built up, forming an elaborate anastomosis of the finer bile capillaries. It follows, therefore, that the liver cells are genetically related to the pancreatic DIGESTIVE GLANDS. 219 cells and sister cells of the columnar epithelium of the alimentary tract. The fully developed liver consists of five lobes: right lobe, left lobe, quadrate, caudate, and spigelian lobes. Five fissures: umbilical, ductus venosus, transverse, gall bladder, and vena cava fissures. Five ligaments: ligamentuni teres (remnant of the umbilical vein), falciform, coronal, and two lateral ligaments. Interlobular vein. Interlobular bile duct. Intralobular bile duct. Liver cells. Intralobular vein. Fig. 163.-Diagram of liver lobule. Sublobular vein. The description of these structures belongs to gross anatomy. The liver is the largest gland in the body, weigh- ing from three to four pounds, or one-fortieth the weight of the whole body. It measures ten to twelve inches in its transverse diameter, six to seven inches in its antero-posterior, and about three inches thick at the back part of the right lobe, which is the 220 NORMAL, HISTOLOGY AND ORGANOGRAPHY thickest part. This heavy organ is held in position not only by its ligaments but by the abdominal pres- sure, and also by the connective tissue of the vena cava, which forms a dorsal fissure between the right and left lobes. The organ is enclosed in a firm connective-tissue capsule {capsule of Glisson'), which is very dense over the lower surface in the region of the fissures, par- Interlobular vein. Blood capillaries. Intralobular vein. Cord oj liver cells. Fig. 164.-Injected blood-vessels in liver lobule. ticularly the transverse, where the blood-vessels and bile duct enter. Septa from this capsule ramify between the lobes and lobules, and finer branches interlace between the liver cells, giving everywhere support and consistency to the organ. Here, as in every organ, blood-vessels, lymph-vessels, and fat are associated with this connective-tissue fabric. The capsule is closely invested with peritoneum, except- ing a circular area bounded by the coronal ligament, DIGESTIVE GLANDS. 221 where the capsule, and therefore the liver, is in direct apposition with the lower surface of the diaphragm. The blood supply of the liver consists of the hepatic artery, and a branch of the celiac axis, and the portal vein, formed by the junction of the splenic and supe- rior mesenteric veins. The portal vein is by far the larger vessel. These vessels accompany the bile- Intralobular vein. Branch oj portal vein. Bile duct. Branch oj he- patic artery. Interlobular connective tissue. Fig. 165.-Section through liver of pig, showing chains of liver-cells (Bohm and Davidoff). duct, and wherever one branches the others do, even to the finer terminations between the liver lobules. The duct, vein and artery form the ventral border of the foramen of Winslow. Their relation at this place is, bile duct to the right, artery to the left, and vein between and behind the other two. This rela- tion is an important one in the surgery of these parts. 222 NORMAL HISTOLOGY AND ORGANOGRAPHY. The Portal Canal.-This consists of an artery, a bile duct, and a vein, with accompanying lymphatics and connective tissue. Sections of the portal canal may be found between the liver lobules where the vessels are small, or between the liver lobes where the structures are large. The bile duct can be recog- nized by the columnar simple epithelium and the artery and vein by their respective histology. In Intralobu- lar vein. Boundary of lobule. Fig. 166.-Reticulum (Gitterfasern) of dog's liver (gold-chlorid method) (Bohm and Davidoff). pathological sections, where the lobules can no longer be recognized, the portal canal usually re- mains patent and is therefore a valuable criterion in the identification of this tissue. The common bile duct is formed by the junction of the hepatic and cystic ducts at the mouth of the transverse fissure, and passes downward anterior to DIGESTIVE GLANDS. 223 the foramen of Winslow to open into the descending part of the duodenum three and one-half to four inches beyond the pylorus. It passes obliquely through the intestinal wall, where it is joined by the pancreatic duct, and opens by a common orifice on the bile papilla, as already described. The common bile duct is about three inches long and one-quarter inch in diameter. The histology of the bile ducts resembles that of the gall bladder. There is on the inside a mucous mem- brane clothed with simple columnar epithelium rest- ing upon a base- ment membrane. Smooth muscle cells are found in the membrana propria of the mu- cosa. The sub- mucosa is a nar- row vascular layer composed of con- nective-tissue elements. The muscularis consists of an inner circular layer and an outer longitudinal layer of smooth muscle. On the outside is a strong connective-tissue coat whose fibers are continuous with the capsule of Glisson. The passage of bile into the intestine is not a pas- sive but an active process. The smooth muscle of the bile duct contracts in a peristaltic manner, and the bile is thus expelled into the intestine, periodi- cally, in jets. This activity is normally under con- trol of the nerves, largely a reflex action of the sym- Lymphatics. Bile duct. Vein. Artery. Fig. 167.-Section of portal canal of liver. 224 NORMAL, HISTOLOGY AND ORGANOGRAPHY. pathetic nerves associated with the intestine. If there is an obstruction to the free passage of bile, as in the passage of a calculus, the musculature of the ducts contracts violently and spasmodically, giving rise to the characteristic pain of plain muscle con- traction described on page 96. If the obstruction occurs in the hepatic or the common duct, the liver becomes saturated with bile which is absorbed by the blood, and jaundice follows. If the obstruction is in the cystic duct the liver does not suffer and there is no jaundice. Smaller Excretory Bile Ducts and Gall Bladder.- Small bile ducts of the liver begin within the liver lobules, where they form a complex system of anas- tomosing channels or tubes called bile canaliculi. Interlobular Ducts.-The bile canaliculi unite to form interlobular ducts that lie between the liver lob- ules. These unite into larger and larger ducts and converge to pass out through the transverse fissure, where five or six ducts are found. The latter unite into two short main ducts that drain respectively from the right and left lobes of the liver. The hepatic duct is formed by the union of the two main ducts at the bottom of the transverse fissure and thus receives the bile from the whole liver. It is from one to one and one-quarter inches in length and one-quarter inch in breadth, and extends downward from its origin, taking an irregular course, to its junction with the cystic duct, which unites with it to form the common bile duct. The gall bladder, with its cystic duct, is an evagina- tion of the bile duct. The gall bladder is a pear- DIGESTIVE GLANDS. 225 shaped receptacle for the retention of bile, and has a fundus, body, and neck. It is usually about three inches in length and one to one and one-quarter inches in diameter with a normal capacity of one to one and one-half fluidounces. Structurally it has an outer coat of perito- neum, a middle coat of connective-tissue elements, with a liberal mixture of smooth muscle fibers, and an inner coat of mucous membrane raised into folds and covered with simple columnar epi- thelium. The cystic duct begins at the neck of the gall bladder and extends downward to its junc- tion with the hepatic duct, with which it forms an acute angle. It takes ^n irregular course and is from one and one-quarter to one and one-half inches long; therefore longer than the hepatic duct, but only about one-half its diameter. Liver Lobules.-These are minute units of the liver about the size of a pinhead. They are cylindrical Fig. 168.-Portion of gall bladder and bile ducts: i, Cavity of gall bladder; 2, cavity of calyx; 3, groove separating the calyx from the bladder; 4, promontory; 5, superior valve of calyx: 6, cystic canal; 7, common bile duct; 8, hepatic duct (Testut). 226 NORMAL HISTOLOGY AND ORGANOGRAPHY. or irregularly polyhedral in shape, about 2 mm. in length and 1 mm. in breadth. Their arrangement is quite irregular except just beneath the capsule where they usually lie with their apices toward the surface. Each lobule has a connective-tissue in- vestment in which the finer branches of the portal Blood capil- laries. Intralobular vein. Cord of he- patic cells. I nterlobular vessel. Fig. 169.-Injected blood-vessels in liver lobule of rabbit (Bohm and Davidoff). canal ramify. This investment is particularly dense in the pig, which renders the organ in this animal very fibrous and tough, quite unfit for the market. In certain chronic liver diseases the same condition obtains, when the organ is spoken of as the "hob- nailed" or "nutmeg" liver. DIGESTIVE GLANDS. 227 In the center of each lobule is a blood-vessel known as the intralobular vein, while the small veins be- tween the lobules are called the interlobular veins. These two sets of veins are connected by irregular blood capillaries that radiate from the periphery of the lobule to its center. They are typical capillaries whose walls consist of but a single layer of flattened Intralobular vein. Fig. 170.-Human bile capillaries. The capillaries of one lobule are seen to anastomose with those of the adjoining lobule (below, in the figure) (chrome-silver method) (Bohm and Davidoff). endothelial cells. The blood in the portal vein passes to the interlobular veins, then through the capillaries to the intralobular vein. The latter opens into sublobular veins which unite to form the hepatic veins, and these in turn open into the vena cava just below the diaphragm. The arterial blood of the hepatic artery supplies the connective tissues, 228 NORMAL HISTOLOGY AND ORGANOGRAPHY. the walls of the bile ducts and blood-vessels, and doubtless some of this arterial blood finds its way into the liver capillaries where it blends with the venous blood from the portal vein. From the center of each lobule toward its periph- ery irregular strands of liver cells radiate and freely anastomose with each other, as well as in- terlace between the blood capillaries. These are called hepatic cords and con- sist of double irregular rows of liver cells. The cords constitute the bile capillaries and unite at the periph- ery of the lobule with the bile ducts of the portal canal, situated between the lobules. The bile capillaries, there- fore, are very fine tubes lying between the liver cells that constitute its walls. These tubes anasto- mose freely with each other and are the terminal endings of the bile passages or its secreting portions. The liver, as a Fig. 171--Schematic diagram of hepatic cord in transverse sec- tion. At the left the bile capillary is formed by four cells, at the right two; the latter type occurs in the human adult (Bohm and Davidoff). Bile capillaries. Small bile duct, Lareer bile, duct. Fig. 172.-From the human liver, showing the beginning of the bile ducts (chrome-silver) (Bohm and Davidoff). DIGESTIVE GLANDS. 229 gland, thus differs from all other glands (i), that the secreting tubules anastomose, and (2) that the wall of the secreting portions consists of but two cells. The liver cells have no cell wall. They are large poly- hedral or irregular epithelial cells, con- taining sometimes two, but usually one, nucleus. The cyto- plasm is granular, containingbile drops and vacuoles. The chief function of these cells is twofold: (1) to secrete bile into the bile capillaries, and (2) receive and contribute sugar to the blood capillaries. In junction with this it is affirmed that definite cyto- plasmic or intracellu- lar channels exist, particularly for the passage of bile. These channels end in minute dilatations within the cells, from which finer passages lead to and arborize around the nucleus. According to some investigators, the finer passages may penetrate the nucleus and are then called intranuclear canals. Intracellular bile passage. Intercellular bile duct. Fig. 173.-Diagram of liver cells, show- ing bile passages. Blood capillary. Intercellular bile duct. Intracellular bile passage. Blood capillaries. t . Fig. 174.-Diagram of liver cells, showing bile ducts and blood capillaries. 230 NORMAL HISTOLOGY AND ORGANOGRAPHY. Fig. 175.-From preparation from the liver of a rabbit, showing the so-called stellate cells of Kupffer: a, Stellate cells; b, liver cells (Huber). I nterlobular connective tissue. Intra- lobular vein. Stellate cells. Fig. 176.-Part of a section through liver lobule from dog, showing stel- late cells (Bohm and Davidoff). DIGESTIVE GLANDS. 231 Whether this intracellular system is an artifact due to manipulations or a normal condition is at present unsettled. In either case the liver cells play a deli- cate role, and a slight functional disturbance may allow the bile to escape to the blood capillaries, with jaundice as a natural sequel. In such a case there may or may not be any pain depending on the pres- ence or absence of an obstruction in the bile duct. Stellate Cells of Kupffer.-These are uniformly distributed in the lobules. The cells are irregular, elongated, and end in two or three pointed projec- tions. They are smaller than the hepatic cells and are seen only after a special method of treatment. According to Kupffer these cells belong to the endo- thelium of the intralobular blood capillaries, and possess a phagocytic function. Lastly, each lobule is interlaced by a fine reticular connective fabric that comes from the connective- tissue investment of the lobule. This gives support and consistency to the lobule. Lymphatics of the Liver.-These may be divided into (i) the interlobular lymphatics, which accom- pany and in some places surround the blood-vessels, and (2) subperitoneal lymphatics on the surface of the organ which in the upper portions communicate through the ligaments with the thoracic lymphatics. Nerves of the Liver.-The liver receives medullated fibers from the left pneumogastric and non-medul- lated fibers from the solar plexus. The nerves reach the organ between the two layers of the small omen- tum and accompany the portal canal, therefore enter the liver at the transverse fissure. The sympathetic 232 NORMAL HISTOLOGY AND ORGANOGRAPHY. fibers innervate the walls of the blood-vessels. The medullated pass to the liver lobules where they lose the medullary sheath and then accompany the he- patic cords or bile capillaries to ramify ultimately between and around the liver cells. CHAPTER VI. ORGANS OF RESPIRATION AND THYROID GLAND. The organs of respiration comprise the larynx, trachea, bronchi and lungs. More than forty per cent, of all deaths are directly due to diseases of this tract, which renders a thorough knowledge of this system of primary importance. These organs de- velop as a ventral median outgrowth of the fore-gut, and the mucous epithelium is therefore derived from the entoderm. The primitive connection with the alimentary canal is maintained in the adult, the upper extremity of the larynx opening on the anterior wall of the pharynx. The larynx in the male averages 44 mm. in length, 43 mm. transverse diameter, and 36 mm. antero- posterior diameter. In the female these dimensions are 36 by 41 by 26 mm. It is a cartilaginous mus- cular tube that contains the two vocal cords, the latter being transverse folds of mucous membranes. In the wall are three single symmetrical cartilages, the thyroid, cricoid, and cartilage of the epiglottis; and three pairs, namely, two arytenoids, two corniculce laryngis (cartilages of Santorini), and two cuneiform, making in all nine pieces. The two last pairs are very THE LARYNX. 233 234 NORMAL HISTOLOGY AND ORGANOGRAPHY. small, while only the thyroid and cricoid are visible on the front and sides of the larynx. The cartilage of the epiglottis, the arytenoids, the corniculae laryn- Fig. 177.-Articulations and liga- ments of the larynx, anterior view: A, Hyoid bone, with a its greater, and a' its lesser cornua; 1-5, liga- ments; 6, lateral cricothyroid artic- ulation; 7, junction of cricoid and trachea (Testut). Fig. 178.-Articulations and lig- aments of the larynx, posterior view: A, Hyoid; B, thyroid, with b and b' its cornua; C, cricoid; D, arytenoids; E, cartilages of San- torini; F, epiglottis; G, trachea; 1-6, ligaments; 2, opening for su- perior laryngeal artery; 7, junc- tion of trachea and cricoid (Tes- tut). gis, are of the elastie or yellow fibrous variety and do not tend to ossify with age. The rest are composed of the hyaline cartilage, which tends to ossify with age. Many pairs of muscle control the manipulation of ORGANS OF RESPIRATION. 235 these cartilages, regulating the vocal cords and modulating the voice. The mucous membrane of the larynx is continuous Glands in false vocal cord. Stratified pavement epithelium of true vocal cord. Stratified ciliated col- umnar epithelium. ■ Muscle. Glands. ' Muscle- Fig. 179.-Vertical section through the mucous membrane of the human larynx (Bohm and Davidoff). with that of the mouth and particularly sensitive about the upper part above the glottis. This mu- 236 NORMAL HISTOLOGY AND ORGANOGRAPHY. cous membrane is covered in the greater part of its extent with stratified columnar ciliated epithelium. The cilia are found higher up the front wall than on each side, reaching in the former to the base of the epiglottis and at the sides to a point just above the false vocal cords. Above these points the epithelium is stratified squamous, like that of the pharynx. Upon the true vo- cal cords the epi- thelium is also stratified squa- mous. Mucous glands are found everywhere in this membrane but are particu- larly abundant upon the epiglot- tis. The membrana propria, on which the epithelial cells rest, is not only very vascular but has a rich supply of elastic fibers and other connective-tissue elements. It is this tis- sue that becomes edematous and greatly swollen in infections, such as diphtheria. This is nature's method of eliminating the disease, with, however, the accompanying danger of suffocation. The vocal cords are transverse elastic ligaments Fig. 180.-Diagram to illustrate the thyro-arytenoid muscles; the figure repre- sents a transverse section of the larynx through the bases of the arytenoid carti- lages: Ary, arytenoid cartilage; p.m, proc- essus muscularis; p.v, processus vocalis; Th, thyroid cartilage; c.v, vocal cords; Oe is placed in the esophagus; m.thy.ar.i, in- ternal thyro-arytenoid muscle; m.thy.ar.e, ex- ternal thyro-arytenoid muscle; m.thy.ar.ep, part of the thyro-ary-epiglottic muscle, cut more or less transversely; m.ar.t, transverse arytenoid muscle. (Redrawn from Foster.) ORGANS OF RESPIRATION. 237 covered with a very thin mucous membrane. They are attached anteriorly to the thyroid cartilage, close to each other, and diverge posteriorly to their attachment in the arytenoid cartilages. The glottis is the slit-like opening between the vocal cords. The thyroid gland is not a part of the respiratory tract, but it is so closely associated with this tract in development and in position that it seems advisable to describe the organ in this place. The gland is a highly vas- cular body con- sisting of two lat- er al lobes and connected by a transverse bar, iheisthmus. The rudiments of the lobes develop from the epithe- lium of the fourth gill cleft, while the isthmus and a large part of the lobes come from the floor of the mouth, the thyroglossus duct at the base of the tongue being a remnant of this origin. The gland is therefore an epithelial organ derived from the ento- derm. In position the gland lies low down in the neck and in close apposition to the trachea. The isthmus crosses in front of the trachea and covers the second THE THYROID GLAND. Vein. A rtery. Colloid. Connective tissue. Fig. 181.-Section from thyroid gland, show- ing vesicles or alveoli. 238 NORMAL HISTOLOGY AND ORGANOGRAPHY. and third cartilage ring. The lateral lobes are closely applied to the sides of the trachea and extend up- ward to cover the lower part of the thyroid cartilage. Each lobe measures about two inches in length, one and one-quarter inches in breadth, and one-half inch in depth. The gland, however, is subject to great variations both in size, form, and position. It is gen- erally larger in females, and appears to undergo a periodic enlargement during each menstruation. It reaches its maxi- mum growth at pu- berty, and is fre- quently much di- minished in size in old age. Structure.-The thyroid gland is in- vested by a thin layer of areolar tis- sue which not only binds it fast to the trachea, but divides it into small lobules of irregular size and form. It is a duct- less gland consisting of epithelial vesicles varying in size from .05 mm. to 1 mm. in diameter. These vesi- cles vary greatly in form and are grouped and held to- gether by areolar connective tissue in which many blood-vessels ramify. These vesicles are generally filled with colloid substance, a yellow viscid fluid, that in sections stains a yellowish red with eosin. They are 'Gland alveoli. Connective tissue. Fig. 182-Portion of a cross sec- tion of thyroid gland of a man; c, col- loid substance (Sobotta). ORGANS OF RESPIRATION. 239 lined by a simple cubical epithelium made up of two kinds of cells, (i) a smaller number of colloid cells engaged in the production of colloid, and (2) inter- vening chief cells which replace the former in case they are lost. It is affirmed by some that the two kinds of cells represent merely different stages of secretion. The thyroid, being an epithelial organ, may be the seat of a cancer. Goiter is a more common thyroid tumor, consisting of accumulations within its vesi- cles of colloid substance; or an increase of the con- nective-tissue elements; or a multiplication of the thyroid vesicles. Removal of the thyroid produces myxedema, while a congenital absence of the gland is the cause of cretinism. In the latter case, thyroid extract, regularly administered, will establish a nor- mal growth of the child. In exophthalmic goiter the thyroid gland is enlarged, but in this case the en- larged thyroid is a symptom of a more general disease involving other organs and systems. The thyroid gland may be removed and grafted almost anywhere in the body. It will readily grow in its new position and assume its normal function with good results. Vessels and Nerves.-The arteries of the thyroid gland are the superior and inferior thyroid arteries on each side, to which is sometimes added a fifth vessel, the thyroidea ima. The organ has, therefore, a very rich supply of blood. The smaller vessels and capil- laries ramify in the connective-tissue elements be- tween the gland vesicles. The veins, which are also large, form an extensive plexus near the surface of the gland, from which a superior, middle, and inferior 240 NORMAL HISTOLOGY AND ORGANOGRAPHY. vein are formed on each side. Extensive lymphatics accompany the blood system. The nerves are derived from the middle and inferior cervical ganglia of the sympathetic. They accompany the blood-vessels, whose walls they innervate, sending also branches that extend close to the base of the epithelial cells. PARATHYROIDS. The parathyroids are two flattened bodies, one- fourth to one-half inch in diameter, that are con- Fig. 183.--From parathyroid of man (Huber.) stantly present and placed in close proximity to the upper and posterior surface of the lobes of the thy- roid gland. They consist of solid masses of epithelial cells. Lymphoid follicles are usually closely asso- ciated with these masses. The function of these little bodies is not known; however, if the thyroid gland be removed and the parathyroid left, the effect of a complete thyroidectomy is not obtained. ORGANS OF RESPIRATION. 241 The trachea extends from the cricoid cartilage, a point opposite the lower border of the sixth cervical vertebra, to the level of the intervertebral disc be- THE TRACHEA AND BRONCHI. Thyroid cartilage. Crico-thyroid membrane. Cricoid cartilage. Thyroid gland. Trachea Eparterial bronchus. Left bronchus. Hyparterial bronchus. Fig. 184.-The trachea and bronchi. tween the fourth and fifth dorsal vertebrae, extend- ing therefore one to two inches into the chest. The 242 NORMAL HISTOLOGY AND ORGANOGRAPHY. trachea measures from four to four and one-half inches in length, and three-fourtlis to one inch in width. It is smallest at its commencement, and, although quite uniform in its dimensions, is usually a little wider midway between its two ends. At the lower end the trachea bifurcates to form the right and left bronchi, which pass each to the root of the corresponding lung. The right bron- chus is larger than the left and more nearly vertical, so that in looking down the trachea more of the right than of the left bronchus can be seen. The right bronchus di- vides into branches, one to each root of the three lobes of the right lung, while the left gives off two branches, one to each lobe of the left lung. Structure.-In the wall of the trachea there are from sixteen to twenty C-shaped cartilage rings that make a little more than two-thirds of a cir- cle. The outer surface of these cartilages is flat, but the inner surface is convex from above downward, so as to give greater thickness in the middle than at the edges. The cartilage is of the hyaline variety and is Ciliated epi- thelium. Longitudinal elastic fbers. Mucous glands. Fat cells. Cartilage. Fig. 185.-From longitudinal sections of trachea. ORGANS OF RESPIRATION. 243 enclosed in a periosteum. The cartilage rings are held together by a strong elastic fibrous tissue, which not only occupies the space between them but is pro- longed over their surfaces, so that each ring appears imbedded in this tissue. Each cartilage terminates abruptly behind by rounded ends, between which Stratified cili- ated columnar epithelium. Elastic fibers, cut trans* versely. Gland. Mucosa. Cartilage. Connective tissue. Fig. 186.-Transverse section through human bronchus (Bohm and Davidoff). stretches a thin layer of smooth muscle tissue. This muscle not only unites the ends but is also found in the intervening space between the cartilage rings, along the posterior wall of the trachea. Outside of the transverse fibers are a few fasciculi having a lon- gitudinal direction. The cartilage rings of the bronchi resemble those 244 NORMAL HISTOLOGY AND ORGANOGRAPHY. of the trachea in being incomplete behind. The right bronchus has from six to eight rings, while the left has from nine to twelve. The left bronchus is longer but narrower. The mucous membrane is smooth and contains a considerable amount of lymphoid tissue and many mucous glands. The epithelial lining consists of long columnar ciliated cells, often very irregular and even branched at their fixed ends. One or two rows of small irregular cells intervene between the basal ends of the ciliated cells, and this epithelium is therefore stratified although very thin. The cells rest upon a basement membrane through which nerves pass to reach the sensitive epithelium. Ex- ternal to the basement membrane, in what consti- tutes the membrana propria, there is a strong layer of longitudinal elastic fibers. This tissue extends the whole length of the air passages, and gives not only great elasticity but is an obstruction to invading bacteria. A vascular submucosa, not very exten- sive, intervenes between the mucosa and the carti- lage. In this may be found the bodies of small race- mose mucous glands, the largest being in the poste- rior wall. The excretory ducts of these glands open on the inner surface. Lymphoid tissue is present both in the mucosa and the submucosa. THE LUNG. The lungs occupy the greater part of the chest cavity, of which they form an accurate mould. The right lung is the larger and has three lobes, while the left has two. Each lung is suspended freely in this ORGANS OF RESPIRATION. 245 cavity and is attached only by a small part of its flattened or mesial surface called the root. The outer surface of each lung it covered by a serous membrane, the visceral pleura, which is reflected over the chest wall, where it is called the parietal pleura. The histology of the pleura is identical with that of the peritoneum. Each lobe has one bronchus which divides rapidly into smaller bronchi. The latter, instead of having cartilage rings, are supplied with small cartilage plates. These plates are not present in bronchi whose diameters are less than o.i mm. Mucous glands are rather numerous but also disappear in bronchi less than o.i mm. in diameter. These smaller bronchi differ further from the larger ones in having a circular layer of smooth muscle that in- tervenes between the cartilage plates and the mucous membrane. The contraction of this muscle reduces the caliber of the smaller bronchi and thus regulates the amount of air that passes to the lung tissue. In asthma there is a spasmodic or more or less chronic contraction of this muscle tissue, which causes diffi- culty in breathing. The air is forced through the narrow tubes, and this brings about a dilatation of the terminal passages and a hypertrophy of the chest muscles, the latter being due to the forced efforts in securing sufficient air. Asthmatic patients, therefore, have resonant lungs and usually an en- larged chest. The primary trouble in this disease is not in this smooth muscle tissue, but seems to involve the nervous system and the innervating nerves. Smooth muscle is present in all the bronchi, 246 NORMAL HISTOLOGY AND ORGANOGRAPHY. even in the smallest tubes whose diameters measure 0.2 mm. Structure of the Lung.-The structure of the smaller bronchi, which form a part of the lung tis- sue, has just been described. Our knowledge of the terminal air passages has recently been greatly in- creased by the work of Dr. Miller, of the University of Wisconsin, whose account will be followed. The smallest bronchioles, whose diameters are 0.2 mm., are called terminal, or respiratory bronchi. In these Epithelium. Longitudinal elastic fibers. Involuntary muscle. Cartilage. Mucous gland. Air sacs. Fat cells. Fig. 187.-Section from lung showing portion of small bronchus and adjacent lung tissue. tubes the character of the epithelial lining changes. Patches of small pavement epithelial cells appear among the ciliated cells, while at the end of the res- piratory bronchus all are of the pavement variety. At this point the tube, slightly dilated, opens into three to six distinct chambers called atria. Each atrium opens into a variable number (2 to 5) of larger irregular spaces called air sacs, the walls of which have concave spherical depressions called air ORGANS OF RESPIRATION. 247 cells, or alveoli. Simple pavement epithelium lines the atria and air sacs, consisting of two varieties of cells: (i) small nucleated elements, and (2) larger non-nucleated plates. The latter line the alveoli and are applied directly against the blood capillaries, while the nucleated elements intervene at the free margin of the alveoli. Before birth the air sacs are collapsed and all the pavement epithelium is com- posed of nucleated cells. With the first breath of air the air sacs become distended, not uniformly, but to form vesiculated walls, the small vesicles being the alveoli. The walls of the latter suffer greater distention, due to a less resistance offered by the opposing blood capillaries, and the nucleated cells in this region become changed to non-nucleated plates, through which an exchange of gases takes place dur- ing the functional activity of the lung. The atria and air sacs vary in size according to their distention with air. An average diameter is 1.0 mm. for the atria, and 1.0 by 1.5 mm. for the air sacs. Each air sac has from six to eight air cells, or alveoli, that also vary greatly in size, an average diameter being 0.25 mm. One system of atria and air sacs constitute a lobule and is separated from adjacent lobules by in- tervening areolar tissue. The base of each lobule is directed toward the surface of the lung and the apex towards its root. These lobules can be seen in a macroscopic surface examination of the lung. The elastic fibers of the membrana propria, de- scribed in the wall of the trachea and bronchi, ex- tend to the distal end of the air passages, where they spread out to form a thin reticular fabric just ex- Artery. Ltmg tissue. Bronchiole. Fig. 188. Respiratory bronchiole. Lung tissue. Alveolar duct. Fig. 189. Figs. 188 and 189.-Two sections of cat's lung (Bohm and Davidoff) 248 ORGANS OF RESPIRATION. 249 ternal to the pavement epithelium, giving great elasticity to the air sacs and functions in the expul- sion of air during normal breathing. The term in- fundibulum is sometimes applied to the distal air passage lined by pavement epithelium. The following is a resume of the tissues found in the walls of the respiratory passages: N on-mtcleated epithelial cell. N ucleated epi- thelial cell. Fig. 190.-Inner surface of human alveolus treated with silver nitrate, showing respiratory epithelium (after Kolliker). i. Epithelium extends the whole length. In the trachea and bronchi this is stratified ciliated. In the atrium and air sacs it is simple pavement and made up of two kinds of cells, namely, nucleated and non- nucleated. 2. Elastic fibers extend the whole length. In the respiratory parts the fibers form a reticulum just 250 NORMAL HISTOLOGY AND ORGANOGRAPHY. external to the pavement epithelium and give elas- ticity to the lung tissue. 3. Mucous glands are found in the walls of the large passages down to tubes 1.0 mm. in diameter. Cartilage is found in the trachea and bronchi down to tubes 1.0 mm. in diameter. In the trachea and larger bronchi the cartilage forms C-shaped rings, while in the smaller tubes the car- tilage appears in plates. 5. Smooth muscle is found in the larger passages down to tubes 0.2 mm. in di- ameter, or down to the respiratory parts. In the trachea and the larger bronchi this muscle is placed in the posterior wall and be- tween the ends of the cartilage rings. In the smaller bronchi it forms a circular layer between the lining epithelium and the cartilage plates. Blood Supply.-The lungs, like the liver, receive blood from two sources, arterial blood through the bronchial vessels, and venous blood through the pul- monary artery. The bronchial arteries, from one to three for each lung, are much smaller than the pul- monary vessels, and carry blood for the nutrition of the lung. They arise from the aorta or from an Fig. 191.-Scheme of lung lobule (after Miller): b. r., respiratory bronchiole; d. al., alveolar duct (ter- minal bronchus); a, a, a, atria; 5. al., air sacs; a. p., air-cells or alveoli. ORGANS OF RESPIRATION. 251 intercostal artery and follow the bronchial tubes through the lung, to be ultimately distributed in three ways: i. They supply the bronchial lymph glands, the coats of the large blood-vessels, and the walls of the bronchial tubes, forming in the latter an outer and an inner plexus for the irrigation of the muscle coat and the mucous membrane. 2. They supply the interlobular areo- lar tissue; and 3, They spread out over the surface of the lung beneath the pleura. The bronchial veins do not have so extensive a distribution be cause some of the blood sup- plied by the bronchial arteries returns by the pulmonary veins. The superficial and deep set of bronchial veins unite at the root of the lung to drain on the right side into the large azygos and on the left into the left upper azygos vein. The pulmonary artery, which supplies the venous blood, is a very large vessel that gives branches to each lobe of the two lungs. The relation of the pul- monary artery to the bronchi is different on the two sides. On the right side the first branch of the pul- monary artery turns backward below the bronchus of the upper lobe, and then passes along the posterior Fig. 192. - Reconstruc- tion in wax of a single atri- um and air sac with the alveoli: V, Surface where atrium was cut from alveolar duct; P, cut surface, where another air sac was re- moved; A, atrium; 5, air sac with air cells (alveoli) (after Miller). 252 NORMAL HISTOLOGY AND ORGANOGRAPHY. surface of this bronchus. On the left side the cor re - spending artery turns backward above the level of the first bronchial branch. The bronchus to the upper lobe of the right lung is therefore called an eparterial bronchus. All the other bronchi are be- low their respective arteries and are called hyparterial bronchi. Because of these relations it is believed that the upper lobe of the right lung has no homo- logue on the left side, and that the middle lobe on the right side is homologous to the upper lobe on the left. The pulmonary ar- tery divides with the bronchi and closely ac- companies them along their posterior or superior walls. The correspond- ing veins pass along the anterior or inferior walls. These blood-vessels are very large, often as large as the bronchial tubes, but in no case do they supply blood to the walls of the bronchi. At the apex of the pulmonary lobule, the pulmonary artery breaks up into several small twigs, one for each antrum, supplying blood to an extensive capillary plexus that spreads over the surface of atria and air sacs. The capillary meshes are very dense, and the capillary tubes very large, so that the intervening spaces are barely wider than the capillaries themselves. Because of the large size of the lung capillaries it is possible for fine Fig. 193.-Section from in- jected lung showing capillaries of an air sac. ORGANS OF RESPIRATION. 253 shreds from a blood clot, or emboli in the blood, to filter through and reach the left side of the heart by the pulmonary veins. If so, these emboli are quickly carried by the blood current around the aorta and up the right carotid, as the latter is the most direct route. This course takes them to the right side of the brain, in which the capillaries are narrow, and where the emboli lodge often with fatal results. Such emboli or shreds of blood clots pri- marily enter the venous system at the seat of a bone fracture, or in the walls of the uterus after parturi- tion, or from clots of blood anywhere in the system. The pulmonary veins carry blood from the pul- monary capillary plexus. Each venous radicle drains an area corresponding to several air cells or alveoli. At first these small veins take an inde- pendent course in the interlobular tissue, but after they have attained a certain size they accompany the arteries and the bronchi, and, as a rule, along the lower and front aspect of the latter. At the root of the lung there are formed two pulmonary veins on each side which open separately into the left auricle. The pulmonary veins have no valves, and unlike the veins of other organs are more capacious than their corresponding arteries. Lymphatics.-The lymphatics of the lung are very extensive and accompany the two blood systems. We may therefore divide them into two sets, a bronchial and an alveolar. The bronchial consists of an elaborate, fine plexus that ramifies through the mucosa and submucosa of the bronchial tubes. This set anastomoses freely with a second plexus just ex- 254 NORMAL HISTOLOGY AND ORGANOGRAPHY. ternal to the smooth circular muscle layer of the bronchi. Lymph nodes are interpolated every- where in these plexuses. Just beneath the pleura, all over the surface of the lung, lymphatics ramify and drain toward the root of the lung, where they join the lymphatics located in the bronchial walls. The alveolar set accompany the pulmonary vessels. These lymphatics have their origin in a plexus that surrounds the respiratory or alveolar portions of the lungs, and then accompanies the pulmonary arteries and veins along the external surfaces of the bronchial tubes to the root of the lungs, where they ultimately unite with the bronchial lymphatics. While lym- phatic nodes are present everywhere, they are par- ticularly abundant at the root of the lung. As tuberculosis spreads along the lymphatics, the dif- ferent clinical aspects of this disease depend to a considerable extent on which of these systems be- comes involved. Nerves.-The nerves of the lung come from the pneumogastric and the sympathetic, and are made up of medullated and non-medullated fibers. They enter at the root of the lung and accompany the blood-vessels to the terminal air passages, where they arborize about the lung alveoli just external to the epithelial lining. Many nerve ganglia are located along their course and many fine fibers are given off that innervate the musculature and epithelial lining of the bronchial tubes and the walls of the blood- vessels. CHAPTER VII. THE URINARY ORGANS. The following organs will be considered under this topic: Suprarenal glands, Kidney, Ureter, and Blad- der. The urethra will be described in connection with the generative organs. THE SUPRARENAL GLANDS. The suprarenals, morphologically, belong to the nervous system, but their close proximity to the kidneys makes it advisable to describe them here. They are two triangular flattened organs covered with fat that lie one on either side of the spine, in close proximity to the upper kidney border. The left one is slightly larger and measures from one and one-fourth to one and one-half inches from above downward, one and one-fourth inches from side to side, and one-sixth to one-eighth inch in thickness. Embryologically, the organs consist of a cortical part that develops in connection with the Wolffian body and therefore comes from the mesoderm, and a medulla which is associated with the sympathetic nervous system and is derived, at least in part, from the ectoderm. The medulla decomposes very rapid- ly after death, and the organ then resembles a cap- sule; hence the name, suprarenal capsule, is often used. 255 256 NORMAL, HISTOLOGY AND ORGANOGRAPHY. Each suprarenal is invested in a fibrous capsule and a liberal supply of fat. The capsule contains many elastic fibers and some smooth muscle cells. The cortex shows a radial structure and has been divided into three zones, which are not very well de- fined. i. The zona glomerulosa, next to the capsule, con- sists of a row of columnar epithelial cells folded in such a way as to form oval bodies or elongated heads separated by strands of connective tissue from the cap- sule. The oval nuclei are in the middle of the cells. 2. The zona jasciculata makes up the larger por- tion of the cortex and consists of anastomosing col- umns of epithelial cells, a continua- tion of the zona glomerulosa. Each column has two rows of polygonal cells that are smaller than those of the glomerulae. 3. The zona reticularis borders on the medulla. Here the columns anastomose and freely interlace. The cells resemble those of the fasciculata. Con- nective tissue ramify between the columns, hence the radial appearance of the cortex. The medulla is coarsely vascular. The cells are smaller than those of the cortex and are grouped in round or oval masses. These cells are finely gran- ular, often pigmented, and stain a brown color. Cortex'. Medulla. Hilum. Blood-vessels. Fig. 194.-Cross section of suprarenal gland of man. PLATE IV. Diagrammatic Representation of the Development of the Genito- urinary System, the Wolffian Body and its Derivatives Being Colored Red, the Mullerian Duct and its Derivatives, Green (Heisler): i, Indifferent type; 2, indifferent type, later stage, the Wolffian and Mullerian ducts and the primitive ureter now opening into the urogenital sinus; 3, male type, lower ends of Mullerian ducts fused to form the sinus pocularis; 4, female type. PLATE IV. THE URINARY ORGANS. 257 Numerous ganglion cells are present and many nerve fibers. Blood-vessels.-Each suprarenal gland receives three arteries,-one each from the aorta, the phrenic, and the renal. The arteries break up into small branches, most of which enter the medulla through the hilum. Some branches ramify in the capsule Capsule. Zona glootrulosu Zona fasdtulata. Zona reticularis Fig. 195.-Section of suprarenal cortex of dog (Bohm and Davidoff). and from there enter the cortex, where they form capillaries around the columns of epithelial cells. Those that enter the medulla form a coarse plexus in this part, and then send smaller capillaries into the cortex to anastomose with those from the capsule. The veins pass out from the center, usually one from 258 NORMAL HISTOLOGY AND ORGANOGRAPHY. each organ. The vein from the right suprarenal enters the vena cava, while that from the left empties into the renal. Lymphatics accompany the blood- vessels. Fig. 196.-Arrangement of the intrinsic blood-vessels in the cortex and medulla of the dog's adrenal (Fig. 17, Plate V, of Flint's article in " Con- tributions to the Science of Medicine," dedicated to Professor Welch, 1900). The nerves are exceedingly numerous and come from the solar and renal plexuses of the sympathetic, and medullated fibers from the phrenic and pneumo- gastric. They ramify freely among the ganglionic cells of the medulla and between the cells of the cor- tex, particularly those of the glomerulosa. the: urinary organs. 259 The function of the suprarenal gland is not known. Its extirpation in the dog is followed by death in a few days. There are at least three interesting clini- cal features connected with this organ: i. Suprarenal extract, taken internally, increases arterial tension by contracting the small arterioles. The extract has the same effect when sprayed upon surfaces, therefore it is much used in nose, throat, and eye work, to check hemorrhage and reduce con- gestion. 2. The cortical cells may produce a malignant growth called a hypernephroma. The malignant cells may invade and replace the kidney. The growth usually spreads to the liver and adjacent or- gans, causing death in one to three years. 3. Addison's Disease is a chronic, usually tubercu- lar, inflammation of the suprarenal glands, fatal in one or two years. It is accompanied with a striking bronze pigmentation of the skin, and digestive and ner- vous disturbances. It is a rare disease of middle life. The above facts support the view that the organ secretes a substance that is regularly gathered up by the blood. This secretion may control, in a measure, arterial pressure. The organ is also a relay in the sympathetic nervous system which, when destroyed, as in Addison's Disease, accounts for the gastric and nervous symptoms. The kidneys, two in number, are compound tubular epithelial glands derived, embryologically, from the mesoderm. They are situated behind the peri- THE KIDNEYS. 260 .NORMAL HISTOLOGY AND ORGANOGRAPHY. toneum, one on each side of the vertebral column and on a level with the last dorsal and the upper two or three lumbar vertebrae. They are held in position by the renal vessels, by a loose areolar tissue that surrounds them which contains much fat, and by the abdominal pressure. Each kidney measures four inches in length, two and one-half inches in breadth, and one and one-fourth to one and one- half inches in thickness. Their developmental history is rather complex and can be but briefly given here. It involves the history of the pronephros, mesonephros, and meta- nephros, three sets of excretory organs which re- place each other in the sequence in which they are mentioned. i. The pronephros, or head kidney, develops in connection with the nephrotomes of the first three or four embryonic somites. These nephrotomes unite with a longitudinal duct, the pronephric duct, which opens posteriorly into the cloaca. With this organ fluid from the celomic or peritoneal cavity can be eliminated, and also waste products from the blood, as a tuft of blood capillaries or glomerulus is present near the peritoneal opening of each nephro- tome. This kidney is exceedingly rudimentary in mammals and functional only in larval stages of amphibians and in bony fishes. 2. The mesonephros, or Wolffian body, develops in connection with the nephrotomes posterior to those that form the pronephros. The pronephric duct becomes the Wolffian duct and drains from the peritoneal cavity in the same manner as in the head THE URINARY ORGANS. 261 kidney. The glomerulus in this case is situated in the wall of the nephrotome, which makes the meso- nephros a more efficient organ. The mesonephros is an elongated segmented organ and a permanent structure in amphibians. It is an embryonic organ in birds and mammals, in which it is replaced by the metanephros. 3. The metanephros, or permanent kidney, develops as a diverticulum from the cloacal end of the Wolffian duct. The diverticulum lengthens into a tube, the ureter. The upper or anterior end of the tube Artery. Vein. Fig. 197.-Kidney of new-born infant, showing a distinct separation into reniculi; natural size. At a is seen the consolidation of two adjacent reniculi (Bohm and Davidoff). branches to form a number of smaller tubes, the uri- niferous tubules of the kidney. The surrounding mesoderm becomes condensed and vascular, inter- lacing between the tubules to form the adult kidney. The development of the urinary system is closely associated with that of the generative system, and will be referred to again when the latter is described. Structure.-The hilus of the kidney is an opening through which the ureter and blood-vessels pass. On making a longitudinal section of the kidney, it will be seen that the hilus leads to an expanded fis- 262 NORMAL HISTOLOGY AND ORGANOGRAPHY. sure, the renal sinus. The pelvis is a funnel-shaped expansion of the ureter that occupies a large portion of the sinus. The contents of the sinus may be re- moved, when the exposed wall will be found to be kidney substance. Each kidney is enclosed in a smooth fibrous cap- sule of areolar tis- sue, a part of which also lines the sinus. The capsule is finely vascular and can easily be de- tached. If it ad- heres to the kidney substance it is evi- dence of disease. It is customary to describe the kid- ney as made up of two layers, an out- er, or the cortex, and an inner, the me- dulla, although there is no sharp line dividing the two. The medulla consists of ten or twelve separate conical masses called Malpighian, or medullary pyramids, so arranged that their bases bor- der on the cortical layer and their apices point toward Fig. 198.-Longitudinal section through the kidney: 1, Cortex; 1', medul- lary rays; 1", labyrinth; 2, medulla; 2', papillary portion of medulla; 2", boun- dary layer of medulla; 3, transverse sec- tion of tubules in the boundary layer; 4, fat of renal sinus; 5, artery; *, transverse medullary rays; A, branch of renal artery; C, renal calyx; U, ureter (after Tyson and Henle). THE URINARY ORGANS. 263 the renal sinus where they form papillae. The medullary substance is more dense than the cortical and is strictly striated, which is due to the radiating course of the tubules in this part. At the base of each Malpighian pyramid these tubules pass up into the cortical substance and are grouped to form cone-like masses called medullary rays, or pyramids of Capsule. Glomeruli. Pyramid o} Fer rein. Malpighian Pyramid. Fig. 199.-Section through cortex and medulla of kidney. Ferrein, the apex of each being in close proximity to the periphery of the kidney. There are thus a great many medullary rays for each Malpighian pyra- mid. The portions of the kidney that intervene between the medullary rays are called the labyrinth, and consist largely of convoluted tubules. The cortical substance not only covers the bases of the 264 NORMAL HISTOLOGY AND ORGANOGRAPHY. Malpighian pyramids, but sends prolongations be- tween them down to the renal sinus. These cortical prolongations are called the columns of Bertini, of which there are as many as there are Malpighian pyramids. It is convenient to describe the kidney tubules as consisting of nine parts. Each tube commences in the labyrinth of the cortex with (i) an invaginated dilatation called Bowman's capsule. This capsule is lined by simple squamous epithelium which, when invaginated, makes two layers, the lumen of the tube being between these layers. Into the in- vaginated cavity is crowded a tuft of blood capil- laries called a glomerulus. A liberal supply of con- nective tissue blends with these capillaries. The capsule and glomerulus are frequently called a Malpighian corpuscle. At the base of the cap- sule each tube is constricted, forming (2) the neck, after which it becomes much convoluted and wide, forming (3) the proximal convoluted tubule. The cells of this part are large with very thin cell walls. The cytoplasm immediately around the nu- cleus is granular, but toward the basement membrane it is striated with lines at right angles to the mem- brane. The tube now approaches the medulla, becomes nearly straight, but rapidly narrows to form (4) the spiral portion. It now passes straight down a Malpighian pyramid, where it makes a short curve, and returning thus forms (5) the loop of Henle. This loop has a narrow descending limb with a short curve, and a wider ascending limb. The narrow descending limb and curve has simple THE URINARY ORGANS. 265 flat epithelium, so that the lumen is practically as Bowman's capsule. Glomerulus. Proximal convoluted. Neck Junctional tubule. Distal convoluted. Irregular tubule. Spiral portion. Descending limb of Henle's loop. Collecting tube. Ascending limb of Henle's loop. Loop. Fig. 200.-Diagram of kidney tubule large as that of the preceding part. The ascending 266 NORMAL HISTOLOGY AND ORGANOGRAPHY. limb is larger but the epithelium takes on the char- acteristic of the proximal convoluted tube, although the cells are a little smaller and may contain pig- ment granules. The ascending limb passes straight up a medullary ray, from which it emerges to again enter the cortex, where it becomes irregular in out- line forming (6) the irregular tubule, which quickly becomes much twisted and coiled to form (7) the distal convoluted part. In the irregular part the cells are very un- equal in size and a rod- like struc- ture of 1 he cytoplasm is very dis- tinct, while the base- ment mem- brane is said to be ab- sent. The cells of the distal convoluted tube are rather long, with a distinct membrane and a highly refractive appearance of the protoplasm. Near the basement membrane minute projections from adjacent cells may be seen to inter- lock. Finally, this portion terminates in (8) a short junctional tubule, which leaves the cortex and enters a medullary ray to join the last part (9), the collecting tubule. The latter passes straight through the Malpighian pyramid to open on its surface in a small pore. In its course the collecting tube receives Convoluted portions. Howman's capsule. •Glomer- ulus. -Neck. Fig. 201.-Section of a portion of the labyrinth of the kidney cortex. THE URINARY ORGANS. 267 not only other junctional tubules but also unites with other collecting tubes. The junctional part is narrow but its lumen relatively large, being lined by clear flat or cubical cells. The collecting tubes are large and have a lining of simple cubical epithelium. The location of the different parts of the kidney tubules may be tabulated as follows: Portion of Tubule. Location. 1. Bowman's capsule cortical labyrinth. 2. Neck cortical labyrinth. 3. Proximal convoluted cortical labyrinth. 4. Spiral portion medullary rays. 5. Loop of Henle: (a) Descending limb .... medulla. (6) Loop medulla. (c) Ascending limb medulla and medullary rays. 6. Irregular part cortical labyrinth. 7. Distal convoluted cortical labyrinth. 8. Junctional tubule medullary rays. 9. Collecting tubule medullary rays and medulla. It will be observed that the walls of these tubules consist of simple epithelium; that this is made up of pavement cells in the capsule, neck, and descending limb of Henle's loop; while large cubical or columnar cells with granular and rod-like structure of the cyto- plasm are found in the convoluted parts and ascend- ing limb of Henle's loop; and a low cubical epithe- lium invests the junctional and collecting tubules. Casts.-It is common in high fevers and in diseases of the kidney to find moulds of the uriniferous tubules in the urine. In high fevers blood may enter and congeal in the uriniferous tubules, the kidney secretion forces out this obstruction, which then appears in the urine as a blood cast. A clear scrum mould is called a hyaline cast. In more chronic cases the cells of the tubules are carried away 268 NORMAL HISTOLOGY AND ORGANOGRAPHY. and the mould is then ealled an epithelial cast. The cells may have decomposed, when it becomes a granular cast. Hyaline casts often show granula- tions and are then also called granular casts. Finally, fatty degenerations may appear and form jatty casts. The recognition and identification of casts form an important subject in clinical analysis. If small pieces of kidney are treated with strong hydro- chloric acid and the detritus thus produced be ex- amined in gly- cerin, under a low magnification, many pieces of the uriniferous tubules are read- ily observed. These pieces are practically iden- tical with the epi- thelial and gran- ular casts of the diseased kidney. Blood-vessels.-The kidneys are highly vascular and receive a large amount of blood in proportion to their size. The renal artery and renal vein pass through the hilum, the artery between the vein and ureter. In the renal fissure the artery breaks up into four or five branches which lie external to the pelvis of the ureter. These branches pass directly to the columns of Bertini, where they break up into smaller vessels and rise to the level of the Mal- pighian pyramids. At this level they pass across the pyramids, between the latter and the cortex, Collecting tubule. Capillary. Ascending limb of Henle's loop. Descending limb of Henle's loop. Capillary. Fig. 202.-Section of a portion of a kidney medulla. THE URINARY ORGANS. 269 forming what are called arterial arches. The ar- teries form incomplete arches across the base of the pyramid, while the accompanying veins, in this place, form complete 'venous arches across the base of the pyramid. From the arches interlobular arteries pass outward be- tween the me- dullary rays and among the convoluted tu- bules, taking a direct course toward the sur- face of the kid- ney. At inter- vals they give off curved short branches which pass directly to the glomeruluc of a Malpig- hian corpuscle, where they break up into a spongy mass o f capillaries. A vein, smaller than the artery, emerges from the glomerulus close to the point where the artery enters. The artery is called Stellate vein. Capsule. Interlobular artery. Vas afferens. Interlobular vein. Pas efjerens. Glomerulus. Arterial arch between the cortex and medulla. Pseudo-arteria recta. ' Arteries recta. Fig. 203.-Diagram of blood supply of kidney. 270 NORMAL, HISTOLOGY AND ORGANOGRAPHY. the vas afjerens and the smaller vein the Tas efjerens. The latter, instead of uniting with other veins to form larger trunks, as is the case in other organs, passes directly to the convoluted tubules, where it forms a dense capillary system that ramifies everywhere over the walls of these tubules. Many of the effer- ent vessels from the lowermost glomeruli, that is, those nearest the medulla, break up into pencils of straight vessels called pseudo-arteria recta, which pass directly into the medulla to form capillaries around the tubules of this part. Interlobular Teins convey the blood from the kid- ney cortex to the venous arches at the base of the pyramids. Near the periphery of the kidney other veins converge to form a stellate appearance just beneath the capsule. These stellate veins receive blood from the venous arches and also connect with the veins of the capsule. The blood supply of the medulla is to a great ex- tent independent of that to the cortex, excepting that supplied by the false arteriae rectae. Branches from the concave side of the arterial arches pass directly into the medulla, where they form bunches of pencils of small parallel vessels, the arteria recta, which sup- ply blood to the walls of the uriniferous tubules of this part. Veins return this blood to the venous arches that lie between the cortex and medulla. These arches form veins that pass through the col- umns of Bertini and ultimately drain into the renal vein, which passes through the hilum to join the inferior vena cava. On account of this extensive blood supply any renal disturbance is, as a rule, accompanied by a cor- THE URINARY ORGANS. 271 responding circulatory disturbance. Conversely, a disturbed circulation or an enlarged heart is indica- tive of a possible nephritis. Nerves.-The nerve supply is derived from the cerebrospinal system and the sympathetic. Many of these supply the blood-vessels, which they always accompany, but some arborize among the renal tubules, particularly those of the renal cortex. The ureters are two muscular tubes that conduct the urine from the kidneys to the bladder. The dilated commencement of each ureter is called the pelvis and lies with its base in the renal fissure, and extends through the hilum to the lower portion of the kidney where the ureter proper begins. Lateral expansions of this pelvis extend to and enclose the papillae of the Malpighian pyramids, on the surface of which the collecting tubules open. These ex- pansions are called calyces. The ureters measure from fourteen to sixteen inches in length, and one-fourth inch in diameter. Each ureter lies behind the peritoneum and passes downward and inward to the brim of the pelvis, and then forward and inward to the base of the bladder. The ureters are about two inches apart as they enter the wall of the bladder, through which they pass obliquely for three-fourths inch to open on the inner surface in two narrow and slit-like openings. The oblique passage through the bladder wall acts as a valve to prevent a return flow of urine. Structure.-The walls of the ureter consist of an THE URETERS. 272 NORMAL, HISTOLOGY AND ORGANOGRAPHY. outer fibrous, a middle muscular, and an inner mucous layer. The latter has many longitudinal folds and is lined by transitional epithelium of four or five layers of cells. The superficial cells are flat, or low cubical, and may contain two nuclei. Their lower surfaces have depressions that fit upon the rounded ends of the second layer, which consists of oval or pear-shaped cells. Between the apices of the latter are two or three rows of small, irregular interstitial cells. Mucous glands have been described in the renal pel- vis and so have lymphoid nod- ules, but the presence of glands in the ureter of man is doubtful. The membrana propria is com- posed of areolar tissue which becomes gradually loose toward the muscularis. This membrane is like others of its kind, having a limited blood supply. The muscular coat is composed of smooth muscle cells and consists chiefly of a circular layer between two thin longitudinal layers, particu- larly well defined in the lower part of the ureter. The fibrous coat is relatively thick and strong, con- tributing fibrous elements that interlace the muscle tissue. Stratified epithe- lium. Mucous layer. Muscular cent. Fibrous coat. Fig. 204.-Cross section of the ureter. THE URINARY ORGANS. 273 The function of the ureter is an active one. A few drops of urine enter the ureter and are propelled along by the peristaltic contraction of its muscula- ture, which forces the urine in intermittent jets into the bladder. In case of overdistention the force ex- erted by this mechanism is sufficient to rupture the bladder. In case of an obstruction in the ureter, as in the passage of calculi, a violent contraction of the smooth muscle follows, accompanied by severe pains. In surgical operations ureters have been sewed into the upper end of the bladder, or even into the intestine. In the latter case the kidney usually becomes infected with bacteria from the bowel. THE URINARY BLADDER. The urinary bladder is a receptacle for the reten- tion of urine, with an average capacity of one pint, although capable of much greater distention. When empty it lies wholly within the pelvis, but if dis- tended it rises into the abdomen. When moderately filled it has a rounded form, but when completely distended it becomes egg-shaped, the larger end, called the base or fundus, being directed downward and backward toward the rectum, and its smaller end, the summit, resting against the anterior ab- dominal wall. When distended the peritoneum covers the bladder, excepting a triangular space of two inches above the symphysis pubis known as the space of Retzius. This is of surgical importance, as the bladder can be opened through this space without going through the peritoneum. The mucous membrane on the inner surface of the 274 NORMAL HISTOLOGY AND ORGANOGRAPHY. bladder is loosely attached to the muscularis, and is slightly corrugated or folded in the contracted form of the organ. At the lower part of the bladder is found the orifice leading into the urethra, and im- mediately behind this is a smooth triangular surface called the trigone. The orifices of the ureters are found at the posterior angles of the trigone, and in the distended bladder are about one and one-half inches apart and about the same distance from the urethral orifice. When the bladder is contracted this space is diminished. An exact knowledge of these relations is important in any attempt to pass a catheter into the ureter. Histology of the Bladder.- There is a mu- cous, submu- cous, muscular, and serous coat to the bladder. The mucous mem- brane resembles that of the ureters, with which it is continuous. It is covered with a transitional epithe- lium whose cells vary according to the distention of the bladder. As a rule, epithelial cells have but very little elasticity and mucous membranes, therefore are frequently much folded. The bladder cells are capable of considerable distention, when they become very flat. When the organ contracts they accommodate themselves to this condition and become cubical. The cells of the surface layer are squamous and have Transitional epithelium. Connective tissue stroma. Fig. 205.-Section through the mucosa of the bladder. THE URINARY ORGANS. 275 concave depressions into which the rounded ends of the second layer or pear-shaped cells are adjusted. Two or more layers of irregular interstitial cells inter- vene between the apices of the pear-shaped cells. The interstitial cells divide regularly by karyokinesis and are then crowded to the surface to replace the superficial cells that normally exfoliate. There are no glands in the bladder, but solid cell projections are sometimes found that resemble glands. The blad- der is a part of the allantois, a vesicular evagination of the hind-gut. The bladder epithelium, therefore, Pavement cell. Pear-shaped cell. Pavement cells. Fig. 206.-Epithelial cells from the bladder. Interstitial cells. is of hypodermic origin, while that of the ureter is from the mesoderm. A vascular submucosa intervenes between the mu- cosa and the muscularis. This is a thin layer of areolar tissue, but sufficient to give the mucosa apparent elasticity and enable it to move upon the muscularis. The muscular coat consists of smooth muscle fibers which may be divided into bundles of outer longi- tudinal fibers, a middle strong circular layer, and an imperfect inner longitudinal or diagonal stratum. 276 NORMAL HISTOLOGY AND ORGANOGRAPHY. At the urethral opening the middle layer is thickened to form a sphincter muscle, according to some au- thors. The bladder musculature forms a basket- work fabric, and when much distended intervals may arise in its walls which become points of weak- ness through which the mucosa may protrude, when the organ is said to be sacculated. Vessels and Nerves.-The bladder is supplied with blood from the superior and inferior vesicle arteries, and in the female also from branches of the uterine artery. The veins form large plexuses, particularly around the neck, sides and base. They eventually drain into the internal iliac. The nerve supply is from the third, fourth, and sometimes the second sacral nerves, and from the hypogastric plexus of the sympathetic. The latter are nearly all non-medul- lated. CHAPTER VIII. REPRODUCTIVE ORGANS IN THE MALE. Under this heading are included (1) the testes and their ducts, (2) epididymis, (3) penis, and (4) pros- tate gland. THE TESTICLES. The testes are two glandular organs for the produc- tion of spermatozoa, suspended in the scrotum by the spermatic cord. Each testicle is about one and one-half inches long, one and one-fourth inches wide, and nearly one inch thick from side to side. The corresponding dimensions of the ovary are, one and one-half by three-fourths by one-half inches. The coverings of the testes are, (i) skin, (2) dartos; these two form the wall of the scrotum. The skin is thin and pigmented. The dartos is a reddish tissue continuous with the two layers of superficial fascia of the groin. It is vascular and consists of smooth areolar tissue and smooth muscle fibers. The latter give involuntary contractility to the scrotum and produce folds or rugae in the skin. (3) Inter colum- nar fascia, which is a thin connective-tissue layer closely associated with (4) the cremasteric fascia. The latter is continuous with the internal oblique muscle. (5) The infundibuliform fascia comes next and is a continuation downward of the fascia trans- versalis. (6) The tunica vaginalis envelops each 277 278 NORMAL HISTOLOGY AND ORGANOGRAPHY. testicle and is derived from the peritoneum during the descent of the organ. It is therefore a serous coat that has the same histology as the peritoneum, and may be divided into two parts, one the visceral portion that invests the surface of the organ, and the other the parietal portion that is reflected over the surface of the infundibuliform fascia. The interval between these portions constitutes the cavity of the tunica vaginalis, and it is in this space that hydro- Tunica vaginalis, visceral portion. Tunica albuginea. Tunica vagi- nalis, parie- tal portion. Epididymis. . Corpus of Highmore. - Artery. - Vein. ■ Vas deferens. Lobule. Fig. 207.-Cross section of human testicle. cele fluid collects. (7) The tunica albuginea comes next and is a firm fibrous covering. This tunic sends fibrous cords or trabeculae into the testis, which divide the organ into lobules. It is par- ticularly dense along the posterior margin of the organ where it also invests the vas deferens, forming at this margin a mediastinum called the corpus of Highmore. (8) The tunica vasculosa is a delicate vascular layer that covers the inner surface of the REPRODUCTIVE ORGANS IN THE MALE. 279 tunica albuginea. The three tunics just mentioned form the wall or capsule of each testicle, and are so closely associated that it is difficult to distinguish one from the other. Structure.-The testis is a compound tubular gland divided into three hundred to four hundred lobules. Each lobule is conical in shape with the apex directed toward the mediastinum and the base toward the surface of the organ. The lobules differ in size ac- cording to their position. Each lobule represents several coiled tu- bules which, when unraveled, aver- age two feet in length. There are at least six hundred to eight hundred of these tubules to each testicle. Their walls are lined with stratified epithelium which is in- vested with a thin layer of connective-tissue ele- ments. The epithelium rests upon a basement membrane and may be arranged in at least three irregular groups or layers: i. A layer of cubical cells, with small nuclei, rests upon the basement membrane. The cells of this layer are called sper- matogonia. The columns of Sertoli, or sustentacular cells, also belong to this layer. These columns are elongated columnar cells that extend from the Spermatozoa. Spermaloblasts. Spermatocytes. Spermatogonia. Sustentacular cell. Fig. 208.-Section of convoluted tubules of testicle. 280 NORMAL HISTOLOGY AND ORGANOGRAPHY. basement membrane inward toward the lumen of the tube. They give off lateral processes that form a reticulum about groups of young spermatozoa, to which they give both support and sustenance, according to the views of some authors. 2. Within the first layer there are one or two rows of large cells with large deep-staining nuclei. These are the spermatocytes. The latter multiply rapidly and continually to form, 3, s per matoblasts or sper- matids. The spermatids are small spherical cells and each one in due time develops into a spermato- zoon. The latter ripen regularly in groups which seem to cluster about individual sustentacular cells. The nucleus of the spermatids elongate and each little spherical cell gradually assumes the form of a mature spermatozoon. The different stages in this development can be worked out by a study of the spermatids as seen in the different tubules. In the cross section of a single tubule all the spermatids will be in the same stage of development. The spermatozoa when mature are crowded into the lumen of the convoluted tubules, where they mix with a viscid secretion which probably comes from the epithelial wall. The convoluted seminiferous tubules end blindly near the surface of the testis, where they are also said to anastomose with each other. In the other direction, each tubule becomes straight and forms the tubuli recti, which approach the mediastinum and function as excretory ducts. These erect tubules anastomose to form the rete testis. Interstitial Elements of the Testis.-Like any other REPRODUCTIVE ORGANS IN THE MALE. 281 organ the testicle has a fine reticulum of connective tissue that is associated with the capsule or tunica albuginea. This reticulum consists of areolar tissue that not only intervenes between the lobules, but interlaces between the seminiferous tubules. Blood and lymph vessels are everywhere associated with this tissue. In addition to ordinary connective- tissue cells, there is associated with this reticulum patches of cells that re- semble epithelium and have yellowish granules or pigment. These are called interstitial cells, and, like the areas of Langerhans of the pan- creas, are supposed to se- crete products regularly absorbed by the blood. We can postulate a pos- sible function of these cells when we consider the function of the testi- cle and its influence on the body as a whole. (i) Physiologically the testis exerts a marked influ- ence on the development of the body. (2) It is ac- tively engaged in the production of spermatozoa. (3) It is essential for the act of copulation. Early castration in domestic animals is a striking evidence of the influence the testicle exerts upon development. The change manifest is both physi- cal and mental. As the infantile testis does not Fig. 209.-Sustentacular cells (cells of Sertoli) of the guinea-pig (chrome-silver me- thod) ; profile view: c, c, Depres- sions in the sustentacular cells due to pressure from the sper- matogenic cells; d, basilar por- tion of sustentacular cells (Bohm and Davidoff). 282 NORMAL HISTOLOGY AND ORGANOGRAPHY. produce spermatozoa, it is believed that the secre- tions from the interstitial cells react upon the devel- opment of the body as a whole. While the semi- niferous tubules function in the production of sper- matozoa, it is not clear that the accumulation of semen prompts the sexual act. For instance, the testicles sometimes do not descend into the scrotum but remain in the body cav- ity. Frequently such testi- cles are of the infantile type, that is, no semen is devel- oped; and yet the copulation act in such males is not only possible, but the sexual crav- ings may be actually exagge- rated. The interstitial cells of such testicles are well de- veloped and the male is other- wise normal. Again, the im- potency that sometimes comes with old age is said to be due to impaired functional activity of the interstitial cells rather than to lack of spermatozoa. We have no specific medical treat- ment for such cases, extracts from normal testes having been tried without satisfactory results. Spermatogenesis and Spermatozoa.-The develop- ment of spermatozoa begins in man in early youth and usually continues into old age. This phenom- enon is in marked contrast to ovulation in woman, where there is a cessation or menopause at about the - Head. Middle piece. ■ Tail. End piece. Fig. 210.-Human sper- matozoa, side and flat view. reproductive organs in the male. 283 age of forty-five. The explanation offered to ac- count for this difference in the sexes is sought in the blood supply to the generative organs. There is a decrease in the nourishment to the ovaries as the menopause approaches, due to a contraction of the blood-vessels that supply the organ. The testes, on the other hand, have a liberal supply of blood throughout life. A study of the stratified epithelium of the semi- niferous tubules will reveal spermatozoa in all stages of development. Cells in the spermatogenic layer divide by normal karyokinesis to produce the second layer or spermatocytes. Each spermatocyte divides twice to produce four spermatids, which develop regularly into four spermatozoa. The development of four spermatozoa is regarded as analogous to the maturation of the ovum, which results in a ripe ovum and three polar bodies. The first division of a spermatocyte is regarded as normal mitosis. The second division is regarded as atypical, resulting in the reduction of one-half the original number of chromosomes; and the resulting nucleus, when it becomes the nucleus of the ripe spermatzoon, is called the male pronucleus. The union of male and female pronuclei, which takes place in fertilization, is supposed to reestablish the normal number of chromosomes, a number that is regularly maintained in all later cell divisions. Structure of Spermatozoa.-A spermatozoon is a minute ceil, about 0.055 mm- long and consisting of ci nucleus or head, a middle piece or body, and a vibra- tile tail. In man the head is a flattened ovoid, ap- 284 NORMAL HISTOLOGY AND ORGANOGRAPHY. pearing pear-shaped or pointed in one view and rounded in another. It contains the nucleus and stains heavily with nuclear dyes. It measures about 0.0045 mm. long, 0.0025 mm. broad, and 0.0015 mm. thick. The middle piece, or body, is cylindrical in man, and measures about 0.006 mm. in length, and 0.001 mm. in thickness. In some animals, as the rat, a spiral thread can be seen coiled about the periphery, whilst through its center a slender filament seems to pass and be continuous with the central filament of the tail. This filament ends in a terminal enlarge- ment placed in close proximity to the nucleus and known as the terminal globule. The tail is about 0.045 mm. long and tapers toward the extremity, ending in an extremely delicate fiber, the end piece. Again, in the rat this end piece seems to be the terminal part of the central filament of the middle piece, which thus extends the whole length of the tail. The spermatozoon is propelled forward by a spirally lashing movement of the tail, similar to the movement of cilia. Movement of cilia, however, ceases as soon as they are removed from their cell, which is not the case with the tail of a spermatozoon, in which motion seems to be an in- trinsic quality. So long as spermatozoa remain in the male passages they are inert, but become active as soon as expelled. Spermatozoa differ a great deal in the different species of animals. They are very hardy cells, and in the female passages may live for days and even weeks. In some domestic birds, as turkeys, they REPRODUCTIVE ORGANS IN THE MALE. 285 live at least a month, while in bats copulation takes place in the fall and fertilization follows in the spring. Excretory Ducts of the Testis.-These ducts are the tubuli recti, rete testis, vasa efferentia, epididy- mis, and vas deferens. Tubuli Recti.-The seminiferous tubules, towards the mediastinum, unite at acute angles to form a Vas dejerens. Epididymis (globus major). Vasa efferentia. Tubuli recti. ■ Rete testis. Epididymis (globus minor). Fig. 211.-Diagram of human testicle, longitudinal section. series of short parallel straight tubes called the tu- buli recti. They are clothed by a simple layer of low cubical epithelium. The rete testis consists of a reticulum of tubules formed by an anastomosis of the tubuli recti in the mediastinum. They are lined by simple columnar epithelium. The vasa efferentia are tubules that lead from the 286 NORMAL HISTOLOGY AND ORGANOGRAPHY. upper portion of the rete testis through the tunica albuginea to the epididymis. There are about fif- teen of them. They are lined by simple columnar ciliated epithelium, and represent tubules that em- bryologically belong to the mesonephros. Outside of the epithelium is a thin investment of areolar tissue in which smooth muscle cells interlace. The epididymis is a very much coiled canal, about twenty feet long, formed by the confluence of the vasa efferentia. At the upper and posterior border of the testis the vasa efferentia and epididymis form a globular mass of tubules called the glo- bus major. At the lower and posterior bor- der there is a smaller mass of coiled tubules formed by the epididymis, and called the globus minor. The epididymis is lined by simple epithelium which is ciliated in most places, but interposed are patches of nonciliated cells. The latter form small areas that resemble glands. External to this epithelium there is a thin layer of smooth muscle fibers which blends with vascular areolar tissue. The vas deferens begins at the lower margin of the globus minor and is a direct continuation of the Fig. 212.-Cross section of epididymis. REPRODUCTIVE ORGANS IN THE MALE. 287 canal of the epididymis. It is a duct about twelve inches long, but when unraveled and extended it is eighteen to twenty inches in length. At first it is rather tortuous, but soon becomes straight and ascends along the inner border of the epididymis to pass directly to the external abdominal ring, taking a vertical course and forming a part of the spermatic cord. It then passes through the inguinal canal, and reaching the internal abdomi- nal ring, turns quickly down- ward and inward to the side of the bladder upon which it descends, curving backward and downward to the neck of the bladder, where it enters the urethra through the pros- tate gland. In its abdominal course it lies external to the peritoneum, and along the bladder wall it arches between the latter and the ureter. Along this wall it becomes sacculated and near its terminus gives off a lateral, enlarged, and sacculated diverticulum, the seminal -vesicle. The distal end beyond the opening of the seminal vesicle, is a narrow straight tube called the ejaculatory duct. Structure.-The wall of the vas deferens has three Fibrous coat. Longitudinal muscle. Circular muscle. Membrana propria. Simple epi- thelium. Fig. 213.-Cross section of vas deferens. 288 NORMAL HISTOLOGY AND ORGANOGRAPHY. coats, an inner mucous, a middle muscular, and an outer fibrous. The mucous membrane generally presents two or three longitudinal folds and is lined with simple columnar epithelium. According to some investigators it may be ciliated in places and even resemble the transitional epithelium of the ureters. The membrana propria resembles that of other mucous membranes. No glands are present. The muscular layer is of the smooth variety. It con- sists of a strong inner circular and an outer longi- tudinal layer. Near the epididymis an extremely thin layer of longitudinal muscle fibers is present inside of the circular layer. The fibrous layer con- sists of loose areolar tissue, with which are asso- ciated blood and lymph vessels. Paradidymis.-This consists of a set of branched tubules that leads off as blind diverticulae from the canal of the epididymis or the vas deferens. There is one diverticulum or several of them. The length of these tubules when unraveled varies from two to twelve inches, and histologically they resemble the structure of the vasa efferentia. Morphologically the paradidymis is analogous to the paroophoron found in the broad ligament of the ovary, the origin of both being associated with the development of the tubules of the mesonephros. Hydatid of Morgagni.-There are two of these bodies. One of them, more constant than the other, lies usually between the globus major and the testi- cle and is called the sessile hydatid. It is a small cone-shaped body of epithelial cells and represents the peritoneal end of Muller's duct, the analogue of REPRODUCTIVE ORGANS IN THE MALE. 289 the fimbriated end of the Fallopian tube in the female. The other is less constant and lies usually just external to the globus major and is called the stalked hydatid. It is an epithelial body and repre- sents vestiges of the peritoneal end of the pronephric or Wolffian duct. The stalked hydatid is also present in the female, where it resembles a small cyst closely associated with one of the fimbriae of the Fallopian tube. The distance passed by the spermatozoa, before being eliminated by the urethra, is approximately twenty-four feet. The chief ducts and their lengths are: seminiferous tubules, each two feet long; epi- didymis, twenty feet; and vas deferens, two feet. The spermatozoa are themselves perfectly inactive in making this passage. During the copulation act they are discharged probably from the whole length of the vas deferens by peristaltic contraction of this duct, and not only from the seminal receptacle as formerly supposed. The supply of spermatozoa is extensive. If each testicle has eight hundred seminiferous tubules, each two feet long, then there are sixteen hundred feet of epithelial lining for each organ engaged in the production of spermatozoa. The semen consists of a fluid part, secreted mainly by accessory reproductive glands, and cell elements or spermatozoa that develop in the testes. In man there are about sixty thousand spermatozoa to each cubic millimeter of semen. Vessels and Nerves.-The spermatic artery supplies the tubules of the testicles and the epididymis with blood directly from the abdominal aorta. It is a 290 NORMAL HISTOLOGY AND ORGANOGRAPHY. long, slender artery that joins the spermatic cord as the latter passes through the inguinal canal. As the vessel approaches the testicle, it sends branches to the epididymis and then divides into other branches that ramify among the seminiferous tubules. The vas deferens receives a slender branch from one of the vesical arteries. This is called the artery of the vas deferens, and reaches as far as the testis, where it anastomoses with the spermatic artery. The spermatic veins begin in the testis and epi- didymis and pass out at the posterior border of the organ, where they unite into large veins that form a plexus along the spermatic cord. Inside the abdo- men this plexus unites to form a single trunk, the spermatic vein, which on the right side opens into the vena cava, and on the left side into the renal veins. The lymphatics are very extensive and accompany the veins. They terminate in the lymphatic glands which encircle the large blood-vessels in front of the vertebral column. The nerves are derived from the sympathetic system. There is a spermatic plexus that accom- panies the spermatic artery, and some fibers from the hypogastric plexus that accompany the artery of the vas deferens. THE PENIS. The penis is a vascular organ composed principally of two corpora cavernosa, one corpus spongiosum, which encloses the urethra, and the glans, which is really the distal end of the corpus spongiosum. The integument of the penis is very thin and loosely REPRODUCTIVE ORGANS IN THE MATE. 291 attached. It is devoid of fat and hair and darker in color than the skin generally. Over the glans it is redoubled in a loose fold, the prepuce or foreskin. The inner layer of this fold is attached firmly to the base of the glans or cervix, and from there it becomes closely adherent to the glans as far as the orifice of the urethra, where it meets the mucous membrane of the latter. Over the glans it is red, thin, and moist, and beset with numerous large vesicular and Corpora cavernosa. Prepuce. Dorsal artery. Corpora cavernosa. Corpus spongiosum. Urethra. Corpus spongiosum. Urethra. Fig. 214.-Cross section of penis: a, through the glans; b, through the body. nerve papillae, but devoid of glands, excepting around the cervix, where large sebaceous glands are numerous, called glands of Tyson, which secrete a white, waxy, odoriferous substance, the smegma. The corpora cavernosa are two parallel cylindrical masses of erectile tissue that lie in the dorsum of the penis. They blend together in the anterior portion, and toward the root of the penis diverge to become firmly attached to the pubic and ischial rami. The anterior extremity of the corpora cavernosa is cov- ered by the glans penis. Structure of Corpora Cavernosa.-There is a median 292 NORMAL HISTOLOGY AND ORGANOGRAPHY. fibrous septum between the two corpora cavernosa which becomes thin anteriorly and incompletely separates the two bodies. There is an external fibrous investment, very strong and elastic. This is composed mostly of longitudinal bundles of white fibers with interlacing elastic fibers. These fibers are intimately associated with the median septum and also with connective-tissue trabeculae that ramify through the substance of the cavernous bodies. The substance of the latter is called erectile tissue and is of a spongy nature. The trabeculae anastomose and interlace freely to form a multitude of interstices or cavernous spaces. These are filled with venous blood, and are really a complex system of veins lined by a layer of flattened epithelium as in other veins. In the anterior portion of the penis the venous labyrinth of one corpus cavernosum intercommunicates with that of the other through the incomplete septum. In the erectile condition the corpora cavernosa are distended with blood which is carried away by two sets of veins, the one set joining the prostatic plexus and the pudendal veins, and the other draining into the dorsal vein of the penis. The arterial blood is supplied mainly by branches of the pudic arteries, but the dorsal artery of the penis sends a few branches through the fibrous sheath, particularly in the forepart of the organ. The arteries ramify in the trabeculae and terminate in minute capillary branches that open into intertrabecular spaces. Some of the smaller arteries project into the spaces, forming peculiarly twisted or looped vessels called helicine arteries. REPRODUCTIVE ORGANS IN THE MADE. 293 The corpus spongiosum is also composed of erectile tissue, but is a single cylindrical body that lies below and between the corpora cavernosa. Its posterior extremity is much enlarged and rounded, and is called the bulb. This lies in the ventral portion of the root of the penis just in front of the triangular ligament. Anteriorly the corpus spongiosum forms the glans penis, which caps the corpora cavernosa. The border of the glans is rounded and projecting and is called the corona glandis, behind which is a constriction of the penis, the cervix. In the whole of its extent the corpus spongiosum encloses the urethra. Structure of Corpus Spongiosum.-This resembles the erectile tissue of the corpora cavernosa, and like the latter is distended with blood during erection, but is less rigid. The venous labyrinth is a finer meshwork and the trabeculae and fibrous tunic is much thinner. In the glans the meshes are particu- larly small and uniform. Plain muscle fibers enclose the urethra and also form a part of the external coat. Urethra in the Male.--The male urethra extends from the bladder to the end of the penis, in length about eight and one-half inches. Its walls are in apposition, excepting during the passage of urine or semen. The urethral cleft in the glans is vertical; in the body of the penis it is transverse; and through the prostatic portion near the bladder it is crescentic. It is lined by a mucous membrane, external to which is a double layer of smooth muscle fibers, the inner fibers disposed longitudinally and the outer circular. For descriptive purposes the urethra is divided into 294 NORMAL HISTOLOGY AND ORGANOGRAPHY. a prostatic portion, a membranous portion, and a spongy or penile portion. i. The prostatic portion is about one and one- fourth inches in length and passes through the prostate gland. This is the widest portion of the urethra and passes vertically from the neck of the bladder to the triangular ligament of the perineum. In cross section the canal is crescentic with its con- vexity turned forward. The lining membrane pre- sents longitudinal folds, and along the posterior wall is a prominent median ridge which gives rise to the crescentic form of the urethra when seen in sec- tions. This ridge is called the crista, or 'uerumon- tanum. The longitudinal groove on each side of the crista is called the prostatic sinus, which is pierced by numerous orifices of the prostate gland. In the middle of the crista is the orifice of a blind recess, and at the lateral margins of this are the slit-like openings of the seminal or ejaculatory ducts. The median or blind recess is a cul-de-sac which passes upward and backward for a distance of one-fourth to one-half inch, and is called the sinus pocularis or masculine uterus. It represents embryologically the fused ends of Muller's duct, and is therefore mor- phologically equivalent to the female uterus. The epithelium of this part of the urethra resembles that of the bladder and is of the transitional variety. In the sinus pocularis it is said by some to be simple ciliated like that of the uterus. 2. The membranous portion is about three-fourths inch in length and lies between the two layers of the triangular ligament. It is the narrowest part of the REPRODUCTIVE ORGANS IN THE MARE. 295 urethra, not more than one-fifth inch in diameter, and curves so as to be directed downward and slightly forward beneath the pubic arch. The epi- thelium in this part varies. Por- tions of it resem- ble that of the bladder, but more often it presents the appearance of p s e u do-stratified with two or three layers of nuclei. 3. The spongy portion is by far the longest and most variable in length and direc- tion. Its length is about six inches, and its entire course is in the corpus caverno- sum. The epithe- lial lining near the meatus is strati- Opening oj ureter. Prostate gland. Sinus pocularis. Ejaculatory duct orifice. Urethra, membranous portion. Cowper's gland. Urethra, spongy portion Glands oj Liltre. Fig. 215.-Diagram of male bladder and urethra, front view. Ureter. Vas dejerens. Seminal vesicle. Ejaculatory duct. Prostate gland. Cowper's gland. Corpus caverno- sum (bulbus portion). Corpus spongio- sum. Fig. 216.-Diagram of male bladder and urethra, posterior view. 296 NORMAL HISTOLOGY AND ORGANOGRAPHY. fled squamous, and directly continuous with the skin. The rest of this portion is lined by columnar pseudo- stratified epithelium with two or more rows of nuclei. The whole length of the urethra, excepting its distal end, is beset with small racemose mucous glands called glands of Littre. These vary much in size, some of them being sacculated. Most of them open in the floor of the urethra, their ducts passing obliquely for- ward through the lining membrane. In urethral infec- tions these glands become involved, as a rule, which increases the difficulty of eliminating the disease. The Urethra in the Female.-The female urethra is about one and one-half inches in length, and cor- responds to the male urethra between the bladder and the opening of the ejaculatory ducts. It is directed downward and forward parallel to the an- terior wall of the vagina, to which it is attached. The transverse diameter of the closed tube is about one-fourth inch, but it is capable of great disten- tion, sufficient to admit the index finger. The ex- ternal orifice, or meatus, is a vertical slit with prom- inent margins, on which may be seen the orifices of two small glands, called Skene's glands. The latter are subject to infection in urethral disturbances and often give rise to severe irritations. THE PROSTATE GLAND. The prostate gland is a muscular as well as glandu- lar organ that surrounds the prostatic portion of the male urethra. It atrophies in the adult after cas- tration, and remains undeveloped if the testicles aie removed in infancy, which supports the view REPRODUCTIVE ORGANS IN THE MALE. 297 that it is an accessory organ of generation. Its size varies considerably, but its average transverse or longest diameter is one and one-half inches, its antero-posterior diameter about three-fourths inch, and its vertical diameter one and one-fourth inches. Since the urethra, and also the ejaculatory ducts, pass through the organ, the gland on this account may be divided into three lobes. The wedge-shaped portion that lies between these ducts and the cervix of the bladder is called the middle Artery. Vein. Fat. ■ Gland epithelium. Prostatic bodies. Connective tissue. Fig. 217-Section from the prostate gland lobe, and the rest of the gland is spoken of as the lateral lobes. It is the latter that often hypertrophy in old age and are removed in prostatectomy. The gland lies in close apposition to the rectum, and with the finger in the latter it can readily be palpated. The prostate is a compound tubulo-alveolar gland whose ducts open into the prostate portion of the urethra. Smooth muscle fibers not only surround the organ, but interlace radially toward its center, form- ing a network in whose meshes the glandular parts are located. Areolar tissue and blood-vessels accom- pany the muscle tissue. The alveoli of the glands 298 NORMAL HISTOLOGY AND ORGANOGRAPHY. are lined by simple columnar epithelium, which sometimes show two rows of nuclei. These alveoli contain a serous acid coagulum and usually oval laminated concretions called prostatic bodies. The latter are more numerous in old men. The numer- ous excretory ducts unite to form twelve to fifteen collecting tubes which open into the urethra, most of them into the prostatic sinus. These ducts are lined by simple columnar epithelium, except near their terminations where it is transitional. The organ dorsal or in front of the urethra is mostly smooth muscle tissue. In old people the prostate gland frequently hyper- trophies and produces urethral stricture with reten- tion of urine. Prostatectomy or the removal of the lateral lobes, usually corrects this defect, but is a serious operation on account of the commonly feeble condition of these patients. Vasectomy, a much simpler operation, sometimes gives satisfactory re- sults, but is not to be relied upon. Cowper's glands are a pair of small oval bodies about the size of a pea, situated in the space between the triangular ligaments and in close proximity to the membranous portion of the urethra. They are compound tubulo-alveolar mucous glands lined by simple cubical epithelium. Their excretory ducts, one for each gland, are one and one-half inches long and run forward near each other to open into the floor of the bulbous portion of the male urethra. In the female the analogue of these bodies is called the glands of Bartholin. They open into and lie in close apposition to the female urethra. They may be pal- pated in the lateral walls of the vestibule of the vagina. CHAPTER IX. REPRODUCTIVE ORGANS IN THE FEMALE. Under this head will be described the ovaries, Fallopian tubes, uterus, vagina, and mammary gland. THE OVARIES. The ovaries are two dehiscent glandular organs that develop from the mesoderm in close apposition to the mesonephros. Each ovary measures about one and one-half inches in length, three-fourths inch in breadth, and nearly one-half inch in thickness. In early fetal life the ovaries lie close to the kidneys, but later they pass down into the pelvis where they lie in close proximity to the iliac fossa. The exact position varies considerably, but in the majority of cases they will be found placed against the side wall of the pelvis with their long axis parallel to that of the body. Each ovary is held in position by a suspen- sory ligament, which is a peritoneal fold that passes downward from the brim of the pelvis and contains the ovarian vessels and nerves, and also by the ova- rian ligament, which passes to the uterus and is really a reduplication of the broad ligament. The Fallopian tube partly encircles the ovary and also contributes to its support. Capsule of the Ovary.-The external surface of the 299 300 NORMAL HISTOLOGY AND ORGANOGRAPHY. ovary is of a pale color and in early life is smooth and even, but in later life it becomes rough and marked by pits and scars. This is caused by the rupture of Graafian follicles and the expulsion of ova. It is covered by an epithelium which is continuous with that of the peritoneum, but differs from the latter Uterus. Isthmus. Fallopian tube. Ampulla. Parovarium Internal os. Stalked hydatid. Neck. External os. Ovary Fimbria. Vagina. Labia minora. Ureth- ral orifice. Labia majora. Fig. 218.-Diagram of female genitalia. in being lined by cubical cells instead of the simple pavement variety. This ovarian epithelium is the germinal epithelium of embryos, from which the ova and the other epithelial cells of each Graafian follicle are derived. The germinal epithelium rests upon a rather dense investment of fibrous tissue, analo- REPRODUCTIVE ORGANS IN THE FEMALE. 301 gous to a like structure in the testicle, and is there- fore called the tunica albuginea. This is not a dis- tinct tunic but rather a condensed part of the ova- rian matrix. It is not well defined, and is difficult to demonstrate in sections. The medulla is practically the core of the ovary and consists of a fibro-muscular matrix well supplied Young follicle with ovum. Primordial ova. Germinal epithelium. Stroma of ovary. Ovum with follicular epithelium. Fig. 219.-Section from ovary of adult dog. At the right the stellate figure represent" a collapsed follicle with its contents. Below and at the right are seen the tubules of the parovarium (copied from Waldeyer). with blood- and lymph-vessels. In this substance may be found connective-tissue cells, connective- tissue fibers and a limited supply of smooth muscle fibers. The Cortex.-Between the medulla and the cap- sule is the cortex. It is a broad zone, not well de- fined, in which are found the same elements as in the 302 NORMAL HISTOLOGY AND ORGANOGRAPHY. medulla, and in addition Graafian follicles in different stages of development, and in older ovaries also cor- pora lutea. Young Graafian Follicles.-Early in embryonic life, when the ovary is clothed with the germinal epi- thelium which later becomes the epithelium of the capsule, epithelial buds or strings of epithelial cells push their way into the ovarian cortex. These buds soon lose their connection with the germinal epithe- lium and form little groups or nests of cells known as young Graafian follicles. In each follicle one cell takes a central posi- tion and is the egg cell or ovum, des- tined, under proper conditions, to de- velop into a new be- ing. The ovum in- creases rapidly in size, receiving pro- tection and possibly nourishment from the investing cells. The repro- ductive cells, both ova and spermatozoa, can thus be traced directly from the germinal epithelium, which is of mesodermic origin and closely related to the pavement epithelium of the peritoneum. The Graafian follicles occupy the cortical layer of the ovary. They are all formed during embryonic life, and whatever influence environment has upon the offspring, that influence leaves its impression not upon the origin of the reproductive cells, but upon their later development. At time of birth it is esti- Epithelial buds. Germinal epithelium. Y oung Graafian follicle. c .. t vanner Fig. 220.-Section from ovary ot young dog. REPRODUCTIVE ORGANS IN THE FEMALE. 303 mated that there are thirty-five thousand eggs or ova to each ovary. Only a small number of these ripen and become discharged as mature eggs. The extrusion of these eggs from the ovary is known as ovulation, and in woman is supposed to occur during the menstruation period, one from each ovary. Menstruation in a normal woman extends generally^ over a period of thirty-two years, between the ages of thirteen and forty-five. If thirteen eggs ovulate yearly from each ovary, there will be a possible total Follicular cavity. Ovum. Nucleus. Nucleolus. Ovum. N ucleolus. Nucleus. Fig. 221.-Young Graafian follicles: a, follicle with one layer of epithe- lial cells; b, follicle with two layers of epithelial cells. of eight hundred and thirty-two that may ripen dur- ing the life of a woman, allowing no interruption for pregnancies. After the menopause, ovulation is supposed to cease. The Ripe Graafian Follicle.-It has already been stated that only a small number of the young ova ripen and ovulate. These mature in the following manner: The ovum of such follicles occupies a cen- tral position where it accumulates food and grows into a large spherical cell. The investing epithelium 304 NORMAL HISTOLOGY AND ORGANOGRAPHY. forms at first a single layer of cells. These remain small and multiply rapidly, forming two layers of cells between which, at one side of the follicle, a cavity appears. As the follicle grows larger this cav- ity, which is eccentric in position, becomes filled with a fluid called the follicular fiuid.. The ovum remains attached to the side of the follicle and be- comes surrounded by several layers of cells called the discus proligerus. The outer layer also multi- 7 heca. Follicular cavity. Stratum granu- losum. Discus proligerus. Ovum. Fig. 222.-Ripe Graafian follicle. plies, forming eight to twelve layers of cells and is then called the stratum granulosum, to which the discus proligerus is attached. External to the stratum granulosum a connective-tissue envelope forms, called a theca. This theca develops from the ovarian stroma and consists of two layers, an ex- ternal, the theca fibrosa, and an internal, the theca vasculosa, the latter being supplied with a fine plexus of lymph- and blood-vessels. The mature REPRODUCTIVE ORGANS IN THE FEMALE. 305 Graafian follicle is thus a sphere that measures from one-twentieth to one-sixth of an inch in diameter, and lies immediately beneath the surface epithelium of the ovary. The manner in which such follicles rupture has been variously explained. One rational theory is Germinal epl* thelium. Tunica albu- ginea. Follicular epithelium. Ovum. Granular layer of large Graafian follicle. Fig. 223.-From ovary of young girl (Bohm and Davidoff). that the pressure of the accumulated follicular liquid obliterates the blood-vessels in the theca vasculosa next to the ovarian epithelium. This establishes a point of least resistance at this place, the follicle ruptures, and the follicular fluid with the ovum is discharged upon the surface of the ovary, the 306 NORMAL HISTOLOGY AND ORGANOGRAPHY. stratum granulosum and most of the discus pro- ligerus remaining behind in the ovary. The Ovum.-The ovum has already been men- tioned as a large spherical cell with a large accumu- lation of food material. It measures 0.2 mm. in diameter and is barely visible to the naked eye. When examined under the microscope, even before the rupture of its follicle, it is found encircled by a clear substance called the zona pellucida, which upon a closer examination may be found to contain trans- verse striations, hence it has also been called zona radiata. It is not uncommon for a few of the epi- thelial cells of the dis- cus proligerus to re- main attached to this layer, if so they are called the corona radi- ata. The zona pelluci- da is a secretion from the adjoining cells, and one theory of the trans- verse striations is that they are produced by minute cellular processes from the cells that form the corona radiata; that is, the first row of epithelial cells in- vesting the ovum. It is affirmed by some that these processes are in direct communication with the sub- stance of the ovum and are the means by which elaborated food material is contributed to the latter. The zona pellucida no doubt serves to strengthen the delicate ovum after its expulsion from the ovary. The transverse striae in this membrane may serve a further purpose as primitive channels for the entrance Corona radiata. Zona pellucida. Germinal spot. Germinal vesicle or nucleus. Fig. 224.-The ovum. reproductive organs in the female. 307 of spermatozoa, only one of which penetrates the substance of the ovum. The substance of the ovum is known as the vitellus. It is a soft semifluid substance composed of cyto- plasm in which is deposited a liberal supply of food material called deutoplasm. The nucleus of the Primordial egg-cell. Germinal zone. Zone of mitotic division. {The number of gen- erations is much larger than here represented.) Oogonia. ' Zone of growth. Oocyte I. order. Oocyte II. order. I. P.B. Zone of maturation. Matured ovum. II. P.B. Fig. 225.-Scheme of the development and maturation of an ascaris ovum (after Boveri): P. B., Polar bodies. (From "Ergebn. d. Anat. u. Entw.," Bd. I.) ovum is called the germinal vesicle, which is placed to one side of the cell. The nucleus is unusually large, about 0.05 mm. in diameter, and has all the characteristics of an ordinary cell nucleus. This was first described by Purkinje in the ovum of birds in 1835. There is a well-defined nuclear membrane 308 NORMAL HISTOLOGY AND ORGANOGRAPHY. which encloses a clear nuclear substance in which there is a limited amount of chromatin, and the nu- cleus, therefore, does not stain heavily. The nucleo- lus, on the other hand, is very prominent and is called the germinal spot. Not infrequently two nucleoli may be found. There is some doubt whether a cell membrane to the ovum is present before fer- Primordial sexual cell. Spermatogonia. Zone of proliferation. (The generations are much larger.) Zone of growth. Spermatocyte I. order. Spermatocytes II. order. Zone of maturation. Spermatids. Fig. 226.-Schematic diagram of spermatogenesis as it occurs in ascaris (after Boveri). ("Ergebn. d. Anat. u. Entw.," Bd. 1.) tilization. After fertilization such a membrane appears and is called the 'vitelline membrane. As a rule each Graafian follicle contains one ovum; in rare cases follicles are found with two and even with three ova. When a Graafian follicle ruptures and an ovum is REPRODUCTIVE ORGANS IN THE FEMALE. 309 expelled, a great activity is at once manifest in the ovum, whether it is fertilized or not. The nucleus, which is near the margin of the ovum, divides in a few hours, extruding what is termed the first polar body. This is normal cell division, or mitosis. A second division quickly follows, resulting in a second polar body. Meanwhile the first polar body may also divide. This second division results in a reduc- tion of one-half the number of chromosomes, and the nucleus thus reduced is called the female pro- nucleus, which is now ready to unite with the male pronucleus of the spermatozoon and complete the process of fertilization. The phenomenon manifest in the extrusion of the polar bodies is known as maturation of the ovum, and seems to be an attempt on the part of the ovum to develop into a new indi- vidual without the process of fertilization; that is, parthenogenetically. If the ovum is not fertilized, it shows no further activity and is lost. If the ovum is fertilized it continues to divide regularly and in a short time develops into the embryo. The developmental history of ova is full of interest. They are very numerous and develop so very early in embryonic life. During childhood they grow large and accumulate a liberal storage of food, while the sister epithelial cells that form the Graafian fol- licle remain small and multiply rapidly to form the ripe follicle. This latent condition extends over a period of fifteen to forty years. When the ripe fol- licle finally ruptures and the ovum is eliminated, a rapid segmentation quickly follows resulting in the extrusion of the polar bodies. This is followed by a 310 NORMAL HISTOLOGY AND ORGANOGRAPHY. second passive period, unless fertilization takes place, when the ovum rapidly develops into a new being. By far the large majority of the ova remain undeveloped in the ovarian cortex, where they seem to pass merely a passive existence. We have no explanation of these phenomena beyond attributing them to heredity, the nature of which is still highly speculative. The Corpora Lutea.-A corpus luteum is the modi- fied Graafian follicle after its rupture and discharge Surface of ovary. Epithelial cells. Connective-tissue cells. Fig. 227.-Section of corpus luteum. of the ovum. This follicle remains permanently in the cortex of the ovary as a scar. When the rupture takes place the follicular cavity fills up with an exudate and an infusion of blood from the rup- tured blood-vessels. This coagulum is quickly in- vaded by white blood-corpuscles, connective-tissue cells from the theca, and epithelial cells from the stratum granulosum. The corpus luteum thus ulti- mately shows a uniform distribution of epithelial REPRODUCTIVE ORGANS IN THE FEMALE. 311 cells and connective-tissue cells. If the ovum be- comes fertilized and pregnancy follows, the corpus luteum continues to grow until it becomes many times larger than the original Graafian follicle, causing a rounded elevation at that point on the surface of the ovary. This kind is called a true corpus luteum. On the other hand, if the ovum is not fertilized the corpus luteum shrinks and becomes smaller than the original follicle. This kind is called a false corpus luteum. The corpus luteum is at first well defined by the investing follicular theca, but after a time its limits are less distinct, so that as age advances the ovarian stroma becomes gradually pervaded with cells like those of the corpora lutea. THE FALLOPIAN TUBES. The Fallopian tubes are two ducts for the passage of ova from the ovary to the uterus. They differ from the ducts of other glandular organs in being detached from the organs whose secretions they con- vey. They are from four to five inches long and pass almost horizontally outwards from the fundus of the uterus. When they reach the ovary they ascend along the pelvic floor and nearly encircle each organ, passing up the external and down the internal or mesial margins. Bach tube is enclosed in the free margin of the broad ligament, which is a peritoneal fold that also contains the round ligament of the uterus, the ovary, parovarium, and numerous blood- and lymph-vessels. For descriptive purposes each duct is divided into an isthmus, an ampulla, a neck, and a fimbriated ex- 312 NORMAL HISTOLOGY AND ORGANOGRAPHY. tremity. The isthmus is smooth and round, about one inch in length, and opens into the fundus of the uterus by a small orifice that will barely admit an ordinary bristle. It is a straight and narrow part of the duct, about 2 to 3 mm. in diameter. The am- pulla encircles the ovary and is at least twice the size of the isthmus. It is also less firm to the touch, Longitudinal muscle. Circular muscle Ciliated epithelium Fig. 228.-Cross section of ampulla of Fallopian tube. being flabby while the isthmus is cord-like. The neck is an annular constriction between the ampulla and fimbriated extremity, the latter being a funnel- shaped expansion of the ovarian end of the tube, which terminates in a number of irregular processes called fimbriae. The fimbriae vary considerably in size and number. Many of them are branched, and REPRODUCTIVE ORGANS IN THE FEMALE. 313 one is particularly long and attached to the upper end of the ovary. Structure.-The Fallopian duct is a muscular tube lined the whole length by a mucous membrane clothed with simple ciliated columnar epithelium. This mucous membrane is thrown up into longitudi- nal folds that are very broad and numerous in the wide portions of the tube and in the narrow portions less conspicuous. It is continuous on the one hand Longitudinal muscle. Circular muscle. Ciliated epithelium. Fig. 229.-Cross section of isthmus of Fallopian tube. with the mucous membrane of the uterus, and at the other end of the tube with the serous lining of the peritoneum, being one example of a direct conti- nuity of a mucous and a serous membrane. Glands, so numerous in the mucous membrane of the uterus, are absent in the Fallopian tube. The mucosa rests upon a thin vascular submucosa composed of areolar tissue. External to the sub- mucosa there is a muscular coat consisting of a thick inner circular layer and a thin outer longitudinal 314 NORMAL HISTOLOGY AND ORGANOGRAPHY. layer of smooth muscle fibers. Externally the tube is practically enclosed by the peritoneum, forming a serous covering. Embryologically, each Fallopian tube represents a Mullerian duct, which is derived from the mesoderm. In the male the Wolffian duct develops into the vas deferens. This duct, which is rudimentary in the female, is called Gartner's duct, and lies parallel to the Fallopian tube, between the latter and the round ligament. The round ligament extends from the uterus to the internal abdominal ring in nearly the same position as the vas deferens does in man. Fertilization, as a rule, takes place in the upper part of the Fallopian tube. In cases of tubal preg- nancy the ovum does not reach the uterus but finds lodgment in the tube. The much-folded mucous membrane allows considerable distention, but ulti- mately the rapidly growing embryo ruptures the tube, with serious complications resulting from in- ternal hemorrhage. Usually the ova pass down the tube on the corresponding side, but it is possible for the ova from one ovary to pass down the tube of the opposite side. Experimentally, the right ovary and the left tube may be removed in the dog and the ani- mal still become pregnant. The ovaries have a marked influence on the devel- opment and mentality of a woman and their removal, prior to the menopause, is followed by deleterious results, much the same as the removal of the testes in the male. While extracts from certain organs, such as the thyroid gland and the suprarenal bodies, have specific medicinal properties, extracts from the REPRODUCTIVE ORGANS IN THE FEMALE. 315 ovaries give no satisfactory results. Its potency is manifest only by the living organ in the performance of its normal function. The ovary or fragments of it will readily grow in other parts of the body, and has been successfully grafted from one animal to an- other. The Parovarium, or Epodphoron.-The organ bearing this name lies in the broad ligament lateral to the ovary and between the latter and the tube. It consists of a number of closed epithelial tubules which can usually be seen by holding this part of the ligament up against the light. Embryologically they represent the upper portions of the Wolffian duct and some of the attached tubules of the meso- nephros, and correspond to the vasa efferentia in the male. The paroophoron represents vestiges of tubules similar to the parovarium, situated in the broad liga- ment below the ovary. They correspond to the paradidymis in the male. Being lined by epithelial cells, either of these or- gans may develop into parovarian or paroophoron cysts, the former being more common. THE UTERUS. The uterus, or womb, is a hollow muscular organ, with thick walls, placed in the pelvic cavity between the bladder and rectum. In case of pregnancy it receives and nourishes the ovum and later expels the fetus at the end of pregnancy. During gestation, and also periodically during menstruation, it is sub- ject to marked physiological and structural changes. 316 NORMAL HISTOLOGY AND ORGANOGRAPHY. It is therefore an organ in which great activity is manifest during the greater part of adult life. The fully developed virgin uterus is a pear-shaped organ, flattened from before backward, free above, Fig. 230.-Arrangement of uterine muscle, as seen from in front after removal of serous coat (Helie). and connected below with the vagina, into which its lower extremity projects. Its average dimensions are, three inches in length, two inches in breadth at its upper and widest part, and one inch in thickness. REPRODUCTIVE ORGANS IN THE FEMALE. 317 For descriptive purposes it is divided into fundus, body, and neck, or cervix. The fundus is the broad convex upper end that lies above the attachment of the Fallopian tubes. It is chiefly this part that expands in case of pregnancy. The body is the part between the fundus and neck. This part tapers downward with convex sides. The Fig. 231.-A, Isolated muscle-elements of the non-pregnant uterus; B, cells from the organ shortly after delivery (Sappey). neck, or cervix, is about one inch long, cylindrical, and projects into the anterior part of the upper end of the vagina. The projecting portion is called the vaginal part, and has a transverse oval aperture, called the os uteri, which communicates with the cavity of the uterus. The latter is a triangular 318 NORMAL, HISTOLOGY AND ORGANOGRAPHY. cavity, so flattened that the anterior and posterior uterine walls touch each other. The base of the cavity is in the fundus and is convex downwards. The two Fallopian tubes open into the upper angles each by a small aperture that will barely admit a bristle. The cavity tapers gradually toward the cervix, where it becomes constricted to form the in- ternal os. The peritoneum covers the fundus and Mucosa. Gland. Muscular layer. Serous layer. Fig. 232.-Cross section of wall of uterus. body of the uterus, and posteriorly extends down- ward to clothe the upper posterior wall of the vagina. It is then reflected back over the rectum, forming a a sac called the pouch of Douglas. This makes it possible to open the peritoneal cavity by a puncture through the upper posterior vaginal wall, an operation which establishes free drainage to the female pelvis. REPRODUCTIVE ORGANS IN THE FEMALE. 319 Anteriorly the peritoneum does not cover the whole uterus, but at the junction of the body with the neck, it is reflected back over the bladder wall form- ing the utero-vesical pouch. Structure.-The histology of the uterus resembles that of the Fallopian tubes, and the layer of the one is continuous with that of the other. Embryologi- cally, these two structures, and also the vagina, de- velop from the Mullerian ducts, the uterus and Ciliated epi- thelium. Gland, cross section. Connective tissue. Muscularis. Fig. 233.-Diagonal section of the uterine mucosa. vagina representing the fused lower ends of Muller's ducts. The whole uterus, including the epithelial lining, is therefore of mesodermic origin. The uter- ine wall is composed of a mucosa, muscular, and serous layer. The Fallopian tube has a submucosa which is absent in the uterus. The mucosa, or endometrium, is the inner layer and is lined by simple columnar ciliated epithelium, which at the external os changes to the stratified variety of the vagina. It has a rich supply of 320 NORMAL HISTOLOGY AND ORGANOGRAPHY. branched tubular mucous glands which, in the cer- vix, are very large and have a tendency to become sacculated. These glands extend radially as far as the muscularis, and some of them may even pene- trate a short distance into the muscle coat. The gland ducts are lined by ciliated epithelium, while in the deeper portions cilia are absent and the epi- thelium becomes simple cubical, resembling a glandu- lar type. Most of these glands take a tortuous or spiral course, and are separated from each other by an interstitial tissue composed of connective-tissue cells. These cells are of the embryonic type, rich in chromatin and therefore stain heavily with nuclear dyes. The relative amount of interstitial and glandular tissue in a normal uterine mucosa should be approximately equal parts. The connective tissue predominates in interstitial endometritis, and the glandular tissue in adenitis. The whole uterine mucosa is unusually thick and very vascular. In a mature woman it is normally subject to marked periodic changes resulting from menstrual condi- tions, which reach a high degree of complexity in case of pregnancy. The action of the cilia tend to produce a downward movement of the uterine secretions and, therefore, opposite to the upward movement of spermatozoa. The Muscular Layer.-The muscularis is an unusu- ally thick layer of smooth muscle cells which in the non-pregnant uterus measure forty to sixty mi- crons, while at the end of pregnancy the cells measure four hundred to six hundred microns in length. These muscle cells are arranged in bundles with a considerable amount of connective-tissue fibers and REPRODUCTIVE ORGANS IN THE FEMALE. 321 cells interlacing them, imparting strength and elas- ticity to the uterine wall. There has been consid- erable discussion as to the exact disposition of the different layers of this musculature which, in a gen- eral way, may be divided into three strata: (i) an inner layer of longitudinal fibers, by some called the muscularis mucosa; (2) a middle circular layer, and (3) an outer thin layer of fibers that run diago- nally or somewhat irregularly. The inner layer is much the thickest; none, however, is sharply de- fined. The serous coat is the peritoneal lining which con- sists of connective-tissue elements and an invest- ment of simple pavement epithelium. Vessels and Nerves.-The arteries that supply the uterus are arranged in two pairs,-the uterine and ovarian. The uterine artery is a branch of the an- terior division of the internal iliac. It reaches the upper portion of the vagina, and then ascends in a very tortuous manner along the lateral border of the uterus to the fundus, where it divides into two branches, one of which anastomoses with the ovarian artery and the other supplies the Fallopian tube. From the ascending portion many side branches are given off which penetrate the uterine wall and ramify in the muscle tissue and the mucosa. These branches are very tortuous so that the uterus can expand in pregnancy without breaking the vessels. The -veins are very large and have no valves. They form large sinuses mostly along the lateral walls, from which the blood is collected into two trunks: (1) the uterine vein accompanies the uter- 322 NORMAL HISTOLOGY AND ORGANOGRAPHY. ine artery and empties into the internal iliac vein; (2) vessels communicate with the ovarian or pam- piniform plexus which drains through the ovarian veins. The lymphatics begin in the interstitial substance of the mucosa, and uniting with lymphatics from the muscularis, emerge to form a rich plexus just beneath the serous covering. This plexus drains along two channels: (1) by lymphatic vessels that accompany the uterine veins; (2) vessels that ac- company the ovarian veins. The blood and lymph drainage is therefore in two directions. That of the fundus is toward the ovary, and that of the body and cervix is in the opposite direction along the uterine vessels. This is of clinical importance in the spread of infections. The nerves are non-medullated fibers from the in- ferior hypogastric plexus, and medullated from the third and fourth sacral. The non-medullated sup- ply the muscle while the medullated fibers have been traced to the mucosa, where they form a plexus from which fibers pass to the surface epithelial cells. An- other set arborize about the mucous gland cells. Sympathetic-nerve ganglia are associated with the non-medullated fibers. Menstruation.-This consists of a hemorrhagic and mucous discharge from the uterus, which recurs about every twenty-eight days in the non-pregnant woman between the ages of thirteen and forty-five. It is accompanied by more or less severe systemic disturbances of a neurotic nature, and also by in- creased activity of the glandular system as a whole. REPRODUCTIVE ORGANS IN THE FEMALE. 323 Enlargement of the thyroid gland usually accom- panies the menstrual flow. From five to ten days before the menstrual flow begins there is a marked hyperemic condition of the Fig. 234.-Uterus during menstruation, cut open to show the swelling of the whole organ, and particularly the mucous membrane: A, Mucous membrane of cervix; B, C, mucous membrane of corpus, much thickened; D, muscular layer; E, uterine opening of tube; F, os internum (the mu- cous membrane tapers down to these openings) (Courty). uterine wall. The congestion of blood causes a marked swelling and growth of the uterine mucosa, so that it attains a thickness of 6.0 mm. This mu- cosa is then called the decidua menstrualis. After these changes have occurred the menstrual flow be- 324 NORMAL HISTOLOGY AND ORGANOGRAPHY. gins and usually lasts for four days. This results in a complete or partial exfoliation of the superficial part of the mucous membrane of the uterine fundus and body, but does not involve the cervix. The exfoliation begins at the internal os and advances progressively toward the fundus. The restoration of the mucosa proceeds in the same order, from be- low upward, and in the course of five or six days the mucous membrane is restored. The epithelial lining regenerates from the free ends of the mucous glands that did not partake in the exfoliation. The uterus is thus a seat of great physiological activity. During at least one-half the menstrual period of twenty-eight days there are marked struc- tural changes manifest in the uterine mucosa. In such an active organ pathological disturbances are naturally of frequent occurrence. Menstruation and ovulation are related phenom- ena, and yet there is evidence that neither one de- pends on the other. Pregnancies may occur before the menstrual period is inaugurated. Even at the early age of nine years pregnancy has been reported; also in mature women after confinement, but before menstruation has reappeared, pregnancy may occur. A woman who does not menstruate does not become pregnant, as a rule, but there are exceptions. Ovu- lation, therefore, may go on without menstruation, and there is evidence that menstruation may prevail without ovulation. For a further discussion of this subject, see Raymond's "Human Physiology." REPRODUCTIVE ORGANS IN THE FEMALE. 325 PREGNANCY. During pregnancy the mucous membrane of the uterus becomes modified into a membrane called the decidua graviditatis. This membrane may be divided into (i) the decidua serotina or basalis, that part of the mucosa to which the ovum is attached and in which the placenta develops; (2) the decidua re- flexa, that which envelops the ovum, and (3) the decidua vera, the part that lines the rest of the uterus. In the early stages of pregnancy the changes in the uterine mucosa resemble those of the decidua men- strualis. At the end of the first half of pregnancy the decidua serotina is 1 cm. thick. The epithelial lining has disappeared and two layers can be recog- nized: (1) a superficial compact layer, and (2) a deep spongy layer. The compact layer consists of con- nective-tissue elements and some very large pig- mented cells called the decidua cells. These cells usually have one large nucleus, but some of them may be polynucleated. The cells are thirty to one hundred /z in diameter, and oval or elongated, re- sembling epithelial cells, although they are supposed to develop from the interstitial connective-tissue cells of the normal mucosa. They are of diagnostic value in uterine curetments where they become a probable evidence of pregnancy. In post-mortems they have no medico-legal significance, as these cells may be found in the decidua menstrualis. In the spongy layer the connective-tissue cells form septa between the flattened and sacculated as well as tor 326 NORMAL HISTOLOGY AND ORGANOGRAPHY. tuous mucous glands. Blood-vessels also form a plexus in the spongy layer. The decidua reflexa disappears during the first months of pregnancy, while the decidua serotina enters into the formation of the placenta. Placenta.-The placenta is a vascular organ for the nourishment of the fetus, and serves the purpose of bringing the fetal and maternal blood into closest proximity without actually blending. The organ Villi. ' Compact layer of de- cidua with decidual cells. Spongy layer of de- cidua with gland spaces. Fig. 235.-Section of the decidua serotina at the margin of the placenta. may be divided into an embryonic part, the placenta foetalis, and a maternal part, the placenta materna. The latter is the modified uterine mucosa or decidua serotina. The fertilized ovum usually finds lodgment in the fundus of the uterus. Very early it becomes en- closed in an envelope of its own production called the chorion. This chorion has an outer epithelial Plate V. I. Semi-diagrammatic section of gravid uterus, showing contained ovum of about five weeks (modified from Allen Thomson). 2. Semi-diagrammatic section of uterus, showing relations of fetal and maternal placenta (Ahlfeld). ' Cervix. Cavity of uterus. Chorionic villi. Wall of uterus. Decidua sero- tina. - Villi of chorion. Cavity of ovum. * Decidua reflexa. • Decidua ver a. • Cavity of uterus. _ Muscular wall of uterus. Fused decidua vera_ and reflexa. Peripheral sinus Placental septum.-. Decidua serotina.- Remains of um- bilical vesicle." Uterine muscle.. Amnion.- Chorion.- Blood space.- Fetal villi of_ chorion. " REPRODUCTIVE ORGANS IN THE FEMALE. 327 layer and an inner connective-tissue layer, the latter being vascular. It is this vascular chorion that enters into intimate relations with the uterine mucosa to form the placenta, the former the fetal part and the latter the maternal part. These parts become intimately associated. The chorion very early produces a large number of villi which invade the mucosa, where they ultimately become large and much branched, like the root of a tree. These are the chorionic villi and belong to the fetal pla- centa. Each villus consists of a connective- tissue core with an epithelial lining. The fetal blood cir- culates through the connective- tissue core while the maternal blood bathes the external sur- faces of the villi. The terminal ramifications of each villus becomes firmly anchored in the uterine mucosa, while the branched lateral twigs float freely in the maternal blood spaces or intervillus sinuses. These villi serve a double purpose. They attach the fetal placenta firmly to the uterus, and establish a close relation between fetal and maternal blood whereby the embryo receives proper nourishment. Upon closer examination each villus should present in cross section an outer la ver of simple squamous Blood capillaries. Zcllknaten. Syncytium or protoplasmic coat. Epithelial cells. Fig. 236.-Cross section of two human chorionic villi at end of pregnancy. 328 NORMAL HISTOLOGY AND ORGANOGRAPHY. epithelial cells and a core of connective-tissue cells in which two or more small capillary blood-vessels ramify. The epithelium of the villi undergoes great alterations and may entirely disappear, to be re- placed by isolated accumulations of large round nuclei that stain intensely with nuclear dyes, and that form protuberances on the surfaces particularly of the large villi. These are called zellknoten, or cell knots. Their origin and significance is doubtful. In the earlier months of pregnancy the epithelial in- vestment of each villus is clothed externally by a continuous protoplasmic mass, called the syncytium, containing small and irregularly scattered nuclei. It is generally supposed that the syncytium repre- sents the modified and disintegrated uterine epi- thelium and is therefore of maternal origin. Some embryologists affirm that in some villi there is a membrane external to the syncytium which mor- phologically represents the epithelial wall of the uterine blood-vessels. The maternal blood, how- ever, very soon breaks through the capillary spaces of the uterine mucosa atnd enters the intervillus sinuses clothed by the syncytium. The fetal cir- culation is a closed system and nowhere is there a direct intermingling of fetal and maternal blood. The- oretically the exchange of gases, in the early stages of development, takes place through (i) the epi- thelial wall of the maternal capillaries; (2) the uter- ine epithelial lining, probably represented by the syncytium; (3) the epithelial lining of the chorion, and (4) the epithelial wall of the fetal blood capilla- ries. The first of these membranes is not always Plate VL Diagrammatic Section through the Human Placenta at the Middle of the Fifth Month (after Leopold). The fetal placenta consisting of the chorion (w) with its villi (z), has grown into the maternal placenta; the villi present attached points (h\h2) and free processes (//); sp is the spongy layer of the decidua serotina, in which the separa- tion takes place along the line Tr; CS is the compact layer forming the inner part of the uterine placenta, which consists of the basal plate (BP), the closing plate (SP), the arteries (a), the cavernous blood-spaces (c), and the marginal sinus. Line of Lepor <Mon- Uterime muscle Peripheral sinus Decidnia refiexa Amnion Chorion reproductive organs in the female. 329 present, as maternal blood ruptures this wall. The second investment, or syncytium, disintegrates. The third also disappears, at least in parts, or be- comes so thin that it can scarcely be detected. Ulti- mately, therefore, the fetal and maternal blood is practically separated by only one membrane, the epithelium of the fetal capillaries. The maternal placenta does not differ structurally from the histology of the decidua already described except in degree of complexity. There is an inter- nal compact portion and a deeper spongy layer. The latter rests against the uterine muscularis and is very vascular. Numerous blood- vessels penetrate the compact layer to open freely into the intervillus sinuses already de- scribed. These blood-vessels usually take a very tortuous course, and they are thus able to adjust themselves to contractions and expansions of the uterine wall. Decidual cells are especially conspicuous in the compact layer of the placenta. These cells are sometimes present in the spongy layer but never in the chorionic villi or fetal portions of the placenta. The fetal blood reaches the placenta through the umbilical cord. There is regularly present two ar- teries and one vein, imbedded in a gelatinous con- nective-tissue matrix known as Wharton's jelly. The blood in the arteries is carried to the placenta and is venous. That in the vein returns from the placenta and is arterial. After birth, when the pla- Fig. 237.-Four decidual cells from decidua serotina. 330 NORMAL HISTOLOGY AND ORGANOGRAPHY. centa comes away, it is always at the expense of the uterine mucosa, which leaves a raw, bleeding surface. The uterine muscles at once contract, reducing the uterine cavity and checking the hemorrhage. A normal mucous membrane at once regenerates, the ciliated epithelium and mucous glands developing from remnants of glands that were not entirely ob- literated by the placental growth. As a rule regular menstruation is inaugurated when lactation ceases, but there are exceptions to this. A second preg- nancy may follow without any intervening menstrual period, but this is rare. THE MAMMARY GLAND. The mammary gland is a skin gland that is present in both sexes. In the second month of embryonic life there is a linear thickening of the skin, extending from each axilla to the groin, and at regular inter- vals in this ridge a series of mammary glands develop in many vertebrates. In the human race only one pair is produced, which represents the fourth or fifth pair of this series. In rare cases accessory mam- mary glands are found in man both above and below the normal pair. In childhood the mammary gland is identical in both sexes, but with approaching puberty it enlarges in the female, reaching its highest development at the end of pregnancy. The menopause brings about a retrogression and shrinkage of the organ. The gland is therefore to be considered an accessory sexual organ. The mammary gland is a segregation of fifteen to REPRODUCTIVE ORGANS IN THE FEMAEE. 331 twenty separate compound tubulo-alveolar glands which open separately on the nipple by an equal number of pores. These glands are arranged radi- ally and enclosed by a variable supply of fat and connective tissue in such a way that it is possible to divide the breast into fifteen to twenty lobes, which may be further divided into lobules. Each pore leads to a narrow vertical tube, the lactiferous duct, which widens just below the base of the nipple to form a receptacle called the milk sinus, be- yond which it again becomes a narrow tube. The latter be- comes branched to form interlobular ducts that open into distal dilata- tions or alveoli, which constitute the secreting por- tions of the gland. The lactiferous ducts and sinus are lined with simple columnar epithelium, which becomes strati- fied near the orifices where it is directly continuous with the stratified epithelium of the skin. The finer structure of the alveoli varies according to the func- tional activity of the organ. During lactation the alveoli are distended with milk. The cells of the Lactiferous duct. Milk sinus. Alveoli. Fig. 238.-Diagram of one-half of mammary gland, dissected to show gland. 332 NORMAL HISTOLOGY AND ORGANOGRAPHY". simple glandular epithelium become distended with the products of secretion that consist of granules and deposits of fat. The granules liquefy and along with the fat globules are discharged into the alveoli as milk. Many particles of fat are taken up by migra- ting white corpuscles, called phagocytes, which mix with the secretion and thus become converted into the colostrum corpuscles of early lactation. The gland cells after secretion accumulate a second sup- Fat cells. Connective tissue -Gland alveoli. Fig. 239.-Section of a portion of the mammary gland. ply, and this process is repeated many times. The secreting cell does not disintegrate as is the case in the sebaceous glands of the skin. When the gland is not engaged in the secretion of milk, many of the alveoli shrink up and disappear, while the remaining ones become much reduced in size, and the gland as a whole is smaller. The cells of the alveoli become columnar, resembling the cells that line the ducts. The epithelium rests upon a REPRODUCTIVE ORGANS IN THE FEMALE. 333 basement membrane and a membrana propria, the latter containing basket cells whose processes mingle with the glandular epithelium. The interstitial tissue just external to the alveoli is composed of connective-tissue cells that stain heavily with nuclear dyes, while in the intervening spaces between the alveoli, connective-tissue fibers and fat cells are abundant. A supply of plain muscle fibers intervene and surround the ducts in the nip- ple. The fibers placed longitudinally function in the erection of the nipple, while the circular ones constrict the ducts. The nipple does not develop until after birth. Its normal po- sition is in the fourth in- tercostal space, about four inches from the sternum. It is clothed with stratified pig- mented epithelium and devoid of hair follicles and sweat glands. The skin immediately around the nipple is also pigmented, forming an areola with numerous small papillae, giving a rough or wrinkled appearance. Besides large sweat glands, twelve or more large sebaceous glands, called glands of Mont- gomery, are present in this area. These glands open at the apices of the small papillae just mentioned, and are usually considered as accessory milk glands. Vessels and Nerves.-The arteries that supply the breasts are the long thoracic, the internal mammary, Epithelial cells. Connective-tissue cells. Fig. 240.-Section through two alveoli of mammary gland. 334 NORMAL HISTOLOGY AND ORGANOGRAPHY. and the intercostals. These anastomose freely and approach the gland from all directions. The veins are equally extensive. They accompany the arteries and bear the same names. Lymphatics are very numerous and form extensive lymph spaces around the alveoli of the gland. For the most part they drain to the lymph glands in the axilla, but from the deeper part of the breast they drain along the course of the internal mammary artery. CHAPTER X. THE SKIN. The skin covers the entire body and is directly continuous with the mucous membranes of the ali- mentary canal and urogenital organs at their external orifices. It contains sensory nerve endings and in the deeper layers there is a liberal supply of both blood- and lymph-vessels. It is the chief factor in regulating body temperature, and is an efficient mechanical protection to the deeper tissues, while the sweat and sebaceous glands render it an important excretory organ. Hairs and nails represent modi- fications of the superficial layers. It varies consid- erably in thickness, being 4 mm. thick on the palms of the hand and 0.5 mm. over the back and shoul- ders. The color is imparted by pigmentation and the blood supply. The color is characteristic of races and variable in the different parts of the body as well as subject to modification depending on age and dis- ease. The skin moves freely upon the deeper tissues, excepting over bony prominences where it is more firmly attached. On the palm of the hand and the sole of the foot it is also bound down to the subjacent tissues. The external surface presents in places numerous permanent ridges which correspond with rows of underlying papillae, and which in criminals are utilized for the purposes of identification. The 335 336 NORMAL HISTOLOGY AND ORGANOGRAPHY. hair follicles appear with regularity in external de- pressions practically all over the body, forming dis- tinctive patterns. Cutaneous blood-vessels and Sweat gland. Corneum. Stratum lucidum. Stratum granulosum. Malpighian layer. Papilla oj dermis. Dermis. Fat cells. Sweat gland. Fig. 241.-Section of skin through palmar surface of fingers. tendons form ridges and lines readily detected by the unaided eye, and over which the skin is freely movable. THE SKIN. 337 Structurally the skin or integument consists of two chief strata that may be subdivided into layers in the following manner: I. Epidermis epithelial layers derived from the ectoderm. i. Corneum or horny layer,-superficial epithelial plates. 2. Stratum lucidum,-absent where the skin is thin. 3. Stratum granulosum,-absent where the skin is thin. 4. Malpighian or germinal layer,-nucle- ated growing cells. 11. Dermis or corium,-connective -tissue elements from the mesoderm. 1. Papillary layer. 2. Reticular layer. Epidermis.-The horny layer of the epidermis forms the outer covering of the skin and consists of several layers of scaly epithelial cells in which the nuclei have disappeared. The cells are dead and constantly exfoliating superficially, while new strata are regularly added from below. Bacteria are usually present in its external parts, and in surgi- cal operations, therefore, the skin is thoroughly scrubbed, a process that removes most of this layer and renders the field of operation practically sterile. At birth the horny layer is less compact and of a red color. It is then called the vernix caseosa, which exfoliates in a few days, when the complexion 338 NORMAL HISTOLOGY AND ORGANOGRAPHY. changes to that of the particular race to which the child belongs. The strata lucidum and granulosum are two thin layers that lie between the corneum and the Mal- pighian layers and are best developed in the sole of the foot and the palm of the hand. Each consists of two or three rows of epithelial cells. The stratum lucidum overlies the stratum granulosum and is a refractive layer consisting of cells with disintegrating Corneum or horny layer. Stratum lucidum. Stratum granulosum. Malpighian or germinal layer. Fig. 242.-Section of epidermis of skin from palm surface of finger. nuclei, and possessing a homogeneous substance called eleidin. The latter is colored with eosin but does not take nuclear dyes. The cells that compose the stratum granulosum possess many granules called keratohyalin granules, which are regarded as products of cell disintegration. These granules in- crease in size and coalesce to form the semifluid sub- stance called eleidin of the stratum lucidum. The granules take nuclear dyes; the eleidin does not. THE SKIN. 339 The Malpighian layer is made up of growing epi- thelial cells and constitutes the deeper parts of the epidermis. Its lower surface is beset with numerous depressions that receive connective-tissue papillae from the dermis. The epidermis and dermis thus interlock by means of an extensive system of papillae from each layer. The Malpighian layer is thicker than the horny layer, excepting in the sole of the foot and the palm of the hand. It consists of ten to fifteen layers of epithelial cells. The cells in the lower row are columnar and are so arranged that their long axis is vertical to that surface. In colored races these cells are pigmented and impart to the skin the par- ticular color of the race. Pigmentation has been discussed on page 76, to which the reader is re- ferred. The other cells of the Malpighian layer are cubical or flattened and so placed that their long axis lies parallel to the surface of the body. The cells of the deeper strata have numerous minute short processes and have been called prickle cells. These processes form intercellular bridges, which give rise to a complex system of minute intercellular channels that permit more freely the passage of nourishment. These cells are constantly dividing and adding new strata to the horny layer that is ex- foliating at the same rate. The dermis, corium, or cutis vera, is of connective- tissue origin and lies just beneath and intimately associated with the epidermis. It may be divided into a papillary portion, next to the epidermis, and a deeper reticular portion which shades off into the subdermal fascia. The papillary portion consists of 340 NORMAL HISTOLOGY AND ORGANOGRAPHY. vascular and nerve papillae that fit into depressions on the lower surface of the epidermis. The two layers of the dermis pass into each other without any sharp line of demarcation. In both layers there is an abundance of connective-tissue fibers, both elastic and non-elastic, forming what has been termed areo- lar tissue. These fibers form bundles that interlace to produce a network, particularly in the reticular or deep portions. In the meshes of this reticulum are to be found the bodies of the sweat glands, and a variable amount of adipose tissue, while hair follicles with their sebaceous glands find lodgment in the dermis with greater regularity. It is the dermis, and particularly the areolar tissue, that gives elas- ticity and mobility to the skin. The epidermis is not very elastic, consequently wrinkles of the epi- dermis are formed when the fat is absorbed, and also in old age, by shrinkage of the areolar tissue. A variable amount of muscle is everywhere present in the dermis. Smooth muscle is associated with the hair follicles, forming the arreetor pili muscle. In the face and neck voluntary muscle fibers may be traced into the papillary layer, while a third set of muscle elements is associated with the sweat glands. The latter is of the smooth variety and will be de- scribed along with the sweat glands. The dermis everywhere is very vascular. Blood- and lymph-vessels ramify freely through it, but in no case do they enter the epidermis. Nerve fibers, on the other hand, enter the Malpighian layer of the epidermis and arborize around and between the epithelial cells. In the dermis these fibers form an THE SKIN. 341 extensive nerve plexus, from which some terminal fibers proceed to the hair follicles, and others to special nerve papillae in the dermis. These and other nerve terminations will be described as peripheral nerve endings in another chapter. The hairs are distributed practically over the whole surface of the body, with the exception of the palms of the hand, the soles of the feet, and the red border of the lips. They are distributed with con- siderable regularity, as a rule one hair for each fol- licle, but there may be two and sometimes three. The part of the hair buried in the skin is called the root, and the part that projects beyond the surface is the shaft. The lower part of the root is thickened to form the hair bulb, into which is pushed from below a vascu- lar connective-tissue projection called the hair papil- la. The root is inserted deep in the skin, usually reaching the subdermal elements. It is placed diagonally to the surface and becomes enclosed in a specially modified wall made up of several layers de- rived partly from the epidermis and partly from the dermis. Most hairs are composed of three layers: an outer cuticle, a middle cortical, and a central portion, the HAIRS. Medulla. Cortical layer. Hair cuticle. Fig. 243.-Portion of a hair. 342 NORMAL HISTOLOGY AND ORGANOGRAPHY. medulla. In thin and light hairs the medulla is usu- ally absent. The hair cuticle, or outer hair membrane, is made up of structureless transparent epithelial scales that overlap each other in the direction of the distal end of the hair. A hair feels smooth, therefore, if pulled tnrough the fingers from the root to the free end. These scales overlap each other sometimes to such an extent that the cuticle has. the appearance of being stratified. The scales are derived from epi- thelial cells that have become cornified, and they are thus closely related to the horny epithelial plates of the epidermis. The cortical substance forms the main bulk of the hair and lies just beneath the cuticle. The cortex consists of spindle-shaped nucleated cells which show a distinct fibrillar structure, giving the whole hair the appearance of being longitudinally striated. Pigment granules are deposited in these cells and between them, to which the hair owes most of its color. Numerous small spaces filled with air are frequently formed between the cells of the cortical layer, and these give a white color to hairs that have a scanty supply of pigment. Hairs that have en- tirely lost their pigment and have none of these air spaces, are gray but not white. The medullary substance forms the axis of the hair and may be absent, but is usually present in thick hairs. It is made up of nucleated cubical epithelial cells forming two or three rows in thick- ness. Pigment is also present in the medullary cells. THE SKIN. 343 Hair Follicles.-The hair follicles are the pits in the skin occupied by the roots of the hairs. These pits are placed diagonally to the surface, and in the scalp where the skin is thick they are at least half an inch in length. It is estimated that the normal scalp has about one hundred and twenty thousand of these follicles, or an average of eight hundred to the square inch. Each follicle is really a minute tubular de- Longitudinal connective-tissue fibers. Circular fibers. Glassy membrane Outer root sheath. Henle's layer. Huxley's layer. Inner root sheath. Hair shaft. Fig. 244.-Cross section of a hair follicle. pression or invagination of the skin, and its wall is therefore made up of constituents from both the epi- dermis and the dermis. These layers may be tabu- lated as follows: I. Outer tunic. 1. Connective-tissue fibers arranged longi- tudinally. 2. Connective-tissue fibers, circular. 3. Glassy membrane. 344 NORMAL HISTOLOGY AND ORGANOGRAPHY. IL Outer root sheath; resembles Malpighian layer of the epidermis. III. Inner root sheath. i. Henle's layer,-non-nucleated ele- ments. 2. Huxley's layer,-nucleated cells. 3. Root sheath,-structureless membrane. The outer tunic is derived from the dermis and is of connective-tissue origin. Externally there is a layer of connective-tissue fibers arranged longitudi- nally, in which may be found a few connective- tissue cells and a delicate plexus of nerve fibers. The non-elastic connective-tissue fibers predominate, but the elastic variety is also present. Internal to the longitudinal fibers is a compact circular layer of non-elastic connective-tissue fibers, and internal to this is the glassy membrane, a very thin hyaline sheath often difficult to find. The outer tunic in- vests the lower half of the root sheath. This tunic, in the so-called tactile hairs of many mammals, has a rich nerve innervation and a liberal blood supply. In such hairs nerve fibers have been traced to the glassy membrane, while others apparently penetrate to tactile cells in the outer root sheath. The root sheaths encase the root of the hairs and are derived from the epidermis, being therefore of ectodermal origin. The outer root sheath is a direct continuation of the Malpighian layer and diminishes in thickness toward the bottom of the follicle. It is composed of nucleated epithelial cells which possess intercellular bridges and a fibrillar protoplasm. This sheath always stains heavily with nuclear dyes. THE SKIN. 345 The inner root sheath is less conspicuous, and in good sections will be found to consist of an outer layer of two rows of non-nucleated elements, representing cornified epithelial cells and called Henle's layer, and Hair shaft. Epidermis. Arrector pili muscle. Sebaceous gland. Fat cells. Hair papilla. Fig. 245.-Cross section of the human scalp. internal to this about two rows of nucleated cells, called Huxley's layer. These layers are absent from the upper half of the follicle. Internal to Huxley's layer, and in direct contact with the root of the hair, is the root sheath, which has much the same structure as the hair cuticle. Many scaly plates are imbricated 346 NORMAL HISTOLOGY AND ORGANOGRAPHY. upon each other and interlock with those of the hair cuticle in such a manner that if a hair is pulled out the root sheath comes away with it, the break taking place along Huxley's and Henle's layers. The hair papilla indents the lower end of the root and is of connective-tissue origin. It has a rich blood supply which contributes nourishment to the adjacent epithelial cells of the root which are con- stantly dividing. It is this cell division that brings about the growth of a hair. If the papilla is de- stroyed the hair dies. When a hair is pulled out with its root the papilla and some adjacent epithelial cells usually remain uninjured. The epithelial cells in due time reproduce a new hair. The arrector pili muscle consists of bundles of smooth muscle fibers that pass obliquely downward from the upper surface of the dermis to be inserted in the connective-tissue tunic of the hair follicle near its lower extremity. The insertion of these fibers is always on the side toward which the hair inclines, so that when the fibers contract the root is drawn to a vertical position and the hair becomes erect. The hair on the scalp grows approximately at the rate of twelve inches a year, or one inch a month. The average duration of a hair is about four years. Many vertebrates, as horses and cattle, shed their hair annually, every spring, a phenomenon called moulting. In mankind the hair of the scalp is con- stantly dropping out and being replaced by growths of new shafts. Occasionally hair grows where it normally does not belong and for cosmetic effect requires removal. This is done by electrolysis, THE SKIN. 347 which consists in passing an electric needle down along the root of each hair to the hair papilla, which is then destroyed by a weak current of electricity. The hair is then readily removed and does not re- turn. The loss of hair on the scalp is due to a va- riety of causes, many of which we cannot explain. It often accompanies a prolonged illness, such as typhoid fever, and is then doubtless due to a general emaciation resulting in lack of proper nourishment of the scalp. The loss of hair in such cases is only temporary. Certain neurotic diseases result in a permanent loss and the same may be attributed to some germ diseases of the scalp that infest and de- stroy the hair papillae. In other cases baldness seems to be hereditary. It naturally follows that a healthy condition of the scalp will contribute to a rich growth of hair. Regular massage with a stiff brush no doubt accelerates the blood flow and thus brings about a better nourishment and growth to the hair. The natural preservation of hair after death is well known. In Egyptian mummies the hair is well preserved even to its natural color. The hair is thus an important factor in the identification of unknown deceased persons. THE NAILS. The nails are epidermal structures that are mor- phologically analogous to the hoofs and claws of lower animals. Each nail may be divided into a body, the part that is exposed, and the root that is hidden from view and lies in a fold of the skin. The 348 NORMAL HISTOLOGY AND ORGANOGRAPHY. lateral margins are also covered by a fold of the skin called the nail -wall. The nails have a pink color imparted by the subjacent blood, excepting near the root, where there is an opaque area called the lunula. The lunulae diminish in size from the thumb to the little finger. Each nail rests upon a very vascular dermis which has been called the nail bed or matrix. This connective- tissue bed has many fine longitudinal ridges and alternating grooves which fit closely into correspond- ing grooves and ridges on the lower surface of the nail. Each nail consists of two parts: a deep soft stratum that represents the Malpighian layer of the epidermis, and an external hard cornified layer that Bodyofnaii. Lunula. Mantle. Fig. 246.-Thumb nail. Body of nail. Root of nail. ■ Mantle. Phalanx, Nail bed. Fig. 247.-Longitudinal section of nail. represents the horny layer. The former consists of nucleated polygonal prickle cells which fill the fur- rows and cover the nail bed several cells deep. It is affirmed that the cells of this Malpighian layer, in the distal part of the nail, do not produce any of the overlying horny material, but that growth of the nail THE SKIN. 349 is exclusively due to epithelial proliferation from the Malpighian layer at the root of the nail and from that part directly under each lunula already de- scribed. A stratum granulosum is present in the upper portion of the matrix and absent in the other portions of the nail. The external cor- nified layer consists of flat epithelial scales in which rem- nants of a nucleus may frequently be found. These scales are derived from epithelial cells and overlie each other, forming hardened lamellae called nail leaves. The hoof of the horse corresponds to the finger- nail of man, and is divided for descriptive purposes into the wall, the sole and the frog. The part which is visible when the foot rests on the ground is the wall, while the sole and frog are invisible in this position. As the human nail rests on a grooved matrix, so the inner surface of hoof wall is extensively folded into leaf-like structures which interlock or digitate with like growths from the enclosed con- nective tissue, those from the wall being called horny or insensitive laminae, and those from the connective tissue or dermis the sensitive or vascular laminae. Horny Laminae.-These are known collectively as the keraphyllous tissue, and clothing the inner sur- face of the wall dovetail with the sensitive laminae Nail wall. Body. Matrix. Nail bed. Phalanx. Fig. 248.-Cross section of nail. 350 NORMAL HISTOLOGY AND ORGANOGRAPHY. like interlocking leaves of two books. Each lamina extends approximately from the upper and inner margin of the hoof to its plantar border. There are from five to six hundred of these laminae in each foot and they all increase in width from above to below. In a horizontal section of the hoof these laminae appear like so many papillae (Fig. 248a). From such a sec- tion it will be seen that along the sides of each lam- ina there are about sixty secondary folds, called lamel- la, by which the surface between sensitive and in- sensitive laminae is enormously in- creased. These secondary leaves establish a fine se- ries of longitudinal grooves along the lateral sides of each lamina, as seen in Fig. 2486. The surface lining of each horny fold consists of a single layer of cubical or low colum- nar epithelial cells analogous and continuous with the germinal layer of the skin. The cells are rich E°rn tubes epi- thelial cells. „ Horn matrix, epi- theiiai ceils. Insensitive lamina, epithelial tissue. Secondary lamina or lm^ShilaTiayebryof epithelial cells. Sensitive lamina con- nective tissue. Blood-vessel. Fig. 248a.-Horizontal section of hoof of horse. THE SKIN. 351 in chromatin and are doubtless capable of active multiplication. A few scaly epithelial cells are always found in the body of each lamella, but in the substance of each lamina the tissue appears to be compact and of a fibrous variety. It is this compact tissue that is called collectively the insen- sitive lamina. This fibrous tissue can be traced outward to the bases of the laminae, where it mingles with and is ultimately lost in the epithelial horn wall of the hoof. While nuclei are absent, the tissue should be regarded as made up of scaly epi- Horny tubes and wall matrix. Outer surface of hoof' Horny lamina. Secondary lamina or lamella. Fig. 2486.-Diagram of horizontal section through wall of hoof. thelial plates so arranged as to give it a fibrous ap- pearance very similar to the stratum lucidum of the human skin. Vascular Lamina.-These structures, collectively known as the podophyllous tissue, are leaf-like growths of the dermis, which interlock very snugly with the horny laminae and lamellae just described. They form an expansive fibrous and vascular tissue uniting the distal phalanx with the horny epidermal laminae of the hoof. They are also called the sensi- tive lamina, and, while the nerve endings in them have 352 NORMAL, HISTOLOGY AND ORGANOGRAPHY. not been worked out very carefully, it is reasonable to suppose that we have much the same structure as in the human nail-bed, such as free nerve endings, end-bulbs, and perhaps Rufini corpuscles. Hoof Horn.-Like bone, this is tubular, re- sembling Haversian systems, but, unlike bone, it consists of compact layers of epithelial cells. As the human nail develops from the germinal epithelium at the root of the nail, so the wall of the hoof de- velops from similar epithelium that covers the coronary cushion situated at the upper margin of the hoof wall. This cushion has an abundance of epithelial papillae, and from the surface of these papillae cells proliferate to form the wall of the hoof tubes, while from the epithelium at the bases of these papillae cells proliferate to form the hoof matrix. Thus, the hoof horn is exclusively an epithelial tissue, composed of flattened, scaly cells, with often an easily detected nucleus, cemented together com- pactly, their protoplasm being replaced by keratin granules, a protein-like substance very insoluble and containing 4.23 per cent, sulphur. The horn tubes extend downward fro'm the papillae of the coronary cushion and are parallel to each other. These tubes are smaller near the surface of the hoof and become larger in the deeper portion. The scaly cells of the tube wall are placed with their flat surfaces facing the tubes, that is, their long axes are perpendicular, while the long axis of the matrix cells are horizontal. This conforms to their origin, the former prolifer- ating from the sides of the vertical coronary papillae, while the latter come from the horizontal coronary THE SKIN. 353 surface between the bases of these papillae. Frag- ments of epithelial cells may usually be found in the lumen of these tubes. The laminae just described provide an enormous surface of contact between the inner face of the wall and the external surface of the pedal bone. It is estimated that this surface is equal in area to eight or ten square feet in each hoof, and its chief function is doubtless to furnish support to the body weight of the horse. The sensitive laminae thus act as an extensive and delicate cushion, tempering the jar sustained in walking or running. An inflammation of the sensitive laminae is known as laminitis, a malady not uncommon in the horse. The normal growth of the hoof is estimated at nearly one-half inch a month. Just how the horny laminae move imperceptibly downward past the softer lami- nated structure is a subject of much speculation among veterinarians, but one on which opinions differ. It seems to me any sliding process is difficult to explain and that the solution sought is one of cell growth. During embryonic development it is easy to conceive of a rapid multiplication of the germinal epithelium, that is, the cells that form the membrane clothing the insensitive laminae. Such a growth produces lateral pressure and accounts for the extensive folding of these laminated structures. In the adult foot the cells of the germinal layer show nuclei rich in chromatin, and being epithelial cells their multiplication con- tinues through life. The horny laminae, lying exter- nal to this layer, doubtless owe their origin, as well as their constant and regular growth, to the cells of NORMAL HISTOLOGY AND ORGANOGRAPHY. 354 the germinal epithelium. In fact, embryologically, this layer is to be considered as a part of the horny laminae rather than interposed between the horny and the soft laminae, as is done by most authors. The hoof wall, on the other hand, grows exclusively from the epithelial surface of the coronary cushion, and its downward progress is synchronous and uni- form with the growth of the horny laminae, as de- scribed above. The provisional horn that appears after removing a part of the hoof wall, surgically or otherwise, is explained as a cell proliferation of the germinal epithelium. If the human nail is removed this germinal epithelium is torn, but enough remains to proliferate epithelial cells in a few days which cor- nify to form a thin provisional nail analogous to the provisional hoof in a like injury to the horse's foot. THE GLANDS OF THE SKIN. Sweat glands are coiled simple tubular glands dis- tributed over the whole surface of the skin, with the exception of the inner surface of the prepuce, the glans penis, and the red borders of the lips. In the axilla and around the anal opening they are excep- tionally large and often branched. They are most numerous on the palm of the hand and the sole of the foot, where they number two thousand seven hundred to the square inch. On the forehead there are one thousand two hundred, and on the cheek about five hundred to the square inch, while over the back they are the least numerous. Their total num- ber over the whole body has been estimated at nearly two million four hundred thousand, which, with an THE SKIN. 355 average length of three-fourths of an inch, makes the united length approximately twenty-eight miles. This vast secreting surface is constantly secreting moisture, either as insensible or sensible perspiration. The amount of this perspiration within a given time Fig. 249.-Under surface of the epidermis, separated from the cutis by boiling. The sweat glands may be traced for a considerable part of their length; a, Sweat gland ; b, longitudinal ridge; c, depression, d, cross ridge (Bohm and Davidoff). varies considerably, but in the average person in good health it is estimated at about two pints every twenty-four hours. The excretory ducts open on the surface of the skin by numerous sweat pores along the crests of the epidermal ridges. These pores may be seen with a low magnification or ordinary hand lens. The duct is spirally twisted in the stratum corneum and enters the dermis between two dermal papillae; that is, at the apex of an epidermal papilla. In the dermis it takes a sinuous or nearly straight course and pene- 356 NORMAL HISTOLOGY AND ORGANOGRAPHY. trates to the lower stratum of the skin, or even deeper, to the subcutaneous connective tissue. This distal end is very much coiled and constitutes the secreting portion of the gland. In the epidermis the duct has no other wall than the epithelial cells of the various layers through which it passes, but in the dermis the wall is composed of a single layer of short cubical cells outside of which there is a delicate basement mem- brane. The secreting portion is also lined by simple epithelium, but the cells are larger and have a finely granular protoplasm. Between the gland cells and the base- ment membrane there is found in the larger glands, a single layer of non-striated muscle cells arranged longitudinally. This muscle is derived from the ectoderm, while the other musculature of the body comes from the meso- derm. The muscle of the sweat glands probably aids these glands in expelling their products of secre- tion. Non-medullated nerve fibers of the sympa- thetic system form a delicate network just external to the basement membrane called the epilamellar plexus. From this plexus delicate fibers pass through the basement membrane to ramify between the gland cells, where they end in clusters of small terminal granules. The physiological activities of the sweat glands are thus directly under the control of the nervous system and do not depend on the Basement membrane. Nonstrialed muscle. Gland cell. Fig. 250.-Cross section of deep portion of sweat gland. THE SKIN. 357 blood supply, a fact that may also be demonstrated by physiological experiments. Sebaceous glands are associated with hair follicles, into which they pour their contents. They are also found on the red borders of lips, the labia minora, the glans and prepuce, where hairs are absent. They are simple branched alveolar glands that se- crete an oily substance called sebum. This is a Hair follicle. Hair jollicle. Fig. 251.-Model of a sebaceous gland with a portion of the hair follicle, reconstructed by Born's wax-plate method (Huber). fluid at the temperature of the body, keeps the skin soft and flexible, and also supplies a natural dressing for the hair. In the scalp there may be an exces- sive secretion of sebum which dries and exfoliates with the horny epidermis as dandruff. Each hair follicle has two or more sebaceous 358 NORMAL HISTOLOGY AND ORGANOGRAPHY. glands that vary in size from 0.2 to 0.5 mm. The excretory duct is short and wide and opens into the upper third of the follicle. This duct is lined by stratified epithelium that is directly continuous with the outer root sheath of the hair follicle. The cells of the alveoli are very large and contain fat globules that vary in size and give a reticular appearance to the cytoplasm. The nuclei are rela- tively small. The cells completely fill the alveoli so that the latter appears to be solid. The cells disintegrate and change directly into secre- tion, which is then poured into the follicle as sebum. The renewal of lost cells takes place by constant proliferation of basal cells. It is quite common in the scalp to find sebaceous cysts, or wens, which result from an occlusion of the duct and an enlargement of the gland. These cysts are lined by a simple layer of epithelium and filled with a white, waxy, or semisolid fluid quite analo- gous to the sebum. Wens are of slow growth and cause no disturbance, unless they get very large or become infected by being carelessly opened. The radical cure consists in their complete removal, in- cluding the epithelial wall. Fig. 252.-Section of two alveoli of a sebaceous gland. CHAPTER XI. PERIPHERAL NERVE TERMINATIONS. Physiologically, nerve endings may be classified as motor or sensory. MOTOR NERVE ENDINGS. (The Telodendria of Nerve Fibers in Muscle Tissue.) i. In Striated Muscle.-The nerve endings in stri- ated muscle are called muscle-end plates, or sole plates. In the higher vertebrates these are found in the muscle sarcoplasm just beneath the sarcolemma of each muscle fiber. A motor nerve fiber as it ap- proaches its termination becomes much branched so as to innervate from ten to twenty muscle fibers. The axis cylinder enters the sarcoplasm where it im- mediately terminates in a web-like, flat end-brush with numerous dilatations. The axilemma, or Henle's sheath, is continuous around the brush. The me- dullary layer stops short at the level of the sarco- lemma; that is, at the surface of the sarcoplasm. The neurolemma is continuous with the sarcolemma of the muscle fiber. The adjacent sarcoplasm of the muscle fiber is granular and a liberal supply of muscle nuclei is also present in the proximity, which results in an elevation of the muscle fiber at the point of nerve contact known as Doyer's elevation. 359 360 NORMAL HISTOLOGY AND ORGANOGRAPHY. 2. In non-striated and in heart muscle the nerve termination is more simple. The muscle is supplied with neurons from the sympathetic system, most of which are of the non-medullated variety. These fibers branch repeatedly to form an extensive Nerve-end brush. So-called gran- ular sole. : Nerve. Nerve. Muscle fiber. Fig. 253.-Motor endings in striated voluntary muscles. From Pseudopus Pallasii. As a consequence of the treatment the arborescence is shrunken and interrupted in its continuity. The end plate is in con- nection with two nerve branches (Bohm and Davidoff). primary plexus surrounding the muscle bundles. From this plexus non-medullated fibers, that is, just the axis cylinders, penetrate the heart muscle, or the involuntary muscle, where they anastomose to form a delicate secondary plexus, from which lat- eral short twigs pass to end in minute dilatations or granules upon the muscle cells. PERIPHERAL NERVE TERMINATIONS. 361 SENSORY NERVE ENDINGS. The sensory nerve terminations are essentially the terminals of dendrites as distinguished from the motor plates which are the terminals of axones. The cell bodies of these sensory neurons are found in the spinal and cranial ganglia, often at a consid- erable distance from the sensory termination. In (Telodendria of Dendrites.) Fig. 254.-Motor nerve ending on heart muscle cells of cat; methylene- । blue stain (Huber, De Witt). Fig. 255.-Motor nerve ending on involuntary non- striated muscle cell from intestine of cat; methy- lene-blue stain (Huber, De Witt). this case the dendrite is a long one, medullated, and structurally identical with an axis cylinder or axone. The nerve impulse is, however, normally carried toward the nerve cell, while in axones the impulse goes the opposite way. As stated in another place, such sensory neurons have a long dendrite that ex- tends peripherally and a short axone that passes centrally; that is, to the spinal cord or brain. 362 NORMAL HISTOLOGY AND ORGANOGRAPHY. These sensory endings form telodendria or end- brushes that vary in complexity according to the tissue elements that take part in their formation. 1. Free Sensory Nerve Endings.-These are the simplest forms of nerve endings and occur in epi- Stratum corneum. Nerve fibers in the epi- dermis. Stratum Malpighii. Papilla:. Nerve fiber. Fig. 256.-Nerves of epidermis and papilla from ball of cat's foot (Bohm and Davidoff). thelial tissues and in some parts of the connective tissues. The sensory nerve fibers near its termina- tion repeatedly branch, the latter retaining the medullary sheath. The branches appear always at the nodes of Ranvier. From this coarse plexus a PERIPHERAL NERVE TERMINATIONS. 363 finer non-medullated system of branches appear which innervate the epithelium and terminate in varicosities, discs, or minute granules that lie in appo- sition to epithelial cells. Similar free terminations occur in tendons, and liga- ments, and other fibrous connective tissue. 2. Tactile Cells.-These are also called Grandry's corpuscles, and may be found in the duck's bill just beneath the gum epithelium. The cells are of epithelial origin, oval, and meas- ure about 50 // in diameter. One to five cells are surrounded by a connective-tis- sue capsule. These cells are superposed on each other, with their long axes always parallel to the surface of the bill. A me- dullated nerve fiber may be traced to the cap- sule, which it penetrates and then becomes non- Connective-tissue capsule. Nerve fiber. Epithelial cells. F1S- 257.-Tactile cells from the bill of a duck, Nucleus of lamelle. End-cell of core. Lamellae. Axis-cylinder in core. Cubic cells of core. Termination of meduk lary sheath. Axis-cylinder of nerve-fiber. Medullary sheath of nerve-fiber. NofrHcXaandsheath Fig. 258.-Corpuscle of Herbst from bill of duck (Bohm and Davidoff). 364 NORMAL, HISTOLOGY AND ORGANOGRAPHY. medullated. The latter terminates in tactile discs that are interposed between the tactile cells. A group of three cells will have two discs; five cells will have three discs. 3. Corpuscles of Herbst.-These are much larger bodies and may also be found in the bills of aquatic birds, in close association with the tactile cells just described. They are ovoid bodies 75 /z wide and 150 // long. There is an inner core sur- rounded with con- nective-tissue lamel lae. The core con- tains the axis cylin- der, which is thick- ened at the end and is encased between two rows of cells that seem to have the same function as Grandry's corpus- cles. The nerve fiber enters at the end of the corpuscle and becomes non-medullated only after reaching the inner core. 4. Meissner's Corpuscles.-These are found beneath the epidermis of man, particularly of the hand and foot, and occupy the dermal papillae of the dermis. Fig. 259.-Meissner's tactile corpus- cle; methylene-blue stain (Dogiel, "In- ternat. Monatsschr. f. Anat. u. Phys.," vol. ix). PERIPHERAL NERVE TERMINATIONS. 365 They are oval bodies and approximately the same size as the corpuscles of Herbst. There is a thin connective-tissue capsule and a loose complex core. One or more medullated nerve fibers enter at the lower end of the corpuscle. These soon become non-medullated and their axones then make a vari- able number of spiral turns which interlace, branch, and are beset with many granules or varicosities. One or more axis cyl- inders occupy the center of the core. 5. Genital Cor- puscles. - These are oval or round bodies located in the mucosa, just beneath the epi- thelium of male and female geni- talia. Their size varies from o. 1 mm. to 0.4 mm. They are sur- rounded by a thick fibrous capsule and each cor- puscle is innervated by one to ten medullated nerve fibers. The latter become non-medullated after passing through the capsule, and the axones then form a complex core quite analogous to that of Meissner's corpuscle. In fact, the two are very similar structures. Fig. 260.-Genital corpuscle from the glans penis of man; methylene-blue stain (Dogiel, " Arch. f. mik. Anat.," vol. xli.) Lamella:. Granular cove. ■ Axis cylinder, Fig. 261.-Pacinian corpuscle from mesentery. Fig. 262.-Neuromuscular nerve-end organ from the intrinsic plantar muscles of dog; from teased preparation of tissue stained in methylene- blue. The figure shows the intrafusal muscle fibers, the nerve fibers and their terminations; the capsule and the sheath of Henle are not shown (Huber and De Witt, "Jour. Comp. Neurol.," vol. vii). 366 PERIPHERAL NERVE TERMINATIONS. 367 6. Pacinian Corpuscles.-These are oval bodies and the larger ones are easily visible to the naked eye, being over 2 mm. long. Structurally they seem related to the corpus- cles of Herbst. They are found in the dermis of the hand and foot, particularly along the lower surface of the fingers and toes. They are also found in the joints, the peritoneum, pleura, pericar- dium, and are especially abun- dant in the mesentery. The greater portion of the corpuscle consists of concentric lamellae of connective-tissue origin. Be- tween these flat endothelial cells intervene. A granular core forms the axis of the corpuscle, in the center of which the axis cylinder may be traced. Usually one large nerve fiber goes to each corpuscle. After entering the core this forms a plexus of fine branches and becomes non-med- ullated. 7. Tendon and Muscle Spin- dles.--A tendon spindle is an ex- pansion of tendon bundles en- closed in a well defined connec- tive-tissue sheath. The nerve fiber enters the middle of the spindle, divides re- Fig. 263.-Neuroten- dinous nerve-end organ from rabbit; teased preparation of tissue stained in methylene- blue (Huber and De Witt, "Jour. Comp. Neurol.," vol. x). 368 NORMAL HISTOLOGY AND ORGANOGRAPHY. peatedly, becomes non-medullated and finally ter- minates in varicosities or expanded clavate ends. The muscle spindle is a collection of delicate muscle fibers enveloped in a dense perimysium sheath, the whole being innervated by sensory nerve endings much as in tendon spindles. The sensory endings both in tendon and muscle transmit the sensation of tension which becomes the basis for coordinate movements. CHAPTER XII. THE SPINAL CORD. The spinal cord is an organ composed largely of neurons, with which are associated blood-vessels, connective-tissue elements, and a limited amount of epithelial and muscle cells. It represents the ter- minal portion of the cerebrospinal axis and is a direct continuation of the encephalon. It is one of the first organs to develop in the embryo where it makes its appearance as a dorsal ectodermal groove. This neural groove gradually closes to form a canal which lies at first just beneath the ectoderm and later becomes encased in connective-tissue layers and the bony axial skeleton. The cord is bilaterally symmetrical and flattened dorso-ventrally. It presents two enlargements: (i) the upper or cervical, which extends from the third cervical vertebra to the second thoracic and corresponds to the origin of the nerves of the arm, and (2) the lower or lumbar, which extends from the ninth thoracic vertebra to the terminal cone at the level of the body of the second lumbar vertebra. The lumbar enlargement marks the origin of the nerves of the leg. From the apex of the terminal cone there extends a slender rudimentary prolonga- tion, the filum terminale, which, with the spinal nerves of this region, is called the cauda equina. The 369 NORMAL HISTOLOGY AND ORGANOGRAPHY. 370 spinal cord, therefore, does not extend the whole length of the vertebral canal but only to the level of the second lumbar vertebra. Its length is about eighteen inches, its diameter one-half inch or less. Membranes of the Cord or Meninges.-1. The Dura.-This is a thick strong membrane composed of Blood capillaries in white matter. Posterior root o] spinal nerve. Ligamentum denticulatum. Bloodvessels in gray matter. A nterior root of spinal nerve. Posterior root. A nterior root. Dorsal spinal ganglion. Dura mater. Arachnoid. Spinal ganglion. Pia mater. Blood-vessels. Fig. 264.-Portion of spinal cord and membranes dissected white fibrous tissue which forms the outer covering of the cord. Many blood-vessels find lodgment in this membrane. It is analogous and continuous with the dura of the brain, the most striking differ- ence being that the dura of the cord does not form THE SPINE. 371 the internal periosteum of the vertebral canal. Be- tween the dura and the vertebrae is a space called the epidural space, which is filled with areolar tissue, fat, and a plexus of spinal veins. 2. The Pia.-This is a thin connective-tissue layer that lies close to the surface of the cord, dips into the anterior fissure, and also sends fibers or trabeculae into the cord substance. Many small blood-vessels accompany this layer. 3. The Arachnoid.-This is a delicate membrane between the other two, but much nearer the dura. Its external surface is clothed with a single layer of flat epithelial cells which secrete a serous fluid. The arachnoid is therefore a serous membrane. Fissures.-1. Posterior Median Fissure.-This is a median dorsal fissure that extends the whole length of the cord. It is extremely narrow but deep, as it penetrates to the central gray matter, being inti- mately connected with the two sides in its course. The single septum is derived from the neuroglia tis- sue, and not from the pia, which sends no prolonga- tion of any kind into it. 2. Anterior Median Fissure.-This also extends the whole length of the cord. It is shallower but wider than the posterior fissure and does not quite reach the central gray matter. The pia forms a fold into this fissure with which is associated many blood-vessels. The two median fissures or clefts divide the cord into a right and a left half, each practically identical with the other. 3. Postero-lateral Groove.-This is a shallow de- pression on each side of the posterior fissure and 372 NORMAL HISTOLOGY AND ORGANOGRAPHY. marks the entrance into the cord of the dorsal roots of the spinal nerves. In a like position, anteriorly, is the exit of the anterior roots of the spinal nerves, but there is no depression or groove as in the case of the posterior roots. The two roots of the spinal nerves divide each half of the spinal cord into three regions or major tracts known as the posterior, Posterior root-fibers with col- laterals Posterior horn cell. Crossed pyram- idal column. A nt.-post. reflex fibers. Golgi cell of posterior horn. Direct cerebel- lar column. Column cells. Collaterals oj crossed pyramidal column. Golgi's commis- sural cells. Howers's column. Motor cells. Collaterals ending in the gray matter. Fig. 265.-Schematic diagram of the spinal cord in cross section after von Lenhossek, showing in the left half the cells of the gray matter, in the right half the collateral branches ending in the gray matter (Huber). Direct Pyramidal column. lateral, and anterior columns. The posterior column is limited by the posterior fissure and the posterior roots, the lateral is the region between the roots, and the anterior lies between the anterior root and the anterior fissure. Spinal Nerves. -Thirty-one pairs of nerves arise from the side of the cord. These are classified into THE SPINE. 373 8 cervical, 12 dorsal, 5 lumbar, 5 sacral, and 1 coc- cygeal. Each nerve is attached to the cord by a dorsal and a ventral root. Each root, before uniting with the cord, breaks up into secondary bundles and spreads out like a fan, making a continuous linear attachment. The dorsal ganglion is located upon the dorsal within the vertebral canal, near the union of the two roots. Gray Matter of the Cord.-The gray matter of the cord is centrally located and takes the form of a capital letter H. The gray matter in each lateral half resembles a crescent which is joined to the op- posite side by an isthmus, in the center of which is the central canal. The latter is usually obliterated in the adult man, and is filled as well as surrounded by the gelatinous substance of Rolando, which is a reticular structure. That part of the isthmus above the central canal is called the posterior gray com- missure, while the gray matter ventral to the canal is the anterior commissure. Each crescent may be divided into a posterior, lateral, and anterior horn. The anterior horn is the largest and the lateral horn is the smallest. The posterior horn is pointed and approaches near to the posterior lateral groove. The apex of this horn is called the zona terminalis. At the base of this apex there is a reticular substance called the zona reticu- laris, while next to this and apparently capping the posterior horn is a gelatinous mass, similar to that which surrounds the central canal, called the sub- stantia gelatinosa of Rolando. The nerve cells of the posterior horn are irregularly 374 NORMAL HISTOLOGY AND ORGANOGRAPHY. distributed and some of them are particularly small and have a stellate appearance. At the base and mesial surface of this horn there is a group of large nerve cells called the column of Clarke. This column extends from the second lumbar up through the dorsal region of the cord to the cervical. In the cervical region it is absent; however, Stilling's nu- cleus of this region may represent a remnant of the column of Clarke. At the base of the dorsal horn, deeper down and lateral to Clarke's column, another group of nerve cells may be found that is called Waldeyer's central cell column. This is reciprocal with Clarke's column; that is, in the dorsal region where Clarke's column is conspicuous, only rem- nants of Waldeyer's tract can be found, while in the other regions of the cord this cell tract is particu- larly prominent. The lateral horn is a small lateral prominence at the side of the gray crescent. In the substance of this, a small collection of nerve cells may be found, while just beneath this the gray matter cuts into the white matter, forming processes called the processus reticularis. The anterior horn is not only large but presents a blunt, rounded appearance. The nerve cells of this horn are very large and have been classified according to their position into antcro-mesial, postero-mesial, antero lateral, and postero lateral. The axis cylin- der of most of these cell bodies goes to form the an- terior root of the spinal nerves. They therefore carry only motor impulses. White Matter of the Cord.-The white matter of THE SPINE. 375 the cord consists of medullated nerve fibers. Most of these fibers have no neurilemma, and the cord there- fore is soft and pulpy, in contrast to the nerve trunks whose fibers have a neurilemma which with the connective-tissue elements make nerves tough and strong. The white matter practically encloses the gray. The fibers which compose it vary con- Postero-latcral horn. Posterior fissure. Lissaur's marginal ground bundle. Comma trad. Pia via ter. Posterior horn. Direct cerebellar tract. Lateral horn. Gowers's tract. Anterior horn. Processus reticularis. Lowenthal's tract. Anterior commissure. Anterior fissure. Direct pyramidal tract. Fig. 266.-Cross section of the spinal cord, dorsal region. 1, Zona terminalis; 2, zona reticularis; 3, substantia gelatinosa of Rolando; 4, stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's central cell column; 7, cells of lateral horn; 8, central canal; 9, antero- mesial cells; 10, postero-mesial cells; 11, antero-lateral cells; 12, pos- tero-Iateral cells. siderably in size, both large and small being mixed up together. In sections of the adult healthy cord no evidence of definite tracts of fibers can be seen. We know, however, that longitudinally arranged groups of fibers* run a definite course, have definite connections, and carry impulses that result in defi- nite sensations and actions. The physiological evi- 376 NORMAL HISTOLOGY AND ORGANOGRAPHY. dence of this fact is experimental and positive. A nerve fiber detached from its cell body dies. In this way tracts will degenerate in the cord, some above and some below a transverse cut. The em- bryological evidence rests on equally positive facts. In development certain tracts acquire medullary Postero-lateral horn. Posterior fissure. Lis saur's marginal ground bundle. Comma tract. Posterior horn. Pia mater. Crossed Pyramidal tract. Lateral horn. A nterior horn. Gowers's tract. Processus reticularis. Lowenthal's tract. Fig. 267.-Cross section of the spinal cord, lumbar region. 1, zona terminalis; 2, zona reticularis; 3, substantia gelatinosa of Rolando; 4, stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's cen- tral cell column; 7, cells of lateral horn; 8, central canal; 9, antero- mesial cells; 10, postero-mesial cells; 11, antero-lateral cells; 12, postero- lateral cells. Anterior root oj spinal nerve. Anterior fissure. sheaths earlier than others. This fact has greatly extended our knowledge of the white matter in the cord. The pathological evidence is a third factor. Certain diseases produce degenerate lesions in the cord. Proper interpretations of these lesions have enabled us to map out definite nerve tracts in the cord, and to determine their relations as well as pos- THE SPINE. 377 sible functions. The information evolved from these sources makes a classification of tracts, in the cord, possible. Tracts of the Cord.-Posterior Region. i . Column of Goll.-This lies adjacent to the dorsal fissure and extends the whole length of the cord. Its fibers arborize about nerve cells in the nucleus gracilis of the lower region of the medulla. 2. Column of Burdach.-This extends parallel to the column of Goll between the latter and the pos- terior horn of gray matter. It extends the whole length of the cord and its fibers arborize about nerve cells in the nucleus cuneatus of the medulla, adjacent to the nucleus gracilis. The column of Goll becomes wider in the upper portions of the cord and that of Burdach narrower. This is due to nerve fibers that gradually pass into the column of Goll from the col- umn of Burdach on their way to the brain. 3. Comma Tract.-This is a small tract found in the column of Burdach, and represents sensory fibers from the posterior roots of the spinal nerves that pass down the cord for a short distance, and then turn into the anterior horn of gray matter to arborize about nerve cells of this region. 4. Lissaur's Marginal Ground Bundle.-This is a small commissural tract placed near the surface of the cord just lateral to the entrance of the posterior root fibers. It is formed by some of the fibers of this root. The tract extends the whole length of the cord, but each individual fiber runs but a short distance and then turns inward to arborize about nerve cells of the posterior horn. 378 NORMAL HISTOLOGY AND ORGANOGRAPHY. These four tracts are composed almost entirely of nerve fibers that enter the cord by the posterior roots of the spinal nerves. They are therefore sen- sory tracts and forward impulses toward the brain. The termination of the posterier root fibers may be enumerated as follows: i. Column of Goll, Burdach, comma tract, Lis- saur's tract. 2. Arborize about the cells in Clarke's column. 3. Arborize about the cells in posterior horn. 4. Arborize about the cells in anterior horn on same and opposite side. Lateral Region.-The tracts of this region are: (1) Direct Cerebellar; (2) Gowers's, or Ascending Antero- lateral; (3) Crossed Pyramidal; (4) Lowenthal's, or Antero-lateral Descending; (5) Mixed Lateral. 1. The Direct Cerebellar.-This is a band of fibers that lies at the surface of the cord just lateral to the dorso-lateral groove. Its nerve fibers are derived from the cells of the column of Clarke, consequently the tract extends from the last dorsal up to the medulla on the same side. It is an ascending or sensory tract, and, as it is traced upward, becomes wider from the acquisition of axones from the col- umn of Clarke. It enters the cerebellum through the inferior peduncle and finally terminates in the cerebellar cortex of the superior worm on both sides, chiefly the opposite. 2. Gowers's tract lies just in front of the direct cerebellar and also at the surface of the cord. It is an ascending or sensory tract and some of its fibers are supposed to reach the cerebellum by passing THE SPINE. 379 through the formatio reticularis of the medulla, and making a backward turn through the superior med- ullary velum of the same side. Other fibers of this tract have been traced to the corpora quadrigemina, the thalamus, substantia nigra, and the lenticular nucleus of the cerebrum. The fibers of this tract extend the whole length of Posterior root. Posterior fissure. Lissaur's marginal ground bundle. Comma tract. Pia mater. Posterior horn. Lateral horn. Direct cerebellar tract. A nterior horn. Gowers's tract. Processus reticularis. Lowenthal's tract. Direct pyramidal ' tract. A nlerior root of spinal nerve. Anterior fissure. Fig. 268.-Cross section of spinal cord cervical region. 1, Zona ter- minalis; 2, zona reticularis; 3, substantia gelatinosa of Rolando; 4, stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's cen- tralcellcolumn; 7, cells of lateral horn; 8, central canal; 9, antero-me- sial cells; io, postero-mesial cells; 11, antero-lateral cells; 12, postero- lateral cells. the cord and probably have their origin in the cells of t*he posterior horn. 3. The crossed pyramidal tract is a large and well-defined bundle that lies just beneath the direct cerebellar; that is, between this and the posterior horn. Below the point where the direct cerebellar 380 NORMAL HISTOLOGY AND ORGANOGRAPHY. begins, the crossed pyramidal comes to the surface of the cord. The fibers of this tract have their origin in the large pyramidal cells of the cerebrum in the region of the area of Rolando. Traced downward from this source, they cross in the lower part of the medulla to the opposite side of the cord, making at this point the motor decussation. As it descends the tract gradually diminishes in size, due to the fact that fibers leave it to arborize around the large motor cells of the anterior horn. In this way the entire tract is ultimately exhausted near the lower extremity of the cord. It is thus a descending or motor tract that governs the opposite side of the body from where it has its origin. 4. Lowenthal's tract is closely associated with Gowers's. Its position is anterior and mesial to Gowers's, encroaching some upon the anterior region of the cord. The fibers of this tract are supposed to come from cells in Deiters' nucleus of the medulla which may be regarded as an internode between the cerebellum and the medulla. This tract descends as far as the lumbar region and its fibers are supposed to arborize around the motor cells of the anterior horn of the spinal cord. 5. The mixed lateral bundle represents the re- mainder of the lateral region. Its fibers probably come from cells in all parts of the gray matter of the cord, and from cells on the opposite side of the cord. At intervals these fibers ultimately reenter the gray matter and arborize about nerve cells. It is there- fore an intersegmental or commissural tract, both sensory and motor. THE SPINE. 381 Anterior Region. i. Direct Pyramidal Tract.-This is a small well- defined tract that lies next to the antero-median fissure. As a rule this tract can only be traced down to the middle of the dorsal region. These fibers originate jointly with those of the crossed pyramidal tract; that is, from the large pyramidal cells of the cerebral cortex. The fibers, however, do not cross in the medulla but pass directly down the cord on the same side. The fibers cross in the cord at inter- vals in its course, making use of the anterior com- missure to reach the opposite side, where they ar- borize around the cells of the anterior horn in a manner like those of the crossed pyramidal. It thus follows that the motor cells on one side of the cerebrum control the muscular contraction on the opposite side of the body, either through the crossed or the direct pyramidal tract or through both. 2. The anterior ground bundle is really a part of the mixed lateral tract already described. It is composed of ascending and descending fibers that have both their origin and their termination in the gray matter of the cord and is therefore an inter- segmental or commissural tract. 3. Anterior White Commissure.-This is composed of medullated nerve fibers passing parallel to the gray commissure between the latter and the bottom of the anterior fissure. It is a decussation of fibers of a mixed variety, many of them being derived from the direct pyramidal tract as already stated. CHAPTER XIII.1 THE BRAIN. The brain, or encephalon, develops jointly with the spinal cord, and represents the anterior extremity of the cerebrospinal axis. The average weight of the brain is about forty-eight ounces, while the cord weighs less than one ounce. Like the cord it is an organ in which all the elementary tissues may be found but in which the neurons predominate. During embryonic growth the brain and cord are a hollow tube and this cavity is never obliterated, but remains in the brain as its ventricles. Develop- mental history further discloses the fact that the brain, like the cord, is made up of definite segments or joints called neuromeres. These primary units are soon replaced by three larger vesicles called primary fore-brain, mid-brain, and hind-brain. It is generally affirmed that the first of these repre- sents 3 neuromeres, the second 2 neuromeres, and the third 6 neuromeres. Later the primary fore- brain divides to form the cerebrum and the 'tween- brain, while the hind-brain also divides to form the cerebellum and medulla. In the adult brain, there- fore, five divisions may be recognized, each of them presenting a central canal or cavity as designated in the table below: 382 383 THE BRAIN. Primary Divisions. Secondary Divisions. Cavity. Fore-brain or prosen- cephalon f i. Telencephalon or cerebrum. Lateral ventricle. < 2. Thalamencephalon, or dien- Third ventricle. ( cephalon, or 'tween-brain. Mid-brain. 3. Mesencephalon or mid-brain. Aqueduct of Sylvius. Hind-brain or rhomb- encephalon f 4. Metencephalon or cerebel- Upper part of fourth < lum. . ventricle. ( 5. Myelencephalon or medulla. Fourth ventricle. The brain is thus a hollow multiple organ. Its central cavity is lined with a serous membrane, the ependyma, which secretes a serous fluid, the cerebro- spinal fluid. The outer vascular investments are the meninges, which serve as a delicate packing between the brain wall and the bony vault of the cranium. The Meninges.-These are three connective-tissue investments to the brain that are practically identical and continuous with those already described inclos- ing the cord. It will be sufficient, therefore, to men- tion the points wherein these membranes slightly differ. , The dura of the brain forms the periosteum of the investing bones, while each segment of the vertebral column has its own periosteum. Several broad prolongations of the brain dura extend between the different divisions of the brain. These are the ten- torium between the cerebrum and the cerebellum; the jalx cerebri which dips into the great fissure be- tween the two lobes of the cerebrum, and the jalx cerebelli, which is a small median septum between the cerebellar hemispheres. At the basal skull fora- mina, the dura accompanies the cranial nerves and is continuous with the areolar sheaths of these nerves. The pia is composed mostly of areolar tissue and 384 NORMAL HISTOLOGY AND ORGANOGRAPHY. small blood-vessels. It is the nourishing tissue of the brain and clothes its entire surface, dipping down to the bottom of fissures, and sending strands, associated with blood-vessels, into the brain sub- stance. The brain pia is more vascular than that of the cord. The arachnoid is a web-like membrane between the dura and the pia, but much nearer the dura. The space beneath the dura is called the subdural space, and is small. That between the arachnoid and pia is larger and is called the subarachnoid space. The former has a little serous fluid, and the latter is filled with lymph and some cerebrospinal fluid. This fluid reaches the external surface of the brain through a small foramen or pore in the thin roof of the fourth ventricle. Trabeculae intervene between all these membranes. The medulla is about one inch in length, and rep- resents the portion of the brain next to the spinal cord. Its lower extremity is at the lower margin of the foramen magnum. From this point it passes upward in nearly a vertical direction to its upper ex- tremity at the lower border of the pons. Being the nerve center for the large cranial nerves, the medulla is the most vital part of the brain, and the best pro- tected. Its lower portion resembles the cord, having the same fissures and grooves. The upper portion is expanded in such a manner as to bring its cavity or fourth ventricle to the dorsal surface. This ex- panding process has carried the dorsal tracts later- THE MEDULLA. THE BRAIN. 385 ally, leaving a very thin roof, consisting of the ependyma and a vascular pia, to cover the ventricle. The lower half of the fourth ventricle is found in the upper half of the medulla, while the upper half of this ventricle extends into the pons region and is overlaid by the cerebellum. The central canal of the cord opens into the lowest point of this ventricle and therefore extends through the lower half of the medulla, but nearer its dorsal surface. The lower Pineal body. Superior quadrigeminal body. Inferior quadrigeminal body. Valve of Vieussens. ■ Crus cerebri. Middle peduncle of the cerebellum. Superior peduncle of the cerebellum. Eminentia teres. Area acusticce. Stria acustica. Restijorm body. Trigonum vagi. Calamus scriptores.. Trigonum hypoglossi. Clava. Rolandic tubercle. Funiculus gracilis. Funiculus cunealus. Fig. 269.-Dorsal view of the medulla, pons and mid-brain. half is therefore spoken of as the closed medulla while the upper part, that has the ventricle, is called the open medulla. Two ridges, the funiculus gracilis and funiculus cuneatus, may be recognized on the dorsal surface of the medulla, and represent the continuation of the columns of Goll and Burdach. The funiculus gra- cilis terminates anteriorly in a blunt expansion 386 NORMAL HISTOLOGY AND ORGANOGRAPHY. called the clava. On the dorsal aspect of the open medulla is found the restiform body, which passes in- to the inferior pedun- cle of the cerebellum and represents fiber tracts, the most im- portant being the di- rect cerebellar tract. The lower half of the fourth ventricle is V- shaped and its apex is called the calamus scriptorius, from its resemblance to a pen. In its floor three tri- angular areas are found, called trigo- num vagi, trigonum hypoglossi, and area acusticce. It is in these areas that we find, respectively, the origin of the tenth, twelfth, and eighth cranial nerves. The striae acusticce are transverse ridges in the floor of this ventri- cle, extending across its middle part from the median sulcus to Fig. 270.-View, from below, of the connection of the principal nerves with the brain: I', the right olfactory tract; II, the left optic nerve; II', the right optic tract (the left tract is seen passing back into i and e, the internal and external corpora geniculata); III, the left oculomotor nerve; IV, the trochlear; V, V, the large roots of the trifacial nerves; -|-H the lesser roots (the + of the right side is placed on the Gasserian ganglion); 1, the oph- thalmic; 2, the superior maxillary; and 3, the inferior maxillary divi- sions; VI, the left abducens nerve; VII, VIII, the facial and auditory nerves; IX-XI, the glossopharyngeal, pneumogastric, and spinal accessory nerves; XII, the right hypoglossal nerve; Cp the left suboccipital or first cervical nerve (Nancrede). THE BRAIN. 387 the lateral margins, and represent nerve fibers car- rying impulses from the eighth cranial nerve. On the lateral surface of the medulla a prominent oval elevation appears called the olivary body, which represents a crescent collection of nerve cells. Just dorsal to the olivary body is the continuation of the dorsal groove of the cord, and it is from this groove that fibers of the ninth, tenth, and eleventh cranial nerves emerge. Near the anterior extremity, at the lower margin of the pons, is the superficial origin of the seventh and eighth nerves. The origin of these nerves corresponds to the entrance into the cord of the posterior root of the spinal nerves. Just median or ventral to the olive is a groove that cor- responds to the points of exit of the anterior root of the spinal nerves. From this groove the fibers of the twelfth cranial nerve escape. The ventral region of the medulla presents a median fissure, the continuation of the anterior fissure of the cord. The upper end of this fissure forms a pit at the lower margin of the pons, called the foramen cecum. Just lateral to this cecum, and curving around the pons, is the superficial origin of the sixth pair of cranial nerves. On each side of the median fissure is a longitudinal ridge called the pyr- amids which represents the fibers of both the crossed and the direct pyramidal tract. Near the lower ex- tremity of the medulla the fissure seems partly obliterated by ridges recrossing. These represent pyramidal fibers crossing to form the crossed pyr- amidal tract, and constitute, therefore, the motor decussation. Just below the olive curved striae may 388 NORMAL, HISTOLOGY AND ORGANOGRAPHY. be seen, that appear to come from the median fissure and sweep around the olive and enter the cerebellum through the restiform body and inferior peduncle. These are called the superficial arcuate fibers, and many of them come from the nerve cells of the olive of both the same and the opposite sides. Sections of the Medulla.-Cross Sections of the Closed Medulla.-These verify the surface markings Central canal. Funiculus gracilis. Nucleus gracilis. Funiculus cuneatus. Nucleus cuneatus. Spinal root oj fijth nerve. Substantia gelali- nosa Rolando. Deep arcuate fibers. Formatio ■ reticularis. Median raphe. Mesial olive. Decussation oj fibers. Superficial arcuate. Olive nucleus. Arcuate nucleus. Fig. 271.-Cross section of the closed medulla. Anterior pyramids. already described. In the dorsal region is the funiculi gracilis and cuneatus, fiber tracts of the columns of Goll and Burdach. Beneath these are the nuclei of gracilis and cuneatus, nerve cells around which arborize the telodendria of the fibers of the columns of Goll and Burdach. From these nerve cells axones spring that sweep downward and across to the oppo- site side, and in crossing form the sensory decussa- THE BRAIN. 389 tion. It thus happens that the sensory impulses also cross and reach the opposite side of the brain. Ex- ternal to the nucleus gracilis is the substantia gelati- nosa of Rolando, a continuation of that of the cord. Just external to this is a cross section of nerve fibers, the ascending root of the fifth nerve. The central area of each half of the section shows a large number of scattered nerve fibers interlacing and in cross sections. This area is called the formatio reticularis. Anterior to it, a collection of nerve cells represents the olivary body, median and dorsal to which a second and smaller collection of cells consti- tute the mesial olivary nucleus. The bulk of the anterior portion shows a cross section of the pyra- mids. Some of these fibers may be seen to sweep to the opposite side, thus making the motor decus- sation. In doing so they seem to pass over in large alternate bundles, rather than uniformly, as is the case with the sensory decussation. At the anterior surface on each side of the median fissure and sweep- ing around the pyramids are the superficial arcuate fibers, and also a collection of nerve cells, the arcuate nucleus. In cross sections of the open medulla the resem- blance to that of the cord is less distinct. The thin roof of the fourth ventricle is usually broken, leaving a dorsal expanded cleft. The lateral margin or remnant of the roof is called the lingula. Just be- neath the floor and close to the median sulcus are the nerve cells of the twelfth nerve. Lateral but in close proximity to these are the nerve cells of the tenth nerve. The axones from these cells may be 390 NORMAL HISTOLOGY AND ORGANOGRAPHY. traced through the substance of the medulla to their ventral exit. The superficial origin of the twelfth nerve is just anterior to the olive, and the fibers of the tenth nerve may be traced to their superficial origin just dorsal to the olive. In serial cross sec- Nucleus of nerve VI. Nucleus of nerve X. Nucleus of nerve XII. Posterior longitudinal bundle. Fasciculus solitarius. Fourth ventricle. Ascending root of nerve Vil. ' Solitary nucleus. ' Restiform body. Lingula. Nucleus am- biguus. 'Substantia gelatinosa Rolando. Descending root o] nerve K. Nucleus lateralis. A nt. lat. ascend- ing tract. Olive. ■ Superficial arcuate fibers. Arcuate nucleus. Anterior pyramids. Fig. 272.-Cross section of the open medulla (composite drawing). tions it will be seen that the nuclei of the other cra- nial nerves, from the sixth to the twelfth, lie in the floor of the fourth ventricle. The fasciculus solitarius is a bundle of nerve fibers, cut in cross section, and placed just lateral to the THE BRAIN. 391 nucleus of the tenth nerve. This bundle represents fibers from the ninth and tenth nerves. Just in- ternal or mesial to this bundle are a few cells called the solitary nucleus. This is probably a motor nu- cleus of the ninth and tenth nerves. Lateral to the solitary fasciculus are the fibers of the large restiform body on their way to the cerebellum. The posterior longitudinal bundle is a tract of nerve fibers that appears in cross section just an- terior to the nucleus of the twelfth nerve, and lies in close apposition to the median plane. The formatio reticularis occupies the greater part of the center of each lateral half of the medulla, and presents the same appeareance as in sections of the closed med- ulla. Likewise the cells of the olivary body, which in the open medulla form a large conspicuous nu- cleus that takes the form of a U with wavy sides, and with the open extremity turned inward and upward. Nerve fibers from its hilum sweep across to the oppo- site side and some curve around to join the super- ficial arcuate fibers of the same side. The arcuate fibers are divided into the deep and the superficial set. The deep set come from the nuclei cuneatus and gracilis and from the sensory nuclei of the cranial nerves. From this source they arch to the opposite side and then turn to pass upward in the brain stem, where they form the middle filet. The superficial set may be divided into an anterior and a posterior group. The anterior group originate in the nuclei gracilis and cuneatus, accompany the deep set to the opposite side of the medulla, where some of them become superficial in the anterior mesial fissure, then curve around the anterior pyra- 392 NORMAL, HISTOLOGY AND ORGANOGRAPHY. mid in the superficial border of the medulla, and finally enter the restiform body and the cerebellum through the inferior cerebellar peduncle. Others become superficial in the antero-lateral groove lateral to the anterior pyramid, passing also to the cerebel- lum, through the inferior cerebellar peduncle. The posterior group originate in the nuclei gracilis and cuneatus and pass directly forward and up- ward in the cerebellar peduncle of the same side to terminate in the cerebellum. All the arcuate fibers carry sensory impulses. The arcuate nucleus is a collection of nerve cells interposed in the anterior superficial arcuate fibers at a point just anterior to the pyramids of the medulla. SUMMARY OF TRACTS, THEIR ORIGIN AND TERMINA- TIONS. Columns. Origin of Axones. Terminations. I. Column of Goll • • • -j 1. Cells of dorsal ganglion. 2. Cells of posterior horn. I- Nucleus gracilis. 2. Column of Burdach . . 1. Same as column of Goll. I. Nucleus cuneatus. 3. Comma tract 1. Dorsal ganglion . . . 1. Cells of post. horn. 4. Lissaur's tract . . . . 1. Dorsal ganglion . . . I. Cells of post. horn. 5. Direct cerebellar . . . 1. Cells of col. of Clarke I. I. 2. Cerebellum. Cerebellum. Corp, quadrigemina. 6. Gowers's tract . . . . 1. Cells of post, horn . 3- 4- I 5- 1. Thalamus. Substantia nigra. Lenticular nucleus. 7. Lowenthal 1. Deiters' nucleus . . . Cells of ant. horn. 8. Lateral ground bundle. 1. Cells of cord I. Cells of cord. 9. Crossed pyramidal . . 1. Cerebral cortex . . . I. Cells of ant. horn. 10. Direct pyramidal . . . 1. Cerebral cortex . . . I. Cells of ant. horn. 11. Ant. ground bundle . . 1. Cells of cord .... I. Cells of cord. The sensory tracts are Nos. I, 2, 3, 4, 5, 6. The motor tracts are Nos. 7, 9, 10. The mixed tracts are Nos. 8,11. THE PONS. The pons represents the anterior basal portion of the hind-brain. It is an oval body, one inch long, one inch thick, and about one and one-half inches broad. It is a junctional piece between the medulla THE BRAIN. 393 and the mid-brain and the overlying cerebellum. The upper half of the fourth ventricle is confined to its dorsal aspect; that is, between the pons and the cerebellum. Viewed from the ventral surface it pre- sents the appearance of a rhomboid with striations that pass transversely and become constricted later- ally to form the middle peduncles of the cerebellum. Restijorm body. Nucleus of nerve VI. Floor of fourth ventricle. Descending root of nerve V. Arcuate fibers. Posterior longitudinal bundles. Nucleus of nerve VII- Ascending root of nerve Vil. Superior olive. Formatio reticularis. Median raphe. Middle peduncle of ■ cerebellum. Fillet. Trapezium. Nuclei pontis. ■ Pyramidal bundles. Transverse fibers oj pons. Fig. 273.-Cross section through the lower part of the pons. The fifth cranial nerve, with its large sensory root and its small motor root, is attached to the ventral aspect of the pons, nearer its upper than its lower border. The anterior pyramids seem to enter the pons from below, and emerge above the pons, where they become lost in the crura cerebri. In a transverse section the pons presents the fol- lowing parts: 394 NORMAL HISTOLOGY AND ORGANOGRAPHY. I. White matter. i. Transverse fibers-(a) superficial, (6) deep (trapezium). 2. Longitudinal fibers-(a) superficial (an- terior pyramids), (b) deep. 3. Posterior longitudinal bundle. 4. Fibers of fifth, sixth, seventh, and eighth cranial nerves. 5. Formatio reticularis. 6. Median raphe. 7. Fillet-mesial and lateral. II. Gray matter. 1. Nucleus pontis. 2. Superior olive. 3. Nuclei the origin of fifth, sixth, seventh, and eighth cranial nerves. Transverse Fibers.-The superficial and the deep- set of transverse fibers of the pons pass into the cere- bellum through the middle peduncle. Some of the fibers are commissural between the two halves of the cerebellum, while others connect with the nuclei pontis on the same side or the opposite side. In the lower portion of the pons, near the medulla, the deep- set are called the trapezium, on account of their trapezoid arrangement. Longitudinal Fibers.-The superficial set repre- sents mostly longitudinal bundles of the anterior pyramids that interlace the transverse fibers. The deep-set are near the dorsal aspect of the pons and comprise at least three groups: (1) the posterior longitudinal bundle near the median raphe in which THE BRAIN. 395 are found fibers from the antero-lateral column of the cord; (2) the lemniscus or fillet, a continuation of the sensory decussation; (3) the fasciculus teres, just dorsal to the posterior longitudinal bundle, and which contain fibers of the seventh cranial nerve. Fibers of the cranial nerves pass through the medulla from their nuclei in the dorsal portion to their various su- perficial exits on the ventral surface. The formatio re- ticularis is similar to that described in the medulla. The median raphe is also a continuation of that described in the medulla. Gray Matter of the Pons.-The nuclei pontis are nerve cells that are scattered among the superficial transverse fibers and are nodal points forming connections between the medulla, cerebellum, and higher brain centers. The superior olive lies in the formatio reticularis and is seen only in the lower portions of the pons. The nuclei of the cranial nerves are found in the dorsal aspect, most of them just beneath the floor of the fourth ventricle. Dendrite. Purkinje's cell. Large stel- late cell. Cells oj granular layer. Nerve- fiber layer. Fig. 274.-Section through the hu- man cerebellar cortex vertical to the sur- face of the convolution. Treatment with Muller's fluid (Bohm and Davidoff). 396 NORMAL HISTOLOGY AND ORGANOGRAPHY. THE CEREBELLUM. The cerebellum is next in size to the cerebrum and overlies the fourth ventricle. It is characterized by transverse curved sulci which divide it into lamellae, giving the organ a foliate appearance. A cross sec- tion of the lamellae shows a central core of white matter with a gray cortex, giving the section the appearance of a branching tree, hence the name arbor Ditce. A section taken in this plane presents the following layers: i. Molecular layer-on the outside. (i) Small cortical cells. (2) Stellate cells. (3) Cells of Purkinje. 2. Granular layer. (1) Granular cells. (2) Large stellate cells. 3. Medullary substance-core of nerve fibers. (1) Centrifugal neuraxes from Purkinje cells. (2) Centripetal neuraxes. (a) Mossy fibers. (6) Climbing fibers. (3) A few ganglion cells forming the central gray nucleus. Molecular Layer.-The small cortical cells are found in all parts of this layer, but more especially near its periphery. They are multipolar cells and but little is known of the distribution of their neu- raxes. The stellate cells are evenly distributed, and of particular interest are their neuraxes. The latter pos- sess two types of collaterals. One set forms branches among the cortical cells, while a second class branches Large stellate cell. Neuraxis of cell of granular layer. Fig. 275.-Schematic diagram of the cerebellar cortex: A, by ordinary nuclear staining (omitting the layer of Purkinje's cells); B, vertical to the surface of the convolution; C, longitudinal section through the convolution; B and C, by the chrome-silver method (Bohm and Davidoff). Stellate cell. Tolodendrion of collateral of climbing fiber. Climbing fiber. B Neuraxis of cell of granular layer. Cell of granular layer. Moss fiber. 4 Neuraxis of Purkinje's cell. Stellate cell. Molecular layer. Granular layer. Medullary layer 397 398 NORMAL HISTOLOGY AND ORGANOGRAPHY. at a level with the Purkinje cells, where it forms a basket-like net around the bodies of these cells. The cells of Purkinje are the largest nerve cells in the body (about 60// in diameter or seven times the diameter of a red blood-corpuscle). They form a single row of cells, placed with considerable regularity some distance apart, along the inner margin of the molec- ular layer. Their neuraxes arise from the basal end of the cell body and extend through the granular layer and enter the medulla as the centripetal fibers. The other extremity of the cell body passes into one or more prominent dendrites that arise toward the Dendrite. Cell body. Neuraxis. Fig. 276.-Cell of Purkinje from the human cerebellar cortex. Chrome- silver method (Bohm and Davidoff). periphery of the cerebellum. These dendrites branch freely in one plane, like an ivy growing against the wall, and this plane is always at right THE BRAIN. 399 angles to the lamellae of the cerebellum, and therefore sections of the cerebellum should be made in this plane. Granular Layer.-This layer is densely packed with nerve cells of two varieties. The granular cells are most numerous, small, and have only a few dendrites that end in hook-like telodendria. The neuraxes from these cells pass vertically into the molecular layer, where many of them form a T- shaped division, the two end branches passing par- allel with the laminae and therefore into a plane vertical to that of the den- drites of the Purkinje cells. Large stellate cells form the second variety of this layer. They are few in number and lie close to the mo- lecular. Their dendrites branch in all directions and their neuraxes form telo- dendria among the granu- lar cells. The medullary substance may be divided into centri- petal fibers,-those that carry nerve impulses toward the granular and molecular layers, and centrifugal fibers; those that carry impulses in the opposite direction. The latter are the neuraxes of the cells of Purkinje. The centripetal fibers are the mossy fibers, that form mossy telodendria in the granular layer, and also so- called climbing fibers that pass through the granular Neuraxis. Claw-like teloden- drion oj dendrite. Fig. 277.-Granular cell from the granular layer of the human cerebellar cortex. Chrome-silver method (Bohm and David off). Layer of small pyramidal cells. Layer of large pyramidal cells. Layer of polym- orphous cells. Fig. 278.-Portions of vertical section of human cerebral cortex, treated by the Golgi method. The figure shows the arrangement of the different cells of the cerebral cortex (Sobotta). 400 The brain. 401 layer and connect with the dendrites of Purkinje cells, up which they seem to climb. Collaterals are given off in their passage through the granular layer. The central gray nucleus forms the central core of each lateral cerebellar hemisphere. It forms a cap- sule of gray matter from whose hilum many nerve fibers pass, the majority to enter the superior cerebel- lar peduncle. The cerebrum is such an extensive and complicated organ that only a description of the cortex in the region of the fissure of Rolando will be given here. From without inward this region presents, rather indistinctly, the following layers: (i) molecular layer; (2) small pyramidal cells; (3) large pyr- amidal cells; (4) polymorphic cells; (5) medullary substance of nerve fibers. It is to be borne in mind that this cortex presents many fissures and minor folds into which the pia dips, and that a transverse section is any plane that is vertical to the folded surface. 1. The molecular or outer layer is composed chiefly of nerve fibers which interlace in all directions but which have chiefly a direction parallel to the external surface. The chief dendrite of the pyramidal cells terminates in this layer in tuft-like telodendria, and also ascending neuraxes, mostly from the polymor- phous cells. The cells of this layer are few, and have been described as polygonal, spindle-shaped, and triangular, or stellate. Their neurons are nearly all confined to this layer, the axones of only a few reach down to the deeper layers. THE CEREBRAL CORTEX. 402 NORMAL HISTOLOGY AND ORGANOGRAPHY. 2. The layer of small pyramidal cells is not well defined and usually not so broad as the molecular layer. The nerve cells have a triangular body, the apex being directed toward the surface of the cortex. From this apex a primordial dendrite ascends and Brush-like telodendrion.^ Main dendrite. Secondary dendrite. Basal dendrite.' Neuraxis with collaterals- Fig. 279.-Large pyramidal cells from the human cerebral cortex. Chrome-silver method (Bohm and Davidoff). gives off a number of branches that end in terminal filaments or telodendria in the outer layer, frequently at the brain surface. Several short dendrites arise THE BRAIN. 403 from the basal surface of the cell body where also the axone is attached. The latter passes toward the medullary substance, and near the cell body is pro- vided with col- laterals that connect with adjacent neu- rons. The layer of large pyramidal cells comprises a broad area. The cells meas- ure 20 fl tO 30/Z in diameter, be- ing twice as large as those of the preced- ing layer. In all other re- spects the cells of this layer re- semble 'the small pyram- idal cells. Their dendrites and axones also occupy the same relation as those of the preceding layer. 4. The layer of polymorphic cells usually includes Fig. 280.-Schematic diagram of the cerebral cortex: a, Molecular layer with superficial (tan- gential) fibers; b, striation of Bechtereff-Kaes; c, layer of small pyramidal cells; d, stripe of Baillarger; e, radial bundles of the medullary, substance; f, layer of polymorphous cells (Bohm and Davidoff). 404 NORMAL HISTOLOGY AND ORGANOGRAPHY. a few large pyramidal cells, and it is not well defined from the preceding layer. There is present in this layer: (i) multipolar cells with short neuraxes (Golgi cells) whose dendrites project in all directions; and (2) cells with slightly branched dendrites and with neuraxes passing toward the surface of the brain where they terminate in the molecular outer layer. The cells of this layer are triangular or spindle-shaped and vary considerably in size. 5. The medullary substance is composed of a mass of nerve fibers that take a radial course and in which we can detect no structural difference. Physio- logically, however, we can divide them into four classes as follows: 1, projecting or centrifugal fibers which indirectly connect the cerebral elements with the periphery of the body; that is, they carry im- pulses away from the nerve center; 2, commissural fibers that connect corresponding parts of the two cerebral hemispheres through the corpus callosum; 3, association fibers that connect different parts of the same hemisphere; 4, centripetal fibers or terminal fibers,-those that come from cell bodies in the same or the opposite hemisphere, or in some more distant nerve center, and that ultimately arborize about nerve elements in the cerebral cortex. In a strict sense the second and the third class fall under either the centrifugal or the centripetal group. The neuroglia tissue represents a special form of supporting elements found exclusively in the central nervous system and in the retina. It develops from THE NEUROGLIA. THE BRAIN. 405 the ectoderm while all other supporting tissues are derived from the mesoderm. The development of neuroglia cells is closely associated with the origin of neurons, as both are derived from epithelial cells that lie primarily near the central canal of the nervous system. The embryonic neuroglia cells are called spongioblasts, while those that develop into true nerve elements are called neuroblasts. Both kinds pass out very early and per- manently lodge in the gray matter. The neuroglia ele- ments appear as cells with many ra- diating, slender pro- cesses that are usu- ally unbranched, and because of their peculiar ap- pearance have been called spider cells or mossy cells, or astro- cytes. The cell bodies contain but very little protoplasm, and their shape is modi- fied according to their surroundings, being triangu- lar, or quadrangular, or polyangular, the protoplas- mic processes arising from their angles. According to the length of their processes attempts have been made to classify them as short-rayed astrocytes, pos- Fig. 281.-Neurogliar cells: a, from spinal cord of embryo cat; b, from brain of adult cat; stained in chrome-silver (Huber). 406 NORMAL HISTOLOGY AND ORGANOGRAPHY. sessing a few short processes, and long-rayed astro- cytes, having many long, slender processes. The former appear among the nerve cells only, the latter are found both in the gray and the white matter. Fig. 282.-Typical neuroglia cells, from cross section of the white mat- ter of the human spinal cord, stained after Benda's selective neuroglia tissue staining method (Huber, "Studies on Neuroglia Tissue," Vaughan Festschrijt, 1903). Not infrequently detached processes may be found and processes that can be traced directly through the bodies of adjacent astrocytes. The neuroglia thus forms a delicate web-like fabric that interlaces THE BRAIN. 407 the whole central nervous system, to which it gives substance and support. It is to be remembered that supporting tissue of mesodermic origin does the same thing, especially in the cord. The connective-tissue elements usually accompany the nutrient blood- vessels. BLOOD-VESSELS OF THE CENTRAL NERVOUS SYSTEM. The spinal cord receives its blood supply from a plexus of blood-vessels in the pia mater. There is an anterior median artery just in front of the anterior fissure. Some two hundred branches from this vessel pass at right angles directly into the fissure and enter the gray matter, where each divides into a right and left branch that enclose the central canal. Each arterial branch ultimately bifurcates, just in front and external to the cell column of Clarke, forming minute ascending and descending terminals, which become lost in an extensive capil- lary system of the central gray matter. The white matter receives its blood supply from a plexus of vessels situated on the dorsal and lateral surfaces of the cord. From this system small branches enter the cord anywhere and form capillaries among the nerve fibres; that is, supplies blood to the white matter. The gray matter has a more liberal blood supply than the white matter. The brain substance also receives its blood supply from a plexus of blood-vessels in its pia. The capil- laries are particularly numerous and closely meshed wherever the nerve cells are segregated, that is, in the ganglion centers. In the cerebellum the gran- 408 NORMAL HISTOLOGY AND ORGANOGRAPHY. ular layer is the most vascular. The arterioles have thin walls, and in old age may become brittle and may easily rupture. No lymphatic vessels with definite walls have been discovered in the central nervous system. The blood-vessels are, however, surrounded by peri- vascular spaces which probably function as lymph channels CHAPTER XIV. THE EYE. The eyes begin to develop during the fourth week of embryonic life, and appear then as a pair of lateral evaginations of the fore-brain. A pair of vesicles are thus formed called the primary optic 'vesicles. When the latter reach the ectoderm an invagination of these vesicles takes place, like pushing in one side of a hollow rubber ball. The cavity of the primary optic vesicle becomes obliterated by this process, and a new vesicle forms, called the secondary optic vesicle. It will be observed that the cavity of this vesicle is practically the same as would be pro- duced by an invagination of the brain wall. Later it will be seen that this cavity corresponds to the space occupied by the vitreous humor of the adult eye, while its wall becomes the retina. The stalk that connects this vesicle to the brain is the optic stalk, in which later optic nerve fibers appear. At the time the secondary optic vesicle is forming there is a disc-like thickening of the adjacent ecto- derm, which soon invaginates and becomes con- stricted as an ectodermal vesicle. This is the lens, which later takes a position at the mouth of the secondary optic vesicle. The latter presents, at this stage, a fissure in its ventral surface called the cho- roid fissure. Connective-tissue cells migrate through 409 410 NORMAL HISTOLOGY AND ORGANOGRAPHY. this fissure and fill the cavity of the secondary vesicle. Fig. 283.-Part of a section through the head of an early human embryo, showing the connection of the primary optic vesicles with the fore-brain (His): olj, Olfactory area of epiblast; ch., part of fore-brain which gives rise to cerebral hemispheres; th, thalamencephalon; p.o.v., primary optic vesicles. Fig. 284.-Three successive stages of development of the eye, showing formation of secondary optic cup and crystalline lens in human embryos of 4 mm. (/I), 6 mm. (B), and 8 mm. (C) (Tourneux): a, a, primitive optic vesicles; b, external layer of secondary optic cup (future pigment layer of retina); c, inner layer of cup (retina proper); d, lens pit (thick- ened and depressed ectoderm); e, lens vesicle. These cells form the 'vitreous humor, while the choroid THE EYE. 411 fissure closes and permanently disappears. The ex- ternal coats of the eye-that is, the sclera and the choroid-develop from the surrounding connective tissue. Fig. 285.-Plastic representation of the optic cup with lens and vitre- ous body (Hertwig): ab, Outer wall of the cup; ib, its inner wall; h, cavity between the two walls, which later disappears entirely; Sn, fun- dament of the optic nerve (stalk of the optic vesicle with a furrow on its lower surface); aus, optic (choroid) fissure; gl, vitreous body; I, lens. The parts of the adult eyeball may be tabulated as follows: I. Tunica externa. i. Sclera. 2. Cornea. II. Tunica media. i. Choroid coat. 2. Ciliary body. 3. Iris. III. Tunica Interna. 1. Retina. 2. Pigment membrane. The refracting media, or transparent media of the eye traversed by a ray of light, are: . 1. The cornea. 412 normal histology and organography. 2. Aqueous humor. 3. Lens. 4. Vitreous humor. i. The sclera is a dense connective-tissue covering of the eye that terminates anteriorly in the cornea. It is of interest to note that, in birds of prey, horny plates develop in the sclera for the better protection TUNICA EXTERNA. Canal of Schlemm. Tunica externa. Tunica media. Iris.' T unica interna. V itreous humor. Cornea. Macula lutea. Aqueous humor. Blind spot. Lash. Optic nerve. Iris. • Ciliary body. Ora serrata. Fig. 286.-Diagram of the eye. of the eye. Posteriorly the sclera is perforated by the entrance of the optic nerve. Connective-tissue fibers, known as the lamina cribrosa, pass across this point and interlace the optic fibers, while others sweep backward along the optic nerve as its external envelope. The sclera consists of interlacing bundles of con- THE EYE. 413 nective-tissue fibers closely felted together. The tendons of the ocular muscles are continuous with the scleral fibers. The external scleral surface is clothed with a layer of flattened endothelial cells which belong to the capsule of Tenon. The latter is a loose connective-tissue fabric that invests the eye- ball, and is so intimately connected with the eye muscles that coordinate movement of the arti- ficial eye, or glass shell, is made possible after the enucleation of an eye. Pigmentation is regularly present at the corneal margin and the surface next to the choroid. This inner pigmented scleral sur- face is lined by a layer of flattened endothelial cells, forming a sepa- rate membrane and called by some the lam- ina fusca; generally, however, it is regarded as the outermost layer of the choroid and known as the lamina chowidea. 2. The Cornea.-The cornea is inserted into the sclerocorneal junction in which is found an annular venous sinus, the canal of Schlemm, which may ap- pear as a single canal or as several canals. The cornea is a perfectly transparent medium and free Corneal epithelium. .4' terior elas- ie membrane. Substantia propria. Posterior elas- tic membrane. Endothelium. Fig. 287.-Section of the cornea of the eye. 414 NORMAL HISTOLOGY AND ORGANOGRAPHY.. from red blood corpuscles, the nearest blood supply being that of the sclerocorneal margin in the region of the canal of Schlemm. Histologically the cornea is made up of five layers: i, the anterior epithelium; 2, the anterior elastic membrane, or Bowman's membrane; 3, the ground substance, or substantia propria; 4, Descemet's membrane; 5, the endothelium of Descemet's membrane. The corneal epithelium is of the stratified squamous variety, a little thicker near the corneal margin than at its center and in the human eye is composed of five layers of cells. It is related to the epidermis of the skin, the cells being provided with short prickles that are very difficult to demonstrate. This epithe- lium forms an efficient and important protection to the front of the eye. The anterior elastic membrane measures 8 // in thickness, about the width of a red blood corpuscle, and becomes thinner towards the sclerocorneal junction. It is a compact layer of con- nective-tissue fibrils and is regarded by some as a basement membrane to the overlying epithelium. Nerve fibers penetrate this membrane to connect with the corneal epithelial cells. The substantia propria constitutes the bulk of the cornea. It con- sists of bundles and lamellae of connective-tissue fibrils, and peculiarly flattened cells called corneal corpuscles. The fibrils of each lamella are cemented together and run parallel to each other and to the corneal surface, but so arranged that those of ad- jacent lamellae cross at an angle of about twelve degrees. The lamellae are also cemented to each other. The THE EYE. 415 corneal cells have irregular processes and lie in special cavities called corneal spaces, in which are also found a varying number of leucocytes. These spaces seem to be part of a complicated lymphatic system, and communicate with each other by means of a complex system of canals. While blood does not irrigate the cornea, lymph does, freely and extensively. The posterior elastic or Descemet's membrane resembles the Lymph canaliculi. Corneal space. Fig. 288.-Corneal spaces of a dog (Bohm and Davidoff). anterior elastic membrane, and may be separated into shreds of fine, elastic, connective-tissue fibrils. The endothelium of Descemet's membrane is com- posed of low, hexagonal cells forming a single layer. It will be found that Descemet's membrane with its investing endothelium is reflected to form the an- terior layer of the iris, enclosing therefor the anterior portion of the aqueous chamber. 416 NORMAL HISTOLOGY AND ORGANOGRAPHY. 1. The Choroid Coat.-The choroid is the vascular tunic of the eye, and may be divided into four layers. From without inward these are named: 1, lamina suprachoroidea; 2, lamina vasculosa Halleri; 3, lamina choriocapillaris; 4, glassy layer, or vitreous membrane. This entire tunic is derived from the TUNICA MEDIA. Sclera. Lamina supra- choroidea. La mina vascu- losa Halleri. Lamina chorio- capillaris. Glassy layer. Fig. 289.-Section through the human choroid (Bohm and Davidoff). mesoderm and is largely composed of connective- tissue elements. The Lamina Suprachoroidea.-This layer is closely applied to the sclera, and is composed of a loose fabric of areolar tissue in whose meshes are con- nective-tissue cells and lymph spaces lined with endothelium, known as perichordeal lymph spaces. THE EYE. 417 Pigment cells are also present. The lamina vascu- losa is the broadest layer and is also composed of areolar tissue. The blood-vessels constitute its principal portion, and they are so distributed that the larger ones, the veins, occupy its outer portions. The lamina choriocapillaris consists chiefly of capil- Anterior epithelium. Lens. Iris. . Pars ciliaris iridical. Canal of Petit. Cornea. Processus ciliares. Canal of Schlemm. ' Ciliary muscle. Pars ciliares retime. Ora serrata. Conjunctiva. Fig. 290.-Section through the ciliary body. lary vessels that are particularly abundant in the region of the macula lutea, or yellow spot of the retina. In other respects this layer resembles the lamina suprachoroidea, except that pigment cells are absent. The glassy or vitreous membrane is but 2 g. thick, homogeneous, clothes the inner choroid 418 NORMAL HISTOLOGY AND ORGANOGRAPHY. surface, and also forms a lining membrane against which the pigment cells of the retina are applied. 2. The Ciliary Body.-The ciliary body is that por- tion of the tunica media extending between the ora serrata of the retina and the base of the iris. On the inner surface of this body there are about seventy meridional folds called the ciliary processes. Second- ary folds and processes appear on and between the primary folds, while the whole surface is clothed with two rows of epithelial cells, the pars ciliaris retince. Of these the outer layer is deeply pig- mented and represents the outer layer of the second- ary optic vesicle, while the inner layer is non- pigmented and develops from the inner layer of the optic vesicle. The greater bulk of the ciliary body is made up of smooth muscle tissue called the ciliary muscle, or muscle of accommodation. This muscle may be divided into three portions. The outer por- tion is made up of meridional fibers. The middle division of radial fibers have their origin near the canal of Schlemm, from which they spread out like a fan. The inner portion is near the base of the iris and the fibers are circular. The combined action of these fibers is to pull the choroid coat forward and inward and thus slacken the tension on the suspen- sory ligament of the lens, as this ligament joins with the epithelial cells of the ciliary body as well as with the hyaloid membrane that encloses the vitreous humor. Under this condition the lens becomes more convex and the eye is focused to near objects. 3. The Iris.-The iris is a pigmented circular cur- tain that occludes the rays of light from the periphery THE EYE. 419 of the lens. The circular opening in the iris is the pupil. Three layers may be recognized in the iris, enumerated from before backward, as follows: 1 anterior endothelium; 2, stroma with sphincter muscle; 3, pigment epithelium, or pars iridica retinae. The anterior endothelium is a single layer of cells that is continuous with the posterior endothelium of the cornea. The stroma forms the bulk of the iris and is very vascular and muscular. Large pigment cells are present and a fine reticular tissue. Smooth muscle fibers, the sphincter muscle of the pupil, encircle the pupil. Along the posterior surface radial fibers probably function as a dilator muscle of the pupil. The posterior epithelium, or pars iridica ciliaris, is a direct continuation of the pars ciliaris retinae and extends to the margin of the pupil. It is composed of two layers of cells and both, in this case, are pigmented. TUNICA INTERNA. The inner tunic is the retina of the eye, which may be divided into ten layers, named from within out- ward as follows: i. Internal limiting membrane. 2. Layer of nerve fibers. 3. Ganglion cell layer. 4. Inner molecular layer. 5. Inner nuclear layer. 6. Outer molecular layer. 7. Outer nuclear layer. 8. External limiting membrane. 9. Rods and cones. 10. Pigment layer. 420 NORMAL HISTOLOGY AND ORGANOGRAPHY. (1) The internal limiting membrane is a very deli- cate homogeneous layer formed by lateral expansions of processes of neuroglia elements. It is closely ap- plied to (2) the optic nerve fibers. The latter are non- medullated and radiate toward the entrance of the op- tic nerve, composed of both centrifugal and centrip- etal axones. The latter arise from (3) the ganglionic cells, that are irregularly distributed along the inner Internal limiting membrane. Layer oj nerve fibers. Ganglion cell layer. Inner molecular layer. Inner nuclear layer. Outer molecular layer. Outer nuclear layer. External limiting membrane Rods and cones. Pigment layer. Fig. 291.-Section of retina of the eye. border of the retina. These cells are large, multi- polar, and their dendrites extend outward and con- tribute to the substance of (4) the inner molecular layer. The latter is a network of neuroglia fibrils and nerve processes, contributed in part by the cells of (5) the inner nuclear layer. This layer is com- posed of several rows of nucleated cells of which some are sustentacular, or neuroglia elements, some bi- polar ganglion cells, and others multipolar ganglion the eye. 421 cells situated in the outer region of this layer and expanding in a horizontal direction. (6) The outer molecular layer, like the inner molecular, is a net- work of fibrils, processes from all the ganglion cells of the retina and also neuroglia elements. The ex- ternal portion of this molecular layer is not so densely packed with fibrils and has been called Henle's fiber layer. (7) The outer nuclear layer is composed of many compact rows of nuclei and is the most con- spicuous layer in stained sections of the retina. The cell bodies enclosing most of these nuclei are the visual units of the eye and are called rod-visual and cone-visual cells, as the rods and cones are merely processes of these cells. The cells are elongated units whose long axis is placed radial to the eye, and whose multiple processes enter the outer molecular layer as already mentioned. The cone-visual cells are least numerous and their nuclei are placed at regular intervals in the outer portion of the layer. Their nuclei are somewhat larger than the nuclei of the other cells. Rod-like neuroglia elements give sup- port to the visual cells. (8) The external limiting membrane invests the outer nuclear layer. It is a thin, transparent, homogeneous membrane, derived from the neuroglia tissue, and forming a dividing line between the rods and cones and the outer nuclear layer. (9) The rods and cones are processes from the visual cells whose nuclei form the bulk of the outer nuclear layer. The rods are 40 // to 50 // in length, and consist of two segments, the outer being doubly refractive to light, and may be separated into numer- ous transverse discs by the action of certain reagents. 422 NORMAL HISTOLOGY AND ORGANOGRAPHY. The inner segment shows a superficial longitudinal striation, due to impressions from fiber baskets of the neuroglia network. The cone is 15 // to 25 long and its inner segment considerably broader than the rod. The rods are more numerous than the cones, three or four of the former intervening between two of the latter. (10) The pigment layer forms a com- pact background to the rods and cones. It consists of hexagonal cells that contain black pigment gran- ules. The inner surfaces of these cells possess thread- like filaments that interlace between the rods and cones. The nuclei of these cells lie in the outer ends of these cells, the so-called basal plates, and are not pigmented. The granules are mobile and their dis- tribution in the cells varies according to the illumi- nation of the retina. In strong light the pigment is evenly distributed throughout the cytoplasm, while in weak light it is collected at the outer portion of each cell. This single row of pigment cells represents the outer layer of the primary optic vesicle, while the other nine layers of the retina develop from the inner layer of this vesicle. The neuroglia elements of the retina differ from those of the brain in that they form radial sustentac- ular fibers, called fibers of Muller, which penetrate the retina to the rods and cones. Each fiber repre- sents a modified epithelial cell which terminates in basal plates, the latter forming the limiting mem- branes of the retina. The end plates that form the external limiting membrane give off externally short, inflexible fibrils, which form fiber-baskets enclosing the basilar portions of the rods and cones. The THE EYE. 423 bodies of Muller's fibers are very plastic and adjust Centrifugal nerve fiber. Nucleus oj a Muller's fiber. Impressions or. Mul- ler's fiber oj elements oj outer nuclear layer. Fiber basket oj M tiller's fiber. Fig. 292.-Schematic diagram of the retina according to Ramon y Cajal: The line a, after pass- ing through a Muller's fiber, crosses a bipolar rod cell, then two bipolar cone cells, and finally ends in the body of a bipolar cone cell (Bohm and Davidoff). Bipolar cone cell. Bipolar cell. Dijjuse spongioblast. Large horizontal cell. Spongioblast. Cone. . ft* Nerve fiber layer. Ganglion cell layer. Inner molecular layer. Nucleus oj a Muller's fiber. Inner nuclear layer. Spongioblast. Outer molecular layer. V 8 5 j- © $ Outer nuclear layer. themselves to the pressure exerted by the various 424 NORMAL HISTOLOGY AND ORGANOGRAPHY. elements that constitute the different layers of the retina through which they pass. In certain areas of the retina there are peculiar- ities that differ from the above description. These areas are: (i) the macula lutea, or yellow spot; (2) the optic papilla, or blind spot; (3) the ora ser- rata; (4) the pars ciliaris retinae; (5) the pars iridica retinae. 1. The macula lutea, or yellow spot, is a crater- like area of the retina that lies in the visual axis of Layer of nerve fibers. Fovea centralis. Ganglion cell layer. Inner molecu- lar layer. Inner nuclear layer. Outer molecu- lar layer. Outer fibrous layer. Outer nuclear layer. Cones. Fig. 293.-Section through human macula lutea and fovea centralis. As a result of treatment with certain reagents, the fovea centralis is deeper and the margin more precipitous than during life (Bohm and Davidoff). the eye. The central depression is called the jcrvea centralis. Its margin is somewhat thickened and presents all the layers of the retina, while in the fovea the layers are practically reduced to the cone-visual elements. From this center the cell bodies of the cones radiate in curves to reach the outer molecular layer, which gives rise to obliquely directed fibers known as Henle's fiber layer. The macula lutea is the most sensitive spot in the retina and derives its The Eye. 425 name from the yellow pigment held in solution within the cell layers. 2. The optic papilla, or blind spot, is the point of entrance of the optic nerve. It is found a little to the nasal side of the macula lutea. From the center of this papilla the nerve fibers spread out radially to supply the various parts of the retina. The optic fibers lose their medullary sheaths in their passage through the sclera and the choroid, so that the optic nerve at this point becomes suddenly thinner. Be- Physiologic excavation. Blood-vessels. Layer o] nerve fibers-. Inner molecular layer.; Inner nuclear layer- Outer molecular layer. Outer nuclear layer Rods and cones. Pigment layer. Sclera.. Lamina cribrosa. ■ Fig. 294.-Section through point of entrance of human optic nerve (Bohm and Davidoff). cause of this and the fact that the fibers curve radi- ally, there is produced a deep circular depression in this region. At this point the retina is absent, the choroid coat is interrupted, while connective-tissue fibers of the sclera, called the lamina cribrosa, inter- lace and cross the optic fibers. 3. The ora serr ata is that portion of the retina that marks the posterior limit of the ciliary body. At this point there is a rapid diminution of the retinal layers until but two rows of cells remain, the outer one pigmented. The optic fibers and visual cells 426 NORMAL HISTOLOGY AND ORGANOGRAPHY. disappear first. Then the outer molecular layer is lost, so that the nuclear layers become confluent. Ultimately but two rows of cells remain, which are continued over the ciliary body as the pars ciliaris retinae, already mentioned in the description of the ciliary body. The ora serrata forms a zigzag line which marks the posterior border of the ciliary folds. The iridica retinae has already been described in connection with the description of the iris. REFRACTING MEDIA. The refracting media of the eye are the cornea, aqueous humor, lens, and the vitreous humor. The cornea is described on another page. i. The aqueous humor is a structureless fluid re- sembling lymph that fills the chamber of the eye in front of the lens. The iris is suspended in this fluid and divides the chamber into an anterior and a posterior compartment. The fluid is largely a se- cretion from epithelial cells, or, according to some, from epithelial glands said to be located in the region of the ciliary body. The aqueous humor is re- placed if accidentally lost. 2. The Lens.-The origin of the lens has already been described as an ectodermal invagination in the form of a vesicle. The cells of the posterior wall of this vesicle form the bulk of the lens. These cells become long and slender and are known as the lens fibers, while the cells of the anterior wall remain low and cubical and form the anterior epithelium of the lens. Surrounding the lens on all sides is the lens capsule. This capsule is a homogeneous membrane, THE EYE. 427 thicker on the anterior surface of the lens than on the posterior, and with certain reagents appears to be made up of lamellae. The latter connect with fibers of the suspensory ligament. In adults the anterior epithelium forms a single layer of flattened or cubical cells which extend as far A nlerior capsule. Anterior epitheliuni. Lens fibers. Fig. 295.-Crystalline lens: A, longitudinal fibers; B, posterior surface view of anterior epithelium (Leroy). as the equatorial margin of the lens. At this mar- gin the cells increase in height to form the lens fibers. These are flattened hexagonal prisms, thickened at the posterior ends. They pass in a meridional direc- tion from the anterior surface backward, and are 428 NORMAL HISTOLOGY AND ORGANOGRAPHY. held together by a small amount of cement sub' stance. The suspensory ligament connects the capsule of the lens with the epithelium of the ciliary body and the hyaloid membrane of the vitreous humor. From this point the fibers pass forward and inward to be- come inserted into the capsule of the lens. The in- sertion occupies a wide zone at the equator of the lens, which reaches some distance on the anterior and posterior surfaces. Between these fibers there is consequently a canal around the lens, divided by septa, the canal of Petit, which communicates by minute openings with the anterior chamber. 3. The vitreous humor fills the chamber of the eye back of the lens. It is a transparent tissue that contains about 98 per cent, of fluid substance and fine interlacing fibers, as well as a few connective- tissue cells and leucocytes. Toward the surface the fibers are more densely arranged, forming the hyaloid membrane which encloses the entire vitreous body. The origin of the vitreous humor has been described in connection with the developmental history of the eye. BLOOD-VESSELS OF THE EYE. The arteries of the choroid are derived from the short posterior ciliary, the long ciliary, and the an- terior ciliary arteries. The short posterior penetrate the sclera in the vicinity of the optic nerve, and supply blood to the choroid of that region. These arteries also anastomose with branches from the retinal vessels. The long posterior ciliary penetrates THE EYE. 429 the sclera near the optic nerve, and course forward between the choroid and the sclera to the ciliary body. It supplies blood to the ciliary muscles, the ciliary processes, and the iris. The anterior ciliary arteries lie close to the straight ocular muscles and penetrate the sclera near the sclerocorneal junction. They give off branches to the iris and the ciliary body, anastomosing with branches from the long posterior ciliary artery. Veins return the blood from these regions and bear the same names as the arteries they accompany. Sclera.- Ocular muscle. Choroid. Conjunc. cul-de-sac. Ciliary muscle. Iris.. ■ Retina. Ant. chamber and aqueous humor. Crystalline lens. Optic nerve with central retinal artery. A ngle oj ant. chamber. Posterior chamber.. Suspensory ligament o] the lens. Ocular muscle. Fig. 296.-Vertical section through the eyeball and lids (Pyle). Cornea. Vitreous chamber. The retina is supplied with blood from a central artery and vein that enter and leave the retina at the optic papilla, or blind spot. Each divides into a superior and inferior papillary artery and vein. The latter again divide into two branches, making in all four arteries and four veins known according to their position as superior and inferior nasal, and superior and inferior temporal vessels. Within the retina 430 NORMAL HISTOLOGY AND ORGANOGRAPHY. itself a coarse plexus of vessels blends with the nerve fiber layer. This connects with a fine network lying Non-strialed muscle fibers of the tarsal muscle and tendon oj the levator palpebrce superioris. Lymph node of the con- junctiva palpebrce. Accessory lacrimal gland. M. orbicu- laris pal- pebrarum. Tarsus. Meibomian gland. Arterial ar- cus tarseus. Excretory duct of Meibomian gland. Ciliary gland (Moll). Ciliary gland (Moll). Ciliary muscle of Riolani. Cilia. Fig. 297.-Vertical section of the upper eyelid of man (Sobotta.) within the inner nuclear layer. The visual cell layer is non-vascular. The EyE. 431 The eyelids are two movable folds of the skin whose inner surface is covered by a mucous membrane, the conjunctiva. The skin on the outer surface is thin, movable, and presents fine hairs with small seba- ceous glands, and also a few sweat glands. At the lid margin papillae are developed and the epidermis is thickened. Along the outer bor- der there are two or three rows of large hairs, the eyelashes, the poste- rior row of which possesses seba- ceous glands and modified sweat glands, called the glands of Moll. The eyelids are further provided each with twenty-five to thirty large glands, known as Meibomian or tarsal glands, whose ducts open on the palpebral margin just in- ternal to the eyelashes. Each gland has a large central duct lined by stratified epithelium and into which numerous branched alveoli open. The latter resemble the al- veoli of sebaceous glands. The Meibomian glands lie close to the in- ternal surface of the eyelids and their cells undergo a fatty change and give out a fat-containing secre- tion. In each lid there exists a frame- Fig. 298.-Mei- bomian or tarsal gland, reconstructed after Born's wax- plate method (Hu ber). 432 NORMAL HISTOLOGY AND ORGANOGRAPHY. work of condensed fibrous tissue, which gives con- sistency and shape to the lid, and is termed the tar sal plate, or tarsus. The orbicularis oculi muscle lies, beneath the subcutaneous tissue of the outer surface and is composed of voluntary muscle fibers that arch between the angles of the eyelids. Fig. 299.-Lacrimal and Meibomian glands, the latter viewed from the posterior surface of the eyelids. (The conjunctiva of the upper lid has been partially dissected off, and is raised so as to show the Meibomian glands beneath.) I, Free border of upper, and 2, free border of lower lid, with openings of the Meibomian glands; 5, Meibomian glands exposed, and 6, as seen through conjunctiva; 7, 8, lacrimal gland; 9, its excretory- ducts, with 10, their openings in the conjunctival cul-de-sac; II, con- junctiva (Testut). The conjunctiva is a mucous membrane that lines the inner surface of the eyelids and is reflected over the front of the eye. Over the cornea it forms the anterior stratified epithelium, and has already been described. The line along which it is reflected on to the globe of the eye is called the fornix. The pal- THE EYE. 433 pebral portion adheres intimately to the tarsal plate and presents numerous papillae. It is covered by a layer of columnar cells beneath the bases of which are small flattened cells. Goblet cells are to be found among these cells. Over the globe of the eye it ad- heres closely to the sclera, and this portion of the conjunctiva is perfectly smooth and is composed of stratified squamous epithelium. The conjunctiva that clothes the eyelid is thinner than that which covers the cornea and any for- eign particle, therefore, tends to cling to the eyelid rather than to the eye. The Lacrimal Apparatus.- This consists of (i) the lacri- mal or tear gland, (2) the lac- rimal canals, and (3) lacrimal sac, or nasal duct. The lacrimal gland is a branched tubular gland situ- ated in the upper and outer part of the orbital cavity. Its structure resembles that of a serous gland. The ducts, which are numerous, are clothed with stratified epithelium and open on the conjunctival surface, over which the secretion is evenly distributed by the action of the eyelids. The lacrimal canals begin as two minute orifices at the apices of the papillae lacrimales situated near the inner canthus. They are lined by stratified epithelium and open directly into the lacrimal sac. The latter is lined with simple pseudostratified epi- Fig. 300.-1, Canalicu- lus; 2, lacrimal sac; 3, na- sal duct; 4, plica semilu- naris; 5, caruncula lacri malis (Leidy). 434 NORMAL HISTOLOGY AND ORGANOGRAPHY. thelium, having two strata of nuclei, and represents the upper expanded portion of the nasal duct. This duct has a similar epithelium and opens into the inferior meatus of the nose. Ciliated epithelium has been described as being present in the nasal duct, and also mucous glands in the lower parts. CHAPTER XV. THE ORGAN OF HEARING. The organ of hearing consists of three portions,- external, middle, and internal ear, the last being the essential part, as within this are the peripheral termi- nations of the auditory nerve. i. The External Ear.-The pinna or auricle pro- jects from the side of the head and is covered with a thin layer of skin, in which are found hairs, sebaceous glands, and sweat glands. A cartilage matrix of this portion is of the elastic variety with interposed areas of non-elastic cartilage. The lower lobe is free from cartilage and is composed of adipose tissue. The external auditory meatus is the passage leading inward from the concha as far as the tympanic mem- brane. Its average length is about one inch. This tube may be divided into an external cartilaginous portion and an internal osseous portion. The skin lining the cartilaginous portion is clothed with coarse hairs and possesses modified sweat glands called ceruminous glands. These are branched, of the tubulo-alveolar variety, and empty into hair fol- licles near the surface of the skin, or on the surface of the skin in the neighborhood of the hair follicles. The skin of the osseous portion is supplied with neither hair nor glands, but possesses slender papillae. 435 436 NORMAL HISTOLOGY AND ORGANOGRAPHY. At the bottom of the auditory canal is the tympanic membrane. It is an elliptical disc placed at an ob- lique angle to the ear canal, with its antero-inferior border most distant from the outer orifice. This membrane is composed of three layers, an external cutaneous, a middle fibrous, and an inner mucous. The external layer is continuous with the integu- mentary lining of the meatus and consists of a thin layer of cutis covered by epidermis. The middle layer, or membrana propria, consists of two sets of fibers,-external or radial fibers next to the integument, and internal or circular fibers next to the in- ner mucous lining. The circular fibers are numerous near the circumference but scattered and few in number near the center. In the upper and anterior margin of the membrane is a small triangular area that is thin and lax and is called the pars flaccida. The main portion of the membrane is, on the other hand, tightly stretched and termed the pars tensa. Both radial and circular fibers are absent from the pars flaccida. 2. The Middle Ear.-The middle ear, or tympanic cavity, is a small air chamber in the tympanic bone, intervening between the inner end of the external auditory meatus and the outer wall of the internal Fossa of helix. Helix. Anthelix. Fossa of anlhelix. Concha. Antilragus. Tragus. Lobule. Fig. 301.-External ear (Randall). THE ORGAN OF HEARING. 437 ear or labyrinth. It is lined by a mucous membrane and contains the bones of the ear, malleus, incus, and stapes. The mucous membrane is folded over these ossicles and has a pseudostratified ciliated epithe- lium, having two strata of nuclei. Cilia are, how- ever, absent on the surface of the auditory ossicles, their ligaments, and the tympanic membrane. The Fig. 302.-Semidiagrammatic section through the right ear: G, Exter- nal auditory meatus; T, membrana tympani; P, tympanic cavity; o, fenestra ovalis; r, fenestra rotunda; B, semicircular canal; 5, cochlea; Vt, scala vestibuli; Pt, scala tympani (Czermak.) tympanic cavity communicates with the mouth by a narrow canal, the Eustachian tube, which transmits air and conveys mucous secretion from the middle ear. This tube is about one and one-half inches in length and is directed downward and inward from the anterior part of the tympanum to open on the 438 NORMAL HISTOLOGY AND ORGANOGRAPHY. upper part of the nasopharynx by a wide orifice. Its anterior part, about one inch in length, is enclosed in cartilage, while its posterior portion is encased in bone. The mucous membrane is ciliated and glands are absent. 3. The Internal Ear.-The internal ear is the es- sential part of the organ of hearing and consists of a bony and a mem- branous labyrinth. The latter is contained within the former and represents the same general shape, the two being separated by a lymph space containing the perilymph. A se- ries of cavities constitute the bony labyrinth, which are named from before back- wards-cochlea, vestibule, and semicircular canals. The membranous labyrinth situated within these cavities consists of the membranous cochlea, utriculus, and sacculus, and membranous semicircular canals. (1) Vestibule, Utriculus, and Sacculus.-The vesti- bule forms the central portion of the bony labyrinth Fig. 303. - Otoscopic view of left membrana tympani : 1, Membrana flac- cida; 2, 2', folds bounding the former; 3, reflection from processus brevis of malleus; 4, processus longus of incus (occasionally seen); 5, membrana tym- pani; 6, umbo and end of manubrium; 7, pyramid of light (Morris). THE ORGAN OF HEARING. 439 and communicates behind with the bony semicircu- lar canals, and in front with the cochlea. Its outer wall forms the inner wall of the tympanic cavity, and in it is seen the fenestra ovalis, into which the foot of the stapes is adjusted. The posterior part of the vestibule receives five apertures that lead to the semicircular canals, while its anterior part leads by an elliptical opening into the scala vestibuli of the cochlea. Superior semicircular canal. A mpulla:. Horizontal semi- circular canal. Posterior semi circular canal. Fenestra. Ampulla. Bony cochlea. Vestibule. Fig. 304.-Right bony labyrinth, viewed from outer side: The figure represents the appearance produced by removing the petrous portion of the temporal bone down to the denser layer immediately surrounding the labyrinth (from Quain, after Sommering). Fenestra rotunda. The utriculus and sacculus are two sac-like struc- tures enclosed in the bony vestibule. The two are indirectly connected by the ductus endolymphaticus, which is a Y-shaped channel that terminates in a blind recess, the saccus endolymphaticus. The latter lies against the dura on the posterior surface of the temporal bone. The utriculus is larger than the sacculus and occu- 440 NORMAL HISTOLOGY AND ORGANOGRAPHY. pies the postero-superior portion of the bony vesti- bule. It communicates by five apertures with the membranous semicircular canals. Its wall is com- posed of fibrous tissue, lined internally with a single layer of columnar epithelium. The floor and an- terior wall is thickened to form the macula acustica utriculi, which is innervated by fibers of the auditory nerve. The epithelium of this region is composed .Macula acus- tica sacculi. .Utriculosac- cular canal. -Macula acus- tica utriculi. ■Ant. semicircular canal. Auditory nerve with its vestibu- lar and cochlear branches. .Sacculus. -Ampulla. ,Ampul!a. ,Utriculus. Post, semicircular canal. Cochlear duct. Canalis reuniens. Ductus endolymphaticus. Ampulla. Horizontal semicir- cular canal. Fig. 305.-Membranous labyrinth of the right ear from five-months hu- man embryo (from Schwalbe, after Retzius). of two kinds of cells: (i) slender sustentacular cells resting on a basement membrane, and (2) hair cells, or auditory cells. The latter support a number of stiff hairs and constitute the neuro-epithelium, around which arborize the neurons of the auditory nerve. Crystals of calcium carbonate, known as otoliths, are found on the surface of the epithelium. The sacculus occupies the lower portion and fore THE ORGAN OF HEARING. 441 part of the bony vestibule. It is oval in shape, smaller than the utriculus, its longest diameter measuring about 3 mm. From its lowest part a short canal, the duct of Hensen, opens into the ductus cochlearis. Anteriorly there is an oval, whitish thickening, the macula acustica sacculi, innervated by the neurons of the auditory nerve. The histology of the sacculus is like that of the utriculus. (2) Semicircular Canals.-There are three osseous canals situated behind and above the vestibule. The superior canal is vertical, the external is hori- zontal, and the posterior is vertical. They open into the vestibule by five apertures, since the inner ex- tremity of the superior and the upper extremity of the posterior join to form a common duct, the canalis communis. Each canal presents an en- largement or osseous ampulla near its origin with the vestibule. The membranous semicircular canals partly fill the bony canals, to which they conform. The peripheral border of each canal is fixed to the periosteum of the bony canals while the opposite part is free. Each canal is dilated in the bony ampulla to form a membranous ampulla. These canals com- municate with the utriculus and possess a fibrous wall clothed with simple pavement epithelium, ex- cepting in the ampullae, where it is columnar. In the latter slender sustentacular cells intervene between shorter neuro-epithelial cells, or hair cells, similar to those of the maculae. The neurons of the auditory nerve arborize around the bases of the hair cells. (3) The Bony and Membranous Cochlea.-The bony cochlea assumes the form of a short cone and con- 442 NORMAL HISTOLOGY AND ORGANOGRAPHY. sists of a spirally arranged tube which forms from two and one-half to two and three-quarter coils around a central pillar termed the modiolus. The length of this tube is about 30 mm. and its diameter, near the base of the cochlea, about 2 mm. The Menibrana vestibu- laris or Reissner's membrane. Ligamen- tum spirals. Membrana spiralis. Scala vestibuli. Cochlear duct. Spiral ganglion. Scala tympani. Osseous cochlear wall. Nervus cochlearis. Fig. 306.-Longitudinal section of the cochlea of a cat. This figure gives a general view of the cochlea. The cochlear duct is met with six times in the section (Sobotta). modiolus is about 3 mm. in height and transmits the nerve. A flat shelf of bone, the lamina spiralis, winds around the modiolus like the thread of a screw, and projects about half-way into the cochlear tube and thus incompletely divides this tube into two passages, of which the upper is named the scala vesti- THE ORGAN OF HEARING. 443 buli, and the lower the scala tympani. A mem- brane-the membrana basilaris-stretches from the free edge of the bony lamina spiralis to the outer wall of the cochlea and completes the scala vestibuli Fig. 307.-Section through one of the turns of the osseous and mem- branous cochlear ducts of the cochlea of a guinea-pig: I, Scala vestibuli; m, labium vestibulare of the limbus; n, sulcus spiralis internus; o, nerve fibers lying in the lamina spiralis; p, ganglion cells; q, blood-vessels; a, bone; b, Reissner's membrane; De, ductus cochlearis; d, Corti's mem- brane; /, prominentia spiralis; g, organ of Corti; h, ligamentum spirale; i, crista basilaris; k, scala tympani (Bohm and Davidoff). and the scala tympani, but the two communicate at the apex of the cochlea. The scala tympani begins at the fenestra rotunda, in the inner wall of the 444 NORMAL HISTOLOGY AND ORGANOGRAPHY. tympanum just below the fenestra ovalis, and the scala vestibuli leads to the perilymphatic space of the vestibule. The fenestra rotunda is closed by the tympanic membrane. From what has been stated it is evident that an injection into the scala tympani through the fora- men rotunda will pass into the scala vestibuli at the apex of the cochlea, and travel down the passage above the lamina spiralis to ultimately reach the perilymphatic space of the vestibule and exert press- ure against the base of the stapes through the fenes- tra ovalis. « The membranous cochlea (ductus cochlearis or scala media) forms a spiral canal inside the bony cochlea, and ends at the apex of the latter in a blind ex- tremity, the lagena. This scala media lies near the free margin of the lamina spiralis and just above the membrana basilaris. It thus forms a spiral tube that gradually increases in size from its lower to its upper or distal end. Its lower end communicates with the sacculus through the ductus reunions of Hensen. Triangular in transverse section it has a roof, called Reissner's membrane, which separates it from the scala vestibuli. Its outer wall is the peri- osteal lining of the bony cochlea, while its floor is the outer border of the lamina spiralis and the membrana basilaris. This membranous labyrinth is clothed throughout its whole length by a single layer of epithelial cells. Reissner's membrane consists of an exceedingly thin connective-tissue lamella lined on the vestibular side with a single layer of endothelial cells, and on the THE ORGAN OF HEARING. 445 cochlear duct by a single layer of flat epithelial cells. The outer wall of the scala media is the periosteal lining of the bony cochlea which is thickened and modified to form what is termed the ligamentum spirale cochlea. The ligament has a projection, the crista basilaris, to which the outer edge of the mem- brana basilaris is attached. The inner surface of Fig. 308.-Organ of Corti: At x the tectorial membrane is raised; c, outer sustentacular cells; d, outer auditory cells; /, outer pillar cells; g, tectorial membrane; h, inner sustentacular cells; i,p, epithelium of the sulcus spiralis internus; k, labium vestibulare; e, tympanic investing layer; m, outer auditory cells; n, n, nerve fibers which extend through the tunnel of Corti; o, inner pillar cell; q, nerve fibers; b, b, basilar mem- brane; a, epithelium of the sulcus spiralis externus; r, cells of Hensen; s, inner auditory cell; I, ligamentum spirale (after Retzius). this wall is clothed with simple epithelium of the columnar type, which in places appears to be strat- ified and to possess darkly granulated cells. On the floor of the scala media and resting on the basilar membrane is the complicated structure termed the organ of Corti. This consists of the fol- lowing structures: (i) Corti's rods or pillars; (2) 446 NORMAL, HISTOLOGY AND ORGANOGRAPHY. hair cells (inner and outer); (3) supporting cells of Deiters; (4) the cells of Hensen and Claudius; (5) the lamina reticularis, and (6) a cuticular membrane, the membrana tectoria. 1. The rods of Corti form two rows, an inner and an outer. The bases of the two rows are planted on the membrana basilaris, some little distance apart, and the outer ends come in contact so that between the two rows above and the basilar membrane below there is enclosed a triangular tunnel, the tunnel of Corti. This tunnel increases both in height and width toward the apex of the cochlea. The inner rods number nearly six thousand. The outer rods number about four thousand, and are longer than the inner. They are also more inclined toward the bas- ilar membrane and form with it an angle of about forty degrees. 2. The hair cells are placed on each side of the rods and thus form an inner and an outer set. The inner hair cells form a single row and number about three thousand five hundred, so that each cell is sup- ported by a little more than one rod. Their free ex- tremities are surmounted by about twenty fine hair- like processes arranged in the form of a crescent. Each cell is oval and contains a large nucleus. The lower end is rounded and reaches about half-way down the rod, and in contact with this end are the arborizations of the nerve terminations. To the inner side of these cells are several rows of columnar cells that function as supports. The outer hair cells number about twelve thousand, and form three rows in the basal coil and about four rows in the upper two THE ORGAN OF HEARING. 447 coils. The free extremity of each cell supports some twenty hair-like processes, while the outer extremity reaches half-way to the basilar membrane and is in contact with nerve arborizations. 3. Deiters' supporting cells alternate with the rows of the outer hair cells. Their lower ends expand upon the basilar membrane, and the upper end tapers Fig. 309.-Section of Corti's organ from guinea-pig's cochlea: ST, scala tympani; TC, tunnel of Corti; a, bony tissue or spiral lamina; b, b, fibrous tissue covering same continued as substantia propria of basilar membrane; c, c, protoplasmic envelope of Corti's pillars (e, e,)i endothelial plates; /, heads of pillars containing oval areas; g, head plates of pillars; h, h', inner and outer hair cells; in, membrana retic- ularis; k, I, cells of Hensen and Claudius; n, n, nerve fibers; i, cells of Deiters (after Piersol). and extends to the free surface of the hair cells. Each cell has a nucleus near its middle and contains a bright thread-like structure, called the supporting fiber. 4. The cells of Hensen are outer supporting cells and consist of several rows just outside of Deiters' cells, where they form a well-marked elevation on the floor 448 NORMAL HISTOLOGY AND ORGANOGRAPHY. of the scala media. The columnar cells just external to this elevation are named the cells of Claudius. 5. The lamina reticularis is a thin cuticular structure which lies over Corti's organ and extends from the outer rods as far as Hensen's cells. This membrane has numerous small apertures into which the outer hair cells project. 6. The membrana tectoria is an elastic membrane attached to the free margin of the lamina spiralis and reaching outward as far as the outer row of hair cells. This membrane has no nuclei and shows fine radial striations. The membrane is supposed to act as a damper to the hair cells. The Auditory Nerve.-The auditory nerve divides into two main parts, the ramus vestibularis and the ramus cochlearis. The vestibularis divides into three branches which are the macula acustica, utric- uli, and the ampullae of the inferior and external semicircular canals. The ramus cochlearis supplies a branch to the macula acustica sacculi and one to the ampulla of the posterior semicircular canal. The remainder of the ramus cochlearis is distributed to the hair cells of Corti's organ. Near the base of the osseous spiral lamina there is situated, in a special bony canal, a ganglion called the spiral ganglion of the cochlea. The ganglion cells are bipolar, having a dendrite that extends inward through the lamina spiralis to the organ of Corti, and a neuraxis that passes out the modiolus and thence to the medulla. Some of the dendritic processes pass through the tunnel of Corti, so called tunnel fibers, to reach the outer hair cells. THE ORGAN OF HEARING. 449 DEVELOPMENT OF THE LABYRINTH. The epithelial lining of the membranous labyrinth is derived from the ectoderm and develops as a vesic- ular invagination on each side of the epencephalon. After being constricted off from the ectoderm this vesicle develops a dorsomesial evagination, which gradually grows larger and becomes the ductus endo- Fig. 310.-Three transverse sections showing development of otic vesicle of human embryo (Tourneux): A, from embryo of 3 mm., showing auditory pit; B, from embryo of 4 mm., showing the transformation of the pit into the otic vesicle; C, from embryo of 6 mm., showing otic vesicle detached from surface ectoderm, and presenting a posterior diverticulum, the recessus vestibuli. lymphaticus. By means of folds and constrictions the dorsal utriculus and ventral sacculus are formed, and also the semicircular canals which connect with the utriculus. The membranous cochlea or scala media grows both in a longitudinal and a spiral direction, retaining its connection with the sacculus through the canalis reuniens. This complex mem- 450 NORMAL HISTOLOGY AND ORGANOGRAPHY. branous labyrinth becomes invested with developing bone, and is filled with endolymph and surrounded with perilymph. The developmental history of the middle and external ear is closely associated with that of the first gill cleft of which they primarily form an associate part. CHAPTER XVI. OLFACTORY ORGAN. The olfactory region may be divided into the vesti- bule, respiratory organ, and the olfactory organ. i. The vestibule is cov- ered with a continuation of the skin, which grad- ually takes on the char- acter of a mucous mem- brane. The epithelium is of a stratified squa- mous variety, and pre- sents hairs, sebaceous glands, and mucous glands. The vestibule comprises the region of the anterior nares. 2. The respiratory re- gion is lined by ciliated epithelial cells, the nuclei of which are placed at various levels. Hairs and sebaceous glands are absent, but branched al- veolar glands having mucous and serous cells are present. Numerous leukocytes are usually found upon the surface. Fig. 311.-Olfactory mucous membrane; a, sustentacular cells; olfactory cells; c, basal cells; d, submucous fibrous tissue; e, glands of Bowman; j, nerve fibers (Leroy). 451 452 NORMAL HISTOLOGY AND ORGANOGRAPHY. 3. The olfactory region is usually confined to the superior turbinated bone and to the adjacent nasal septum. In the fresh condition the region may be Fig. 312.-Diagram of the connections of cells and fibers in the ol- factory bulb: olj. c, cells of the olfactory mucous membrane; olf. n, deepest layer of the bulb, composed of the olfactory nerve fibers which are prolonged from the olfactory cells; gl, olfactory glomeruli, containing arborization of the olfactory nerve fibers and of the dendrons of the mitral cells; me, mitral cells; a, thin axis-cylinder process passing toward the nerve-fiber layer, n. tr, of the bulb to become continuous with fibers of the olfactory tract; these axis-cylinder processes are seen to give off collaterals, some of which pass again into the deeper layers of the bulb; n', a nerve fiber from the olfactory tract ramifying in the gray matter of the bulb (Schafer). distinguished by its yellow color, which is due to pigment in the sustentacular epithelial cells. The olfactory cells are true bipolar ganglion cells. The upper process of these cells reaches to the free OLFACTORY ORGAN. 453 surface of the epithelial layer and is short. It ter- minates in six to eight short firm hairs. The lower thinner process is a neuraxone which passes through the cribriform plate to terminate in telodendria in the region of the olfactory bulb. The sustentacular cells are long columnar elements with oval nuclei. They give support to the ganglion cells. Large branched tubular glands are present, called the glands of Bowman. They secrete an albuminous or serous fluid. Beneath the epithelium there is a rich supply of capillary blood-vessels and lymphatics. Fibers from the trigeminal nerve terminate in telo- dendria among the epithelial cells of the entire olfactory region. CHAPTER XVII. LABORATORY DIRECTIONS. The following is a brief outline of the tissues to be prepared for a laboratory course accompanying the text. Special technique is cited whenever indicated, otherwise standard laboratory methods may be em- ployed. This outline is abbreviated and should be expanded according to the skill of the instructor or student and according to the laboratory equipment. Mitosis. i. Growing point of onion or lily root tip, hardened in Flemming or corrosive sublimate, and cut in longi- tudinal section. 2. Testicle of grasshopper taken in June, or ova, or skin stripped from tail of growing tadpoles. Iron hematoxylin stain is excellent. Epithelium. i. Isolated epithelial cells from intestine, trachea and bladder (see Introduction). 2. Epithelium exfoliated from skin of frog (pieces gathered from water where frogs are kept). 3. Fresh cells scraped from mucous surface of cheek. 4. Sections of intestine, cornea of the eye, and skin. 5. Endothelial cells of mesentery. Prepare endothelium as follows: (1) Kill a small animal, as a rat. 454 LABORATORY DIRECTIONS. 455 (2) Open abdominal cavity. (3) Wash out cavity with sterile water; do not handle the mesentery. (4) Fill cavity with f per cent, silver nitrate solution, 5 min. See that mesentery is bathed. (5) Wash cavity with | per cent, nitric acid solution, 5 min. (6) Fill cavity with alcohol 95 per cent, one-half to one hour, as convenient. (7) Remove mesentery with intestine attached. (8) Immerse in fresh 95 per cent, alcohol one to twelve hours. (9) Cut intestine away from mesentery and im- merse the latter in fresh 95 per cent, alcohol, one-half to one hour. (10) Transfer mesentery to clove oil and expose to sunlight in shallow wide dish, three to five hours. Direct sunlight is not good. (11) Cut mesentery into small pieces and mount in balsam. Handle mesentery as little as possible during the whole process. Glands. 1. For simple mucous and serous glands make cross sections of the skin of a salamander. Connective Tissue. 1. Sections of young umbilical cord and of em- bryos show connective-tissue cells. 2. Sections of fat and teased fresh pieces of fat. 3. Salamander skin, dehydrated and mounted with lower side up shows connective-tissue pigment cells. 456 NORMAL HISTOLOGY AND ORGANOGRAPHY. 4. Brown connective-tissue pigment cells may be scraped from the choroid coat of the eye after re- moving the retina. 5. Sections and teased preparations of ligament uni nuchae of the ox. 6. Sections and teased preparations of a tendon. 7. Elastic fibers of the mesentery of a rat. PREPARATION OF ELASTIC FIBERS. (i) Fill abdominal cavity of a rat with 95 per cent, alcohol, one hour. (2) Remove intestine with mesentery attached and place in fresh alcohol. (3) Cut away the mesentery and mordant with 6 per cent, solution of boric acid. (4) Stain. Orcein 1 part. Alcohol, 95 per cent 100 parts. Hydrochloric acid 1 part Stain for one to twelve hours. The fibers should appear dark brown. If stained too deeply, treat with acid alcohol, | per cent, hydrochloric acid. If too red, dip the pieces in fifty per cent, alcohol satu- rated with ammonium picrate. Cartilage. i. Cartilage sections may be cut with a razor from bone joints obtained at a meat market. 2. Sections of trachea for hyaline variety. The sections must be cut thin and not overstained. Bone. i. Ground sections, mounted dry. A dry white and fat-free bone is the best. With a turning table ring a glass slide with balsam. Before the balsam LABORATORY DIRECTIONS. 457 sets the bone may be mounted dry by covering with circular cover glass, which sticks to the ring of balsam. 2. Sections of decalcified bone. Place a fresh bone in 95 per cent, alcohol to fix and harden soft parts. Next day begin process of decalcification. Use nitric or hydrochloric acid, | to 1 per cent., using a large quantity and changing fluid twice daily. Nitric acid may be used in 1 to 10 per cent, strength. Time required varies from one to seven days. By means of sharp needles it is possible to determine when decalcification is complete. After decalci- fication wash in running water for twenty-four hours. Muscle. 1. Smooth muscle. Pieces stripped from the intestinal wall may be stained for twenty-four hours with dilute hematoxylin. Tease in glycerin and alcohol, or, for permanent mounts, dehydrate and tease in oil. 2. Cross sections of the intestine will show smooth muscle in cross and in longitudinal sections. 3. Heart muscle. Teased specimens and very thin sections. 4. Voluntary muscle. Sections of a tongue will show fibers both in cross and in longitudinal section. 5. Injected muscle. Sections should be cut very thick to show capillaries. Such muscle carefully teased is very satisfactory. 6. Fresh voluntary fibers may be teased in alcohol and glycerin. Nervous Tissue. 1. For bipolar cells study sections of the spinal ganglion. 458 NORMAL HISTOLOGY AND ORGANOGRAPHY. 2. For multipolar cells study sections of the cere- bral cortex and spinal cord stained with Cox-Golgi method, as follows: Potassium bichromate 20 parts. Corrosive sublimate 5 per cent, sol 20 parts. Distilled water 40 parts. Potassium chromate, 5 percent, sol 16 parts. Specimens remain in this two weeks or two months; after which wash thoroughly twenty-four hours. Cut sections free-hand as thin as possible and place them in a saturated solution of lithium carbonate for twenty-four hours. Transfer to 95 per cent, alcohol, and then to clove oil, from which they are mounted in balsam on a glass slide and covered with a cover glass. 3. Fix a sciatic nerve with 0.5 per cent, osmic acid. Wash thoroughly in water and tease either in glyc- erin or dehydrate and tease in oil. Study structure of medullated fibers. 4. Make cross section of sciatic nerve. Blood. 1. Dip a thin strip of filter paper in the blood of a frog and make a spread either on a cover glass or a glass slide. Dry in air and fix in 95 per cent, alcohol. Stain with hematoxylin and eosin. Wash in water and dry in air, after which the specimen may be mounted in balsam. 2. Study fresh specimens of human blood for rouleaux and crenated red blood corpuscles. 3. Thin blood spreads may be made: (1) On glass slides by placing a drop of blood near LABORATORY DIRECTIONS. 459 one end and with the end of a second slide spread it by making a single stroke toward the opposite end. (2) Placing a small drop between two cover glasses and drawing them apart in such a way that their surfaces are always parallel. (3) Saturate the end of some thin blotting paper and make a spread either on a cover glass or a glass slide. 4. Spreads are dried in air and then fixed, by heat (1200 C.), for two hours, or equal parts of absolute alcohol and ether for two hours. They are then dried and stained. Wright's stain is a short method and fixes and stains a film at the same time. (1) Stain a blood film with Wright's fluid one minute. (2) Distilled water 2 min. Add in drops upon cover glass or slide. (3) Wash in water until the film of blood becomes pink. (4) Dry between filter paper and mount in balsam. (For preparation of Wright's stain see "Pathological Technique," Mallory and Wright, Third Edition.) 5. Blood platelets are obtained by pricking the finger through a drop of 1 per cent, osmic acid. 6. Hemin crystals. Grind together on a slide equal parts of dry blood and salt. Add glacial acetic acid and cover with cover glass. Heat until gas bubbles escape. Examine with high-power of micro- scope. Red Marrow.-With a pair of pinchers squeeze a drop from the end of a rib and spread on slide or 460 NORMAL HISTOLOGY AND ORGANOGRAPHY. cover glass. Fix and stain as for blood. A spread may be made from the end of the femur or any of the long bones. Blood-vessels. i. Sections of the aorta. 2. Small arteries can be found in sections of the tongue or any other organ. 3. Sections of any large vein. Lymphatics, Thymus Gland, Spleen. 1. Sections of lymphatic nodes. 2. Sections of thymus gland. 3. Sections of the spleen. These tissues must be cut thin and not overstained. Digestive System. 1. Teeth. Ground sections, technique as for bone. 2. Tongue. Section foliate papillae of rabbit for taste buds. 3. Cross section of esophagus. 4. Sections of cardiac and pyloric end of stomach. 5. Small intestine. Injected specimen must be cut thick. 6. Sections of ileum for Peyer's patches. 7. Large intestine, including vermiform appendix. Digestive Glands. 1. Sections of parotid and submaxillary gland. 2. Pancreas. Injected pancreas for areas of Langerhans. 3. Liver, including sections of injected organ cut thick. Organs of Respiration. 1. Sections of thyroid gland. 2. Sections of trachea. LABORATORY DIRECTIONS. 461 3. Lung, including thick sections of injected organ. Urinary Organs. i. Suprarenal bodies. 2. Kidneys. Sections of injected kidney and kidney pieces macerated with hydrochloric acid (see Introduction). 3. Sections of ureters. 4. Bladder, preferably sections of one distended with fixing fluid. Reproductive Organs. 1. Sections of testes with epididymis attached. 2. Vas deferens. 3. Sections of penis, preferably of baby or a fetus. 4. Prostate gland, preferably an old one. 5. Ovaries. Old enough to show corpora lutea. 6. Fallopian tubes. Sections of fundus and isth- mus. 7. Uterus. 8. Placenta, preferably at half term. 9. Mammary gland. The Skin and Appendages. 1. Sections of palm surface of finger. 2. Sections of the scalp, tangential and cross. 3. Nails. Sections of finger of fetus are very good. Peripheral Nerve Endings and Spinal Cord. 1. Sections of duck's bill. Iron hematoxylin stain. 2. Pacinian corpuscles may be found in sections of the skin of the finger or in the connective tissue of sections of the pancreas. They may be teased out from the mesentery. 462 NORMAL, HISTOLOGY AND ORGANOGRAPHY. 3. Spinal cord. The cord of the horse or ox is very satisfactory. Brain. 1. Sections of cerebral cortex. 2. Sections of cerebellar cortex cut across the folds. 3. Sections of closed and open medulla. 4. Sections of the pons. Sections of the medulla and pons should be cut thick and stained with Pal-Weigert method. Celloidin method of imbedding is preferable. The Eye. 1. Sections of the whole eye imbedded in celloidin. 2. Sections of the cornea. 3. Sections of the retina. 4. Sections of the eyelid. The Internal Ear. Sections of the cochlea must be decalcified. Cochlea of a young kitten is very satisfactory. STANDARD FIXING SOLUTIONS. Carnoy's Acetic-alcohol Mixture. Glacial acetic acid 1 part. Absolute alcohol 3 parts. Pieces one centimeter thick are fixed in one-half to one hour. The after-treatment is with absolute alcohol. Osmic Acid.-One-half to one per cent, aqueous solution. Fix for three to twenty-four hours and then wash thoroughly in running water. LABORATORY DIRECTIONS. 463 Flemming's Solution. Osmic acid, 1 per cent, aqueous solution 10 parts. Chromic acid, 1 per cent, aque- ous solution 25 parts. Glacial acetic acid, 1 per cent, aqueous solution 10 parts. Distilled water 55 parts. Fix for twenty-four hours or more and wash thor- oughly in running water. Flemming's Strong Solution. Osmic acid, 2 per cent, aqueous solution 4 parts. Chromic acid, 1 per cent, aque- ous solution 15 parts. Glacial acetic acid 1 part. This is a good fixing agent for nuclear structures and therefore for mitosis. Corrosive Sublimate. Saturated solution in distilled water. Fix for twenty-four hours or more and wash in running water. After twenty-four hours, transfer to 70 per cent, alcohol to which a few drops of iodin and potassium iodid have been added. The iodin removes any crystals of sublimate that may have formed. Picric Acid. Saturated aqueous solution. Fix for twenty-four hours, or longer, after which wash in 70 per cent, alcohol. Picrosulphuric Acid. Picric acid, saturated aqueous solution 100 parts. Sulphuric acid, concentrated... 1 part. Distilled water 200 parts. After-treatment same as for picric acid. Nitric Acid.-Aqueous solution, 3 to 10 per cent. 464 NORMAL, HISTOLOGY AND ORGANOGRAPHY. Fix for several hours and wash thoroughly in running water. Chromic Acid.-Aqueous solution | to 1 per cent. Small pieces are fixed for twenty-four hours. Wash in running water and pass through the ascending grades of alcohol, preferably in the dark. Muller's Fluid Potassium bichromate 2.5 gm. Sodium sulphate 1.0 gm. Water 100 c.c. Fix for several weeks, preferably in the dark. At first the fluid should be changed daily. Wash in running water for twenty-four hours and place directly in 70 per cent, alcohol. Dehydrate prefer- ably in the dark. Zenker's Fluid. Potassium bichromate 2.5 gm. Sodium sulphate i.ogm. Corrosive sublimate 5.0 gm. Glacial acetic acid 5.0 gm. Water 100 gm. It is better to add the acetic acid just before using and not to add it to the stock solution. Fix tissues in this fluid for six to twenty-four hours. Wash in running water twenty-four hours and transfer to alcohol, using the grades. Sublimate crystals are removed by iodized alcohol as with corrosive subli- mate solutions. Formalin. Formalin (40 per cent. Formal- dehyde) 5 to 10 parts. Water 90 parts. Small pieces are fixed in twelve to twenty-four hours. As sections do not stain well after this fixation, it LABORATORY DIRECTIONS. 465 is better to transfer the pieces to some standard salt solution and then wash and dehydrate. Potassium Bichromate and Formalin. Potassium bichromate 2 per cent, aqueous solution 90 parts. Formalin 10 parts. Fix for several days or weeks. Wash in running water and dehydrate with alcohol. This is a good fixation for the central nervous system. STANDARD STAINS. Aqueous Borax-carmin Solution. Borax 8 gm. Carmin 2 gm. Water 150 c.c. Grind together the borax and carmin. Add the water and in twenty-four hours filter. Stain sections for twelve hours or longer. Treat with acid-alcohol as necessary. Alcohol Borax-carmin Solution. Carmin 3 gm. Borax 4 gm. Water 93 c.c. Alcohol, 70 per cent 100 c.c. Filter and stain as for the aqueous solution. Cochineal Solution. Cochineal, powdered 7 gm. Alum, roasted 7 gm. Water 100 c.c. Boil down to one-half its volume, stirring freely. When cool filter and add a few drops of carbolic acid. This fluid does not overstain and acts rapidly. After staining wash in distilled water, as alcohol precipi- tates the alum. 466 NORMAL HISTOLOGY AND ORGANOGRAPHY. Alum-carmin (Grenacher). Alum solution, 3 per cent, to 5 per cent 100 c.c. Carmin 1 to 5 gm. Boil for fifteen minutes, cool and filter. Add enough water to replace that lost by boiling. Wash the sections in water after staining. Bohmer's Hematoxylin. Hematoxylin 1 gm. Alcohol, absolute 10 c.c. Potassium alum 10 c.c. Distilled water. 200 c.c. Dissolve the hematoxylin in alcohol and the alum in water. Add the first to the second solution while continually stirring. Allow this preparation to stand in an open jar for two weeks, to ripen, when the color will change from violet to blue. After filtering the stain is ready. Delafield's Hematoxylin. Hematoxylin crystals 4 gm. Absolute alcohol 25 c.c. Ammonium alum, sat. aq. sol. .400 c.c. Alcohol 95 per cent 100 c.c. Glycerin 100 c.c. Dissolve the hematoxylin in absolute alcohol and add the alum solution. Place in open vessel for four days, filter, and add the 95 per cent, alcohol and glycerin. In a few days filter again. Ehrlich's Hematoxylin. Hematoxylin crystals . 2 gm. Absolute alcohol 60 c.c. Glycerin Distilled water saturated with 60 c.c. ammonia-alum 60 c.c. Glacial acetic acid 3 c.c. Expose to light for a long time. It is ready for use when it acquires a deep red color. LABORATORY DIRECTIONS. 467 Heidenhain's Iron Hematoxylin. Sections that have been fixed in sublimate solu- tions are placed in a 2.5 per cent, aqueous solution of ammonium sulphate of iron for four to eight hours. Rinse thoroughly in water and place in a hematoxylin solution prepared as follows: Hematoxylin crystals 1 gm. Absolute alcohol 10 c.c. Distilled water 90 c.c. Dissolve the hematoxylin in the alcohol and add the water. This solution should stand in an open vessel for four weeks, and before using should be diluted with an equal volume of distilled water. Stain the above sections twelve to twenty-four hours, rinse in tap water and return to ammonium sulphate of iron solution until black clouds cease to be given off from the sections. Rinse in distilled water, dehydrate, and mount in balsam. This is a good stain for mitosis. Anilin Stains. These are basic or acid stains. The basic stains are safranin, methylene-blue, methyl green, gentian violet, methyl violet, Bismarck brown, thionin, and toluidin blue, and stain nuclei. The acid stains are eosin, erythrosin, acid fuchsin, orange G. and nigro- sin, and stain cytoplasm. These stains are used in water solutions and of | to i per cent, strength, to which a little alcohol may be added. Pal-Weigert Method of Staining Sections of Brain or Cord. Mordant celloidin sections for twenty-four hours 468 NORMAL HISTOLOGY AND ORGANOGRAPHY. in 3 to 5 per cent, aqueous solution of potassium bichromate. Wash in water and transfer to the following stain: Hematoxylin crystals 1 gm. Alcohol 95 per cent 10 c.c. Lithium carbonate, sat. aq. sol. 1 c.c. Water 90 c.c. Dissolve the hematoxylin in alcohol first, and then add the balance at the time of using. Stain the sections in this for twenty-four hours. Wash in water and transfer to a 0.25 per cent, fresh solution of potassium permanganate for one-half to two min- utes. Wash freely in water and place in the follow- ing Pal solution: Oxalic acid 1 gm. Potassium sulphate 1 gm. Water 200 c.c. This will differentiate the gray and white matter in one to three minutes. The nerve fibers should stain blue. If the sections are too dark they may be carried through the permanganate and Pal's so- lution a second time. Transfer to water for several hours, dehydrate, and mount in balsam. For a more complete description of laboratory methods, including injections, fixing of tissues, and special staining methods, see the following texts: "Pathological Technique," Mallory and Wright, Third Edition. " Microtomist's Vademecum," Lee. Bohm-Davidoff-Huber, "Histology," Second Edi- tion, 1904. INDEX Abomasum, 194 Accessory thyroid glands, 213 Accommodation, muscles of, 418 Acetic-alcohol, Carnoy's, 462 Achromatin, 40 Acid, chromic, 464 nitric, 463 osmic, 462 picric, 463 picrosulphuric, 463 Acini, 216 Acrodont dentition, 171 Adenoids, 182 Adventitia of blood-vessels, 111, 113 Agminated lymph-nodules, 200 Air cells of lung, 246 sacs of lung, 246 Alimentary canal, classification, i38 lymphatics of, 207 nerve-supply of, 208 Alum carmin, 466 Alveoli of lung, 247 Amitosis, 46 Amphipyrenin, 41 Ampullae of Thoma of spleen, 135 Anaphase, 45 Anilin stains, 467 Anisotropic muscle, 92 Anterior gray commissure of cord, 373 ground bundle, 381 horn of cord, 374 Appendices epiploicae, 203 Aqueous humor, 426 Arachnoid of brain, 384 of cord, 371 Arbor vitae of cerebellum, 396 Arch, mandibular, 140 maxillary, 141 Archenteron, 32 Arcuate fibers, 388, 389, 391 nucleus, 389, 392 Area acusticae, 386 Areas of Langerhans, 64 Areolar connective tissue, 74 Arrector pili, 346 Arteries, 111 helicine, 292 Arteriosclerosis, 125 Asthma, 245 Atheroma, 125 Atria of lung, 246 Attraction sphere, 39 Auditory meatus, 435 nerve, 448 Auerbach's plexus, 192, 208 Axis cylinder of nervous tissue, 97, 101 Bartholin's glands, 298 Bertini's columns, 263 Bile duct, 222, 224 Bipolar nerve cells, 99 Bladder, 273 mucous membrane of, 274 trigone of, 274 vessels and nerves of, 276 Blastophore, 32 Blood, 118 crenated red blood-corpuscles 119 ghost corpuscles, 118 hemin crystals, 122 hemoglobin, 118 platelets, 121 red blood-corpuscles, 118 rouleaux, 118 stroma, 118 white blood-corpuscles, 120 Blood-poisoning, 136 Blood-supply of bone, 82 469 470 INDEX Blood-supply of brain, 407 of large intestine, 205 of lungs, 250 of muscle, 94 of small intestine, 205 of spinal cord, 407 of stomach, 205 of teeth, 168 of tongue, 182 Blood-vessels, 111 adventitia of, in, 113 arteries, in capillaries, 117 general considerations, 125 intima, in media, 112 of central nervous system, 407 of eye, 428 of kidney, 268 of suprarenal bodies, 257 stigmata and stomata, 118 vasa vasorum, 114, 126 Body cavity, 34 Bone, 68, 83 blood-supply of, 82 canaliculi, 80 cancellate, 82 development of, 83 diploe, 82 endochondral, 83 general considerations, 86 Haversian system, 80 intramembranous, 83 lacunae, 79 ossification of, 85 osteogenetic layer, 82 primary areolae of Sharpey, 83 regeneration of, 85 secondary areolae of Sharpey, 84 Sharpey's fibers, 82 Volkmann's canals, 82 Bones of ear, 437 Borax carmin, 465 Bowman's capsule of kidney, 264 glands, 453 Brain, 382 arachnoid of, 384 blood-supply of, 407 development of, 35, 382 divisions of, 382 dura of, 383 Brain, meninges of, 383 pia of, 383 Bronchi, 242 eparterial, 252 hyparterial, 252 respiratory, 246 Brunner's glands, 201 Burdach's columns, 377, 378, 385, 388 Calamus scriptorius, 376 Canal of Petit, 428 of Schlemm, 413 Canaliculi, bone, 80 Cancellate bone, 82 Capillaries, 117 lymphatic, 127 Capsule, lens, 426 of Glisson, 220, 223 of kidney, Bowman's, 264 Tenon's, 413 Cardiac muscle, 89 Carmin, alum, 466 borax, 465 Carnoy's acetic-alcohol, 462 Cartilage, 68, 76 elastic, 78 general considerations, 79 hyaline, 77 lacunae of, 75, 77 of trachea, 242 white fibrous, 78 Cartilages of larynx, 233 Casts of kidney, tubular, 267 Cauda equina, 369 Cell, 26, 28 air, of lung, 246 cleavage of, laws of, 46 column, Waldyer's central, 374 cortical, 397 decidual, 325 defined, 26, 37 Deiters' supporting, 447 endothelial, of artery, 111 fat, 57 general considerations, 47 giant, 124 goblet, 60 inclusions of, 41 interstitial, of testis, 64 mast, 121 INDEX 471 Cell, membrane of, 42 mossy, 106 multipolar, 100 nerve, bipolar, 99 of posterior horn, 373 unipolar, 98 of connective tissue, 68 of Hansen, 447 of liver, 229 of marrow, 124 parietal, of salivary glands, 212 pigment, 69 plasma, 71 polymorphic, of cerebrum, 403 polynuclear, 121 prickle, 339 Purkinje's, 398 pyramidal, of cerebrum, 403 spider, 106 stellate, of cerebellum, 397 of Kupffer, 231 tactile, 363 theory, 37 wandering, 71, 121 Celloidin imbedding, 20 advantages of, 22 disadvantages of, 23 sections, staining of, 22 Cementoblasts, 165, 166 Cementum, 161 Centro-acinal cells of pancreas, 216, 217 Centrosomes, 39 Cerebellar tract, direct, 378 Cerebellum, 396 arbor vitae of, 397 climbing fibers of, 399 cortical cells, 397 granular layer, 399 inferior peduncle of, 386 medullary substance, 399 mossy fibers, 399 Purkinje's cells, 398 stellate cells, 397 Cerebrospinal system, 106, 107 Cerebrum, 401 fibers of, 403 medullary substance, 404 molecular layer, 401 polymorphic cells, 403 pyramidal cells of, 403 Ceruminous glands, 435 Cervical enlargement of spinal cord, 369 Chondrin, 75 Chorion, 326 Chorionic villi, 327 Choroid coat, 416 fissure, 409 Chromatin, 40, 43 Chromic acid, 464 Chromosomes, 31, 45 daughter, 45 in mitosis, 43 Ciliary body, 418 muscles, 418 processes, 418 Circulatory endocardium, no epicardium, 110 heart, no myocardium, no system, no Circumvallate papillae of tongue, 178 Clarke's column, 374, 378 Clava, 386 Cleavage, 31 of cells, laws of, 46 Cleft palate, 144 Climbing fibers of cerebellum, 399 Cochineal solution, 465 Cochlea, 438, 441 Coelenteron, 32 Cohnheim's fields, 91 Collaterals, 97 Colostrum, 332 Column of Bertini, 263 of Burdach, 377, 378, 385, 388 of Clarke, 374, 378 of Goll, 377, 378, 385, 388 of Sartoli, 279 Comma tract, 377, 378 Commissure, posterior gray, of cord, 373 Cone, implantation, 103 Conjunctiva, 431, 432 Connective tissue, 68 areolar, 74 cells of, 68 classification, 72 embryonic, 68 diagnostic points of, 75 fibers of, 72 472 INDEX Connective tissue, general con- siderations, 74 products of, 71 reticular, 73 white fibrous, 72 yellow elastic, 73 Corium, 339 Cornea, 413 Corneum, 337 Corona radiata, 306 Coronary cushion, 352 Corpora cavernosa, 290 structure of, 291 lutea, 64, 311 Corpus spongiosum, 290 structure of, 293 Corpuscles, genital, 365 ghost, 118 Grandry's, 363 Malpighian, 264 of kidney, 264 of spleen, 134 Meissner's, 364 of Hassal, 132 of Herbst, 364 of Highmore, 278 Pacinian, 367 red blood-, 118 crenated, 119 white blood, 120 Corrosive sublimate, 463 Cortex of kidney, 263 Cortical cells, 397 Corti's organ, 445 rods, 446 Cowper's glands, 298 Cremasteric fascia, 277 Crenated red blood-corpuscles, 119 Crescents of Gianuzzi, 212 Cretinism, 239 Crossed pyramidal tract, 379 Crura cerebri, 393 Crypts of Lieberkiihn, 199 of stomach, 188 Crystals, hemin, 122 Cushion, coronary, 352 Cuticle, 52 Cutis vera, 339 Cutting sections, 23 Cystic duct, 222, 224, 225 Cysts, sebaceous, 357 Cytogenic glands, 60, 64 Cytolymph, 38, 42 Cytoplasm, 38, 42 Czermak's interglobular spaces, 224 Dandruff, 357 Dartos, 277 Daughter chromosomes, 45 skein, 45 star, 45 Deciduae, 323 Decidual cells, 325 Decussation, motor, 316, 387 sensory, 388 Dehiscent glands, 60, 64 Dehydrating, 20 Deiters' nucleus, 380 supporting cells, 447 Demilunes of Heidenhain, 212 Dendrite, 98 Dentin, 157 secondary, 159 Dentition, 145 acrodont, 171 pleurodont, 171 thecodont, 171 Dermis, 339 Descemet's membrane, 414, 415 Deutoplasm, 307 Development, general, 26 of bone, 83 of brain, 35, 382 of teeth, 172 Diaster, 44 Digestive glands, 209 Diploe, 82 Direct cerebellar tract, 378 pyramidal tract, 381 Discus proligerus, 304 Dissociation of tissue elements, 18 Diverticulum, Meckel's, 196 Doyer's elevation, 359 Ductless glands, 64 Ductus endolymphaticus, 439 reuniens of Hensen, 444 Dura of brain, 383 of cord, 370 Dust, Hensen's, 441 hepatic, 224 INDEX 473 Dust, lactiferous, 331 of Santorini, 216 of Wirsung, 215 Ear, bones of, 437 external, 435 internal, 438 labyrinth of, 438 middle, 436 Ectoderm, 32, 33 Ectosarc, 39 Ejaculatory duct, 287 Elastic cartilage, 78 Eleidin, 338 Embryology, 26 Embryonic connective tissue, 68 Enamel, 149 rods, directions of, 152 Encephalon, 342 Endocardium, circulatory, no Endochondral bone, 83 Endolymphatic duct, 439 Endometrium, 319 Endomysium, 90 Endoneurium, 106 Endosarc, 39 Endothelial cells of artery, 111 layer of artery, in Endothelioma, 65 Endothelium, 64 End-plate muscle, 359 Enlargement, lumbar, of spinal cord, 369 Entoderm, 33 Environment, 28 Eosinophiles, 121, 124 Eparterial bronchus, 252 Epicardium, circulatory, 110 Epidermis, 337 Epididymus, 286 Epidural space, 371 Epimysium, 90 Epineurium, 106 Epithelial glands, 59 classification of, 63 Epithelioma, 65 Epithelium, 45, 54, 56 germinal, 354 Epoophoron, 315 Erythrocytes, 118 Esophagus, 184 Eustachian tube, 437 Excretory ducts of testicle, 285 Exolemma, 103 Exophthalmic goiter, 239 External ear, 435 Eye, 409 blood-vessels of, 428 coats of, 411 refractory media of, 426 tunica externa of, 412 Fallopian tubes, 311 development of, 314 structure of, 313 Falx cerebelli, 383 cerebri, 383 Fascia, cremasteric, 277 intercolumnar, 277 Fasciculi of muscle, 90 Fasciculus solitarius, 390 teres, 395 Fat cells, 57 Fauces, 139 Fenestra ovales, 439 rotunda, 443 Fenestrated membrane of Henle, in, 112 Ferrein's pyramids, 263 Fertilization, 30 Fibers, arcuate, 388, 389, 391 climbing, of cerebellum, 399 medullated nerve, 101 mossy, 399 nerve, 101 non-medullary, 105 of cerebrum, 403 of connective tissue, 71 posterior root of, termination, 378 Sharpey's, 82 Fibrillar mass, 38 Fibrils of nervous tissue, 101, 102 Fibroblast, 165, 166 Fibroma, 74 Filiform papillae of tongue, 177 Fillet, 395 Filum terminale, 369 Fissure, choroid, 409 Fissures of liver, 219 of spinal cord, 371 Fixing and hardening tissues, 19 474 INDEX Flemming's solution, 463 Fluid, Muller's, 464 Foliate papillae of tongue, 181 Follicle, Graafian, 302, 303 Follicles of hair, 343 Follicular fluid, 304 glands, 64 Foramen cecum of medulla, 387 of tongue, 176 of Winslow, 221 Formalin, 464 potassium bichromate and, 465 Formatio reticularis, 389, 391, 395 Fovea centralis, 424 infundibuliform, 283 Free sensory nerve endings, 362 Frenum, lingual, 176 Frog, 349 Fungiform papillae of tongue, 177, 178 Funiculus cuneatus, 385, 388 gracilis, 385, 388 of nervous tissue, 106 Gall-bladder, 224 Ganglia, 98 Ganglion, spinal, 99 spiral, 448 Gastric glands, 189, 190 Gastrula stage, 32 Gelatinosa substantia Rolando, 373 Genital corpuscles, 365 Germ layer, derivatives of, 36 Germinal epithelium, 354 spot, 308 vesicle, 307 Ghost corpuscles, 118 Giant cells, 124 Gianuzzi's crescents, 212 Glands, cytogenic, 60, 64 defined, 59 dehiscent, 60, 64 ductless, 64 epithelial, 59 classification of, 63 follicular, 64 hemolymph, 131 lymph, 59, 64, 129 of Bartholin, 298 Glands of Bowman, 453 of Littre, 296 of Moll, 431 of Montgomery, 333 of penis, 290, 291, 293 of Tyson, 291 suprarenal, 64, 255 thyroid, 64 unicellular, 59, 64 Glisson's capsule, 220, 223 Globus major, 286 minor, 286 Glottis, 237 Goblet cells, 60 Goiter, 239 exophthalmic, 239 Goll's column, 377, 378, 385, 388 Gowers' tract, 378 Graafian follicle, 302, 303 follicular fluid, 304 stratum granulosum, 304 theca, 304 Grandry's corpuscle, 363 Granular layer, Tomes', 158 Granules, zymogen, of pancreas, 216 Gray commissure of cord, pos- terior, 373 matter of pons, 394 of spinal cord, 373 Ground bundle, anterior, 381 Hair, 341 follicles of, 343 papillae of, 346 Hairs, tactile, 344 Hansen's cells, 447 Hardening tissues, 19 Harelip, 143 Hassal's corpuscles, 132 Haversian system of bone, 80 Heart, circulatory, no Heidenhain's demilunes, 212 Helicine arteries, 292 Hematoblasts, 124 Hematoxylin, 466 Hemin crystals, 122 Hemoglobin, 118 Hemolymph glands, 131 Henle's fenestrated membrane, in, 112 INDEX 475 Henle's layer, 344, 345 Hensen's duct, 441 ductus reuniens, 444 median disc, 92, 93 Hepatic cords, 228 duct, 224 Herbst's corpuscles, 364 Heredity, 26 Highmore's corpuscles, 278 Hilus of kidney, 261 Histology, 26 Hoof horn, 352 matrix, 352 of horse, 349 tubes, 352 Horny laminae, 349 Humor, aqueous, 426 vitreous, 410, 428 Huxley's layer, 342, 345 Hyaline cartilage, 77 Hyaloid membrane, 428 Hyaloplasm, 38, 42 Hydatid of Morgagni, 288 Hyparterial bronchi, 252 Hypoderm, 33 Hypophysis cerebri, 64 Imbedding, 20 celloidin, 20 advantages of, 22 disadvantages of, 23 paraffin, 21 advantages of, 23 disadvantages of, 23 Implantation cone, 103 Inferior peduncle of cerebellum, 386 Infundibuliform fascia, 283 Infundibulum of lung, 249 Insensitive lamina, 349 Intercellular bridges, 51 spaces, 51 Intercolumnar fascia, 277 Interglobular spaces of Czermak, 158 Internal ear, 438 Interstitial cells of testis, 64 elements of testes, 280, 281 Intestine, large, 202 blood-supply of, 205 coats of, 203 sacculae of, 202, 203 Intestine, small, 196 blood-supply of, 205 mucosa, 196 muscular layer, 201, 202 serosa, 202 submucosa, 201 villi of, 198 Intima of blood-vessels, in Intramembranous bone, 83 Involuntary muscle, distribu- tion of, 88 Iridica retinae, 426 Iris, 418 Isotropic muscle, 92 Jaundice, 224 Jelly, Wharton's, 69, 329 KaryokinESis, 43 Karyolymph, 40 Karyoplasm, 42 Keraphyllous tissue, 349 Keratin granules, 352 Keratohyalin, 338 Kidney, 259 blood-vessels of, 268 Bowman's capsule of, 264 cortex of, 262 development of, 261 hilus of, 261 labyrinth of, 263 Malpighian corpuscle of, 264 medulla of, 262 medullary rays of, 263 nerves of, 271 pelvis of, 262 renal sinus, 280 structure of, 261 tubules of, 264 Knots, nuclear net, 42 Krause's membrane, 92 Kupffer's stellate cells, 231 Laboratory directions, 454 Labyrinth of internal ear, 438 of kidney, 263 Lacrimal apparatus, 433 groove, 143 Lacteals, 198 476 INDEX Lactiferous duct, 331 Lacunae, bone, 79 of cartilage, 75, 77 Lamellae, 350 Lamina choroidea, 413 cribrosa, 412, 425 fusca, 413 horny, 349 reticularis, 448 insensitive, 349, 351 spiralis, 442 sensitive, 349, 351 vascular, 349, 351 Laminitis, 353 Langerhans, areas of, 64, 217 Lantermann-Schmidt segments, 105 Large intestine, 202 blood-supply of, 205 coats of, 203 sacculae of, 202, 203 Larynx, 233 cartilages of, 233 mucous membrane of, 235 Lateral horn of cord, 374 Laws of cell cleavage, 46 Layer, endothelial, of artery, 111 Henle's, 344, 345 Huxley's, 344, 345 Malpighian, 339 Tomes' granular, 158 Weil's, 161 Lemniscus, 395 Lens, 409, 426, 427 capsule, 426 Leucocytes, 120 large mononucleated, 121 Lieberkuhn's crypts, 199 Ligaments of liver, 219 Ligamentum spirale cochleae, 445 Lingual frenum, 176 Lingula, 389 Linin, 40 Lipoma, 71 Lissaur's marginal ground bun- dle, 377 Littre's glands, 296 Liver, 218 blood-supply of, 221 cells of, 229 fissures of, 219 function of, 229 Liver, ligaments of, 219 lobes of, 219 lobules of, 220 lymphatics of, 231 nerves of, 231 Lowenthal's tract, 316 Lumbar enlargement of spinal cord, 369 Lungs, 244 air cells of, 246 sacs of, 246 alveoli of, 247 atria of, 246 blood-supply of, 250 infundibulum of, 249 lobules of, 247 lymphatics of, 253 nerves of, 254 respiratory bronchi, 246 structure of, 246, 249 Lunula, 348, 349 Lygoeus bicrucis, 49 Lymph duct, thoracic, 128 glands, 59, 64, 129 node, agminated, 200 function of, 135 solitary, 130 Lymphatic capillaries, 127 vessels, 127 Lymphatics of alimentary canal, 207 of liver, 231 of lungs, 253 of mammary glands, 334 of testicle, 290 Lymphocytes, 121 Lymphoglandulse, 59, 64 Macula acustica sacculi, 440 utriculi, 440 lutea, 424 Malpighian corpuscle of kidney, 264 of spleen, 134 layer, 344 pyramids, 262 Mammary glands, 330 lymphatics of, 334 nerves of, 333 vessels of, 333 Mandibular arch, 140 INDEX 477 Marrow, 123 cells of, 124 myelocytes, 124 Masculine uterus, 294 Mast cells, 121 Matrix, 348 Maturation, 28, 30, 309 Maxillary arch, 141 Meatus, auditory, 435 Meckel's diverticulum, 196 Median raphe, 395 Medulla, foramen cecum of, 387 of kidney, 262 pyramids of, 389 Medullary rays of kidney, 263 sheath, 101, 103 substance of cerebrum, 404 Medullated nerve fibers, 101 Meibomian glands, 431 Meissner's corpuscles, 364 plexus, 192, 208 Melanin, 70 Melanotic sarcoma, 75 Melting-point of paraffin, 22 Membrane basilaris, 443 cochlea, 444 eboris, 160 tectoria, 448 Meninges of brain, 383 of cord, 370 Menstruation, 303, 322 Mesial olivary nucleus, 389 Mesoblastic somites, 35 Mesoderm, 33 Mesonephros, 260, 261 Metanephros, 261 Metaphase, 44 Microsomes, 38 Middle ear, 436 Milk sinus, 331 Mitosis, 43 chromosomes in, 43 reduction, 30 somatic, 30 Mixed lateral bundle, 316 Modiolus, 442 Molecular layer of cerebrum, 401 Moll's glands, 431 Monaster, 43 Montgomery's glands, 333 Morgagni's hydatid, 288 Morula stage, 31, 32 Mossy cells, 106 fibers, 389 Mother skein, 43 Motor decussation, 316, 387, 389 nerve endings, 359 Moulting, 346 Mounting tissues on block, 20 Mouth, 138 Mucigen, 212 Mucous coat of small intestine, 196 of stomach, 187 membrane, defined, 61 of larynx, 235 of trachea, 244 tissue, 69 Muller's fluid, 464 Multipolar cells, 100 Mumps, 211 Muscle, 87 anisotropic, 92 blood-supply of, 94 cardiac, 89 ciliary, 418 Cohnheim's fields, 91 endomysium, 90 end-plate, 359 epimysium, 90 fasciculi of, 90 general considerations, 95 Hensen's median disc, 92, 93 involuntary, distribution of, 88 isotropic, 92 Krause's membrane, 92 myoma, 95 nerve supply, 94, 95 non-striated, peripheral nerve terminations in, 360 of accommodation, 418 of skin, 340 perimysium, 90 red, 94 sarcolemma, 91 sarcomere, 93 sarcoplasm, 91 sarcostyle, 88, 91 sarcous element, 93 spindle, 368 striated, peripheral nerve ter- minations in, 359 voluntary, 90 distribution of, 95 478 INDEX Muscle, white, 93, 94 Muscular layer of small intes- tine, 201, 202 of stomach, 192 of uterus, 320 tissue, 87 Myelocytes, 124 Myeloplaxes, 124 Myocardium, circulatory, no Myoma, 95 Myotomes, 35 Myxedema, 239 Nail leaves, 349 Nails, 347 Nasofrontal process, 142 Nerve, auditory, 448 cells, bipolar, 99 of posterior horn, 373 unipolar, 98 endings, free sensory, 362 motor, 359 sensory, 361 fibers, 101 medullated, 101 non-medullary, 105 plexus, 98 supply of alimentary canal, 208 of muscles, 94, 95 of teeth, 169 of tongue, 182 terminations, peripheral, 359 in non-striated muscle, 360 in striated muscle, 359 Nerves of kidney, 271 of liver, 231 of lungs, 254 of mammary gland, 333 of suprarenal bodies, 258 of testicle, 290 of uterus, 321 spinal, 372 Nervous system, central, blood- vessels of, 407 tissue, 96 axis cylinder, 97, 101 bipolar, nerve cells, 99 classification of, 98 collaterals, 97 dendrite, 98 Nervous tissue, endoneurium, 106 epineurium, 106 exolemma, 103 fibrils, 101, 102 funiculus of, 106 ganglia, 98 general considerations, 108 implantation cone, 103 medullary sheath, 101, 103 medullated nerve fibers, 101 multipolar cells, 100 nerve fibers, 101 plexus, 98 trunk, 106 neuroma, 108 neuron, 96 theory, 109 neuroplasm, 103 neuropodia, 106 node of Ranvier, 105 non-medullary nerve fibers, 105 perineurium, 106 Schmidt-Lantermann seg- ments, 105 spinal ganglion, 99 unipolar nerve cells, 98 Net knobs, nuclear, 42 Neumann's sheaths, 158 Neural canal, 35 groove, 369 Neuroglia, 106, 404 Neuroma, 108 Neuromere, 382 Neuron, 96 theory, 109 Neuroplasm, 103 Neuropodia, 106 Neutrophiles, 121 Nipple, 333 Nitric acid, 463 Nodes, lymph, function of, 135 Ranvier's, 105 solitary lymph, 199 Nodules, agminated lymph, 200 Nuclear membrane, 463 sap, 40 Nuclei pontis, 395 Nucleolus, 40 Nucleoplasm, 42 Nucleus, 40 arcuate, 389, 391 INDEX 479 Nucleus, cuneatus, 377 Deiters', 380 gracilis, 377 mesial olivary, 389 Nucleus, solitary, 391 Stilling's, 374 Odontoblasts, 158, 160 Olfactory organ, 451 Olivary body, 387, 391 nucleus, mesial, 389 Olive, superior, 395 Omasum, 194, 195 Ontogeny, 27 Optic papilla, 425 vesicle, primary, 409 secondary, 409 Ora serrata, 425, 426 Organ, defined, 26, 28 of Corti, 445 Osmic acid, 462 Ossification of bone, 85 Osteoblasts, 86, 124, 167 Osteoclasts, 86, 124, 167 Osteogenetic layer of bone, 82 Os uteri, 317 Otoliths, 440 Ovaries, 299 ' tunica albuginea, 301 Ovulation, 28, 29, 303 Ovules, 60 Ovum, 26, 302, 306 Pacinian corpuscle, 367 Palate, 144 cleft, 144 Pal-Weigert stain, 467 Pancreas, 214 centro-acinal cells of, 216, 217 zymogen granules of, 216 Papilla of hair, 346 of tongue, 177 circumvallate, 178 filiform, 177 foliate, 181 fungiform, 177, 178 optic, 425 Paradidymis, 288 Paraffin imbedding, 21 advantages of, 23 Paraffin imbedding, disadvan- tages of, 23 melting-point of, 22 sections, staining of, 24 solidification of, 22 Paralinin, 40 Paraplasm, 38 Parathyroids, 240 Parietal cells of salivary glands, 212 Paroophoron, 315 Parotid glands, 101, 103 Parotitis, 211 Parovarium, 315 Pars ciliaris retinae, 418 Patches, Peyer's, 131, 200 Peduncle, inferior, of cerebel- lum, 386 Pelvis of kidney, 262 Penis, 290 glands of, 290, 291, 293 Pepsin, 190 Pepsinogen, 190 Perichondrion, 77 Peridental membrane, 163 Perimysium, 90 Perineurium, 106 Periosteum, 82 Peripheral nerve terminations, 359 in non-striated muscle, 360 in striated muscle, 359 Peritoneum, 65 Petit's canal, 428 Peyer's patches, 131, 200 Pharyngeal tonsils, 182 Pharynx, 182 Phylogeny, 27 Pia of brain, 383 of spinal cord, 371 Picric acid, 463 Picrosulphuric acid, 463 Pigment cells, 69 Pigmentation, 75 Placenta, 326 Plasma cells, 71 Platelets, blood, 121 Pleura, 65, 245 Pleurodont dentition, 171 Plexus, Auerbach's, 192, 208 Meissner's, 192, 208 480 INDFX Plexus, nerve, 98 Podophyllous tissue, 351 Poisoning, blood-, 136 Polar bodies, 29, 309 rays, 44 Polymorphic cells of cerebrum, 403 Polynuclear cells, 121 Pons, 392 gray matter of, 394 trapezium of, 394 white matter of, 394 Portal canal, 222 Posterior gray commissure of cord, 373 horn of cord, 373 longitudinal bundle, 391, 394 root-fibers, termination of, 378 Potassium bichromate and for- malin, 465 Pregnancy, 325 Preparation of material, 17 Preparing tissue, review of, 25 Prepuce, 291 Prickle cells, 339 Processus reticularis, 374 Pronephros, 260 Pronucleus, 30 Prophase, 43 Prostate gland, 296 Prostatic sinus, 294 Protoplasm, 37 theory, 37 Pupil, 419 Purkinje's cells, 398 Pyramidal cells of cerebrum, 403 tract, crossed, 379 direct, 381 Pyramids, Malpighian, 262 of Ferrein, 263 of medulla, 389 Ranvier's node, 105 Raphe, median, 395 Receptaculum chili, 128 Red blood-corpuscles, 118 crenated, 119 muscle, 94 Reduction mitosis, 30 Refractory media of eye, 426 Regeneration of bone, 85 Reissner's membrane, 444 Renal sinus, 262 Reproductive organs in female, 303 Respiratory bronchi, 246 Restiform body, 386 Rete testis, 280, 285 Reticular connective tissue, 73 Reticulum, 194, 195 Retina, 419 Retzius' lines, 151 Review of preparing tissue, 25 Rods of Corti, 446 Rolando's substantia gelatinosa, 373, 389 Rouleaux, 118 Rufini corpuscles, 352 Rumen, 194 Ruminants, stomach in, 194 Sacculte of large intestine, 202, 203 Sacculus, 438-440 endolymphaticus, 439 Salivary glands, 209 accessory, 213 parietal cells of, 212 Santorini's duct, 216 Sap, nuclear, 40 Sarcode, 87 Sarcolemma, 91 Sarcoma, 74 melanotic, 75 Sarcomere, 93 Sarcoplasm, 91 Sarcostyle, 88, 91 Sarcous element of muscle, 93 Sartoli's column, 279 Scala tympani, 444 vestibuli, 444 Schlemm's canal, 413 Schmidt-Lantermann segments, 105 Sclera, 153 Sebaceous cysts, 357 glands, 357 Sebum, 357 Secondary dentin, 159 Secreting membranes, 64 Sections, cutting, 23 Segmentation, 31 Segments, Schmidt-Lantermann, 105 INDEX 481 Semen, 289 Semicircular canals, 438, 441 Seminal vesicles, 287 Sensitive lamina, 349, 351 Sensory decussation, 388 nerve endings, 361 free, 362 Serous coat of small intestine, 202 of stomach, 192 membrane, defined, 62 Sex, determination of, 50 Sharpey's fibers, 82 primary areolae, 83 secondary areolae, 84 Sheaths of Neumann, 158 Sinus, milk, 331 pocularis, 294 prostatic, 294 renal, 262 Skein, daughter, 45 mother, 43 Skin, 335 layers of, 337 muscle of, 340 Small intestine, 196 blood-supply of, 205 mucosa, 196 muscular layer, 201, 202 serosa, 202 submucosa, 201 Smegma, 291 Sole plates, 359 Solidification of paraffin, 22 Solitary lymph node, 130 nucleus, 391 Somatic mitosis, 30 Somatopleure, 34 Somites, mesoblastic, 35 Spermatids, 280 Spermatoblasts, 280 Spermatocytes, 280 Spermatogenesis, 282 Spermatogonia, 279 Spermatozoa, 60, 282 structure of, 283 Sphere, attraction, 44 Spider cells, 104 Spinal cord, 369 anterior gray commissure of, 373 horn of, 374 31 Spinal cord, arachnoid of, 371 blood-supply of, 407 cauda echina, 369 central canal of, 373 cervical enlargement, 369 dura of, 370 filum terminale, 369 fissures of, 371 gray matter of, 373 lateral horn of, 374 lumbar enlargement, 369 membranes of, 370 meninges of, 370 origin of, 35 pia of, 371 posterior gray commissure of, 373 horn of, 373 tracts of, 377 summary, 392 white matter of, 374 ganglion, 99 nerves, 372 Spindle muscle, 368 Spiral ganglia, 448 Spirem, 43 Splanchnopleure, 34 Spleen, 133 function of, 136 ampulla of Thoma of, 135 in typhoid fever, 137 Malpighian corpuscle of, 134 Spongioplasm, 38, 41 Staining celloidin sections, 22 paraffin sections, 24 Stains, 465 anilin, 467 Pal-Weigert, 467 Stellate cells of cerebellum, 397 of Kupffer, 231 Stenson's duct, 209 Stigmata, 66 of blood-vessels, 118 Stilling's nucleus, 374 Stomach, 186 blood-supply of, 205 crypts of, 188 glands of, 189 in ruminants, 194 mucosa, 187 muscular layer, 192 serosa, 192 482 INDEX Stomach, submucosa, 191 Stomata, 66 of blood-vessels, 118 Stomodeum, 140 Stratum granulosum of ovum, 304 of skin, 338 lucidum, 338 Striae acusticae, 386 Striated muscle, peripheral nerve terminations in, 359 Stroma, blood, 118 Subarachnoid space, 384 Subendothelium of arteries, in, 112 Sublingual gland, 211 Submaxillary gland, 213 Submucous coat of small intes- tine, 201 of stomach, 191 Substantia gelati nosa of Ro- lando, 375, 389 Superior olive, 395 Supporting tissue, 66 Suprarenal glands, 64, 255 blood-vessels of, 257 clinical features, 259 nerves of, 258 structure of, 256 Sweat glands, 354 Sympathetic system, 107 Syncytium, 328 System, defined, 26 Tactile cells, 363 hairs, 344 Taeniae coli, 202 Tarsal glands, 431 plates, 432 Taste buds, 179 Teasing, 17 Teeth, 145 attachment of, 170 blood-supply of, 168 cementum, 161 dentin, 157 development of, 172 enamel, 149 rods, directions of, 152 lines of Retzius, 151 nerve supply, 169 Teeth, secondary dentin, 159 structure of, 149 Teichman's crystals, 122 Telophase, 46 Tendon spindle, 367 Tenon's capsule, 413 Tentorium, 383 Testes, interstitial elements of, 280, 281 Testicle, 381 excretory ducts of, 285 function of, 281 interstitial cells of, 64 lymphatics of, 290 nerves of, 290 structure of, 279 vessels and nerves, 239 Theca, 304 Thecodont dentition, 171 Thoma, ampullae of, 135 Thoracic lymph duct, 128 Thymus gland, 131 function of, 135 Thyroglossus duct, 237 Thyroid gland, 64, 237 structure of, 238 vessels and nerves of, 239 Thyroidima, 239 Tissues, classified, 189 defined, 26, 28 Tomes' granular layer, 158 Tongue, 174 blood-supply of, 182 foramen cecum of, 176 glands of, 181 nerve supply of, 182 papillae of, 177 circumvallate, 178 filiform, 177 foliate, 181 fungiform, 177, 178 Tonsil, 183 pharyngeal, 182 Trachea, 241 cartilage of, 242 mucous membrane of, 244 structure of, 241 Tracts of cord, summary, 392 Trapezium of pons, 394 Trigone of bladder, 274 Trigonum hypoglossi, 386 vagi, 386 INDEX 483 Tubular casts of kidney, 267 Tubules of kidney, 264 Tubuli recti, 280, 285 adventitia of artery, in, 113 albuginea, 278, 301 externa of eye, 412 intima of artery, in media of artery, in, 112 vaginalis, 276, 277 vasculosa, 278 Tympanic cavity, 436 membrane, 436 Typhlosole, 198 Typhoid fever, spleen in, 137 Tyson's glands, 291 Unicellular glands, 59, 60 Unipolar nerve cells, 98 Ureters, 271 function of, 273 structure of, 271 Urethra in female, 96 in male, 293 Urinary organs, 255 Uterus, 315 masculine, 294 muscular layer, 320 structure of, 319 vessels and nerves of, 321 Utriculus, 438 Vacuoles, 41 Valvulae conniventes, 197 Vas deferens, 286 structure of, 287 Vasa efferentia, 285 vasorum, 114, 126 Vascular laminae, 349, 351 Veins, 115 Vermiform appendix, 204 Vernix caseosa, 337 Verumontanum, 294 Vestibule, 438 Villi, chorionic, 327 of small intestine, 198 Visceral arches, 140 Vitelline membrane, 308 Vitellus, 307 Vitreous humor, 410, 428 membrane of, 417 Vocal cords, 236 Volkmann's canals, 80 Voluntary muscle, 90 distribution of, 95 Waldeyer's central cell column, 374 Wandering cells, 71, 121 Washing tissues, 20 Weigert-Pal stain, 467 Weil, layer of, 161 Wens, 358 Wharton's duct, 72, 213 jelly, 69, 329 White blood-corpuscles, 120 fibrous cartilage, 78 connective tissue, 72 matter of pons, 393 of spinal cord, 374 muscle, 93, 94 Winslow's foramen, 221 Wirsung's duct, 215 Wolffian body, 260 duct, 260 Yellow elastic connective tissue, 73 Zellknoten, 328 Zenker's fluid, 464 Zona pellucida, 306 radiata, 306 reticularis, 373 terminalis, 373 Zymogen, 211 granules of pancreas, 216 SAUNDERS' BOOKS on SURGERY and ANATOMY W. B. SAUNDERS COMPANY West Washington Square Philadelphia 9, Henrietta Street Covent Garden, London Our Handsome Complete Catalogue will be Sent You on Request Crile and Lower's Anoci-Association Anoci-Association. By George W. Crile, M. D., Pro- fessor of Surgery, and William E. Lower, M. D., Associate Professor of Genito-urinary Surgery, Western Reserve University. Octavo of 275 pages, illustrated. JUST OUT-EXTREMELY IMPORTANT Anoci-association robs surgery of its harshness, diminishes postoperative mortality, lessens postoperative complications (shock, nausea, vomiting, gas pains, backache, nephritis, pneumonia, etc.). You get here, first of all, a monograph on shock. Then follow chapters on the principles of anoci-associa- tion; the technic of its application in the administration of the anesthetic in abdominal operations, in gynecologic operations, in genito-urinary work, in operations for cancer of the breast, rectum, stomach, uterus, larynx, and tongue; in exophthalmic goiter operations ; in operations on the brain and the extremi- ties. Then come chapters on anoci-association and blood-pressure and the technic of nitrous-oxid-oxygen anesthesia. 2 SA UNDERS 'BO OKS ON Keen's New Surgery Surgery: Its Principles and Practice. Written by 82 eminent specialists. Edited by W. W. Keen, M. D., LL. D., Hon. F. R. C. S., Eng. and Edin., Emeritus Professor of the Principles of Surgery and of Clinical Surgery at the Jefferson Medical College, Philadelphia. Six large octavo volumes of over 1050 pages each, containing 3100 illustrations, 157 in colors. Fer volume: Cloth, $7.00 net; Half Morocco, $8.00 net. VOLUME VI GIVES YOU THE NEWEST SURGERY In this sixth volume you get all the newest surgery-both general and special-from the pens of those same international authorities who have made the success of Keen's Surgery world-wide. Each man has searched for the new, the really useful, in his particular field, and he gives it to you here. Here you get the newest surgery, and fully illustrated. Then, further, you get a complete index to the entire six volumes, covering 125 pages, but so arranged that reference to it is extremely easy. If you want the newest sur- gery, you must turn to the new " Keen " for it. Bryan's Surgery Principles of Surgery. By W. A. Bryan, M.D., Professor of Surgery and Clinical Surgery at Vanderbilt University, Nash- ville. Octavo of 677 pages, with 224 original illustrations. Cloth, $4.00 net. JUST ISSUED Dr. Bryan here gives you facts, accurately and concisely stated, without which no modern practitioner can do modern work. He discredits many fallacious ideas, giving you facts instead. He shows you in a most practical way the relations between surgical pathology and the resulant symptomatology, and points out the influence such information has on treatment. Dr. A. Vander Veer, Albany Medical College " It comes to us full of new ideas. So much that is clear and concise has been added that it is fascinating to study the work. It is bound to receive a hearty welcome." SURGERY AND ANATOMY. 3 Hornsby and Schmidt's The Modern Hospital The Modern Hospital. Its Inspiration; Its Construction; Its Equipment; Its Management. By John A. Hornsby, M.D., Secretary, Hospital Section, American Medical Association ; and Richard E. Schmidt, Architect. Large octavo of 644 pages, with 207 illustrations. Cloth, $7.00 net; Half Morocco, $8.50 net. ADOPTED AT ONCE BY THE U. S. GOVERNMENT AS "THE LAW" "Hornsby and Schmidt'' tells you just exactly how to plan, construct, equip, and manage a hospital in all its departments, giving you every detail. It gives you exact data regarding heating, ventilating, plumbing, refrigerating, etc.-and the costs. It tells you howto equip a modern hospital with modern appliances. It tells you what you need in the operating room, the wards, the private rooms, the dining room, the kitchen-every division of hospital house- keeping. It gives you definite diets for the patients and the hospital house- hold. It gives you hundreds of valuable points on the business management of hospitals-large and small. Allen's Local Anesthesia Local Anesthesia. By Carroll W. Allen, M. D., In- structorin Clinical Surgery at Tulane University of Louisiana. Octavo of 625 pages, illustrated. JUST READY This is a complete work on this subject. You get the history of local anesthesia, a chapter on nerves and sensation, giving particular attention to pain-what it is and its psychic control. Then comes a chapter on osmosis and diffusion. Each local anesthetic is taken up in detail, giving very special attention to cocain and novocain, pointing out the action on the nervous system, the value of adrenalin, paralysis caused by cocain anesthesia, control of tox- icity. You get Crile's method of administering adrenalin and salt solution, the exact way to produce the intradermal wheal, to pinch the flesh for the inser- tion of the needle-all shown you step by step. You get an article on anoci- association, the production of local anesthesia in the various regions, spinal analgesia, and epidural injections. There is a large section on dental anesthesia. 4 SAUNDERS' BOOKS ON Cotton's Dislocations and Joint Fractures Dislocations and Joint Fractures. By Frederic Jay Cotton, A. M., M. D., First Assistant Surgeon to the Boston City Hospital. Octavo volume of 654 pages, with 1201 original illustrations. Cloth, $6.00 net. TWO PRINTINGS IN EIGHT MONTHS Dr. Cotton's clinical and teaching experience in this field has especially fitted him to write a practical work on this subject. He has written a book clear and definite in style, systematic in presentation, and accurate in state- ment. The author is himself the artist, so that the illustrations show just those points he wished to emphasize. Boston Medical and Surgical Journal "The work is delightful, spirited, scholarly, and original. It brings the subjects up to date-a feat long neglected." Murphy's Famous Clinics Surgical Clinics of John B. Murphy, M. D., at Mercy Hospital, Chicago. Issued serially, one number every other month (six numbers a year). Each issue about 175 octavo pages, illustrated. Per year: $8.00 ; Cloth, $12.00. Sold only by the calendar year. YOU NOW GET DR. MURPHY'S METHODS OF DIAGNOSIS This is just the work you have been waiting for-a permanent record of the teachings of this great surgeon. These Clinics are published just as de- livered by Dr. Murphy, an expert stenographer taking down everything Dr. Murphy says and does. In this way these Clinics retain all that individual force and charm so characteristic of the clinical teaching of this distinguished surgeon. But the most vital point about these Clinics is that they are abso- lutely fresh. They are surgery-practical, applied surgery-right down to the minute, published practically as soon as delivered. There is no stale matter. Everything is new, never having appeared tn print before. It is all live clinical material. SURGERY AND ANATOMY 5 Crandon and Chrenfried's Surgical After-treatment Surgical After-treatment. By L. R. G. Crandon, M. D., Assistant in Surgery, and Albert Ehrenfried, M. D., Assistant in Anatomy, Harvard Medical School. Octavo of 831 pages, with 265 original illustrations. Cloth, $6.00 net. THE NEW (2d) EDITION This work tells how best to manage all problems and emergencies of sur- gical convalescence from recovery-room to discharge. It gives all the details completely, definitely, yet concisely, and does not refer the reader to some other work perhaps not then available. The postoperative conduct of all operations is given. There is an elaborate chapter on Vaccine Therapy, Im- munization by Inoculation, and Specific Sera, by Dr. George P. Sanborn. Therapeutic Gazette " This book is one which can be read with profit by the active surgeon and practitioner and will be generally commended." Collected Papers by the Staff of St. Mary's Hospital, Mayo Clinic Collected Papers by the Staff of St. Mary's Hospital, Mayo Clinic. By William J. Mayo, M.D., Charles H. Mayo, M.D., and their Associates at St. Mary's Hospital, Rochester, Minn. Papers of 1905-09, Papers of 1910, Papers of 1911, Papers of 1912, Papers of 1913. Each $5.50 net. A Collection of Papers (published previous to 1909). By W. J. and C. H. Mayo. Two octavos of 525 pages each, illus- trated. Per set: Cloth, $10.00 net. 6 SAUNDERS' BOOKS ON Mumford's Practice of Surgery The Practice of Surgery. By James G. Mumford, M. D., Instructor in Surgery, Harvard Medical School. Octavo of 1032 pages, with 683 illustrations. Cloth. $7.00 net. JUST OUT-NEW 12d) EDITION This is a clinical surgery, giving those methods and operations which the author has personally followed for the past twenty years. The plan of the work is somewhat off the conventional lines, the diseases being taken up in their order of interest, importance, and frequency. John B. Murphy, M. D., Northwestern Medical School, Chicago "This work truly represents Dr. Mumford's intellectual capacity and scope, and pre- sents in a terse, forceful, yet pleasing manner, the live surgical topics of the day. It is in every particular up to date." DaCosta's Modern Surgery Modern Surgery-General and Operative. By John Chalmers DaCosta, M. D., Samuel D. Gross Professor of Sur- gery, Jefferson Medical College, Philadelphia. Octavo of 1515 pages, with 1085 illustrations. Cloth, $6.00 net; Half Morocco, $7.50 net. JUST READY-NEW (7th) EDITION A surgery, to be of the maximum value, must be up to date, must be com- plete, must have behind its statements the sure authority of experience, must be so arranged that it can be consulted quickly; in a word, it must be practical and dependable. Such a surgery is DaCosta's. Always an excellent work for this edition it has been very materially improved by the addition of much new matter and many additional illustrations. Rudolph Matas, M.D., Professor of Surgery, Tulane University of Louisiana. " This edition is destined to rank as high as its predecessors, which have placed the learned author in the fore of text-book writers. The more I scrutinize its pages the more I admire the marvelous capacity of the author to compress so much knowledge in so small a space." SURGER Y AND ANA TOM Y 7 Scudder's Fractures WITH NOTES ON DISLOCATIONS The Treatment of Fractures : with Notes on a few Com- mon Dislocations. By Charles L. Scudder, M. D., Surgeon to the Massachusetts General Hospital, Boston. Octavo volume of 708 pages, with 994 illustrations. Polished Buckram, $6.00 net. THE NEW (7th) EDITION, ENLARGED OVER 33,500 COPIES Seven large editions of this remarkable book is a decisive indication of the value of Dr. Scudder's work. For this new edition numerous ad- ditions have been made throughout the text and a large number of new illustrations added, greatly enhancing the value of the work. In every way this edition reflects the very latest advances in the treatment of fractures. J. F. Binnie, M. D., formerly University of Kansas. " Scudder's Fractures is the most successful Look on the subject that has ever been published. I keep it at hand regularly." Scudder's Tumors of the Jaws Tumors of the Jaws. By Charles L. Scudder, M. D., Surgeon to the Massachusetts General Hospital, Boston. Octavo of 395 pages, with 353 illustrations, 6 in colors. Cloth, $6.00 net. WITH NEW ILLUSTRATIONS Dr. Scudder in this book tells you how to determine in each case the form of new growth present, and then points out the best treatment. As the tendency of malignant disease of the jaws is to grow into the accessory sinuses and toward the base of the skull, an intimate knowledge of the anatomy of these sinuses is essential. Dr. Scudder has included, therefore, sufficient anatomy and a number of illustrations of an anatomic nature. Whether gen- eral practitioner or surgeon, you need this new book because it gives you just the information you want. 8 SAUNDERS' BOOKS ON Sisson's Veterinary Anatomy Text-Book of Veterinary Anatomy. By Septimus Sis- son, S. B., V. S., Professor of Comparative Anatomy in Ohio State University. Octavo volume of 826 pages, with 588 illus- trations, mostly original and many in colors. Cloth, $7.00 net. WITH SUPERB ILLUSTRATIONS This is a clear and concise statement of the essential facts regarding the structure of the principal domesticated animals, containing many hitherto unpublished data resulting from the detailed study of formalin-hardened subjects and frozen sections. The author has devoted much time and care to the illustrations. This is the only veterinary anatomy in thirty years, and is used in every veterinary school in the country. Boston Medical and Surgical Journal "This fine piece of bookmaking is comparable to the best works on human anatomy, and is a decided addition to good veterinary literature." Gant's Intestinal Stasis (Constipation and Obstruction) Intestinal Stasis (Constipation and Obstruction). By Samuel G. Gant, M. D., Professor of Diseases of the Rectum and Anus, New York Post-Graduate Medical School and Hos- pital. Octavo of 560 pages, with 250 original illustrations. Cloth, $6.00 net. INCLUDING RECTUM AND ANUS The Proctologist " Were the profession better posted on the contents of this book there would be less suf- fering from the ill effects of constipation. We congratulate the author on this most com- plete book." SUE GEE Y AND ANA TOMY g Kelly and Noble's Gynecology and Abdominal Surgery Gynecology and Abdominal Surgery. Edited by Howard A. Kelly, M. D., Professor of Gynecology in Johns Hopkins University; and Charles P. Noble, M. D., formerly Clinical Professor of Gynecology, Woman's Medical College, Philadel- phia. Two imperial octavos of 950 pages each, with 880 illustra- tions. Per volume: Cloth, $8.00 net; Half Morocco, $9.50 net. WITH 880 ILLUSTRATIONS BY BECKER AND BRODEL This work possesses a number of valuable features not to be found in any other publication covering the same fields. It contains a chapter upon the bacteriology and one upon the pathology of gynecology, and a large chapter devoted entirely to medical gynecology, written especially for the physician engaged in general practice. Abdominal surgery proper, as distinct from gynecology, is fully treated, embracing operations upon the stomach, intes- tines, liver, bile-ducts, pancreas, spleen, kidneys, ureter, bladder, and peri- toneum. American Journal of Medical Sciences "It is needless to say that the work has been thoroughly done; the names of the authors and editors would guarantee this, but much may be said in praise of the method of presentation; and attention may be called to the inclusion of matter not to be found elsewhere." Bickham's Operative Surgery A Text=Book of Operative Surgery. By Warren Stone Bickham, M. D., of New York. Octavo of 1200 pages, with 854 original illustrations. Cloth, $6.50 net; Half Morocco, $8.00 net. THIRD EDITION Boston Medical and Surgical Journal " The book is a valuable contribution to the literature of operative surgery. It repre sents a vast amount of careful work and technical knowledge on the p art of the author- For the surgeon in active practice or the instructor of surgery it is an unusually good review of the subject." IO SAUNDERS' BOOKS ON Eisendrath's Surgical Diagnosis A Text=Book of Surgical Diagnosis. By Daniel N. Eisen- drath, M. D., Professor of Surgerv in the College of Physicians and Surgeons, Chicago. Octavo of 885 pages, with 574 entirely new and original text-illustrations and some colored plates. Cloth, $6.50 net; Half Morocco, $8.00 net. SECOND EDITION WITH 574 ORIGINAL ILLUSTRATIONS Dr. Eisendrath takes up each disease and injury amenable to surgical treatment, and sets forth the means of correct diagnosis in a systematic and comprehensive way. Definite directions as to methods of examination are pre- sented clearly and concisely, providing for all contingencies that might arise in any given case. Each one of the four hundred and eighty-two magnifi- cent illustrations indicates precisely how to diagnose the condition considered. Surgery, Gynecology, and Obstetrics " The book is one which is well adapted to the uses of the practising surgeon who desires information concisely and accurately given." Eisendrath's Clinical Anatomy A Text=Book of Clinical Anatomy. By Daniel N. Eisen- drath, A. B., M. D., Professor of Surgerv in the College of Physicians and Surgeons, Chicago. Octavo ot 535 pages, with original illustrations. Cloth, $5.00 net. SECOND EDITION This new anatomy discusses the subject from the clinical standpoint. A portion of each chapter is devoted to the examination of the living through palpation and marking of surface outline of landmarks, etc. The illustrations are original. Medical Record, New York " A special recommendation for the figures is that they are mostly original and were made for the purpose in view The sections of joints and trunks are those of formalinized cadavers and are unimpeachable in accuracy." SURGERY AND ANATOMY n Fenger Memorial Volumes Collected Works of Christian Fenger, M. D. Edited by Ludvig Hektoen, M. D., Professor ot Pathology, Rush Medical College, Chicago. Two octavos of 525 pages each. Per set: Cloth, $15.00 net; Half Morocco, $18.00 net. LIMITED EDITION These handsome volumes consist of all the important papers written by the late Christian Fenger. Not only the papers published in English are in- cluded, but also the translations of those which originally appeared in Danish, German, and French. Sobotta and McMurrich's Human Anatomy Atlas and Text=Book of Human Anatomy. In Three Volumes. By J. Sobotta, M. D., of Wurzburg. Edited, with additions, by J. Playfair McMurrich, A. M., Ph. D., Professor of Anatomy, University of Michigan. Three large quartos, each containing 250 pages of text and over 300 illustrations, mostly in colors. Per volume : Cloth, $6.00 net. Edward Martin, M.D., University of Pennsylvania. " This is a piece of bookmaking which is truly admirable, with plates and text so well chosen and so clear that the work is most useful." Campbell's Surgical Anatomy A Text-Book of Surgical Anatomy. By William Francis Campbell, M. D., Professor of Anatomy, Long Island College Hospital. Octavo of 675 pages, with 319 original illustrations. Cloth, $5.00 net. This is in the fullest sense an applied anatomy-an anatomy that will be of inesti- mable value to the surgeon because only those facts are discussed and only those structures and regions emphasized that have a peculiar interest to him. 12 SAUNDERS' BOOKS ON Moynihan's Duodenal Ulcer Duodenal Ulcer. By Sir B. G. A. Moynihan, M. S. (London), F.R.C.S., Leeds, England. Octavo of 486 pages, il- lustrated. Cloth, $5.00 net. SECOND EDITION For this edition the work has been entirely reset and brought up to date. All the cases operated upon since the appearance of the first edition have been included and a new chapter added on jejunal and Gastro-jejunal Ulcers. Moynihan's Abdominal Operations Abdominal Operations. By Sir B. G. A. Moynihan, M. S. (London), F.R.C.S., Leeds, England. Octavo, illustrated. THE NEW (3d) EDITION-PREPARING Edward Martin, M. D., University of Pennsylvania. " It is a wonderfully good book. He has achieved complete success in illustrating, both by words and pictures, the best technic of the abdominal operations now commonly performed." Moynihan on Gall-stones Gall-stones and their Surgical Treatment. By B. G. A. Moynihan, M. S. (Lond.), F.R.C.S., Leeds, England. Octavo of 458 pages, illustrated. Cloth, $5.00 net. SECOND EDITION British Medical Journal " He expresses his views with admirable clearness, and he supports them by a large number of clinical examples, wiiich will be much prized by those who know the difficult problems and tasks which gall-stone surgery not infrequently presents." Dannreuther's Emergency Surgery Minor and Emergency Surgery. By Walter T. Dann- reuther, M. D., Surgeon to St. Elizabeth's Hospital and to St. Bartholomew's Clinic, New York City. i2mo of 225 pages, illustrated. Cloth, $1.25 net. SURGERY AND ANATOMY 13 Gould's Operations on Intestines and Stomach The Technic of Operations Upon the Intestines and Stomach. By Alfred H. Gould, M.D., of Boston. Large octavo, with 190 original illustrations, some in colors. Cloth, $5.00 net; Half Morocco, $6.50 net. " The illustrations are so good that one scarcely needs the text to elucidate the steps of the operations described. The work represents the best surgical knowledge and skill."-New York State Journal of Medicine. McClellan's Art Anatomy Anatomy in its Relation to Art. By George McClellan, M.D., Professor of Anatomy, Pennsylvania Academy of the Fine Arts. Quarto volume, 9 by 12^ inches, with 338 original drawings and photographs, and 260 pages of text. Dark blue vellum, $10.00 net; Half Russia, $12.50 net. Griffith's Hand-Book of Surgery A Manual of Surgery. By Frederic R. Griffith, M. D., Sur- geon to the Bellevue Dispensary, New York City. I2mo of 579 pages, with 417 illustrations. Flexible leather, $2.00 net. Keen's Addresses and Other Papers Addresses and Other Papers. Delivered by William W. Keen, M. D., LL.D., F. R. C. S. (Hon.), Professor of the Principles of Surgery and of Clinical Surgery, Jefferson Medical College, Philadelphia. Octavo volume of 441 pages, illustrated. Cloth, $3-75 net- Keen on the Surgery of Typhoid The Surgical Complications and Sequels of Typhoid Fever. By Wm. W. Keen, M. D., LL.D., F. R. C. S. (Hon.), Professor of the Principles of Surgery and of Clinical Surgery, Jefferson Medical College, Philadelphia, etc. Octavo volume of 386 pages, illustrated. Cloth, $3.00 net. American Text-Book of Surgery Fourth Edition American Text-Book of Surgery. Edited by W. W. Keen, M. D., LL. D., Hon. F. R. C. S., Eng. and Edin.; and J. William White, M. D., Ph. D. Octavo, 1363 pages, 551 text-cuts and 39 colored and half-tone plates. Cloth, $7.00 net; Half Morocco, $8.50 net. Robson and Cammidge on the Pancreas The Pancreas : Its Surgery and Pathology. By A. W. Mayo Robson, F. R. C. S., of London, England ; and P. J. Cammidge, F. R. C. S., of London, England. Octavo of 546 pages, illustrated. Cloth, $5.00 net; Half Morocco, $6.50 net. 14 SAUNDERS' BOOKS ON American Illustrated Dictionary New (7th) Editio„ The American Illustrated Medical Dictionary. With tables of Arteries, Muscles, Nerves, Veins, etc. ; of Bacilli, Bacteria, etc.; Eponymic Tables of Diseases, Operations, Stains, Tests, etc. By W. A. Newman Dorland, M. D. Large octavo, 1107 pages. Flexible leather, $4.50 net; with thumb index, $5.00 net. Howard A. Kelly, M. D., Professor of Gynecology, Johns Hopkins "Dr. Dorland's dictionary is admirable. It is so well gotten up and of such convenient size. No errors have been found in my use of it.'' Golebiewski and Bailey's Accident Diseases Atlas and Epitome of Diseases Caused by Accidents. By Dk. Ed. Golebiewski, of Berlin. Edited, with additions, by Pearce Bailey, M.D. Cloth, $4.00 net. In Saunders' Hand-Atlas Series. Helferich and Bloodgood on Fractures Atlas and Epitome of Traumatic Fractures and Dislo- cations. By Prof. Dr. H. Helferich, of Greifswald, Prussia. Edited, with additions, by Joseph C. Bloodgood, M.D., Asso- ciate in Surgery, Johns Hopkins University, Baltimore. 216 colored figures on 64 lithographic plates, 190 text-cuts, and 353 pages of text. Cloth, $3.00 net. In Saunders' Atlas Series. Sultan and Coley on Abdominal Hernias Atlas and Epitome of Abdominal Hernias. By Pr. Dr. G. Sultan, of Gottingen. Edited, with additions, by Wm. B. Coley, M.D. Cloth, S3.00 net. In Saunders' Hand-Atlas Series. Warren's Surgical Pathology Edition Surgical Pathology and Therapeutics. By J. Collins Warren, M.D., LL.D., F.R.C.S.(Hon.), Professor of Sur- gery, Harvard Medical School. Octavo, 873 pages, 136 illus- trations. Cloth, $5.00 net; Half Morocco, $6.50 net. Zuckerkandl and DaCosta's Surgery Edition Atlas and Epitome of Operative Surgery. By Dr. O. Zuckerkandl, of Vienna. Edited, with additions, by J. Chalmers DaCosta, M. D., Samuel D. Gross Professor of Surgery, Jefferson Medical College, Philadelphia. 40 col- ored plates, 278 text-cuts, and 410 pages of text. Cloth, $3.50 net. In Saunders' Atlas Series. SURGERY AND ANATOMY . 15 Schultze and Stewart's Topographic Anatomy Atlas and Text-Book of Topographic and Applied Anatomy. By Prof. Dr. O. Schultze, of Wurzburg. Edited, with additions, by George D. Stewart, M. D., Professor of Anatomy and Clinical Sur- gery, University and Bellevue Hospital Medical College, N. Y. Large quarto of 189 pages, with 25 colored figures on 22 colored lithographic plates, and 89 text-cuts, 60 in colors. Cloth, $5.50 net. " I regard Schultze and Stewart's Topographic and Applied Anatomy as a very admirable work, for students especially, and I find the plates and the text excel- lent."-Arthur Dean Bevan, M.D., Professor of Surgery in Rush Medical Col- lege, Chicago. Haynes* Anatomy A Manual of Anatomy. By Irving S. Haynes, M. D., Professor of Practical Anatomy, Cornell University Medical College. Octavo, 680 pages, with 42 diagrams and 134 full-page half-tones. Cloth, $2.^0 net. American Pocket Dictionary New (8A) EdWon The American Pocket Medical Dictionary. Edited byW. A. Newman Dorland, A.M., M.D. 677 pages. Full leather, limp, with gold edges, $1.00 net; with patent thumb index, $1.25 net. Barton and Wells* Medical Thesaurus A Thesaurus of Medical Words and Phrases. By W. M. Barton, A. M., M. D., Assistant to Professor of Materia Medica and Therapeutics, Georgetown University, Washington, D. C. ; and Walter A. Wells, M. D., Demonstrator of Laryngology, Georgetown University, Washing- ton, D. C. I2mo of 534 pages. Flexible leather, $2.50 net; thumb index, $3.00 net. Meyer & Schmieden's Bier's Hyperemic Treatment Second Edition Bier's Hyperemic Treatment in Surgery, Medicine, and the Special- ties. By Willy Meyer, M. D., Professor of Surgery, New York Post- Graduate Medical School and Hospital; and Prof. Dr. Victor Schmie- den, Assistant to Professor Bier, University of Berlin, Germany. Octavo of 280 pages, illustrated. Cloth, $3.oo net. Morris* Dawn of the Fourth Era in Surgery Dawn of the Fourth Era in Surgery and Other Articles. By Robert T. Morris, M. D., Professor of Surgery, New York Post- Graduate Medical School and Hospital. I2mo of 145 pages, illustrated.. $1.25 net. 16 SURGERY AND ANATOMY Moore's Orthopedic Surgery A Manual of Orthopedic Surgery. By James E. Moore, M. D., Professor of Clinical Surgery, University of Minnesota, College of Medi- cine and Surgery. Octavo of 356 pages, handsomely illustrated. Cloth, $2.50 net. Fowler's Operating Room New (3d) Edition The Operating Room and the Patient. By Russell S. Fowlf.r, M. D., Chief Surgeon, First Division, German Hospital, Brooklyn, New York. Octavo of 611 pages, illustrated. Cloth, $3.50 net. International Text-Book of Surgery Second Edition The International Text-Book of Surgery. In two volumes. By American and British authors. Edited by J. Collins Warren, M. D., LL. D., F. R. C. S. (Hon.), Professor of Surgery, Harvard Medical School; and A. Pearce Gould, M. S., F. R. C. S., of London, England. Vol. I. : General and Operative Surgery. Royal octavo, 975 pages, 461 illustrations, 9 full-page colored plates. Vol. II. : Special or Regional Surgery. Royal octavo, 1122 pages, 499 illustrations, and 8 full-page colored plates. Per volume : Cloth, $5.00 net; Half Morocco, $6.50 net. Nancrede's Principles of Surgery Second Edition Lectures on the Principles of Surgery. By Charles B. Nan- crede, M. D., LL. D., Professor of Surgery and of Clinical Surgery, University of Michigan, Ann Arbor. Octavo, 407 pages, illustrated. Cloth, $2.50 net. Nancrede's Essentials of Anatomy. 7th Edition Essentials of Anatomy, including the Anatomy of the Viscera. By Charles B. Nancrede, M. D., Professor of Surgery and of Clinical Surgery, University of Michigan, Ann Arbor. Crown octavo, 388 pages, 180 cuts. With an Appendix containing over 60 illustrations of the osteology of the body. Based on Gray's Anatomy. Cloth, $1.00 net. In Saunders' Question Compends. Martin's Essentials of Surgery. Seventh Revised Edition Essentials of Surgery. Containing also Venereal Diseases, Surgi- cal Landmarks, Minor and Operative Surgery, and a complete description, with illustrations, of the Handkerchief and Roller Bandages. By Ed- ward Martin, A. M., M. D., Professor of Clinical Surgery, University of Pennsylvania, etc. Crown octavo, 338 pages, illustrated. With an Appendix on Antiseptic Surgery, etc. Cloth, $1.00 net. In Saunders' Question Compends. Martin's Essentials of Minor Surgery, Bandaging, and Venereal Diseases. Second Revised Edition Essentials of Minor Surgery, Bandaging, and Venereal Dis- eases. By Edward Martin, A. M., M. D., Professor of Clinical Sur- gery, University of Pennsylvania, etc. Crown octavo, 166 pages, with 78 illustrations. Cloth, $1.00 net. In Saunders' Question Compends.