Ill > !'!' .'I I ''i i'' I II |l V 'ii! '"""■'■'■'lliil fipptii!tti[ittiiii,i;i;iiii I, t'M llHliililill nolo ^J:,,:^!^^ - ^ / FLOWER-SPRECHER Library Digitized by Microsoft® DATE DUE . GAYLORD PRINTED IN U.S.A Digitized by Microsoft® This book was digitized by Microsoft Corporation in cooperation witli Cornell University Libraries, 2007. You may use and print this copy in limited quantity for your personal purposes, but may not distribute or provide access to it (or modified or partial versions of it) for revenue-generating or other commercial purposes. Digitized by Microsoft® Digitized by Microsoft® Digitized by Microsoft® STOHR'S HISTOLOGY ARRANGED UPON AN EMBRYOLOGICAL BASIS BY DR. FREDERIC T. LEWIS ASSISTANT PROFESSOR OF EMBRYOLOGY AT TH8 HARVARD MEDICAL SCHOOL. FROM THE TWELFTH GERMAN EDITION DR. PHILIPP STOHR PROFESSOR OF ANATOMY AT THH UNIVEKSITY OF WUIiZBOKG Siitb amertcan Ebition Mitb 450 tr I lustrations PHILADELPHIA P. BLAKISTON'S SON & CO. I0I2 WALNUT STREET 1906 Digitized by Microsoft® Copyright, 1903, by Dr. Alfred Schaper Copyright, igo6, by Estate of Dr. Alfred Schaper PRESS OP WM. F. FELL COMPANY 1220-24 SANSON! Street PHrLADELPHIA, PA. Digitized by Microsoft® NOTE. In the new edition of the American translation of my hand-book a number of additions and changes have been made by the translator with my permission. It is there- fore reasonable that I should not take the same responsibility for the translation as for the text of the German original, and I would ask those of my colleagues who wish to question the correctness of my assertions in their papers, to convince themselves, by making comparisons with my last German edition, that the paragraphs in question were written by me. Philipp Stohr. Digitized by Microsoft® Digitized by Microsoft® PREFACE. The need of a text-book of histology arranged upon an embryological basis has long been felt. At the Harvard Medical School this need has been urgent. There Professor Schaper, the editor of the five previous American editions of Stohf's Histology, planned such a book, and after his return to Germany its preparation was begim. It is greatly to be regretted that at the time of his death the work was only commenced, for there was • promise of a notable production. When the writer was informed that Professor Stohr had given gener- ous permission to adapt a new edition of his Histology to American needs it was decided to rearrange the book upon an embryological plan. This has been accomplished with the loss of some characteristic features of the German edition, for which the added material will, it is hoped, make com- pensation. Thus in order to have space for describing the controUing de- velopmental features of the organs, and for presenting their adult structure somewhat more fully, the directions for preparing sections have been reduced to the minimum. These may be supplemented by directions in the class room; and for the small proportion of students who intend to practice elaborate microscopical methods, a special text-book may be rec- ommended. It is not essential that a physician should be familiar with the details of many staining processes, but the structure of the adult organs and the developmental possibilities of their constituent tissues must be known. The nomenclature adopted is that published by the committee of the German Association of Anatomists in 1895 (Arch. f. Anat. u. Phys.; Anat. Ahth.; Supplement-Band), and which is now widely used. It is founded upon the sound principle that the name of a structure should be the simplest possible descriptive Latin term or phrase. Since the Latin names may be translated into the various modem languages the nomenclature is inter- national. Moreover a large number of the names are commonly used in their Latin forms. Personal names have been discarded (except Wolffian and Miillerian), thus greatly assisting the student. It is obviously easier to learn intestinal glands, duodenal glands, parotid duct, etc.-, rather than Lieberkiihn's glands, Brunner's glands, Stenson's duct, and the Hke. It has been estimated that five thousand synonyms have been rejected and are to be removed from the anatomist's vocabulary as soon as possible. In the following pages the more common of the rejected names have been placed in square brackets, [ ]. However difficult it may be for the older V Digitized by Microsoft® VI PREFACE. anatomists to conform to this nomenclature, it seems clearly a duty to the overworked medical students to adopt it. Excellent as the German nomenclature is, as a whole, it is not beyond improvement, and it may be desirable for a committee of the Association of American Anatomists to publish in their English forms a corresponding list of names.* As few changes as possible should be made, but it is certain, for example, that the ventral surface of the body will not be called anterior, or the dorsal surface posterior. In the following pages anterior always means toward the head. Common general terms should be made even more specific. For instance, it is questionable whether follicle (Latin, a small leather bag, a husk or shell) should be appHed to anything other than closed cysts like the follicles of the ovary and thyreoid gland. Its ap- pUcation by the Germans to the sheath of the hair and by many Amer- icans to solid nodules of lymphoid tissue may lead the student to wonder if "follicle" is not a colloquial rather than a scientific term. The attention of all students should be called to the American Journal of Anatomy, the quarterly publication of the Association of American Anatomists, which contains the results of current American anatomical and histological investigations. It probably affords the most satisfactory means by which a physician may keep in touch with these sciences. The writer has many acknowledgments to make for help received. Messrs. P. Blakiston's Son &l Co., and Mr. WilUam T. Ohver, the artist who has drawn the more elaborate of the new figures, have rendered all the assistance possible. Members of several departments at the Harvard Medical School have given valuable advice, and Dr. G. H. Wright, As- sistant in Dental Histology, has arranged a considerable portion of the section on the teeth. It is a privilege to present for the first time in a text- book, the discoveries of Dr. James H. Wright regarding the origin of blood plates. His remarkable conclusion that they are fragments of pseudopodia of the giant cells seems established beyond doubt by an examination of his specimens. Finally it is a pleasure to record that after studying histology and em- bryology under Professor Charles S. Minot, the writer has for several years enjoyed the closest association with him in his scientific work. The results of such unusual privilege should be found reflected in this edition of Professor Stohr's Histology. Frederic T. Lewis. Cambridge, Massachusetts, September, igo6. * The writer has since been informed that Messrs. Blakiston's Son & Co. have in press such a list prepared by Professor Barker and entitled "Anatomical Terminology." The orderly arrangement of these descriptive names makes the Latin list — and undoubtedly their English version also — an excellent means by which students may review anatomy. Digitized by Microsoft® CONTENTS. PART I. MICROSCOPIC ANATOMY. I. CYTOLOGY. PAOB I The Cell, Protoplasm. Nucleus. Centrosome. CellWaU. Form and Size of Cells; 7 PAGF. 7 Vital Phenomena, Amoeboid Motion. Formation and Reproduction of Cells, 9 Mitosis. Amitosis. Cytomorphosis, 15 II. GENERAL HISTOLOGY. Histogenesis, Segmentation and the Formation of the Germ Layers. The Fundamental Tissues. Epithelia, Origin. Shapes of Epithelial Cells. Number of Layers. Differentiation. Processes of Secretion. The Nature and Classification Glands. Mesenchymal Tissxtes, Reticular Tissue. Mucous Tissue. Connective Tissue. Tendon. Cartilage. 26 of 38 Nerve Tissue, Development of, — The central tract. The spinal ganglia. The ventral roots. The sympathetic system. The cerebral nerves. Structure of, — Nerve fibers and nerves. Sensory endings. Motor endings. Ganglia. The spinal cord. 90 Bone. Joints. Teeth (including the Ectodermal Enamel Organs). Muscle Tissue, Smooth Muscle. Cardiac Muscle. Striated Muscle. 77 Vascular Tissue, Blood Vessels. Development. Capillaries. Arteries. Veins. The heart. Lymphatic Vessels. Blood. Red corpuscles. White corpuscles. Blood plates. Plasma. Lymph. 124 Digitized by Microsoft® VIU CONTENTS. III. SPECIAL HISTOLOGY. PAGE Blood Forming and Blood Destroy- ing Organs, 152 Bone Marrow. Lymph Nodules and Lymph Glands. Haemolymph Glands. Spleen. The Entodermal Tract,.. 165 The Mouth and Pharynx, 165 Development. Palatine tonsils. Thymus. Thyreoid gland. Parathyreoid glands. Glomus caroticum. Tongue. Oral and pharyngeal cavities. Glands of the oral cavity. The Digestive Tube 193 Development. Oesophagus. Stomach. Small Intestine. Large Intestine. Rectum and Anus. The Liver, 218 The Pancreas, 230 The Respiratory Tract 234 Development. Larynx. Trachea, Bronchi. Lungs. Urinary Organs, 244 Wolffian Body. Pronephros. Kidney. Renal pelvis and ureter. Bladder. Urethra (in the female). Male Genital Organs, 263 Development. Testis. Epididymis. Ductus deferens. Seminal Vesicles and Ejaculatory Ducts. Appendices and Paradidymis. Prostate. Urethra and Penis. Female Genital Organs, 285 Development. Ovary. Epoophoron. Uterine Tubes. Uterus. Menstruation. Development of the decidual membranes. Structure of the membranes and placenta. Umbilical Cord. Vagina and External Genital Or- gans. Skin, 312 Nails. Hair. Sebaceous glands. Svjreat glands. Mammary glands. Suprarenal Glands 33 1 Brain and Sense Organs, 334 Brain, 33 j Development. Medulla oblongata. Pons. Cerebellum. Hemispheres. Hypophysis. Pineal body. Meninges. Eye, 353 Development. Retina. Optic nerve. Lens. Vitreous body. Tunica vasculosa. Tunica fibrosa. Vessels, chambers, and nerves. Eyelids. Lachrymal glands. Ear 378 Development. Internal ear, — Sacculus. Utriculus. Semicircular ducts, and Digitized by Microsoft® CONTENTS. Brain and Sense Organs — Continued. Cochlea. Middle ear. External ear. Brain and Sense Organs — Continued. Nose, Respiratory region. Olfactory region. IX PAUE ■ 395 PART II. THE PREPARATION AND EXAMINATION OF MICRO- SCOPICAL SPECIMENS. Fresh Tissues, Isolation. Sectioning Fresh Mateeiai.. Fixation. Decalcieication. Imbedding. • 40.0 Staining and Mounting, General Stains. Special Stains. The Microscope. Drawings. Reconstructions . PAGE . 408 Digitized by Microsoft® Digitized by Microsoft® PART I. MICROSCOPIC ANATOMY. I. CYTOLOGY. THE CELL. Since 1839 it has been known that all plants and animals are composed of small structural elements called cells (Latin, cellula; Greek, kOtoc). The lowest forms of animals and of plants are alike in being single cells throughout Hfe. The more complex organisms are groups of cells which have been derived, by process of repeated division, from a single cell, the fertilized ovum. Thus the human body, which begins as one cell, becomes in the adult an aggregation of cells variously modified and adapted to special functions. Since the liver is a mass of essentially similar cells, the problems of its functional activity are the problems of the functions of a single one of its cells. The diseases of the liver are the result of changes occurring in these cells, which must be restored to a normal con- dition to effect a cure. As this is equally true of other organs, it is evident that cytology, the science of cells, is a basis for both physiology and pathology. A cell may be defined as a structural element of limited dimensions which under certain conditions can perform the functions of assimilation, growth, and reproduction. Because of these possibihties a cell may be considered an elementary organism. It is described as a mass of proto- plasm containing a nucleus. A third element, the centrosome, is 'found in the cells of animals, but not in those of the higher plants. The centro- some becomes prominent when a cell is about to divide. At other times, in many kinds of cells, it has been found as a minute granule which may be in the center of a very small clear spot in the protoplasm. Ordinarily it cannot be seen unless cell division is about to occur. Some authorities regard the centrosome as a temporary structure which forms shortly before division begins and disappears after it is completed. Others I I Digitized by Microsoft® 2 HISTOLOGY. regard it as a permanent and essential pjart of a cell, which accordingly consists of protoplasm, nucleus, and centrosome. PROTOPLASM. Protoplasm is the li^'ing substance of which cells are composed. JNIore specifically the term is apphed to this hving substance exclusi\'e of the nucleus, or to the corresponding dead material, provided that death has not changed its physical properties. It has been proposed to substitute the name cytoplasm for protoplasm in the restricted and earher sense of the^term, to call the nuclear substance nucleoplasm [karyoplasm], and to consider both cytoplasm and nucleoplasm as varieties of protoplasm. Although these names are often employed, the cell substance apart from the nucleus is ordinarily called protoplasm. / Xuclear niembi f Diplosonie in AchromaUc subslaiRcs , of tlie nu- cleus. Exo|.lasm. -_LA'5 Chromatic substances of tlie nu- eus. Microsomes. Cell membiane. r'n^. I.— Diagram oi" a Chi.l. INIicreiS'inies and filar mass onh' partly skclrlied. Protoplasm is a heter<_)geneous mixture of substances forming a soft, viscid mass of neutral reaction. In distilled water it swells but does not disappear. It consists of water, salts and organic sulDstances, some in solution, and some in a colloidal state. The organic bodies are classed as proteids, glycogen or some allied carbohydrates, and hpoid (fat-like) bodies. Proto])]asm may exist in a numljerless varictv of forms. On microscopic examination protoplasm is seen to contain small granules, microsomes. In different cells these vary in abundance and in character. They may ]je absent from the outer layer of protoplasm, the exoplasm, which is ilrmer and chemically different from the inner ciido- plasm, and perhaps has a separate function. The microsomes liave been Digitized by Microsoft® PROTOPLASil. considered both as inert bodies and as the essential h\'ing basis of proto- plasm. The simplest description of protoplasmic stmcture is that it consists of a fluid ground substance in wliich microsomes arc embedded. With high magnification it appears that the protoplasm contains a network of filaments (called mitome, or the filar mass, from the Greek ij-iror and Latin filiuii, both meaning "a thread," — spongioplasm is another synonj-m). This network is embedded in a more or less homo- geneous and chemically different ground substance (paramitome, interfilar mass, or hyaloplasm). Some of the filaments appear as rows of micro- somes, but small particles may also be found in the ground substance between the filaments. The conception of protoplasm as fibrillar or reticular has been considered at variance with the "granular theory," yet undoubtedly both fibrils and granules occur in protoplasm. According to a third interpretation protoplasm has the structure of foam, or of an emulsion, — that is, it consists of minute droplets of one substance completely surrounded by walls of a different substance. This view, AA'hich has much in its favor, is not inconsistent with the presence of granules or of fibrils scattered through the mass. In addition to these general char- acteristics the protoplasm of particular cells may contain other stmctures of ^•arious significance. These may be grouped as fohows: ,^*«i I. Fibrils. Although an obscure fibriUar netAVork may be characteristic of all cells, a high development and orderly arrangement of fibrils occurs ^ only in certain specialized cells, as for example, in muscle, nerve, and connective tis- sue cells. Tliese Jlbrils are of very different sorts and will be described more fuh)' in the section on General Histology. 2. Granules. These are not the micro- somes found in aU protoplasm, but arc larger bodies of definite staining reaction, wlfich often are important secretory products elaborated by the cell. In many gland cells, and in the "granular" white blood corpuscles, these structures are conspicuous. Other granules may be excretory or waste products of the cell, and some of these, wlfich, without being stained, are deeply colored, are called pigment granules. Digitized by Microsoft® \ -FiHRTi,s i.N ,A Nkr\'e Cell. 1 Fig. -^.—Clumps of Gk -\m;lks (Xissl's Dudihsj in a Nb.R\K Ceix. HISTOLOGY. W F]r,. 4. — \'acl 0( i-:s in ^'ouN'2 5 6 8 10 Munilcs. Fig. .s.— Lecc DCVTKS OF A Froi;. :■' sho Chc^nges in form observed HuniiLT Kii minutes CELL DIVISION. 9 FORMATION AND REPRODUCTION OF CELLS. In the past, two sorts of cell formation have been recognized, namely the spontaneous generation of cells, and the origin of cells through the division of pre-existing cells. According to the theory of spontaneous generation it was once thought that animals as highly organized as intes- tinal worms came info existence from the fermentation of the intestinal contents. After this had been disproved it was stiU thought that cells might be formed directly from a suitable fluid, the cytoblastema. Some- thing of the sort may have occurred when life began, and it is the expecta- tion of certain investigators that conditions may yet be produced which shall lead to the formation of organic bodies capable of growth and repro- duction. At present, however, only one source of cells is recognized, — the division of existing cells. "Omnis cellula e cellula." A nucleus Ukewise can arise only by the division of an existing nucleus. There is no satisfactory evidence that a nucleus may be formed from non- nucleated protoplasm. In cell division the nucleus divides first and then the protoplasm, generally into two nearly equal parts. During the process a special grouping and transformation of the nuclear substance occurs in accordance with fixed laws. The ordinary mode of cell division is called mitosis or indirect division [karyokinesis] and the characteristic groups of nuclear material are commonly known as mitotic figures. Mitosis is arbitrarily but conveniently divided into three successive phases, the prophase, metaphase, and anaphase, in which respectively the nuclear material prepares for division, divides, and returns to its usual condition. (The final stages of reconstruction are often grouped as a fourth phase, the telophase.) In the details of mitosis there are considerable variations, not only in different animals but also in different kinds of cells in a single species. The account of the process which follows will apply only in a general way to a particular case of cell division which the student may be examining. MITOSIS. Prophase. The centrosome and nucleus approach one another until the centrosome is close to the nuclear membrane where it lies surrounded by the clear zone of archoplasm. The archoplasm contributes to the formation of radiating fibrils which extend from the centrosome in all directions, and are known collectively as the centrosphere [astrosphere]. The two parts of the centrosome which had formed in the "resting stage" by the division of one, are in the midst of the centrosphere. They move Digitized by Microsoft® lO HISTOLOGY. apart, the diplosome thus separating into two centrosomes, and the centro- sphere becoming divided into two spheres, each of which contains a centre- some. Fig. 9. Tlie nucleus meanwliilc enlarges and its chromatin stains much more deeply. The branching portions of the chromatin networic are withdrawn, so that instead of a net, the entire chromatic material forms one convoluted thread, a monospireme, as this mitotic figure is called. The thread is at first more closely coiled than it is later. It divides transversely into a definite number of segments, called chromosomes. These bodies may be spherical or rod-like, but generally they are U- or V-shaped. The apices of all the V's may at first point toward the centrosome witlr their free ends directed away from it as shown in the diagram. Fig. 9. Instead of being arranged in the orderly manner of the diagram, however, the chromosomes CeTitral spinillc. Chromosuiiies. CeiitrosiMiie. Fig. 9.— Early Pkopi-iASK ; I\IONO- Fig. lo. — Later Propii -vsi.: ■ AIona)- SPIRliMli. SPIREME. are so massed that they can scarcely be counted. This is shown in Fig. 15, representing mitoses in the salamander. In man they are even harder to count and have been estimated both as sixteen and twenty-four. This is of importance, since in any one species the number of chromosomes is beheved to be constant for aU the cells except the sexual cells. Certain worms in which the chromosomes are only two or four in number and hence can be followed with certainty, have furnished the strongest evidence for this. Except in the sexual cells, the number of chromosomes is always even. Since it has been found that the same numlDcr of chromosomes which entered into the formation of the chromatin network of the restinf' nucleus, Avill emerge from that net preceding mitosis, the suggestion is made that the chromosomes retain their inthviduality in the quiescent nucleus. They are regarded as disguised by numerous branches. In the prophase of mitosis the chromatin in manv cases does not form a Digitized by Microsoft® MITOSIS. II continuous thread but passes from the network condition directly into that of a group of chromosomes. Such a group is, however, properly called a monospireme. The centrosomes, in moving apart from one another, travel along the nuclear membrane to points 90° from their original position. Thus if before division the centrosome was on one side of the nucleus, now the two centrosomes into which it has divided will be found one at either end of the nucleus. Fine fibrils extend between them as they separate, con- stituting the central spindle. Outside of these, there are other fibrils passing from the chromosomes to the centrosomes (Tig. 10). These fibrils, which are sometimes derived from those of the centrosphere aiid sometimes from the linin framework of the nucleus, are known as mantle fibrils. Toward the end of the prophase the nuclear membrane disappears, together with the nucleoh. j\Ietap}iase. The V-shaped chromosomes become arranged about Pohir radialinii Xitelear sihikH Fkj. II.— Earl\' Mkt.M'Hask: Mcin- Fig. 12 — iMiixArH asi: : Dn ision ASTKR. OF THE Ch ROMi 'Si);MES. the equator of the spindle in such a way that their apices point toward the axis of the spindle and their free ends radiate from it in all directions, Fig. II. At either apex of the spindle is the centrosome surrounded by the centrosphere, the radiating fibrils of which are noAv called polar radiations. If the cell at this stage is viewed from one of its ends or poles, the chromo- somes together constitute a single star and this mitotic figure is accordingly called the monaster. Fig. 15 shows the monaster both in side and polar views. In the prophase, before the chromosomes have formed, the convoluted thread of chromatin is sometimes seen to Idc spht longitudinally into halves. During the prophase, therefore, each V-shaped chromosome may consist of parallel portions which remain together until the monaster is complete. Then, beginning at the apex of the V, the halves' of each Digitized by Microsoft® 12 HISTOLOGY. chromosome are dra\OTi apart as if by means of the outer spindle, or mantle fibrils. In an unusual but important form of mitosis, known as hetero- typical mitosis, the partially divided chromosomes remain for some time united by their ends, in the form of rings. How sucli ring-shaped chromo- somes may occur is sho\\Ti in Fig. 12. Ordinarily the V's are completely divided, and the separate halves travel, apex forward, toward their re- spective poles. Two stellate groups are now observed and this stage is called the dyaster (Fig. 13). Stretching between these groups are the central fibrils of the spindle, not shown in the drawing. A development of^ granules in these fibrils along the equatorial plane may take part in forming a new transverse cell wall. The metaphase is the stage of division of the chromosomes, and by some writers it is considered very brief, the monaster being counted the last ofjhc prophase, and the dyaster being included in the anaphase. Fig 13. — Latk .MiiTAl'jiASK : D\'ASTKK. Fig. 14. — .\nafhasi:: Di- SPIREME. Anaphase. The chromosomes of either portion of the dyaster are the same in number as those of the nucleus from which they came. Each group represents half of the chromatic material. These new chromosomes unite with one another, each group forming a spireme. The mitotic fi,gure thus produced is the dispircmc (Fig. 14). The centrosphere loses its radiations, becoming reduced to a zone of archoplasm, and the centro- some often divides to form a diplosome. A nuclear membrane forms, beginning at a point opposite the centrosomes. The nucleoli reappear as the chromatin thread returns to a network by sending out branches. Thus two resting nuclei have formed. Meanwliile the protoplasm along the equator constricts, and here, sometimes aided by the granules of the central spindle, the new cell wall develops to comjilete the process of mitosis. Summary. The stages described have been successively the reticular quiescent stage, the monospireme, monaster, dyaster, dispiremc, and the return to the reticular condition. These terms refer to the arrangement Digitized by Microsoft® MITOSIS. 13 of the chromatic material. The achromatic structures were successively the centrosome surrounded by archoplasm; the diplosome in a centro- sphere ; two centrosomes connected by a spindle and each surrounded by polar radiations ; the division of this ampJiiasicr, as it is called, into two cen- trospheres each with its centrosome; and, finally, the reduction of the cen- trosphere to archoplasm. Each new cell ordinarily receives half of the protoplasm, spindle, centrosome and chromatic material of its parent, and becomes a cell of the same sort. The process of mitosis rec[uires probably about half an hour, but the time is variable and it may last several hours. In the blood ceUs of amphiljia it is said to take two hours and a half. Mitoses will be found Close itiorHispirenie Loose nionuspireine (\ic\veil Irotii (viewed Iroiii aho\e— Uie side). i. c, from Uie pole). ^^ollaster (\-iewed from fhe side). Polar side. Polal- radiafioii. — Spindle. _^,,.««JJ".«{ii,^ .rtg-* V. ,:iji^!^&* *%4iAr-'- V^-iAt' Monaster (viewed from abo\-e). Comfiletcd. Duisioii (.il the protoplasm (Dispiremes). Fig. 15. — Mitotic Ficurks fro.m the Epitmelipm oi'- THt: Or.al Cavity' of Triton Ai.PESTRis. >( s6o. in all well preserved, rapidly developing tissues. They are abundant in embryos; and if numerous in tumors they furnish evidence of rapiid growth and mahgnancy. After death, if the tissues are not hardened by cold or reagents, it is thought that mitoses may go on to completion, as they are absent from specimens which are not properly preserved. Varieiies of mitosis. In connection with the formation of sexual cells (the ova and spermatozoa) there occur two successive mitotic divisions of a unique sort. A cell which had itself been formed by ordinary mitosis, in preparing for cUvision converts its chromatic material into one lialf oj the usual number oj chromosomes. It divides into two cells, each with the reduced number, and these divide once more in the same way. Thus Digitized by Microsoft® 14 HISTOLOGY. four cells, each ha^'ing one half the usual number of chromosomes, arise from the one which first presented this peculiarity. With some modifi- cations but without further division they may become the mature sexual cells. The process of their formation is called maiuralioii, and the two pecuhar and linal mitoses through which every mature sex cell has passed are called reduction divisions. In the process of fertilization two mature sexual cells, a spermatozoon and ovum respectively, fuse, and the normal number of chromosomes is restored. Thus each parent contributes an equal number of chromosomes to the fertilized o^oim and these have been considered bearers of hereditary quahties. The reduction divisions will be further considered under Testis and Ovary. An unusual form of mitosis is that in which the centrosome di\'ides into more than two parts and the cell correspondingly divides at once into several. These jiluri- or multiqiolar mitoses are said to occur normally in parts of certain higher plants; they have been induced by injecting a, .As> ninietl i6.— MiTiisES IN HrM\.\ Cancer Ceils. ( From Wilsi.n, after Galc-oUi. l ;iiilu--is\\ nil unequal distril.utii.'ii uf iiliixinialin; b, tiipMlar tnilusis; c, quad ri polar mi lusis. drugs into the skin of salamanders; and are sometimes found in human cancer cells and in the rapidly growing connecti\-e tissue of scars. Thev may lead to an unequal distribution of the chromatic material in the cells which they produce. For further information regarding mitosis, and for definition of the many terms frequently emplo}-cd but not mentioned in this account, the student is referred to Prof. E. B. Wilson's book entitled "The Ceh." AMITOSIS. Amitosis or direct cell di\-ision takes place without spindle formation or the rearrangement of nuclear material. The nucleolus, nucleus, and cell body successively divide by fission, or by elongation and constriction, into two parts. The role of the centrosome has not been determined. This form of divison is rare and its significance unknomi. The suggestion that it is more primitive than mitosis lacks suiqiort. Generally it is regarded as a sign of cell degeneration, since it occurs in old cells— leuco- Digitized by Microsoft® CYTOMORPHOSIS. IS cytes and the superficial cells of the bladder— the cell bodies of which often fail to divide following the division of their nuclei. Thus cells with two or more nuclei may be produced by amitosis. It occurs in wounded '^f^%\. \ IM '^ I .^ A\, ' ^ FJ(j. 17. — A.MII.JSISIN El'iri-IKLIAL Clil.LS KKCiM TIIK BlA1>DKR OK A M<3USE. y 560. tissues where it has been interpreted both as a result of injury and as evidence of activity toward repair. In the egg tubes of certain insects amitosis is a common and normal process. CYTOMORPHOSIS. Cytomorphosis is a comprehensive termfor the structural modifications which cells or successi^•e generations of cells may undergo from their origin to their final destruction. It imphes that the hfe of a cell is Hmited, and that during its life it may change in structure by becoming difjcrenliated, or adapted to the performance of special functions, and that finally it will pass through regressive changes to its death. Successive generations of cells may represent stages along a certain line of difl'erentiation. The cells resulting from mitotic division begin their specialization where the parent cell left olf, and the j^hcnomena of regression are then reserved for the final generations in the series. Four successive stages of cytomor- phosis have been recognized: First, the unclillerentiated stage; second, that of progressive differentiation; third, the stage of regression; fourth, the removal of dead material. These may be considered in turn. Undifferentiated cells, as can be seen in sections of young embryos, are characterized by large nuclei and relatively httle protojilasm. They have great power for undergoing division. The subsequent increase of cvtoplasm which makes functional differentiation possible, retards the rate of mitosis. In the adult, relatively undifferentiated cells are found in many situations, as, for example, in the deep layer of the epidermis. These ceUs are a source of supply to replace the outer cells as they differ- Digitized by Microsoft® i6 HISTOLOGY. entiate, die, and are cast off. Since they can produce only epidermal cells, they are themselves partly differentiated. The fertilized ovum which can produce all kinds of cells must be regarded, in spite of its size and great mass of yolk-laden cytoplasm, as the least differentiated. The progressive specialization of cells concerns chiefly their proto- plasm, yet in the case of the muscle fibers of the salamander it is accom- panied also by marked nuclear changes. Typical muscle nuclei from Xectuiiis embryos 7 mm. and 26 mm. long, respectively, are shown in Fig. iS. The significance of the differences between them is not kno\^Ti, as they have been but recently de- tected. The cytoplasm of muscle cells difl'erentiates its contractile function beyond all others, and becomes filled with contractile fibrils. Many kinds of cells are specially modified for producing secretions which may either be discharged, as from gland cells, or in a somewhat solid state may remain in contact with the cell, thus forming certain of the intercellular suhstances. Small amounts of structureless intercel- lular substance, such as is some- times found between epithehal cells, are cahcd ccinciit substance, even though it may be fluid. Between connective tissue cells the intercellular substances are formed in such quantity that they far exceed the bulk of the cells which produced them. These ground suhstances may be homogeneous, or permeated with fibrils and granules, formed either by the exoplasm or by the transformation of the intercellular substance. The remnant of ground substance between the fibrils is another so-called cement stibsta)iee. In cartilage and bone, the cells appear scattered through the ground substance which bv their differentiation tlicy have produced. Regression or degeneration is the manifestation of approaching death. Normally it is not seen in nerve cells and probably not in the voluntary muscle cells. Subtle and unrecognized changes mav occur in them in ■ Striated Musclk Fjbkrs from (Eycltishy- FiG. iS-^Npclki OTi \'orNG Salamandf-:rs (Nhctlm mer. ) A, I'^i'L'tn a 7 niTii. eml)r\ n , B, frMiii 1 >iit ot 26 mm.; ch., cliromatid kiKjl ; g. S., .t^ruuml Milistancc; I, liiim w^ , n. m.. mu.li-iar mfnilnane. fibr , nil elf Digitized by Microsoft© CYTOMORPHOSIS. 1 7 old age, but they remain active throughout life; if destroyed, they can never be replaced. In many glands, in the blood and in the skin, however, the cells are constantly dying and new ones are being differentiated. In a few organs the cells perish, but no new ones form, so that the organ to which they belong atrophies. Thus the mesonephros (Wolf35an body) largely disappears during fetal life; the thymus becomes vestigial in the adult; and the ovary in later years loses its chief function through the degeneration of its cells. The optical effects of regression cannot at present be properly classi- fied. In a characteristic form, known as "cloudy swelling," the cell en- larges, becoming pale and opaque. In another form the cell shrinks and stains deeply, becoming either irregularly granular or homogeneous and hyaline. The nucleus may disappear as if in solution (karyolysis, chromato- lysis), or it may fragment and be scattered through the protoplasm (karyo- rhexis). If the process of degeneration is slow, the cell may divide by amitosis. It may be able to receive nutriment which it cannot assimilate, and thus its protoplasm may be infiltrated with fat and appear vacuolated. It may form abnormal intercellular substances, for example, amyloid, or the existing intercellular substances may become changed to mucoid masses or have lime salts deposited in them. In short, together with optical changes in the cell substance there is often an impairment or perversion of function. The removal of dead cells is accomplished in several ways. Those near the external or internal surfaces of the body are usually shed or des- quamated, and such cells may be found in the saliva and urine. Those which are within the body may be dissolved by chemical action or devoured by phagocytes. Every specimen of human tissue exhibits some phase of cytomorphosis. In some sections a series of cells may be observed from those but slightly differentiated, to the dead in process of removal. Because of the similarity and possible identity of this normal, "physiological" regression, with that found in diseased tissues, such specimens should be studied with particular care. Digitized by Microsoft® HISTOLOGY. II. GENERAL HISTOLOGY. HISTOGENESIS. Segmentation and the Formation of the Germ Layers. The body is composed of groups of similarly differentiated cells, similar therefore in form and function. Such groups are known as tissues. Histology (Greek, '"TOf, "a textile fabric") is the science of tissues, and histogenesis deals with their origin. There are as many tissues in the body as there are "sorts of substance"; thus the liver consists essentially of hepatic tissue, and the bones of osseous tissue. All of these, however, are modifications of a small number of fundamental tissues, the histogenesis of which may now be considered. It has already been noted that a new human individual begins existence as a single cell, the fertilized ovum, formed by the fusion of two mature sexual cells, the spermatozoon and ovum respectively. The fertilized ovum then divides by mitosis into a pair of cells, Fig. 19, A; these again divide making a group of four, Fig. 19, B; by repeated mitosis a mulberry- like mass of cells results, called the morula, Fig. 19, C. Development to this point is known as the segmentation of the ovum. A section through the morula is shown in D. An outer layer of cells surrounds the inner cell mass. Soon a cup-shaped cleft, crescentic in vertical section, forms between the outer and inner cells as shown in E, and this enlarges until the entire structure becomes a single-layered, thin- walled vesicle, within and attached to one pole of which is the inner cell mass. This mass gradually spreads beneath the outer layer until it forms a complete lining for the vesicle, which becomes consequently two layered. Fig. 19, G. The inner layer is called entoderm, and the outer layer, ectoderm.^ The entire embryonic structure at this stage is called a blastodermic vesicle. On the upper surface of the vesicle the future axis of the embryo is indicated by a thickened streak called the primitive streak. In front of this there is a groove in the ectoderm, also in the axial Hne of the future body. It is named the medullary groove, and just beneath it i^s a rod * The ectoderm is in part derived from the superficial cells of the inner cell mass, and in part from the primary outer layer of the vesicle. The former portion is to cover the body of the embryo, and the latter [named trophoblast] covers the fetal membranes. These membranes are to be described in a later chapter. They are omitted in the diagrams of Fig. xg. Digitized by Microsoft® GERM LAYERS. 19 of entodermal cells called the notocJiord. These ma}' be seen in cross section in Fig. 19, G and H. In G, on either side of the medullary groove Neph ^ 1"|G 19, — Diagrams siitaving tju; Development of the Germ LA^'ERs. (A lo F, Liflti\-an Bcnudcu's figures of the rabbit.) A, Two-celled staL:e ; B, four-celled stage ; and C, morula stage of the segmenting o\'inn, all being surf.ice \ie\vs. D to I re[iresent sections described in the text. The uuiri cell mass and etitudf^rm arc hea\-i1y shaded; \_h(i ouler layer 2.^id ectod^^riu 3.r(tV\^\\i; and the wt'j . Neph., nephr V\\ of Incubation. (Miiiot.) Mes., Splanchnic mesoderm ; Ent.. entoderm, four distinct cells of which are shown at c , V. V., blood \ c^scls cnntaining a few \ount^ blood cells. either side, to the heart, a single median vessel under the pharjux made by the junction of the \-eins (Fig. 20, B). The heart divides into two aorlae which pass around the anterior end of the jiharynx to its dorsal side and then extend through the body posteriorly, lying under the segments. Their branches pass off laterally to the vitelline network, thus completing the circulation. All future vessels in the body are branches of this simple system. The Fundamental Tissues. It has been said that there are two fundamental tissues, epitJielium and mesenehyma. Epithelium is a la)'er of cells co\'ering an external or an internal surface of the body, having one side free and the other resting on underlying tissue. The epidermis, and the linings of the intestinal tract, of the blood vessels, of the peritoneal cavity and of the joint cavities Digitized by Microsoft® THE FUNDAMENTAL TISSUES. 25 are all examples of epithelia. The epidermis is ectoderm; the lining of the intestine is entoderm; that of the blood vessels, called endothelium, is from the angioblast; the peritoneal epithelium (mesofhelium) is part of the splanchnic and somatic layers of mesoderm; and the joint cavities are lined by flattened mesenchymal cells, the cavity being, as it were, a large intercellular space. Thus epithelia are derived from all the germ layers. Mesenchyma is a non-epithelial portion of the mesoderm, which has just been described as consisting of branched cells, the protoplasmic processes of which form a continuous network. In its meshes is a clear intercellular fluid. Mesenchyma is essentially a tissue of the embryo. In the adult it is represented by connective tissue, bone, and other deriva- tives which preserve certain of the characteristics of mesenchyma. Three other forms of tissue depart so far from the epithelial and mesenchymal types that they are naturally placed by themselves. These are muscle, nerve, and vascular tissue. Muscle tissue exists in three forms, of which the smooth and cardiac varieties are derived from mesenchyma, and the striated (voluntary) muscles from the mesodermic segments. The epithelial character of the latter is lost. Nerve tissue is ectodermal, con- sisting of an epithehal tube which later becomes essentially non-epithelial, and of detached masses of cells which send processes to all parts of the body, forming the nerves. These are never epithelial. Vascular tissue includes the blood and the lymph, which are of obscure origin, perhaps mesenchymal; also the endothehum which lines the vessels, provided that the blood and the endothelium have a common origin. It will be con- venient to describe the entire blood vessels and lymphatic vessels in connec- tion with their contents. In the following pages the several tissues will be considered in the order above outlined. In connection with them, certain organs may be examined. An organ is a more or less independent portion of the body, having its own blood, lymphatic and nerve supply, and connective tissue framework, together with its characteristic essential cells. Thus an organ should consist of several tissues. The pancreas or lungs are obviously organs. An individual muscle or a particular bone has a connective tissue framework or covering, blood vessels and nerves, besides its essential substance. Thus it is an organ. Even a blood vessel of ordinary size comes within the definition. The organs which are of wide occurrence like the bones, muscles, tendons, nerves and vessels, may be described with their essential tissues. The more complex organs are reserved for the later section entitled "Special Histology." Before presenting in summary form the derivatives of the germ layers it should be noted that the ectoderm becomes continuous with the ento- Digitized by Microsoft® 26 HISTOLOGY. derm at the mouth, anus, and urogenital opening. The line of separation is not that of transition from skin to mucous membrane, but is indicated by the transient membranes (the oral and anal plates) found in young embryos. Nothing in the adult remains to show where the layers join. ORIGIN OF THE TISSUES FROM THE GERM LAYERS. The ectoderm produces: 1. Epithelium of the following organs: — the skin, including its glands, hair and nails; the cornea and the lens; the external and internal ear; the nasal and oral cavities, including the salivary glands, the enamel of the teeth and an- terior lobe of the hypophysis ; the anus ; the cavernous and membranous parts of the male urethra; together with that epithelium of the chorion which is toward the uterus and of the amnion which is toward the fetus. 2. Nerve tissue forming the entire nervous system, central, peripheral and sympathetic. 3. Muscle tissue, rarely, as of the sweat glands, and perhaps also some muscle fibers of the iris. The mesoderm produces: 1. Epithelium of the following structures: — the urogenital organs except most of the bladder and the urethra; the pericardium, pleurae, and peritonaeum and the continuation of this layer over the contiguous surfaces of amnion and chorion; the blood and lymphatic vessels; and the joint cavities and bursae. 2. Muscle tissue, striated (voluntary), cardiac, and smooth (involuntary). 3. Mesenchyma, an embryonic tissue, which forms in the adult, connective and adipose tissue, bone (including the teeth except their enamel), cartilage, tendon, and various special cells. 4. Vascular tissue, the cells of the blood and lymph, consequently the essential elements of the lymph glands, red bone marrow and spleen. The entoderm produces: I . Epithelium of the following organs : — the pharynx, including the auditory tube and middle ear, thyreoid and thymus glands; the respiratory tract, including larynx, trachea, and lungs ; the digestive tract, including the oesophagus, stomach, small and large intestine, rectum, liver, pancreas, and the fetal yolk sac; and part of the urinary organs, namely most of the bladder, the female urethra, and prostatic part of the male urethra. 2 NoTOCHORDAL TISSUE, which disappears ( ?) in the adult. EPITHELIA. Epithelium has already been defined as a layer of cells covering an external or an internal surface of the body, having one side therefore free, and the other resting on underlying tissue. Epithelia differ from one another in embryonic origin, in the shape of their cells, in the number of layers of cells of which they are composed, and in the differentiation of these cells. All of these features should be recorded in any complete description of an epithelium, and, except the origin, something of each is to be observed in a single specimen. These four characteristics may be considered in order. Digitized by Microsoft® EPITHELIA. 27 Origin. Epithelia arise from all three of the germ layers as described in the section on Histogenesis. The terms which may be applied to adult epithelia indicating their origin are eclodermal, entodermal, mesodermal, mesothelial, and mesenchymal. Mesothelium is a term applied sometimes to all meso- dermal epithelia except the mesenchymal. There is a tendency, howeyer, which seems desirable, to limit its application in the adult to the pericardial, pleural, and peritonaeal epithelia. Endoihelium is from the " angioblast" and lines the heart, the blood yessels and the lymphatic vessels only. The loose but rather common application of this name to mesothelium and mesenchymal epithelium is much to be regretted. Mesenchymal [or false] epithelia are formed by flattened mesenchymal cells, developing relatively late in embryonic life. They line the bursae, tendon sheaths, joint cavities, the chambers of the eye, and the scalac tympani and vestibuli of the ear. The table on page 26 indicates to which germ layer the epithelia belong. Shapes of Ei^ithelial Cells. Epithelial cells may be groujjed, according to their shape, in three classes, fiat, citboidal, and columnar. These names apply to the appearance 5@ (S&W fa)b-\f'^|^|QJg(©Jgj -SCEpi. Fir,, ji — Ammi)^.- 'A' Ph.. iA Fkial Mkmi:i.',.\m.: Cm\|..kin(. i hi-: Mmbk^o.) S C Epi , Simple Lub.ililal CI. itlicliuiii ; Mesen., u mescri.. h\ nial II-.MI.; ; MeSO., mcsothflmin, a simple Hill L-pilliflium. of the cells when cut in a plane perpendicular to the free surface. On surface view all three kinds are usually polygonal and often six sided. If the epithelium consists of but a single layer of cells it is called simple. Fig. 24 shows along its upper surface a simple citboidal epilhelium. The sections of its cells are approximately square. On the lower surface is a simple fiat epithelium, which, being an extension of the layer lining the coclom, is a mesothelium. A surface view of mesothelial cells on a smaller scale is shown in Fig. 25, A. Endothelium, Fig. 25, B, is quite hke meso- thelium in appearance; its cells, ho\veyer, are usually more elongated, parallel with the course of the vessel which they line. It is a simple epi- thelium, so llat that the thickest part of its cell is that which accommodates Digitized by Microsoft® 28 HISTOLOGY. the nucleus. In Fig. 26 there is both a surface \-icw and a section of simple columnar epithelium. Often columnar cells arc nearly cujjoidal and are described as low columnar. Gradations between all the types described are to be expected. (The / following synonyms are in common \* -/^ >-' ' A Cross section of a lerniinal bar. h f' B Fig. 25. A. Surface \\c\v of nicsollicliuni from Llic nii:"^(_'ii- U.T\ ; B, surface \ iL-\\ ol emlMUiuliuni I'omii :iti ait.er\ . Fig. 26.— SiMiM c C Tin: I.Ni A, Surface \-ie\v B Ticii I cell out e R EPITHKLKM FRO-M \ L s OF Man. ■ -x tion. The promi- A d e to ti'vinhial bars, ir left of B, and \\\ IG j; — Mt\gi'\moi- PsT-.riir S I l< XTll' IKD I>ri J lilil.ILM. iMi.. 2S.— Stk Mil II r. Mi-i- ril I- I lUM 1' ROM 111 |. Ml M \\ I M.'VNX. :,|, 1, (^llllInll:l|■ I ,-lls: 2. |„,U^ l;"ii,iI Lulls, 3. Hal l-„|ii,i- iiiMiis) rulls ^ir.. 29. — I ii r \CHi- n Si^ua- MiiLS C'liLl.S FROM THE Moi- ITI. below, but ma)' fail to rcacli the free surface. Their nuclei arc at different levels. Such pseudo-strati jlcd epithelium is found in parts of the rcspira- Digitized by Microsoft® EPITHELIA. 29 tory and genital tracts. A slralified epithelium is one which actually consists of several layers of cells (Fig. 28). In descriptions of stratilicd epithelia the number of layers should be recorded, especially if few. We may say that it is 2-layered, 4-6-layered, or many layered, as the case may be. The shapes of the cells in the basal, middle, and saperlicial strata should be noted. The cells are formed in the basal layer, and as they are pushed outward they become changed in shape and character. The superficial cells, for Avhich the entire stratified epithelium is often named, may be columnar, cuboidal, or flat. The flat ones are called squamous, especially when they have become detached and are found in urine or saliva (Fig. 29). (Transitional epithelium is an ^undesirable name for that form of stratilicd epithelium found in the bladder, ureter, and pelvis of the kidney. It will be described in connection with those organs. j Peripheral Differentiation. The differentiation of epithelial cells is chiefly along three lines, — first, the transformation of entire cells into cornified masses as in the outer cells of the skin, in the nails, and hair; second, the development of various stmctures around the borders of the cells, particularly along the free surface; and third, the elaboration of secretion within the protoplasm. The last two forms will be considered in detail. Cell walls in young epithelia are generally lacking. In the early embryonic skin and in its basal la)'ers in the adult, they are often absent, so that the cells are in very close contact. Later they become separated from one another by "ce- ment substance," probably fluid. This is true of mesothelial and endo- thelial cells also. Since silver nitrate is precipitated by the intercellular substance, their cell boundaries become very distinct after treatment with this reagent. Lymph corpuscles and leucocytes may pass out from thin- waUed blood vessels, between the endothelial cells, into the mesenchymal spaces. They may enter the intercellular substance between the columnar cells of the intestinal epithelium. Here they are prevented from reaching the free surface by terminal bars. The diagram, Fig. 30, illustrates Xetwork of terniitial bars. Iiitercelliilar substanct. Fx... 30 — UiAi.RWi oi~ 'i'ii\-: NicrwoR}^ oi' Tkrmi.nal r.Aks he twu cells on the left are dividei s Glanu-celi s kkmm thk Si i;\i axm i \R^" Gi.and of a Guinea-pk-. v 1260. Tn cell B tliu -laiiulcs ha\'i-- [inssed iiitn lliu uii^lainalrk ^talu ; new stainabk- L^raTiulcs are bei^iniiiiiy; lo dc\LlL'p in Uie prutojilasm. mufoiis, which form a thick secretion such as occurs in the nose and throat. The nucleus of empty gland cells often has a tine chromatin network together with distinct nuclear granules. The granules are lacking when the cell is full of secretion and the chromatin takes the form of coarse fragments. Doubtless the granules pass from the nucleus into the proto- plasm, but whether they become true secretion granules is uncertain, since similar phenomena have been observed in nerve cells. The protoplasm of serous gland cells at the beginning of secretion exhibits distinct granules, coarser than microsomes, staining intensely with certain dyes (Fig 34, A). The granules enlarge, lose their staining capacity, and are transformed into drojis of secretion with which the cell becomes charged. As a whole, the cell is larger and clearer than before. Digitized by Microsoft® SECRETION. 33 if v-:l c Fit., 35. — Epithkmal Cells Secreting IMdci's. ni a 'section of the niucnus nienibrMiierif the stomaeh of man 560. p. Pr<_itop>lasni : s. secretion ; a, t^\ o enipt)- cells , the cell hetween thcni shows he;;iinii[is: nuicoicl metamorphosis , e. the cell on the ri.tjht is ciischariJini? its contents ; the i^Tanular pvotoplasin has in- creased and the nucleus has become round a.L;ain. The fluid secretion and sometimes the granules are discharged from the free surface. Such cells are striking examples of the polarity (A cells, Ijv which is meant a dif- ferentiation of proto- plasm along the axis of the cell. The basal portion receives the nutriment to Ije made into secretion. It often exhibits striations, rods, or filaments known as crgaslo [>lasm (I''ig. 34, A). The distal portion which contains llie elaborated jjroduct is ob\dously of a different nature. \^ery man)' kinds of cells gi\X' evi- dence of polarity. The nuclear constituents also ma}- be arranged in relation to this same axis or to another, but nuclear pf)larity which is manifest during mitosis ma\' be disguised or lost at other times. In mucous cells as in serous, secretion begins with granule formation. The granules soon change into clear masses of mu- cus, which accumulate toward the free surface and are more or less sharply separated from the unchanged protoplasm beneath. The mucus is, however, pene- trated by strands of proto])lasm which contain the centrosome. As elaboration of mucus continues the nucleus is crowded to the base of the cell, and may become round or flattened (Fig. ^-,). Then the secretion is gradually discharged, apparently with the rupture of the to]j jilate. If the cell is not de- stroved the nucleus returns to its Protoplasm and nucleus. Glanil lumen. Fig. 36. — Inte.stinal Gland from a Section of THE Large Intestine of .Man. •; 165 The secretion formed in the .tjoblet-cells is colorer! blue In zone i the globlet-cells show the be,q:iii- iiiiic^ of secretion: that expulsion has bec;nii is e\ideiit from tlie presence of drops of secretion in Ihe lumen of the inland. 2, Goblet-cells with nuu h secretion. .^, Goblet-cells containing less secretion 4, Dying goblet-cells, some of which still-contain remnants of secretion. Digitized by Microsoft® 34 HISTOLOGY. central position and the protoplasm refills the cell now greatly reduced in size. Most gland cells are not destroyed by the discharge of secretion, but may repeat the process several times. In the sebaceous glands, however, cells and secretion are cast off together, and many of the mucus- producing goblet cells, such as have just been described, are thought to perish after once filling with secretion. In the large intestine, goblet cells are formed near the bottom of tubular depressions in a simple columnar epithelium, Fig. 36. By the addition of new cells below them, they are pushed toward the outlet of the tube where the oldest cells are found. Mucus is discharged while its formation continues. For a time the secre- tion develops faster than it is discharged, so that it accumulates within the cell (Fig. 36, 2), but later, as elimination exceeds production, the cell becomes emptied and dies (Fig. 36, 4). In stratified epithelium, mucus may be formed in the deeper cells, but it cannot be discharged until these have reached the surface. The Description of an Epithelium. In describing an epithelium the student should record its origin if it is remembered, and should note from observation, first, the nxmiber of layers (whether the epithelium is simple or stratified; in the latter case, the number of strata); second, the shapes of the cells (columnar, cuboidal, or flat, and in a stratified epithehum the layers, basal or superficial, in which such shapes occur) ; finally, the special structures should be sought, including basement membranes, intercellular bridges, terminal bars, striated, brush, or ciHated borders, and forms of secretion within the protoplasm. A detailed description of nucleus and protoplasm should be given of such epithelial cells as are of special importance. THE NATURE AND CLASSIFICATION OF GLANDS. A preliminary description of glands may be inserted at this point, since glands in the strictest sense are groups of such secreting epithelial cells as have just been described. Two other classes of structures are called glands, however. In one of these, cells instead of secretions are formed and set free. Cell-producing glands are called specifically cytogenic glands. These include, first, the ovary and testis which produce sexual cells; and, second, the lymph glands, haemolymph glands, spleen, and red bone marrow, all of which produce blood corpuscles. Tissue similar to that of the lymph glands when found in a diffuse form is not called glan- dular, but merely lymphoid tissue. The term gland, as here employed, suggests a well-defined, macroscopic mass of cell-producing tissue, epithe- Hal in the sexual glands, and, non-epithelial in the lymphoid group. Digitized by Microsoft® GLANDS. 35 Besides the cytogenic glands, there are epithelioid glands consisting of clumps or cords of cells resembling epithelium, yet having no free surface. These masses of cells, which may be detached from an epithelium or formed from mesenchyma, are generally penetrated by blood or lymphatic vessels into which their secretions are discharged. Secretions eliminated in this manner are called internal secretions. The epithelioid glands can produce only internal secretions. The suprarenal gland is a large example of this class. Epithelial glands are such as consist of true epithelium, discharging their secretions from its free surface. Most glands are of this nature. In simpjlest form they are merely the occasional mucous or- other secret- ing cells found scat- tered over an epithe- lium. These are sometimes called unicellular glands. Others are simple tubular or saccular depressions in the epithelium, lined with secreting cells as shown in Fig. 36. Glands of this de- scription, perhaps coiled at their lower end, or having a few branches, or con- sisting of a cluster of saccular secret- ing spaces, often occur in large numbers as parts of some organ. Thus they are found in the intestine, the uterus, and the skin, where they are named intestinal glands, uterine glands, sebaceous and sweat glands respectively, each kind having its special characteristics. They are named as classes and not as individuals, and have been grouped as the simple glands. On the other hand, there are epithehal glands which occur singly or in circum- scribed groups, having their own connective tissue capsule, blood, nerve, and lymph supply. Such forms are considered as separate organs, for example, the liver, pancreas, mammary gland, and prostate, and for this group the name compound glands has been introduced. These glands develop in the embryo generally as a solid downgrowth Intercctlated duct. End pieces. r-"iG. 37.— Diagram oi- the Dhvelopmknt of a Compound Gland. The arrangement ul iUilLs in D is that of the liuman submaxillary gland. Digitized by Microsoft© 36 HISTOLOGY. of the cpillieliuni. Tliis fli\idcs by Ijranching, and subdivides as shown in the diagram, Fig. .i;;, A, B, and C. A cavity aj^jears in the cord of cells which then become clearly epithelial. Simple glands, as in the intestine, may remain in the stage A, and be lined throughout with secreting cells; in glands of greater size and complexity only the terminal portions contain the essential secreting cells. The trunk and its main Ijranches serve to con\-ey the products of the "end ijieces" to the surface, and constitute the duds. Stage B is permanent in such simjjle glands as those of the stomach, in which a short duct without branches is formed by the union of a few tubular end pieces. The compound glands generally have branching ducts as in C and D. The secreting portions of the gland may he tuljular, spheroidal, or of some intermediate shape. A round termination is called either an acinus (Latin, a grape) or an alirolus (Latin, a small rounded vessel). The intermediate forms are called alvcolo-tulnilar [tubulo- acinar, etc.]. The cavity of these parts is called the /;/;»('» of the gland, and is directly continuous with the ca\-ity of the ducts. The secretion may pass from the cells di- rectly into the gland lumen, or it may enter extensions of the lumen found either between the cells or actually \\-ithin their protoplasm. These are the inlcrcdhihir and intracellular sccrclorx capillaries respecti^•ely. They may be Ijranched or anastomosing, — that is, form- ing networks by the union of their branches. The intracellular ca])illaries Yiiwe less distinct walls than the others, and are considered transient formations related to vacuoles. The diagram, Fig. 38, represents one half of a simple ah'eolar gland with intercellular secretory capillaries on the right, and intracellular ones on the left. Both kinds are found in the sweat glands, the liver, and the gastric glands. Intercellular capillaries only are found in the serous glands of the tongue and in the serous portions of the sali\-ary glands, also in the bull3(.i-urctlu-al, pyloric and lachr)-mal glands. Secretory cajiil- laries are apparenth- absent from mucous, duodenal, intestinal, uterine and thyreoid glands, and from the kidnev and hvpophvsis. Having reached the gland lumen, the secretion mav jtass into a narrow duct lined with simjile cuboidrd or llal epithelium, the inlercalaled duel of Fig. 37, D. The transition fmm this to the larger duct, lined ])erhaps with columnar epithelium, is not as aljrupt as in the diagram. In certain Fig. 3^ — Di \r,ivAM i:il' a Simi-lk .-\l- \ tLM. AK Gl AND, ShdWIM, INTEK- CELLULAP SECRKTORI' CaPII.LA- RiKS OR Canals on the Right, ANT) Intracellular Canals on THE Left Digitized by Microsoft® EPITHELIAL GLANDS. 37 glands the cells here show basal striations, due to rows of granules, which indicate that this portion of the ducts produces a secretion. The terminal part of the ducts of a large gland may be formed of stratified epithelium, perhaps containing mucous cells. The ducts of the liver produce a considerable quantity of mucus, and the bronchi, which from their develop- ment and form may be considered the ducts of the lungs, also contain scattered mucous cells and small secondary mucous glands. Important secretions are elaborated by the efferent and some other ducts of the testis. In the kidney there is no terminal secreting portion as in most glands. The duct-like tubules serve rather to transfer selected materials from the blood to the lumen than to form new substances. This is more obviously true of the alveoli of the lung which merely transmit oxygen and other substances through inert modified cells. Morphologically, that is, in their form and development, both the kidneys and the lungs are glands. All epithelial glands arise as outgrowths from an epithelium, as has been described. A few, by the obliteration of their ducts, become separated from their place of origin. This occurs in some small glands associated with the brain and in the thyreoid gland. The closed end pieces of the thyreoid become filled with a secretion that cannot escape. Derived from or in addition to this, there is an internal secretion which is taken up by the vessels adjacent to the basal surfaces of the cells. For completely closed epithelial sacs, such as occur in the thyreoid gland and in the ovary, the term follicle is used (Latin, folliculus, "a little bag"). If such closed spaces are pathological or degenerative, they are called cysts. Small round solid masses of lymphoid tissue, occurring singly or as parts of lymph glands, are called nodules (Latin, nodulus, "a little knot"). Very often and improperly lymph nodules are called follicles. In examining sections of glands the student should observe to what class they belong, and should record in case of epithehal glands whether they are unbranched or branched, together with the shape of the end pieces. It is often difficult to determine this shape without resort to reconstructions from a series of sections. The various appearances of the ducts should be studied with the idea of picturing the gland as a whole. As a summary of the preceding paragraphs the following tabular classification of glands may be presented: I. Epithelial glands, with persistent ducts, producing external secre- tions. 1. Unicellular glands. 2. Simple glands. a. Ectodermal, e. g., sweat and sebaceous glands. Digitized by Microsoft® 38 HISTOLOGY. b. Mesodermal, e. g., uterine glands. c, Entodermal, e. g., gastric and intestinal glands. 3. Compound glands. a. Ectodermal, e. g., mammary and lachrymal glands. 6. Mesodermal, e. g., epididymis and kidney. c. Entodermal, e. g., pancreas and liver. II. Epithelial glands, with obliterated ducts, producing internal secretion. a. Ectodermal, pineal body ; both lobes of the hypophysis. b. Entodermal, thyreoid gland. III. Epithelioid glands, never having duct or lumen, producing internal secretions only. a. Ectodermal (through their relation to the sympathetic nerves), glomus caroticum; glomus coccygeum; and me- dulla of the suprarenal gland. b. Mesodermal, cortex of suprarenal gland; interstitial cells of the testis; corpus luteum. c. Entodermal, islands of the pancreas; epithelioid bodies in relation with the thyreoid gland; thymus in its early stages. rV. Cytogenic glands, producing cells. a. Mesodermal, epithelial, — the ovary and testis. b. Mesodermal, mesenchymal, — the lymph glands, haemolymph- glands, spleen, red bone marrow, and many smaller struc- tures. THE MESENCHYMAL TISSUES. In an early stage the embryo is composed of two tissues, epithelium and mesenchyma. Mesenchyma has already been defined as a non-epithelial portion of the mesoderm composed of branching cells. Their protoplasmic processes anastomose, forming a continuous network of protoplasm, — a syncytium, in the meshes of which is a homogeneous intercellular substance or matrix (Fig. 22, page 23). Those derivatives of mesenchyma which diverge greatly from this embryonic type will be reserved for later considera- tion. Such are the vascular systems, smooth muscle and certain epithelioid cells. Reticular tissue, mucous tissue, connective tissue, tendon, cartilage and bone, sometimes grouped as the supporting tissues, may now be con- sidered in turn. They are all mesenchymal tissues which have undergone transformations both of their cells and of the intercellular substance. Reticular Tissue. Reticular tissue is that form of adult tissue which most closely re- sembles mesenchyma. It is a network of cells with a fluid intercellular Digitized by Microsoft® 'J RETICULAR TISSUE. 39 substance. The protoplasmic processes, however, have been transformed into stiff slender fibrils containing a substance known chemically as reticulin. Whereas ordinary connective tissue may be made to yield gelatin, reticular tissue gives both gelatin and reticulin. Since connec ive and reticular tissues occur so closely associated that it would be difficult to obtain pure specimens of the latter, the gelatin has been ascribed to a mixture with connective tissue elements. On the other hand, it has been asserted that reticulin is merely a variety of gelatin due to the method of analysis. Reticular fibers, by their greater resistance to pancreatic digestion and by dissolving in dilute acid, differ from the elastic elements of connective tissue. They are said to be more resistant to acids or alkalies than the fibrillar part of connective tissue. Such a distinction is hard to establish, especially since some reticular tissues are more resistant than others. Chemically, therefore, the validity of reticulin is questionable. Histologically reticular tissue is quite /" /' /'^ clearly defined by the abundance and fluidity of its fl matrix. Small round cells, the lymphocytes, which may be scattered through ordinary connective tissue, are always abundant in the meshes of reticular tissue. They are so numerous and closely packed that the dehcate reticular fibers are mostly hidden, and can be studied to advantage only after the loose cells have ^ been disengaged from their meshes. This may be ac- ^ f) complished by shaking or brushing the sections, or by ' ® artificially digesting the specimen (which destroys the fig 39.-reticular -/ •-> O L "- •' 1 ISSUE FROM THE reticular cells along with the others, but leaves the fibers) spleen of the pig. II,, Nucleus; f., fiber, of orbv the method of Prof. Mall, used in obtaining Fig. 39. reticulin; i. s., imer- •^ ' 00 yj ^ cellulai" space. A piece of fresh spleen was distended by injecting gelatin into hs substance; then frozen and sectioned. The sections were put in warm water which dissolved out the gelatin, carrying the loose cells with it, and leaving areas of clear reticular tissue. In ordinary sec- tions the student will recognize reticular tissue by the cells in its meshes, but some of its nuclei and libers can always be detected upon close ex- amination. It may contain cells other than lymphocytes, for it forms the framework not only of lymph glands, but of red bone marrow and the spleen. A layer of reticular tissue is found under the epithelium of the digestive tract, and it has been reported in many organs. Mucous Tissue. Mucous tissue forms the substance of the umbihcal cord, where it was formerly called Wharton's jelly. There it occurs as a gelatinous Digitized by Microsoft® 40 HISTOLOGY. after thcv have left the cells. tissue of pearly luster, containint:; neither ea|)illar\' nor h'mphatic vessels, nor nerws. In the umbilical cords of ^•ounL^ embr\'os it closely resembles mesench\"ma. At l)inh its cells, which retain their protoplasmic con- nections with (jne another, appear fusihjrm (spindle-shapedj or triangular rather than stellate. The intercellular substance consists of fibrils in irregular bundles, embedded in a matrix containing mucus. It has long been debated whether these fibrils oiaginate in the matrix directly, by a sort of p)recipitation or coagulation, (jr develoj) in the outer protoplasm (exoplasm) from which thev later become separaterl. The tendency is toward the latter interj^retation. In specimens spjecially stained. Fig. 40, the protoplasm may present a sharjj libriMike border staining differently from the intercellular fibrils. Chemical changes in the fibrils may occur Elastic fibers, to be described under con- necti\'e tissue, are not found in the mucous tissue of the umljilical cord. The mucins are a groujj of com- jiound proteid bodies containing a car- Ijohydrate complex in their molecule and therefore known as glycoproteids. There are manv \'arieties, the mucus of gland cells and of the mucous tissue I just descriljcd bcith containing true mucins. Related substances, called initroids, ha\'e Ijeen cibtained from ten- , 40.— Ml-coi-s Tissue from the Himan ,1 ,„ pn,-tilTcrr- qnd lionp Tlip rlp-v-plnn- umhilicalCord.atiiirtik Maiiorv's cun- eion, caiiuagc anci Donc. ineae\ciop- nective tissue 5ta„,. ^^^^^^ ^^ mucus bv conncctive tissue d. I.. Oense bundle ot nbrils, m.. uuuus — con- taining intercellular substance; l.f., loo=e p.aic A,-.,.n ,-,,■,(- ririidlirH in\-flTiniT rorrp- librils, c, cell with (Ihril-like border CCnsUOCS noC piOCIUCC an_\ UlUlg COllC- sponding with goblet cells. It is only in connection with tjtlier sorts of secretion that connecti\-e tissue cells are said to elaborate granules which are con\"erted into A'acuoles. All embryonic connective tissues are thought to contain mucus, and a variety of tumor (m}'xoma) is of this t}'pe. The peculiar connccti\-e tissue of the cornea, to be descrifjed in connection with the eve, contains no elastic fibers and is rich in mucin; ne\-ertheless its structure is vcrv different from that of the substance of the umbilical cord, to which the name "mucous tissue" is particulary a])plicaljle. Connective Tissue. Connective tissue is that ileri\'ati\"e of mesenchvma which consists of cells either connected with one another or disconnected, antl of intercellular spaces largel}- occupied by fibers of two sorts, u'liitc and clastic fibers Digitized by Microsoft® CONNECTIVE TISSUE. 41 respectively. In the dense forms of connective tissue the fiber-bundles tend to be parallel and are closely packed. In loose or areolar connective tissue the fibers run in various directions, and among them are cells which have become charged with fat. When these are numerous they constitute jat tissue (adipose tissue). Areolar connective tissue ordinarily contains fat cells. In every specimen of connective tissue three features should be examined: the fibers, the cells, and the remains of the intercellular substance. Fibers. If a small piece of fresh connective tissue, such as envelops the muscles of a guinea pig, be pulled apart on a slide and examined in water, it will exhibit the structures shown in Fig. 41 . Most of the specimen may be obscure, but in such parts as were properly spread out the white fibers can be seen as pale, wavy bands, without sharp borders. ^ ^ They are faintly striated longi- tudinally, due to the fact that they are bundles of minute fibrils bound together by a small amount of cement sub- stance. The addition of picric acid causes them to separate into their constituent elements. The white fibers divide, as shown in the figure, by the separation of the fibrils into smaller groups ; the fibrils themselves do not branch. If dilute acetic acid is put upon the specimen, these fibers swell, as shown in Fig. 41, B, often presenting a series of constrictions ascribed to the remains of encircling cells, to rings of elastic fiber, or to remnants of a sheath which enveloped the bundle. Ultimately the white fibers disap- pear in acids or in alkahes. Chemically they are said to consist of collagen, an albuminoid body which on boiling yields gelatin (glutin, the source of glue). The white fibers are supposed to arise in the exoplasm. Those seen in mucous tissue were of this variety. Elastic fibers are probably always present in connective tissue, though varying greatly in their abundance. They are said to develop later than the white fibers and are absent from corneal tissue, mucous tissue, and generally, though not always, from reticular tissue. In Fig. 41 they are seen as sharply defined, straight or stififly bent, homogeneous structures Fat CeU Wh.E Fig. 41. — Fresh Connective Tissue from Around the Shoulder Muscles of a Guinea Pig. A, Before and B, after adding dilute acetic acid. El. F., Elas- tic fiber; Wh. F., white fiber; n., nucleus of connective tissue cell. Digitized by Microsoft® 42 HISTOLOGY. which are highly refractive, — that is, they so reflect light as to change from bright to very dark objects on varying the focus. They may be extremely fine, or quite broad, but the latter are not divisible into smaller elements or fibrils. Seen in specimens which have not been torn apart, the elastic fibers form a network, F-ig. 42, A, and the smooth maimer in which they fuse at its angles is charac- teristic. When the net is broken the fibers retract in irregular spirals. The elastic fibers are thought to be of exoplasmic origin, as is suggested by Fig. 42, B. Elastic sub- stance may appear within the cell as fila- ments, or as granules which later fuse. In some cases the fibers forming the elastic net are wider than its apertures, as shown in the lower part of Fig. 43, A. Here they constitute a perforated elastic plate, called a fenestrated membrane, and such occur in many blood vessels. B and C of the same figure present elastic elements from the ligamentum nuchas, a structure containing relatively little white Fig. 42. A, Elastic fibers of the subcutaneous areolar tissue of a rabbit. (After Schafer.) B, Cells in relation with elastic fibers, after treatment with acetic acid. Subcutaneous tissue of a fetal pig. (After Mall.) .•^(hA Fig. 43. — Elastic Fibers. A, Network of thick fibers below, passing into a fenestrated membrane above. (From the endocardium of man.) B, Thick elastic fibers, f, from the ligamentum nuchae of the o.x ; b, white fibers. C, Cross section of the ligamentum nuchae, lettered as in B. .fiber, and hence used for the chemical analysis of elastic fiber. The stylo-hyoid ligament and the ligamenta flava are also elastic hgaments. Elastic fibers are not destroyed by dilute acids (Fig. 41, B) or alkalies. They consist of elastin, an albuminoid body which does not yield gelatin Digitized by Microsoft® FAT CELLS. 43 on boiling. Because of the difference in chemical composition, elastic fibers may be stained with dyes which fail to color white fibers: thus resorcin-fuchsin stains them dark purple, but scarcely aft'ects the white fibers; on the other hand, MaUory's connective tissue stain makes the white fibers deep blue, the elastic elements remaining colorless or pale pmk. These special stains are of the greatest importance in studying connective tissue. In ordinary specimens white fibers appear blended in masses and the small elastic fibers are invisible. There may be other sorts of fibers than the white and elastic, such as the fibroglia of Prof. Mallory, but these are still very little understood. Cells. Usually the cells of connective tissue are conspicuous only through their flattened nuclei, which are broadly eUiptical on surface view, and rod shaped when seen on edge. The protoplasm forms a wide, thin layer, and since it is closely applied to the fiber bundles which it may encircle, and ordinarily stains like them, very often it can scarcely be distinguished. As a €? (Tj)^" whole, the cells are irregularly polygonal, flat- ^^'^ tened, and bent to conform with the fibers. In ^ "'' some lamellar tissues these flat cells are in con- O tact with one another along their edges, thus *^ simulating an epithelium. In loose connective ^, -7 G] tissue they may be widely separated. They ^^ possess processes which may or may not unite with those from other cells, and in their proto- *'°ni^o1.^ Fl?'''(':^iLLs. " 'human ^ . , ,. , FhTus OF Fi\-E ^Months. plasmic bodies there are often a few small fat „., Nucleus- f v fat v.icuoie ■ p r droplets. " p-'iopi-"'.ic .-in.. Fat cells, as may be seen in the subcutaneous tissue of a five months' fetus (Fig. 44) arise from mesenchymal cells by the development of vacuoles of fat within their protoplasm. The vacuoles enlarge and coalesce, so that the nucleus is crowded to one side, lying in a rim of unaltered protoplasm. Gradually the protoplasmic processes disappear. The re- sulting form of cell has often been compared with a "signet ring," referring to its appearance when seen in section. The vacuole of fat further enlarges so that the nucleus is flattened and the protoplasmic layer becomes very thin. In fresh cells it cannot be seen. The entire stmcture appears as a large refractive drop of oil, Fig. 41, spheroidal if occurring singly, or polyhedral if compressed by adjoining cells. Small fat drops may be scattered through the specimen due to rupture of the cells. In order to study fat in sections it is necessary to employ special reagents. TJie tissue may be preserved either in osmic acid which l^lackens the fat, or in a formalin solution and afterwards stained with Sudan III or Sharlach R, Digitized by Microsoft® 44 HISTOLOGY. whicli rolor llii' fat (jroplels flmI and demonstrate tlum e\'en wlicn minute. In ordinary sections all the fat has been dissolved by treatment \vith alcohol, lea\-ing the protoplasmic rims enclosing empty spaces. The spaces, howc\'er, correspond in size and shape with the flrf)]jlets of fat which ha\'e iLil (Iroplels arc \ isible. Connecti\e tissue Blon<] vussd coiilain- iiii< c<->ipusLlcs Fat cell and its lUKleiis m side \ iew Bin I'~li^. 4s — F \T 'rr >d eapdlai"\ Coiinecti\e tissue. ^I I-- FROM "IHK HtMAN SlAI.P. Ijeen rcmowd. Pri)\-ided that tlie cells haw not collapsed, they appear as large, rcumd or polygonal structures (Fig. 45). Some are seen in surface \-ie\v, as if looked down upon, and ma)- show a broadly elliptical nucleus containing jjerhaps one or Uxd small \'acuoles. Most of the cells in thin sections arc cut across. The protojilasmic rim, reduced to a line, may Ije seen to widen and enclose the nucleus, liut f)ften no nucleus is found. This is because the fat cells are s(.) large that they ma}' be cut into sc\'eral slices, only one oi which carries with it the nucleus. Filling the spaces between the cells there is more or less connective tissue containing l^lood \-essels. The student should distinguish the nuclei within tlie fat cells from such connecti\-e tissue nuclei as mav 1)0 closelv adjacent to them. In some sections, radiating slender crystals, often ill defined, will be seen ^ within the fat A'acuole. These are Jul cryslals [margarin crystals] which formed as the fat cooled and solidifieil ; in the living jjod)' fat is lluid. All fat cells do not contain a single large vacuole. As described by Or. H. A. Christian there occur both at birth and in the adult such fat Digitized by Microsoft® CONNECTIVE CELLS. 45 cells as are drawn in Fig. 46. Their protoplasm contains a number of large vacuoles and the nucleus is sometimes central. Such cells may be found in subcutaneous tissue, but are more often seen in the omentum or around the kidneys. In extreme emaciation the fat cells become flattened and several small vacuoles replace the one large one. These cells are said to produce a mucoid substance appearing both between and in the cells. Fat cells develop in the fetus in lobular groups around small blood vessels. They are always found under the skin, behind the eye and in other definite places, so that they have been regarded as secretory organs. Like gland cells they take material from the vessels near by, either fat which is stored with but little change, or sugar and probably albuminoid bodies which are transformed into fat by the activities of the cell. The process has been said to begin in or near the nucleus with the formation of granules, which disappear as the vacuoles develop around them. The small vacuoles in the nucleus have been described as containing an alkaline fluid which is not fat, and which is discharged into the proto- plasm. They are also described as fat droplets and are observed in cells full of fat rather than in those beginning its formation. Like an internal secre- tion, fat is taken from the cells into the vessels, though probably not in the form in which it is stored. It should be remembered, however, that most cells take material from the blood and trans- form it into new substances. They also very gen- erally may effect the body by the products of their activity. Unless the term "gland cell" is to be so extended as to lose its significance, lobules of fat should not be considered glands. Fig. 47.- Fat Cells from the Axilla of an Extremely Emaciated Individual. k, Nucleus ; f , fat droplets ; c, cap- illary blood vessels ; b, connec- tive tissue. Besides the mesenchymal cells which early become differentiated into fat cells, the cells of adult connective tissue, of cartilage, and the epithelium of the liver all form fat vacuoles which may or may not coalesce. Pathologically fat appears in many kinds of cells, sometimes representing an accumulation of nutrient material which the cells are unable to as- similate, sometimes resulting from the breaking down of the normal, combined fats into vacuoles of free fat. It is customary to speak of such cells as "fatty liver cells," "cartilage cells containing fat," etc., and to restrict the term "fat cell" to those of mesenchymal origin distended with one or a few large vacuoles. .Pigment cells are cells of mesenchymal t3^e the protoplasm of which contains colored granules. The granules, which are generally unaffected by stains, appear brown or black in sections, and are composed of melanin in some of its various forms. The changes of color in the chameleon are largely due to the contraction or extension of the processes of such Digitized by Microsoft® b 46 HISTOLOGY. pigment cells. In man this type of cell is of limited occurrence, being found cliiefly around the eye (Fig. 48, A). The same sort of pigment may be found in epithelial cells. Thus it appears in the epithelium of that part of the conjunctiva which covers the bulb of the eye in the guinea pig (Fig. 48, B), and as has recently been noted, it occurs there in all human races but the European. The pigment of the skin in the negro races and of the nipple in others is of this sort. It has been discussed whether such pigment arose in epithelial cells or was transferred to them from underlying connective tissue cells, or actually remained in such underlying cells (Fig. 48, C). The retina affords positive evidence that pigment may develop in epithelial cells, and it has even Ijcen said that some of these become detached and send out branches. The term "pigment ceU" as ordmarily used refers to a branched cell of mesenchymal origin. Others are said to "contain pigment granules," or to be "pigmented epithelial cells." Finally, it should be added that the melanin series of pigments is one of three which give color to the body. The others are the fat pigments, or lipocJiromes, and the blood pigments, or haemoglobin derivatives. CeUs containing these other pigments are seldom caUed pigment cells. ---■^_.^ |?^©[ iH A B Fig. 4S. A, T\\ o pii^ment cells from the deep, peripheral part of the cornea of the rabbit. B, Pi2;mented epithelium from the cunjuiictiva of the i^ulnea pi£|:. The pi.gment is chiefly in the basal la\er. C, Pignietit cells sendmg processes between the epithelial cells ut the skin of an enibr\o lizard, Laccrta. (After Prenant.) Besides the pigment cells, fat cells, and hber-producing cells {pbro- blasts) several other forms occur in the meshes of connective tissue. These are free from one another and are merely lodged in the connective tissue meshes. Some of these cells emigrate from the blood vessels in adult life. Others may be descendants of cells which emigrated from the vessels in the young embryo, or else they may have arisen directly from mesenchyma in the neighborhood of the vessels. A more dehnite statement concerning them is not justified. The free cells in connective tissue have been recently classed as lymphocytes, plasma cells, "resting wandering cells," mast cells, and eosinophilcs. All of these types' except the resting wandering cells are well known and generally recognized. Digitized by Microsoft® THE CELLS IN CONNECTIVE TISSUE. 47 Lymphocytes (Fig. 49, 1) are a form of blood corpuscle consisting of a round nucleus containing block-Like masses of chromatin, and of a narrow rim of protoplasm. Plasma cells (Fig. 49, p) are derived from lymphocytes by an increase in their protoplasm which stains deeply with most stains, but especially with basic dyes such as methylene blue. It is a dense protoplasm which contains no distinct coarse granules. A clear area around a diplosome or a group of centrosome granules may be found in favorable specimens. The resting wandering ceUs (Fig. 49, r. w.) are said also to be derived from lymphocytes. They resemble connective tissue cells (fibroblasts) but do not produce fibers. Their nuclei are smaller, darker, and more irregular. Their protoplasm, which extends in irregular processes, contains scattered coarse granules staining deeply with basic stains. These ceUs have been called clasmalocytcs. In amphibia there are connective tissue cehs with slender processes full of granules. These are described as producing detached frag- ments, and so were named clasmato- cytes. In mammals the fragmentation has not been observed and the "clas- matocytes" are so different from those of amphibia that the term is scarcely applicable. The resting wandering ceUs or clasmatocytes have been con- sidered varieties of mast cells. The mast cells (Fig. 49, ni) are characterized by coarse protoplasmic granules stain- ing intensely with basic stains. These granules are soluble in water and are poorly preserved in ordinary sections. Eosinophiles (Fig. 49, e) also have coarse granules, but they do not stain with basic dyes; they have great affinity for acid stains, particularly eosine. Their nuclei are round or indented. The free cells of connective tissue occur especially along the courses of small blood vessels. They will be better understood by the student after examining blood, for they are closely related to the white corpuscles to be described later. All forms of blood corpuscles are to be found at times in the meshes of connective tissue. The inlercdhilar spaces of connective tissue are of special importance. Between the fibril bundles, the cells and the elastic network, there remain spaces filled with fluid. They are extensive in reticular, mucous, and loose connective tissue, but are reduced to slender channels in the dense Fig 49. — The Cells of Loose Connective Tissue, the Lowest Row from a Rabrit, THE Rest from a Guinea Pic. {Alter M.iximow.) e., Eosinopbiii- ; f., fibroblast; I., l\inplioc\ te; m.. mast li-II ; p., plasma cell ; r.w., vesting wanderm.L' cell. The nuclei are usually round. Digitized by Microsoft® 48 HISTOLOGY. forms. Fluids circulate in them, conveying nutriment from the vessels to epithelial and other cells and conducting waste products back to the vessels. White blood corpuscles pass out between the endothelial cells of the vessels to enter these spaces in which they may travel about or multiply. Some corpuscles may originate in them, formed from adjacent connective tissue cells. The intercellular or tissue spaces (lymph spaces) differ from small vessels, either blood or lymphatic, in having no endothelial walls; and the tissue fluid which they contain ordinarily differs from either the blood plasma or the lymph. It undoubtedly resembles lymph with which it has been considered identical. Summary of connective tissue. Connective tissue consists of inter- cellular spaces and fluid, white fibers, elastic fibers, and cells. It sur- rounds the various organs, and through it pass the nerves, bipod and lymphat- ic vessels. Its spaces are intermediate paths between the vessels and the cells of the organs. Its elastic fibers which though varying in size are not divisible into smaller ele- ments, form slender networks or coarse fenestrated mem- branes, and are of exoplasmic origin. Its white fibers are bundles of fibrils cemented together, and either densely packed or loose and areolar. Its cells are those which produce the fibers, together with fat and pigment cells, and various forms lodged in the intercellular spaces. ^ These include lymphocytes, plasma cells, resting wandering cells, mast cells, and eosinophils. Tendon. Tendons consist essentially of very dense connective tissue with parallel fibers. The dense tissue as seen in cross section. Fig. 50, is covered by a sheath of ordinary connective tissue, prolongations of which extend into the substance of the tendon. There they unite to form a network Septum. Blood vessel. Tendon bundle. Fibrous sheath. Fig. 50.— From a Cross Section of a Tendon from an Adult Man. X40. Digitized by Microsoft® TENDON. 49 of partitions or sepia. This ordinary connective tissue contains nerves which supply the tendon, to be further described on page 103; also blood vessels in relatively small number, and lymphatic vessels which are confined to the outer sheath. The septa surround bundles or jasciculi of tendon libers, called "secondary tendon bun- dles" in distinction from the smaller " primary bundles" of which they are composed. The latter are groups of fibers more or less definitely sur- rounded by wing-like processes of the tendon cells, which appear as dots in Fig. 50, but are clearly shown in Fig. 51. The tendon cells are charac- terized by their compressed branches which extend between and around the fiber bundles, anastomos- ing with similar branches of neighboring cells. The fibers are white, consisting of collagen (the gelatin-producing substance) and of tendo-mucoid- which may be found in the cementing matrix. Elastic elements are said to occur in small quan- tity especially near the cells and their processes. Intercellular spaces are very small and are not shoAATi in the figure. In longitudinal sections, Fig. 52, the parallel arrangement of the fibers is ap- parent, and the nuclei are in rows. The protoplasm is often indistinguish- able, but in special preparations from delicate tendons it appears as a thin folded layer with plate-like projections, Fig. 53. ■ A[ TI[E C\[-*:rV- NKAN TkNLiON [TeNDO ACHILLIS] OF A Rabbit. (."-Ifter Prenant.) b., Priniar>- bundle; sh., slieath of the bundle; p., process from a tendon cell, t. c, extending into a pri- mary bundle. The entire fit,'-ure is a portion of a sec- ondary bundle. r:*5E;S35.:cSSP¥?'--- FlG. 52. — Longitudinal Section of a Calca- NEAN Tendon of AtAN. Fig. 53. — Tendon Cells from the Tail of A "Rat. Stained \vith Methylene P.lue, Intra \'it.\m. (Huber.) The fibrous sheath, vagina fibrosa, Avhich surrounds the tendon, may contain a cavity filled with fluid. Such a tendon sheath is called a mucous sheath, vagina mucosa. The cavity arises as a cleft in the embryonic connective tissue and its walls are formed of mesenchymal epithelium. The cells have become flattened and the fibers felted together to bound 4 Digitized by Microsoft® 5° HISTOLOGY. the space. It contains a fluid like tliat of the joint cavities, being chiefly water and a mucoid substance (not a true mucin) which renders it viscid, together with proteid and salts. The function of the mucous sheath is to facilitate the movements of the tendon. By its formation the tendon is freed from the local connection with surrounding tissue, and the sheath generally occurs where such connection would especially interfere with motion. The mucous hursac are similar structures in relation with muscles or bones. The joint ca\'ities, to be described later, belong in the same class, having a similar origin and function. Aponeuroses and fasciae are connecti^'e tissue formations, resembling tendon in possessing a more or less regular arrangement of cells and fibers. Elastic elements may be aljundant. Mes # Pre Cart ■e:> .© , ©7, ®/ l^m- Cartilage. Cartilage is a deri\-atiA-e of mescnchyma wliich ma}' develop as shown in Fig. 54, A. The mesench)'inal cells multiply and become crowded together so that the inter- cellular spaces are obliter- ated. Thus precartilage is formed, consisting of large closely adjacent cells sepa- rated from one another by thin walls staining red with eosin. Precartilage becomes cartilage by the thickening of these exoplasmic walls which become changed chemicaUy so that they stain blue with haematoxylin. The endoplasm may shrink from them so that the cell is seen to occupy a little ca^-itv in the exoplasmic matrix. The ca\-ity is a lacuna and if the matrix around it appears to form a special wall for the lacuna, the wall is called a capsule. The ceU is the center of matrix formation, producing it in concentric layers; and the capsule, being that portion of the matrix nearest the cell, is the part most recently formed. The cells consist of a s]iongv jirotoplasm due to vacuoles of fat, and to spaces from which glycogen has been removed. Within a lacuna the cells may divide by mitosis so that there may be four or eight in one capsule. Ordinarily they move apart, by resorbing the adjacent matrix fStohr) or by forming new ground substance which forces them apart (Mall). New exoplasmic walls develop between them, pro- Fl 54- — DMUKNMS of IIIE I)K\'KI OPMENT Ol'" (ARTIl FR' )M MeSFMHN ma. A, Based upon StudniLk.i's studies ot iKIi , B. upon :M study of mauiniats Mes., IVKseiich\ m;i , Pre. Cart.. cartjla>>e; Cart., cartMay:e. Digitized by Microsoft® CARTILAGE. 5 1 ducing characteristic groups and rows of cells such as are shown in the diagram. It has been reasserted that some of the cells undergo a mucoid degeneration and become lost in the matrix. Around the entire cartilage of the adult there is a connective tissue envelope, the perichondrium, containing undifferentiated cells which by growth and division become cartilage cells. They are added to its surface. The young generations of cartilage cells are therefore at the periphery, and the old are in the center of the cartilage. Between them an interesting series of cytomorphic changes may be seen. The perichondrium contains vessels and nerves. Blood vessels may extend into the cartilage of young embryos, and into cartilages which are being replaced by bone, but ordinarily cartilage is non-vascular, receiving its nutriment by diffusion through the matrix. In surgical operations the preservation of the perichondrium may be of importance, since it can produce new cartilage. Fig. 54, B, presents Prof. Mall's idea of the formation of precartilage in mammals, differing from that just described which followed Dr. Stud- nicka's work on fishes. In B, by the development of fibrils which are exoplasmic structures staining with eosin, the nuclei and endoplasm become "extruded from the syncytium" and lie in the intercellular spaces. The exoplasm becomes transformed into the matrix of the cartilage. The crowded condition of the nuclei in precartilage makes it difficult of interpretation. Glycogen, which occurs in cartilage cells, is a carbohydrate resembling starch and known as "animal starch." It is soluble in water, and soon after death is converted into glucose. For these reasons it disappears from ordinary sections. Fresh tissues preserved in strong alcohol, and stained with tincture of iodine, exhibit glycogen as brownish red masses, tending to be round, but often not sharply outlined. Glycogen is abundant- in embryos in the epithelium of the skin, in liver cells and striated muscles and in cartilage cells. It is found in similar situations in the adult, espe- cially in well-nourished individuals, but is apparently not as abundant relatively as in the embryo. It occurs also in other cells. Its production, like that of fat, may be considered a nutritive rather than a glandular phenomenon. The matrix of cartilage chemically is a mixture of collagen, chondro- mucoid, chondroitin sulphuric CLcid (in combination), and albuminoid sub- stances (albumoid). [The old term "chondrin" really means little else than the matrix of cartilage.] The collagen may occur in white fibers which abound in the matrix of that form of cartilage called fibro-cartilage. Elastic fibers predominate in the matrix of elastic cartilage. If, however, on ordinary microscopic examination the matrix appears homogeneous, Digitized by Microsoft® HISTOLOGY. it denotes a hyaline cartilage. Hyaline, elastic, and fibro-cartilages require special examination. Hyaline cartilage macroscopicall}' is a pale bluish or pearly trans- lucent substance, firm and elastic. It forms some of the cartilages of the larvnx, and those of the trachea and bronchi, the nose, ribs and generaUy .*^?*^ '<^' «. Q^MMmi^.\ >*5^.^^ ^s^c^'- A B c Fh:. 55. — The Three T^'PES of Cariilage: A. Hyaline; B, Klastic; C, Fibrol's. (Radasch.) d, b, (Juler and inner la\ urs <>f pLTiclmndriuni ; c. \ unn^ c;i Ullage eells ; d, older cartilage cells ; e. f, cap- snle ; g. lacuna. the covering of the joint surfaces, together with the cartilaginous skeleton of the enibyro. Its matrix, though apparently homogeneous. Fig. 35, A, is actually fibrillar, as shown by its behavior under polarized liglit, and by its separation into fibers after artificial digestion. WTicther its lacunae are connected with eaelr other by small canals as in bone and in the carti- lage of some invertebrates, is ^'ery doubtful. Such canals as have been observed are ascribed to shrinkage caused by reagents. Sometimes, as in portions of the laryngeal and costal cartilages, the matrix may develop coarse fibers, neither white nor elastic, which have a luster hke asbestos. In old age, and even by the twentieth year in the case of some lar} ngeal cartilages, lime salts may be deposited in the matrix, first as granules but later combining to form shells enclosing the cartilage cells. Calcified cartilage, together with calcified tendon and other stnictures, should not, howe\er, Ije regarded as bone. Elastic cartilage is a pale yellowish stnicture containing in its matrix Digitized by Microsoft® CARTILAGE. S3 granules, libers, or networks of elastic material, Fig. 55, B, and Fig. 56. Specific elastic tissue stains are as applicable to cartilage as to connective tissue, and should be used in all cases of doubt as to the nature of the fibers. The elastic elements are found near the ceUs, but agreement has not been reached as to whether the)' arise in the matrix or in the exoplasm. Elastic l^lt't^r a. 3. Fig. 56, — Ei--\siii: Cartilage. ;-: 240. 1. Portion of a section of Uie vocal process of an arytaeiioid cartijacre i:)f a woman thirty years old; the elastic substance is in the form of granules. 2 and 3, Portions of sections of tlie epi.tjlottis of a woman sixty years old ; a (iiie network of elastic fibers in 2, a denser network in 3. z, Cai tilage'Cell, nucleus iii\ isibie , k. capsule i ? ). cartilage occurs in the external ear and the auditory (Eustachian) tube; also in the epiglottis, the cuneiform and corniculate cartilages, and the vocal process of the arvtaenoid cartilages, the last groujj being parts of the larynx. Fibrocariilage, Fig. 55, C, appears as a cartilaginous modification of dense connective tissue. A chondro-mucoid matrix forms among the fibers, and the cells wliich occur singlv or ( I. in small groupjs at considerable intervals, '' \ J ' are surrounded by capsules. Filjrocar- f >'' \rt \ tilage is found in the intervertebral liga- J ' ) -^ ' ments, Fig. 57, in the symphysis pubis, .?— t't^I \ \ around the mandibular and sternoclavicu- / / \ ' ' lar ioints, at the head of the ulna, in the ^ ^ !' I 1 I /"^ , ■ r , 1 • • • 1 • , - V, 1^ / / ( ® / / hgamentum teres of the hip-jomt and m - ] -J 1 '^ / \^^ other places associated Avith joints. Yes- ^' "~' j 1 icitlar supporting tissue is the name given | j to a tissue found in lower animals, resem- fig. sr-— fk..m a il.rizo.nt.al skctk.n 01-' I HE Intkr\"ertkbral Disk OF Man. bling precartilage, and consisting of A'CS- g, Fibrillar connective tissue; 2 canilage- . , - . 11 o 1 '-^■" (nucleus invisible); k, capsule ICular cells AVlth lirm resistant walls. bUCn surrounded b> calcareous granules. cells may occur singly. They have been described in various tendons, and in the sesamoid iDone in the tendon of the human peroneus longus. Bone. Bone develops relatively late in embryonic life, after the muscles, nerves, vessels, and many of the organs have been formed. At this time Digitized by Microsoft® 54 HISTOLOGY. the skeleton consists of hyaline cartilages which correspond with the bones of the adult. Around the cartilages, or in some places quite apart from them, the bone is formed in the following manner: Osteoblasts. Calcifying citiincctU'c tissue bundles. Bone cells. J ; Eoiic matrix. O @ 1 a 1 'li Fic. 5S.— Frcpm \ Seciion of the Mamjiblh of a Hl'm.ax Fkti'S Fcii'r Months Old. X 240. In the embryonic connective tissue certain homogeneous strands become apparent, staining deeply with eosin, Fig. 58. These represent the matrix or ground substance of bone, and are considered either trans- formations of tlie exoplasm of the neighboring cells, or as secretions of those ceUs, or as modifications of connective tissue fibrils. They blend with the con- nective tissue as sho\Mi in the lower part of the figure. As these strands become distinct, they are seen to be covered with pecuhar cells of mesenchymal origin which lend to form a distinct layer. Since they produce bone they are called osteo- blasts. (Blast is a designa- tion for a formative cell, and is used m many combina- tions with a prefix denoting the stmcture which it pro- duces.) Osteoblasts are They are cells with rounded nuclei and abun- Bone cell. Osteoblast becoiniiiL;" a bone cell. 1 ,« =- ft 1 ^n .^'&i c iAiV Fig ,s9, — P.viiT t \ ( I ss srr i Hl;.mekus 01 V FIlmknj Lm showm in Figs. 58 and 59. Shai .\lo.\ dant protoplasm, varying in shape from flat to columnar, often beina Digitized by Microsoft® BONE. 55 triangular and resting against tlie strand of bone either by tlieir base or apex. Tliey form bone only along that surface which is applied to the matrix. As the strand of bone grows broader tlirough their activity, it encloses here and there an osteoblast which becomes thereby a bone cell (^ig- 59)- Apparently bone cells do not divide, and if they produce matrix, thus becoming more widely separated from each other, it is only to a slight extent and in young bones; they are therefore quite inactive. Each bone cell occupies a space in the hyaline matrix, called as in cartilage, a lacuna, -^a^! ,■'» a^ ^^b * ,a> I /.^ a,-— '"^^^-^''^ tliL- process of foi ma '*: ^ 'K^-- !, •>i ■; 't'^^', - , '._ >V. -^^■'"3^-' Blood vessels. 3 ■" ^ihr"^ */f*^^',^^ " '^-^ ./" -v. ^ Perichondral b, .T))<£' ■ ."V^ ,-,." W '* aj^ Finished Haversian V/ <-' ,. ! ,,,, i- ' l.*-«J/ ■ canal. .1 V V« »~) ^ - ' -'^ i*^ .--■^-~^"' ~Z, 11^ Eniptv lacunae if'' * '■- ■ ,.,:*"t'^ "r*--* ' " ^-^ ''*i , ,' EndoclH.ndral border- line. iCndochondral bon FiG.no. — Portion of .^ (!'ross SRcriON oi'~ a Triiri .\r Bone of /\ Nk\\'i:orn Kittkn. but unlike the lacunae of cartilage those in bone are connected by numerous delicate canals, the canalicidl. In ordinary sjjccimens the canaliculi are visible only as they enter the lacunae, which are thus made to appear stellate. The matrix around the lacunae resists such acids as destroy the ordinary matrix and thus may be isolated in the form of " bone corpuscles." The "corpuscles" correspond with the capsules of cartilage. The bone cells nearly fill the lacunae and send out slender processes into the canaliculi. These may anastomose with the processes of neighboring cells, as can be seen in the embryo, but it is considered doubtful if this condition is Digitized by Microsoft® 56 HISTOLOGY. retained in the adult. The ])roccsses, moreover, are so line as to be invisible ordinarily, and formerly their e.xistence was denied. The strands of Ijone containing bone cells, and beset \\-ith osteoblasts, increase in size and unite so as to enclose areas of embryonic connective tissue containing blood ^-essels, as shown in the upper part of Fig. 60, and in the diagram, Fig. 61. The connective tissue surrounding the entire network of bone becomes differentiated into a distinct layer, the periosteum. This includes an outer stratum of ordinary connective tissue (not drawn in the figures), a middle layer of dense fibrous tissue, and an inner cellular Ia}'er including the osteoljlasts in contact with the outer surface of the bone. Fig. 61 shows the way in which a portion of this inner stratum may be enclosed in the bone matrix. It is about to occur around the blood vessel, ?^^^s!^-^^<^^l<-s^£:^fii^=^S^^r/^—i B. v., and has taken place in the space H. C. Within such an enclosure the osteo^ blasts continue to form bone in concentric layers or lamellae, thus gradually re- ducing the central space until it contains only a few cells and the blood vessels as in H. C". Such spaces occur abundantly in adult Ijone, and are called Haver- sian eanals (in recognition of the anatomist Havers). They are always surrounded by eoneeiilric lamellae, or layers of bone, of which tlic innermost is the youngest. Between these Haversian systems there are irregular lamellae, called interstitial lamellae, and sometimes a blood \-essel runs through them, not surrounded by con- centric layers. It is said to occupy a Volkmann's eaiial. Transitions from a Volkmann's to an Ha\'ersian canal are gradual, and are made not bv a change in the canal but by a rearrangement of the surrounding lamellae. Coarse fibers may extend from the periosteum into the interstitial lamellae, known as Sharpens fibers. They consist of more or less calcified bundles of connective tissue fibers, including both wliite and elastic elements, though chiefly the former. If abundant, the periosteum is most closclv adherent to tlie bone. They are absent from the Haversian systems. Besides the interstitial and concentric lamellae, anotlier set is deposited under the peri- \RlJiPMENTOF r.ONH. (Ill pail, aller Duval.) f., lMl")r, lus ]a\ er of periosteum ; o., osteogenic layer of perios- teum; OS., osteoblast: b. c, bone cell; B. V., blood acs- sl-1 ; H. C, bet^innine; Ha\-ersian canal ; H. C-., complete llaAcrsian canal; i. I., interstillal lamelhie; c. I., eoneeii- lric lamellae ; Sh,, Sharpey's fibers. Digitized by Microsoft® BONE. 57 ostciim, parallel with the surface of the Ijonc, the periosteal lamellae [outer circumferential or outer ground lamellre]. If the bone is hollow, having a marrow cavity, similar lamellae mav be deposited over the inner surface of the shaft by a formative la}-er called the e)iJoslcitm. These lamellae are end- osteal lamellae [inner ground or circumferential lamellae, marrow lamellae] and they line the marrow ca\-ity. The four sets of lamellae are shown in Fig. 62. Lamellar bone is compact, differing notably from the spongy network of trabcculae seen in the embrj'o. Compact bone is found in the outer parts of the long and flat bones and as a thin outer layer in short bones. Spongy hone is found in the interior of long bones, and of llat bones (where it is called diploe), and it constitutes the greater part of short bones and epi- physes. It is due in part to the persistence of the embrj'onic trabeculae, and in part to the reduction of compact bone to slender spicules through processes of absorption. Scarcely has bone formed before portions of it begin to be resorbed. The osteoblasts disappear locally and in place of them there are large irregular masses of protoplasm con- taining several separate nu clei. The idea that these structures arise by the fusion of se\'eral osteoblasts is not acce])ted; the nuclei are thought to arise by repeated division within a mass of protoplasm which enlarges but does not divide. The form of <7iant cell resultinij is called an osteoclast, from its supposed function of destroying bone. The osteoclasts. Fig. 60, are often seen in hollows which they are thought to ha^•e exca\'ated in the ground substance, and which are called Howshifs lacunae. There seems to be no satisfactory evidence that the osteoclasts are the cause rather than a product of those conditions which lead to the dissolution of bone. The process of resorp- tion is of the greatest importance, since it prevents bones from becoming solid and heavy. While new bone is forming on the periosteal surface, old bone is being dissolved, both around the marrow cavity and in the deeper Haversian canals. This process ];roduces most of the spongy bone of the adult. Reviewin<^ the preceding paragrajihs, it may be said that bone appears first as strands of ground substance produced by osteoblasts derived from Fig. 62.— From Cross Si'Xtion of a .Mktacarp.al of Man. X 50. Resru'iilinii line at k. Digitized by Microsoft® 5^ HISTOLOGY. Ha\ersia caiial-s. mcscnchyma. The osteoblasts may be enclosed by the matrix which they form, thus becoming bone cells. The trabeculae of bone produced in this manner unite in a network, described as sjjongy bone. By the deposi- tion of new layers or lamellae of bone, which conform with the surfaces on which they are laid down, the spongy bone becomes compact. By resoi"{Dtion of the inner part, the marrow cavity forms and parts of the compact bone become spongy. It remains to consider the substances and appearances of adult bone, and to describe the manner in which the cartilages are replaced by bone. The matrix of bone is at first uncalcified and soft, apparently homo- geneous, but actually con- sisting of cemented fibrils. It consists chiefly of col- lagen — the gelatin-pro- ducing substance, and of a mucoid called osseo- mucoid. Through it there may be distributed fine elastic fibers (said to be lacking in the bones of the vertex of the skull) besides the coarser con- nective tissue bundles of Sharpey. Soon after this organic matrix is estab- lished, calcification begins by the deposition of lime salts either in or between the fibrils. Over So % of the inorganic matter is calcium phosphate, Ca3(P0J,, the remainder includmg chlorides, carbonates, fluorides and sulphates of calcium, sodium, potassium, and magnesium. The proper- ties of bone depend largely upon the intimate blending of the organic and inorganic constituents, possibly in chemical combination. The two parts may be separated, however. Acids remove the salts leaving the organic portion as a flexible counterpart of the entire bone. Heat or maceration may be employed to destroy the organic part. Microscopic preparations are made in either way, but usually from decalcified bones. All of the drawings thus far referred to were of such specimens. The cross section of a decalcified long bone of an adult, Fig. 62, Fat iln.ps. MAN l-at .h 0).c — tRJ^t \ L^N 1TLE1N\1 Si ri 1\ I Ul Met al \kp \l ^ 30 arc seen in the Haversian canals. At x Haversian canals ] llif onter, and at XX on tlie inner surface of tlie bone. Digitized by Microsoft® BOXE. 59 shows the periosteum on its outer surf;ice. In fa\'orable specimens it is seen to inchide an outer vascular, rather loose connective tissue layer, and an inner dense filDro-elastic la3'er, in which elastic elements predom- inate. Into this layer the tendons are inserted, which means that they blend with it and may contribute to the fibers penetrating the bone. The mnermost cellular layer of the periosteum has become reduced to oc- casional osteoblasts. These may multiply after an injury; in )'oung individuals, if the periosteum is slit and the shaft of bone shelled out, they may produce a new bone. The cross section further shows the contents of the Haversian canals, which include one or two blood vessels, and a fcAv connectiA'e tissue or fat cells. Nerve fibers which are found in the periosteum, where they some- times terminate in lamellar cor- puscles (page 107), have been de- scribed as extending into the Haversian canals. They are not easily detected there. Lamellae may be observed as indistinct layers. They are said to be due to the differences in direction of the fibrils which they contain, as sho^vn under polarized light. They may also represent differ- ences in texture, from variations in the food supply at the time of their formation. The lacunae may apjpear either in or between the lamellae. They are nearly filled by the bone cells, which, however, are seldom well pre- served. The cells are generally flattened, parallel with the lamellae, and are provided with processes extending into the canaliculi. They do not fill them and it is supposed that tissue fluids may circulate through the lacunae and canaliculi. Wandering blood cells are too large to enter them. The lymphatic vessels are limited to the superficial layer of the periosteum. The blood supply of bone is abundant. One or more nutrient arteries enter a bone through its periosteum and break into branches which run in the Haversian canals, thus extending through to the marrow cavity in which they ramify freely. The blood vessels and Haversian systems are parallel with the long axis of the bone, so that they are cut across in Fjg. 64. — Cross Section of Compact Bone, from THE Shaft of the Humerus, sho\ving Three Haversian Systems and Part of a Fourth. {S/uu/'ry,irom Bailee's " Text-bocik of Histolog\-.") Digitized by Microsoft® 6o HISTOLOGY. cross sections. In longitudinal sections they appear as in Fig. 63. Veins pass back from the marrow, through the Haversian canals, emerging through the periosteum. It will be noticed that in longitudinal sections the lamellar systems are scarcely distinguishable. On the marrow side, the endosteum forms a thin fibrous layer containing occasional osteoblasts and osteoclasts. The marrow will be described with the blood-forming organs. ': N'. Center of ral-. cificatioii Pninnrv niarrnw syiact J'cnchoiiilral i Fh, ^s — Fr'")m a Dr)Rsr>-p\i-MAR l,(iNGiTi'niNAL S^:cTIo^' OF A Ph\ranx of the Little FiNCKR OF A Human Ffti^s Six j\1on]-hs Old. )< 60. Preparations from washed and dried bones show onlv the calcareous framework. Sections made by sawing shoAv macrosct)pically an arrange- ment of the spongy bone in arches and trusses to resist comjtression. Microscopic sections are made by grinding thin sawed slices until they become translucent, and mounting them so that the lacunae and canaliculi remain full of air. Since the air is refractive it appears black. Thus the canaliculi are tlearh' deiuonslrated, as in Fig. 04. The\- extend from one Digitized by Microsoft® BONE. 6i lacuna to another, connecting the different Haversian systems, and openinj^ into the Haversian canals. The Relation of Bone to Cartilage. Some bones develop cjuite independently of cartilage. These include, besides the teeth, the so-called membrane bones [intramembranous, connec- tive tissue or secondary bones]. In the midst of the embryonic connective tissue, spicules of bone are formed in the man- ner already described, and they unite to form a bone. The membrane bones are the bones of the face, and the flat bones of the skull; — the interparietal or upper part of the occipjital, the squamous and tympanic parts of the temporal, the medial pterygoid plate of the sphenoid, the parietal, frontal, nasal, lachrymal, zygo- matic (malar), and pal- ate bones, together with the vomer, maxilla, and almost the entire man- dible. The remaining bones, being preformed in cartilage, are grouped as cartilage bones [pri- mary bones]. They de- velop) like membrane bones except that the matrix is in part deposited in contact with cartilage in the following manner. Fig. 65 shows a longitudinal section of a developing phalanx. On either side of the shaft a strip of bone is seen, formed from undifi:erentiated cells of mesenchymal origin, situated in the perichondrium. It is called perichondral or periosteal bone, and arises hke membrane bone. As a whole, it forms a band encircling the shaft of cartilage. Within it, the cartilage cells have enlarged, and divided so that several cells may be in Calcified nialrix of cartilage. Spicule of calcified matrix. Marrow space. Pcrichon- ■ dral bone. Fic. 66 — FrO-M a DoRso-r.ALMAR Longitudinal Section ok a Middle-finger Phalan.\ of a Hitman Ff.tus Four Months Old. X 60. Digitized by Microsoft® 62 HISTOLOGY. one lacuna. The lacunae also have increased in size. The matrix in this region stains a deeper blue with haematoxylin than elsewhere, due to the deposition of lime salts within it. On the left a cavity is seen ex- OsLeo.LTeiiic tissue. ■ Hyaline carti- I la,y:e (cells in ^L^roups). ii'l''" '-r^ M' '"' *:-' > ^^^^u^^ :iVi\v'-lWfi Periusleum. ^ Pension, Iral / bone. / Oslcohla-ils. r '■ * e EikIol liiHidial bone Fig. 67, — From a Longitidinai, Shction 01 tuf Pn \i \n\ m iiif.: First Finc:er ov \ Hi'man Fl'Tl'S UF F'.so. the cartilage cells set free by the absorption of the walls of the lacunae became osteoblasts, but now they are considered as dying cells without further function. The osteoblasts belong with the invading cells. As seen in Fig. 67, both the perichondral bone on the surface of the cartilage and the endochondral bone forming within it, develop like membrane bone. As the bone grows, the older parts which have formed around the calcified cartilage are resorbed, and in the shafts of adult bones probably no trace of the cartilage remains. In the ear bones, however, calcified Digitized by Microsoft® 64 HISTOLOGY. CCP cartilage may be found throughout hfe. Fig. 68 shows a part of the humerus of a fetus in which the calcilied cartilage remains, forming in one place a boundary between endochondral and perichondral bone. The vascular tissue within the shaft becomes marrow, — a reticular tissue associated with fat cells, and having developing blood corjjuscles in its meshes, to be described later. In brief review it may be said that cartilage bones are formed by the deposition of perichondral bone on the outside of a hyaline cartilage, and of endochondral bone upon the lining of excavations within the carti- lage. The cartilage is not transformed into bone, although the matrix in part becomes calcified and encased in bone. In the long bones this process of ossification produces a shaft of bone tipped with a mass of cartilage at either end. Fig. 69, A, B, C. The shaft is the diaphysis; the cartilage ends arc epiphyses. At various times after birth, or in the tibia shortly before birth, 11'*, I I osteogenic tissue invades the epiphysis and I lap,,--.-- gradually replaces its cartilage by bone. Um^ -A layer of epiphyseal cartilage between the epiphysis and diaphysis, and a layer of articular cartilage covering the joint surface persist longest. Until adult life the epiphyseal cartilage grows, chiefly to- ward the diaphysis, and the addition as fast as it forms is replaced by bone. Thus the epiphyseal cartilage is an essential provision for the lengthwise growth of bones. The epiphyseal cartilages be- come entirely calcified at different ages in the various bones, generally from 18 to 22 years, at which time the epiphysis is said to unite with the diaphysis. After that the articular cartilages are all that remain of the original cartilaginous structure which preceded the corresponding bone. Fig. 6q — Pl.a.n ok Ossimc.\tii)n- in- x LriNG EoNE, Based upon the Tibi.\, Carlila,s:e is drawn in black, aiul bone is slipplfd. Art., Articular cartilai^e ; ep., epiph\ sis : diaph., iliaph\'sis. The Joints. Bones may be joined in two ways, either fiy a sxnarlhrosis which allows little or no motion between them, or b}- a diarihrosis which permits them to move freely upon one another. In a synarthrosis the mesenchymal tissue between the adjacent bones may become a dense connective tissue, either like a fibrous tendon or an elastic ligament, thus forming a synJesiuosis: or it may become cartilat^e, usually of the filjrous tyijc, making a syncliomlrosis. The sutures are forms Digitized by Microsoft® JOINTS. 65 of s}Tidesmosis in which the serrate borders of bones are connected by short trljrous ligaments. The intervertebral ligaments are synchondroses, each consisting of a fibrocartilage Avhich has at its center a soft mucoid substance containing large groups of cartilage cells. This niiLiciis pidposus is usually inter- ;. preted as the remains of the notochord, but ^j^r.—i.--- ■'■■■.■ ■■/;■ some consider that the notochord is entirely ■:'':::'■.■■}']. ''i-^ absorbed, making the nucleus pulposus an ^f 1 ,■:■:,:■■■ ';•.■ independent formation. The term //^a;);cH/, it ss-— -^ ■ . ,- ' will be noted, is applied to bands of various J'=~^ , ■ ■;/-. r-S-'-- sorts, Iibrous, elastic, or cartilaginous. ' " ■.;.■.■:;;■•.■ ■■;:#|--; In a diarthrosis the mesenchymal tissue ^ ■,.■■ ■■ ; ■5,-; between the bones remains comparatively loose , .^^ , .' ^' •■ :? ^ in texture and a cleft forms in it, containing ' ' ■ ' '" ' " I li ,. 70.— Phalan'geal Joint from tissue fluid. This is the joint cavitv, Fig. 70. ^^ fo'-'R months' fetus. . Ill 1 1 'i! 1-1 Car., Cartilage: j. c, jonit cavity, It IS bounded by mesencliymai cells which s. f.. stratum nhrosuin; s. s.. str.itQin s> iHi\ ialu. Spread out and form an epithelium, shoAA-n in Fig. 71. The epithelium may fuse with the articular cartilage so that the latter, uncovered by perichondrium, forms a part of the wall of the joint ■'*'- ^^S- Fin. 71.— Ax E-N-LARGED Drawing of the Left P\rt of the Joint sho\vn in Fio. 70. b. v.. BliHj.l \ Lb'cl ; car., cartila,c;e ; j. c, joint cavit\ , mes. epi,, mesencliymai cpillieiium. cavity. Articular cartilages are usually hyaline layers from 0.2 mm. to 5 mm. tliick, becoming thin at the periphery. The cells near the joint are flattened paraUel with the free surface, and some of the deeper of these 5 Digitized by Microsoft© 66 HISTOLOGY. arc said to have lobcd nuclei. The Hat cehs are succeeded by groups of rounded ones which are described as having protoplasmic processes. In the dee])cst layers the cells tend to be in rows perpendicular to the joint surface and the matrix is calcified. In Fig. 72 a line is seen separating the calcified from the uncalcified part. Marrow (fat cells). Blood vessel. Fig. 72.— \'i.-rtical Section thkoii.ii the Hk-\l) of Mktacakpal of an .Adult Man. >: 50. ';".•: v'Haa.'S Fig. 73, — S\NO\'IAI. \'ILLI "WTTH Bi boD Vessels from .\ Hu- man Knee Joint. >x 50. The epithelium has fallen from the ap)ex of the lett villus, exiiosing the coiiiK-cti\e tissue. The ioitil capsule consists of an outer layer of dense connective tissue, the stratum fibrosum; and an inner loose layer of \\'hich the mesenchymal epithelium is a part, the stratum syiioviale (Fig. 70). The fibrous layer is specially thickened in \-arious places to form the ligaments of the joint. It may cover the end of the bone, coming between it and the joint cavity; thus the distal articular surface of the radius is covered with dense fibrous tissue. In other joints, as in the shoulder and hip, such tissue forms a rim, deepening the socket of the joint. These rims are called labra glaioidalia. The synovial layer consists of loose tissue, generally with abundant elastic elements, and in places containing fat cells. It has nerves which may terminate in lamellar corj)usclcs, numerous blood vessels, and lymphatic vessels which extend close to the epithelium. The opillielium is a smooth, glossy layer of connective tissue with parallel fibers and small round or Digitized by Microsoft® TEETH. 67 Stellate cells containing large nuclei. They may be spread in a single thin layer, or heaped together, making an epithelium of three or four layers. The synovial membrane may be thrown into coarse folds (plicae) or into slender pjrojections often microscopic (villi). The synovial vilh, Fig. 73, are variously shaped but are usually finger-like; they ordinarily contain blood vessels and impart a reddish velvety appearance to the membrane. The large folds of embryonic tissue projecting into the joint, \mt always covered with the mesenchymal epithelium, may become dense fibrous articular discs such as are interposed in the sternoclavicular and mandib- ular joints, or they mav form the fibrous cartilage-like menisci of the knee joint. Nerves and blood ves- sels are absent from the discs, men- isci, and labra glenoidaha. S}TLOvia [synovial fluid] is 94 % water, the remainder being salts, proteids, and mucoid substances, together with fat drops and frag- ments of cells shed from the mem- brane. Teeth. A tooth consists of three parts, crown, neck, and rool or rools. The crottTi is that portion which projects above the gums; the root is the part inserted into the ali'colus or socket in the bone of the jaw; and the neck, which is covered by the gums, is the connecting portion between the root and crown. A tooth contains a denial cavity filled with pulp. The cavity is prolonged through the canal oj the root to the ape.x oj the root whcrt it opens to the exterior of the tooth at the foramen apicis denlis. The foramen is shown, but is not labelled, in Fig. 74. The solid portion of the tooth consists of three calcified substances, the dentine or ivory (suh- stantia eburnea), the enamel (substantia adamantina), and the cement (substantia ossea). Of these the dentine is the most abundant. It forms a broad layer around the dental cavity and root canal, and is iaterrupted Ct-ment. Hi'.- niTiniNAL Groind Shction of ■\N Incisor Tooth , 4. Digitized by Microsoft® 68 HISTOLOGY. only at the foramen. Nowhere does the dentine reach the outer surface of the tooth. In the root it is covered by the cement layer which increases in thickness from the neck toward the apex; and in the crown it is enclosed by the broad layer of enamel. The enamel, however, becomes thin toward the neck, where it meets and is sometimes overlapped by the cement. The pulp, dentine, and cement are of mesenchymal origin, the dentine and cement being varieties of bone. The enamel is an ectodermal formation, but so intimately associated with the others that it may be described with them. In the human fetus of about two months the ectoderm covering the jaws is continuous with the entoderm lining the mouth and throat, as shown in Fig. 75, and there is nothing to indicate where they join. To- ward the front of the mouth, in either jaw, the epithelium sends a plate-like prolongation into the underlying mesenchyma. This is called the dental ridge. There is a continuous ridge parallel with the circumference of each jaw, and that it is entirely ectodermal is known from the study of earlier stages when the oral plate is still present. In the diagram. Fig. 76, at A, a part of the ridge in the lower jaw and of the oral epithelium from which it grows, is repre- sented as free from the surrounding mesen- chyma. The labial side of the ridge is toward the left and the lingual side toward the right. The ridge later produces a series of inverted cup-shaped enlargements along its labial sur- face and these become the enamel organs. There is an enamel organ for each of the ten deciduous or temporary teeth in either jaw. Within the inverted cups the mesenchyma becomes very dense, producing in each a dental ^papilla from which the pulp and dentine are derived. The enamel organ produces the enamel, and perhaps controls the shape of the tooth. The cement is derived from the surrounding mesenchymia. , Three stages in the formation of enamel organs and papillae are shown in Fig. 76. The dental groove in C is a transient depression which is relatively unimportant. In D the enamel organs are connected with the dental ridges by slender necks of epitheUal tissue which subsequently become severed. At about eleven weeks all the papillae and enamel organs of the deciduous teeth have formed. The permanent teeth develop from similar organs and papillae which arise later; the first molars are indicated at five months, and in embryos of six months (30-40 cms.) all of the permanent front teeth may be found. Their enamel organs ■ Fic. 75- Part of a sagittal section of a human embryo, to sliow the position of the dental ridges, D. R.; M., mouth; Md., mandible; My., niaxilla; N., median nasal sep- tum ; P., palate. Digitized by Microsoft® TEETH. 69 appear on the laljial side of the deep portion of the dental ridge, as shown in Fig. 77, but tliey are on the inner side of tlie deciduous teeth. The portion of the dental ridge which is not included in the enamel organs EpilliuliUTii <.l llie niai-i ot llif law . Denial iid^t. Papillat. Euanifl organs. c Necks of unaniel t D Fig. 76. — Dr.ACR.AMS si!'>\\ini: titf, L-M^r.v Dexklopment (jf Tdkee Tketh, Onk of Wi-nCH IS SHOWN IN \'ERTIC..VL Sl-:CT!ON. k, Fi't-e border of the dental nd.i^^e. sends irregular projections into the niesenchyma and becomes perforated and detached from the oral epithelium. Its remnants found in the gums at birth have licen mistaken for glands. A portion of the ridge extends beyond the necks of the enamel organs for the permanent teeth, and this has been said to indicate the possibility of a third set of teeth, — a possibility never real- ized in mammals. The second and third molars are formed from a dorsal or backward extension of the dental ridge free from the oral epithelium. The second molars appear in a child of six months, and the third or late molars (wisdom teeth) at five years. The latter are not at the extremity of the dental ridge but are on the labial side of it, so that there is a theoreti- cal possiljility of fourth molars. ;oE. DR. EG. 77 — Teeth from \ Hi m.\n Fetus of 30 cms. (Modilied, from Rose.) lid E. 0.. Knamel or;;,-ans of a di.cirlnons and of a permanent t"olh lesperlivelv; D. R.. denial ridije , 0. E.. oral epithelinm ; P..|.ip!ll.i, EXAMEL ORG.\NS AND ENAMEL. The enamel organ is at first a mass of undifferentiated epithelial cells, but soon it becomes di\-isible into three parts as shown in Fig. 78. The inner enamel cells arc applied to the dense mesenchymal papilla; the outer enamel cells, continuous at tlie rim of the cup with the inner cells, are toward the loose niesenchyma; and the enamel pulp fills the space between the outer and inner layers. The outer enamel cells form a single layer of cuboidal cells, with which some flattened ceUs of the enamel pulp are in close contact. In later stages the layer appears as a feltwork of Digitized by Microsoft® 70 HISTOLOGY. flattened elements. It is in close relation with the surrounding vascular mesenchyma, but no blood vessels penetrate it. The enamel pulp is at first a compact mass of ectodermal cells, but by peripheral vacuolization or by the enlargement of intercellular spaces it forms a network con- siderably resembling mucous connecti\X' tissue (Fig. 79J. Its slender fibers have been considered as elongated intercellular bridges. The inner enamel cells form a single laver of cylindrical cells separated from the enamel pulp by a cuticular plate, yet connecting with the pulp cells by bridges. Beszinninc; at the summit of the crown the inner enamel cells ;rt%^. f: Thickened OIMl epithelium. Outer enamel cells. Enamel pnl|i. ^ — ■ -.^f/SSi C Inner ennniel cells. Neck nf the enamel organ. Free eclge of the deiuairidire. Papilla. Fig 7S.— From a Cross Skciii^n of thf I'pper ] \w uv a Him vn Embryo Fivii iMijNTHs 01. D. > 4J. produce cuticular basal plates \\\\\c\\ become long and slender, and later, calcilied. They extend from the enamel cells towartl the dental papilla. These are the enamd prisms, and the cells which produce them are called adamaniohlasts [ameloblasts]. The formation of enamel prisms spreads from the summit over the sides of the crown and neck, but although the root is enveloped in the enamel organ, no prisms are formed there. The inner enamel cells of the root flatten and by disappearance of the enamel Digitized by Microsoft® TEETH. 71 pulp they come in contact \^ith the outer cells. The two layers form the epithelial sheath of the root (Fig. 86j. The adamantoblasts are columnar cells with elongated nuclei toward their outer ends. (Since the enamel organ is an inpocketing of ectodermal epithehum, it is clear that the basal stirjaccs of the enamel cells are toward the mesenchyma, and the oii/er surjaces toward the enamel pulp.j Diplosomes have been found near the nuclei. There are terminal bars CiiticLilai h<.>ri.lcr. Eiiainel |.risms. CeiueiiL substiuice. Calcilied,. miLalcillud ilcntitic. ; I ■ ' Enaniel pulp. ■ Rectant^Ie cuclosiiia: the porLion I OdoutiildasLs. I'Lilp, of the tO'iLh shown lin^hl\' Dia^^iii- '*uter fiiamel cells. Inner enaiTiel cells lied in the adjoining part of tlie (adamantoblasts 1. figure. Fig. 79 — Portion ok \ Longitijdin.^l Skciion of .\n Incisor Tooth OF A Newborn Kitten, x 300 In this section the \ounq- enamel prisms ha\-e been pulled out of their spaces in the cenienf substance. ('rile cement of the enamel must not be confused with the cement which co\ers the roiiL.I and a cuticular border at the basal surface, toward which the protoplasm contains granules which blacken with osmic acid. Between the cells there is a cement substance. The long columns (prisms) which grow out from the basal surface of the cells are likeiA-ise surrounded by cement substance. The columns at lirst are not calcified [and are often called Tomes' processes]; they have a honey-comb stmcture and tend to split into longitudinal fibers. They may connect with one another by wing- like expansions. Later both the prisms and the cement substance become calcified, the former increasing in diameter at the expense of the cement. Eventually little (2-5 %) or no organic matter remains in the enamel. The prisms extend across the enamel from its inner to its outer surface. Digitized by Microsoft® 7 2 HISTOLOGY. As they increase in length the enamel layer broadens. Their course does not remain straight. A vertical median section of the enamel shows in its middle part (Fig. Si, c) ahernating layers of prisms in cross and longitu- dinal section. At the borders of these layers the prisms are in transition from one laver to the other. At either end the prisms are said to be per- pendicular to the enamel surfaces, but in the midst of their course they bend laterally in opposite directions. Thus they reflect light in such a way as to form alternating light and dark bands (Schreger's lines) which cross the enamel, and are related to the layers of j)risms as shoAvn on the right of Fig. Si,c. The lines are seen in reflected light. Contour lines (lines of Retzius) cross the prisms obliquely. They are due to jiauses in the enamel formation, and in poorly developed teeth especially they are jilanes alon" which the enamel maA' most readih' Ije fractured. Since they often h\ < Enamel prisms, isolated. Fig. So.^Fk:om a Cii AT Birth. oootU I". Sj. — a. Cross section of etiainel virisms (afur Sh'ilir); b. cross s<.clioiis of oiiaiiiLl prisms (after SnirL]ushes out through the tissue of tlie jaw in which it is embedded, so tliat its crown becomes exposed. In this process Digitized by Microsoft® TEETH. 73 of eruption the outer enamel cells and the enamel pulp are broken through and disappear. That portion of the inner cells which is applied to the enamel prisms remains as an uncalciiied but very resistant laver about i n thick, the culicula dculis [Xasmyth's membrane]. It may be detached by acids which dissolve the enamel but have little effect upon the cuticula. The latter, howc\'er, yields readily to mechanical erosion, and is soon worn away. The enamel is the hardest portion of the tooth, surpassing the dentine which is harder than bone. DENTAL PAPILLA AND DENTINE. The dental papilla has already been dcscriljed as a dense mass of mesenchyma enclosed and probably moulded by the enamel organ. Its cells branch and anastomose, producing hbrils. The cells next to the inner elim-"- . . - ' - r'-m^'m ABC Fi(_;, ^2- — Thk 1>h\ ici.oPMKNT OF Dkx'iine Fig .S3 l.v Pig E.MBR'iOS. (.After v Korff ) d., (.'alcified dentine; e. C, inner enamel cells ; Six odrmlol. lasts with dental libers, f, p., Jjiilp pn-ic- f.. (lbr<.ius i^ntnnd stihstance of dentine; esses. I'^roni tlie ]jnl[> at birth. /, 240. od., odontoblasts; p., niesench\ inal l-iulp eells. enamel layer become elongated as shown in Fig. 82, A, and soon constitute a simple epithelioid layer as in B. Between them there are groups of fibrils which spread beneath the enamel layer. Calcareous granules are de- posited between the fibrils and produce the matrix of the dentine. The elongated cells which are comparable with osteoblasts are called odonlo- blasts. Unlike the former they never l^ecome buried in the matrix, but remain on its inner surface. Long processes extend from the odonto- blasts radially through the dentine as seen in the isolated cells in Fig. S3. These processes are lodged in the dental caiialiculi and are called dental fibers [Tomes' fibers]. As in l;one the canalicuh have an incom- pletely calcified lining which resists acids. [The canaliculi of the teeth have therefore been described as bounded by Neumann's membrane.] Thev follow a wavy or spiral course from the outer to the inner surface of the dentine, often jjeing S-shaped as seen in median longitudinal sections. Digitized by Microsoft® 74 HISTOLOGY. Their diameter increases toward the inner surface Avherc it is from 2 to 4 !>■. They branch freely, as shown in Figs. 84 and 85, and terminate blindly or bv connecting with neighboring canalicuh. Sometimes they are pro- longed into the enamel for a short distance; they may end abruptly as if the terminal part had been destroyed or, in the permanent teeth, the enamel may form knobs in\-ading the dentine. Orduiarily the contact between enamel and dentine is smooth. The calcihcation of dentine begins shortly before the formation of enamel and spreads from the crown o\'cr the neck and root (Fig. 86). The calcitied portion increases in thickness, and contour lines, indicative of stratification, are sometimes seen. Near the enamel there are large irregular spaces of uncalcilied matrix Avhich occur in the course of the i^-%-^f^:^- Dciil Eimintl. Flij. S4. — From a Lom;ititiin al Skciion "F 'IMK L-\t- liRAi, Part ni- the Crown of ^ IIim^n M(.i|-AR Tooth. ,■ 240. 1, Dental canahculi, some exteniliii;;^ inln the t-ii;!!!!! I , 2, dental globules projecting towaid llie interji L 1 L lainel cells. D 1 1 Odoiitolilatt Dental papilla (future pulp) Blood \'essel. '' Eon>' trabecula of the low i law Fig. 86. — L0NGITUD1N.VL Section of v DECiDU. 42. The \\ lijte spaces between the inner enamel ceils and the enamel are artilicial, and due to shrinkac:e. ah'eolar nerves pass through the foramen, lose their sheaths and form a loose ple.xus beneath the odontoblasts, between which they terminate in free endings. Odontoblasts persist throughout the life of a tooth, and in case of disease or injury they may deposit dentine as a reparative process. Digitized by Microsoft® 76 HISTOLOGY. DENTAL SAC, CEMENT AND ALVEOLAR PERIOSTEUM. The papilla and enamel organ together are surrounded by loose mesenchyma extending to the oral epithelium and to the bone trabeculae of the developing jaws, as shown in Fig. 87. The portion of mesenchyma between the trabeculae and the teeth forms the so-called dental sacs. Toward the enamel organ the sac is a vascular and very loose tissue (Fig. 86) which may form elevations between projections of the outer enamel layer. The peripheral part of the sac is much denser. After birth. Cross section of the orbicularis oris muscle. .^;*-'^-i " Labial gland. Dental ridge. ^>j;v_^_ Enamel 1.--- --^"^ organ. "^ " 'ci Enamel. ^ , / ,_* ; < - ". , ^~ Dentine. ■J .,^" ';'"'! Pulp. . . '■■W-_ _t..„ Bone. Fig. 87. — Vertical Section through the Lip and Jaw of a Human Fetus OF Si.v and a Half Months. X 9- but before the eruption of the teeth, the sac surrounding the root produces the cement or substantia ossea. This is a layer of bone, containing typical lacunae and canaliculi and penetrated by many uncalcified connective tissue fibers (Sharpey's fibers). These may be so numerous as to suggest the columnar appearance of enamel. Their direction is generally radial. Lamellae in the cement are parallel with the surface of the root. Haversian canals are absent except in the outer part of the cement of old teeth. As the tooth grows and fills the alveolar socket in the jaw bone, the dental sac is reduced to a vascular fibrous layer, continuous with the connective tissue of the gums at the neck of the tooth. Elastic fibers are Digitized by Microsoft® MUSCLE. 77 absent. It is a single layer serving as the periosteum of the cement on one side and of the alveolus on the other and being intimately joined to both bones by Sharpey's fibers. It is named the alveolar periosteum [peridental membrane]. Its numerous blood vessels are branches of those which enter the apical foramen together with vessels from the gums and perhaps from the mandible and maxilla. Its nerve endings are the terminations of branches from the dental and alveolar nerves. Lymphoid tissue has been found in the gums, but apparently it does not extend into the alveolar peri- osteum. MUSCLE TISSUE. Contractility is a fundamental property of protoplasm. Muscle cells are those in which the contractile function has become predominant. They are elongated cells containing fibrils parallel with their long axes. By the shortening of these fibrillkted cells muscular action results. Em- bryologically muscles arise either from mesenchyma or from epithelium. Mesenchyma produces two types of muscle, smooth (non-striated, involun- tary) and cardiac (the striated, involuntary mus- cle of the heart). Mesodermal epithelium pro- duces one type, the striated voluntary skeletal muscles, ordinarily called striated. In the in- vertebrates ectodermal and entodermal epithe- lia also produce muscle cells. In mammals the muscle fibers of the sweat glands are generally recognized as ectodermal, and some in the iris have been described as such; entodermal mus- cles have not been observed. The three principal classes of muscles, smooth, cardiac, and striated, may be described in turn. epi. \>.m. Smooth Muscle. l.m; ^ - Fig. Smooth muscle develops around the large lymphatic and bloodvessels; around the intes- tinal canal, including the principal gland ducts opening into it and the large respiratory tubes ; also around the bladder and ureters, the uterus and ducts of the genital system; and, finally, in connection with the hairs, in the capsule of the spleen, and in other minor places. In general terms, it forms the musculature of the viscera. The development of smooth muscle may be studied in a cross section of an i8mm. pig embryo (Fig. 88). The stratified entodermal epithelium .—From a Cross Section OF THE Oesophagus of an i8 MM. Pig. epi.. Epithelium; b. m., basement membrane; c. t., connective tissue; c. m., circular smooth muscle cut lengthwise ; n, c, nerve cells ; I. m., longitudinal smooth muscle cut across. Digitized by Microsoft® yS HISTOLOGY. which lines the oesophagus, a part of which is shown in the figure, is seen to be surrounded by mesenchymal tissue in which the smooth muscle cells are being differentiated. There is a layer, c m., in which the cells have become spindle-shaped, and since they are parallel and close together, they form a band encuxling the oesophagus. Outside of this there is a broader layer of elongated cells, 1. m., all running lengthwise of the oesoph- agus and therefore cut across in this section. This layer of longitudinal muscle passes into mesenchymal tissue on the outside. The figure illus- trates that smooth muscle cells are elongated mesenchymal ceUs, gener- ally parallel and ar- ranged in layers. In the embryonic stage they are con- FiG. 89.— Smooth Muscle Fibers from the Small Intestink -nprfpi^ Kv nrntn OF A Frog. X 240. iicuLcu uy piuLu plasmic processes. Smooth muscle cells in the adult may occur singly or in the form of interlacing networks. Generally they are in layers and so closely packed that separate cells are hard to follow. Moreover they often extend be- yond the planes of the section so that only portions of them are included in the specimen examined. If a piece of fresh tissue is treated with a 35 % aqueous solution of potassium hydrate or 20 % nitric acid, the cells may be shaken apart, and appear as in Fig. 89. They vary in length from 0.02 mm. in some blood vessels to 0.5 mm. in the pregnant uterus; in the intestine they are said to be about 0.2 mm. Their width ranges around 0.005 '^ni. (s /j). They are fusiform or cylindrical, rarely being branched as has been recorded for muscle '^^23^5^ cells in the bladder, the ductus deferens, and the aorta (Fig. 156, p. 131). The nucleus, situated near the center of the cell, CZIIZI2222uZ25 is cylindrical, with its chromatin in a network and in ^'°g mo^th' muscle masses lining the nuclear membrane. In favorable prep - aLTe'ry otT dog^ arations it has been observed to contain several nucleoli, and a diplosome has been found just outside of its longitudinal border. When the muscle cell contracts the nucleus shortens and may be bent or spirally twisted, Fig. 90. (Such nuclei have been interpreted as distor- tions of resting nuclei caused by the contraction of neighboring cells.) The protoplasm of the smooth muscle cells early produces coarse fibrils called border fibrils [myoglia], since they tend to be at the periphery of the cell. They are said to extend from cell to cell, which is made pos- sible by the syncytial arrangement of mesenchyma. In one interesting but unique instance, the fibrils from the mesentery of a salamander showed Digitized by Microsoft® SMOOTH MUSCLE. 79 ^- '% T f"''" ' ^~7' ^-"ualfli*^ Eiiil III 11 muscle liber Nev\e cell. Ftg. 9T — Apparf.nt Tntkrchllul\r Bruh.i.s ok SMon-iii Mlisclh: Fiuers. A, Transverse section ul the intestine of a rabbit. B, Longitudinal section of the intestine of a L;uinea pig, , 420. alternating light and dark bands, verj' distinct in photographs. The fibrils of cardiac and striated muscles are alwa)'s banded in this way. Some investigators consider that the border fibrils are the contractile elements. Others liold that by their elasticity they cause the muscle cells to elongate after contraction, thus being an obstacle to contraction. The elongation of the relaxed muscles, either in the blood vessels or in the intestinal wall, may be accomplished by the pressure of the contents of these organs, or by the elastic connective tissue which is outside of the muscle cells. In the endoplasm of smooth muscle cells, and thus surrounded by the border fibrils, minute inner fibrils have been described and said to be contractile. Among them is the unaltered protoplasm. Where the fibrils diverge to pass around the nucleus, that is, at the ends of the nucleus, the granular protoplasm is most readily distinguishable. In the intestine it has been observed to contain pigment. Surrounding the smooth muscle ceUs there is probably a delicate cell membrane, but the nature of the structures observed is still under discussion. The ceU mem- brane of a muscle cell is called a sarcolcmma; its protoplasm is named sarco plasm; and the entire cell is called a muscle fiber. Fibril is applied to the filaments within the fibers. Smooth muscle cells are bound together so that they may act in unison. They may lie joined end to end by the border filjrils. Protoplasmic bridges ha\-e been described between them (Fig. 91). KkL-\ I 1(.)N W 1 1 If S M It o r H MlSCI.K FlBEkS, I'ROAl lllti I'lLADDfcR oi- A Pike. (Alter I-'renaiU ) (.^oiiiicclive tissue network; n., p., f., nucleus, j^ratuilar protoplasm, and llbrillav pro- If.iplasrn uf a nuiSLle cell. Digitized by Microsoft® 8o HISTOLOGY. They are certainly closely invested by connective tissue membranes or net- works (Fig. 92), consisting of white and elastic elements and extending from cell to cell. These may be formed from the protoplasmic processes of the mesenchymal muscle cells, or from distinct interspersed connective tissue cells. Tissue spaces exist in this network between the muscle fibers. The loose muscular coat of the blood vessels in the umbilical cord is a particularly favorable place for the study of fibrous tissue in relation to smooth muscle. In ordinary sections the student should recognize smooth muscle by the parallel arrangement of its cells, with which the nuclei correspond, and by the protoplasmic appearance of muscle substance as compared with fibrous connective tissue. In doubtful cases Mallory's connective tissue stain may be used, making the muscle substance red and the white fiber blue. In cross section smooth muscle appears as in Fig. 93. Since the cells taper the sections near their ends are smaller than the others. Only those cut near their centers show nuclei. Between groups of muscle cells there are generally bands of „ ,, , , V ,<,wo ,i. connective tissue containing lym- Connective tissue ll Ut^I^^AtOV-vV^* septum. "ninvTr^ClKy^f phatic and blood vessels, and nerves which terminate in contact with the Smooth muscle fibers-) \ Cji.-J [J y&CJ] ^y^i! cclls in a manner to be considered and nuclei in cross > -Jk_AAw< X y^L,-^^ section. J __o;3u;^&^,7- later. In describing smooth muscle Fig. 93.-Sect,on OF THE Circular Muscle the Student should alwayS reCOrd COAT OP THE HUMAN INTESTINE. X s^o. ^hcthcr it is circukr, longitudiual, or oblique in relation to the organ of which it forms a part. This relation is independent of the plane in which the organ has been sectioned, and in many small sections it cannot be determined from observation. He should add the way in which the fibers are cut, whether lengthwise or across, and this depends entirely on the way in which the sections happened to be made. It can always be observed in the specimen. Thus in Fig. 88 the student should observe an inner layer of muscle fibers cut lengthwise and an outer layer cut across. If he knows that the inner layer of intestinal muscles is generally circular, and the outer layer is longitudinal, he infers that Fig. 88 is from a cross section of the oesophagus. If the oesophagus had been split, the irmer circular fibers would have been cut across and the outer ones cut lengthwise. Being told that Fig. 93 represents the circular layer of muscle, he can state whether it is from a transverse or a longitudinal section of the intestine. Caediac Muscle. Cardiac muscle begins as a mesench)Tna with very broad protoplasmic connections between its cells. This syncytial condition is retained in the Digitized by Microsoft® CARDIAC MUSCLE. gl adult, cardiac muscle being a network of broad protoplasmic bands, in and near the centers of which nuclei are situated at irregular intervals Lateral i.iiM,!,. (Fig. Q4). The intcrcellular spaccs are reduced to clefts occupied by a small amount of connective tissue, ~ which is either a part of the original CaiHl- fc, * ■» *| I P t / zj3 Xin.Ieusof XucIlus of [ntercalalefl a inuSL-L a loiiikh tue ilisc lllier. ti-,MU; ix-ll. ' Fir, <,4. — From \ Lonlitiiun-al Section <)!■ Fig. gs. — Part of the Mi scoi.ar S\NC\'Tn'M \ PAPI^^AR^■ ^h"sCTK of tiiiv Hum \n from tmk Heart of a Ll'CK I".^MiR^■o of Heart. X 360. 3 Lavs, l A/. /-/,-:, /,'i,/: wriii 'iaji\ziN Rkd and TciLuiDiN Bli'E Tur i^tRmiind AlKMrR ANi;S ARE Letiered 2. iHeldcil- haiii ) the bands appear as has been described. x\t irregular intervals, in cardiac muscle only, trans\'erse lines of another sort may be found, called inier- calalcd discs and formerly Icnown as cement lines. Intercalated discs are seen in Fig. 94, and as pictured 1j}- Prof. Heid- enhain, in Fig. 99. He descrijjes them as deeply staining plates almost invariably not as wide as a muscle segment. The segment in the human heart is 2 n, whereas the intercalated discs \'ary from i to 1.7 11.. A disc may extend straight across a fiber, or it may be interru[)ted so as to form a succession of steps, usually from tAvo to four. The discs arc always Digitized by Microsoft® S4 HISTOLOGY. connected with ground membranes. It may be said that here and there within the cardiac muscle two successive ground membranes are closer together than usual and the Ubrils in crossing such an interval become expanded and more stainable, thus making an intercalated disc. The discs have been variously interpreted, for example, as locally contracted segments; as lines where the tibrils are inserted and upon which they may pull in contracting; or as places where the fibrils may grow to form new segments, being comparable with the unhanded embryonic fibrils. The older iflea that they are cell boundaries, either cement hnes, or protoidasmic bridges, is supported b}' - -- ' /> ^,.-^?"*\ the tendencv of heart I ^ ,.r,„^^_^....^> . m ^, ■■..:.lA muscle to rupture along '(' -■■'"-■'..* - "« \ their course. Theymark ], ■ • ■ ■ ;. - "■■.■-■ •■ ' off irregular spaces, how- /^ / ' ''.■•■■■:■■■-'-"'■■ ■.■-' w ever, some containing I 9 ' I •'.' V,,' ■.i^l-v-, ' '^' more than one nucleus, \ ' ';"'■■# ■'•:;>"•■,■>.'''■«> "\ i-..,,ii and others non-nucle- \ Ml f ■ / '.' •, ^y' '■"""■ ated. Intercalated discs / '.'"--. # ;■ * '^r^-- ..1 should be distintruished ■ ' - '■ ■- - V- ■ .;■■■,/ -• ■■■■, :'■:] '^ ■ , . V."'.;- ., ■ -^ ■ 'I from the cut edges of a ■""'- ■ .. ' / hber, made Avhere a ;,;•., '..,;.- branch of the syncytium \\\ 'C:'...''''J?r:'U..:'^,. .,: .'- ^,-,.^'^ extending toward the ob- jV \ r«'^';'.'^^5^;^'s;""j\J?^"'''^-:| server, passed out of the / \\ ' ^ \/ "'^i-:*-' jI^oI*- V The nuclei of cardiac ^' ' '" ' muscle are round or oval ihchnni. fiinrs. of a sl-cii.his Ola in c iissiK' ceiw. and are tound near the coiiiici.li\u of tiuiM le tis-ue mus,.ic ffbui. central axes of the fibers. ^ull, ilbi.is. Fig, loo— FKrjM a Cross Section of a I'm'ii.lak\ ^^^;sll.E As the fibrils S[)read OUt OF THE Human Hkart. X 3'to. , , to pass around them, often a considerable quantity of granular protoplasm may be seen, con- taining fat droplets and pigment granules which increase with age. A delicate membrane (sarcolemma) has been described as surrounding the cardiac fibers, and in it the groinid and median memljranes are said to terminate. Some of the clefts in cardiac muscle are protoplasmic (sarco- plasmic) intervals bet\\"een bundles of Jibrils. Others, bounded hx the sarcolemma, arc spaces which contain capillary \-essels closely applied to the mi'scle. I'robably always a little connective tissue intervenes between the \'essel and sarcolemma. The connccti\-e tissue, which is more abundant toward the surfaces of the heart, contains tissue spaces and the nerves Digitized by Microsoft® STRIATED MUSCLE. 85 which terminate in contact with the cardiac muscle fibers. Lymphatic vessels are found in the larger layers and bands of connective tissue, but they end before penetrating between the separate fibers. Although the cardiac muscle fibers form a network, they are in layers, each having one general direction. Since the predominant direction varies in different parts of a single section it is possible to find places where the fibers are mostly cut lengthwise as in Fig. 94, and others where they are cut across (Fig. 100). Here transverse bands and intercalated discs cannot be seen. The nuclei surrounded by some protoplasm are near the centers of the fiber's. The fibrils cut across appear as dots which shift about but do not disappear on focusing, since even in thin sections they are not granules but short perpendicular rods. They are arranged in radiating fines, or in clumps known as muscle columns. Close to the inner lining of the heart the muscle fibers may be imperfectly developed, con- taining only a peripheral ring of fibrils. These fibers (of Purkinje) are abundant in the sheep but are infrequent in man. COMPARISON OF MESENCHYMAL MUSCLES. Smooth muscles are slender mesenchymal cells containing contractile fibrils which are not banded. The cells, surrounded by a fibro-elastic network, are generally closely associated in layers. If the border fibrils actually pass from cell to cell, as has been said, then smooth muscle, like other muscle, is syncytial in nature. Cardiac muscle is a syncytium of mesenchymal origin, consisting of broad approximately parallel branches. It contains banded contractile fibrils not limited by cell areas. It is distinguished from smooth muscle by its cross striations and by the width of its fibers; and from striated (voluntary) muscle by its mesenchymal origin, the branching of its syncy- tium, the central position of its nuclei, and the possession of intercalated discs. Striated Muscle. Striated muscle, as the term is ordinarily used, does not include the striated cardiac muscle, but only the striated muscle which develops from the epithelium of the mesodermic segments [protovertebrae]. The segments form a series of paired masses of cells found on either side of the medullary tube. They have been briefly described on page 22. At first they are epithehal structures bounding a part of the coelom or body cavity. Later they lose their connection with the coelom (Fig. 21) and become rounded masses of cells, each mass enclosing a cavity. From the median side of the segment, near its ventral border, a stream of mesenchymal cells is Digitized by Microsoft® 86 ITISTOLOGY. given off, which surrounds the notochord and produces the vertebral cartilages and intervertebral discs. It also extends around the medullary tube. This stream of cells is called the sclerotome. The rest of the seg- ment becomes ilattcned and jjlate like, by the approximation of its lateral and medial walls. Thus the central cavity is obliterated. Fig. loi, i, shows a cross section of such a segment. Its medial layer is called the muscle plate or myotome. Here the cells multiply rapidly by mitosis and become elongated lengthwise of the embryo. They are called myohlasls and become the striated muscle cells. The lateral layer of the segment, named the cutis plate or dermatome, was supposed to form only mesen- chyma which became the deeper part of the skin. It also forms striated muscles, however, and in the pig it is said to be concerned only with muscle formation. The elongated cells of the mvotome become separated from one another by mesenchyma, containing blood ves- sels. Thus the myotome is subdivided into la\-ers and grouy)S of cells which shift about in various directions to become the skeletal muscles of the adult. The mesenchyma around them forms fascia and tendon, and connects with the periosteum which is often derived from the sclerotome. In the adult some of the myo- tomes remain quite clearly defined; thus the muscles of each intercostal space are derived from a single mesodermic segment, the ribs having de^■eloped between them. In the ab- dominal muscles several segments ha\-e fused. The muscles of the limbs are supposed to arise from myoblasts which ha^■e migrated into them from the myotomes of the adjacent body wall. Apparently they come dircctl}' from mesenchyma. All the striated skeletal muscles, how- ever, are believed to come directly or indirectly from the epithelium of the mesodermic segments. In cross section the mvoblasts arc of rounded outline (Fig. 102), bounded by a delicate cell membrane or sarcolemma. This memlirane is in close relation with yirocesses from the adjacent mesenchymal cells and it has been said that the \\q\\ detined sarcolemma of the adult is essentially a product of such cells. The myolilasts consist of granular protoplasm (sarcojilasm) witl; coarse filirils near the periphery and nuclei in the central part. In a gi\-en cross section the nuclei of many of the Flc. im. — Ttirkk MisnnFRMir SKr;MKNrS FKOM AMfHIRIAN (SiREDONI EMBRNOS, Ul'" SlC- CESSU'ELN" CILDKR StAC.KS. ( Diagrams after Maunii' ) m.. l\riiS(Me platf; c, oilis pl.^tc ; thu fMi-niri isnjsohrd iiilonui^- ^le rlbe^^, m. f., the latter in part into nui^Lle iiber'^ and in part into nieseneliN nia, mes. Digitized by Microsoft® STRIATED MUSCLE. 87 myoblasts will not be included. In becoming muscle fibers the myoblasts increase to a diameter of from 10 to 100 //. The fibrils multiply by longi- tudinal splitting so as to form groups of fibrils, or muscle columns, which in cross section are called Cohnheim's areas. Fig. 103 shows four adult muscle filjers cut across, in all of which Cohnheim's areas are distinct. Often such areas are not distinguishable, however, and when present they may appear as though due to shrinkage. Pjctwecn the areas is the sarco- plasm which may show "interstitial granules" of fat or lecithin. The nuclei of striated muscle fibers, not seen in the figure, are usually flattened and close to the sarcolemma. The fibers just described belong to the pale or ivhitc type. In the dark or red form the protoplasm is more abundant and granular, the diameter is less, tlie fibrils fewer, and the nuclei may be central or imbedded among the fibrils. Clearly this type f.j ui^^g Bundles of fibrils ^^ (Coluiheim's ''^- — areas i. 3. 102. — Cross Skctio.n oi'" ^\I^■r.I;l.AS|-s ANTJ MESENCHVMAI. CkLLS FROM AN IS MM. Pig. S., Mesenchymal cell; f., fibril, n.. tiii- eleu'^ ; s., sarcolemma, ^ Ulr-^'' Fig. 107. — Part of a Longi- tudinal View of a Hu- man Striated Muscle Fiber. a., Anisotropic ; i., isotropic band; k., nucleus; q., ground membrane X .560. (Z). . 108. — Branched Stri- ated Muscle Fiber from THE Tongue of a Frog. Digitized by Microsoft© go HISTOLOGY. The diameter of muscle fibers is greater in large animals than in small ones; it is increased by functional activity; and varies with the general nutrition so that the caliber may become perhaps trebled. It is doubtful, however, if any new striated muscle fibers develop in the adult. Some have said that they are constantly being worn out and that new ones form to take their places, developing from latent myoblasts. It seems to be generally considered that the formation of new fibers ceases in the embryo; muscle destroyed by injury is not restored in the higher animals. The origin of muscle fibers by division of those already formed, rather than by the development from myoblasts, is also generally denied. Striated muscle occurs not only in the muscles of the limbs and body wall, but also in the ocular and ear muscles, the diaphragm, the tongue, pharynx, larynx and upper half of the oesophagus, and in parts of the rectum and genital organs. NERVE TISSUE. Irritabihty and conductivity have already been mentioned as funda- mental properties of protoplasm. Response to particular irritants be- comes the chief function of certain cells. Thus some cells in the eye are differentiated to react to light; some in the ear respond to jound; the taste cells of the tongue and olfactory cells in the nose are affected by solutions ; tactile cells are influenced by pressure, and muscle cells contract at the stimulus of the nervous impulse. The effects of irritation may be conveyed from one part of the cell to another through its power of conduction. Thus when a muscle fiber is stimulated at one point, a wave of contraction may be transmitted along its whole extent; or when an olfactory cell is stimulated, the effects may be conveyed through a long fiber-like basal prolongation toward the brain. For the purpose of connecting these particularly irritable cells there exists a specially modified median longitudinal tract of ectoderm, the nervous system. Some of its cells send out slender prolongations, know as nerve fibers, to meet the taste cells, the auditory cells, the processes of the nasal cells, the cells of the muscle spindles or the epithelial cells of the skin, and to branch in contact with them. The effects of stimulating the various irritable cells enumer- ated, are conducted along these nerve fibers back to the central nervous tract. Such fibers as convey peripheral stimuli to the central system are called afferent or sensory fibers; they are the outgrowths of sensory cells. Another set of nerve fibers grows out from the central tract and branches in contact with muscle cells, smooth or striated. Since they transmit stimuh which cause the muscles to contract they are called mo^or fibers, and Digitized by Microsoft® NERVE TISSUE. 9 1 the cells of which they are a part are the motor cells. The efferent fibers, or those which bear impulses from the central tract to the periphery, in- clude the motor fibers, and also some which pass to the epithelium of glands to control their activity. Besides the afferent sensory and the efferent motor fibers there is a third set of commissural cells and fibers, serving to connect the other two. Sensory and motor cells may connect without the intervention of commissural cells, thus providing a path for the simplest form of unconscious reflex action, but often one or more commissural cells are interposed and the brain consists essentially of these cells. As the nervous impulse is transferred from cell to cell, being further removed from the primary stimulus, it is suggested that it becomes "more sub- jective and personal." The nervous system, then, is a median longitudinal tract of ectodermal cells, divisible into afferent (sensory), efferent (motor), and commissural cells. The sensory and motor cells send out processes or fibers, which in bundles called nerves extend through the mesenchymal tissue to all parts of the body. The central tract is called the central nervous system and consists of the brain and spinal cord. The nerves constitute the peripheral nervous system. Associated with the nerves there are clumps of nucleated bodies of nerve cells, known as ganglia. The afferent and efferent fibers to the viscera and blood vessels, together with numerous ganglia, constitute the sympathetic nervous system. The nervous system, therefore, is composed of central, peripheral, and sympathetic portions. Development of Nerve Tissue. The Central Tract. The ectoderm in an early stage forms a flat layer covering the embryo (Fig. 109 A). Along the axial line and extend- ing on either side of it, the ectoderm thickens to form the medullary plate. The plate becomes depressed so as to make a longitudinal groove, the medullary groove [or neural groove] (Fig. 109 B). The dorsal edges of the groove come together and fuse, transforming it into the medullary [or neural] tube (Fig. 109 C). Thus the tube becomes separated from the general layer of ectoderm which is to form the epidermis. This medullary tube is the central nervous system. In its anterior part the cavity is trans- formed into a series of connected dilated spaces or ventricles, and its walls become very thick, thus forming the brain. The posterior part makes the spinal cord; its walls are less extensively but more uniformly thickened than those of the brain, and its cavity remains small, becoming the central canal. This canal is continuous with the ventricles of the brain and a line of division between the spinal cord and brain must be Digitized by Microsoft® 92 HISTOLOGY. arbitrarily drawn. Tlie relations of the meelullary tube to other structures in the emljryo have been shown in Figs. 19-21, p. 19-22. spf dra mr^^ Fig. 100, — The 1)i-:\ ) i.op.MhCNT oh iiii.: Xkk\ous S\sti.;m as skkn in' Cross Skctkins ok Rabbit E.MBKVos A,7l-2 Days; B. S'i Da^s, C, .i U.^^s, D, i.i'-; Uays; E, 14 Days c. c Central <.a\iu- ; d. r., dorsal root ; d. ra., dursal ramus ; ep., epeud) nial la\er; g. c, ,^:ant:;]ion cells ; g. I., ,L;i"a>- layer , m. 9., medullary g;re>e)\ e , m. t., uicdullar\' Lube ; 0. b., o\al bundle , s. g.. s\ mpiatlielic eauLjlitju : sp. g., spinal ganglion ; s. ra., sympathetic ramus ; v. r., ventral root ; v. ra., \ entral ramus ; w. I., white la\ er. The .Spin.al G.\ngli.\. At about the time when the medullary tube separates from the epidermal ectoderm, some cells which arc detached from its median dorsal portion jjass down on either side of the tube, as shown in Fig. loq C and J). Through mitotic di\']sion these cells ac- cumulate in paired masses corresponding in number Avith the segments of the body. Thev are the spinal gaiit^lin. A topical cell of a spinal ganglion is at first round, but later becomes bipolar by sending out two ])rocesses, one toward the periphery and the other toward tlie medullary tube. These processes grow out from opposite sides of the cell (Fig. no). With further groAvth the nucleated cell body passes to one side of its jirolongations, with which it remains connected Ijva slender stalk. These T-sha]ied cells are characteristic of the spinal ganglia. 'J'he liljcrs A\-hich grow toward tlie nieduUarA- tube enter its outer part and fork, sending one branch toward tlie brain and the oilier flown tlie (ord. "J'here aix- many of these parallel lil)ers extending toward the lirain so that they form distinct bundles, one on either side of the cord, known as oval bundles (Fig. 109, E). Since they receiA'c acces- ^ no. — SriNAl GANr^rTHN Cei.t s, 1111 I'lfoi \i-: For \ts l^loiM A T- 1 > \N Ciiii h: p"\ii;K'N n Digitized by Microsoft® NERVE TISSUE. 93 sions of fibers from every spinal ganglion, they enlarge as they approach the brain. The fibers of the oval bundle branch freely at their termination and also gi\'e off collateral hrancJics along their course, Avhich enter the deep substance of the cord. The peripheral libers from the sjjinal gangha elongate through the mesenchyma, and terminate in branches applied to cells in the skin or muscle spindles, in ways to be described presently. The fibers of the spinal ganglia are esscntiallv afferent or sensory, and they proceed from sensory cells. Tfe Ventral Roots. The efferent, motor filx-rs arise chiefly from cells, the bodies of Avliich remain within the central nervous system. Each of these cells sends out one long process called a ncuraxon (a.xone). The neuraxons of the motor cells leave the spinal cord, near its ventral surface, in bundles which are segmentally arranged so that they corre- spond with the spinal ganglia. A Ijiindle of motor fibers joins a bundle of peripheral fibers from a spinal s;anf(lion to form a Spinal nerve. Every spinal nerve conse- quently has a dorsal fsensory) root, and a ventral (motor) root. The fibers from the two roots travel in the same connective tissue sheath, but otherwise they remain entirely distinct. The motor fibers terminate in contact with muscle cells. Soon after a spinal nerve is formed by the junction of its roots, it divides into a dorsal ramus and a ventral ramus (Fig. 109, E). These rami are mixed nerves (containing both sensory and motor fibers) and supply the skin and muscles of the back and of the lateral body wall respectively. Within the cord the motor cells send out a large number of com- paratively sliort branching j.irocesses caUed dendrites. By means of the dendrites the motor cell is [)ut in communication with the collateral fibers of the sensory cells, and with fibers of commissural cells coming either from other parts of the cord or from the brain. This arrangement is shown in the diagram Fig. 11 1. A painful stimulus transmitted along the sensory fiber, b, passes through the spinal ganglion into the cord. Through Fig. Ill, inii>f llie ^[)inal cote], showin.i:;' a mcitc ikI c : ;inil a cominissural fiber, d. li • >m i-T ; sp. g.. '^[>iiial gan.t^^lion. tilicT, a : a sensorv fiber, le brani ; coll.. t ollateral Digitized by Microsoft© 94 HISTOLOGY collateral branches it may be transmitted to the motor fiber, a, causing a muscle to contract involuntarily. This is the reflex path. Or the stimulus from b may be conveyed to the brain along the fiber c, and be transferred to commissural cells of which i is a fiber extending down the cord. This also may stimulate the motor cell a, causing the muscle to contract volun- tarily. The terms dendrite and neuraxon are of wide apphcation. A nerve cell generally has a single process which diiifers from the others, in being clear, non-granular, and sharply defined, often becoming very slender soon after leaving the cell body. It may have collateral branches, usually given off at right angles, but except at its termination its branches are relatively few. It conducts impulses away from the cell body. This process is the neuraxon. The dendrites, which develop later, appear as granular, protoplasmic processes. They fork and branch freely, giving the cell a great extent of exposed surface. They may serve in obtaining nutriment, as well as in providing many opportunities for contact with the processes of other nerve cells. Dendrites conduct impulses toward the cell body. In the sensory cells of the dorsal ganghon the single peripheral fiber is a dendrite of unusual form, and the fiber entering the cord is the neuraxon. The Sympathetic System develops chiefly from the visceral or sympathetic branches of the spinal nerves. A spinal nerve typically has one such branch, extending ventrally and medially toward the aorta, and ending in a clump of nerve cells (Fig. 109 E). These cells, which constitute a sympathetic ganghon, are considered to have migrated along the nerve bundles from the spinal ganghon, or possibly from the spinal cord. They multiply by mitosis. The successive gangha become con- nected by longitudinal nerve fibers so that they form two sympathetic trunks (or cords), one on either side of the vertebral column. The gangha of the sympathetic trunk are cervical, thoracic, lumbar and sacral. There are only three cervical gangha, probably because some in this region have fused. In the adult the sympathetic gangha are each usually connected with the spinal nerves by two bundles of fibers, the white and gray rami respectively. The smaller gray ramus is said to convey fibers from the ganghon to the spinal nerve. These rami may be subdivisions of the orig- inal visceral branch. Besides smaller branches from the three cervical ganglia to neighbor- ing vessels and organs, each of these gangha sends out a large cardiac nerve, the branches of which unite to form the cardiac plexus. From this plexus and the associated cardiac ganglion the fibers continue to the heart muscle which they innervate. In the lower thoracic region the ganglia of the sympathetic trunk send out nerve bundles which unite to Digitized by Microsoft® SYMPATHETIC NERVES. 95 form the splanchnic nerves. These pass along the sides of the aorta, in front of whicli tliey form a large plexus, the cocUac [or solar] plexus, as- sociated with which is the cocliac [or semilunar] ganghon (Fig. ii2j. A plexus is a net of nerves which allows a transfer of hljers from one bundle to another; the individual nerve hbers probably do not anastomose. In the sympathetic plexuses there are usually nerve ceUs, called gangUon cells, often found at the angles of the network. In contact with them the nerve hbers may terminate. Wien these cells are very abundant the plexus becomes a ganglion. From the coeliac ganglion, hbers pass into the intestine and form a ganglionated plexus between the muscle layers, called the myoiteric plexus. Branches from it inner\'ate the muscles and pass on to make another plexus under the intestinal epithelium, tht sub nnicous plexus. Finally they come very close to the epithelium itself. All of the nerve cells of the sympathetic system are believed to be ectodermal, and de- scendants of those which migrated from the spinal gangha or central nervous system. All the sympathetic nerve fibers are processes of such cells, and they are found forming plexuses around the blood vessels and organs, including those of the intestinal tract, the bladder, kid- ney, suprarenal gland and spleen. Two fea- tures of the sympathetic system seem funda- mental; their hbers supply the \ascera, and they are so connected with peripheral ganglion cells that they act more or less independently of the central nervous system. The Cerebral Nerves. The nerves con- nected with the brain are not a series of similar structures hke the spinal nerves. Four of them possess only ventral motor roots. Four others ha\-e dorsal sensory roots provided with ganglia, and lateral motor roots. Lateral roots emerge just ventral to, or beneath the dorsal roots. Their hljcrs are the neuraxons of cells, the bodies of which remain within the central ner- \-ous s\'stem. Lateral root hbers occur as far down the cord as the sixth cervical ganglion. Instead of entering the corresponding cer\'ical ner\'es, howe\X'r, these fibers unite to form a bundle Avhich passes along just outside of the spinal cord, through the foramen magnum into the skuU where it Ijccomes the accessory portion of the vagus nerve. Below the sixth cervical ganglion the lateral root elements have not been demonstrated. (It has been suggested that they pass out in the dorsal roots, and that they form parts of the \-entral roots.) Ill Its lelat int.; A., aorta ithetiL sN'stuin tiK- iiUL'bline, sp. g., spinal .Lcanglion : w. r., white ramus; g. t., ganglion of the synipa- tlietic trunk ; spl., splanchnic iier\'e; coe. g., cocliac ganglion ; my. pi., m\ enteric plexus; sbm. pi., sulimucous plexus. Digitized by Microsoft® HISTOLOGY. 96 In the dia.t^i-am Fig. 113, based upon the nerves in a 12 mm.pig embryo, the roots, gangha, and fundamental branches of the cerebral nerves are indicated'. " The ventral roots have been shaded by lines. The hypoglossal, abducens, trochlear and ooidomolor nerves are ventral roots only, the first going to muscles of the tongue and throat, the other three supplying muscles of the eye. The trochlear nerve is unir4ue in having its neuraxons pass to the upper side of the brain and cross to the opposite side before emerging. Four cerebral nerves are mixed, consisting of dorsal and lateral roots? Beginning posteriorly these are the vagus (its motor part being Fig 113. — The CKRi-:PRAr Ni-R\t-s hf a m mm. Pic.. Vamfd in "ihi. (jrdkr cm^ i-hi^ir (Uxl'rrhncr BkGINNING .\n rFRTr)Rl_\-, WJTIT TUFTR C.AM'.llA AND Cllllir i'R ANCIl ES, OlfiU'toi y innt developed). Optic (fibers in the stalk of the e\'e, the lens of « hich is marked L) Orulo- uio/nr (Oc). Trochlear (Tr.) Tris^enunaJ . — semilunar ^anti;]ion I'S.-I.); ophthalmic ( Oph.V maxil- lary (mx.l and mandibular (md.) branches. Abducens (Ab.). fiitmiiedliis, — s:eniculate .afantriion ig.), ]aru;e superficial petrosal (I. s. p.). chorda t\ mpaiu (nh.ty.),and facial ifa.l brandies. Acoustic {f^.). Its s:fin,iil ion beiiie: later du'ided into a \estibnlar c;an,fe;liou, and a spiral .iijan.^lion. It supplies tVie ntoc>'st (Ot.). G'tossop/nn rni:eal.—sui)er\nr (s.) and petrosal (p.) ,e;an,s:lia; tympanic it.), Hnffual (l.r.) and phaiAiitreal (ph. r.) branches, f-'a^us, — ju.e:nlar (j.) and nodose (n.l san.i^dia ; auricular lau.) and lar>-nj;eal branches, rec. being the recurrent ner\-e ; the main stem proceeds to the stomach. Its accessnr\' portion has nn external ramus (ex.) //v/'^c/o^.w?/ (Hy.). Frr.rifp''^ rudimentary h\po- '-;lrissa! tjan^lirm 1 F.) s^mi'i nnes sends libers to the In [His^^lossal nei\e C.t. c.2. C.3, cer\'ical ner\ es. called t]ie accessory nen-e), the glo-ssof)haryn(icah the iiiliiiucdius (its motor part and its largest branch forming the facial nerve), and the in'gcmifius. In the dia,i^ram the lateral roots are in solid black and the dorsal roots arc not shaded. The accessory ner\X' is seen |)assin,^^ iijt the spinal cord to join the va,[:^us. A part of ils TiIkm-s turn aside in the external ramus, ex, to supply the trapezius and sterno-cleido-ma^toid muscles; others remain with the \'a,i.(us to suytply pharynu;eal muscles, and to pass down the body to the st(jma( h. The \-agus and tlu\t:^lossoph;ir\-n^-cus each ha\'etwogan^1ia. Digitized by Microsoft© CEREBRAL -NERVES. 97 one above the other. The lower ganglia occur near the epidermis of the embryo in positions said to correspond with the epibranchial sense organs of fishes. These organs do not develop in man, but the ganglia are permanent structures. Closely united with the geniculate ganghon of the intermedins is the ganglion of the acoustic nerve. The latter is a purely sensory nerve to the ear. By some comparative anatomists it is considered a part of the intermedins. In the trigeminus it is to be noted that the lateral root joins the mandibular division only. The pecuHar optic and olfactory nerves will be considered with the sense organs. The sympathetic system in the head supplies the smooth muscles of the blood vessels and iris, together with parts of the phar)mgeal mucous membranes and the salivary glands; it sends fibers into the periosteum. The plexuses around the large blood vessels are continuous with the s)mipathetic plexuses of the neck. Although the cerebral nerves do not have any regularly arranged synipathetic or visceral rami, all of them, except the olfactory, optic, and acoustic, are said to communicate with the sympathetic system. In the head there are four sympathetic gangha, the ciliary, sphenopalatine, otic and submaxillary, all of which are connected with the trigeminal nerve. They develop later than the semilunar ganglion from which their cells may migrate. The sphenopalatine, otic, and sub- maxillary gangHa are also connected with the intermedins and may receive cells from the geniculate ganglion. The otic further receives the continua- tion of the t)mipanic branch of the glossopharyngeus. Structure of Nerve Tissue. In the following sections the structure of nerve fibers and of nerves will be considered first; then the sensory and the motor endings; next the gangHa, spinal and sympathetic; and finally the spinal cord as illus- trating the tissue of the central nervous system. Nerve Fibers. The peripheral processes of nerve cells generally appear as slender homogeneous strands varying in diameter. The smallest are found in connection with the sympathetic system and near the termina- tions of the spinal nerves; the largest fibers are the portions near the cord of those which have the longest course. ■ There is no characteristic differ- ence in diameter between sensory and motor fibers. With special methods it has been clearly shown that the nerve fiber consists of longitudinal -fibrils imbedded in a protoplasmic neuroplasm. The fibrils begin in the cell body. At the origin of the neuraxon they may appear as if gathered into one coarse stiff fibril which distally is resolved into a bundle. The fibrils are supposed to divide but presumably they do not form networks. When the fiber branches the fibrils separate into 7 Digitized by Microsoft® gS HISTOLOGY. Fir,. 114. — X( iN-MEDUT LATKTt XlRN!-; FlUKRS. X 400. (After Schal\r,) corresponding groujis. The}' arc considered l(j lie 1lie essential conducting element of nerves, but it is known that conduction occurs in protoplasm in which hbrils cannot be demonstrated. As the libers in the embryo grow out from the central ner\Tjus system they form Inmdles, in and around which there are numerous nuclei. Opinions dilTer as to Mhelher these nuclei belong with the mesenchymal cells through the meshes of which the nerve is growing, or with ectodermal cells car- ried along from the spinal ganglia or cord. In either case thev arc called sJicalli cc/Is, and are ''so closely apphed to the fibers that it becomes a matter of judgment to decide whether the librils are sur- rounded by or imbedded in the sheath cells." Therefore some writers have thought that the ner\'c fiber was not the outgrowth of a single cell, but was produced by the end to end anastomosis of many sheath cells, each of which formed that portion of the nerve fiber which it enclosed. Since the liber may be a meter long and perhajjs ten thousand times the diameter of the cell body from which it comes, such an assumption seems plausible; nevertheless it is not sus- tained by recent embryological in- vestigations. The cells applied to the nerve fiber may unite and thus surround it wdth a delicate homogeneous sheath called the neurolemma [sheath of Schwann]. Some fibers in the adult, especially in the sympathetic svstem, possess only a sheath of this sort, and they are called non-niediillaled fibers (Fig. 114). Other fibers in the sympathetic system and near the nerve terminations mav be sur- 'ciuma rounded only by ordinary connective tissue; these are tion^mcdiiUated fibers without a neurolemma [naked axis cylinders]. (Non-meduUated fibers of the sympathetic system are often called Remak's fibers.) The fibers of the spinal nerves are generally characterized by a deposit of myelin, found iDctween tliem and the neurolemma. The fibers with a myehn sheath are called medultated, and the fibers themselves within the myelin sheath, whether they are dendrites or neuraxons, are called axis cylinders. A-D FiL, 115— Mh u:r 1 Al v.\' N"hr\k KUSEKS. . L-iiuiUi.liii.il s ' . h.nis, E-l. cross sections. (A, B, aU--i (m. iIm, ^1 , C, E, F. alLer Hardesty; D juid 1. <>siiii, : 1(1 prcpaiations. after Prenant and Slmh.mimu I'V ; G, tilcoholic presenation, after Ki>.lliki.i ; H. 1 111. lie acid preservation, after Si hal( 1 1 a. c.. Axis c\liiu cr , in., incis- are ; my.. ni\ c 111 , nil., nucleus if the ncuro- Digitized by Microsoft® NERVE FIBERS. 99 Myelin is a mixture of eomplex fats and lipoid substances, some of which are combined with sugar. Like fat it is dissolved by ether and blackens with osmic acid. It exists as an emulsion, and appears very white macroscopically. Between the myelin globules there is a network of neurokeratin, a substance unstained by osmic acid and not dissolved by ether. Fig. 115, A and B, show the neurokeratin network after treat- ment with ether, surrounding the axis c)iindcr, a.c. The meshes vary greatly in diameter, becoming coarse ^vith the rapid post mortem coales- cence of myelin droplets. Fig. 115, C, sliows a heavier framework which toward the right of the hgure tends to form conical layers, the axis cylinder penetrating their apices; in E a cross section of C is drawn showing a myelin vacuole, my, encircling the iiljer. In specimens stained with osmic acid (D), the myelin is very dark and the framcAvork light. The latter is prominent only in oblique lines called ni- cisures [or Lantermann's segments]. The lines seen on the opposite sides of the fiber are interpreted as optical sections of a cone of neurokeratin. A cross section of D through an incisure would appear as in I. Successive incisures may point in opposite directions. They do not all represent perfect cones, Ijut in that form thev are characteristic post mortem fig- n^i' d ' " I'lc. ii6— .\'ot)iis. UreS. Fig. IIS, F, G, and H, show other a, Di.iLcram ..f the nitracellular explanation ° . "I iiivelin; B, the cross obtained with cross sections of meduUated libers in which --il^er nitrate, C the biconlcal enlarsie- Lnent (after Gedoelst); D, nitercillular the neurokeratin is arranged radially or ;;"i:r"ax!!txo"mma!'m^'inVein,'; ne'.'. in concentric layers. nenroien,;;,a; „o.. n^.ie At regular intervals the myelin sheath is more or less interrupted by nodes [of Ranvier]. The interA-als vary from So /< to a milhmeter, being shorter in growing fibers and in the distal portions of adult fibers. The branching of medullated fibers occurs at these nodes. Fig. 116, A, an osmic acid preparation, illustrates one intci-prctation of the myelin and nodes, according to which the sheath cells are thought to be wrapped around the axis cylinders, and to contain within them the myelin which develops like fat in the mesenchymal cells. The nodes (A, no) are at the [unction of two sheath cells, and there the outer cell membrane or neurolemma is continuous with the axolemma or inner ceU membrane, the latter being in contact with the axis cyhnder. It accords with this view that the neurolemma usually has but a single nucleus, found midway between two nodes. Surrounded by very httle protoplasm it occupies a depression in the outer surface of the myelin. Digitized by Microsoft® lOO HISTOLOGY. \\Tien nerve libers are treated with a solution of silver nitrate a pre- cipitate occurs at the nodes and spreads along the axis cyhnder forming a cross (Fig. ii6, B). This has been interpreted as indicating a penetrable intercellular sul)stance at the nodes through which nutriment has access to the liber. Silver niti'ate sometimes causes a transverse banding of the axis cylinder, which is considered artificial and without significance. In crossing the node the fibrils may sjjread apart forming a "biconical enlargement." As shown in C, the liljrils in the midst of the enlargement have been said to be thickened. The same figure suggests that the neuro- lemma is not continuous with an axolemma but passes the node without internijjtion. This is clearly shoA\-n in 13, Avhere the mvelin layer also, though constricted, is i:nljroken. The m^'clin has therefore been regarded as an exojjlasmic part of the axis cylinder. The inter- fibrillar substance es uf ncr\ 'linder is shown in "peripheral de- generation.'' When a ner\-e is se\-ered, that portion of the axis cylinder which is cut off from the ceU Ijody from which it grew, degenerates bv fragmentation. The myehn at the same time breaks up into drops of a different chemical nature which later disappear. The sheath cells multiply. Recently it has been slated that the myehn should be considered an intercellular substance due to a transformation of tissue fluid by the joint activity of the a.xis cyhnder and sheath cells. It lirst appears in the embryo as vesicles attached to the ner\-e hber. These unite to form a nodular or beaded la)-er which later becomes smooth. The axolemma is considered a condensation of the myehn framework such as occurs also just beneath the neurolemma. The m)'elin itself is said to be derived from the blood. Digitized by Microsoft® NERVES. lOI Nerves are bundles of nerve libers enveloped in connective tissue sheaths. According to the nature of their constitutents they are classed as mcdullaled and non-meduUated a distinction which the student should remember to record. The spinal and cerebral nerves consist mostly of medullated fibers of varying diameter (2-20 /'), scattered among which are a few that are non-mcduUated. ]\Iedullated nerves arc white in rellected light. They are surrounded by loose connective tissue [the epincurium] wihcl/contains lymphatic and blood vessels, and small nerves, and has manv elastic libers. It extends around the entire ner\-e and between the several well defined bundles of which a large nerve consists fFig. 117). Each of these bundles is covered by a dense lameUar layer of fiattencd connective tissue, F]l)Lr sh -ath. Fig iiS. — Medl'llated Nkrne. Part (ii.- a Cross Sectu.in ok the Hl'man Median Ner\e. / 220. called the perineurium fFig. iiSj. The cells in the perineural la\x*rs are in contact with one another along their borders so that on surface view they resemble a mesothelium. The perineurium sends septa into the nerve Isundle and becomes continuous with the connective tissue which, outside of the neurolemma, surrounds each individual nerve fiber [Henle's sheath]. The inner extensions of the [jerineurium may be called internal perineurium (or endoneurium). The perineurium contains capillaries, generLiUv pjarallel with tlie ncr\-e fibers, and tissue spaces, but no l}"mphatic vessels. The outer sheaths of the nerves are continuous ^vlth tlie dura mater of the cord and brain. The large sympathetic nerves vary in color. The splanchnic nerves contain many medullated fibers and are whiter than the nerves of the plexuses. Medullated fibers in the latter are few and very slender. Xon- medullated nervous tissue is gray. A part of the medullated fibers of the sympathetic nerves come directly from the spinal nerves, and a ]jart are medullated processes of the sympathetic ganglion cells. Small non- Digitized by Microsoft® I02 HISTOLOGY. niedullatecl nerves are shown in Fig. 119; A represents a nerve which is easily recognized by the two large nerve cells which it contains; B is a bundle of tine tibers containing a few nuclei, probably of connective tissue. The recognition of small nerves in ordinary sections may be facilitated bv remembering that they are fibrous bundles extending through con- nective tissue and found in the same situa- ^ ' "' c t -^^^^ — -■"■»; , ..^ tions as the vessels. The latter are tubes A /TS^'f?) •'. "^ "-Lss .. lined with endothehum. Sometimes they are ~ ' '^,["'1'^ - '-■---- ■ filled with coi-puscles (Fig. iiS) but the cor- puscles never appear fibrous and usually stain unhke anything else in the specimen. Bt«L:°, - "^« -e I? .fvV Nerves differ in texture from the white fiber of connecti\'e tissue, which forms a diffuse network or laver instead of occasional dis- FKoM ^ CATh iN-ihsTiN-K ^j^ct clrcu m scrlbcd bundles. A, I-~roni lliL' submucous .iml B. fiMm ihc nixuiiteric pie.Mis, c. t.. inn- Sensory Endings. The wav has al- necCi\e tissue; n.. s\ inp.illiii [r "on-nif.iuiiaiL-d nc■r^c nhers n.c, rcadv bccn described, in which ectodermal iierx e cull , s. m,, stiujotn musi II- - ' cells become detached from the medullary tube to form spinal and cerebral gangha, afterwards becoming bipolar and then T-shaped, sending a long dendrite through the nerve bundle to the periphery. Soon after it leaves the cell body, this process becomes sur- rounded by the neurolemma and myelin slieath. Its branches are very few until it nears its distal end when it forks repeatedly at the nodes. Finally it loses its sheaths and is resolved into manv small fibers which terminate in contact with epithelial, connective tissue or muscle cells. These terminal branches of the dorsal root fibers are the sensory nerve endings. Apart from those of the special sense organs, to be described with the eye, ear, etc., they are as fol- lows. Free nerve endings. Sensory ner^'es to the epi- thelia, such as the epidermis, or that which forms part of the mucous membrane of the mouth, or the corneal epithehum, lose their myelin sheaths and divide repeat- enuin,,. in En- -KRl-:t£ Nt-:R\E N(,, IN Eri- THKLU'M. GOLGl edlv in the connective tissue iust beneath. The un- Tw.'^.^'iJ.I^^N'^^'' sheathed slender fibers thus formed pass between the epithehal cells where they ramify further, and terminate with pointed or club-shaped ends (Fig. 120). Such ]ree endings are too dehcate to be seen in ordinary preparations. Sometimes the terminal fibers in the lower layers of the epidermis expand into '-rcsrentic structures called taetile menisci (Fig. 121 j. An epidermal cell, the base of which rests upon a Digitized by Microsoft® SENSORY ENDINGS. I03 meniscus, may thereby be modified so that it is larger and dearer, having a more vesicular nucleus, than those around it. Cells thus differentiated are called tactile cells. The sensory nerves to muscles similarly may end freely, or may be in special relation with modified muscle fibers. In the former case (Fig. 131, sensory fibers) the nerves become non-medullated and their fibers arborize extensively, terminating in long slender filaments between the muscle cells. The specially modified muscle fibers in contact with which sensory -nerves end, constitute the muscle spindles (Fig. 105, p. 88). These are bundles of from 3 to 20 muscle fibers, i to 4 mm. long, varying in width from 80 to 200 1^. They are surrounded by a thick connective tissue sheath or capsule, continuous with the perimysium and described as divided into an inner and an outer portion by a considerable tissue space filled with fluid. The muscle fibers of the spindle are distinctly striated toward their tapering and very slender ends. In their middle Epidermis Tactile meniscus Nerve fiber Connective tissue. T? Fig. 121.— From a Vertical Section of the Skin of the Great Toe of a Man Twenty-five Years Old. X 240. The outlines of the cells and the nuclei of the epidermis can only be indistinctly seen, x. Tactile cells in the corium, resting upon the ramifications of a delicate nerve fiber. portions the striations are obscure; there the sarcoplasm is abundant and the muscle nuclei are numerous. Three or four nerves terminate in each muscle spindle. Their connective tissue sheaths blend with the perimysial capsule, and they, branch and lose their myehn as they pass through this capsule to the muscle cells. They may encircle the muscle fibers of the spindle, forming spirals or rings (as in the upper part of Fig. 122) or they may form a panicle of branches with enlarged club-shaped ends. Muscle spindles are not found in the muscles of the eye, phar3mx, larynx, and oesophagus, the muscles of expression, the diaphragm and the ischio- and bulbo-cavernosus muscles. They are especially numerous in the muscles of the hand and foot. The nerves of the spindles are stimulated by pres- sure caused by the contraction of adjoining muscle fibers. In tendons there are said to be free nerve endings, but the sensory fibers which terminate in tendon spindles are better known. These are small portions of the tendon, from i to 3 mm. long, 170 to 250 /i wide. Digitized by Microsoft® io_i jnSTOI.OGV. containing many nuclei and staining more deejily tlian the surrounding tendon. Thev are enclosed in sheaths of ordinary connective tissue. MrcliilhitLd ftUi^cle A ^Mjij ;( 1 crnunal I amilical . MuilullaU-d nerve llbei-. ■Mustle litjers Fig 123.— Tkndon M'Inim.f <»!■ \n Alui-t Cai. ■ No. *f. !k Fig. i24.~Thk LlI'T Portkin i>f Fk,. 123. )< 345. 1:1 The lcA\- nerve iiliers which terminate in a tendon spin- dle lose their sheaths and branch freely, ending in club- shaped enlargements (Figs. 123 and 124). They are found in all tendons and serve to transmit the sensation of tension, being acti\'e in connection with C(i6rdinated movements. In connecti\'e tissue, sensory nerves ma}" citlier end free or surrounded with a connecti\'e tissue capsule. In the subcutaneous tissue near the coils of the sweat glands, anrl in the corium of the fingers and toes, there are lcr))iiiuil cy/iiidirs [of RufliniJ which resemble tendon spindles in the ;i ,. 122 — M n s c 1. 1-, S !■ I N I) L E 01 AN Adult Cat .■'' i3,s. Digitized by Microsoft© E^'CAPS^LATED SENSORY ENDINGS. 105 way that the nerves ramify (Fig. 125). These cyhnders lack the distinct capsules which characterize the nerve corpuscles. Terminal corpuscles are nerve endings consisting of a coarse nerve fiber or knot of small Ijranches surrounded Ijy a semilluid intercellular substance (which ib granular in ]jreser\'ed tissue) and enclosed in a con- nective tissue capside. The terminal ramifications of the nerve show irregular swellings or varicosities, such as are found along terminal nerve fifjcrs generally and which are not cf)nsidered artificial. Some authorities describe the interlacing termi- nal branches as ending; blindlv, but others beheve that they unite so as to make a netAvork. Often more than one fiber en- ters a cor]iuscle and it has been suggested that the}- include afferent and elTercnt fibers. Generally the connecti\'e tissue sheaths of the entering fibers blend with tlie capsule of the corpuscle, and the mye- lin sheaths are lost just inside the capsule. Terminal corjiuscles have been grouped as tactile, ^qenilal, bulbous, articular, (cylin- drical), and lamellar. -'I'hRMlNAl, e V I, I N U li R . Kullitii, fruiii FcTiiUSOn's gH. MeihiUaiy shtaLh , il, ti--niiinrLl ramincaliniis ol llie axis c\ limiLi' , L, cimiKulu e tissue. Fig. 126. — T.^CTlLl.- CoRPLSCi.H from a P|..Rri';NDlCL'I.AR Section oi.- tiik Or hat Toi: ' 560, n, Medullaled nerve fibers; e, ^-ariceisiUes ; h, eonnectivc tissue stieath. The niielei are iiu-isiblc- Tactile corpuscles [of ^leissner] are elliptical structures, 40-100 ," long and 30-60 ,"- broad (Fig. 126J. They arc characterized by transverse markings due to the corresponding elongation of their capsule cells and nuclei. From one to five medullated libers enter the lower end of a tactile corpuscle, losing their sheaths on entering. Some fibers may pass straight Digitized by Microsoft® 1 o6 HISTOLOGY. through lliL' axis of the corpuscle, the others making spiral turns about them before breaking up into numerous varicose branches. Tactile corpuscles are found in certain of the connective tissue elevations (papillae) just beneath the epidermis, being especially numerous in the soles and palms (23 in i sq. mm.) and at the fe^§S51lgS&i:^ linger tips; also "in the nipple, bor- der of the e3'elids, lips, glans penis and clitoris." Genital corpuscles are large, round or o\'al bodies 60-400 /' long Fill. 127. — GiiNiTAL Corpuscle fk^m tuv Gi_.\Ns Penis of Man. Mi.i iini.i. ni-: Dn'E Sl'AIN. (After Dot^iei, Iruni ]iuhin and \-on Da\iduff,) Fig, 12S —r.rLBOus Corpuscle from the Con- juNCTi\'A op- Man. Mp:thvlene Blue Stain. (Alter Dogiel, from Bolim and von I)avidofT. I (Fig. 127) ^vhich may recei\'e as many as ten ner^-e libers. These ramify and send branches to neighboring coi'piuscles and also to the epidermis. The genital coqjuscles are deejily placed beneath the epithelium of the glans penis and clitoris an(i the adjoining structures. Bulbous coi^juscles [of Krause] are smaller than the genital corpuscles and are most numerous (1-4 in a scp mm.) in the superficial connective tissue of the glans penis and clitoris. '^„ L Similar structures, either round or o\-al, are found in the conjunctiva and "edge of the cornea, in the hps and lining of the oral cavity, and probabl)' in other parts of the co- rium." They ^■ary in length from 20 to 100 /(; they have thinner capsules and recei\x' fewer nerves than the genital coriuiscles which the)' resemble (Fig. 128). The articular cor- puscles, found near the joints, behjng in the same categorv. Cylindrical coi-jjuscles [cyhndrical end bulbs f)f Krause] contain a single axial nerve fiber with few or no branches, terminating in a knob-hke or rounded extremity (Fig. 129). The fiber is surrounded by a semifluid Fig. I2g. — Cvlinlrp \ TKRI\U;SC( LAR Si' P I Blue St-m.n ( Hni- CoRPLisCLp;.s, p'ROM I.\'- .\i t.'p" C\r Mp'ph\lp:np. Digitized by Microsoft® MOTOR ENDINGS. 107 A\is c\"]nKlcr. Inner bulb substance, sometimes described as an inner bulb, and tliis is enclosed in a few concentric layers of cells which are continuous with the sheath of the nerve. Cylindrical corjiuscles are found in the mucous membrane of the mouth and in the connective tissue of muscles and tendons. Lamellar corpuscles [Pacinian coqjuscles] are macroscopic elliptical staictures, 2-4.5 rnm. long and 1-2 mm. ivide (Fig. 130). They may have as many as tifty concentric layers of flattened capsule cells between which there are spaces containing fluid. A single large nerve fiber enters one end of the corfxiscle and loses its myelin as it traverses the lamellae. It extends through the semifluid inner bulfj without ob\'ious branches, sometimes being flattened and Ijanddike; it may fork at its further end or form a coil of branches. Special metliods have shown that the axial fiber may possess many short lateral ^__^ branches ending in knobs, and that one or more delicate fibers mav enter (or lea\-ej the corijuscles in addition to the large one just described; they form a net surrounding the axial fiber. A small artery may pass into the corpus- cle beside the nerve and supply the lamellae with capillaries. Lamellar corpuscles are abundant in the subcu- taneous tissue of the hand and foot and occur in other parts of the skin, in the nipple, and in the territory of the pu- dendal nerve ; they are found near the joints (particularly on the flcxr)r side) and in the periosteum and perimysium, the connective tissue around large blood vessels and nerves, and in the tendon sheaths ; also in the serous mem- branes, particularly in the mesenteries. As they are usually cut obhquely or transverselv the student should e.xpcct to laid the lamellae completely encircling the inner bulb. jMoTOR Endings. The motor nerve endings are the terminations of efferent nerves in contact with smooth, cardiac or striated muscle fibers. The nerves to the smooth muscles are a part of the sympathetic system. They are non-medullated fibers which branch repeatedly, forming plexuses. From the plexuses very slender A'aricose fibers proceed to the muscle cells, in contact with the surface of which they end in one or two terminal or lateral nodular thickenings. Probabh' eacli muscle cell receives a nerve termination. Except that the nerve endings in heart muscle are a Uttle Fn:; 130, — Small Lamellar Corpuscle from THK Mesentery of a Cat. >, 50. rhe cells lining the capsules can be recos^nized by tbeir sbacled nuclei The myelin of the nerve liber may be traced to the inner bulb. Digitized by Microsoft® loS HISTOLOGY. larger, often provided with a small cluster of terminal nodules, they are like tliose f)f smooth muscle. They belong with the sj'mpathetic system. The accessory iibcrs of the \'agus which enter the cardiac plexuses, are not known to terminate U|_ion the muscle libers. Scnsovx Muscle tjl)ers M.il.ir plait Medullated nerve fibers. F|i;. ij;t — Mi.itor Nkrx'i-: FmiIni.'^ or l.s ) kr.i isi ai. Misri i- jmi;iks cj|. \ Rarkit. .' iso. Striated muscles are innervated by the neura.xons of the ^-entral roots, which grow out from cell bodie.-, remaining within tlie central system. These neuraxons, as medullated hbers, extend through the spinal and certain cerebral ner\-es to tlie muscles. They form plexuses of medullated fibers in the perim_\'sium, fr(.)m which Ijranching medullated libers pass on to the muscle (Fig. 131 ). Eacli muscle Ii1)er recei\-es one of these Ijranches, or sometimes two placed near together. They are usually implanted near the middle of the muscle liber. The C()nnecti\'e tissue sheath of the nerve Ijlends ^vith tlie perimvsium; the neurolemma is said to Ije continu- ous with the sarcolemma, the nerve ha\-ing Ijecome attached to the em- bryonic muscle liber before the sarco- lemma had dex'eloped. Under this membrane the myelin sheath ends a]jru])tly, and tlie llljcr ramifies in a granular mass considereil to be moflified sarcojilasm. It ma\- contain muscle nuclei. This granular mass witli the ner\-c ending appears as a distinct elevated area, estimated lo average from 40 to ()o /'. in diameter, and has been named the molar ['laic. \ surface \'iew and a section of a motor plate are shown in Fig. 13^. A -MoroR I'LAi A. s I U', I I B. li. ,li;cii..i;-, (.\U.r Mull \ uii I ':t\ kImIT,) g.. I iriiiiilar suIi^luk e RlMl.ii \A:\{<- . m.. -ti 1 ilrd inns. Ic ; n.. (Ihei , t. r., Icrniinal ra nil la.atlcins ol lln 111 Digitized by Microsoft® GANGLIA. 109 Ganglia. The ganglia are enlargements, usually macroscopic, oc- curring in the course of the peripheral or sympathetic nen'cs. They always consist of nerve fibers between which there arc rows or rounded groups of the bodies of nerve cells. Nerve cell bodies vary in diameter from 4 to 150 /!. Thus they include some of the largest cells in the body. Each has a single round or oval nucleus AAdiich appears ^'esicular because of its small amount of chromatin. It contains usuallx' one large round nucleolus. These nuclei are so characteristic that the student should soon learn to recognize them. Near the nucleus the centrosome has been detected, sometimes represented b)' a number of granules; but mature nerve cells never divide and if destroyed they cannot be re])laced. In ordinary Blood vcssc Perineuriuni. Fig. i^^t — Longiti'DIXat, Si-:ction tmrough a Spinal Ganglion of a CAf. iS. specimens the protoplasm is densely granular. There is no cell membrane. Except in the embryo, nerve cells all have one or more processes; and according to the number of these, one, two, or several, they are designated unipolar, bipolar, and multipolar respectively. The processes cannot be traced in ordinary specimens because of their thick entanglement with those of other cells. In stud}'ing them the special methylene blue and silver (Golgij methods are employed. If pieces of very fresh nerve tissue are placed in a dilute solution of methylene Ijlue, after an hour or more the processes of certain cells are stained so that they can be followed satis- factorily. By Golgi's silver method a black precipitate occurs in and on Digitized by Microsoft® ijo insTorooY. individual nerve cells, following their brunches to their smallest subdivisions, whereas similar adjoining cells are entirely unaffected. This extraordinary method is of the greatest value, but it is capricious and the silhouettes produced are in part coarse and artiJicial appearances. The ganglia are surrounded by connective tissue sheaths, continuous with the perineurium, which send j)r(jlongations into their interior to invest the cell Ijodies and libers. They contain an abundance of blood vessels so that a cell bod}' ma)' be surrounded Avith capillaries. The spinal and sympathetic gangha will be described in turn. Spinal ga)iglia are found on the dorsal roots of spinal nerves; similar Cross sccUlih ot meilullatcd nerve libers. V Xei \'e Lon tu 1 i] of mediillat^i. nervt libur.s. <^ '^ *='# '*j' fi,^^ Sui fare \ lew of IIULl<--.UtJll slK.'llh- I'lG. 134 —From a Cross Section oi-' niR Skmil.i'nxr TtXhclion ok M.j,n. X 240, The cell processes cannot he seen. At X the piMtui-Iasm ni the -an^li-n cell has rutrai ted atul simulate a process. In the axis ol the traiisvcrselv ciil ncr\c fihcrs the axis c\ 1 ■IS aie se seclH structures occur on the dorsal roots of tlie cerebral nerves. The general relations of the cell bodies and libers are shown in Fig. 133, a longitudinal section through the dorsal and ventral roots. Fig. 134, from the semilunar [Gasserian] ganglion of the trigeminus, shows the component structures on a large scale. In the upper part of the hgure there are characteristic nerve cells such as have the T-shai^ed ]jrocess, the de\'elopment of which from Ijipolar cells has already been described. The jn-ocesses are not seen in the section. Each of these cell bodies is surrounded by a nucleated capsule said to be continuous widi the neurolemma of its hber. Fig. i:;c; shows one of these cell Ijodies containing canaliculi which ]-ia\'c been regarded as nutriti\'e passages from the exterior, and as secretory or Digitized by Microsoft® SPINAL GANGLIA. Ill excretory vacuoles. Fig. 136 is a similar cell containing a reticular network \vithin its protoplasm. Nerve libers branch over the outer surface of ganglion cells, forming pericapsular and pericellular nets or baskets, and have been said to penetrate the protoplasm. This, however, is denied, and sucli formations as are represented by Fig. 136 are thought not to pass outside of the cell. Ganglion cells often contain areas of yellow or brown fatty pigment granules which increase Avith age. The results of special investigations of the course of the dorsal ganglion fibers, made by the methylene Ijlue method, are shown in the diagram, Fig. 137. The large round cells (i) gi\'e rise to a single spirally twisted process which begins at the ape.x of a conical ele\'ation on the cell body. The spiral fiber has a neurolemma and accjuires a m^'clin sheath. It may give off collateral branches {2). At the first or second node, sometimes further on, it divides into a celhdipclal or afferent branch, which is an a.xis cylinder with a per- ipheral sensory ending, and a cell ill ifugal or efferent branch which enters the spinal cord (Fig. III). Thecelhihp- etal fiber may have a branch in the dorsal ramus and another in the ventral ramus (2); and the cellulifugal liber may fork near the cell body (3) or at some distance from it (2). Besides the large cells there are similar smaller ones, the fibers from which have little or no medullary sheaths (4). It is to be noted that in all these forms the cell bodies become virtually appended to single fibers, which in relation to the central nervous system are afferent. A second 1)^36 of cell, which occurs less frequently, is the round unipolar form (6) the process of which divides into many meduUated branches. After losing their myehn these form pericapsular and peri- cellular ramifications around the cell bodies of the first t}'pe. Each of the latter is in relation with branches from several cells of the second type. A third form is a multipolar ceU with two meduUated fibers which are thought not to pass beyond the hmits of the ganglion (7). Fibers from sympathetic cells enter the ganghon from the jjeriphery and branch about the blood vessels and cells of the second type. Through 135. — Spinal Gancmon (rKi-i. OK AN Adult Cat ,: 430- paratus Fig. 136. — Si'iNAL Ganglion Cell 01-- A Nkwhokn Kir- TKN.t {Coi)Kil al'Iijr Clolyi.) Digitized by Microsoft® HISTOLOGY. the cells uf the second type a few sympathetic fibers are put in communi- cation with a large numlaer of T-cells. Ajjparently in mammals there are no fibers which traverse the spinal ganghon without entering into relation with its cell bodies. The oljservation that there are types of spinal ganglion lal ijatifrlion. P.lootl \cssel. Dc'isal lamus. Visceral ramus, evil of a s>nipatheLlc gan-lifiri Fic. 137— Diagram ut thl Ni-i'vors Ei ements of a Si'inil Ga.nu Mhrini.Kx;! Hli k Pitti-AHA riM\s The sensory fibers are represented li\ cnnlintious hnes, the sMnpallKlic lihers hbers by linear series of dasfies Tlie niedullar\ slieaths of the niolor liher-- nol been drawn. )^, Basi:[> upon by doited lines, the motor i of the \'entral root iKue cells with processes confined within the ganglion, and that some of the cells have non-meduUated fibers, accords with the fact ascertained by counting, that the ganghon may contain about si.x times as many cells as there are medullated fibers in the dorsal rof)t. Sympatliclic ,t;anglid consist of smaller cell bodies, often pigmented. Digitized by Microsoft® SYMPATHETIC GANGLIA. "3 and sometimes having two nuclei, and of tibers some of whicli merely traverse the ganglia. The cells are enveloped in nucleated sheaths. They include three types of multipolar cells shown in Fig. 138. Most of the cells are of rounded oval form, often flattened, having stellate spmy dendrites and a non^medullatcd neuraxon with very slender collateral M.jl" Pericellular L S\'mpalheUc? iier\ e Jllier. \'ie\\' in scctiiiii t pericapsular Smoot nruscle fibers Lamellar c^)rpuscle Fig. 138.— Di-vgr-\m of tme Elkment-s cif Two S\"-\iF-\"n-ii-:ric G.ancfia, B.asfd upo.'^ MErH\LENE Blue PKEPAR.^'riONS, branches (i). These are motor cells, and their neiiraxons terminate in contact with smooth muscle cells. The second type (2), possibly sensory, includes rounded potygonal cehs with slender dendrites which extend in the sympathetic nerves even to the neighboring gangha. Their neuraxons may acquire myelin sheaths at some distance from the cell body or may remain non-medullated. They pass to other ganglia but their termination s Digitized by Microsoft® 1 14 HISTOLOGY. is unknown. Cells of the third type (3) are few in the large ganglia and are not found in small ones. They have long dendrites which form a ' ' general peripheral plexus " but do not extend beyond the limits of the gangUon. Their neuraxons enter the sympathetic nerves as non-meduUated fibers, the destination of which is unknown. Sympathetic gangha contain also stellate connective tissue cells, and chromaffine cells to be considered presently. The ganglia may be traversed by sensory medullated fibers to lamellar corpuscles, and by medullated motor fibers which lose their myehn sheaths and have non-meduUated collateral branches. The motor fibers and their collaterals terminate in rather coarse pericellular ramifi- cations about the sympathetic cells of the motor type. There are other nerve fibers, non-medullated and varicose, which form pericapsular plexuses, and these are considered to be branches of sympathetic cells. Paraganglia are masses or cords of cells which originate in the em- bryonic sympathetic gangha, and are characterized by being colored yellowish brown by preserving fluids containing chromic acid or chromium salts. The cells are therefore called chromaffine (meaning that they have an affinity for chromium, and not, hke 'chromatic material,' for coloring matters generally). The paraganglia are either closely or shghtly con- nected with the sympathetic nerves. In the latter case they are applied to large vessels, and in the fetus, between the branches of the spermatic vessels, to the paroophoron and paradidymis. The glomus caroticum at the bifurcation of the carotid artery, and the glomus coccygeum associated with the median sacral artery, are knots of vessels both of which contain clumps of chromaffine cells. The organs discovered by Zuckerkandl at the origin of the inferior mesenteric artery may be classed with them. Single chromaffine cells, or small groups of them, occur diffusely in the sympathetic ganglia and nerves. The entire medulla of the suprarenal gland in the higher vertebrates is composed of them. Since the extract of such cells, on intravenous injection, causes a marked increase in the blood pressure, the chromaffine cells are considered to secrete into the blood a specific substance which maintains the normal tonus of the vessel walls. Spinal Cord (Medulla spinalis). Development. The early develop- ment of the medullary tube has been shown in Fig. 109, p. 92. The tube at first consists of separate cells but these soon unite to form a syncy- tium. Those nuclei of the syncytium which border upon the central canal divide repeatedly by mitosis and many of them are forced outward radially. The protoplasm of the syncytium increases more rapidly than the nuclei, and forms a non-nucleated network at the periphery of the tube; this is the white layer [sometimes called mantle layer]. The fibers Digitized by Microsoft® SPINAL CORD. from the spinal ganglia enter its dorsal portion and grow up and down the medullary tube through its meshes, thus forming the o\'al bundles. ]\Iean- while the nucleated layer becomes divisiljle into two portions, a thick cpcndymal layer composed of undifferentiated cells around the central canal; and a :^ray lavcr [mantle layer] C(.)mposed of cells which have moved outward and Ijecome partly differentiated. The gray layer is at first triangular, Ijcing thick ventrally and narrow dorsally. It consists of two sorts of cells, the neitrogUa cells (glia cells), wliicli are IItc cells of the protoplasmic syncytium; and tire nerve cells (in their }'oung stage, called neuroblasls), which are imbedded in the neuroglia networiv and send out processes to ramify among its me.■^hes. The neuraxons of the moltjr cells grow out from neuroblasts in the \'cntrodateral part of tlie gray layer; after crossing the Avhite layer, they pjass out of the medullary tufje as fibers of the ventral roots. This stage of develo[)ment is shown in Fig. 109, E. Blood vessels are seen growing into the tulje under the dorsal roots and near the ventro- median line. They carry some connective tissue cells with them, to mingle with the neuroblasts and neuroglia, both of wJrich are ecto- dermal. Fig. 139 rcjiresents a later stage in which the form of the adult cord is clearly suggested. The Avails of the dorsal portion of tlic central canal have fused and disappeared so that the canal is reduced in size. It is surrounded by an ependymal layer Avhich is becoming thinner, since its cells are being added to the gra}- la}'cr faster than they arc replaced Ijy mitosis of the inner ceUs. The gray layer in the preceding stage showed two \-entral protuberances, one on each side. These extend the length of the cord and are knoAvn as the ventral columns [horns]. In the ])resent stage in addition to these, there are two dorsal columns [horns] which ha\-e been formed Ijv the dorsal proliferation of the epend\'mal layci'. As a wdiole the grav is shaped like an H. That portion wliich extends from side to side beneath the central canal is the ventral gray commissure. The white layer has become wider. Its neuroglia network has a predominant radial arrancrement. Nuclei ai'c found in its strands of neuroglia which Fig. iy\ \ inf -SiTNAL Cord of a RABurr Kmbkno OF 20 Da'i s. C. C, Central canal ; d. c, dorsal column : d. m. s.. dorsal median siilnt, ep.. ependymal layer ; v. c, xcnlrai culinnn ; v. g. c. ventral ii-i'ay commissure, v. m. f.. xenlr.il Tired I an (rssui e ; V. r.. \-eiul,il 1 not ; v. w. c. \ en- tral white c Mninnssiire ; w, l.,\\liite la\er (lat- eral funiculus). Digitized by Microsoft® I lO HISTOLOGY. ha\'e become fibrous, but it lodges no nerve cell bodies. It is permeated with tlie processes of ner\'e cells, tlie bodies of which remain within the gray layer, or the spinal gangha. On the outer surface of the cord there are longitudinal grooves which form the boundaries of certain subdivisions of the white layer. These groo\-es are the dorso-mcdian sulcus; the dorso-lalcral sulcus, along which the dorsal roots enter the cord; the vcntro- lalcral sulcus, along which the \'entral roots lea\-e the cord; and the vcntro- Dorsal MLiliaii ) Pi,rliO}i s I ,N , Pia mater. ,K,t?' External limiting; membrane ; ^~^ Lateial ) funiculus. ; Doisn- / ^ Wntial column, lateral ' I'll ,..,'-«« r -^ * '«,jSa r\c clis Central canal. \ Vcinral root Wliite \'cntral W-ntral lunicalns. coninnssurc. incih.in llssurc. Fig. i.to. — Ckmss Seci iriN r n." ihe LuMn.vR Il.nl.\rgi':mi-:nt oi-- ihi-: HrM.\N SriN.M. Cciri-\ S. median fissure, which unlike the others becomes a very deep narrow depression. Bet^^•een these four groo\-es the while substance on cither side of the cord forms the dorsal, the lateral, and the vculral juiiiculi. Each dorsal funiculus recei\ es the enlt'ring iiljcrs from the dorsal roots on one side of tlie cord; it represents the OA'al bundle Avhich has enlarged and been folded in toward tlie mecHan dorsal line. Later a dorsal median septum becomes more e\'ident se])arating the tAvo dorsal funicuh. Ven- Digitized by Microsoft® SPIXAL CORD. ii: trally there is a narrow layer of white substance extending from one side of tlic cord to the other; this is tlie ventral ivhilc commissure. In the adult cord (Fig. 140) tlie central canal is usuall)' reduced to a cavity 0.5 to i.o mm. broad; sometimes it is obliterated. The canal is surrounded by tlie cpeinlyma ^A'hich appears as a single layer of neuroglia cells. Around the ejiendyma is the central gray siihstance, containing special ncurogha cells to be described later. In addition to the ventral gray commissure of the younger stage, there is now a dorsal commissure, by Avhich the vertical portions of the gray H are united dorsal to the central Fig. 141.— Neuroglia Cklls xnd P'ibicrs i^^ro^i 'ihe Spin\l Cord of an ra.EPiixNi. (/Au,l,:lr—i\om Feisjuson's Hislnloiiv) Tlif letters indicate ihc Tieur(iL;-lia cell-;.. I., a lcucuc>te. Benda's stain. X 940. canal. Besides tlie dorsal and ventral columns, a lateral column may now be recognized as a bulging of the ventral column on a hne with the central canal. Lateral columns are most evident in the upper thoracic part of the cord. On the lateral side of the dorsal column there is a network of strands of gray substance called tlie reticular jormation (formatio retic- ularis). Near the dorsal commissure in the dorsal colunm there is an important group of nerve cell bodies named the dorsal nucleus [column of Clark]. ('Nucleus' is a term applied to many such groups of cell l)odies in the brain.) The dorsal nucleus extends through the thoracic cord and is weU defined in the anterior lumbar portion; it is not wholly absent Digitized by Microsoft® ii8 PTISTOLOGY. Blood \ from other ])arts of the eord. Toward the tip of the dorsal column there is a macroscopic, apparentl)' gelatinous mass called the gelatinous substance (substantia gelatinosa) ; and dorsal to this there occur successively the spongy zone, and the terminal zone (zona spongiosa and zona terminalisj. The latter consists chiefly of ner\-c ilbers ninning lengthwise of the cord. The dorsal median septum, generally described as formed of compressed strands of neuroglia, is well marked; it resemljles the ventral median fissure since the walls of the latter have been brought so close together. Stnietiire oj the cord. From the preceding account of the develop- ment and topograjih}' of the cord, it is e\'ident that there are three layers to be examined, the Avhite layer, the gra\' layer, and the ependyma; these may be considered in turn. The iL-hile sub- stance [matter] con- sists of a syncytial framework of neurog- lia through which pass blood vessels: and nerve fibers mostly medullated. The m}X'lin sheaths of the latter produce the ^x-r}- white macro- scopic appearance of this la}-er when freshly cut. The nature of the neuroglia syn- cytium is seen in the longitudinal section, Fig. 141. Stiff fibrils ha\-e de\x-loi>cd in its exoplasm, and they arc continuous from one cell territory to another. As the nerve filjcrs which occupv the neuroglia meshes increase in numlier, and in size by becoming medullated, the neurogha nuclei surrounded Id}- j)rotoplasn-i are compressed into stehate forms (Fig. 144, A). In tlie Golgi preparations they appear as in Fig. 142, and are described as long ra}x-d, and short raved or moss\- cells. These forms reijresent clumps of neurogha fijjcrs, sometimes clogged with precipitate, in tJTe center of which there may or may not be a nucleus. Fig. 143 shows the appearance of the neuroglia net in ordinarv sections. 0\X'r the outer surface of the cord it makes a dense fellwork, generally free from nerves. It has Ix'cn called tire exlernal limiting memljranc. Outside of it is a \x'ry \-ascular connective tissue laver, the t?ia mater. The Fic Short ra\ o -NbAROuL I-ons ra\ ed colls. Ci LT.s I Rn\[ THK Brain- of an Adi.'lt M \x. .01 (jl MhJTIIOD. X ^'"^O. Digitized by Microsoft® AVHITE AXD GKAY SUBSTANCE. 119 Ciriss S(.-rli(]iis of me.lull.ilud Axis c\ limler and "'- Medullary sheath. --, Nturo'^ha cells. CoTiiiucLix c tissue. Clood \ essels. figure shows a prolongation of the pia mater, containing blood vessels, into the white substance. It has not been established beyond doubt that such ingrowths of connecti\'e tissue may not take part in form- , ^^''"'^ K>;ti-rn;,i iimitiii« ing supporting tissue around the ' ^ nerves. _ -■ '; The nerve fibers of the white substance A'ary in diameter, the coarsest being found in the ven- tral and the lateral parts of the dorsal funiculi; the finest are in the median parts of the dorsal and lateral funiculi. Elsewhere coarse and fine ones are inter- mingled. Their general direc- tion is parallel A\'ith the long axis of the cord. Like other nerve fibers they consist of neuroplasm and fibrillae. jNIost of them are medullated and in cross section the m}'elin often forms concen- tric rings. Although a few observers ha^'e described nodes it is generally considered that there are no nodes in the central ner\-ous system. During the development of the m}-elin, iibers ha\-e been found en- circled Ijy shcatli cells. Fig. 144, B. In longitudinal view, these sheath cells are seen in depressions of the m}-elin, where they greatly resem- jjle the neurolemma cells of per- ipheral ner\-es. ^A'id■^ the increase of myelin the_\' become A'cr}' slender and can sekh^ni be detected in the adult. It is ordinarily stated that the medullated fibers of the central nervous system are without a neuro- lemma. The gray subsUiiicc [matter] is composed of a neuroglia framework containing capjillar\- Ijloorl vessels and some larger ones, together Avith the cell bodies and non-meduUatecl processes of many nerve cells. The ,. 143 — IM.,.,^^ii' , ) nal vessel, the dorsal aorta. The ■b.c '^^^^%/"\^:;?./'X$>[ ^ part of the net folded under the '. ■ |4\, ■'" y^-'' y /~"" pharynx constitutes successively the _ / ' / , \ '©■■>' L„, "^^ vitelline veins, ih.t heart, dinAih.Qven- '^^^feii^' *^,;fe3>„^ % tral aortae continuous in front of the J.' *-....-'-; ^ g. pharynxwith the dorsal aortae. The ' ""•--. 'isp heart first appears as two dilated ^"=- ''*5- vessels, one on either side, which are Blood vessels from a rabbit embryo of 13 flays, developing as endothelial sprouts (en) from parts of the general nctwork. They pre-existmg vessels (b.v.); b.c, blood corpus- x o j cie within a vessel. ^j-g brought together in the median hne under the pharynx and fuse. At first the heart pulsates irregularly, but with the establishment of the circulation, its beats become rhythmical. The blood flows from the net Digitized by Microsoft® SINUSOIDS. 12 = through the veins to the heart, and thence through the arteries back to the net. All of the future vessels of the body are believed to be offshoots from the endotheUal tubes just described. They grow out, as shown in Fig. 149, through the mesenchyma with which they are inseparably connected. The sprouts are at first solid but soon become hollow except at the growing tips. They may encounter similar offshoots from the same vessel or from other vessels and fuse with them. Through the anastomosis of Such sprouts, networks of vessels of small caliber are produced which have been divided into two types, the sinusoid and capillary types. Sinusoids are formed as branches or subdivisions of a single vessel. A vein passing near a developing epithehal organ may send out branches over its surface, and if the organ itself is a ramifying structure its sub- divisions may be nearly enveloped by these venous branches. The hver v:CJ. Int. .V Ar Fig. 150.— Diagram Showing on the Left the Liver and its Sinusoids ; on the Right the Pancreas and its Capillaries. The connective tissue is represented by dots. Ar., Artery ; Int., intestine ; V., veins ; V. C. I., vena cava inferior; V. P., portal vein. is related in this way to the vitelline veins (in which the umbilical veins later come to empty). In the left portion of the diagram, Fig. 150, the liver is shown in heavy black as a branching outgrowth of the intestine. The portal vein (V. P.), which is a persistent part of the vitelline v-eins, forms a net of small branches, the endothehum of which is quite closely apphed to the hepatic tissue. A thin but important layer of connective tissue intervenes, which could not be shown in the figure without great exaggeration. The subdivisions of the portal (viteUine) vein are the sinusoids and they come together to join the inferior vena cava, this part of which is also persistent vitelline vein. A relatively small hepatic artery later suppKes the connective tissue around the ducts of the Hver, but the essential vascular system of the liver is a single large vein which has been resolved into a net of sinusoids. In the human adult, this is perhaps the only instance of sinusoidal circulation. In the embryo the mesonephros (a renal organ of large size) is supphed by sinusoids derived from the Digitized by Microsoft® 126 HISTOLOGY. posterior cardinal veins; the musculature of the heart grows into the cavity of the ventricle in plates and columns covered with endothelium (Fig. i6o), thus producing a net of vascular spaces or sinusoids. Although the sinusoidal circulation persists in these organs in lower vertebrates, such as the frog, it is not retained in man. The sinusoids of the heart are reduced to shallow spaces between the columns of muscle seen on its inner surface, and those of the mesonephros disappear with the transformation of that organ into the epididymis and epoophoron in the male and female respectively. Thick walled subdivisions which may occur in the course of a vessel are not sinusoids. The latter have essentially the structure of broad capillaries, from which they differ in that they arise from a single vessel. They are therefore whoUy venous or wholly arterial. Capillary circulation arises by the union of vascular outgrowths from two vessels, the blood in which flows in more or less opposite directions, in other words, from an artery and a vein. The vessels to the lungs are at first a slender blind branch from a part of the aorta, and another blind outgrowth from the left atrium [auricle] of the heart. These extend through a column of mesenchyma to the epithelial ramifications of the lung, over which they branch and become united. The blood flows to the lung through the pulmonary artery, passes into capillaries and returns to the heart through a vein. A similar circulation is shown in the diagram. Fig. 150. It is essentially an arttrio-venoQS circulation. From their mode of development, capillaries have more connective tissue around them than the sinusoids. A glomerulus is a round encapsulated knot of small subdivisions of an artery which reunite before leaving the capsule, and soon after form capillaries. Glomeruli occur in the kidney and mesonephros. They are probably to be regarded as encapsulated capillaries rather than as sinusoids. All the blood vessels of the young embryo, including the aorta and the heart, are merely endothehal tubes. Capillaries and certain sinusoids retain this structure in the adult, but the larger vessels have thick walls formed by transformation of the surrounding mesenchyma. The wall of the larger vessels consists of three coats or layers; the tunica inlima, which is the endothelium with a thin layer of elastic connective tissue ; the tunica media, which is chiefly smooth muscle with elastic substance intermingled; and the tunica externa [adventitial which is a dense layer of elastic connective tissue sometimes containing muscle. In the heart the intima is called endocardium; the media, myocardium; and the externa, which there is covered with the pericardial mesothelium, is the epicardium. Capillaries, arteries, veins, and the heart will be described in order. Digitized by Microsoft® CAPILLARIES. 12: Fig. 151.— Capillary from the Tail OF A Tadpole. Silver Nitrate Preparation. (After Koelliker.) Capillaries are endothelial tubes of varying diameter, the smallest being so narrow that the blood corpuscles are distorted in passing through them in single file. Their walls are composed of elongated, very flat cells with irregularly wavy margins as shown in Fig. 151, from a silver nitrate preparation. Between the cells the corpuscles, both red and white, may make their way out of the vessel. There are no preformed openings for this purpose, and the endothelial cells come together after the corpuscles have passed out. Two cells form the circumference of small capillaries, 4.5 to 7 n in diameter, and three or four cells bound the larger ones of 8 to 13 jJ-. Nerves end in contact with them and it is possible for the endothehal cells to contract. The bulging of their nuclei into the lumen of the vessel, often seen in specimens of capillaries and of larger vessels, is probably an artificial appearance. The lining in life is thought to be smooth. Certain endothehal cells are said to be phagocytic, devouring objects which float in the blood, and some endothelial cells have been described as becoming detached and entering into the circulation. Small capillaries divide without decrease in caliber, and by anastomosis with neighboring capillaries they form networks differ- ing widely in the size of the meshes. The closest meshes occur in the secre- tory organs and in the lungs and mucous mem- branes; the widest are in muscles, the . serous membranes and the sense organs. The close net- works consist of capil- laries of large caliber ; and those with wide meshes are formed of more slen- der vessels. Thus the blood supply of glandular organs is particularly abundant. The sinusoids of the hver are close meshed and large. Arteries, in approaching their terminal branches, become small {arterioles) and as 'precapillary vessels' pass without line of demarcation into capillaries. The smallest arteries are endothehal tubes encircled Fig. 152. — Small Arteries of Man. Nuclei of endothelial cells ; m, nuclei of circular muscle fibers, at m' seen in optical cross section ; a, nuclei of connective tissue. In A, since the endothelium is out of focus, its nuclei are not seen. X 240. Digitized by Microsoft® 128 HISTOLOGY. by occasional smooth muscle fibers. In Fig. 152, C, the oval nuclei of the endothelium are seen to be elongated parallel with the course of the vessel. As is usually the case, the walls of the endotheUal cells are not visible. The rod shaped nuclei of the muscle fibers are at right angles with the axis of the vessel. In the somewhat larger artery, B, the muscle fibers form a single but continuous layer, the media, outside of which the connective tissue is compressed to make the externa. Its meshes tend to be parallel with the vessel. The walls of such an artery are so thick that it is possible to focus on the layers separately; thus in A, the endothe- lium which with a delicate elastic membrane beneath it constitutes the intima, is not seen, being out of focus. The nuclei of the media and ex- terna are evident. The structure of the larger arteries is illustrated by the cross section, Fig. 154. The intima consists of endothelium resting on a layer of con- nective tissue containing flattened cells and a network of fine elastic fibers. Endothelial cell. Indentations made by smooth muscle fibers. Fig. 153.— Endothelium of the Mesenteric Artery of a Rabbit. Surface View. X 260. The meshes of the fibrous and elastic tissue are elongated lengthwise of the vessel and on surface view they present a longitudinally striped appearance. Toward the media, the intima contains a conspicuous inner elastic membrane which is fenestrated and usually thrown into longitudinal folds. (Fenestrated membranes have been described on page 42.) In the smaller arteries (those under 2.8 mm. in diameter) the endothelium rests directly upon the inner elastic membrane; and in such large ones as the external iliacs, the principal branches of the abdominal aorta, and the uterine arteries in young persons, the subendothelial connective tissue is said to be lacking. The inner elastic layer is very thick in the larger arteries of the brain, and may be double. In the media the number of layers of circular smooth muscle fibers increases from the precapillary vessels which have but one, to large arteries hke the brachial which have many. Sometimes the media near the intima contains a few longitudinal fibers; these have been reported in the sub- Digitized by Microsoft® CAPILLARIES. 129 cla\'ian, splenic, renal, and dorsalis penis arteries, and in the umbilical arteries they form a consideraljle inaer la_\'er. They are said to occur especially near the places of branching. Between the circular muscles there is a varying amount of connecti\-e tissue with wide meshed nets of elastic fibers. The proportion between the muscle and elastic substance varies greatly. In the aorta and pulmonary arteries the elastic tissue far surpasses the muscular, and it predominates also in the carotid, axillary and common ihac arteries. Muscular tissue is ascendant in the distal arteries. The former group of vessels contains the conducting arteries. Erifrjlheliuiii InLenial vlastn mt-inbiant.- ) — P RI I 1 [n i R \(„Hi \l \r Ti N which always remain freely open; the latter are distributing arteries which by changing their caliber control the blood supply in their areas of distribution. After death tliese vessels contract, the muscle nuclei becoming spirally twisted, and the intima thro\vn into longitudinal folds. The blood is forced on into the capillaries and veins. Then as the rigidity of the muscles passes off, the elastic tissue distends the vessel which remains comparatively emptA' of blood; for this reason the ancients supposed that arteries contained air. The umbihcal arteries are exceptionally deficient m elastic tissue and remain contracted, which aids in preventing haemor- rhage when the umbilical cord is ruptured at birth. 9 Digitized by Microsoft® HISTOLOGY. Coriiiectne tissue. Siiioolli muscle fibers Kkistie fibers The externa consists of connective tissue, which is denser and contains more elastic fibers in its inner portion. A prominent layer of elastic tissue near the media is called the outer elastic membrane, and is especially well developed in the carotid, brachial, femoral, coehac, and mesenteric arteries. It is absent from the basilar artery and most of those within the skull. Sometimes the externa contains scattered bundles of longitudinal muscle. In the larger vessels it contains sniaU nutrient blood vessels, the vasa vasorum. These may Enduiheiiuiu. -___.^___^^--,,,-,_^ ^^^_ __^ ^ I penetrate the outer part of the media. Lymphatic vessels often accompany the blood vessels and have Ijranchcs in the ex- terna. Their deeper ]ienetration is doubt- ful, although they have been reported in the intima of certain large vessels. Sen- sory nerves may ter- minate in the externa with free endings or in lamellar corpus- cles, the latter being numerous in the ab- dominal aorta; free sensory endings are also found in the in- tima. The vaso-motor jiervts are non-medul- lated sympathetic libers which forni plex- uses in the media and terminate in contact willi the muscle fibers. These plexuses are said not to contain ganglion cells. The largest arteries, the jjulmonary and the aorta (Fig. 155), have a broad intima which increases in thickness with age. It consists of an endothelium of cells less elongated than those of smaller arteries, resting on iibrillar connective tissue with llaltened round or stellate cells. Its elastic fibers are broader toward the media, but there is no distinct inner elastic membrane. Tlie media consists of very many concentric elastic Elastic fibers Coiinectne tissue Cfoss Skciion of rnii Thoracic Aor i a OF M \X. ,■ 100. Digitized by Microsoft® VEINS. lamina connected with one another across the muscle layers which he Vjetween them, by elastic bands. The muscle fibers of the inner portion have been described as short, broad and flattened elements joined to one another so that they resemble cardiac muscle (Fig. 156). The outer muscle is of a more ordinary form. The elastic ele- ments greatly predominate and on section the fresh aorta appears yellow, not reddish like smaller vessels. The externa contains no outer elastic membrane. It is relatively and absolutely thinner than the externa in some medium sized arteries. Veins. The veins ha\'e thinner walls, containing less muscle and less elastic tissue than the corresj)onding arteries. Since the artery to any structure and the returning vehi often are side by side, it is fre- quently possible to make such comparisons in a given specimen. Because of thinner walls the veins often collapse, or at least are not as circular as the arteries; they may be distended with blood, and frequently have a larger lumen than the contracted artery. In many large veins the media Fig. 156, Branched Smooth Mus- cle Cells from the THOR.\crc Aorta of a Child at Birth (a) AND A"r Four Months (b) lAflev Koelliker ) '' S:%^K oT^i ci^f I rTTrf-r^UT \2 ^^ "^ ..^ JHf J '^-^rK- {t\- Nuclei of smuolli muscle ribcr^. ^ \:.^^ _ ^ C.niiii'Cllxx- Fig. 157.— r'\RT OF A Cross Si."ction of a \ ein fklt,- 'luKtl siTinotli iniiM 1 fibers cut acri.^s. 4 - - ^Vi i:;2 HISTOLOGY. not form bO compact a layer and llicir nuclei arc oval rather than rod shaped. For some distance from the capillaries muscle fibers are absent although encircling bundles of connecti\e tissue may be present. In the larger \'eins (Fig. 137) the intima consists of an enrJothelium of polygonal cells resting on connective tissue and bounded by the inner elastic membrane. The latter is structureless in small \-eins but is repre- sented by elastic nets in the larger ones. In the intima of \'arious veins occasional oblique or longitudinal muscle libers have been found. (These occur in the iliac, femoral, saphenous and intestinal veins, the intramus- cular jiart of the uterine \'eins, and especially in the dorsal vein of the penis near the suspensory ligament. J The media is best developed in the veins of the lower extremity (especially in the poplitealj, less developed in those of the u]:)per extremity, and still less in the larger \-eins of the abdominal cavity. It consists of circular muscle fibers, elastic nj^'tworks, and fibrous connective tissue, the last being more alaindant than in the arteries. In many veins the media is represented only by connective tis- sue, as in the superior vena cava and its principal tributaries; the veins of the retina and of the bones; and ^ ^ „Ty^- those of the jiia and dura mater. ^ Thin vailed A'cins of large diameter Fic^. is^. — PvRT ss Sfction of thi^ Human rfxal \-KiN. ^, 50. in thc (lura and elsewhere are called sinuses. The externa of \-eins is their most highly dcwloped layer. It con- sists of crossed bundles of connective tissue, elastic fibers, and longitudinal smooth muscle which, as in the tnmk of the portal vein and in the renal vein (Fig. 15SJ, form an almost complete muscle layer. The blood and nerve supph' of \'eins is similar to that of arteries. The \-asa \-asorum are said to be more nimierous in veins, into wliich they emjit^'. The vah'es of \-eins are paired folds of the intima, each shaped like half of a cup attached to the wall of the \'ein so that its convex surface is toward the lumen. In longitudinal sectif)n they apipear like the \'ah"es of the lymphatic \'essel shown in Fig. if)4. The valves are generallv found distal to the point where a branch eni])ties into the vein, and thev prevent its blood from jlowing away from thc heart. The \-al\-es do not oc- cur in small \-eins. They are most numerous m thc \'eins of the extremities, but apjjear also in the intercostal, az)'gos and spermatic \-eins. Elsewhere they are absent. The endothelial cells on thc surface of the \'al\'e toward the lumen of the vein are elongated parallel with the current, but on the side t(jward the wall of the vein they are transversclv placed. Under the Digitized by Microsoft® HEART. -33 former there is a thick elastic networlc; the transverse cells rest on a delicate fibered connective tissue. The He.art. Development. The heart has already been described as a median longitudinal vessel beneath the jjharynx, formed posteriorly by the union of the vitelline veins and terminating anteriorly in the two ventral aortae. Such a heart from a rabbit embryo is shown in Fig. 159, A. It soon becomes bent hke a U, the venous opening being carried forward dorsal to the aortic part as shown in B and C. The ventral or aortic hnib of the U at the same time is carried to the right of the median plane (C). Tlie dorsal limb is divided into two ]jarts by an encirchng constriction, the coronary sulcus (s.c). Its thick walled portion ventral A D E F ¥ IC, 759. — KmBRVCjNIC HlvARTS. A aiul B, From rabbits o da\s after coitus ; C. from a human enibr\o of 3 (?) weeks ; D aixf E, fronj a 12 mm. pic;- fD sectioned on tlie left of tlie median sei)tum. and E on the ri^ht of it) ; F, froin a 13 6 nun. liunian embryo, sectioned like E. The hearts are all in corresponding positions with the left side toward the observer, the anterior end toward the top of the Jjage, the dorsal side to the rig;ht- ao., Aorta; c, S., coronary sinus; f. 0., foramen ovale; i. f,, intei ventricular foramen; 1. a., left atrium; p, a., pulmonary artery ; p. v., pulmonary vein ; r, a,, rii^ht atrium ; s. C, coronar\' sulcus , v., ventricle ; V. b., bicuspid \al\-e , v. t., tricuspid \'al\e , v. v.. \ itelline \-ciii ; v. v. s.. \ aU-es of the \-enous sinus. to the sulcus is to form the ventricles of the heart; the thin walled dorsal portion becomes the atria [auricles]. In the human embryo of three weeks (C) the atria are represented by a single cavity sulxli\'ided into right and left parts only Ijy an external depression in the merlian jjlane. The right portion receives all the veins which enter the heart (the vitelline \'cins and their tributaries) and is much larger than the left portion. The cavities of the atria not only connect with each otlier l3ut they have a common outlet into the undivided ventricle. From the ventricle the blood flows out of the heart through the aortic limlj. In a complex manner, described in text-books of embryology, a median septum develops, dividing the heart into riwht and left hah'cs. Digitized by Microsoft® 134 HISTOLOGY. In the heart of a 12 mm. pig embryo the septum has formed (Fig. 159, D) and has been exposed by cutting away most of the left atrium and left ventricle. The septum between the atria becomes perforated as it develops, so that in embryonic hfe the atria always communicate. The perforation in the septum is the foramen ovale. (The figure shows the bhnd sprout of endothelium (p.v.) growing from the left atrium to form the pulmonary veins.) Between the left atrium and ventricle the median septum forms a flap-like fold; this and a similar fold from the outer wall of the heart constitute the bicuspid valve [mitral]. The median septum between the ventricles is never complete. It leaves an interventricular foramen through which blood passes to the root of the aorta, which is shown in E, a section of the same heart made on the right of the median septum. The pulmonary artery and the part of the aorta near the heart, develop first as a single vessel; they become separated from one another by the formation of a partition across its lumen. As long as the dividing wall is incomplete, the blood from either ventricle may pass out through either artery as shown in E. In the more advanced human embryo, F, the partition between the aorta and pulmonary arteries has extended so that it joins the interventricular septum, and causes the interventricular foramen to open into the root of the aorta only {s). The figures E and F further show that the veins which empty into the right auricle unite to form the venous sinus just before terminating. The outlet is guarded by a valve with right and left flaps. The left is said to assist in the closure of the foramen ovale, which occurs at birth, and leads to the formation of the fossa ovalis of the adult. The right flap of the venous sinus forms the valve of the vena cava [Eustachian valve] and the valve of the coronary sinus [Thebesian valve]. The coronary sinus, Fig. 159, F, c.s. is the persistent terminal portion of a vein which conveyed the blood from the left side of the embryo to the right atrium. Most of its branches are lost by anastomosis with other vessels so that in the human adult its territory is limited to the heart itself. .It is found in the coronary sulcus. Between the right auricle and ventricle is the tri- cuspid valve, similar to the bicuspid in its development. These valves are seen in section in Fig. 160. Embryologically the heart is composed of three layers, the endothelium, mesenchyma, and mesothelium. The endothelium is continuous with that which lines the blood vessels. The mesenchyma which surrounds it, becomes in part differentiated into connective tissue which with the endothehum makes the endocardium. In part it forms cardiac muscle, the myocardium, together with the tendinous rings (annuli fibrosi) between the atria and ventricles. As fibrous connective tissue it extends into the valves, Digitized by Microsoft® HEART. 135 and in looser form it unites witli tlie mesotliclium to nialve the epicardium. The epicardium or %'isccral pericai-diiim is continuous with the parietal pericardium in such a way tliat the two layers form a closed sac which envelops all of the heart except its base, where the large vessels enter and leave it. The pericardial ca\'ity within this sac was originally continuous with the peritonaeal cavity, and in the adult the walls of these subdivisions of the coelom have essentially the same structure. It contains the serous pericardial iluid. Adult structure 0} the heart. The endf)cardiumis a connective tissue layer co^'ered with an en- dothehum composed of irre.gu- larly polygonal cells. It contains some smooth muscle fibers, and elastic networks which, in the atria especially, form fenestrated membranes. In the deeper part of the endocarchum, partially developed cardiac muscle fibers occur in some mammals, but rarely in the human adult. Such muscle fibers, characterized by containing only a peripheral ring of banded fibrils, are called 'Purkinje's fibers'. They may be transformed into typical car- diac muscle. The valves of the heart are essentially folds of endocardium containing dense fibro-clastic tissue con- tinuous with the annuli fibrosi. In the atrioventricular valves there are smooth muscle fibers, most abundant near the attached borders; and some blood vessels. The semilunar valves of the pulmonary artery and aorta consist of connective tissue which is denser and more elastic on the side toward the ventricles, and particularly at the periphery and nodules of the valves. The nodules are thickenings in the center of the circumference of each segment of the valve, which perfect their approximation when closed. The endocardium contains free sensory nerve endings, associated with modified connective tissue cells, and undoubtedly motor nerves to its few muscle fibers. Lymphatic vessels have been described in it, together with the terminal capillaries ■SKcnON OF THE Heart shuw.^ in Fig. 72 ca., Capillaries ; en., endothelium ; 1. a., left atrium ; l.v., lett ventricle ; mes., mesotlielium (of the epicardium, or visceral pericardium); p c., pericardial cavit\; p.p., parietal pericardium; r. a., right atrium; r. v., ri^^ht \-entricle; si., sinusoids ; v. b., bicuspid valve ; v.t., tricuspid \al\e ; v. V. s., vahes of the venous smus. Digitized by Microsoft® 136 HISTOLOGY. of the epicardial blood vessels. The capillaries of the heart are derived from venous outgrowths of the coronary sinus which unite in the epicar- dium with arterial outgrowths from the root of the aorta. The branches of these vessels invade the myocardium where they form abundant capil- lary networks and finally reach the endocardium. Some of them, especially in the right atrium, empty into the cavities of the heart as small veins, the venae minimae [of Thebesius]. Since under certain conditions the blood may flow from the heart cavity to the myocardium through these vessels, they are of considerable importance. Their embryological history is unknown, so that nothing can be said concerning their possible relation to the sinusoids. The myocardium consists of cardiac muscle, the structure of which has been described on pages 81-85, together with intervening connective tissue, poor in elastic elements but containing many capillaries, motor nerve fibers, and tissue spaces. Some lymphatic vessels pass through it. The musculature of the atria is not completely separated from that of the ventricles; there is an uninterrupted portion in the median septum. An outer obHque layer of muscle covers both atria extending from one to the other. Each has a separate inner layer of longitudinal bundles, which, as found in the prominent ridges seen in the interior of the right atrium, are called pectinate muscles. There are similar but less prominent struc- tures in parts of the left atrium. Besides these two layers, more or less definite, there are irregularly placed cardiac muscle fibers, and some which extend over the terminal parts of the large veins. The aimuK fibrosi serve for the attachment of the ventricular muscles. The right annulus is larger than the left. Similar bands of fibrous tissue surround the openings of the arteries. The complex muscle layers of the ventricle may be separated by maceration into bands which arise in the annuU, wind spirally around the heart, and terminate in the opposite ventricle. The deeper layers pass through the septum and are arranged in 8 or S shaped figures. Mus- cular elevations projecting into the ventricles are called trabecutae carneae if columnar, or papillary muscles, if conical. The latter may be connected with the margins of the cuspid valves by fibrous prolongations, mostly non-muscular, named the chordae tendineae. These structures represent the trabecular framework of the embryonic heart. The epicardium consists of the single layered, very flat mesothehum and the underlying layer of connective tissue, which contains groups of fat cells. Its elastic fibers are continuous with those in the externa of the large veins, but they cannot be traced beyond the roots of the aorta and pulmonary artery. The epicardium contains lympathic vessels, the main branches of the coronary blood vessels, and important nerves. Digitized by Microsoft® LYMPHATIC VESSELS. 1 37 The nerves to the heart are the cardiac nerves from the cervical sympathetic gangha, and certain branches of the vagus. Together these form the cardiac plexus with the associated cardiac ganglion [of Wrisberg] at the base of the heart. Their fibers extend in plexuses containing groups of cell bodies, over the dorsal walls of the atria, along the coronary sulcus, and over the ventricles where, however, cell bodies are less numerous. They He in the epicardium but extend into the myocardium and appear as bundles of non-meduUated fibers. A few meduUated fibers, supposed to belong chiefly with sensory nerves, are found with them. Free sensory endings, comparable with those in tendon, are numerous in the epicardium and occur in the connective tissue of the other layers. They include vagus fibers, which also terminate in baskets around the cell bodies in the plexuses, but none are believed to pass directly to motor endings. The motor terminations belong with ganglion cells in or near the heart. Fibers from the cervical sympathetic ganglia may end in pericellular baskets Uke the vagus fibers, or may pass directly to the muscles. Their exact termination is not known. Lymphatic Vessels. The lymphatic vessels are widely distributed through the body and physiologically they are perhaps quite as important as the bloo.d vessels. They are however far less conspicuous. For this reason they are often neglected by the student, who with some study should be able to find them in a large proportion of the specimens examined. In a rabbit embryo of 14 days and i8 hours. Fig. i6i, the lymphatic system consists of several spaces in close relation with the veins, lined with endothelium Uke that of the blood vessels. The largest sac hah encircles the internal jugular vein and sends a considerable branch into the deep connective tissue of the neck. Another large lymph space is near the renal veins; smaller ones are with the mesenteric vessels, the azygos, and the external mammary veins. An examination of younger embryos indicates that these lymphatic vessels are detached branches of the adjacent veins. They are closed endothelial tubes which send out ramifying branches into the subcutaneous and other connective tissue, where they anastomose with one another or end bHndly. They do not anastomose with the blood vessels, which they resemble, except for thinner walls and larger lumen. All of the l)nn.phatic structures in the rabbit of 14 days become connected with each other and with similar new lymphatic vessels so as to form a system which empties into the veins at two points, namely, into the subclavian veins near the internal jugulars, on either side of the body. These openings have been described as persistent original connections of the lymphatic vessels with Digitized by Microsoft® 138 HISTOLOGY. the veins, but they cannot be detected in the rabljit ligiired; they may be formed later when the lymphatic system is essentially complete. In the adult the lymphatic vessels from the legs follow the femoral, hypogastric and common iliac vessels to the aorta, in front of -which they form a net- work. Here they are joined by lymjihatics from the viscera, notably from the intestines. The latter vessels were called lac- teals from their milky appearance when filled with fat obtained from the alimentary canal. The net is continued into the thorax as one large vessel, the thoracic duct, Avhich may or may not be enlarged at its origin, forming the cisierna chyli. The thoracic duct receives intercostal branches; in places it may be irregularly re- solved into several small vessels which reunite. Near its termination in the left subclavian vein the thoracic duct receives subclavian and jugular trunks from the left arm and left side of the head respectively. On the right side there is a rigJit lympliaiic duct formed by the union of vessels from the right arm, the right side of the head and heart, and the right lung. Sometimes the thoracic duct bifurcates in the thorax sending a branch to the right lymphatic duct, or its main stem mav be on the right side. Instead of a single opening of each duct into the ^■ein, there may be i6i. — Lymphatic Vessels and \'ei,\s in a Rabbit oi-" 14 Days, 18 Hours; 14.5 mm. .- 11. 5. The lymphatics are heavily shaded, x bem^^ along the lett vagus nerve and y along the aorta. The subcla\"ian vein is formed by the union of the primitive ulnar, Pr. Ul., and external mammary veins, Ex. M. The other veins are In. J. and Ex. J., internal and e.\ternal jugulars ; Ce., cephalic , Az.,azygos; V., vitelline ; G., gastric ; S. M., superior mesenteric ; R. A., renal anastomosis ilett renal vein); V. C. I., inferior vena cava; Fe., femoral; An. T., anterior tibial ; Pr. Fi., primitne fibular, c, b., branch to cotiiicct with the femoral vein Digitized by Microsoft® LYilPHATIC VESSELS. 139 , Fig. ir,2. Ci'iiiicctive tissue from the submucous layer of llic small intestine of a cat, showing" one lilixid \-essel, b. v.; three U'mphatic vessels, I. v.; and nuiueious intercellular spaces, i. S. two or more. From its development the lymphatic system is a part of the venous system, consisting of endothelial tubes ramifying in connective tissue, anastomosing with each other or ending blindly. Its striking char- acteristic is that it is wholly afferent; it is like a venous system which has no corresponding arteries. The fluid within it is deri\-ed from the intercellu- lar tissue fluids. The smaller lymphatic vessels may be studied advantageously in sec- tions of the small intestines from, animals in which intestinal digestion is in progress. The lymphatics are then dilated. They appear as spaces in the connective tis.sue (Fig. 162) which are sharply defined, thus contrast- ing with the intercellular spaces. Their distinct Hning is due to endothehum, the nuclei of which are often seen. They have the struc- ture of capillaries but are of larger size; blood vessels of similar cahber have thicker walls. The lymphatic ves- sels often appear empty or contain a granular coagulum, whereas red blood corpuscles are to be expected in the blood vessels. A stmcture containing many red corpus- cles may be safely regarded as a blood vessel, but obviously an empty vessel is by no means a lym- phatic. Occasional red cor- puscles find their way into lymphatic vessels. In silvei" nitrate preparations (Fig. 163) the lymphatic endo- thehum is seen to be simi- lar to that of the blood vessels. Valves are numer- ous even in small lymphatic vessels. They are folds of endothehum such as would result if the distal part of proximal part. The vessels are often^distended on the proximal side of Fig. 163. — Sn-\"KR Xitr.xtk Preparation of a L\-aipha"tk \'esskl from a Rabbit'.'^ Mesentery, Showing thi-. Boundaries of the Endothelial Cells, and ,\ Bulging Jlst BEYONr.i a \'al\'e. Fig. i''i4. Lymphatic vessel from a section of a human bronchus, show- inj? a valve, v.; distal to the branch, br. Bundles of smooth muscle fibers are seen at m. f. the vessel were piisJied forward into the Digitized by Microsoft© 140 HISTOLOGY. the valve, as may be shown in injected specimens especially. One of these swellings is shown in Fig. 163. The valves of a larger lymphatic vessel appear in Fig. 164. In lymphatic vessels having a diameter of 0.2-0.8 mm. or more, three layers may be distinguished very similar to those of thin walled veins. The ititima consists of endotheUum and connective tissue containing deli- cate elastic nets with longitudinal meshes. The media has circular smooth muscle and but little elastic tissue. The externa has bundles of longitu- dinal muscle fibers, and similarly arranged connective tissue. The nerve supply is like that of the blood vessels. Although the present tendency, based upon the similar results of several investigations, is to make a sharp distinction between tissue spaces and lymphatic vessels, it should be noted that these have long been regarded as inseparable. Some authorities still consider that the lymphatic vessels open freely at their distal ends and blend with connective tissue. Lymphatic vessels have also been described as opening into the peritoneal cavity and other parts of the coelom through definite mouths or siomata. The stomata are thought to be artificial. The endothelium remains entirely separate from mesothelium so far as is known. Blood. Blood consists of rounded cells entirely separate from one another floating in an intercellular fluid, the plasma. The plasma also contains fragments of cells called blood plates or platelets, together with smaller granular bodies. The blood cells or corpuscles are of two sorts, (i) red corpuscles (erythrocytes) which become charged with the chemical com- pound, haemoglobin, and which lose their nuclei as they become mature; and (2) white corpuscles (leucocytes) which are of several kinds, all of them retaining their nuclei and containing no haemoglobin. The redness of blood is not due to the plasma, but is an optical effect produced by super- posed layers of the haemoglobin-filled red corpuscles. Thin films of blood, like the individual red corpuscles as seen fresh under the micro- scope, are yellowish green. Blood has a characteristic odor which has been ascribed to volatile fatty acids; it has an oily feeling associated with its viscosity, an alkahne reaction and a specific gravity said to average in the adult from 1.050 to 1.060. Red corpuscles. The first cells in the blood are apparently all of one sort, derived from the blood islands. They are large, round cells with a delicate membrane and a pale granular protoplasmic reticulum; their relatively large nuclei contain a chromatin network with several coarse chromatin masses. Haemoglobin develops in their protoplasm giving it Digitized by Microsoft® RED CORPUSCLES. I4I a refracti\'c homogeneous appearance. Stained with orange G or eosin it is clear and brightly colored, generally quite unlike any other portion of the specimen. Often the haemoglobin has been more or less dissolved from the coipuscles Avhich then appear granular or reticular. Mean- while the nucleus becomes smaller and so dense as to appear a structureless mass, stained nearly Ijlack with haemotoxylin. This transformation of the cells is shown in Fig. 165. Cells which are destined to produce red cor- puscles are called crythrohlasls, especially in the stages with reticular nuclei. The later stages when the cells are smaller and have dense nuclei are called nonnohlasls. The nuclei of normoblasts have been seen to be extruded as in Fig. 165. ISefore they disapjpear they may become mul- berry, dumb-bell, or trefoil shaped, (as in the group in the lower left hand corner of Fig. 174, p. 152) or they may fragment into several dark masses. These are said to be extruded so that they lie free, outside of the cell, where they are devoured b)' phagocytes. On the other hand it is believed by some that extrusion never occurs as a normal process, but that the nuclei are dissolved within the cell. The question has long been discussed and is not set- tled. The loss of the nuclei begins in human embryos of the second month; at the third month nucleated corjruscles are still more numerous than the non- fig. 165,— thk DEvELnpMUNT of rhd COJiJ'l Si_"Ll£S. nucleated. At birth and afterwards it a, successive stages in the development of ervthroblasts, from a cat eml^rvo ; b, tlie is unusual to find nucleated red corpus- extrusion of tlie nucleus in cat embryos, cles in the circulating blood. The erythroblasts at first divide b}- mitosis in the bloodvessels every- where. Later they gather about the sinusoids of tlie liver. Apparently they are not onl\- within the blood vessels but also outside of them, in the reticular tissue l^etween the endothehum and the hejjatic cells. Red blood corpuscles both nucleated and non-nucleated are fiexible bodies incapable of amoeboid movement; accordingly they pass out between endothelial cells less readilv than the leucocytes. The emigration of red coiTiuscles is called diapcdcsis. In fetal life erythroblasts multiply not only in the liver but also in the spleen. Exce]jt in a few mammals the spleen does not normally retain this function in the adult. The red Ijone marrow becomes the essential permanent location for the production of red corpuscles, and throughout hfe it contains the multiplying erythroblasts. In certain important diseases normoblasts leave the marrow and occur in the circu- lating blood, sometimes together with large forms having reticular nuclei, and called megalohlasts. The megaloblasts ha\-e been regarded as younger erythrocAtes than the normoblasts. Digitized by Microsoft® 14^ HISTOLOGY. With the loss of the nuclei the red corpuscles become smaller and cup shaped; they are convex on one side and concave on the other. ('Bell shapjed,' implying a flaring rim, is a less descriptive term; 'saucer shaped,' signifying that they are often shallow cups, has lately been employed.) The protoplasmic reticulum has disappeared and the mature corpuscle has been said to be a drop of dissolved haemoglobin enclosed in a mem- brane. With special methods a granular network has been demonstrated in some apparently homogeneous corpus- cles. Others in the same preparation may contain no reticulum. The network has been interpreted as the remains of the original protoplasmic net, and also as an artificial decomposition of haemoglobin. It occurs especially in the newly formed corpuscles (seen in cases of anaemia). Instead of a net there may be rings or round bodies the nature of which is not clear. The existence of a membrane around the coipuscles is still debated. It does not stain distinctly, and seems to blend with its contents. Sometimes it is described as an exoplasmic, fatty layer. The osmotic changes in the corpuscles show that they are surrounded by structures which are not composed of haemo- globin, and which act as membranes. Cup shaped corpuscles may be observed circulating in the omentum of a guinea pig. The etherized animal should be placed beside the stage r.. i66. — Red Corphsclks, Sketchki ^\■lTn,E ClRCUl-ATING IN THE VkSSKL^ OF THE OtVIliNTUM OF A GUINEA PiG .^i/Mfi. Fig 1(^7. — RF_n Corfusci Fs in \'\rigis CiiNniTiGNS. of the microscope and the omentum spread o\-cr the condenser. A cover glass is put directly upon it, and the coquiscles arc examined with an oil immersion lens. Some of them drawn freehand while they were under observation are showm in Fig. i66. If a drop of Ijlood from the linger is spread upon a slide in a thin layer and examined al oiicc some cup shaped forms are seen. Tliey soon flatten into biconcave discs, appearing as in Fig. 167, A. Their thin centers appear light in ordinary focus, but become Digitized by Microsoft® RED CORl^USCLl'.S. I43 dark if the objective is raised (Fig. 167, C). Tlie biconcave sliape is appar- ent when a corpuscle is seen on edge (Fig. 167, Bj. Tliis form of the red corpuscles is still ordinarily described as normal, since it is observed in freshly drawn blood. The making of the thin layer has, however, sub- jected the blood to very unnatural conditions. Very quickly the corpuscles arrange themselves in rows, or rouleaux (Fig. 173), suclr as are not found within the blood vessels. In most of the sections which the student examines, in preparing which various preserving fluids have been used, cup shaped corpuscles will be seen like those in Fig. 167, D. Often tliey will show irregular contractions and distortions (E). If the corpuscles are placed in a dilute fluid, their haemoglobin is dissolved out and water enters them. They become mere flattened membranes or shadows (Fig. 167, F). Such barely ^'isible structures arc sometimes found in urine. In dense solutions, or in ordinary fresh preparations as they begin to dry, water leaves the corpuscle, which shrinks, producing nodular, refractive masses of haemoglobin called crcnatcd corpuscles (Fig. 167, G). A 0.6 % T /A '-,- <-dx AJ '■■ I 1, llacmin cr\stals ariH 3. IiatniiUoidin cr\sta]s from liuman blotid ; 2,cr\stal5of irMiimon salt {/ 560); 4, liaemoi^'lubjii crystals from a ilo':,' (,■ 100). aqueous solution of common salt is said to cause the least distortion from SAvelhng or shrinkage. In hfe, corpuscles presumably change their shape with variations in the plasma and in the nature of the haemoglobin. A small number of spherical corpuscles is said to occur normaUy. When a drop of blood is heated to excess the coqjusclcs form small globules united by stalks or entirely separate. This indicates a viscid membrane, but does not prove the entire absence of membrane as has been asserted. In strong picric acid the coi-puscles burst, discharging their contents through a rent in a capsule which may be largely due to the reagent. Haemoglobin is an exceedingly complex chemical substance which combines readily with oxygen to form oxyhaemoglohiii. To the latter the bright color of arterial blood is due. Venous blood becomes similarly red on exposure to air. Through the oxyhaemoglobin, oxygen is transferred from die lungs to the tissues. Haemoglobin may be dissolved from the corpuscles by mixing blood with ether, and upon evaporation it crystaUizes in rhombic shapes which vary with different animals. Those from the dog arc showoi in Fig. i68, 4 ; in man they are also chiefly prismatic. Haemo- 1 Digitized by Microsoft® T-I HISTOLOGY. globin is readily decomposed into a variety of sii Instances, some of which retain the iron wliich is a part of tlie li;emogloljin molecule; others lose it. Haemaioidiii, considered identical with a pigment (bilirubin) of the bile, is an iron-free substance occurring either as yellow or brown granules, or as rhombic crystals. The crystals (Fig. i68, 2) may be found in old blood e.\tra\-asations AA'ithin the body, as in the corjius luteum of the ovary. Hacmosiderin, which contains iron, ajijjears as yellowish or bro^ATi granules sometimes extremely fine, either within or between cells. The iron may be recognized b}' the ferro-cyanide test which makes these minute granules bright blue. If dry blood from a stain is placed on a slide with a crystal of common salt the size of a pin-head, and fjoth are dissolved in a large drop of glacial acetic acid which is then heated to the boiling point, a com- bination of a haemoglobin product with hvdrochloric acid is formed, called haemiii. It crystalhzes in rhombic plates or prisms of ma- hogany brown color (Fig. 16S, i). Such crystals would show that a suspected stain was a blood stain, Init the}' afford no indication of the species of animal from which it was dcri\-ed. The dimensions of red cor- puscles are quite constant. Those in human blood average 7.5 ,"■ in diameter and ordinarily vary from 7.2 to 7.S /'. They some- times surpass these limits. In biconcave form they are about 1.6 "- thick. The cups average 7 /( in diameter and are 4 /'- in depth. Spherical coipuscles are said to be 5 y- in diameter. The blood of mammals otlier than man also contains cups which become discs. The latter are o\-al in the camel group but round in all others. Their a\-erage diameters are less than in man (7.3 /< in the dog, 7. 4.8 ,"- in the guinea-pig), but the species of animal cannot satisfactorily be determined from the diameter of the corpuscles. It should be noted that the blood of amphibians, reptiles and birds, in the adult contains only nucleated red corpuscles which are oval discs more or less biconvex. Tliey are very large in amphibia (Fig. 169). The number of red coqjuscles in a cubic miUimeter of human blood averages five million for men, and four million hve hundred thousand for women. IJy rliluting a small measured quantity of blood and spreading it over a sfiecially nded slide, the corjiuscles may l)C counted, and the num- Pl SCT.HS 1 RriM \ KrCiG. L\'R\\^ morphonuclear neutrophiles. philic granules to be described presently. These cells are notably phagocytic. They form only from I to 3 ' of the leucocytes. In certain respects they are inter- mediate between lymphocytes and polymorjjhonuclear cells. Polymorphonuclear leucoc)'tes are cells somewhat larger than red corpuscles, being from 7.5 to 10 // in diameter. They are characterized by having nuclei with irregular constrictions leading to an endless variety of shapes (Fig. 170, C). The nodular subdivisions may be connected by broad bands or by slender filaments. It is said that in degenerating cells the nucleus is divided into several separate masses. Such unusual forms can properly be called 'polynuclear,' an abbreviated term which is a mis- nomer as apphed to the ordinary cells; 'mononuclear' as designating the preceding t}-pes is also unfortunate since it implies that others have several nuclei. The irregular shape of the polymorphous nuclei has been ascribed to degeneration, comparable with irregularities in the er_\'throblast nuclei, and also to amoeboid changes associated with those of the cell body. It has been asserted that the nuclei become rounded when the cells are at rest. The latter explanation appears improbable. In the protoplasm a Digitized by Microsoft® WHITE CORPUSCLES. 14; centrosome, or a group of its minute suljdi\-isionb, has been found in tlie concavity of tiie nucleus. A delicate cell membrane has been described, but membranes are usually considered lacking in all forms of leucocytes. A fundamental characteristic of poh'morphonuclear leucocytes is the devel- opment of distinct granules in their protoplasm. These are more dehnite structures than occur in ordinary protoplasm, so that lymphocytes together with the large mononuclear cells are considered non- granular . Not only &J^ 14 Fig. 171.— The Bi-OOD Corpuscles. (Wright's Stain.) (E. F. Fahcr, from Da Costa's Clinical Heniatolog\ . ) I, Red corpuscles. M. Lvmphocvtes and large mononuclear IcucocNtes. III. Neulrophiles. IV, Eosinr.philcs. V, M\'eloc\tes {not found in normal blood). VI. Mast cells. do the granules differ in size but also in staining reaction as may be seen by employing the ' blood stains.' A drop of blood is spread thinly on a cover glass and dried, afterwards being stained with a mixture of acid and basic dves. The details of nuclear structure are not preserved, but the granules are clearly differentiated. With several of the blood stains the line granules stain purple or hlac and the coarse ones are red in some cells and blue in others. Only one sort of granule occurs in a single cell. Figure 171 shows corpuscles from such a preparation. Digitized by Microsoft® 148 HISTOLOGY. Cells containing coarse blue granules, which often obscure the nucleus, are called mast cells. (The German word mast, meaning food, was applied to them because of supposed nutritive functions.) They form about 0.5 % of the leucocytes in the blood. Along the blood vessels, especially in the mesentery, mast cells may be found in connective tissue if it is hardened in alcohol and stained with a basic stain hke methylene blue. Zenker's fluid, a preservative often used, destroys these granules. (The mast cells of connective tissue are larger than those in the blood, and generally have rounded nuclei. They have been said to arise independently of the "mast leucocytes.") Polymorphonuclear cells with coarse granules which stain red with eosin, an acid stain, are called eosinophiles [oxyphiles, acidophiles]. They form from 2 to 4 % of the leucocytes in the blood, a proportion greatly increased in certain diseases. Eosinophilic cells occurring in connective tissue sometimes have round nuclei. It is questionable whether such forms are derived from the eosinophiles which migrate from the vessels. The third type of granular cell, unHke the other kinds, contains fine granules, and these stain purple or hlac by taking both stains to some extent. They are called neutrophiles and form 70 to 72 % of the leucocytes in the blood. They are actively amoeboid and are the principal wandering cells of the body, leaving the blood vessels more readily than other forms. The relation of the various leucocytes to one another has not yet been determined. The first forms which appear in embryonic blood have rounded nuclei and are perhaps intermediate between lymphocytes and large mononuclear leucocytes. They resemble the young erythroblasts from which they may be derived. Many authorities consider it probable that there is a conmion origin for all the blood cells. Like the red cor- puscles the leucocytes in the adult are produced in the meshes of reticular tissue outside of the blood vessels; the lymphocytes chiefly in the l3Tnph glands, and the granular leucocytes chiefly in the red bone marrow where the red corpuscles also develop. The lymphocytes appear in the circu- lation before the granular leucocytes. An investigator (Engel) of the blood in pig embryos found that well defined leucocytes similar to lympho- cytes appeared first in pigs of 8 cms. Another investigator (Sabin) has recorded that in the lymph glands of an 8 cm. pig the lymphocytes are first recognizable. From these independent studies it seems that l)miphocytes appear in the lymph glands and in the blood at about the same time. "In the guinea pig there seems to be a connection between the time of the appearance of the polymorphonuclear leucocytes in the marrow and in the blood" (Jolly and Acuna). The granular leucocytes appear in the blood and in the marrow at first as cells with round nuclei. Such cells Digitized by Microsoft® >-J-.3 WHITE CORPUSCLES. I49 in the adult are found normally only in the marrow and are called myelo- cytes. They enter the blood when their protoplasm is full of the granules which develop gradually, and when their nuclei are polymorphous. Only in disease are myelocytes and erythroblasts found in the blood of adults but they circulate normally in the blood of young embryos. The important question, whether the leucocytes arise directly from the mesenchymal tissues of lymph gland and bone marrow, or from cells which have emi- grated into them from the blood vessels, has not been determined. The large mononuclear cells with round nuclei are thought by some to be cells from which both lymphocytes and granular forms arise. The granules may be secretory products. Eosinophihc granules were once thought to be transformations of the neutrophihc, occurring in old cor- puscles. Lately they have been regarded as the ingested fragments of red corpuscles, but the fact that they rarely, if ever, are mixed with neutrophilic granules is against this view. The form of granule seems to be determined by unknown factors early in the differentiation of the leucocytes, and to be fixed for a given cell after the first granules have appeared. In connection with the terms apphed to leucocytes it should be noted that those with basophile granules are not called basophiles as would be consistent, but mast cells. The non-granular lymphocytes and large mono- nuclear cells are, however, sometimes called basophiles because their protoplasm takes a pale basic stain. This is undesirable. Mast cells were originally called plasma cells, a term now appUed to oval cells derived from lymphocytes by an increase in their protoplasm (Fig. 49, p. 47). They have eccentric nuclei, and their non-granular protoplasm stains deeply with basic dyes. Plasma cells occur in connective tissue, but probably not in the blood; they are of pathological importance. The varieties of leucocytes may be reviewed as follows: Lymphocytes, 22 to 25 % of the leucocytes, are small (about the szie of a red corpuscle) or large (perhaps twice the diameter of a red corpuscle), non-granular, with round checkered nuclei. Large mononuclear leucocytes, i to 3 %, may be two or three times the diameter of red corpuscles. They are non-granular, or with few granules, and have pale vesicular nuclei, round or crescentic. Polymorphonuclear leucocytes, larger than red corpuscles, are gran- ular, with nuclei variously constricted or bent. They include, — Mast cells, 0.5 %, with very coarse basophihc granules obscuring the nucleus. Eosinophiles, 2 to 4 %, with coarse eosinophihc granules. Neutrophiles, 70 to 72 %, with fine neutrophilic granules. Digitized by Microsoft® ^5° HISTOLOGY. (yi) Img. 172. — Bl I irji Pl.A'l ES IJKSIDI- A Red C u r ■ PCSCLH. Blood plates or platelets are round or irregular protoplasmic structures, 2 to 4 y. in diameter, f'rom 245,000 to 778,000 ha\'e been estimated to occur in a cubic millimeter of human blood. They are readily reduced to gran- ular debris in ordinary sections but when well preserved and stained with Wright's blood stain it a]3pears that they have dark granular centers and clear peripheral zones (Fig. 172). They have formerly , r* . been interpreted as small nucleated cells, and as fragments of leucoc)'tes. Dr. J. H. Wright has recently shown that they are fragments of elongated pseudo]jodia of the giant cells in the bone marrow. Their peripheral zone is ecto- plasm and their inner granular part is endoplasm. Con- sequenth' they are non-nucleated. The giant cells are not always producing blood plates. Only certain of them show the pseuclopodia, which ha^x been observed extending into the bloofl \'essels. In the blood the ])lates exist for some time, as they are found in clots several da\'s old. Tlie function of the plates is unkno\Mi. In draAvn blood the\' rapidly adhere to one another forming masses, but not rouleaux. Sometimes they present irregular projections and so have been described as amoeboid. In the clotting of blood the plasma separates into a solid ])art, the fibrin and a thin tiuid, the scrum. The blood clot or thromljus con- sists of fibrin with the entangled corpuscles, a mass which contracts after it forms, squeezing out the serum. The fibrin is deposited (pre- cipitated ?) in slender threads which radiate from the blood plates and form nets shown in Fig. 173. Therefore the plates ha\-e been considered active agents in the clotting of blood and ha\'e been called tlirombocxles. In the blood of amphibia, s])inflle sha])ed nucleated cells smaller than their red corpus- cles [)ossess adhe>i\-e pi-opeilies and are also named tlu-omhocvtes. Since ^ ;[.;d c 1-^1: \MKN IS R \ Cdita's Clinical •:!'rsri KS }'"11RM1N, I 1 Ni; [.-ROM Hi ood Pi nal,,l,,K^.) Digitized by Microsoft® PLASMA. 151 the plates have been shown to be fragments of giant cells they can scarcely be homologous with the amphibian thrombocytes. Plasma is the fluid intercellular substance of the blood. It contains various granules some of which are small fat drops received from the thoracic duct. Others occurring in variable quantity are refractive parti- cles, not fatty, either round or elongated; they are known as haemato- konia (or haemokonia). In ordinary sections the plasma appears as a granular coagulum. Lymph. The contents of the lymphatic vessels is called lymph. It is a fluid which may contain the various cellular elements of blood in sniall numbers. Red corpuscles and polymorphonuclear leucocytes are occasional. Lym- phocytes are the most abundant cells, and some of them have considerable protoplasm and are phagocytic. The lymph fluid is not identical with plasma or with tissue fluids, yet all three are similar. Nutrient material from the plasma traverses the tissue fluids to the epithelial cells, certain products of which pass back into the tissue fluids. They may be taken up by the blood or by the lymph, first passing through the endothelial cells of the vessels. From the intestine much of the absorbed fat is transferred across the tissue spaces to the lymphatic vessels in which it forms a milky emulsion known as chyle. (The small lymphatic vessels containing it have been known as lacteals.) This example shows that lymph may exist in more than one form. In the subclavian veins it mingles with the blood plasma. In ordinary sections lymph appears as a fine coagulum, containing a few lymphocytes, and occasionally other corpuscles. Digitized by Microsoft® III. SPECIAL HISTOLOGY. BLOOD FORMING AND BLOOD DESTROYING ORGANS. Bone Marrow. Bone marrow is the soft tissue found within the central cavities of bones. Its source in the embryo is the vascular mesenchyma invading a cartilage which is being replaced by bone. Early in its development it contains osteoblasts and osteoclasts, and these cells may be found in adult marrow where it is in contact with the bone. The greater part of the mesenchyma becomes reticular tissue with fat cells intermingled. The meshes of the reticular tissue are occupied by an extraordinary variety of cells, most of which are called myelocytes (marrow cells). In ordinary sections the marrow appears as a com- pact tissue of small cells riddled i,vith large round holes. Under high magnili- cation the holes are seen to be fat cells the nuclei of which are here and there included in the section (Fig. 174). The reticular framework of the marrow con- sists of flattened cells generally seen cut across ; theirnuclei thenappear slender and elongated. The abundant meshwork of fibrils associated with these cells is not ap- fjg. i74.-i-U'si\n Bone Marrow. parent in Ordinary scctions. In the meshes e.. Eosinophilic myelocyte; e-b., erjlhro- „ fniinrl aintlt ri-lh- -hrfm vp] nrvlp^- mil blast; e-C.,erytlirocyte; f. c, part of the dlL lOUTiU- glUfll CiUi, prt7)n etOCyiCS, Viy- protoplasmic nm of a fat cell; q. c, 7 . t. • 1 j ul '7- r t7 •?• eiant cell ; my., neutrophyiic myelocyte , eLocyics which are neutrophilic, oasopliihc n-b., normoblast ; pm., prem^eloc\te , r., .,,.,. ,, , , , reticular tissue cell. ' " OX eosinopliilic ; erytlirocytes; lymplwcytes; and mature corpuscles both red and white. The giant ceUs of the marrow have a single polymorphous nucleus. They have been named therefore ' megakaryocytes,' in distinction from the multinucleate osteoclasts or ' polykaryocytes.' The nucleus is so large that it may be cut into several shces, and by combining these it has been found that the entire nucleus is a hollow sphere with perforated walls. The nuclei, however, are very irregular and some may be of other forms. With Wright's stain the protoplasm clearly shows an outer hyahne exo- plasm and an inner granular cndoplasm. It has been said that the latter 15- Digitized by Microsoft® BONE MARROW. 1 53 is divisible into two concentric zones, which differ from the protoplasm within the nuclear sphere. In ordinary preparations these details are not evident. A large number of centrosome granules (over one hundred) has been found, and pluripolar mitoses have been observed. A phago- cytic function has been ascribed to these giant cells, but it has also been denied. Their origin is unknown, but is said to be from the leucocyte series of cells. The important function of producing blood plates has but recently been established (see page 150). Premyelocytes are cells with large round vesicular nuclei containing one or two coarse chromatin masses, and surrounded by basic protoplasm free from specific granules. It is possible that these cells are parents of myelocytes. Myelocytes are cells larger than polymorphonuclear leucocytes, hav- ing round or crescentic nuclei and protoplasm containing a varying quan- tity of specific granules, either neutrophilic, basophilic, or eosinophiHc. The young cells have round nuclei and few granules. The oldest become the granular leucocytes ready to enter the blood vessels. Several genera- tions derived by mitosis intervene between the young myelocytes and the mature leucocytes. Most of the myelocytes are finely granular and neu- trophihc. Some are coarsely granular and eosinophilic; others contain the basophilic mast cell granules, but these are not well preserved in ordi- nary specimens. In certain diseases myelocytes enter the circulating blood, and they appear in smears as shown in Fig. 171, p. 147. Erythrocytes are generally found in clusters, some being young with vesicular nuclei, others being normoblasts with dense irregular nuclei such as have already been described. Rarely a nucleus may be found which apparently is partly extruded. Cup shaped corpuscles are seen in the tissue meshes. Lymphocytes are not a conspicuous element of the marrow, yet they are present and sometimes in disease become abundant. The relations of the blood vessels to the reticular tissue are of great interest. It has been thought that the endotheHum blends with the retic- ulum so that no sharp distinction can be made between the two. It seems more probable that the endothelium is merely more permeable than usual, by a freer separation of its cells. The same problem is presented by the blood vessels and reticular tissue of the lymph glands and spleen. The functions of the marrow are the production and dissolution of the bone, the storing of fat, the formation of granular leucocytes (neutrophiles, eosinophiles, and mast cells), of red corpuscles, and to a less extent of lymphocytes; to these some would add the destruction of red corpuscles as indicated by ingested fragments and intercellular granules. Digitized by Microsoft® 154 HISTOLOGY. Such marrow as has just been described is called red marrow. It occurs in the bones of embryos and persists in the flat bones of the adult, — those of the skull, the bodies of the vertebrae, the ribs and sternum, the epiphyses, and the heads of the humerus and femur. The shafts of the long bones contain yellow marrow which resembles ordinary fat tissue. Between the fat cells an occasional plasma cell or myelocyte may occur. Yellow marrow is formed from red by the development of true fat cells and not by fatty degeneration of myelocytes. In disease it may resume its blood forming function and become red. In starvation it becomes mucoid hke other fat tissue. Lymph nodules and Lymph glands. Lymph glands, haemolymph glands, and the spleen have a similar origin in the embryo. They are at first small dense areas of mesenchyma developing near blood and lymphatic vessels. The blood vessels extend into these areas producing a notch on one side of the mass, kno^vn as the hilus. Here in the adult the arteries enter and veins leave. After the invasion of the blood vessels the dense tissue is tranformed into reticular tissue containing lymphocytes. The lymphocytes occur especially in that part which surrounds the arteries. The veins tend to be at the periphery of the compact lymphoid tissue surrounding the arteries and to be asso- ciated with a portion of the reticulum which is comparatively free from lymphocytes. Lymphatic vessels spread over the surface and into the substance of the lymph glands, but they are absent from haemolymph glands and from the spleen. Lymph glands (also called lymph nodes) in early stages of develop- ment are shown in Fig. 175, the left half of which represents a younger stage than the right. The left portion shows a mass of reticular tissu^ and lymphocytes penetrated by an artery and a vein which join through capillaries. It is surrounded by a network of lymphatic vessels some of which are afferent and others, toward the hilus, are efferent. Such structures occurring in the adult are called solitary nodules [folhcles]. They are abundant in the walls of the intestine and respiratory tubes. Each is an area of lymphocyte production characterized by crowded nuclei which stain deeply with haematoxylin. Under. low magnification the nodule appears as a mass of dark granules (Fig. 244, p. 216) in the center of which a lighter area is sometimes seen, the germinaiive center. Here the cells are larger, resembling the large mononuclear leucocytes of the blood, and are frequently found in mitosis. They are thought to give rise to lymphocytes. The reticular tissue, which is concealed by the cells Digitized by Microsoft® LYMPH GLANDS. 15 = in its meshes, forms a coarser net in the germinative centers than in the fjeripheral part of the nodule. Blood vessels within the nodule are incon- spicuous and the surrounding lymphatic vessels are sometimes absent. L>'mpboid tissue. L\ inph Slims. L_\mpliatic \'essel L\mvibatic \'essel. Fig. 175. AffereiU hmjilialic \'t.-ssels^ Peripheral sinus. Lymph sinus. Capsule. Medullary cord. Trabecula. EttereiiL 1\ inpl)ati<: vessels. Fig. 176. Diagrams Repkf;sextixg Foi-r Stages in the Development oe Lymph Glands. Certain of the solitary nodules are merely transient local accumulations of lymphocytes which are diffusely distributed in the layer of reticular tissue found beneath the intestinal epithelium. Digitized by Microsoft© IS6 HISTOLOGY. In the small intestine and in the vermiform process, lymphatic nodules occur side by side, so as to form macroscopic areas visible on the inner surface of the intestine. They are broadly elliptical, and usually from I to 5 cms. long though occasionally much longer. From two to forty or more nodules may enter into the formation of one of these aggregate nod- ules [Peyer's patches] and they may remain distinct though adjacent, as in Fig. 241, p. 213, or they may be confluent. In the latter case they may be recognized by their germinative centers. Their structure is that of the solitary nodules. The lymph glands are round or bean shaped structures, varying in length from a few milHmeters to a few centimeters. They occur along the courses of the lymphatic vessels, as is shown in text books of anatomy. In producing a lymph gland, as seen on the right of Fig. 175, a connect- ive tissue capsule forms around the lymphoid tissue, into which it later sends trabeculae and plate-Uke prolongations. These may unite with similar trabeculae from the region of the hilus, as on the right of Fig. 176, thus making columns of connective tissue extending from one side of the gland to the other. Such a complete trabecular system is found only in the larger lymph glands. The capsule consists of connective tissue with elastic elements which increase with age. It contains also scattered smooth muscle fibers; the trabeculae are of similar structure. Beneath the capsule and surrounding the trabeculae, there is a reticular meshwork comparatively free from lymphocytes. This is called the lymph sinus. It is in free communication with the afferent and efferent lym- phatic vessels, and is also continuous with the reticulum of the dense lymphoid tissue. Its embryological relation to the lymphatic vessels has not been satisfactorily determined. Some consider that it is a network of endothelial tubes closely investing slender strands of reticular tissue; others beUeve that the endotheHal tubes are penetrated by the reticular tissue; and still others that the endothelium blends inseparably with the reticulum, into which the lymphatic vessels therefore open freely. It seems justifiable to maintain that endothelium and reticular tissue are distinct, though in close relation. All of the functions and appearances of the sinus can be explained if the endothehal lymphatic vessels are regarded as freely per- meable in the gland, by separation of their cells from one another. Fig. 178 shows the trabeculae highly magnified; between them and the dense lymphoid tissue are the lymph sinuses. Several organs can be divided into an outer and an inner portion, called cortex (meaning bark) and medulla (pith) respectively. The lymph gland is one of these. Its cortical part, shown in Figs. 176 and 179, con- sists of large lymphoid masses resembling nodules and containing germi- Digitized by Microsoft® LYMPH GLANDS. 157 native centers. These are sometimes called secondary nodules. The medullary portion includes cord-like prolongations of the nodules, called medullary cords. The secondary nodules often are incompletely separated from one another and the cords join to form a network. Both the nodules and the cords are enveloped by the lymph sinuses, and the trabeculae if present are in the midst of the sinuses (Figs. 177 and 178). The nodules and cords are both composed of lymphocytes in a close-meshed reticular tissue. The blood vessels of the lymph gland in part enter from various points in the capsule and nm in the trabeculae, but the chief vessels enter at the hilus. The artcrv divides into several branches which remain in 5 t/' e L\'niph ^^ "^c^ s.n.ises. •^o^*^?! ) M In Xu,, (, Flat ^_./i s-e^i-- Fig. 177. 1 11 17^ Fri'M \'i-:rtic\i. Sections niROLGii the Mi^di i la or \ I wirn Ctlvm) oi \n Ox. Fiq". 177. / 50, shows the medullary conis and traheculae cut leiis^thwise in its upper pait, ind cut across in its lower part. Both the cords and the trabeculae torni continuous networks. Fi^-. I7y, >( 240, shows tile fine reticular tissue of the lymph sinus, containincr a fe\\- leuc(.ic\tes. the trabeculae for only a short distance, and then cross the lymph sinuses to the meduUary cords. They extend through the axes of the cords into the nodules, giving off small branches which form capillary networks and unite in veins found at the periphery of the nodules and cords. The veins soon cross the sinuses and enter the trabeculae in which they travel toward the hilus. A central artery, surrounded by lymphoid tissue together with peripheral veins, is found not only in lymph glands but also in the spleen. The lymphatic vessels penetrate the capsule at several points and become involved in the lymph sinuses. Through these, partly in endothelial tubes, and partly in tissue spaces, the lymph flows toward the hilus which it Digitized by Microsoft® 158 HISTOLOGY. leaves in the efferent vessels, fewer in number than the afferent. Lympho- cytes are added to the lymph as it passes across the gland. Nerves to the lymph glands are not abundant. They consist of medul- lated and non-medullated fibers whicli form plexuses about the blood vessels, and supply the muscle cells in the capsule and trabeculae. They have not been found in the nodules and cords. X Capsule, Ti'abcculae, Corticnl "~ ^^'■' substa Germinal center of a secondary nodule. )ir^''~~ "^ Medullary >' y^'A^ " -'.^ substance. Til ^^": - I- *-rieX of Till.. Si o\-e. auditory (spiracular) groove, which is counted as the first gill cleft; it gives rise to the external auditory meatus and around it the auricle develops. The ectodermal groove connected with the second gill cleft disappears. Those of the third and fourth form a single deep depression on the side of the neck, called the cervical sinus, which persists only in pathological cases, and is a source of branchial cysts. The entodermal portion of the giU clefts in a mammal is shown in Fig. i88. The pharynx opens to the exterior at the mouth, ;;;, and divides posteriorly into the trachea, Ir, and oesophagus, oe. In the median dorsal line it gives rise to the an- terior lobe of the hypophysis, cut off at a. I., and in the median ventral hne to the thyreoid gland, t. The latter grows down through the hind part of the tongue, acquiring a pjosition in front of the trachea. Its branching terminal part becomes separated from its outlet, the foramen caecum, by the obhteration of its duct (called the tJiyreoglossal duct). Thus the thyreoid gland is a detached clump of endothelial tubules in front of the trachea. The entodermal ])ortions of the gill clefts are four paired lateral outpocketings. The first (i) extends to the auditory groove in the ectoderm, and it becomes in the adult the auditory tube (Eustachian tube) and the middle ear. It will be further described with the sense organs. The second pharyngeal pouch (2) disappears except as it forms a depression in the lower part of which the palatine tonsil develops. Its . iSS — Diagram of the Pharynx OF .\ Mammali.-\.n E.MBR^■o. , Anterior lobe of the h\poph\ sis; f. c. foramen caecum; m.. mouth; oe., oesophagus; p. b., postbrancliial bod\'; t.. th\ reoii.! , th.. th\inus; tr., trachea; 1. 2. 3. 4, the phai>nc;eal pi.>uches. Digitized by Microsoft® GILL CLEFTS. 167 epithelium may become that of the tonsil. The upper portion of the de- pression made by the second pouch probably becomes the pharyngeal recess [fossa of Rosennuiller]. The third pouch, near where it meets the ectoderm, sends a tubular diverticulum (tJi) down the neck behind the thyreoid gland; it continues into the thorax, lying ventral to the arch of the aorta (Fig. 189). The diverticulum loses its lumen and becomes detached from the pharynx; it forms the thymus. Besides this elongated structure, the third pouch produces a rounded clump of cells which becomes sepa- rated from the upper or anterior end of the thymus. This nodulus thymi- cus has been said to produce the glomus caroticum; but the latter is now generally regarded as a vascular mesenchymal structure. The nodulus thymicus has also been said to form a small body attached to the posterior sur- face of the thyreoid gland in the adult, and called the parathyreoid gland. The origin of the parathy- reoid glands, of which there may be four in man, two on either side, is still uncertain; and the fate of the nodulus thymicus is obscure. The fourth pharyngeal pouch (4) soon becomes Y-shaped by union with the pjostbranchial body (p.b.). The latter is an independent outgrowth of the pharynx, aris- ing near the fourth pouch, and considered either a rudimentary fifth pouch, or a structure not related to the pouches. It elongates and fuses Avith the thy- reoid gland, from the tissue of Avhich it is scarcely to be distinguished. Embryologists differ as to whether it forms any of the adult thyreoid gland. The fourth pouch itself produces a nodule of tissue which has been said to form the anterior pair of parathyreoid glands, but its fate is still uncertain. Since the derivatives of the first pouch are to be described with the ear, it remains to consider the palatine tonsils, as related with the second pouch; the thymus, as deriA'ed from the third; tlic thyreoid, from the floor of the mouth and from the postbranchial bodies; and the parathyreoid glands from the third ( ?) and fourth ( ?) pouches. Fig. 1S9. ; tlnnius, th., and lh\Te- oid, t.,of 2g mm. human embryo; p., .parathyre- oid gland [derived from the 3d pouch (?)]; p.p., parathj reoid gland [de- rived from the 4th pouch (?)]; p. I., pyramidal lobe ot the thyreoid ; ao., aorta ; v., Aena cava superior. (.After Ver- dun.) Palatine tonsils. The palatine tonsils are two rounded masses of lymphoid tissue, one on either side of the throat, between the arches of the palatef. They are covered by the mucous membrane or tunica mucosa, which throughout the digestive tract consists of several layers. The entodermal epithelium rests on a connective or reticular tissue layer, the tunica propria. A structure- Digitized by Microsoft® 1 68 HISTOLOGY. less basement membrane Ijcneath Ihe epithelium is called the mcmhrana propria. The epithelium, membrana propria, and tunica propria together form the mucous membrane. Beneath it, and sometimes not clearly sepa- rable from the tunica propria, is the siibiuiicoiis layer, or tela siihmiuosa. It is a vascular connective tissue Ijv which the mucous membrane is at- tached to underlying muscles or bones. All of the la}-ers named are in- volved in the tonsils which, hove\"er, are essentially lymphoid accumula- tions in the tunica projiria. The epithelium of the palatine tonsils is a stratified epitlielium of many laj-ers, with flattened cells on its smooth free surface, and columnar t.^W^<\„^f. ,_^^ ^ '*! t ' ir>. Fli, ion — A'h.KllCM. Sliri ION- OF A Hl'.MW P\L\I1N-|'- ToXSIL. a, StralifiLd fpilheliiiin ; b. liaseiiifiil nR-nibranr ; c. Umica picinia; d. li al.ci ulae ; e. dilTii^c lymphoid tissuu; f, nodules; h, capsule; i, uiulous ^lancK; k. stllaltd muscle. I. hlooil i esse] ; ' q, liils. (h roni Radasch.) cells Ix'neath. Its attached surface is invaded by connective tissue ele- vadons or papillae so that it appears wavy in sections (Fig. loo). The stratified epithelium hncs from ten to twenty almost macroscojiic depres- sions called tonsillar pits or fossiilac (cryptsK These are irregularlv cylin- drical and sometimes branched. :\Iany ])-mphoc}-les penetrate between the epithehal cells and esca])e from the free surface into the saliva, to be- come 'sahvary corpuscles.' In places the tonsillar epilhelium is so full of lymphocytes as to appear disintegrated. In the reticular tissue of the tunica propria, especiall}- around the jiits, there are many l)-mph nodules, some of which, are \vell dehned with germiaati\-e centers, but manv others are fused in indefinite masses. The lymphoid tissue forms the bulk of the tonsil. Digitized by Microsoft® PALATINE TONSILS. 1 69 The submucous layer forms a capsule for the organ, into which it sends trabecular prolongations. It contains many blood and lymphatic vessels, together with the secreting portions of mucous glands, and the branches of the glossopharyngeal n§rve and of the spheno-palatine gang- lion which supply the tonsil. Some of the small glands empty into the pits but most of their ducts terminate in the mucous membrane surround- ing the tonsil. They resemble other mucous glands of the mouth which are to be described presently. Beyond the submucosa is striated muscle, belonging to the arches of the palate and to the superior constrictor of the pharynx. Except that the palatine tonsils lie in depressions which correspond in position with the second pharyngeal pouches, they afford no evidence of their branchial relations. Only their epithelium is entodermal. The lymphoid tissue is mesenchymal. In these respects the palatine tonsils resemble the median lingual tonsil which forms the posterior part of the tongue (see page 184) and the more diffuse median pharyngeal tonsil on the dorsal wall of the nasopharynx between the openings of the auditory tubes. Irregular enlargements of the latter may obstruct the inner nasal openings, producing the 'adenoids' of clinicians (the adjective adenoid being synony- mous with lymphoid). The pits of the pharyngeal tonsil are smaller than those of the palatine. Thymus. The thymus arises from the two tubular prolongations of the third pharyngeal pouches, which meet in the median line as shown in Fig. 189, and become bound together by their connective tissue coverings. The lumen is lost, and the cells proliferate. They form a broad, flat, bilobed mass with a tapering prolongation up either side of the neck. The bulk of the organ is in the thorax, beneath the upper part of the sternum. At birth it weighs generally between 5 and 15 grams (about half an ounce), and is relatively a large organ. It increases in size and weight for some years after birth, probably until puberty, and then slowly atrophies. At 15 years it is said to weigh from 40-50 grams. It is considered an active organ even to the fortieth year, losing its functions with beginning o^d age (50-60 years). Then it becomes fibrous and fatty. The importance of the thymus has apparently been underestimated. The thymus is subdivided by connective tissue layers into lohes from 4 to II mm. in diameter, and these are similarly subdivided into lobules of about one cubic millimeter each. On either side all the lobules are attached to a cord of medullary substance, 1-3 mm. in diameter, as may Digitized by Microsoft® 170 HISTOLOGY. be seen if the gland is pulled apart. The medullary substance extends from the cord into the lobules (Figs. 191 and 192J where it is partially sur- 0^\f%, Thymic I corpuscles Connecth-e tissue. 1^^ «3h ^.^\ Transverse ,,-i--"; section of '/i blood vessel. cr ^ Medullary cord. Fir,, igi -From a Cross Section of thk Thymus of a Child, i Vhar and 9 Months Old. Y 21. Q irtica' su •)stat ce M edulla r>' substance. '~ © '^v® .,-^~ ,1* >^/'^^^^^i ■yi)a ^\y n ® ® ©8 Fi(,. 196. — Section of a Human P \RATH^RiiOiD Gi-and (Hubtr.) mus. It is not known that two pairs always occur. The parathyreoid glands may be lacking on one side, where in other cases as many as four have been recorded. Both pairs possess a similar structure unlike that of either the thyreoid gland or the thymus, but resembhng the corresponding epithelial bodies of the lower vertebrates. They consist of masses and cords of polygonal, entodermal cells, containing round nuclei with networks of chromatin. The protoplasm is pale, "almost homogeneous" or "slightly granular," sometimes containing vacuoles. Cell membranes are not promi- nent. Between these cells and the large thin-walled blood vessels which pass among them (Fig. 196), there is only a very small amount of connec- tive tissue. A capsule surrounds the entire structure. The blood vessels are branches of those which supply the thyreoid gland. Little is known of the lymphatics or nerves. Digitized by Microsoft® 176 HISTOLOGY. Gloiius CAKOTICUM. Tlie glomus caroticum [carotid gland] has already been described as a knot of blood \'essels ;it the bifurcation of the common carotid artery. It is a reddish bod}- "5-7 mm. long, 2.5-4 mm. broad, and 1.5 mm. thick." Between its thin walled, dilated capillaries there are strands of polygonal cells said to be chromaffine and prone to disintegrate fFig. 197J. ]Many nerve fibers, medulla- ted and non-medu Ha- ted, enter the glomus and a few multipolar ganglion cells are asso- ciated with them. In its arrangement of cells and blood vessels it resembles a para- thyreoid gland, and also the glomus coccyg- ciiiii which is far re- moved from entoder- mal structures. Since the nature of the glomus caroticum is undetermined, the three views regarding it may be mentioned. First, it has been con- sidered derived from the nodulus thymicus, which is now said to form a parathyreoid gland. Recently it has been found that the 'carotid gland' of Echidna comes from the second pharyngeal pouch, and the non-entodermal origin of the human glomus is xiot beyond question. Second, it has been considered ganglionic or paraganglionic in nature, so that it is classed with nervous structures. Third, it is considered essentially a vascular formation, containing strands of modiJied mesenchymal cells. De\'ELOPMENT .\ND StKUCTURE of the TOXGI'E. The tongue consists of two ])arts, an anterior and a posterior, which differ in origin and adult stmcture. Separating the branchial clefts from one another there are columns of tissue known as braiichiiil arclics. They come together in the median \'entral line to form the lloor of the mouth Fig. 1Q7.— Skction of a Part of the Glomus C \kotici <<]'- Man. (After Scliaper.) b.v., BU'od \'essels , e.v., efferent \-ein ; tr., trabei_ula, c.t., cu nectne tissue sci'tiiin. Digitized by Microsoft® TONGUE. 177 F\''.. iqs, — Fi-OoR OF TH1-: I'll\R^^■x oi' .^ 10 m>[ Ml'man Emhr'.c^, I-IV. Elrr.ncliial arches: t' . aiiLerinr part of the tongue; t-. second arcli, joining the posterior part of the tongue to\\'artl the median line. The thyreoid gland is dotted. The epiglottis extends over the 4th arch. (From McMurrich, after His.) as shown in Fig. 198. In this figure the upper jaw and roof of the uharynx have been cut away; the branchial clefts are seen as dark depressions bounded laterally by thin plates. The first branchial arch (i) is between the oral and auditory clefts. In the median ventral line an eleva- tion (tuberculum' impar) arises between this arch and the second; it becomes contin- uous with a larger ele\'ated portion of the mandibular arch to form the anterior part of the tongue (t'j. The second and third arches unite toward the median ventral line and there produce the jjosterior part of the tongue (t"). Be- tween the anterior and poste- rior parts is the opening of the thyreoglossal duct, later the foramen caecum. The epiglottis is an elevated part of the third arch separated from the posterior part of the tongue by a cur\"ed groove. In the adult, Fig. 199, the dorsum of the anterior part of the tongue is covered with papillae. These are chiefly the slender fili- jonn papillae and conical papillae, but knob- like forms, the jungijorm papillae, are scat- tered among them over the entire surface. Near the junction of the anterior and pos- terior parts of the tongue there is a V shaped row of larger papillae, generally 6 to 12 in number, called vallate papillae. Their name refers to the deep narrow depression which encircles them. Behind the apex of the V, Avhich is directed toward the throat, is the foramen caecum. On either side of the tongue, as indicated in the figure, there are from 3 to 8 parallel vertical folds (2-5 mm. long) occurring close together; these are the joliaic papillae. In the foliate and \-allate papillae the organs of taste are most numerous. The under sur- '* v_ /"/^^ / f.c^"^ ep. Fro. 199,— Thk TpPKR Sl.'RFACh; OK Till-; Ad "LT Tongue. C, Conical pap Ilae; ep., epiglotlis ; f,, tolia,te p; jjillae, f. C, foramen caecum ; ff. posilion of the (ili- form and In iLi:iform papillae ; 1.. Iciiticnlar p ipillae ; 1. t.. Ini.i^nal tonsil ; p. t. palatine tonsil ; v.. ^■allat^:; papi lae. Digitized by Microsoft® 178 HISTOLOGY. face uf Ihe longiie is free from eijithelial papillae; its mucosa resembles that Aviiich lines the mouth. The piosterior part of the tongue contains the lingual tnnsil, and has a nodular surface c L^ Cornirtcrl eriilhtlnim. . 1 /■' ■ ■ , ? Secondary t,. ■■:,:" --"■■''"- ,; /• "' ' ! ' .■ .' - _^-- Secoiidar> papillae ^z-T^h-r^''--- '"■■■■- ' • '■ ,. -I'r ^,-^;%',' |iapill:uj jf a fungiform ~'\>-^'^' ■:.:;^ - -. . '-/ ' ■ of V "%:-"ir Ohliqu^section '^ . ^<' : ;' [[ \ ' J ' ' '-V';'":' -^^^--^i Filiform Olahhlorm -», ■ ,. j, ' ■ X. ■ : .v ,;■ ^; -----^ papillae. papilla ':^ , ■- .. ■ - ....;..-- ■■■<;>■ Ner\-es. "^ \'ei„, .\rter' 1 — --A--*., Fascia lin.tcuae. Striaicil mus- cle tifiers. Fig. 201. — Fkrj.M \ Li i\-r,iTUDI.N'AL SlC'lION UF THE HiMAN TONIiUE, V 25. X, Epillieliuni showiiii^ postmortem liisiiitugratloii. in all the fungiform, vallate and foliate forms, together with both surfaces of the epiglottis. They arc destroyed with an infiltration of leucocytes, except those on the lateral walls of the vallate and foliate papillae, small numjjers of those on the anterior and lateral fungiform pjapillae, and those on the laryngeal surface of the epiglottis. In such places they are found in the adult. Each bud consists of two sorts of elongated epithelial cells, among which lymphocytes are frequently seen. Alost of the cells are supporting cells. These may be uniform in diameter or tapering toward the ends. Digitized by Microsoft® iSo HISTOLOGY. TuniLa 1 r prii Secondary papillae. Tasle hud. \'allate pai.illa. .. , Orifice r L^e ^ \ I ' ''i -^'^Kd^'^ '■cr Ls Sma I Epitlicllun Tunica projiria Tela subinucosa. Striated inuscle. %r Wi^i T- iij 1 rp lla. Tf /' y|0 .^ ^&, ) "! ' ^/,.- 4* .^ 1 (k y.-^V^ Muscli- hh rs ii i ^ 1 with F-^=.c 1 and longitudinal ^ceUdn. small ganyluin. liiiyuae Fig. 20J.— Vhktical Shctiox ov a Hi-man \'alt.atk Papilla. X 25. Tasle pin Supportii cells. .-Z).- O cs> «:r3' They are sometimes forked or branched below and at the free surface they may end in a short conical pro- cess. The peripheral halves of !>-« . the cells in a taste bud converge somewhat like the segments of a melon, so that their ends are ^ brought together in a small n area. This area is at the bot- tom of a little pore or short '' canal found among the outer- ■i-u„„,,, most flat cells of the epithehum. '""'"'■' Sometimes it is bounded by the supporting cells. The taste pore opens free!)' to the surface, but in oblique sections it may appear bridged as in '■^^ Fig. 203. Besides the support- ing cells wliich are found at the periphery of the bud and which terminate around or beneath the pore, Digitized by Microsoft® ^^^^- AL^,^^-^ c c .&,'- U^ St rati lied Opltllelllllll Fig. 203. — From a \'i Folia i r C3> K.'^ Skction of TASTE BUDS. l8l there are more slender forms in the interior of the bud, Avhich reach the pore. There are also a few flat ones confined to the lower half of tliebud. The iaste cells are slender stmctures, being thiclcened to accommodate the narrow nuclens. The nucleus is usually in the middle or lower part of the cell. Toward the taste pore these cells generally taper, and they end in a stiff refractive process which is a cuticular formation. These processes extend iato the deeper part of the pore but do not reach its outlet. The taste cells may have a triangular base, or end bluntly. Their protoplasm is darker than that of the supporting cells. Fibers between ^ " ^S:;^!] ' ^--^-O*,^ I'ibei'S \\ ilbin tlie binls. the buds. ^e>- Fibers oxtrUiri.i,- I, /<7^C^ - \ ^__ Coniiecti\e tissue, :i bud, CoiiT]ecti\-e tissue. Fpithelium Fig, 204. — From ,1 \'ertic,al Skctio,^ ok tme l"oLi,\rE I'apiila oi-" a Raf:bit, )', 220, The nerves to the buds are branches of the glossopharyngeus, asso- ciated Avith microscopic sympathetic ganglia. These nerves, both medul- lated and nonmeduUated, make a thick plexus in the submucous con- nectiA-e tissue. The terminal branches probably end in part in bulb- ous corpuscles, but most of them, as nonmeduUated fibers, enter the epithelium. Some are found betAveen the taste buds, extending to the outer epithehal cells generally without branching (Fig. 204). Others enter the buds, Avhere they di\'ide into coarse varicose branches which reach almost to the taste pore. They end freely, Avithout uniting with the cells or anastomosing with one another. The terminal branches are Digitized by Microsoft® lS2 HISTOLOGY. chiefly in relalion willi the taste cells; to a less extent they arc said to ramify about certain of the supporting cells. The taste cells are belie\-ecl to transmit to the ner\-es the stimuli receiyed at the taste pore. The tunica propria of the mucous membrane, a loose connecti^'c tissue layer containing fat, is not sharply separated from the denser submucosa. At the tip, or apex linguae, and oyer the dorsum, the submucosa is par- ticularly tirm and thick, forming the jaseia linguae. Three sorts of glands branch in the submucosa and may extend into the superficial part of the muscle layer. These are the serous glands found near the yallate and folliate papillae; mucous glands occurring at the root of the tongue, along its iDorders, and in an area in front of the median yallate papilla; and the .Mudiaii bcctiun uf a iKidiile lilHllielium DiftLi^L 1\ miilioid lisbue -.^ L} niph nodules. ^ r-^ UucL uf a mucous ylaiid. jy^-'^'.M - '- V; - }KP,. lel um _ . . re,-., .Ik r\ / ^" ■■' 11 n ulc ; Tun lH l.l-r,[ >iia Fihi Ills Lai- sulc Blood \tssel Tli;. 2ns — From \ Si o i kin o\' -i"hi-: Linoi \l Tonsil ok \n A in i- r Man. ■-, 20 I, i'it oonlaiiiing- lfUC £, a> ,j^ I Fi<; :'f/i— From a Thin- Skciion of a Lingcai. Tonsil or- v Man. > left tlie c[^itlielium is free Irom leucocytes, on the ri,L,^lit main- leucocytes are wai hvoid bone, attains its greatest height in the middle of the tongue, and be- comes lower anteriorly until it disappears. It does not extend clear through the tongue since it ends 3 mm. beneath the dorsum. The muscles of the tongue are partly vertical (genioglossus, Jiyoglossus, and vertical is linguae muscles), partly longitudinal (styloglossus, chondroglossus, superior and inferior loiigilnJinalis linguae muscles) and partly trans\'erse (the Irans- vcrsus linguae muscle). The glossopalatine muscle of the jialatine group Digitized by Microsoft® 184 HISTOLOGY. also enters the tongue. Some of the muscle fibers are oblique but many of the bundles cross at right angles. In the connective tissue between them, meduUated nerves are abundant. Some of these are sensory nerves to the mucosa but many are the lingual branches of the hypoglossal nerve which supply all the tongue muscles except the inferior longitudinal; that one is supphed by fibers from the chorda tympani. Sensory spindles have been found in the lingual muscles. The posterior part of the tongue is occupied by the lingual tonsil, this term- being a collective designation for a considerable number of rounded masses of lymphoid tissue. Each of these is from i to 4 mm. in diameter, and is situated in the tunica propria so that it causes a low, macroscopic elevation of the epithelium. In the center of the elevation there is a punctate depression, or pit, lined with stratified epithelium. Around it the lymphoid tissue is partly separable into nodules with germi- native centers (Fig. 205). The entire lymphoid structure is bounded by a sheath of connective tissue. Numerous lymphocytes enter the epithelium, and pass between its cells to the free surface where they escape into the saliva. The temporary disintegration of the epithelium, due to this cause, is shown in Fig. 206. In all these details the Ungual tonsil is essentially like the palatine tonsils. Mouth and Pharynx. The lining of the mouth, like the covering of the tongue, consists of epithehum, tunica propria, and submucosa. At the lips toward the line of transition from skin to mucous membrane, hairs disappear from the skin. The epithelium becomes abruptly thicker but more transparent as it crosses the line. Its outer cells are still cornified, but they are not so flat and compactly placed as in the skin. The deeper cells appear vesicular. Within the mouth, except on the tongue, cornified cells are absent. Gran- ules of the refractive horny substance, keratohyalin, are said to occur in the outer cells, even in the oesophagus. The outer surface of the epithelium is smooth, but its under surface is indented by many connective tissue papillae, which are particularly long and slender in the "hps (Fig. 207) and gums. Cilia occur on the epithelium in the highest part of the nasal pharynx, and in the fetus over the oral part also, and even in the oesoph- agus. They persist only in the nasal pharynx. The tunica propria, as is generally the case in the digestive tract, has few elastic fibers. Some of its tissue is reticular and in this, lymphoid accumulations are frequent; they may extend into the submucosa. On the oral surface of the soft palate there is a layer of elastic tissue between the propria and submucosa. A similar layer is found in the oesophageal end Digitized by Microsoft® GLANDS OF THE ORAL CAVITY. 185 of the pharynx. It increases in thickness upward, at the expense of the submucosa, so that it forms a thick layer in the back of the pharynx in con- tact with the muscles, among the fibers of which it sends prolongations. This elastic layer, as the jascia plioryiigobasilaris, is attached to the base of the skull. In most of the oral region there is no shaip line of separation between the propria and the submucosa. The latter ma}- Ije a loose layer contain- ing fat, and allowing considerable movement of the mucosa, or, as in the gimis and hard palate, it may be a dense layer binding the membrane closely to the periosteum. In the submucosa are the branches of various litheliu \ ^ ^ (- Tii'Ti prc^jiri SuhiDLic ST / Ftc -X'krtical Section through the Mucous Membrane of the Lip of an Adult M an. I, F'npilla ; 2. excretory duct : the lumen is cut :it only one point ; 3, accessor;- ffland ; 4, a brancii of the excrelnrx' rluct in trans\"erse section ; 5, glancl bodies grouped into lobules by coiniecti\ e tissue ; 6, a Inland tuiiulein ti"ans\erse section. glands. On the inner border of the hps and the inner surface of the cheek there are sebaceous glands without hairs, which first develop during puberty. This type is described Avith the skin. The other oral glands are considered in the followina; section. Glands of the Oral Cavity. In the general account of glands (page ^2) it has been stated that serous gland cells Avhich produce a watery albuminoid secretion should be distinguished from the mucous gland cells which elaborate thick mucus. When examined fresh, serous cells are seen to contain many highly refrac- Digitized by Microsoft® iS6 HISTOLOGY. tive granules. In fixed ])rei)arati(jns they may appear dark and granular (empty of secretion j or enlarged and somewhat clearer (full of secretion), as shown in Fig. 34, ]). ^2. The round nucleus is generally in the basal half of (he cell, not far from its center (Fig. 208). ^lucous cells when fresh are much less refrac(i\'e than serous cells. In fixed preparations they are typically clear since (he large area occupied by mucous secretion stains Mrii). IT (,.__ \ '• -^ -y Mucous glands. Serous glands. ;, 20^ — SbCTH tNS b, l^nipt} mucins ctlls , c, nuicim 1 I l;l Its, 1 RriM Ll \( .L" \l GlANPS, IlI I S l i, 4 I IIKIWKI N Ml i/nrs A.N'D SkROI'S (tI.ANI' Ci I l.S fill illi: 1 HFFERENXKS i-Xi'etKMi ; d. luniLii 01 the luhuli;. 240 faindy. Fully elal)orated mucus, howe\-er, ma\' Ije cobired intensely AAith certain aniline dyes, mucicarmine, and E)ela(ield's haemato.wdin. In cer- tain types of mucous cells (he pale secredon area is large in all stages of ac(i\'ity. When full of mucus, the nucleus is )]a((ened against the base of the cell, and when emiity, the nucleus becomes more o\'al ^vithout essen- tially changing its position (Fig. 208). This differs from (he type of mu- cous cell found in the gastric epithelium in which (he secretion area varies consider- ably with the elaboration and discharge of secretion fFig. 3:;, p. -^^z^). Glands ma}- consist entireh' of serous or of mucous cells, Ijut frequenth" they in- clude cells of bo(h sor(s and are called mixal g/aii'Js. The mixed glands con- tain some purel}- serous tulxiles oraheoli; the rest consist of both mucous and serous cells, so arranged that the latter 3™ appear nrore or less crowded a\\-av from the lumen. Often (he)' form a layer outside of the mucous cells partlv encircling the tulnde or alveolus and constituting a crcsccnl [demilune]. Tlu-y are shown in Fig. 216. The serous cells of the crescent are in connection with the lumen ])y means of secretory capillaries (p. 2,6) which branch over their surfaces, ending bhndly, after passing between the mucous cells (Fig. 20,)). Sometimes liileixullula (-.'ipill.ir} FlC. 2og — FriiM a SECTICiX O!" t Sl■l'.^^AXII.LAK^■ Cti.a.nd mi-- a D Digitized by Microsoft® SEROUS ORAL GLANDS. 107 the cells of the crescent are directly in contact with the lumen. Since the serous crescents are always associated intimately and somewhat irregularly with mucous cells, they were naturally interpreted as a functional phase of the latter. It is probably true that some crescents rejjresent empty mucous cells which have been crowded from the lumen by those full of secretion. No secretory capillaries lead to such mucous crescents, A^'Jiich moreover are not aljundant. Another sort of crescentic ligiu'e is made by the basal protoplasm in mucous cells otherwise full of secretion. Fi- naUy, in oblique sections, stellate cells associated with the Ijasement mem- brane may resemble true crescents. The oral glands include serous glands, mucous glands, and mi.xed glands to be described in turn. Serous Glands. The serous oral'glands are tlie [larot- id glands and the serous glands of tlie tongue [v. Ebner's glands]. The latter are branched tuljidar glands limited to the vicinity of the vallate and foliate papillae. Generally they open into the grooves which bound these papillae. Their ducts are lined with simple or Math stratified epithelium, A\-hich is occasionally ciliated. Their small tubules consist of a delicate ''""■■ ^lo. — skction. of \ serous gi,-vnd I^I^OM Tflh: 1 ONGL-K OF A ,MoL"SF. X 240. mcmhrana propria or basement mem- Prepared b> coigrs method, a precipitate has formed in the ducts. The right brane, Avhich surrounds the low columnar lower iiart of the figure has hecn com- ' pleted b\ addmy tlic cell outlines. or conical serous cells. In this simple epithelium, cell waUs are lacking. With special stains and high magnification an outer dark granular zone has been distinguished from the clear basal portion of the cell which contains the nucleus. The lumen of the tubules is \-er}- narrow and receives the still narrower intercellular secretory capillaries (Fig. 210). The parotid glands are the largest oral glands. Each is situated in front of the ear and is folded around the ramus of the mandible; its duct, the parotid duct [Stenson's], empties into tlie mouth opposite the second molar tooth of the up]"ier jaw. The parotid gland is an organic, branched serous glanrl, suljdi^-ided into lobes and lobules. Tiie acccssorv parotid gland appears as a loljc scjjarated from the others. The parotid duct is characterized Ijy a thick memljrana jirojiria and consists of a two lavcred columnar epithelium \\-ith occasional goblet cells. As the duct branches Digitized by Microsoft® iSS HISTOLOGY. repeatedly, the e})ithe!iinn becomes a simple columnar epithelium, after being pseudostratified, with two rows of nuclei fFig. 27, p. 28). Possibly the epithelium near the outlet of the duct is also pseudostratified. The excretory portion of the duct is follo\\-ed by the secretory part formed of simple columnar cells with basal striations, jjerhaps indicative of secretory activit}'. As shown in the diagram. Fig. 211, and in the sections, Figs. 212 and 213, the secretory duct becomes slender, making the intercalated ducts. They are lined by fiat cells, longer than they are Avide, and these form a continuous layer with the large cuboidal serous gland cells of the terminal ah'eoli. The gland cells when empty of secretion are small and ) ^'^ ^:-^^ -, Excrctorv pi / '"'^' Fat ctlN End pi. Intercalau (I duct 'f"^\l cf '^^^. Fli .. 211 — Dl -\GR \M OP" THE Hi.\M,\N Parotid (TiI^and. Fii;. 2I2,^Skction of THhi: Parotid Gland of ax Aoi-LT Man, ' ' 2^2. Tht vui'\ iKinow Innitn of the alvcolu-tubular eiul pieces is not shuwu. darkly granular, and when full are larger and clearer. Thev rest upon a basement membrane containing stellate cells. Intercellular secretory cap- illaries end blindly before reaching the basement membrane. The alveoli of the parotid gland are someAA'hat elongated, and are branched. Between them there is vascular connecti\-e tissue containing fat cells. In flenser form it surrounds the lobides and lobes of the gland, and the larger ducts. The ducts which are found in the connective tissue septa are called interlobular ducts, in distinction from those which are surrounded by the ahx-oli in which they and their branches terminate. The latter are intralobular ducts. The)- are smaller and have less con- nective tissue around them tlian the interloljidar ducts, of which however Digitized by Microsoft® SEROUS ORAL GLAXDS. 189 F t el Al Intercalated (1 t longitudinal se t cross se t ^'i^'^-^ they are the continuations. The arteries generaUy follow the ducts from the connective tissue septa into the lobules, where they produce abundant capillary networks close to the basement membranes. The veins derived from these soon enter the interlobular tissue and may then accompany the arteries. Lymphatic vessels also follow the ducts and branch in the interlobular connecti^-e tissue where they terminate. Only tissue spaces have been found within the lobules. The nerve supply requires further investigation. Sympathetic nerves from the plexus around the carotid artery accompany the blood vessels into the parotid, and by controlhng the blood supply have an important bearing upon secretion. The great auricular nerve, from the second and third cervical nerves, enters the gland, and branches of the facial nerve are involved in it, but branches from the otic ganglion are considered the essential ner^'es to the gland cells. In the other salivary glands which have been more thoroughly studied, nonmeduUated fibers from the sympathetic gangha, either outside of the gland like the otic or from microscopic ganglia along its larger ducts, form plexuses beneath the base- ment membranes. Fibers from these plexuses pene- trate the membranes, within which they form another network before ter- minating in contact with the epithehal cells. Their endings may Ijc simple or branched, and are varicose. Free sensory endings of medullated fibers are said to occur in the epithehum of the ducts. Alucoits Glands. The pure mucous glands of the mouth are simple branched alveolo- tubular glands found only on the anterior surface of the soft palate and on the hard palate (palaline glands), along the borders of the tongue (lingual glands), and in greater numbers in the root of the tongue. There they may open into the tonsillar pits through ducts lined with columnar epi- thelium., sometimes ciliated. The wall of the tubules consists of a struc- tureless basement membrane and of columnar mucous cells, varying ac- cording to their functional condition as shown in Fig. 20S, I-II. The F THr P R 1 F \ b W Digitized by Microsoft® IQO HISTOLOGY. empty cells are smaller than the others, and the nuclei, though at the base of the cell and transversely oval, are not as flat as in cells full of secretion. Seldom can cells be found completely occupied by unaltered pirotoplasm. A single gland, or even a single alveolus, ma}' contain cells in different phases of secretion, as is clearly seen when special mucin stains are used. Secretory capillaries are not found in the purely mucous glands. Mixed Glands. The mixed oral glands are the sublingual, submaxillary, anterior lin- gual, labial, buccal, and molar glands. They all possess crescents of serous cells such as are to be described in the largest glands of this group. — the sublingual and submaxillarv. End pieces. Fii"; 214. — Diagram of iiiK Human Sui:lin(.i. al (iland -f'Z'SSSrf^, J^- ScLlet I \ 111 ^ i_ resceiils. Mucous cells. - E 1 nd \essel. Fh. 215. — SkCIIoN of IMF Si_-1!L1N. .UAI. Gl-AND FRc">M \ M.\N OF 23 \'E \RS. Si:i The suhliiigiiiil glands are two groups of glands, one on cither side of the median line, under the mucous membrane in the front of the mouth. The largest com]>onent is an alveolo-tubular stmcturc emptving bv the diicliis siiblingitalis major on the side of the jrciuiliiiu linguae. The main stem and the principal branches of the large sublingual duct are lined liv a two-layered or pseudostratihed columnar epithelium, as in the parotid duct. They are surrounded by connective tissue containing manv elastic hbers. Ducts less than .05 mm. in diameter ha\'c a simjile columnar epithelium, which in a few places becomes low and basalh" striated to form the secretory ducts (also called salivary ducts). As shown in the dia- gram, Fig. 214, the secretory ducts are \-ery short, and narrow intercalated ducts are ab.^ent. Tlie tubules are surrounded bv basement membranes Digitized by Microsoft® MIXED ORAL GLANDS. I91 containing stellate cells, and consist of both serous and^^mucous cells. The crescents are often ^•ery large and include many cells. Only the serous cells are provided with the branched intercellular secretory capil- laries. The connective tissue between the tubules and lobules contains many leucocytes. The nerves are arranged as described for the parotid gland. The gland cells are supplied Ijy sympathetic tibers from adjacent sublingual ganglion cells, about Avhich fibers from the chorda tympani may arborize. The latter arc said not to proceed directly to the gland cells. Sensory nerves to the ducts may come from the lingual Ijranch of the man- dibular nerve. Besides the gland just described there are from 8 to 20 small separate A 1 scent iionsistni^^ul" t-iL,lu btrous cells. Coniitili\ tissue. a. Fig. 2in — SliCTIoN MF A Hu\f\N SlHLINGI M. GlANH 2^2. ahx'olo-tubular gkmds closely joined to it, and described as part of the sub- lingual gland. They open Ijy sejjaratc duels, the diiclns suhU)i git ales minores. Thev all ( ?) consist almost exclusi\"ely of mucous cells. The suhmiixillary glands arc branched ah-eolar glands, in part tubulo- alveolar, found Avithin the loAver border of the mandible, each being drained by a submaxillary duel [Wharton's] which 0]jens on the sides of the frenu- lum linguae near its front margin. Its oritice ma)- he lined Ijy stratified epitheUum, but this soon gives place to the two layered form. Secretory ducts are well de^■eloped (Fig. 217) and their striated cells contain a yellow pigment. The intercalated ducts, which are lined with simple cuboidal epithelium, lead to terminations of tAvo sorts. iMost of these consist en- Digitized by Microsoft® 192 HISTOLOGY. tirelv of serous cells. The others are mixed, but the crescents are small, composed of onl}' a few or even of single serous cells. Secretory capillaries r-' i. ^ ^ (Oil ■"- '■?> El d \ essels "^L ct r\ duct. Secietory duct. '^ -^c -. y ^ Cof nt ^'®., iTittTLalated 'i^'el it tf^ iliicts. d ' ■ Mucous cells. , i ( res- cent. Stious end piece. Fat cell. FlC 217.— Hi \GR.AM OF THE HlJ.MXN FlG. 2l'^ — S l-""CTION Ol" THE Si 'BM A XILLAR^' GlAND FROM Slt-.m.axili.arn Gi-ANTi. a Max cu 2;^ \'i-:-\ks. X So. such as have ahx-ady been described, are rehiled only to the serous cells. Elastic tissue surroundinp:; the ah-eoli has Ijeen thought to aid in expelling '^^^^^^l ^V-'^''^--^^J^^ A>1 V^ ■.«»^ ^ Ccinnccti\ e tissue. Lumen. Crescent. Sccretor\" duct. Fig. 2in.— Si-XTiciN <'i< the Si t.m wm.i Ah;\ ('.i.\Nn m- ,\x Aiu'lt JM\N. ' 252. the secretion through the ducts. It is laioAvn that the secretion is ehmi- nated from the gland cells under high pressure, and so would not be Digitized by Microsoft© MIXED ORAL GLANDS. 1 93 checked by this action of the elastic membranes. The nerves are sympathetic fibers from the submaxillary ganghon and microscopic gangUa along the ducts. The chorda tympani does not send fibers directly to the gland cells. Sensory nerves may be derived from the branches of the mandibular nerve. In the oral glands, not infrequently degenerating lobules occur, char- acterized by abundant connective tissue between tubules with wide lumens and low gland cells. Sometimes they are surrounded by leucocytes. The Development of the Digestive Tube. The early development of the entoderm has been described in the section on general histogenesis (page i8). At first it forms a layer lining the blastodermic vesicle. Then by a process of folding and constriction the 'pharynx' develops from its anterior part so that the entire entoderm is shaped somewhat like a chemist's retort. The bulbous expansion is the Hning of the yolk sac. An analogous stage has been described in the chick embryo (Fig. 20), where, in place of a thin walled yolk sac, there is a soUd mass of yolk-laden entoderm. From the posterior wall of the yolk sac an entodermal outpocketing is produced, which rapidly becomes long and slender. It is called the allantois (Fig. 220, a/.). At first the allan- tois is directed posteriorly but soon it swings ventrally and then, as in C, it passes from the hind end of the digestive tract along the ventral body wall into the umbiHcal cord. The part within the cord becomes a strand of cells. Within the body, that portion of the allantois which is toward the umbilicus or navel, becomes subsequently a fibrous remnant, the urachus, which leads from the navel to the bladder. The bladder is the dilated lower part of the allantois, and is therefore Uned with entoderm, being embryologically a part of the digestive tube. In mammaUan embryos the allantois and the intestinal tract connect freely at their posterior ends, and the entodermal area common to both is called the cloaca. Here the entoderm comes in contact with the ectoderm and forms the cloacal membrane, a structure comparable with the oral membrane. After this membrane disappears there is no apparent hne of separation between the ectoderm of the skin and the entoderm of the cloaca. In this region in both sexes a conical elevation, the genital papilla, is formed, and the cloaca with its lateral walls closely approximated is found within it. Gradually the allantois becomes divided from the intes- tinal tract as shown in Fig. 220, B, C, and D. The mesenchymal tissue between them thus comes in contact with the ectoderm to produce the perineum which divides the cloaca into the urogenital sinus ventrally and the anus dorsally. In E, the bladder is seen to terminate in the urethra which in the male is considered to be chiefly an elongation of the ecto- 13 Digitized by Microsoft® 194 HISTOLOGY. dermal part of the urogenital sinus; only the part toward the bladder, which corresponds with the urethra in the female, is described as ento- dermal. As already noted there is no line of demarcation between the germ layers at this point, and a portion of the female urethra is by some considered ectodermal. The bladder is to be described with the urinary organs and the urethra with the genital organs. Returning to the intestinal portion of the entodermal tract, it is seen that in early stages, A, the yolk sac extends from the pharynx nearly to the Fig. 220.— Stages in the Development of the Digestive Tube. A, Kabbit of q days. B, Man 2.15 mm. (after His). C, Pig, 12 mm. D, IMaii, 17.8 mm. (after Thyng). E, Man, aljout 5 months, a., Anus; al., allantols ; bl.. bladder; cae., caecum ; cl., cloaca ; du., duodenum ; I. i., large intestine; oe., oesophagus; p., penis; ne., perineum ; ph., pharynx ; r., rectum; s. i., small intestine ; St., stomach; u. c. umbilical cord; ur., urethra; ura., urachus ; u. s., urogenital sinus ; v. p., vermiform process; y. s., yolk sac ; y. St., yolk stalk. posterior hmit of the entoderm. With further growth a posterior intestine becomes formed by folding or constriction, comparable with the pharynx in front (B). The connection between the yolk sac and the intestine be- comes a slender yolk stalk, a part of which is shown in C and D. Later it loses its continuity and the detached yolk sac remains until birth as a small vesicle at the distal end of the umbiUcal cord, with which it will be described later. The yolk stalk which extends from the umbiUcus to the intestine should be completely resorbed. It may persist as a fibrous cord liable to produce intestinal obstruction, or the part near the intestine may Digitized by Microsoft® ■M- DIGESTIVE TUBE. I9S remain as Meckel's diverticulum. This is a blind pouch of intestine, usually less than four inches long but sometimes much longer, found on the small intestine some four feet from its termination. Anterior to the yolk stalk the entodermal tube forms successively the pharynx, oesophagus, stomach, duodenum, and the greater part of the small intestine; posterior to it, the remainder of the small intestine, the large intestine and the rectum. The rectum terminates at the anus which is formed as an ectodermal inpocketing closed in embryonic life by the anal membrane. Rarely this membrane or the adjacent rectum remains im- perforate at birth. A transient embryonic extension of the intestine be- yond the anus toward the tail is known as "post-anal intestine." It early disappears, and has not been drawn in Fig. 219. The stomach is a dilated portion of the tube at first vertically placed in the median plane (C) but later so turned that its left side is ventral (or anterior), as in D. The duo- denum is a subdivision of the small intestine, the remainder of which is arbitrarily divided into the jejunum (the anterior two fifths) and the ileum (the posterior three fifths). Where the ileum joins the large intestine a blind outpocketing of the latter occurs, consisting of the caecum and its slender prolongation the vermiform process (processus vermiformis). At a certain stage (C) the intestines make a simple loop of which the large intestine forms the posterior or lower limb. To produce the arrangement characteristic of the adult, the loop becomes twisted, as in D, so that the large intestine crosses the small intestine not far from the stomach; thus it is possible for the large intestine nearly to encircle the small intestine which becomes greatly convoluted, without, however, changing its fundamental relations. Besides the vermiform process and caecum, the large intestine includes the ascending, transverse, descending and sigmoid colon, the last terminating at an arbitrary line at the rectum. The rectum proceeds to the anus, but not straight as its name impUes. The entoderm forms only the epithehal lining of the digestive tube and that of its associated glands. (Besides innumerable accessory glands these include the Hver, pancreas, and the lungs.) Around the ento- derm, the mesenchyma forms successively the following layers, — the tunica propria which contains the reticular tissue and lymph nodules, and the muscularis mucosae, a thin layer of muscles. The epithelium, tunica pro- pria, and muscularis mucosae together constitute the mucous membrane. It rests on the tela submucosa, a vascular connective tissue layer containing the sympathetic plexus submucosus. The submucous layer is followed by the tunica muscularis. This consists of two or more layers of muscle fibers between which is the sympathetic plexus myentericus. Beyond the mus- cularis is the connective tissue tunica adventitia in case the intestinal tube is Digitized by Microsoft® 196 HISTOLOGY. uncovered by peritonaeum, or the tunica serosa if the peritonaeum is present. The following aceount of the subdivisions of the digestive tube is essentially a description of modifications in these fundamental layers. Oesophagus. The oesophagus is a tube about 9 inches long, the several layers of which are continuous anteriorly with those of the pharynx, and posteriorly with those of the stomach. It is lined with a stratilied, many layered epithelium like that of the pharvnx. The free surface which is smooth but thrfiwn intf) coarse longitudinal folds, (Fig. 221J is covered with 5. .'i . . ;''tj.Ci'i' . SUalified (^jiithe- - hum Mucous Tuiiicn pri>[iri,t membrane / / nuK Msac, /' SiibniLicosa. '■ A. ' ^'yrf falls .-»*", ~ I* Group uf fat clI] / Lxmiili Hoilul. ^ Tunica adventitia MiK Mils L;laini Img. 221 — TR\Ns\tRSE SectH'N ok rHh I'nri'R Third o[^ ti[k Hi'.man Gesurhagi. s X 5- squamous cells; the basal surface is indented by ]iapillae of the tunica pro- pria. A muscularis mucosae, consisting of longitudinal smooth muscle fibers, arises at the le\el of the cricoid cartilage and continues into the stomach. At its anterior end it begins as scattered bundles inside the elastic layer of the pharynx, and as the muscles increase to form a distinct layer, the elastic lamina terminates. Beneath the muscularis mucosae is the submucosa, containing the bodies of the oesophageal mucous glands. They are tubulo-alveolar branched glands, with bodies about 2 mm. long, and closely resemble those of the mouth. Crescents and serous cells are absent, although empty cells may suggest the latter. Their ducts pass Digitized by Microsoft® OESOPHAGUS. 197 ft //IP'^if'^ f '"^ ^ ^^ ^ F > -, x^ spirally through the muscularis mucosae and tunica jjropria, entering the epithelium where it projects outward between the connecti\'e tissue papillae. The ducts generally slaat toward the stomach. The large ones are lined with stratified epithelium, often ciliated, and sometimes they present cyst- hke dilatations. The smaller ducts are of simple epithehum. Lymph(_>cytes may be numerous along the ducts, forming solitary nodules near them in the tunica propria, and extending into the submucosa. Sometimes the glands show signs of degenera- tion. Their number varies greatly in different individuals. Usually they are most abundant in the upper half of the oesophagus. A second type of oesophageal glands closely resembles the car- diac glands found in the oesophageal end of the stomach. The oesopha- geal cardiac glands (Fig. 222) occur in the poste- rior or lowest 2 to 4 mm. of the oesophagus, and also in small numbers at its anterior end be- tween the levels of the cricoid cartilage and the fifth tracheal ring. The latter group is said to be absent in about 30% of the cases examined. The bodies of the oesoph- ageal cardiac glands are confined to the tunica propria, and their ducts enter the epithehum at the summit of a connective tissue papilla. Their ducts have many branches, fined tfiroughout with simple columnar epithehum, and this form of epithelium may spread around their outlets in the lumen of the oesophagus. Because of this, when the ocso]jh- agus is opened, the anterior cardiac glands may appear macroscopically on its lateral walls as small erosions of the fining. The secreting cells of the cardiac glands contain round nuclei and granular protoplasm. Although ■■iii>- [S.hn/- (-,. 222.— LoNCrruDiNAL Section throi;gh tin-- Ji. THE Oesophagus and Siomach of Man. ,-: : fei\ from Bailey's Histology.) ., Oesophagus, iLs stratified epithelium, E., terminating at u: M, stomach ; cd, dd, cardiac glands in stomach and oesophagus respectivelx ; ac, wd, dilated duets of the cardiac glands; S, tuinca propria ; m. m.. muscularis mucosae. Digitized by Microsoft® 198 HISTOLOGY. they are not generally considered mucous cells, it has been found that in the stomach their protoplasm responds to concentrated mucin stains, and it is quite possible that they produce a variety of mucin. Occasionally the oesophageal cardiac glands possess a few parietal cells like those found in the stomach. Cystic enlargements and dilated ducts occur, as shown in Fig. 222. No special function has been assigned to the- cardiac glands. Beneath the submucosa is the tunica muscularis, consisting of an inner layer of circular or obHque fibers, and an outer layer of longitudinal fibers. In the anterior or upper part of the oesophagus the longitudinal fibers predominate. The muscles there are chiefly striated and are con- tinuous with those of the pharynx. Gradually they are replaced by smooth fibers so that the striated forms are infrequent in the lower half of the oesophagus. At its lower end the circular fiber layer is said to be three times as thick as the longitudinal. The oesophageal muscles are Joined by slips from the trachea, left bronchus, aorta, and other adjacent structures. Outside of the muscularis is the connective tissue adventitia. It con- tains branches of the sympathetic nerves and the oesophageal plexus of the vagus nerves. From these, the nerves invade the muscularis forming the ganglionated myenteric plexus between its layers, and pass on into the submucosa where they constitute a poorly developed submucous plexus. The terminal branches include free sensory endings in the stratified epi- thelium, motor plates on the striated muscles and the simpler motor end- ings on the smooth muscle. The blood vessels form capillary networks with meshes between and parallel with the muscle fibers. They also branch irregularly in the submucosa, and form terminal loops in the papillae of the timica propria. Lymphatic vessels are numerous. Stomach. The inner surface of the stomach presents macroscopic longitudinal folds which become coarse and prominent as the organ contracts. There are also polygonal areas from i to 4.5 mm. in extent, bounded by shallow depressions under which the gastric glands have been said to be fewer and shorter than elsewhere. The depressions are also ascribed to the contrac- tion of the muscles in the mucous membrane. Toward the pylorus, or duodenal end of the stomach, there are small leaf-hke elevations of the mucous membrane, called plicae villosae. They may connect with one another to form a network. The gastric mucosa is pinkish gray since its epithelium is thin enough to transmit the color of the blood beneath; this is not true of the oesophagus, the lining of which appears white. The epitheUum of the stomach is simple and columnar, the transition from the stratified epithelium of the oesophagus being abrupt (Fig. 222). Digitized by Microsoft® M STOMACH. 199 Its cells produce mucus and may be divided into a basal protoplasmic por- tion containing the elongated, round, or sometimes even flattened nucleus; Epiltlulium, Tunica propria. -^ « » " Parietal cells. lit! ' Zi* a -,^ 0^ / C^l. fJ-O Leuoi:)C>'tes. i « ~ I'f r./'; \ Gastric pit. Neclv, Smootli muscle fibers. r ")« • Parietal cell. . • » J % ' i 1 , W ^ ff- i7 9 « « a <. a ' a Og * c * i> J r '' * e a ) Gastric glaml. Fk;. 223.— Vertu: \L Skction of the Mucous Mhmbranf of a Hl:man' Stom,\ch, siiowim-. Gastric Glands i'Gi-andui. -vk Gastricae Propriae). y. 220. and an outer portion containing the centrosome and the secretion area. The area varies in size, sometimes being large enough to suggest goblet Digitized by Microsoft© 200 HISTOLOGY. iif a parietal cell Lhief cell. ^,riH~ '^''^"'' I'lTiien. I'ai-ietel tell Fii.. 224, — Transn'erse Section oi-~ Human Gastric Gland. >; 240. Parietal cells with intracellular se- , cretor> capillar- \ cells. It may cause the free surface of the cell to bulge, and in preserved tissue to rupture, but this may be due to reagents. The mucus of the gas- tric cells responds less readily to mucin stains than that of the intestinal goblet cells. It first appears in granular form. The gastric epithelium lines a great many closely adjacent gastric pits ifoveolae) into the bottom of which the glands of the stomach empty. These glands are of three sorts, the gastric glands, cardiac glands, and pyloric glands. None of them extend through the mus- cularis mucosae into the submucosa. The cardiac glands are limited to the oesophageal end of the stomach, occupying a zone from 5 to 40 mm. wide; the pyloric glands may extend from 6 to 14 cms. from its duodenal end; and the gastric glands occur throughout its body and fundus. The gastric glands [fundus glands, peptic glands] are straight or somewhat tortuous tubular glands with narrow lumens, several of which empty into a single gastric pit (Fig. 223). The pits are sometimes considered to be the ducts of the glands. The tubules may join one another before entering a pit, so that they may be described as branched. They are somewhat nar- rowed toward the pits, forming the neck of the glands; their slightly ex- panded base is called the fundus. Each tubule consists of cells of two sorts, chicj cells, and parietal cells. The chief cells in fresh tissue ajjpear dark and tilled with refractive granules; in stained specimens they are clear, cu- boidal or low columnar structures en- closing round nuclei. After death the chief cells rapidly disintegrate. Their granules, which are often destroyed by reagents, are coarse toward the lumen and fine in the basal protoplasm. In the absence of food llie chief cells enlarge and the granules accumulate, but with prolonged acli\ity the cells Intercellular secre- Lur\' capillaries. Cliief cells, y ■-'■,225.— GOLGl PrKTAR A,T10N, SHOWING THE SI•:^.RKTOR^■ C \1MLL.-\RIKS 1 .\ G A STR I C Gl-ANDS. ,-.. 2;o. Digitized by Microsoft© STOMACH. 201 become small; gramiles disappear. They do not respond to mucin stains. It is supposed that the gramiles, called zymogen granules, become con\-erted into pepsin. The chief cells form the greater part of the gastric glands, ' ?rJ. I G:-istric pits. simple i-'pilheliiirii Lilt oMh|Uc'1v, ^o Hull iL nppears \'> W slralihu.l. Tuiiica propria > r Si.litai\ iHiidule Miiscularis mucosae. Fig. 226. — \'erticai. Sectidn of HL'^^A^' r\-T_oRic Glands 90 parietal cells being irregularly distributed among them as in Fig. 223. The latter are fewest toward the base of the gland. Like the cells of serous crescents, they apjpear crowded awav from the lumen with which they are often connected only iDy intercellular secretory capillaries (Fig. 224). The Digitized by Microsoft® riiiiu.ijiKiiii 202 HISTOLOGY. capillaries form a basket-like network within the protoplasm of the parietal cells, as may be demonstrated by the Golgi method. This produces a black precipitate wherever secretion is encountered fFig. 225). Short intercellular secretory capillaries arc found between but not inside the chief cells. In fresh preparations parietal cells are clearer than chief cells. They do not disintegrate so readily. In preserved specimens they appear as large cells with granular protoplasm which stains deeply with anihne dves, each cell containing one or two rather large, round nuclei. After fasting, the [)arietal cells are smaller and their intracellular capillaries disappear. Following Epniu'hinn ,mp,.^ , abundant meals thev enlarge and may con- tain vacuoles due to '*''"'="*^' , I ' ' I 1 ' ^^^^ rapid formation of secretion. They are thought to produce hydrochloric acid, but this is not beyond question. ( ^ ' '' T h e c a r d i a c J - ' _ , glands (Fig. 221) are \ "- ' 'h much branched tubu- l ~ ' s- lo-alveolar mucous I glands, often cystic, \ mil. 1- inn^iuhimai ^ ,^ Containing a few chief and parietal cells in _ __ tubules. Those fur- thest from the ocsoph- Human Stomach. ^^„^g g^j-g jj-^g [gj^gt 11k tunica propi ia contains ,^lands standing' so closf tu,t;i'tlicr that ^ us tissue IS \'isil)le onl\ at the base of the .i;laTi(ls tow aiil the nuis- branchcd and reSCni- cularis mucostle. ble gastric glands. The secreting cells of the cardiac glands suggest those in the necks of the gastric glands; their mucous nature is not apparent and has been but re- cently determined. Although cardiac glands are developed in many animals much more extensively than in man, nothing is known of their special function. The pyloric glands (Fig. 226) consist of very deep pits and of short winding branched tubules. Gastric glands may be mingled with them. The pyloric gland cells are chielly mucous, but occasional parietal cells are found among them, and in animals there are dark thin cells apparently produced by compression. The usual type is cokimnar with a rounded Digitized by Microsoft® STOMACH. 203 nucleus near its base, and protoplasm resembling that of chief cells. In structure the pyloric glands are like the duodenal glands, but the latter extend into the submucosa. The gastric glands are so closely packed that but little reticular and connective tissue of the tunica propria is found between them (Fig. 227). It is sufficient to support the numerous capillaries branching about the glands, the terminal lymphatic vessels and nerves, numerous wandering cells and a few vertical smooth muscle fibers prolonged from the muscu- laris mucosae (Fig. 223). The lymphatic vessels begin blindly near the superficial epithelium and pass between the glands into the submucosa where they spread out and are easily seen; they continue across the mus- cularis and pass through the mesentery to join the large lymphatic trunks. Solitary nodules occur in the gastric mucosa, especially in the cardiac and pyloric regions; they may extend through the muscularis mu- cosae into the submucosa. The muscularis mucosae may be divided into two or three layers of fibers having different directions. The submucosa contains its plexus of nerves and many vessels, together with groups of fat cells. The muscularis consists of a thick inner circular and a thin outer longitudinal layer, together with obhque fibers sometimes described as a third and innermost layer. Owing to the distension and twisting in the development of the stomach the course of the fibers is disturbed, and in small sections they may appear to run in every possible direction. The two layers are clearly marked at the pylorus, where a great thickening of circular fibers produces the sphincter muscle. Longitudinal fibers have been said to be involved in it so that they can act as a dilator of the pylorus. The serosa consists of connective tissue with well developed elastic nets, and of the peritonaeal mesothelium interrupted only at the mesenteric attachments. The serosa contains the vessels and nerves which supply the stomach. The nerves are partly vagus branches (the left vagus supphes the ventral surface and the right vagus the dorsal surface owing to the rotation of the stomach during its development) and partly sympathetic nerves from the cardiac plexus. The distribution of vessels and nerves is similar to that in the intestine, which will be described in detail. Small Intestine — Duodenum. The mucous membrane of both the small and the large intestine con- tains -many simple tubular glands, which reach but do not penetrate the muscularis mucosae. They are called intestinal glands [crypts of Lieber- kiihn]. Besides these, but in the small intestine only, there are cyHndrical, club-shaped or fohate elevations of the epithelium and tunica propria. Digitized by Microsoft® 204 HISTOLOGY. culled villi. Since the villi are from 0.2 to i.o mm, in height tliey may be seen macroscopically rmder fa\'orable conditions. In Fig. 22S, A, which represents an enlarged surface view of the hardened mucosa, the orifices of the intestinal glands and the projecting intestinal villi are clearly indi- cated. The villi of the duodenum are low ('0.2-0.5 nim.) and leaf-hke as seen in the reconstruction Fig. 22S, B. * ® ..^as. A, Surface \ iew uf lli<:* hardeiiud mucosa ci Lhc small iiUestine (aftev Kcjellikei). B, Side \ie\\ ol a w&x rc-coiistruction of the eplLliehum in Ilie human duoilciiiii]i I Hnbc-r l i. g., liUcSlinal ,L;land ; v., \allus. There is no sharper hne of separation between the stomach and duode- num than the sphincter muscle of the pylorus. Intestinal glands have been recorded in the stomach, and pyloric glands are said to extend into the duodenum. Moreover the leaf-like duodenal viUi resemlDle the villous folds of the pvlorus. Infest 1 lipitlielium. \ Duodenal g:laiid m the tunica pixipria Plica I. ircularl^. DuiMit-iial .glands in Fat. thu biilimiKOsa. Tunica pn^pi Muscularismuto?ae — _ Submucosa.--p Stratum of circular ■ inusclf. [ StratUTH 'if lon,s^i- h tiidinal muscle. f C'MHieclive ti'^&ue. — - ^ ^ Fig. 229.— Longitudinal Section oi'- the Human Dl'odenum. X il^. The duodenum differs from the remainder of the small intestine by containing duodenal glands [glands of Brunner]. These are branched tu- bulo-alveolar stiiictures which extend into the subniucosa (Fig. 229). To a small extent they branch among the intestinal glands inside themuscu- laris mucosae, as seen in Fig. 2^iO. Their ducts mav either enter the bases Digitized by Microsoft® DUODENUM. 205 Intestinal glands. of the intestinal glands, or may pass between them to the surface. In form and position the duodenal glands suggest those of the oesophagus, but in structure they so resemble the pyloric glands as to have been considered identical with them. They produce a mucus which stains with difficulty, and are free from goblet cells. As in the pyloric glands, occasional parietal cells have been observed, found chiefly inside of the muscularis mucosae. The dark cells due perhaps to compression, occur, and there are intercellular secretory capillaries. A structureless basement membrane surrounds the tubules. The duodenal glands are so numerous toward the stomach that the submucosa may be filled with their tubules. They are also abundant near the duodenal papilla where the bile and pancreatic ducts enter the descending portion of the duodenum. Beyond this point they become fewer, and disappear before the end of the duodenum is reached. Except for these glands the duodenum is essentially Hke the remain- der of the small intestine, described in the following section. Small Intestine — Jejunum and Ileum. As already stated, the small intes- tine is characterized by its glands and the vilh which impart a velvety appear- ance to its surface. In the jejunum the club-shaped or cyHndrical villi are more slender and numerous than in the ileum; in the distal portion of the latter they are short and scattered, finally dis- appearing on the colic surface of the valve of the colon [ileo- caecal valve]. Each villus consists of an epithelial covering and a core of connective tissue, the tunica propria (Fig. 231). There are other and larger elevations in the lining of the small intestine, known as circular folds (plicae circulares) [valvulae conniventes]. As shown in Fig. 232, their interior is formed by the submucosa and their surface is covered by the entire mucous membrane, — villi, glands, and the muscularis mucosae. Since the tunica muscularis does not enter them they cannot be obliterated by distending the intestine. The circular folds begin in the duodenum of the tubules of a duodenal gland. Fig. 230. — From a Section of a Human Duodenum. X 240. Only the lower half of the mucosa and upper half of the submucosa are sketched. A large portion of the duodenal gland lies above the muscularis mucosae. Digitized by Microsoft® 2o6 HISTOLOGY. (Fig. 229), and beyond the duodenal papilla they are tall and close together. They are also highly developed in most of the jejunum, but distally, as in the ileum, they are lower and further apart. From the last two feet of the ileum, they may be absent. As their name implies, they generally tend to encircle the intestine. They may form short spirals, or branch and connect with one another. Some of them arc so oblique as to appear cut transversely in cross sections of the intestine. #i. ctiuiis uf villi. 1 a J* tl ' Epithtliuiii.. Tunica. Iirupna. A' % Musculari mucosae. SubTiiiuusa Iiilcsliiial ^'lands. C)bli([in.- secli'.'iis nf luu-slmal ,ij:laiitls, I'lG. 231. — \'i-:ktic.^l Skction ui'" the ]Muci>ps Mi^misrank of thk Jkjunl'M of ,\ul"li M.an, X So. The space, a, between Ibe tunica propria and the epithelium of the \'illus is [>erhaps the result of the siirinknii,- action of Ifie fi.xni^^ Huid. .\t b Lite epulielium has been artilicially ruptured. Tlie goblet cells have been diawn on one side ol the vdlns on tiie ri^dit. There is only an arbitrary separation between the jejunum and the ileum; the latter contains fewer and shorter vilh, and its circular folds are more widely separated. The entodermal ej)ithelium of the small intestine is of the simple columnar form and contains many goblet cells. Since that portion which covers the viUi contains perhaps as many goblet cells as the part which lines the glands, it has been suggested that the latter are more properly termed pits. At the base of tlic glands, howe\'er, there are often some cells con- taining coarse granules, indicative of a special secretion. Its nature has Digitized by Microsoft® SHALL INTESTINE. 20/ not been determined. Such cells, known as cells of Paneth, are invariably present in the ileum, and often in the jejunum; they are not found in the glands of the duodenum, or in those of the large intestine, with the possible exception of the vermiform process. They are shown in Fig. 233. The sides of the glands are formed of columnar cells and goblet cells, so arranged that the latter are seldom in contact with one another. It is thought that any of the cells may elaborate mucus and become goblet cells, in the manner described and figured on page ^^^t,. Mitotic figures are often \-iiii Plica circularis liUcbliiial ;;,'laritls Siibnuieuba. ^ Circular mu^ orii^itiKliiial _ niusi. Ic ~ - Serosa '^~'" Fig. 2\2.- Plexus m\ eii- tericus. -X'krtjcal LoiNi.;i luiJiNAi, SHcrir'N of "ri-iE Jiciunum uf Alkilt M.\n. ^ 16. The plua circularis on the rit^lU .suppi.prts two small buliUtry nudiil^js, whlcli do not extt-nd nitu the sub- mucosa; one of tliem exliibits a ij;erminal center, X. The epiLheliinn is slightly loosened from the connective tissue core of nian>' of the \'illi, so that a clear space, XX, exists between the two. The isolated bodies lying near the ^■illi (more numerous to the left of the plic^t' circulares) are partial sections of \-illi that were bent, therefore not cut through their entire length. observed in the glands and seldom elsewhere. (Iq the stomach they occur near the necks of the glands. j From this it is inferred that the outer cells, including those of the vilh, are replaced from below, and that the cells toward the fundus of the glands are renewed from above. The epithelial cells of the vilh are taller than in the glands, and the goblet cells are somewhat larger. The columnar cells are covered by a vertically striated top plate or cuticula, which is thinner in the outer part of the glands and is absent from their deeper parts. The striation is con- Digitized by Microsoft® 208 HISTOLOGY. sidercd due lo protoplasmic processes lodged in pores, also present. Goblct-ctlls CdlS'if Paneth. Fir, 2-,3.— Threk 1nti-:stinal (."il.ANDS M waiulerini; leuen, \les ( l> niplioi \ tes ) . The epllheliiini on the n^ht eoiitaiiis but three Digitized by Microsoft® SMALL IXTESTIXE. 209 tral lymj)hatic, within which they break down and set free the fat, but this explanation of the transfer is not be}'ond question. It is well ^ ^ ■ - \\ Tunica propria. Purtiriii (if acapillar\' bloo'i vesstl. Nucleus of a l\nipiio- c>te. rangential sccfioii of a goblet cell. Mucus in a gohilet cell Nucleus < 1 a tl n le frf r LI | 1 at ve el Fig. 235 — LuNGi ruDiN'AL Sectidn thrcjugh the Af'EX of the \'!Llus rjK .\ Dog. ,- 360. The ,Li"ol)let cells contain less nrucus as the\' appro.icli tlie surnuit of t!ie \'illus. known that fat enters the lymphatic vessels so that they become distended and white, their fatty contents being designated cliyle. In regard to the absorption Op of proteid material, the observa- tions of Pio Alingazzini, Avhich have been confirmed by some and denied by others, are of con- siderable interest. As sho\\Ti in Fig. 236, he found that the basal protopjlasm of the epithelium presented an ordinary appear- ance before digestion fA), but that after absorption had pro- gressed, hyahne spherules ap- appeared in it (B). As these became numerous they were detached from the cells, forming a reticular mass between them and the tunica propria fC). 14 Digitized by Microsoft® A -, J36. — St.ages o\- Intesti.nal Absorption .as Seen in Epithelial Cells of \'illi fro-M \ Hen f After Mingazzini.) 11(1 D, The states of repose i>recerling and followiiiL; the piocess. s., Spherules. 210 HISTOLOGY. After the spherules had broken down and probably been transferred to the blood vessels, the tunica propria entered into its usual relation with the shortened epithehum (D). The basal protoplasm was then restored. Thus proteid absorption was accomplished as a secretory process of the epithehum, the product being eliminated from its basal portion. The spherules accumulate at and near the tips of the villi in spaces which many authorities, including Professor Stohr, describe as due to the artificial retraction of the tunica propria (Fig. 231, a). The spherules have been considered a coagulum of the fluid squeezed from the reticular tissue. In part they may be the boundaries of the basal ends of epithehal cells on the distal wall of the villus. Often a delicate connective tissue artificially Fig. 237. — Diagram of a Mesentery as Seen in Cross Section of the Abdomen. (After Minot.) a., Aorta; c. p., cavity of the peritonaeum; int., intestine; mes., mesentery; p. m. and V. m., parietal and visceral layers of mesothelium. Nuclei of connective tissue cells. Fig. 238.— Surface View of the Greater Omentum from A Rabbit, x 240. * Thick and thin connective tissue bundles form meshes. The wavy striation of the bundles is obscured since the preparation is mounted in balsam. At X the epithelial cells of the opposite sur- face are visible. shrinks from an epithelium, as seen in Fig. 22, p. 23. On the other hand, these considerations are familiar to those who interpret the spherules as the result of proteid absorption. It is well known that a certain amount of proteid is absorbed in the large intestine, and it has recently been found, by Dr. J. L. Bremer, that beneath its epithehum, reticular appearances similar to those in the small intestine occur after proteid digestion. The muscularis mucosae of the small intestine consists of an inner circular and an outer longitudinal layer of smooth muscle. The submucosa is of loose fibrous connective tissue with few elastic fibers. The mus- cularis includes-an inner circular layer of smooth muscle fibers, and a much thinner outer longitudinal layer. Between them is a narrow but important band of connective tissue. Numerous elastic fibers are found not only Digitized by Microsoft® '■■:JM MESENTERY. 211 on the surfaces of the muscle layers but also in their interior. Their abundance is directly proportional to the thickness of the musculature. The serosa consists of connective tissue which is covered with meso- thelium except along the line of attachment between the intestine and its mesentery. As shown in the diagram, Fig, 237, the mesentery is a thin layer of connective tissue bounded on either side by mesothelium, which serves to suspend the intestine from the median dorsal line of the body cavity. It is present unless adhesions occurring in the course of develop- ment have destroyed it, and in the small intestine such adhesions involve only a part of the duodenum. At the root of the mesentery (the portion attached to the trunk of the body) the mesothelium extends laterally and with the underlying connective tissue forms the parietal peritonaeum. The tunica serosa of the intestine and the lateral parts of the mesentery constitute the visceral peritonaeum (this term being appUed especially to the former). The mesothelium of the entire peritonaeum consists of flat, polygonal cells shown in surface view in Fig. 238. The outer por- tions of the cells fit closely, but the deeper parts, containing the nuclei, are joined by intercellular bridges. Beneath the epithelium there is fibrillar connective tissue containing abundant elastic networks parallel with the surface, and having plasma cells and other free forms in its meshes. These cells are found especially along the blood vessels. The connective tissue layer is denser in the parietal than in the visceral peritonaeum. In places where the peritonaeum is freely movable there is a subserous layer of loose fatty tissue, but there is no distinct subse- rous layer in the intestine. The mesothehal layers on the opposite sides of the mesentery are so close together that they may both be seen in a sur- face preparation by changing the focus, or even simultaneously as at X in Fig. 238. The connective tissue between them is thin except where it surrounds the larger blood and lymphatic vessels and nerves which pass through the mesentery to and from the intestine. Blood vessels of the small intestine. The arteries pass from the mesen- tery into the serosa in which their main branches tend to encircle the intestine. Smaller branches from these pass across the muscle layers to the submucosa in which they subdivide freely (Fig. 239, A). In crossing the muscle layers they send out branches in the intermuscular connective tissue. These and the arteries of the serosa and submucosa supply the capillary networks found among the muscle fibers. The capillaries are mostly parallel with the muscles. From the submucosa the arteries invade the mucosa forming an irregular capillary network about the glands, and sending larger terminal branches into the vilK. There is usually a single artery for a villus and it has been described as near the center with the veins Digitized by Microsoft® 112 HISTOLOGY. mm. s m. I.e. l.m. f-V-cl. A J3 C Fig. 2:>,g. A, Diai^ram of the blood \'essels of the smcvll intesliiie; the arteries appear as coarse black lines, the . apiltaiies as fine ones, and the \'eins are shaded (after Malll. B, Diagram of the lymphatic \'essels (Lifter Mall). C, I.")iHgram of tlie T]er\'es, based upon Golsji preparations (after Cajalj. The la\ers of Uic intestine are m., nuicosa ; m. m., niuscularis mucosae ; s. m., subiiiucosa ; c. m., circular muscle ; i. c, intermuscular conntcti\'e tissue ; I. m., long-Jtudinal muscle ; s., serosa, c. I., central l> mphatic , n., uMiiult ; s. p!., submuci'U'^ jilfxus , m. pi., m\-entcric plexus. at the periphery (Fig. 239), or on one side of the villus with a vein on the other. The network of blood vessels in the villi is very abundant as sho^vn Tunica propria I INIusculai IS uuu M^ae. FtG. 240. — \'eKT1C\I- ShCTIHN IIP IHk. Mli:m 1 Mr lilood vessels are iu)ecLcd with llerlin bliiu. fl S Ml.Mr.R\NK <>]■ THE IIlMAN jF|fNl'>[. ■ ,S0. c \ cm n( Lilt- firsl villus on the lelt is cut trans\ crsLly. in Fig. 240. The \'eins I.)ranch frcrly in the sul.)nuicosa and pass out of the intestine beside the arteries. Tlie muscuhiris mucosae has been described Digitized by Microsoft© VESSELS OF THE SMALL IXTESTIXE. 21 • as forming a sphincter muscle for tlie ^•eins which penetrate it. No \a.\\es occur until the veins enter the tunica muscularis; there thev ajjpear, and continue into the collecting ^x-ins in the mesentery. They are absent from the large branches of the portal \-ein ■\\hich recci\-es the blood from the intestines. Lymphalic vessels. The intcbtinal lymphatics [lacteals] appear as central vessels within the vilh (Fig. 239, B). Each \illus usuaUy contains one, which ends in a bhnd dilatation near its tip; sometimes there are two or three which form terminal loops. In some stages of digestion the dis- Intestinal L^'fiu'ls. Muscular mucosae Lymph i.chIuIc ol llic niusciilans. Fig. 241. — Trans\"erse Section of Aggrf.gate Xodtler of the Small Intestine of a Cat. The crests uf four lutdules \\ ere not wilhiii the plane of Ihe section. >, lo. tension of these lymjihatics is vcr}- great and their endothelium is easilv seen in sections. When collajjsed they are hard to distinguish from the surrounding reticulum. Small lateral branches and a spiral prolongation of the central lymphatic have been found by injection, but these mav be tissue spaces. The lymphatics branch freely in the submucosa and ha'^'e numerous ^■ah■es. They cross the muscle layers, spreading in the inter- muscular tissue and the serosa, and pass through the mesentery to the thoracic duct. Lymphoid tissue. The lymjihoid tissue of the intestine occurs pri- Digitized by Microsoft® 214 HISTOLOGY. marily in the tunica propria, and in three forms, — diffuse lymphoid tissue, sohtary nodules, and aggregate nodules. Sohtary nodules are seen in Figs. 232 and 244. The latter shows how the nodule which arises in the propria may extend through the muscularis mucosae and spread in the submucosa, thus being as a whole, flask shaped or pyriform. A per- ipheral section of such a nodule may present only the part beneath the mus- cularis mucosae. The nodules are surrounded by small vessels, the lym- phatics being drawn in Fig. 239, B. Blood vessels may make a similar net, and penetrate the outer portion of the nodule. The germinative cen- ters are similar to those in the lymph glands. Fig. 242. A, Surtace \ie\v of tlie plexus niyeiitericusof an infant. Snrface liew of the plexns niyentericusof an infant. X so. g. Groups of nerve cells ; f, laver of circu far muscle libers reco.gnizeil by their rod-shaped nuclei. B, Surface view of the plexus submucosus o the same nifant. ;< 50. g, Groups ol neri e cells ; b, blood \ essel visible through the overlving tissue Aggregate nodules [Beyer's patches] are oval macroscopic areas, usually from i to 4 cms. long but occasionally much larger, composed of from 10 to 60 nodules placed side by side (Fig. 241). The nodules may be distinct or blended by intervening lymphoid tissue. They distort the intestinal glands with which they are in relation, and immediately above the nodules the vilh are partly or wholly obhterated. Thus they appear as dull patches in the lining of the freshly opened intestine. There are from 15 to 30 of them in the human intestine (rarely as many as 50 or 60) and they occur chiefly in the lower part of the ileum on the side opposite the mesentery. A few occur in the jejunum and the distal part of the duo- denum. In the ^■ermiform process diffuse aggregate nodules are always present, but they do not occur elsewhere in the large intestine. Digitized by Microsoft® NERVES OF THE SMALL INTESTINE. 215 Nerves. The small intestine is supplied by branches of the superior mesenteric plexus of the S3anpathetic sj'stem. This plexus is ventral to the aorta, and sends branches through the mesentery into the serosa. The manner in which they penetrate the other layers, forming the myen- teric plexus [Auerbach's plexus] in the intermuscular connective tissue, and the submucous plexus [Meissner's plexus] in the submucosa is shown in Fig. 239, C. In surface view, obtained by stripping the layers apart, these plexuses are seen in Fig. 242. Their branches supply the smooth muscle fibers. From the submucous plexus the nerves extend into the villi, where nerve cells have been detected by the Golgi method (Fig. 239,0); it has been suspected, however, that some of these 'nerve cells' are portions of the reticular tissue. Their terminations require further investigation. Most of the intestinal nerves are nonmedullated but they include a few large medullated fibers said to have free endings in the epithelium. ::;:^-a!*~». Fig. 243 —Transverse Section of the Huihn Vermiform Process. X 20. (Sobotta.) Note the absence of villi and the abundance of nodnles. Clear spaces in the submucosa are fat cells. Onh- a part of the circular layer of the muscularis has been drawn. L.A.EGE Intestine — Vermiform Process. The entire large intestine is characterized by the presence of intestinal glands associated with the absence of \'illi. In human embryos of from Digitized by Microsoft® 2l6 HISTOLOGY. 4 to 6 months there are vilH in llic large intestine, but they disajjpear be- fore Ijirth, l"j}' becoming flattened out. The ^x-rmiform jjrocess is distin- guislied from the colon by its small diameter and b}' the aljundance of l}-mph nodules in its tunica propria. They are often confluent (Fig. 243). In old age the lumen of the \-ermiform process is frequently obhterated; this has been recorded in 50',";- of persons over 60 years old, and appears to be a normal retrogression. The epithelium \vith its glands, and the nodules disappear and are replaced by an axial mass of fibrous tissue. This is surrounded by the unaltered submucosa, muscularis, and serosa. Large Intestine — C.vecum and Colon. The intestinal glands of the caecum and colon are longer than those in the small intestine, — sometimes twice as long (0.4-0.6 mm.). They contain more goblet cells, but cells of Paneth are absent. Striated cutic- j#^p''-,1''r^.'fr\< '&■: i^ ■l^^v.r "•;••# sT/VT^v •*"'r . "^ - Tunica propri.-.. Fat cells Solilar\- nridul'; with L;ermiiia! center. Fig, 244.— Vkrtical Section of tiik Mrcnip:irc lliu len.^'-tti of tlie glands \\'itti ib,'■■.'* '.: • '.'. t' * ;■■,,; '-V'i (' Uj/i"V''"V'**; ■ . / Lar^e iiUerlohular bile duel. '"-,-..;•.-■;-;- — ■:. ,-■. -sU >S'-. '■" ■.- ^ pVr^'~_^-;^*-,-"L-v! '■".'* :•'-'.', / "■^-'■^^i/fc.' '.^-^ ■' ^ ■"' IntLaiobular connccti :-..^i^-]":,''.^-'-^':-'^'''' -,' ' "j.'' .'ji^-A'' '"' ./'i'..' "^', tissue. Centr.il . / Fig. 250. — From a TANCtiNTiAL Section of the Hu,m.an Li\'er. X 40. i lie three central veins in cross section mark the centers of three lobules, whicli are not sharply separated 1— at the periphery from their neiglibors. Below and at the right the lobules are cut obliquely and tliLir boundaries are not. duct. Its trabeculae are separated by a very small amount of connective tissue from the endothelium of the sinusoids. The latter are essentially subdivisions of the portal vein which reunite in the ^'ena cava inferior. Later in development the connective tissue around the principal branches of the portal vein increases so as to be conspicuous; to a less extent that which surrounds the main hepatic branches of the vena cava is also in- creased. Since the portal branches are associated with the bile ducts they may be distinguished from the caval branches. Moreover the hepatic artery which develops rather late, grows into the connective tissue along the bile ducts. It sui)plies the fibrous capsule and the connective tissue layers with capillaries, which empty into the adjacent sinusoids and into the portal capillaries limited to the connective tissue. Thus there is 'a Digitized by Microsoft® LIVER. 223 capillary circulation in the li^'e^, in addition to the sinusoidal, but the former is essentially confined to the connective tissue. Microscopic appearance oj tJic adult liver. In sections of the adult human liver there will be seen clumps of connective tissue which contain branches of the portal vein, hepatic artery, and bile ducts, the last being easily distinguislied by their columnar or cuboidal epithelium (Fig. 250). Lymphatic vessels and nerves (non-meduUated fibers but no nerve cells) may also be found in this connective tissue. There is a tendency for the connective tissue areas to anastomose with one another. Pathologically The lobules have artifieiallv shrunken from the interlobular tissue, a ; b, bile duct ; c, hejjatic artery ; d, interlobular vein (a branch of the portal) ; e, trabeculaei f, central vein. in man, but normally in certain animals, as in the pig, this anastomosis is complete and polygonal areas of hepatic trabeculae are thus made promi- nent (Ficr. 251). These are the lobules of the hver, and the connective tissue around them is the interlobular connective tissue, containing inter- lobular veins (the branches of the portal). In the center of each lobule is a larf^e sinusoid, the central vein (sometimes there are two). Toward it the sinusoids converge from the interlobular veins on all sides (Fig. 252), and from it the hepatic trabeculae radiate. The central veins open, usually at right angles, into the larger snblobular veins (Fig. 253) The latter, beint^ derived from sinusoids, have notably httle connective tissue Digitized by Microsoft® -^4 HISTOLOGY. in their A\alls. Tlic subloljular \'eins unite to form the he])atic tributaries of the ^'ena cava inferior. The path of the blood through the li\'er is then brief!}' as follows: portal vein, inter- lobular veins, sinus- oids, central veins, sublobular veins, hepatic veins, vena ca'wi inferior. The hepatic artery through capillaries connects with the interlobular ^x-ins and with the sinus- oids at the periph- ery of the lobules. Certain patholog- ical conditions sug- gest that the cells near the center of the lol)ules arc not as well nourished as those at the periphery. llcpalic ccUs. The hepatic cells are arranged in anastomosing tra- Interlobu- lar \eiii (branch ot portal). —From a Shction of thk Hlman AE'L'LT L]\er iNJEcrED THR01_i.f[ THE PORT^L \'K1N. Hepalie lijliuie Inturlribular Cfiiiiiei_li\ t tissue. Central i intralobular) \eins. SublMhular \ ein. Fig. J5'v— b'RiiM - \'rRTicAi, Section m- a Cat's 1,i\i:k, Injected throlch THE \'eN.\ (_" W \ [.\I--ERir)R. rlie central veins ami tlie sublobular vein into wbicli they em|il\ are cat h iir^uthlinall>-. >^ 15. Digitized by Microsoft® LIAEE. beciilae as shown in Fig. 254. Near the central \'eins they form terminal loops. The cells composing the traljeculae are poh'gonal or cuboidal with an exoplasmic layer which sometimes resembles a cell membrane. The cells contain roimd nuclei which are wariable in their staining capacity; 'riLie ineshfjs. LaU'ral liraiiLiius of hilu capillanes. XuLleus of an iH-patic eLll. Xuclei of he[jatic cells. Sinusoids. Portion of a central \'ein. Fig. 254.— From \ Cross Section of -x Himx.n" Hi-;p.-\tic Locule, -300. Gol£;i preparation. The b.nnnl.uies of the hepatic cells could not be seen. The black dots are precipit^5 — Li\ Ik Cells of Man. v, 560. A, Isolated liver cells conlaining smaller and larq;er fat drops, f.; b., imprint from contact with a blood \esstl. B, From a section ; 1, empt>' cells ; 2, ctUs filled \A ith secretion. Blood vessels. FrC. 256.^01 \CRAM OF A TfHULE OF THE Ll\ RR (DlSKKOARDiNG THK ANAsroMosKs wrrii Adjoining Tubules). llepati rell. F.ile cajjillar' V- ---'-'A~) r ' J7)'6f^ h M... 257, — SECTir)X riF THK Ll\ KR OK -\ R \RB1T WITH THE Kii.E Capillaries Injected. X 560. (.\v>/' a Diasram.) Two of Ills; cells are cacli in contact willi four snuisoids II, 2, 3, 41 and four hile capillaries. X. a bile capillar\ w here three cells meet. cells. Its sharp contour is ascribed to a cuticular formation belonging to the cells which bound it. In longitudinal view it appears as a dark inter- cellular Kne suggesting a cell wall. Both A'iews are shown in the injected specimen Fig. 257, where, howe\'er, those seen longitudinallv seem to dis- Digitized by Microsoft® LIVER. 227 Fig 25s.- Sinusoids. -From a Rabbit's Liver. X 570- The cells 1, 2, a and b, are cut in halves ; their four bik- capillaries {including; I and II) may he inter- cellular branches of trabecular bile capillaries shown in the group 3, 4, cand d. The latter are seen in suiface view, the plane of section there being- between the cells. The actual arrangement can be determined only by reconstruction. regard cell boundaries; this is because they lie in intercellular spaces turned toward the observer, the cells beneath presenting an uncut surface. Some- times (as at x) a lumen occurs at the angle where three hepatic cells meet, but usually sinusoids are found at the corners of the cells and as seen in the figure, a lumen tends to be placed as far from the blood vessels as possible. A bile capillary, as the lumen is caUed, follows the trabeculae, branching and anastomosing as they do (Fig. 254). Between the hepatic cells, the bile capillaries send off branches at right angles. These intercellular capillaries are similar in diameter and structure to the trabecular capillaries. They are unbranched and end blindly before reaching the vascular sur- face of the cells (Fig. 254). In cases of pathological obstruction of the bile ducts, however, the intercellular capillaries are said to be prolonged to that surface and to rupture, so that bile enters the tissue spaces and the vessels, producing jaundice. Intracellular bile capillaries also occur; several have been found to extend from the trabecular capillary into a single hepatic cell. As seen in Golgi specimens they may termi- nate in knobs interpreted as vacu- oles of secretion (Fig. 259). Since neighboring capillaries are free from these branches, the intracellular capillaries are regarded as phases of functional activity, accompanying the discharge of secretion. They have been reported as forming bas- kets similar to the secretory capil- laries of parietal cells. In studying intracellular capillaries, care must be taken to exclude surface views of intercellular forms. Sinusoids and perivascular tissue. The endothelium of the sinusoids is'separated from the hepatic cells by a thin layer of reticular tissue. With special methods this tissue is seen to consist of innumerable fine fibers free Bile capillaries without knobs. Bile capillaries with knobs. 9, — From a Golgt Prei'Aration THE Liver cjf a Dog. X 490. Digitized by Microsoft® 228 HISTOLOGY. from elastic elements. The meshes of the reticular tissue are drained by the lymphatic vessels of the capsule and interlobular tissue; the reticular tissue itself contains no vessels. Unlike other reticular tissue, that of the lobules is free from cells in its meshes. In the embryo, however, it con- tains large numbers of erythroblasts and is for a time an important source of blood corpuscles. A few nerve fibers which terminate upon the hepatic cells, have been found in it. The endothelium of the sinusoids is easily penetrated by injections, which spread in the reticular tissue, and even enter the hepatic cells. The Branch of ponat _ _ j^...' ''^^r'S^''"",^''-,.-, ^' vein. " 1 .'<"*. ct'ri'^;.'-'^' ,7-; ',\ Small interlobu- lar bile-duct, continuing in bile capilla- ries. Large interlobu- lar bile-duct. Branch of hepat- ic artery. Bile capillaries. Wall of the central vein. Fig. 260.— GoLGi Preparation of the Liver of a Dog. x 240. blood vessels are not supposed to extend into the cells; the injection mass probably invades the trophospongium or other intracellular canals. In chloride of gold preparations the endothehal cells of the sinusoids appear stellate and have been mistaken for connective (reticular) tissue cells. They are phagocytic. Often they are called the stellate cells [of Kupffer]. The ducts of the liver. The ducts in an island of interlobular con- nective tissue drain the bile capillaries from all the surrounding lobules. If lines are drawn connecting the central veins with one another they will bound areas {structural units) comparable with the lobules of other organs: Digitized by Microsoft© GALL BLADDER. 229 in their centers the ducts are found. The actual connection between the trabeculae and bile ducts is very difficult to observe in ordinary sections, although it is easily seen after the ducts have been injected, or in Golgi preparations (Fig. 260). The transition from hepatic cells to the low cu- boidal cells of the small ducts occurs abruptly at the borders of the lobule. The cuticula of the bile capillaries is continuous with that of the ducts. The larger interlobular ducts have a simple columnar epithelium. They are said to anastomose with one another. The cystic, hepatic, and common bile ducts all have a simple columnar epithelium, containing occasional goblet cells. It rests on an elastic tunica propria, surrounded in turn by a submucosa. In the cystic duct the mu- cosa is thrown into coarse transverse folds, containing muscle fibers, known as the spiral valve. In the hepatic and common bile ducts especially, branched mucous glands extend into the connective tissue layer {glandulae mucosae biliosae). Outside of them is a tunica muscularis consisting chiefly of circular fibers. These form a sphincter around the bile duct at the duodenal papilla (and there are similar sphincters around the outlets of the pancreatic ducts). The parts of the ducts exposed on the under surface of the liver are covered by a serosa. In the gall bladder the mucosa forms a network of folds. The colum- nar epithehal cells are twice the height of those in the common bile duct. Goblet cells are absent and glands are infrequent. Solitary nodules may be found in the mucosa. The muscular layer is of obliquely circular fibers in a plexiform layer. Among them are groups of sympathetic nerve cells, which innervate the muscle. There are also medullated nerve fibers in the gall bladder which terminate in its epithelium. The subserous portion of the serosa is highly developed and contains large lymphatic vessels. The vasa aberrantia of the liver are bHnd ducts which extend beyond the territory of the trabeculae. They are found about the left lobe, and especially around the vena cava, the porta hepatis and the left triangular ligament, and represent portions of the Uver from which the hepatic cells have degenerated and disappeared. The porta hepatis, meaning 'gate of the liver' is the place where the vessels enter and the ducts leave, thus corresponding with the hilus of other organs. There the lymphatic vessels and the nerves are very numer- ous. The latter, chiefly non-meduUated, form networks around the vessels and ducts. They extend into the capsule and interlobular tissue, chiefly supplying the blood vessels. Some, however, continue into the lobules to the hepatic cells. The lymphatic vessels anastomose freely in the capsule and in the interlobular tissue, these sets connecting with one another. They do not enter the lobules. Digitized by Microsoft® 2.W HISTOLOGY. Fit;. 261. — A, Diagram df the PanckI'AS from a 15 MM. 1Ii."M.\n 1-"m- i:rmi B, Dissection of thk Di'odenl'm and Pancreas of .in Adi i.T (After Scliioiner.) a. p. d.. Accessory pancreatic duct ; c. d., c>'stic tluct ; d., duodctunn ; d. c. ductus choledoclnis; d. p., doiial pancreas; h. d., Iiepatic duct, p.. duodenal papilla; p. d., pancreatic duct; St., stomach; V. p., Acnlial pantreas. Pancreas. The pancreas is a large entodermal gland consisting of lobes and lobules and resembling in its general structure the parotid gland. It arises as two distinct out- growths of the di- gestive tract, as seen in Fig. 261, A. The smaller of these, called the ventral pancreas, de- velops from the duc- t u s choledochus near its intestinal orifice. Its duct, called the pancre- alic duct [of Wir- sung], opens beside the common bile duct at the base of the duodenal papilla. The pajiilla is a hollow eleva- tion of the mucosa, which has been spread open in bio-i vessel _. ^^ ^ _ xuciii. Fig. 261, B. The larger part of the pancreas grows out separately, from the dorsal wall of the duode- num between the papilla and the stomach. The duct of this dorsal pancreas is the accessory pancreatic duct [of Santorini]. The dorsal pancreas fuses with the ventral so as to make a single gland of uniform stiiicture, the former pro- ducing its body and tail, and the latter contributing to the head. The two ducts anastomose as shown in Fig. 261, B, and the out- let of the ventral duct becomes predominant. The intestinal end of the Fig. 262.— An Isi.-\nd ok rrir: Pancreas w'lin the Si.'RRouNiiiNi; ,\i \ Koi.i, i.-rom \n .Vdi'i.t. X 400. Digitized by Microsoft® PANCREAS. 231 m accessory duct is sometimes obliterated, but it may remain pervious and be of clinical importance in case of obstruction of the main duct. It opens about an inch above the papilla. (In the pig, which is often studied embryologicall}', the dorsal pancreas enters the duodenum distal to the papilla; its duct persists whereas that of the ventral pancreas is obhter- ated.) As is true of most glands, the developing tubules of the pancreas are at first sohd, but in the pancreas alone certain portions of the prohferating tubules become detached from the rest, forming islands of sohd cords of cells. These islands [of Langerhans] were not found in a human embryo of 28 mm. (53 days) but have been recorded at 54 mm. (73 days). They are then round or oval masses of cells rich in finely granular eosinophilic proto- plasm, which are still con- nected with the developing alveoli. Later they become detached, and by the invasion of capillaries of large diam- eter they are irregularly sub- divided into cords as seen in Fig. 262. The islands are said to appear first in the tail and body of the pancreas, and later in the head where they are always relatively fewer. In an early stage they are at the periphery of the lobules which are bounded by abundant connective tissue, but subsequently they are surrounded by the proliferating alveoli which reduce the connective tissue to interlobular septa (Fig. 263). It is not now supposed that the islands arise from connective tissue, or that they are produced in adult life by the degeneration of alveoli. The islands have neither ducts nor lumen. Their secretion, which is internal, is received by the blood vessels. It is essential for the metabolism of sugar as shown by experiment. After removal of the pancreas, sugar appears in the urine; on the other hand if the pancreatic ducts are tied the alveoh degenerate but the islands remain intact, and sugar does not appear in the urine. Thus the islands constitute an organ within but functionally independent of the pancreas. it3' Vi kk9 Wfim- Fig. 263.- -Section of Human Pancreas, showing Sev- eral Islands, f. Iiiteilobular < diiLt. c: b, (Radasch.j iinecti\-e tissue ccHitainin.L,' ati interloliular apillar\' ; d, interlobular duLt; e, aK'eoli. Digitized by Microsoft® HISTOLOGY. In SL'dions of the ailult [lancreas the ishinds are areas from .07 to 0.3 mm. in diameter, occuijied ])y cords or groups of polygonal cells, the boun- daries of which are often indistinct. The nuclei, round or o\-al, contain chro- matin in man)' small gi'anulcs, together with a few larger ones. The protoplasm is finely granular and in certain of the cells only, it is said to stain intensely with saffranin. Sometimes the protoplasm appjears reticular. The islands may be separated from the ah'eoli by a consider- able layer of connecti\X' tissue in AA-hich the elastic elements are infrequent, or by a thin basement membrane. Sometimes CA'cn the latter is absent. The cndo- iiei-cai,Li.e.i thelium of the cavjillarics is surrounded by a very small amount of reticular tissue. The jjancreatic and accessory pan- creatic ducts are lined with simple col- umnar epithelium which is surrounded b\- an inner dense, and an outer loose la\'er of connecti\-e tissue. The latter contains some smooth muscle fibers which are gathered into s].ihincters at the outlets of the ducts. Oc- casional goblet cells, and small glands resembling mucous glands, Tubu]e r^ic. 264. — Diagram tif thi: Pancrkas. 11® ;:5^\ Cell-? of V -^ » [he a \ fulus. Z\ nuiyu Fig. 265. — From Si-xTioNq Hi man Pancri-as. seclioii A llie m.iiiiilts .ive wanliin;, llic tleimnK dl Ihe inurcalaltd duct arc Hal ai B tliL- KiMiiuIes avf ili;.liii. I, Ihe cells of Ihc iiilercalalc.i duel ale cubical ai .1 dark; d clear. Digitized by Microsoft® PANCREAS. 233 lia\-e been found in the mucosa. Tlic eiiithelial cells Ijecome lower in the smaller ducts, and are cuboidal or llatlened parallel \vith the long axis in the intercalated ducts. There are no secretory ducts in the pancreas. The long intercalated ducts terminate in the alveoli tor acini) in a pecuhar manner. As seen in Fig. 2O5, the cells of the duct seem prolonged into the center of the ah-eolus, \vhere they are knoA\'n as cciilro- acinal cells. In development the duct is not in^aginated into the ahx-o- lus, but the latter de\-elops so as to consist of two la}-ers, onl_\- the outer of which produces the pancreatic secretion'. Sometimes tlie inner cells are lacking. The lumen of the intercalated ducts and alveoli is ver}- small and in many parts of a section it cannot be seen. Intercellular se- cretory capillaries extend from it between the centro-acinal cells to the se- creting cells, as seen in Fig. 266. The\' mav Ije prolonged between the latter, but thev do not reach the basement membrane. Inter- Centroacinc 1 cells. calated duel. ^^ 1 Cells of the alveolus. Iiitercelhilai" seeret'jr)' capillar) . Flo. 266.— A. From a Section of the !'\ncre\s c,f .-\dl'lt Man y 520; B. An Interpret.ation OK THE Right Lower Portion of A. The secreting or pancreatic cells are mosth" arranged in ah'eoli but in part they form tubules. Toward the lumen their protoplasm contains a zone of coarse granules of zymogen, which accumulate ^\I^ile the cell is in- active and are eliminated during secretion. Apparenth" they are trans- formed into lluid as they are discharged, for they are not found free in the intestine. In fresh specimens the granules are refracti\-e and easily seen, but in preserved tissue they are readily destroyed so that the granular zone appears reticular. The granules are soluljle in water, and are darkened by osmic acid. The basal protoplasm of the pancreatic cells is \"ertically striated. It contains the round nucleus Avith coarse masses of chromatin. Within the pancreatic cells there ha\'e been found 'paranuclei' of unknown nature, thought to be functionally important. After the discharge of secretion the cells become smaller and their boundaries more distinct. The pancreatic cells rest upon basement membranes containing ' basket cells.' Digitized by Microsoft® 234 HISTOLOGY. The blood and lymphatic vessels and the nerves resemble those of the salivary glands. The capillaries have notably wide meshes so that con- siderable portions of the alveoli are not in contact with them. The nerves end around the blood vessels, ducts and pancreatic cells. They are chiefly nonmedullated sympathetic fibers from the coeliac plexus, associated with scattered nerve cells within the pancreas. Lamellar corpuscles may be found in the connecti\'e tissue. Development or the Respiratory Tract. The respiratory system, consisting of the larynx, trachea, bronchi. and lungs, arises Beginning opposite as a the gland-like subdivision of the entodermal tract, third or fourth branchial arch, two longitudinal grooves develop, one on either side of the embryonic 'pharynx.' They deepen pos- teriorly and unite, thus separating the ven- tral trachea from the dorsal oesophagus. The trachea and oesophagus open ante- riorly into the pharynx of the adult. The anterior end of the trachea, with the epi- \ glottis, thyreoid, cricoid and other carti- lages which develop in the connective tissue around it, constitutes the larynx. Posteriorly the trachea bifurcates, as seen in the front view of the embr)'o, Fig. 267, A, and these primary subdivisions or bronchi, further subdivide as shown in B. In side view the right lung of an older em- bryo is shown in Fig. 268; the left lung has been cut away. The entodermal outpocket- ings are seen to lie in abundant connective tissue which is invaded by blood vessels from three sources, — the pulmonary arches, the left atrium and the thoracic aorta. Some branches which grow from the azygos veins are not showTi. The pulmonary arches are two arteries, one on either side, extending from the ventral to the dorsal aorta. Approximately midway in its course each sends a branch to the lung of the corresponding side. The part of the arch between this branch and the dorsal aorta is early obliterated on the right side, but on the left it persists until birth^as the ditclus arteriosus (Fig. 268, d.a.). After birth it is reduced to a fibrous cord which sometimes retains a minute lumen. The spiral division of the ventral aorta into the proximal parts of the permanent aorta and pulmonary artery, has beea referred to mm^ Fig. 267. — Reconstkuctions of thk Llngs of Y0(.!NG Embkvos. sekn fRO:\! THK \'p:NTRAL SL'RI'.ACK. A, A iuiiL,-'cr staL^i. than B : ep, .ipical bruiiLlui:^ i I, II, priniarv bronchi: (His. J Digitized by Microsoft© RESPIRATORY TRACT. 235 in connection witli the lieart. The pulmonary artery of the adult leaves the heart as a subdi\'ision of the ventral aorta; it divides into right and left rami, apparently simple vessels, but in reahty each of them consists of the proximal part of a pulmonary arch together with a branch of that arch. In Fig. 268, there is no indication that the left ramus, l.r. includes a part of the left pulmonary arch. The pulmonary veins grow out from the left atrium as a single vein with four main branches. By expansion of the atrium the proximal part of the vein is incor- porated in its wall and the four branches, two from each lung, then open separately. The capillary subdivisions of the veins anastomose with those of the pulmonary artery to form the principal blood supply of the lungs. The small bronchial arteries which supply the connective tissue of the lungs are branches of the thoracic aorta, one or two on each side. Their capillaries join those of the bronchial veins derived from the azygos veins. In part they connect with the pulmonary veins. Since the bronchial arteries convey 'arterial blood' whereas the pulmonary arteries contain 'venous blood,' the former may be compared physiologically with the hepatic artery in the Hver. The connective tissue in Avhich the entoder- mal part of the lungs ramifies, occurs as a pair of lateral swellings of the mediastinum. The mediastinum is the connective tissue surround- ing the oesophagus and extending between the heart and the dorsal aorta. It is bounded on either side by the mesothelium of the body cavity, and so has the structure of a broad mesentery of the heart. The pair of mediastinal swellings or 'pulmonary A\'ings' project into that portion of the coelom which connects the median pericardial cavity, on either side of the mediastinum, with the peritonaeal cavit}'. These portions of the coelom jjecome cut off, first from the pericardium and later from the peritonaeum, thus producing two closed sacs, the pleural cavities. Each of these is lined with a continuous layer of mesothelium, which, with the underlying connecti^•e tissue, con- ih.ao. Fig, 26s. — Reconstruction of a Pari of a Human Embryo OF- 13.8 MM. (Ur. V. \\ Thyng.) ao., Aorta ; d. a., ductus arteriosus; I., entodermal part of tlic- luiic;; I. at., left atrium , I. br., left i)roiiclius ; 1. r., left ramus of pulmonary artery, p. a.: P. P., its rigfit ramus; oe., oesoptia- gus ; p. c, pericaidial cavity; p. v., pulmonary vein ; s. t., septum trdtis^'ersum ; th. ao., thoracic aorta; tp., trachea. Digitized by Microsoft® 236 HISTOLOGY. stitutes the pleura. The parietal pleura is the part attached to the body- wall; the pulmonary pleura covers the lungs; other subdivisions are the medi- astinal, pericardial, and diaphragmatic pleurae. The lung is connected with the mediastinum by a short and broad stem of connective tissue, across which the bi"onchi, vessels and nerves extend. This is the root of the lung. Development oj the alveoli. Fig. 269, A, from an embryo of four months, shows a portion of the lung adjacent to the pleura. The terminal subdivisions of the bronchi are lodged in an abundant, vascular connective tissue. They are lined with a simple cuboidal epithelium and are gland- like in form. This appearance is retained until birth when they become distended with air. Then their cuboidal cells are flattened, and many of them are transformed into thin non-nucleated plates (Fig. 269, B). The Fig. 269. — Sections of the Visceral Pleura, pi., and Adjacent Alveoli, al., from the Lung of A Four Months Embryo, A, and from an Adult, B. ar.. Artery ; b. v., blood vessel ; cap., capillary ; ly., lymphatic vessel ; s., surface view of alveolar wall ; v., vein. connective tissue between the alveoli is compressed into strands scarcely wider than the diameter of a capillary. In fact the capillaries which they contain are in contact with the respiratory epithelium of both of the ad- jacent alveoli. A section of the adult lung is essentially a network of these slender partitions, scattered among which are islands of connective tissue containing the bronchi and vessels. There are also connective tissue septa, dividing the lung into lobules. Summary. The lungs develop as a branched entodermal gland with the trachea and bronchi as its ducts. The terminal alveoli become greatly distended and their cells form flat plates adapted for respiration but not for secretion. The lungs have two sets of blood vessels, both capillary in type, — the pulmonary and the bronchial vessels. The connective tissue forms a peripheral layer which is part of the pleura, and a large mass at the Digitized by Microsoft® LARYNX. 237 root of the lung. Within the lung it forms interlobular septa, and the thin ihteralveolar layers, but it is most conspicuous around the bronchi. In the following sections the structure of the respiratory tract will be considered beginning with the larynx, and proceeding posteriorly. Larynx. The mucous membrane of the larynx is a continuation of that of the pharynx, and Hkewise consists of an epithelium and tunica propria. A submucosa connects it with the underlying parts. In most places the epithelium appears to be stratified and columnar, but it is said to be pseudo- stratified, with nuclei at several levels. It is difficult to determine whether or not all of the cells are in contact with the basement membrane. This type of epithelium, which occurs also in the trachea, is ciliated. The stroke of the ciUa is toward the pharynx. A stratified epithelium with squamous, non-cihated outer cells is found on the vocal folds [true vocal cords], the anterior surface of the arytaenoid cartilages and the laryngeal surface of the epiglottis. The distribution of the two sorts of epithelium anterior to the vocal folds is subject to individual variation. The squamous epithehum often occurs in islands. The tunica propria consists of numer- ous elastic fibers and fibrillar connective tissue, which in the lower animals forms a dense membrana propria under the epithelium. It also includes reticular tissue containing a variable number of leucocytes; solitary nodules may be found in the ventricle of the larynx [sinus of Morgagni]. Pap- illae in the tunica propria are chiefly in the region of the squamous epi- thelium. At the free border and on the under surface of the vocal folds, the papillae unite to form longitudinal ridges. On the laryngeal surface of the epiglottis there are only isolated papillae, against which rest the short taste buds. The submucosa contains mixed, branched, tubulo-alveolar glands, measuring from 0.2 to i.o mm; they are abundant in the ventricle but are absent from the middle part of the free border of the vocal folds. The cartilages of the larynx are mostly of the hyaline variety, resem- bling those of the ribs. To this class belong the thyreoid, cricoid, the greater part of the arytaenoid, and often the small triticeous cartilages. Elastic cartilage is found in the entire epiglottis, the cuneiform and corniculate cartilages, the apex and vocal process of the arytaenoids, and generally the median part of the thyreoid. In women this portion is not involved in the ossification (chiefly endochondral) which begins in the thyreoid and cricoid cartilages between the twentieth and thirtieth years. The triticeous carti- lages (nodules in the lateral hyothyreoid ligaments, named from their resemblance to grains of wheat) are sometimes composed of fibro-cartilage. Digitized by Microsoft® 238 HISTOLOGY. The blood vessels form two or three networks parallel with the surface, followed by a capillary plexus just beneath the epithelium. The lym- phatic vessels similarly form two communicating networks, of which the more superficial consists of smaller Vessels and is situated beneath the capillary plexus. The nerves form a deep and a superficial plexus which are associated with microscopic ganglia. Non-meduUated fibers end either beneath the epitheHum in bulbs and free endings with terminal knobs, or within the epitheUum in free ramifications and in taste buds. Below the vocal folds, subepithelial nerve endings and buds are absent, but many intraepithelial fibers occur which encircle individual taste cells. The nerves and vessels of the larynx are numerous, except in the dense elastic tissue of the vocal folds. The ventricular folds [false vocal cords] consist of loose fatty, glandular tissue rich in vessels. Trachea. The trachea consists of a mucosa, submucosa, and a fibrous outer layer containing the tracheal cartilages. The outer layer is continuous with the tissue of the mediastinum. It forms the perichondrium sur- rounding the succession of hyahne C-shaped cartilages, the free ends of which are toward the oesophagus. In the interval between these ends, there is a layer of transverse smooth muscle fibers, usually accompanied by bundles of outer longitudinal fibers. As in the intestine, elastic fibers are abundant among the muscle cells. The tracheal cartilages may be- come partly calcified in old age. The submucosa is a layer of loose fatty connective tissue, continuous on its outer side with the perichondrium. It contains the bodies of the branched, mixed tracheal glands. On the dorsal or oesophageal wall of the trachea, these glands are larger than elsewhere and extend into or through the muscle layers. The mucosa is separated from the submucosa by a distinct dense layer of elastic fibers, chiefly longitudinal. This layer has been com- pared with the muscularis mucosae of the intestine. Between it and the epitheUum there is a thin layer of tissue, containing elastic fibers and having leucocytes in its meshes. A basement membrane is found beneath the epitheUum. As in the larynx the epitheUum is pseudo-stratified and columnar, with ciUa proceeding from distinct basal bodies. It contains goblet cells. On the oesophageal surface there have been found areas of non-ciUated, stratified epithelium, with connective tissue papillae beneath, and squamous cells on its surface. Digitized by Microsoft® BRONCHI. 239 Bronchi and Bronchioles. The primary bronchi have the same structure as the trachea. In their subdivisions changes occur, the C shaped cartilages being replaced by irregular plates found on all sides of the tube (Fig. 270). These diminish in size and thickness as the branches of the bronchi become smaller, and disappear in those about i mm. in diameter. Branched tubulo-ah-eolar 1 Epillielium. pio] 1l hi i \'pr^'P -- -S'" Blood „Y';c?7 ; X f ^ Cartilage. Connective tissue Broncbial j^Knd Duct of gland. .3 ' 'if u . _ . .- / (I o r r- -c / 1 / 'O Fig. 270. — Cross Sectio.n of a Bronchus 2 mm. in Diami.:ter, from a Chii d. glands occur as far as the cartilages extend. They are situated in a loose connective tissue layer containing many nerves, blood and lymphatic ves- sels, together with small lymph glands. The bodies of the bronchial glands he outside of a rather loose smooth muscle layer with fibers chiefly cir- cular. The mucosa is throwm into longitudinal folds. It consists of a pseudo-stratified ciliated epithehum in the larger bronchi, changing grad- ually to a simple epithelium in the small ones. The stroke of the ciha, as in the trachea, is toward the pharyn.x. The epithehum contains goblet Digitized by Microsoft® -40 HISTOLOGY. cells, and i\-^tb on a tunica |.)r()|.)ria which has many elastic fibers and lym- phocvtes. The latter may accumulate in nodules. Bronchioles are the small subdi\-isions of the bronchi, measuring from 0.5 to i.o mm. in diameter. The\' are free from cartilage and glands but ha^■c a cr)lumnar cihated epithelium thrcjughout. Oliviously the dis- tinction between the smaller bronchi and the bronchioles is arbitrary. The terminal branches of the latter are called rcspiralory bronchioles. Respiratory Bronchioles, zAlveolar Ducts, Alveolar Sacs, Alveoli. An arrangement of the ultimati- branches of a bronchiole is shown in the diagram, Fig. 271. The rcspiralory bronchioles^ 0.5 mm. or less in diameter, at their beginning contain a sim])le columnar ciliated epithelium. Pulnionary artery. Rcsi)irator>' bronchiole. -^ .Al\-eolar duct. ^^^^-^ r- --'....- . ^^ Pleural ca,„l.ancs.' "^^^^-^^^P^C H E 1^^ , ^-^^^ (Lobule.) In.. J71, — LllAi.RAM iji-- \ Lo|;llE mI." THH LI'NG, SHOWING THE P.LOOD \'kSSKI.S \ND rHE TERMINAL P.RAMrHES Cnr A P)RGNCHInLE. Further in their course the goblet cells disappear, cilia are lost, the cells become cuboidal, and among them are found thin, non-nucleated plates of different sizes. These plates together with the isolated cuboidal cells remaining among them constitute the rcspiralory epilhdiuui. The tran- Digitized by Microsoft® ALVEOLI OF THE LUXG. 241 sition from the cuboidal to the respiratory epithehura occurs irregu- larl}', so that a bronchiole may have cuboidal epithelium on one side and respiratory epithelium on the other; or one sort of epithelium may form an island in the midst of the other. Hence the respiratory bronchioles contain a mixed epithelium (Fig. 272, A). The respiratory epithelium steadily gains in extent until the cuboidal epithelium has disappeared. At irregular intervals along the bronchioles the respiratory epithelium forms hemispherical outpocketings or alveoli. The alveolar duels, from I to 2 mm. long, differ from the respiratory bronchioles in that they con- tain onl}' the respiratory epithelium and are thickly beset with alveoli. Ciibuidal cpiLiieh; ^^2> ^'1^- Nuii-imclcalcd plates. A Bf.ndur ot an aKcLilus. B -From Sections of the Hum\n Lu.ng. Fundus oi ail alvenlus. Fig. 272. — rROM SECTIONS OF THE HUM\N LU.NG. y 240. Mixed epit.h<.'liurii of a respiratory bronciiiole ; B, an alveolus sketched with chauL^e of focus; tlie lioriler of the al\-eoliis is shaded ; it is co\-ered hy the same epithelium as that of the (clear) fundus of the aheolus ; the nuclei of the cells are iinisilile. (Siher nitrate preparation,) The layer of smooth muscle fibers may be traced to the end of the ah-eolar ducts, where it terminates. Since the muscles do not extend over the alveoli, but merely surround the main shaft of the duct, the layer is greatly interrupted, and some consider that it ends in the course of the duct. The respiratory bronchiole may be continued as a single alveolar duct or may divide into two or more. The alveolar ducts branch to produce alveolar sacs [infundibula] which are cavities in the center of clusters of alveoh. The sacs resemble the ducts as shown in Fig. 271. According to Professor Aliller, who has made reconstructions of these structures in the human lung, an atrium or round cavity should be recognized between the alveolar duct and the alveo- lar sacs. The alveolar duct opens sometimes into five atria from each of 16 Digitized by Microsoft® 242 HISTOLOGY. J73 — Camhra Iacida Drawim. fko^i \ Skction ok a CALf 's Lung. (Miller.) The stippliiiK indicates smooth muscle and cuboid- al cpithelumi ; the lines, respiratory epithe- lium. B. R., RespiratorN- bronchiole; D. A., aL \eolar duct ; A., ati luni ; A. S., alveolar sac. wliicli sc\-er;tl ah'colar sacs proceed (Fig. 273). If the student in examining this ligiire questions why the atria are not alveolar ducts, and the alveolar ducts arc not respiratory bronchioles, it may he said that these terms are variously employed by different Jiislologists, and that atria are not recog- nized by German writers. It seems questionable that the linal ramifi- cations of the lung are so definitely arranged as to justify the cumber- some nomenclature in current use. Fig. 273 shows, however, exactly what may be expected in any sec- tion of the lung, namely (i) alveoli; (2) spiaces bounded by alveoh f alveolar sacs, atria, alveolar ducts, the last being supposed to have mus- cle fibers associated with them); (3) small bronchioles with alveoH along their walls, therefore consisting of a mixed epithehum (respiratory bronchioles); and (4) bronchioles with no respiratory epithelium. The alveolar walls have been described as consisting of respiratory ejjithelium (Fig. 272, B). The non-nucleated ])lates are presumably derived from the flattened nucleated cells scattered among them, and large jjlates arise from the fusion of small ones. In amphibia, nuclei in small amounts of protoplasm are found attached to the edges of the plates, and projecting into the connective tissue betAveen the capillaries. The abundant capillary network of the alveolar walls is shown in Fig. 274; lym])hatic \'essels are absent. Elastic tissue is highly developed around the ah-eoli and forms rings encirchng their out- lets. In inspiration an aheolus may expand to three times the diameter to which it returns dur- ing expiration (o.i to 0.3 mm.). Pores have been described, leading from one alveohis to another (Fio-. "72, B). The pleura is essentially similar to the peritonaeum, consisting of a connective tissue layer co\'ered with a flat epithelium (mesothelium). Per- ..274. — LrOM a SECriCiN OF TUK LUNC"; OF A Child, Injecceii tiiroliih ihe Pulmon.\ry .\RTER^*. ;■. So. < If the li\ c ahcoli drawn the three upjicr ones are lull) injected. Digitized by Microsoft® PLEURA. 243 manent apertures (stomata) in the epitheliurn probably do not exist. The connective tissue of the pulmonary pleura contains many elastic fibers; these are less abundant in the parietal pleura. Fat is found, sometimes forming folds {plicae adiposae) and the vascular elevations suggestive of synovial villi are called pleural villi. These may be sought toward the median wall, beneath the lung. The nerves of the pleura, derived from the phrenic, sympathetic and vagus are said to possess small ganglia. In the parietal pleura typical lamellar corpuscles and some of their varieties (Golgi-Mazzoni corpuscles) have been found. The blood vessels of the pleura are said to include branches both of the pulmonary and the bron- chial vessels. Lymphatic vessels are numerous and small lymph glands occur. Septa extend from the pleura into the lung thus dividing its super- ficial portion into lobules from i to 3 cms. in diameter. They are visible on the surface as polygonal areas bounded by pigmented hnes. Since these lobules consist of smaller subdivisions also called lobules, the former are designated as secondary and the latter as primary lobules {structural units). In the connective tissue between the secondary or larger lobules, lymphatic vessels make their way to the pleura and thence over the surface of the lung to its root. These lymphatic vessels constitute the superficial system. The deep lymphatic vessels begin along the small bronchioles and the adjoining vessels, and they accompany the arteries, veins, and bronchi to the root of the lung. To some extent the superficial and deep systems communicate. No lymphatic vessels are found beyond the alveo- lar ducts, within the lobules. Along the larger bronchi and toward the root of the lung lymph glands are numerous. Black pigment is generally abundant along the course of the lymphatic vessels. It is not melanin but soot, which is absent from the lungs at birth but accumulates with age, especially in certain environments. It pene- trates the pulmonary epithelium chiefly in the smallest bronchioles, ap- parently passing between the cells. Some of it is taken up by phagocytes. Having entered the lymphatic vessels it becomes distributed along their courses. The blood vessels accompany the bronchi. In the primary or ultimate lobules the arteries are central, producing a tenninal branch for each atrium or alveolar sac (Fig. 271). The veins arising from the alveolar capillaries pass over the peripheral surface of the structural units as shown in the figure. The distribution of the bronchial vessels has already been noted. The nerves, of the lung include a pulmonary plexus from the sympa- Digitized by Microsoft® 244 HISTOLOGY. thetic system, which, entering at the root, accompanies the bronchi and vessels; to them it is chiefly distributed. Small gangha are found within it. The vagus also sends important branches to the lung, which mingle with the perivascular and peribronchial nerves. They contain both meduUated and non-meduUated fibers. 4-W.b. URINARY ORGANS. WoLiTiAN Body. The Wolffian body or mesonephros is the "kidney" of adult amphibia and of certain fishes. It is one of the largest organs found in the human embryo of the second month, but subsequently its renal fuhctions are performed by another structure of later development, — the kidney (meta- nephros). As the Wolffian body degenerates it becomes transformed in the male into the ductus deferens and the epididymis, essential portions of the genital tract. Some vestigial remnants may produce pathological growths. In the female the entire organ is vestigial, with patho- logical possibihties. During its development and regression the Wolffian body is a controlling fac- tor in the arrangement of the large veins of the abdomen. In an embryo of 35 days (Fig. 275) the Wolff- ian bodies are seen as a pair of long, rounded elevations, one on either side of the root of the mesentery. They extend the length of the ab- dominal cavity and each empties through its Wolp ian duct into the allantois (described on p. 193). The excretion of the Wolffian bodies accumulates in the allantois, which in man is a slender but very long tube. In the pig at a certain stage, it is an elongated, thin- walled sac many times the size of the entire embryo; the large amount of fluid which it contains is due to an unusual develop- ment of the Wolffian bodies. After the urogenital sinus opens to the exterior, the contents of the allantois may mingle with the amniotic fluid in which the embryo is immersed. Development of the Wolffian body. In a previous section (p. 22) the development of the mesoderm has been described to that stage when it presents a series of segments (protovertebrse), connected by stalks (nephroiomes) with the layers which line the body cavity. From several -Dissection of a Human Embryo of 35 " (After Coste.) 275-1. Days. al.. Allantois ; I., lung; St., stom- ach ; s.tr., septum transver- sum ; u. c umbilical cord ; W. b., Wolffian body ; W. d., Wolffian duct. Digitized by Microsoft® WOLFFIAN BODY. 245 of the anterior neplirotomes there arise rounded elevations whicli grow posteriorly and unite with one another to form a longitudinal cord of cells on either side of the body. This later loecomes hollow and is known as the Wolffian duel. In a rabbit embr3-o it is shown in Fig. 276, A. As the Wolffian duct extends posteriorly it lies so close to the ectoderm that the latter has been said to participate in its formation. Finally it reaches and fuses with the entodermal allantois. The posterior nephrotomes are not thought to contribute to the formation of the duct. As seen in Fig. 276, B, they become separated both from the segments (my) and the coelomic Fig. 271'..— A, Traxsvkrse Section of a Rabbit Embryo of Nine Da\s; B. Hlman Embryo, 4 mm.; C, Hl'mvn EMBR^"o, 10 MM. ao, .AoiTa ; c, posterior cardinal \ em ; coe., coelom ; al., glomerulus ; g. i'., treuital ri(li;e 1 int.. intestine ; mes., mesentery ; mes. seg., mesorlermic se.^ment ; my., myotome ; nch.. notricliord: neph.. iieplir-itonie ; S-C. v., suljcardiual \'ein ; si., sinusoid ; sy., svmpatlielic ner\ es ; u. v., umbilical vein ; W. d., Wolllian duct; W. t., Wolffian tubule. epithehum. The nephrotomes form ^-esicles (W.l.) Avhich Ijecome tubular and coiled; each acquires connection with the Wolffian duct ("Fig. 276, C). By branching or fission the tubules become more numerous than the cor- responding segments. The aorta sends a succession of branches to the ventro-mcdian border of the Wolffian body. There they terminate in round knots of capiharies known as glomeruli (Fig. 276, C). A glomerulus is at first lodged in a cup shaped depression on one side of a Wolffian tubule, at its blind end. The tubule then grows around the glomerulus so that the latter appears Digitized by Microsoft® U6 HISTOLOGY. invaginated into its globular distal extremity (Fig. 277). The tubule is said to form the capsule of the glomerulus, consisting of an outer and an inner laver between which is an extension of the lumen of the tubule. The layers are continuous with one another at the stalk of the glomerulus. There the efferent vessel may be found near the afferent artery as in the figure, or, as has been described in the pig, several radiating efferent ves- sels may leave the capsule at different points. Whether these all emerge through one crescentic aperture in the capsule, or whether, by coalescence of its edges between the vessels, they leave through separate openings, has not been determined. The stalk and its tubule may both be on one side of the capsule, and not at its opposite poles as in the figure. From the blood circulating through the glomer- ulus, fluid "filters" into the tu- bule, forming the greater part of the urine. The tubules, starting from the ventro-medial glomeruli, fol- low a convoluted course to the Wolffian duct. In the pig two tubules ha\'e been found to unite before entering the duct, and near the glomeruli they may fork so as to connect with two cap- sules. A blind diverticulum is •f shown in Fig. 277. The tubules are hned thoughout with sim- ple epithelium. It is flat in the capsule where, in the pig, it is said to be thinner in the outer layer; the re\'erse condition has been figured for the human emljryo. The remainder of the tubule may be divided into conducting and secretory portions. The latter, found in the middle part of the tubule, has low columnar epithehum with dark basal protoplasm and a clear vacuolated appearance toward the lumen. These cehs are supposed to excrete a portion of the urine. The conducting tubules have a cuboidal epithelium without indications of glandular activitv. The secreting and conducting portions of the kidney tubules have been more thoroughlv studied than those of the Wolffian tubules. Veins oj llic Voljpaii IhmIv. Early in embryonic life two vessels arise from the vitelhne veins close to their entrance ijito the atrium and grow forward into the head, one on either side. These arc the anterior cardinal veins, and from each of them a posterior cardinal vein grows along the Fig. 277. — Rfxonstrl'Ction oi'" a Wolffian Twrulk FROM A Human Embryo of 10.2 mm. (Except tlie glomerulus, after Kolluian.) c. hiner l^t\er, ami c. a., outer la\er of tlie capstilc ( the glomerulus ; div.. dnerticuluui ; gl,, gloiue ulus ; W. d., VVolfTiati duct. Digitized by Microsoft® VEINS OF THE WOLFFIAN BODY. 247 aorta toward and into the tail. (Veins and arteries in its patli contribute to its formation.) Duct oj Ciivicr is tire name of the single vessel on each side which conveys the blood from the cardinal veins to the right atrium; the left duct of Cu\-ier crosses the dorsal surface of the heart in the atrio- ventricular groove. The early arrangement of the cardinal veins is shown in Fig. 278, A. A WoliTian body has developed in the ])ath of each pos- terior cardinal vein, and has been a factor in causing the vein to form 'the elongated loop shown in the figure. The dorso-lateral limb of the loop '■^[ X FlC. 27?. — The TRANSFORMATinN OF THlt P(JSTER10R CaRIHNAL VeIXS OF MaN', C RKPRESKNTIMG THit Aduet. The Woeffian Body is Dotted. d. u., anterior cardinal , as. I., ascendiiitj lumbar ; az.,azygos; c, caudal ; c. c, cislcrna ch\di : c.h., com mon Iiepatic ; c. il., common iliac; c. S., coronarv- sinus ; d. C.,duct ot Cu\-ier; g., spermatic or o\'h- rian ; h., Irepatic , h-az., liemiazy£:os ; h-az.ac, accessor)- lieiri'azyi^os ; i. j., internal iugular ; I. c. i. Ictt coinmon diac; 1. in., left innoin'nate; m. s., median sacra!; p. c., posterior cardinal ; p., renal; r. a., renal anastomosis; r. c. !., ri.2:ht common iliac; r. in., rii^^ht innominate, s., suprarenal ; s-c, subcartliiial , s-Cl., sulHla\ ian ; si., sinusuids ; v. c. i., \eiia ca\a infci ior ; v. c. s., \ eiia ca\-a superior. is the main stem of the posterior cardinal vein; it receives the inlcrscgmcnlal veins (lumbar and intercostal). The ventro-medial limb of the loop is the sithcardinal vein found near the root of the mesenterv, as seen in the cross section, Fig. 276, C. Sinusoids extending among the Wollfian tuljules connect the cardinal and subcardinal limbs with one another. (They arc shown onlv on the right of Fig. 278, A.) The sinusoids are less nu- merous in mammals than in selachians and reptiles. The hepatic veins (Fig. 278, A) are ventral to the subcardinals, Avhich are at the root of the mesentery. When, however, the right lobe of the Digitized by Microsoft® 248 HISTOLOGY. liver fuses with tlie dorsal body wall- making the coronary ligament, the right subcardinal connects with the hepatic system, as shown in Fig. 278, B, thus making the inferior vena cava. The vena cava consists of the right subcardinal vein from the liver to an anastomosis between the two sub- cardinals, known as the renal anastomosis; beyond this point it is continued through WolfSan sinusoids into a portion of the posterior cardinal. The part of the subcardinals distal to the anastomosis is apparently the source of the cistema chyli, and the associated lymphatic vessels (Fig. 161, p. 138). With the formation of the vena cava and the regression of the Wolffian body, the network of Wolfhan sinusoids becomes separated from the veins which entered it posteriorly, and from those which drained it anteriorly. From the network one large vein is differentiated (derived in part from the posterior cardinal) called the spermatic or ovarian vein according to sex; the remnants of the sinusoids are tributaries of this vein. The kidneys come to he opposite the renal anastomosis, from which the renal veins grow out to enter them. The reduction of the posterior cardinal veins to form the azygos system of the adult, and the formation of the superior vena cava from the anterior cardinals are shown in Fig. 278. The arteries of the Wolffian body are a series of branches of the aorta, each of which supphes one or more glomeruU. They pass between the posterior cardinal and the subcardinal veins as seen in Fig. 276, C. The vessels formed by the union of the capillaries of a glomerulus empty into the Wolffian sinusoids. With the regression of the mesonephros one of these arteries, — the future spermatic or ovarian — sends branches into the neighboring genital gland (Fig. 276, C, g. r.). There it unites with veins which grow in from the Wolffian sinusoids to make a capillary circulation. Pronephros. Anterior to the Wolffian body there occurs, in the lower vertebrates especially, another renal organ known as the pronephros. Its development precedes that of the Wolffian body. The pronephric tubules are segmental structures derived from the nephrotomes and characterized by retaining their connection with the coelom and by having their glomerulus (glomus) on the side of the tubule instead of at the end. Since the Wolffian duct is considered to be primarily the duct of the pronephros it is often called the pronephric duct; the Wolffian tubules become connected with it second- arily. In mammals the pronephros is scarcely distinguishable. Its tubules are said to begin with the 4th or 5th segment and to extend to the 9th in sheep or the nth in rabbits. They are transient structures imperfectly formed. In human embryos of 3 to 5 mm. one or two rudimentary pro- Digitized by Microsoft® DEVELOPMENT OF THE KIDNEY. 249 nephric tubules have been described. In one case a detached portion of the Wolfl&an duct opposite the 6th, 7th and 8th segments has been thought to be associated with the pronephros. Kidney. The kidney develops after the Wolffian body has been formed. It arises in two parts, one an outgrowth of the Wolffian duct; and the other, aTmass of dense mesenchyma which is said to be derived from the posterior nephrotomes. In this mesenchyma tubules are formed, which have at one end glomeruh similar to those of the Wolffian body, but smaller. The tubules follow a contorted course and acquire their openings into the outgrowth of the Wolffian duct. The kidney is a more complex organ than the Wolffian body, yet it is constructed on a similar plan. Wd, M.d. M.d. Fig. 279.— The Development of the Renal Pelvis and Ureter. (After Keibel.) fl, Human embryo of 11.5 mm. (4}^ weeks) ; B, 25 mm, (8J^-9 weeks), a., Anus; al. d., allantoic duct; bl., bladder; cl., cloaca; M. d., Mullerian duct ; r,, rectum ; ur., ureter; u. s., urogenital sinus ; W. d., Wolffian duct. Development. An outpocketing of each Wolffian duct near its en- trance into the allantois becomes elongated and dilated at its distal end (Fig. 279, A). The tubular part becomes the ureter and the lobed terminal expansion is the renal pelvis. As the allantois expands to become the bladder, a portion of the Wolffian duct is taken up into its wall so that the ureters acquire orifices independent of the Wolffian ducts; the latter are carried toward the median fine and the outlet of the bladder, as shown in Fig. 279, B. The figure shows their permanent relation to the ureters. In later stages the lobes of the renal pelvis become deeper and form the major and minor calyces. In the adult there are usually two major calyces, one at either end of the pelvis, and from these most of the minor calyces grow out; the others spring directly from the main pelvic cavity. There are about eight in all. From the minor calyces the collecting tubules Digitized by Microsoft® 2 So HISTOLOGY. grow out. Each tubule has an enlarged extremity (Fig. 2S0) which divides into two Ijranches with a U-shajjed crotch, like a tuning-fork. The CORTEX , —Pars Radiata -ParsConvolula — Pyramid ".. 2S0. — RECONSTRI'C- II'JN OF THE IIrETI-R. Renal Pel\'1s, and its Branches in a 20 m.m. Hl'man Embryo. {Hu- ber, Anitr, Jnuvnal of Anat , Suppl. to \ ol. i\'.) Fig. 281. — Cross Section of an Adi/lt KIDNE^■. (Willi modirications, after Brudel.) branches subdivide repeatedly in the same manner, so as to make pyram- idal masses of straight tubules radiating from the calyces. From 2 to 9 primary pvramids are said to fuse to form a macroscopic pyramid of the adult kidney (Fig. 281). The d -^ :?5Vs^. >w ^o m\^ nipple-like apex of the pyramid projects into the renal calyxform- ing a renal papilla. Each pa- ])illa is co\-ered by the pelvic epi- thelium, which is continuous with that which hnes the collect- ing tubules. The trunks of these lul)ules near the papilla are called papillary duels and their outlets are named joraiiiina. Each pa- pilla has from 15 to 20 foramina. Sometimes two papillae project into one calvx. The renal jivramids consti- tute the medulla of the kidney. Except toward their ajiices they are surrounded by coriieal substance. The cortex forms the peripheral part of the kidne\', and it also dips down be- tween the p}'ramids almost to the pch-is. In this way the cortex forms a G. 282.— From a Section of a Kidney of an i8 MM. Human Embryo. X 233, {Huber, Anier. Journal of Anat., Suppl. to vol. iv.) Primary collecting; tubule, with dilated extremit\' ; b, b',, inner layer, and c, outer layer of dense nit-s- Liich\nia; d., lonse niesench\Mna; e., ^'Csicie, the hcgiiniiiig; of a renal tubule. Digitized by Microsoft© DEVELOPMENT OE THE KIDNEY. 251 the renal columns [of Bcrtini], one of which is shown in Fig. 281. The outgrowing collecting tubules derived from the pelvis do not stop at the base of the pyramid but continue in tapering cones through the cortex Fig. 2S3. — A Skries of Models showing Successhe Stacks in the Development of a Urinif- EROL'S TUEULE, INCLUDING THE ASSOCIATED PORTION OF THE COLLEC'ITNG TuiSL'LE. From a human embryo of Ihe se\entli month. X i6o. (Huber, Am. Jour, of Anat., SuppL Lo vol. iv.) almost to its surface. They constitute an essential part of its radiate portion (pars radiala) [medullary rays, pyramids of Ferrein]. Thus far the development of the outgrowth of the Wolffian duct has been considered. The dense mesenchyma Avhich surrounds the pelvis Digitized by Microsoft® 252 HISTOLOGY. has the following history. It becomes subdivided into masses enveloping the enlarged tips of the branching collecting tubules. Some of its cells become arranged so as to form vesicles as shown in the section Fig. 282, and in the reconstruction Fig. 2S3, A. In these the vesicle is independent of the collecting tubule. In B and C it has become elongated making an S-shaped tubule, and has united with the col- lecting tubule. A glomerulus develops in the lower curve of the S and, as shown in the figures, it gradually becomes enclosed in its capsule — the terminal part of the tubule. The glomer- uli begin to form near the surface of the kidney and become buried in the advancing cortex; the oldest glomeruli are nearest the medulla. Between the capsule and the collecting tubule, the tubule of mesenchymal origin be- comes contorted or convoluted. One of the loops in the midst of the coil elongates do\Mi- ward toward the medulla, lying close beside and parallel with the collecting tubules. This Hciilc's loop (shown only in J of Fig. 283) is lodged in the radiate part of the cortex, and ex- tends into the medulla. Three tubules of the adult, with capsules situated in the outer, middle, and inner part of the cortex respectively, are shown in the diagram Fig. 284. Each capsule connects with a proxi- mal convoluted tubule which is continuous with the descending limb of Henle's loop, after hav- ing extended toward the surface of the kidney in the convolute part of the cortex. The de- scending hmb is essentially a straight tube of small diameter, owing to the flatness of its cells and not to a narrowing of the lumen. The portion of the proximal convoluted tubule which descends in a straight course to join the descending limb is called the 'end segment' or 'spiral tubule.' The descending limb generally becomes of large diame'ier before it turns to become the ascending limb of Henle's loop. This returns to the immediate neighborliood of its capsule, Avhere it forms the distal convoluted tubule [intercalated tubule]. By means of the 'junctional' or 'arched collecting tubule' the distal convoluted joins the straight collect in <:; tubule. The G. 2^4. — DiAGRAAr OF ThrKE rR]Nii-^i';Rous Tubules and iHEjR Relation to a Col- lecting Tubule. (Huber.) I., Asceiidins: limb of Henle's lii'ip: c, capsule; c. t., collect- ing- tubule; d. c, distal convo- luted tubule; d. I.. dcscendni.G: limb; p. c. pioximal con\o- luted tubule; p. d.. papillar\- duct. Digitized by Microsoft® KIDXEY. 2 S3 uriniferous tubule has no branches bet\Yeen the capsule and the collecting tubule, but there are many branches connected with the latter, as shown in the figure. The rounded "tuning forli" crotches have become angular. The straight tubules, including Henle's loops and the collecting tubules, constitute the medulla and radiate part of the cortex. The remainder of the cortex [pars convolnta) [labyrinth] contains the capsules together with proximal and distal convoluted tubules and arched collecting tubules. Renal cijrpuscle. Coinoliited tubules. Pars radlata. 1 I ' ,^-mS'-"' r ~ ' I "^"^ « ■!' I ^ Ii t il \\i\i\ \t I \S ,,<.. ! 'I I i ' " i h I I I ( \ ' ; i Henle's loop. Arcilorni \eiti. Arciforni artei'y. Fig. 2.S5. — Part of a Radial Sectici.v of \ Hl'man Kid-ne-i'. < 25. At X a renal corpuscle has dropped out. Since a radial section of the kidney shows both the cortex and the medulla, it is the kind made for pathological examination. Under low magnilication such a section is shown in Fig. 2S5. The renal corpuscles [Malpighian coipuscles] are the glomeruli together with their capsules. With higher magnihcation the ^'arious tubules of the radiate portion may Digitized by Microsoft® 2 54 HISTOLOGY. be idcnlilied (Fig. 2S6); they may be studied to better advantage, however, in tangential sections of the icidney, one through the cortex and one through the medulla. In these the tubules appear in cross section. The radiate parts of the corte.x are seen as islands of circular sections surrounded by the irregular convoluted tubules and renal corpuscles. The greater part of such an island is shown in Fig. 287. Finer structure oj the renal tubules. The renal tubules are lined throughout with simple epithelium. In the inner layer of the capsule of the glomerulus, it is a Hat syncytial layer blending with the small amount of perivascular connective tissue beneath. The outer layer of the capsule is also tiat and is composed of polygonal cells. Terminal bars which occur in all other divisions of the renal tubules have not been demonstrated W, i'^'a«-' ' S#'*'*'V in the capsule. The flat epithelium , ,^ gj © /* ''/%-.. of the outer layer of the capsule ^i'^Y^'^rfT^'s^^J coii'-''--'i"g i"huie. changes at the ' neck' of the capsule • 'jw , Sa/a y ® o e / . '/ » .-/ to the low columnar epithelium of ',®»j' *i&.< Descending limh. , . , , , , , ft\ «.fe at,;;''3>( ' the pro.xmial convoluted tubule. s»'r \ * Here cell boundaries are indistinct. *r J !IS/F — Ascend„,g innb. ^j^^ ^^^^j^- ^^^ towErd the base of the cells which rest on a structure- (K .ij*Jd)*,~-t-( Surface x iew cif less bascmcnt membrane continuous a *'L ."'! I " ■' ,'j,/ '""'■■ with that of the capsule. The pro- _. '^®('«J»'' \^ toplasm contains granules arranged i If® \4)*'j^;^ a/ in vertical rows Avhich toward the s^^{ ®f.4^[*J base of the cell appear as rods (Fig. '"^ ,, ^ 280). In certain animals plaitings I'lG. 286,— TuBUl.ES OF Tin-: Pars Radiata. , ^ i o From a radial sectiun ol :i human kuhiey. X 240. in the CCll Wall haVC been foUnd tO cause a rodded appearance in these cells. Toward the irregular lumen there is a 'brush border' (Fig. 2S9) suggesti\-e of short non-motile ciha. It is uncertain whether this is nor- mal or due to disintegration. Clear spaces are sometimes seen in the outer part of the cells. The lumen is wide and the cells are low after copious urine production; reverse conditions occur when the urine is scanty. It is in the two convoluted portions of the tubules that urea and pigments are believed to be excreted; the fluid part of the urine comes chiefly from the glomeruh. The descending limb both in the radiate cortex and in the medulla (Figs. 2S7 and 28S) is a diin walled conducting tube from 9 to 16 /'■ in diameter. (The proximal convoluted tubule measures from 40 to 60 //)• Cell boundaries are absent. Often in sections the flat nucleus causes Digitized by Microsoft® KIDNEY. 2 q ^ a local thickening of the cell, but this is perhaps a post mortem appearance. The descending hmbs may suggest capillaries as seen in the figures. The ascending limbs, 23-28 fi in diameter, resemble the distal convo- luted tubules said to measure from 39 to 44 //. The cells in the distal con^•oluted tubule are taller than in Henlc's loop and they ma}' have basal v> )t « '"*''«.' C 1 lluliule. ^' -j.-^' / , Capillary. Desceiidiii niontjwicz.) Digitized by Microsoft® BLOOD VKSSELS OF THE KinNEY. 257 around the vessels, in the papillae, and about the renal corpuscles tlian elseAvhere. The normal amount should be carefully studied since an increase in this "interstitial tissue" is indicative of disease. Lohcs and lobules. In emljryonic life the kidney is di\'ided into lobes, bounded by the renal columns and inrlicated bv groo\'es upon the outer surface (Fig. 2C)o). The gi'ooves become olditerated during the iirst year. (In the ox similar grooves are permanent; in most mammals they never exist, as the kidney has but one lobe, papilla and pyramid.) The lobules or structural units of the kidney are the areas centering around each ra- diate division of the cortex, by which they are drained. They are not bounded by connective tissue septa. Blood vessels. The kidney has a capillary circulation. The renal artery, from the aorta, passes to the liilus or notch on the medial border of the kidney. It divides into several branches most of which pass over the ventral surface of the pelvis into the fat around the calyces (Fig. 2S1J. As interlobar arteries they pass to the boundary layer be- tween the cortex and medulla where they are designated arcijorm arteries (Fig. 291). These send interlobular arteries through the convolute part of the cortex and their terminal branches enter the fibrous capsule. It will be noted that the kidney is exceptional in ha\'ing its arteries at the periphery of its lobules. From the interlobular arteries small stems pass to the glomer- uli, each of which receives a single twig (Fig. 292). into a knot of capillary loops, the endothelium of Avhich seems to blend with the surrounding syncytium and possibly with the inner laver of the capsule. The glomerulus often appears lobed, due to the arrangement of its vascular loops. The capillaries unite to form a single efferent vessel which divides into small branches on leaving the capsule. These spread among the convoluted and straight tubules of the cortex and some continue into the medulla. The latter is supplied by other straight branches (arleriolae rectae) from the interlobular, etferent and arciform arteries as shown in Fig. 291. The \-eins of the medulla begin around the papillae and as venulae rectae empty into the arciform ^-eins. The cortical veins are the interlobular vessels which are beside the corresponding arteries. They arise from converging veins in the renal capsule Avhich on surface view form a stellate figure [venae stellatae). The interlobular veins drain the capillaries of the cortex, but haA'c no direct relation with the glomeruli. Interlobar veins follow the arteries, passing out from the liilus of the kidney over the ventral surface of the renal pelvis. 17 Digitized by Microsoft® . 2qo. — KiDNKV OF A Child ai' Birth (Alter Hcilwig) . This is resolved HISTOLOGY. LynipJialic vessels are said to occur ^vithin the cortex and to follow the blood vessels oiil at the hikis. The cortical lymphatics also pass through Arched collt-Lt iiig Lul'U Distal ran- \ olut'::d Uil'ult: — — ' Slc-llate \-eiii. Intci'1(.ibular nrlery. Inlerlobular \ein. Avciform vein. rai>illar\' duct. -i,rr- Fic. 291. — Diagram or thk Coiirsm oih thic Kenm I'.i.MiHi \'i-:ssiiLS. the tunica hbrosa to connect with a network in the adipose capsule. They proceed to neighboring lymph glands. Digitized by Microsoft© XER\-ES OF THE KIDXEY. 259 The nerves are medullaled and n(Kvmedullatcd. There is a sym- pathetic plexus at the hihis associated with small ganglia, and from it Tunica lll^rcjsa Stellate vein r. jmerulus X'as affertiis, ^v^ Vas efferens. \ —\ A Elongated - ^ capillary RouikI / capillar\" nicshes. ^»Partl_v injected g^lomeruli. Intcrlobnlar artery. '^~~ Interlobular \"cin. Fig. 292.— From a Section of the In-jecthd Cortex ok an Adult Huiman Kidney. X zo. inlerlacing nerves extend into the kidney around the vessels (Fig. 293). Fine branches supply the epithelial cells, especially those of the convoluted ,/^' ,„ (Suhnm- cosa. I .f-~L_ik-. oj' 7° y)» t'riiiiicruus tubules. Fig, 293.— From the Kidney of A Mouse. Golgi Prepara- tion. X iSo. Fig. 294. — Transn'erse Section (jf the Lower Hali-- of A Human Ureter. X 15- ;., Epithelium ; t.. ttiuica propria ; I, inner longitudinal iiuiscle bum r, circular la\erot muscle bundles; li, outer long-itudinal mu: bundles. tubules. They form plexuses beneath and above the basement membrane and have free intercellular endint^s. Digitized by Microsoft© 26c HISTOLOGY. Renal Pelvis and Uretee. The renal ];cl\'is and iirclcr both consist of a mucosa fancl submucosa), muscularis and advcntitia (Fig. 294). The mucosa includes the epithelium and tunica propria, the latter blending with the submucosa. In sections Cylinder celts \\ ith a cuticular border. ^ ) rO ' J J '-■ f;,r '_ -! '',/' Leucocyte. — 1 unica propria. F]G.2q5. — \'KR'iic^L Sectii:).n oj-' TiiK MucoLS Memt-r.^ne OF a Hliman Bladdkr. X 560. the epithelium resemljles that of the moderately contracted bladder (Fig. 295), and its cells Avhen found detached in urine are not distinguishable from bladder cells. The epithelium is stratihed but consists of few layers. The basal cells are rounded, those of the middle la_ver are club shaped or conical M'ith rounded ends, and the outer cells are columnar, cuboidal, or somewhat flattened. Their lower surface may be indented by the rounded entls "of several underlying cells, as is particularly the case in the contracted blad- der (Fig. 296). Two nuclei are often found in a superficial cell and in some animals they are known to arise by amitosis. Leucocytes frequently enter the epithelium. In some animals mucous glands have been found extending into the tunica propria, and there are gland-hke pockets in man. Some of these have no lumen and it is said that none are true glands. Capillary blood vessels, which arc abundant in the mucosa, arc found directly beneath the epithcHum and present the deceptive appearance of becoming intra- epithelial. The tunica propria consists of fine connective or reticular tis- sue with few elastic fibers. It contains man}- cellular elements and some leucocytes and passes without a definite boundary into the loose connective tissue of the submucosa. .,. 290 — A Super- ]. ICIAL ErlTHEl-IAL Cele and Two C L u rj - s H A p K D Ceees from a Con- TRACIED BeADDER, (Koelliker.) Digitized by Microsoft® BLADDER. 261 The tunica muscularis is not compact since tliere is consideraljle con- nective tissue among its smooth muscle bundles. The latter form an inner longitudinal and an outer circular layer. In the lower half of the ureter there is a third, outer longitudinal layer. Around the papillae of the kid- ney the circular fibers form a "sphincter." The part of the ureter Avhich passes obliquely through the wall of the bladder has only longitudinal fibers ending in the tunica propria of the bladder. By contracting they open the outlet of the ureter. The adventitia consists of loose hbro-elastic con- necti\-e tissue. ij, Lymphatics and blood vessels are numerous. There are sympathetic nerves to^the muscles, and free sensory endings in the tunica propria and epithelium. Pit. / TanLjciitial sections of pits. Scciftion. Glanil. i i -:-M^ -sf^^^-^-^rv^^g^ ■^'■^i'Z.rriJZ' Tunica propria. Smootli muscles. Fig. 297.— Section THRurcii the Flwdls of the URI^'AR^■ Bladder of an Anrr.T Man. >' 4S. Bl.adder. The development of the bladder from the proximal end of the allan- tois has been described on page 193. Since the allantois is a part of the entodermal tract, the e]3ithelium of the bladder is entodermal whereas that of the ureter is mesodermal. There is howc\'cr no demarcation betAveen the layers in the adult, since both produce the same sort of " tran- sitional epithelium." The bladder consists of a mucosa, subraucosa, muscularis and serosa Digitized by Microsoft® 262 ' HISTOLOGY. The epithelium of the mucosa is two-layered in the distended bladder, the outer cells having terminal bars; in the contracted condition it becomes several-layered and the bars form a net extending into the epithelium. Some of the superficial cells have a cuticular border; they often contain two nuclei and their darkly granular protoplasm has been considered suggestive of secretory activity. Round or oval pockets extend into the tunica propria (Fig. 297). Some have no lumen or are detached from the epithelium, but others are pits containing a colloid substance. The pits are the first stages of gland formation. In the adult, branched tubules hned with cyhndrical epithehum may sprout from the bottom of the pits, thus forming true glands. Their occurrence is limited to the fundus (the dorsally bulging lower part of the bladder) and to the neighborhood of the urethral outlet. In the latter position they present transitions to well developed prostatic glands. The tunica propria sometimes contains solitary nodules. It blends with the submucosa, as in the ureter, and contains lymphatic and blood vessels, the latter extending very close to the epithelium. The muscularis consists of smooth muscle fibers arranged in three interwoven layers, which are seldom separable in sections. They are an inner longitudinal, middle circular and outer longitudinal layer. The circular fibers are strengthened at the beginning of the urethra to form the "internal sphincter" of the bladder, a muscle not always distinct. The serosa is a connective tissue layer covered with mesothehum. In the non-peritonaeal part of the bladder it is replaced by an adventitia or fibrous layer. Non-meduUated nerves, with scattered groups of ganglion cells, are foimd outside of and among the muscles. MeduUated fibers terminate around the ganghon cells; others pass through the ganglia to intra-epi- thehal sensory endings. Urethra (in the Female). The male urethra will be described with the genital organs; only its upper portion is homologous with the urethra of the female which is exclusively the outlet of the urinary tract. The epithehum has been variously described as stratified, with outer squamous cells, or as pseudo- stratified, and columnar. It may be of different form in different indi- viduals. The lumen is irregularly crescentic with longitudinal folds, as seen in Fig. 298. Branched tubular urethral glands are found only in small numbers except near the outlet. Their secretion is mucoid, but is not typical mucus. In the submucosa there are many thin walled veins constituting the corpus spongiosum. It is comparable with the upper Digitized by Microsoft® FEMALE URETHRA. 263 part of the more highly developed corpus cavernosum urethrae of the male. (Compare with Fig. 322, pj. 283). The muscularis consists of inner lon- gitudinal and outer circular smooth muscle fibers, among which the veins extend. Connective tissue with many elastic libers is abundant in the mucularis. The striated constrictor urethrae is outside of the smooth muscle laver, as shown in llic figure. Fig. 2gS.— Ckciss Seciiox of t}[i-: Female I'retiira. (Koelllker.) d., Gland-like diverticiiliini ; e., epithelium ; L.. lumen of the urethra; m., striated muscle; s., corpus spongiosum, containing veiii.'us spaces, v.. and smooth uuiscle. MALE GENITAL ORGANS. Development. The Wolffian body becomes an important part of the male genital organs and its duct serves to transmit the products of the testis to the urogenital sinus. Another duct, parallel with the Wolf&an and close beside it, develops later, and is called the MiiUerian duct. It arises as an inpocketing of the coelomic epithehum near the anterior end of the Wolffian body. The orifice into the peritonaeal cavity becomes surrounded by irregular folds known as fimbriae. As the 2\Iullerian duct grows poste- Digitized by Microsoft® 264 HISTOLOGY. riorly by the elongation of its Ijlind end, it lies in contact with the Wolffian duct as seen in Fig. 299, but the Wolffian duct is said not to contribute toward its formation. The tAvo Miillerian ducts reach the bladder side by side and acquire openings into it, between those of the Wolffian ducts. Near the bladder the two Miillerian ducts fuse AA'ith one another so that their distal part is represented by a single median tube on either side of which is a Wolffian duct (Fig. 279. B, page 249). In the female the united portion becomes the vagina and iilcnis, and the separate parts are the uterine [Fallopian] luhes. In the male the united portion becomes a small blind pocket, the prostatic utricle, opening into the prostatic urethra. Each fimbriated extremity persists in the appendix testis, and the remain- FiG. 2qQ.— From a Reconstruction of a 13.6 ^ni. Human Embryo. (F. W- Thynj?) bl., Bladder; f., fimbriae; g. g., t^enital gland; g. p., genital papilla; M. d., Miillerian iliiel; p., renal ]:ieh-is; r., reeliim ; u.r., ureter; u. s., urogenital sinus; W. d., W'olMan duct. C ., Fig. 300. — Diagram of the Dfaelopment of THE Testis, b.\sed upon Figures by Mac- Cai LUM AND B. M. Allen. c, glomerular capsule; i. c, inner or sex cords; M. d., Miillerian duct; 0. c. outer or rete cords ; W. d., W. t., Wolffian duct and tubule. ing piortion of the ducts, except for occasional fragments, becomes ob- literated. Thus only the two extremities of the ]MuUerian ducts are ordinarily permanent in the male (Fig. 301). The genital glands in either sex begin as a thickening on the ventro- medial border of each Wolffian body (Fig. 299). A section of this genital ridge is shown in Fig. 276, C, page 245. The ridge is a dense mass of mesoderm covered by the peritonaeal mesothelium which here consists of columnar cells. In forming the testis, cords of cells which later be- come tubules, appear in the dense mesenchyma {Fig. 300). These are considered to be invaginations of the peritonaeal layer rather than segre- gations of mesenchyma. The cords near the surface of the genital ridge become the convoluted tnbnles of the testis [tnlndi eontorti) and their con- Digitized by Microsoft® DEVELOPMENT OF MALE GENITAL ORGANS. 265 tinuations into the substance of the organ are the straight tubules (tubuli recti). Both the convoluted and straight tubules (Fig. 301) arise from the cords of cells in the outer part of the genital ridge. The cords in the interior of the ridge are similar and have recently been described as the posterior extensions of the rudimentary peripheral cords formed in the anterior end of the genital ridge. These inner cords produce a net of anastomosing tubes, the rete testis, into which the straight tubules empty. The tubes of the rete acquire openings into the glomerular capsules of ^AU.'r i;/ai: i urethra appt ndix rpiduiynndh appciuiix Icslis connotnu-d liihiU- - slrji'^ltl lubulc dnctiilm abcrrnus Inclns cpididyuddn Fig, 301,— Diagram of the IVTai.e Sfxtai. Organs. ( Modified from Ebertti, aftei' \\'aMi:'\LM- 1 (The eourse of the ^liilleiian duel is iii(.lieated by dashes.) the ^Wolffian body (Fig. 300). The glomeruli atrojihy and disappear. The [products of the con\'oluted tubules thus ])ass in turn througli tlie straight tubules and rete testis into the Wolffian tubules. O] the Wolffian tubules about fifteen persist as the duetuli efjercntes. Each of these is a greatly con\'oluled tube Avhich if straightcnerl measures 8 inches (20 cms.). When coiled it forms a conical mass or lobule oj the epididymis, with its apex toward the rete, and its Isase toward the Wolffian duct which it enters (Fig. 301J. .The Wolffian duct which passes along the dorsal surface of the testis, is also greatly convoluted so that it Digitized by Microsoft® 266 HISTOLOGY. measures about 20 feet when straight (6-7 meters). Together with the efferent ducts this coiled mass constitutes the epididymis. Along the testis the Wolffian duct is called the ductus epididymidis and from the testis toward the urogenital sinus it is named the ductus deferens. Near its termination a saccular outgrowth, hke a distended gland, develops from each Wolffian duct. It is called the seminal vesicle, and that portion of the Wolffian duct between the duct of the vesicle and the urethra is named the ejaculatory duct. Thus the Wolffian duct is arbitrarily divided in the adult into three parts, the ductus epididymidis, ductus deferens, and ductus ejaculatorius; an out-pocketing forms the seminal vesicle. It has been noted that only about fifteen of the Wolffian tubules persist as efferent ducts. Some of the others become detached, producing the paradidymis; and some which are partly detached remain as blind tubes extending from the rete or ductus epididymidis, — they are called ductus aberrantes. The one of these labelled in Fig. 301 is quite constant and may be from 5 to 30 cms. in length. The appendix epididymidis in the figure contains a tube connected with the Wolffian duct. The nature of this appendix is obscure; it has been thought a derivative of the Mul- lerian duct. The urethra. At an early stage (Fig. 299) the allantois is arbitrarily divisible into a 'temporary bladder' which extends to the genital ducts, and a urogenital sinus which receives both urinary and sexual outlets and extends to the surface of the body. A portion of the urogenital sinus is ectodermal having formed from a depression in the outer surface ; its inner part is entodermal and the boundary between these portions is no longer apparent. At a later stage the 'temporary bladder' forms the permanent bladder together with a hmited portion of the urethra. In the female it forms the entire urethra, but in the male only that portion of the pros- tatic urethra which extends to the genital ducts. The remainder of the male urethra is urogenital sinus. By the anatomists the male urethra is divided into the prostatic, membranous and cavernous [penile] portions. The penis and scrotum. In Fig. 299 the outer portion of the uro- genital sinus is seen to be a cleft-like space in an elevation loiown as the genital papilla (or tubercle). In Fig. 302, A, the papilla has lengthened to form the penis; its enlarged distal end is the glans. On the lower sur- face of the penis the urogenital sinus has an elongated opening. Apart from the condition of arrested development called hypospadias, the open- ing is bridged over, except at its distal end; thus it forms the cavernous part of the urethra. The embryonic penis is covered with a layer of sldn described as forming two lateral folds, the lesser genital folds. They meet beneath the penis as the urogenital sinus becomes closed, and a raphe Digitized by Microsoft® DESCENT OF THE TESTES. 267 (seam) remains to indicate their place of fusion. A reduplication of the lesser folds over the glans forms the prepuce. Outside of these folds there are two larger elevations of skin, one on either side of the root of the penis. They extend toward the anus, between which and the penis they fuse in the median Une forming a continuation of the raphe already mentioned. These larger genital folds thus produce the scrotum. Descent of the testes. The peritonaeal cavit)- sends a prolongation, the processus vaginalis, over the pubic bone into each half of the scrotum. The testis and epididymis at this stage he behind the peritonaeum of the abdominal cavity (Fig. 302, B). A large retroperitonaeal column of con- nective tissue, the guhernaouliim testis, extends from the posterior end of each testis into the depth of the scrotum. For reasons still obscure, such as vmequal growth or the shortening of this cord, the testes pass down in front of the pubic bones, into the scrotum (Fig. 302, C). The Wolfhan Fig. 3U2.— a, Diagram of the EMnRVONic E.xternal Ghnital CtRcANS in the Male; B, C. D, Diagrams , granules or subdivisions. They become ring- t 3 shaped before dividing in halves (the ring-shaped ^'^' '^■% arrangement characterizing the heterotypic form of 'W' mitosis) and each half contains two of the four granules. The cells produced by this division are somewhat smaller and pass toward the lumen. Fig. 306. —Primary Sperm- Within their nuclci tlic chromatin returns to the ATOCYTK, Human, SHOW- . r , -i 1 ^ ^1 t^i iNG 12 (?i Chromosomes, spu'cmc torm, and possibiy to a network, ihe chromatic thread again is resolved into twelve chro- mosomes, each in some animals consisting of two granules. In the mitosis which follows, these divide into single granules and each of the cells pro- duced receives twelve. They then form a network in a small nucleus, the entire cells being reduced in size. These cells border upon the lumen. The generations of cells which have been described are named as follows. Those which proceed from spermatogonia, and which iirst present the reduced number of chromosomes are called primarv spermatocytes. They are large cells in the outer part of the tubule, sometimes with vacuolated protoplasm containing rows of granules. Each of them divides into two secondary spermatocytes (praespermatids) which are similar cells, though smaller and nearer the lumen. They also have the reduced number of chromosomes. Every secondary spermatocvte divides into two decidedly smaller spermatids, giving them the reduced number of chromosomes.. The spermatids williout further division are trans- formed into spermatozoa. Thus each [jrimary spermatocyte produces four spermatozoa. Digitized by Microsoft® SPERMATOGENESIS. Stages ill iJie trans']on)ialion oj a spermatid into a spermatozoon are shown in the diagram Fig. 307. The twel\-e ( ?) cliromosomcs of the spermatid disappear in a dense chromatic networlc AA'hich becomes an apparently homogeneous mass. Tliis deeply staining nucleus passes to one end of the protoplasm of the spermatid and Ijecomes the essential part of the liead of the spermatozoon. In man it is a flat- tened structure, oval on surface \\t\\, and p)Tiform Avith its apex forward, when seen on edtje (Fio;. 308). The head is at the anterior end of the spermatozoon Avhich during its development is directed toward the basal layers of the convoluted tubule. The anterior end of the head is probably covered by a thin layer of protoplasm, known as the galea capitis. The archoplasm of the spermatid fknown as the idiozome) is said to leave the centrosome and to enter the protoplasm of the galea capitis where it forms the perforatorium. If this exists in man it is in the form of a cutting edge following the outline of the front of the head; in other animals the perforatorium may be a slender spiral or barbed projection which enables the spermatozoon to penetrate the ovum. The protoplasm of the spermatid forms an elongated mass at the posterior end of the nucleus. It contains the centrosome which soon di^^ides in two. Of these the anterior forms a disc which becomes adherent to the nuclear membrane. The posterior centrosome also becomes a disc after giv- ing rise to a motile axial filament which grows out from it like a cihum. The disc-like centrosome attached to the anterior end of the filament becomes thin in such a A\'ay that its peripheral portion is detached, and as a ring surrounding the filament it passes to the posterior limit of . 307. — Diagrams of the Dk\'elopment of Spermatozoa. (.After Meves ) ;., anterior centrosome; a. f., axial filament; C. p., connecting piece; ch. p., cliief piece; g. C. £;alea capitis: n.,nnc]eiis; nk., necl^ ; p., protoplasm; p. c, posterior centrosome. Fig 30^, — Spermatozoa- 1, 2, 3, Human; 4, from A Bull. a, Head; b, connecting; piece, ami c, chief piece of the tail. 1, 3, and 4, Surface \ie\\s; 2, side view. X 360. Digitized by Microsoft® 2-] 2 HISTOLOGY. the protoplasm. The protoplasm between the two parts of the posterior centrosome is reduced to a thin la}'er in which a spiral lilament develops, \Yinflin_2; about the axial filament. The axial filament, which consists of tine fibrils in some forms at least, distal to the centrosome ring is sur- roiuided jjy a thin membrane which terminates or becomes very thin near the extremity of the filament. This memljrane which in salaman- ders forms a conspicuous undulating frill, is thought to be a product of the filament and not an extension of the protoplasm. In man it is incon- spicuous. In fact most of the detail which is seen in ordinary sections containing spermatozoa is shown in Fig. 30S. Mattire spermatozoa are divided into three parts, the head, neck, and tail. The head (3-5 /i long and 2-3 /< wide) includes the nucleus, galea capitis and perforatorium. The neck consists of the anterior centro- some and the substance, not tra^•ersed by the axial filament, between it Heads of ^^ spermatozoa. ""^^^ ' ^ \K'»»*«r»«.^ • ;f 'i-sa'®' *i- "" *•'.-• Spermatid. "~"'~--,7;> ^ *(^ * aa • » -i't^l * '^ *' ^,- Nuclei of sus- * ^ ■ ■'^■jSft *'® S^ -• ^^.f-"^ tentacular cells. oids in iS.^-:"'^J',-M-^^^^ ' Cr\ stalloic interstitial ~~^»(f): cells. .^'' 1^ '' I ^ ''^''tlDJi ^■^,- " "^^ Interstitial con- •^ ■ ^.^^_i.>_— — -,^^'~' ^^'^^^^ nective tissue. Fig. 309.— FrcoM a LOiNciTt'D]N\L Skction ri-iROtiCH .a Con\oh'ted Tubule OF A Hf.MAN Testis. ;■', 360, and the posterior centrosome. The neck in man is not constricted as in some forms, yet it is a place where the head may become detached. The tail includes three parts, the connecting piece, chief piece and end piece. The connecting piece (6 /'■ long and scarcely i /< wide) consists of proto- plasm, axial and spiral filaments and the two parts of the posterior cen- trosome. The chief piece (40-60 /'. long) is axial filament with a surround- ing membrane, and the end piece (10 //.) is a prolongation of the filament. In the convoluted tubules the heads of the spermatozoa are attached to, or Ijuried in the protoplasm of the sustentacular cells which are supposed to nourish them. Their tails project into the lumen. Later they become detached and float in the albuminous fluid secreted in small quantity by the tubules. They ]jass through the straight tubules and rete to the epi- didymis, in which they accumulate and where they first jjccome motile. Their motility is greater, howe\'er, in the seminal fluid which is a mix- Digitized by Microsoft® SPERMATOZOA. 273 ture of the products of the epididymis, vesicles, prostate and bulbo-ure- thral glands. Then by an undulating movement of the tail the head is propelled against such a current as is made by a ciha, at a rate of \ of an inch in a minute. Water inhibits the motion, which is favored by alka- hne fluids; it occurs also in those faintly acid. Spermatozoa may retain their activity three days after death and in the female urogenital tract they may live a week or more. In addition to normal spermatozoa, ^^-^ ^ ^ { - •^^ . ^ ^ ,-- J. " „ ,^ ■«• c '^ ' 1 ^^^ ^ i { ^ / ' V / >.^~- ^^ 5^ \ V J / / J' ~^ i V \ \ Fig. 310.— Section of the Human Rete Testis. X 96. (Kulliker.) A. Artery; C, rete tubules ; L, Ivmphatic vessels ; s, connective tissue partly surrounded by rete tubules ; Sk, part of a convoluted tubule, to the left of which are sections, probably of straight tubules ; V, vein. (From liiailey's " Histology.") giant forms and some with two heads or two tails occur, but these are of unknown significance. The convoluted tubules of the testis consist therefore of a complex stratified ciliated epithelium, the basal ceUs being spermatogonia and the superficial cells, spermatozoa. The columnar susjentacular ceUs are scattered through this epithehum. Spermatogenesis occurs in "waves" along these tufjules as is seen when they are cut lengthwise (Fig. 309). 18 Digitized by Microsoft® 274 HISTOLOGY. The superficial cells show alternating areas of mature and immature spermatozoa. In cross sections all the superficial cells may be of one stage, which differs from that of the adjoining tubule (Fig. 305). Toward the periphery of the testis the convoluted tubules (140 !>■ in diameter) present many loops and they may anastomose forming a network. Blind endings are also observed, and investigators disagree as to the nature of the usual termination. As they pass toward the epididymis they receive branches at acute angles and their windings diminish. Sexual cells dis- appear, leaving only the sustentacular cells in the form of a simple Blood vessels. Epididymis. Mediastinum, con taini !!,£;: the rete testis. ^^ Straight tubules. Septula. Lobules, con- sisting of coti- \-oluted tubules. "':^jg5^^' Fii:;. 311. — Cross Sixiion of the Thstis ov \ Child at Bh;';h. V lo. columnar epithelium. This flattens abruptly to form the lining of the straight tubules. A distinction between the rclc and straight tubules seems superfluous histologically since both are hned with a simple epithehum of low cells. In some places these are very flat, suggesting endothehum; in others they are columnar. Tlie characteristic dilatations of the rete tubules are shown in Fig. 310. They contain spermatozoa and immature sexual cells together with pigment granules and broken dovm cells. Connective tissue oj the testis. The rete possesses no basement mem- Digitized by Microsoft® CONNECTIVE TISSUE OF THE TESTIS. 275 brancs, such as surround the convokited tubules, but is imbedded in a mass of connective tissue loiown as the mediastinum testis (Fig. 311). From the mediastinum, layers of tissue, the septula testis, extend radially toward the periphery of the testis, dividing the convoluted tubules into pyramidal lobules with apices toward the rete. The periphery of the testis is covered with a dense connective tissue layer, the tunica alhuginea. It contains numerous elastic fibers which increase with age. The vis- ceral layer of the tunica vaginalis rests upon its outer surface. The inner portion of the albuginea is very vascular, forming a distinct layer at birth (the tunica vasculosa). Connective tissue extends from the septula among the convoluted tubules. Immediately surrounding them there is a delicate basement membrane followed by a layer of closely interwoven elastic fibers, and flat cells. In the looser connective tissue between the tubules I cells. CoiinecLive tissue. - Vr^/l "IA- Z^ tubules. ^ < ! .■ '^ N •■ J/ » ; -v. 'i^ » <, Fic. 312.— From « Cross Sectkin of the Testis oj' a Man Twenty-two Ye.^rs Old. X 50. there are clumps of interstitial cells, shown in Figs. 312 and 309. They are said to arise from mesenchymal cells of the genital ridge. Some- times they retain protoplasmic processes, but more often they are rounded or polygonal structures in close contact and without distinct cell bound- aries. In their abundant protoplasm there are pigment and other gran- ules, fat droplets, and rod shaped crystalloids. (Rod and spindle shaped crystalloids are also found in the spermatogonia at ah ages, and after puberty octahedral forms occur. Rod shaped forms in the sustentacular ceUs have already been mentioned. The composition and significance of all these are unknown, but they are not considered post mortem for- mations.) The interstitial cells, although not intimately related with the vessels , are thought to produce an internal secretion, and there is evidence that upon it the sexual instinct depends. During senile atrophy of the testis Digitized by Microsoft® 276 HISTOLOGY. the interstitial cells at iirst increase; later they are destroyed. At the same time the basement membrane becomes thickened and hyaline, fat drop- lets accumulate, and the sexual cells disappear, leaving the sustentacular cells. TJie vessels and nerves of the testis enter the mediastinum and tunica albuginea, having followed the ductus deferens in the spermatic cord. The convoluted tubules are surrounded by capiUary networlis derived from branches of an artery to a Wolffian glomerulus, and are drained by capillary branches of the Wolffian sinusoids. The main stems of these vessels are called internal spermatk. Lymphatic vessels are numerous in the tunica albuginea and they extend among the tubules. Nerves from the spermatic plexus accompany the blood vessels; the presence of intra- epithelial endings has not been established with certainty. Epididymis. The effereni dnels whicli j)ass from the rete to the duct of the epididy- mis are lined with an epithelium in which groups of columnar cells alter- .. Tangential section ,---''' of a ductulus etYerens. ■■\ ■ Eluod \essel. / CoTinectivc tissue. rans\ eise section f a ductulus ctTeicns. P^ijitliclinm Circular muscles of the (liiclus epididyniidis. •'itl; 313-— From a Skction oi.- hie HK\n ok \ Muman lI^'IDIn^■MIs, showing Sfctions of the UiJCTus Epiuidvmidis in thk Center and of Duct lei Eefkrentes on the Sides. X 50. nate with those which are cuboidal (Figs. 313 and 314). Thus the inner surface of the epithelium has depressions suggesting glands, but the basal surface is free from outpocketings. The epithelium is generally simple, although in the tall parts it may appear 2 or 3 layered. The cells con- Digitized by Microsoft® EPIDIDYMIS. 77 rl On ^ Q^M'^r' Sni._)Mih muscle fibi Fig. 314 L I'lincctu'e tissue. us Effkrens Trans\'f:rsk Skction of a Ductii Testis of an Adult Man. he jigtit-hand end of the illustration is schematic. No cilia ruuld lie seen, although those of the epithelium of the epi- didymis were well preser\"ed. >, 360. tain fatty, pigment, and other granules, and produce a secretion \\'liich may appear in vesicular masses on the surface of the cells. Often the tall cells and occasionally the short ones are ciliated. The ciUa vibrate so as to pro- duce a current toAvard the ductus epidiclymidis. The epithelium rests on a striated basement membrane which is surrounded by a layer of circular smooth muscles, several cells thick. The muscle Cuhlcal cells. columnar cells. la}'er is thickest toward the ductus epididymidis. Among the muscle cells there are elastic fibers which, like those of the ductus epiididymidis and deferens, first appear at puberty. There are no glands in the efferent ducts, but the irregulari- ties in the epithelium are thought to be due to glandular activity. Before puberty and in old age these irregularities are slight. The ductus epididymidis consists of a two-rowed epithehum with rounded basal cells and tall outer columnar cells. The latter contain secretory granules and sometimes pigment, and have in the middle of their upper surfaces long non-motile hairs which in sections are usually matted in conical processes - — - (Fig. T,2„ b, p. 31). The epi- -. , ~ thelium may contain round caA'ities opening into the lumen or forming closed cysts. The delicate membrana propria and a thick circular muscle layer complete the wall of the ductus, the convolutions of which occur in a loose connec- tive tissue. Toward the ductus deferens the muscle laA'er thickens. There are no glands in the ductus epididymidis but its cells produce considerable secretion in which the sper- matozoa become active. The blood vessels of the epididymis, AA'hich are few in comparison with those of the testis, lie in part so close to the efferent ducts as to cause the tunica propria to bulge toward the epithelium. The nerves, besides peri- . EpitlKlium. * -^i m ^Tc^lbrana ropna. Circular layer of muscle fibers. Loose comiecti\-c tissue. 315.— Transverse Section of a Hu:^ian Ducti.^s Epididymidis. >., So. Digitized by Microsoft© r / 278 HISTOLOGY. vascular nets, form a thick plexus viyospcrmalicus provided with sym- pathetic gangha. It is found in the muscukir layer and occurs more highly developed in the ductus deferens and seminal vesicles. Its fibers supply chiefly the smooth muscles, and to a less extent, the mucosa. Ductus Deferens. The ductus deferens begins as a convoluted tube continuous with the ductus epididymidis; it becomes straight and passes to its termina- tion in the ductus cjaculatorius. Shortly before reaching the prostate it exhibits a spindle shaped enlargement, about ih in. long and -| in. wide, known as the ampulla (Fig. 317). The ductus deferens consists of a tunica mucosa, muscu- laris and adventitia. -""' ^•~. The epithelium is gen- ' I "' ' '""■ erally in two rows, the tall inner cells producing round masses of secre- tion. Toward the epi- '^J ^:^^^ ' d.aimusci.s. dldyuiis it mav also liavc non - motile ciha. To- ward the ampulla it may be several rowed, resem- bhng the epithehum of the bladder. It rests on a connective tissue tunica '^'*\\^ - - propria which is sur- rounded by the three F,G. 3.6.-Cross^ect,,,n^ok -, he H,:^,AN Ductus j^y^^.^ ^f ^j^g mUSCularis. The inner and outer layers are longitudinal and generally less developed than the middle cir- cular layer. The adventitia is a loose elastic connective tissue, blending with that of the spermatic cord which contains numerous arteries, veins, lymphatics, nerves, striated muscle fibers of the cremaster muscle, and the rudiment of the processus vaginahs. In the ampulla the longitudinal folds which arc low in the ductus deferens, become tall and branched so that they partly enclose irregular spaces (diverlicula). Similar folds occur in the seminal vesicles. It is doubtful whether in either place any of them should be considered glands. Around the ampulla the musculature is irregularly arranged; the longi- tudinal layers separate into strands which terminate toward the ejacu- latory ducts. Digitized by Microsoft® •■ 1 RT ]MtlL;llU- » d 1 al imiscks. f^ Ciicular imi-^cles. ^3 X i r ( )iUi r loiiQ-itu- iiual muscles. ■i - unTiccli\ L- tb.sue. Cross Sectk N OF -1 HE Hi MAN Ductus Deferi :ns. X 24. SEMINAL PASSAGES. 279 Seminal Vesicles and Ejaculatory Ducts. The seminal vesicles grow out from the ductus deferentes at the prostatic ends of their ampullae. Each consists of a number of saccular expansions arranged along the main outgrowth which is irregularly coiled. The hning of the sacs is honeycombed with folds as shown in Figs. 317 and 318. The epithehum is generally simple or two-layered, the height of the cells varying with the distention of the vesicles by secretion. Gran- ules occur in the cells, which produce a clear gelatinous secretion in sago- FiG. 317, — Seminal Vesicle anij Ductus Def- erens. (This is natural size.) (After PIberth.) ad., Adventitia; am., atnptiila; d., diverticultini ; d. d., ductus duferens; d. e., ductus ejacula- tiiriiis; m., uiusctdan^ ; s. v., sciuinal \ esicle ; t. p.. tunica propria. Fig. 31S.— Vkrtical Section of 7he Wall of A Seminal Vesicle. (After Kollilier.) ep., Simple epithelium; g., gland-like depression; m., muscularis; t. p., tmnca propria. like masses. Spermatozoa are generally found in the human vesicles, but except during sexual excitement they are absent from the vesicles of rodents; this and other facts indicate that the function of the or£;an is primarily glandular. Pigment granules in varying quantity occur in the epithelial cells and in the underlying connective tissue. They may im- part a brownish color to the secretion. The ductus ejaciilatorii on their dorso-median side are beset with a series of appendages which do not project externally, but are wholly en- Digitized by Microsoft® 28o HISTOLOGY. closed in the connective tissue wall of the duct. Some of these append- ages show the same structure as the seminal vesicles and therefore might be described as accessory seminal vesicles; others are simply convolu- tions of alveolo-tubular glands, which may be compared with prostate glands. The mucous membrane of the ductus ejaculatorii is like that of the seminal vesicles, except that its folds are not so complicated. Muscle fibers occur only around the appendages. The wall of the duct itself con- sists of an inner dense layer of connective tissue with circular strands, and an outer loose layer (adventitia). Appendices and Par.a.didymis. The appendix testis [hydatid of Morgagni, sessile hydatid] is a small vas- cular nodule of connective tissue covered with peritonaeum of the tunica vaginalis, except at its stalk of attachment. It contains one or more fragments of a small canal, closed at both ends, occasionally having blind oul- pocketings. The canals are lined with simple columnar /;p>-. __c,e epithelium sometimes ciliated. The peritonaeal cells l9^^~]^^^ over a portion of its surface are columnar and have / /lC"jN__at '^"^*^" interpreted as the evaginated end of the Mtiller- / w^ \ ian duct. ----■\-t. The appendix epididymidis[st?i\kt(lh\da.i\6] IS wot 1 always present. Among 105 cases examined by Toldt 'I it was found 29 times. It consists of loose vascular I ■ fi-x-r. connective tissue covered by the vaginalis, and contains &.;,,. .V // a dilated canal lined with columnar epithelium some- ^^' J.,1 times ciliated. The canal has no connection with the ^ . \ ■' size. {After Eberth.) arise from pockets of the tunica vaginalis. „. e.. Appendix cpididy- -pj^g paradidymis is found "frequently but not .nidis; a. t., appendi.x . ,, ', j i.-ii l <- 1 testis; c. e., caput epi- always in older embr)-os and ciiudren, as an elongated, ttlnKa'vagin'ai'il'^' '"" whitish structurc on the ventral side of the spermatic cord. It is sometimes just above the head of the epi- didymis, sometimes higher, but always in front of the venous plexus. A second, lower part of the paradidymis is found in late childhood, but not as a rule in the adult. It is a macroscopic coiled canal with outpocketings, found behind the head of the epididymis and in front of the pampiniform ple.xus." (Eberth.) The upper portion represents the anterior part of the Wolffian body, which is not involved in the formation of the testis. It contains pigment derived from the det^enerated Wolifian glomeruli. Cilia, which occur at birth, later disappear. The lower section may connect with the tubules of epididymis and contain spermatozoa, or it may be completely detached. Its tubules are made of col- umnar epithelium, simple or stratified, sometimes ciliated, and they show elevations suggesting those of the efferent ducts. Often they become cystic. Prostate. The prostate consists of from 30 to 50 jjranched ah'eolo-tulnilar serous glands, which grow out from the prostatic urethra, and surround Digitized by Microsoft® PROSTATE. 2S1 it together with the ejaculatory ducts and the prostatic utricle. The prostatic urethra is embr_vologically the neck of the bkidder, and as the glands grow out they become surrounded by the smooth muscle fibers of the bladder or urethra. The smooth muscle of the adult prostate forms a quarter of the bulk of the organ, and together with an elastic connec- tive tissue it unites the numerous glands in a compact mass. The glandular epithelium is simple and either cuboidal or columnar. It may appear stratified as it passes over the folds in the walls of the tubules. Near the outlet of the larger ducts the epithelium is like that of the bladder and prostatic urethra. In the prostatic alveoli, of older p^ersons espe- n,"l™ie' ghh.k *"™iss''ue'^ "^ daily, round or oval colloid masses 1 from 0.3 to i.o mm. in diameter occur; ^'' ~~i. as seen in sections (Fig. 321) thev -^- > < 1 ; ^ exhibit concentric layers. Their re- ^ '\i^\ ■^■■^ f '-4, actions on treatment with iodine solutions ( \ j\^ \ t suggest amyloid. These concretions are j ^^ 'iii'i-'' ^^\ t "^'''^ probably deposited around fragments ^ ','ii * •t,'' ^ ^^'^/ ' ■/"'^Ji'J of cells. Octahedral crystals also occur , p' t ^ r^ t\^r^^'\ \ ^'^ il in the prostatic secretion, which is a /^>-'" ' / J^'','', " ^^■ thin milky emulsion, faintly acid; it *\mv \r , ^'ii , "Ij" ' '/ I'-^y^ has a characteristic odor which is ab- \\^'^ '|ip/ fMH ^j - f'l sent from the other constituents of the V' k \K ^)t, ' "^"/f'Hl' ^'''^ seminal fluid. ' \M ^ ^ ^ " ; s^rri The smooth muscle fibers are 3^ tl'T^ V i >?4^ found everywdiere between the pros- 1 tatic lobules; toward the urethra they cd a thicken to form the internal sphincter of ^ * the bladder. Smooth muscle is also abundant on the surface of the prostate ^^^ j^q.—from a skction of the pros- , .^ , , ,, - • t 1 rU, r. TATE OF A Man TWKNTV-rHREE YEARS and it borders upon the striated libers ,jlu, rso. of the sphincter of the membranous urethra. The prostate is abundantly supphed with blood and lymph vessels. The numerous nerves form ganghonated plexuses from which non-meduUated fibers pass to the smooth muscles; others of the nerves have free endings; stiU others, both in the outer and inner parts of the "land in doss and cats, end in cvlindrical lamellar corpuscles. Urethr.a. axd Penis. The form of epithelium found in the bladder extends through the l)roslatic lo the membranous part of the urethra. Its outer cells grad- Digitized by Microsoft® 252 HISTOLOGY. ually become elongated and it changes to the simple or few layered col- umnar epithelium of the cavernous portion. In the dilatation of the ure- thra near its distal end, the jossa navicularis, the epithelium becomes stratified with its outer cells squamous; the underlying papillae of the tunica propria become prominent, and the whole is the beginning of the gradual transition from mucous membrane to skin. Glands. Small groups of mucous cells are scattered along the urethra and in the cavernous part, especially on the upper wall, they form pockets caUed nrelltral glands [of Littre]. Often these pockets are on the sides Rcrl corpuscles in a ' 'c "I \ ssel Col ntcL \ e I F.I II e '-^./'^'^ !$*?riniary follicle ; g. blood vessel. (From iMcMurrich.) 327.- Ihan the cpoophoron; it has been found in various mammals and detected in the human adult. Except for the longitudinal duct, the Wolffian duct is ordinarily obhterated in the female. Fragments may persist in the musculature of the uterus and these "canals of Gaertner" sometimes open into the vagina. The ovary, hke the testis, develops from the middle part of the genital ridge. The upper end of the ridge is said to be reduced to the band of tissue (fimbria ovarica) connecting the ovary with the uterine tube (Fig. 326); except for its ovarian attach- ment this fimbria resembles the others. The ovary is covered by a layer of columnar peritonaeal cells containing scattered large sexual cells. From this layer, cords including cells of both sorts, extend into the deeper tissue of the genital ridge (Fig. 327); toward the epoophoron their ar- rangement has been found to suggest a rete. Instead of forming tubules which empty into the Wolffian body as in the male, the sexual cords of the female produce detached islands of cells. The islands become subdivided into groups usually containing a single sexual cell, and known as primary jollicles. Their later history will be considered with the adult ovary. The rete cords become vestigial or dis- appear. The urogenital sinus which receives the urethra and vagina becomes a shallow space called the vestibule (Fig. 326). The genital papilla, tipped by its glans, becomes relatively shorter as the female embryo develops. It foi"ms the clitoris, analogous with the penis, and is covered by the lesser genital folds, the labia minora. (Compare Fig. 328 with Fig. 302, page 267.) The labia form a prepuce for the chtoris but do not unite beneath it making a raphe; they remain separate, as paits of the lateral bomidaries of the vestibule. The larger genital folds, labia majora, likewise remain separate. They receive the ends of the round ligaments of the uterus which correspond with the guber- o. 328. — Diagram of the External Genital Okgans of .\ Female h.MBRVO. Anus; g., glans clitori- dis; g. f., lesser genital folds (labia minora); g. g. f., greater genital tolds (labia majora); U.S., uro-genital sinus (\estibule). Digitized by Microsoft® 288 HISTOLOGY. aacula testis, and sometimes the peritonaeal cavity is prolonged into them forming a processus \'aginahs. In late stages of development the^' become large enough to conceal the clitoris and labia minora which previouslv projected Ijetween them. 0\'ARV. The ovary is an oval body about an inch and a half long, covered by a modified portion of the peritonaeum. Along its Jiilus it is attached to a mesentery, the mcsovariiim, which is a subdivision of the broad liga- ment of the uterus. The ep>ithelium of the mesentery is continuous with that of the ovary, and tlie mesenteric connective tissue joins the mass which forms the central part of the o\'ary. This tissue, rich in elastic Fig. 320. — Cross SEcrmN oi~ thk Ovarv of a Chii d Eight \'l^ars Old. > 10. I, Gc-rniiiial epithelium ; 2, tunica allni,£;iiiea ; 3. periplieral zone \\it!i prin]ar>- [ollicles; 4, vesictilar fol- Inle; 5, stroma o\'arii ; 6, ineilKistimini ; 7,^s, pen[)Iieral sections of vesicular follicles ; 9, hilus. con- taining lart^e veins. fibers and tortuous blood vessels accompanied bv strands of smooth muscle fibers, is sometimes called the medulla of the ovary but may per- haps be better named the mediastinum. The peripheral part, except at the hilus, consists of the connective tissue stroma ovarii together with the primary and large vesicular jollicles which it surrounds. Just beneath the ovarial epithehum it forms a dense layer consisting of two or more strata, the tunica albugiiica. The jormatioii oj jollicles. Tlie germinal or peritonaeal epithehum of the ovary consists of a single layer of small cells which may become low columnar or flat. Even after birth sc.\ual or "egg cells" may be found in it (Fig. 330). The egg cells divide by ordinary mitosis in the epithe- lium and in the detached islands of peritonaeal cells in the stroma. At xual maturity nearly all of these islands have been separated into pri- se Digitized by Microsoft® FOLLICLES OF TFIE OVARY. 289 mary follicles, each being a single egg cell surrounded by a simple layer of flat cells derived from the peritonaeum. Sometimes a follicle contains tAVo or more egg cells, all but one of A\'hich may atrophy; or the egg cell may have two nuclei the signihcance of \Ahich is obscure. The number of follicles in an ovary has been estimated to be from 8,000 to 16,000. Some consider that no new ones are formed after birth, but others believe that they may be produced in the adult. At all events only about 200 of them become mature; the others degene- rate at various stages of de- velopment. With further growth the follicular cells become columnar and then stratihed (Fig. 331); the egg cells enlarge as their protoplasm becomes charged with nutritive material (yolk granules or deutoplasm). The connective tissue around the follicle is compressed to form a distinct layer, the theca folliciili. Later the theca is divisible into a dense fibrous tunica externa, and a vascular tunica interna containing many cells with abun- l( GermiiDil epiUiuliiirn. Ktjff cell. J>\/rs'::^f£^5 iSLicleolus. -.^ Nucleus. -^'Jtl riy,i&f^^i:^if4^i Protoplasm. '''^^-^,^^J.^"^''-^'0J /C?) T — s«ev»!£' Follicular cells. Fig. 330 F^Rij.M A Sectihn of 'ihi-: 0vAR^■ OF A Child Fi)i;r \\'i.:fks (".)i.ri. ;■', 24-.). Germhial Tuuica Priiuary epithelium, albuyinea. follicle. A degenerating folli ' Fig. 331. — Fro.m a dant protoplasm (Fig. 332). A dehcate membrana propria is found between it and the follicular cehs. After the folhcles have attained a certain size a crescentic cleft appears among their stratified ceUs. By distention of the cleft and enlargement of the folhcle the condition shown in Fig. 332 is produced. These vesicular jollicles [Graafian follicles] vary in diameter from 0.5 to 12.0 mm. Besides the theca, the follicle includes Digitized by Microsoft® 2qo HISTOLOGY. a siraliiiii i^rdiiii/osiiiii or jiLTijjhcral la\'er of follicular cells, and the nimu- lus oophonis or heap of such cells containing the immature ovum. The cumulus is connected ^\■ith one side of the follicle although in certain rt'^ f Tunita exLei'na — ^3 I Tunica iiUi^riia -——^ \ Stratum granulosum Cum ulus nophonis. Egp cell \\-\\.h /r.ria Ijelluciiia, nucleus ami nucleii'Uis. r y ./ Fig. 332 — Skciion of a L\rgi.: \'ksicl'i.ar Folltci h oi-" a Child I^igmt ^'kars Old. >; 90. 'Ihe clear spacu witliin tlie follicle coiilams the liqmjr tollicLili. sections (such as a horizontal section near the top of the cumulus in Fig. 332) it would appear completely detached. The columnar cells of the cumulus adjacent to the ovum are radially arranged, forming the corona radiaia. The cavity of the follicle, at first cres- centic, becomes so distended with lluid as to be nearly spherical. The fluid, or liquor jollic- itli, is an aqueous transudate from the blood \'essels. Certain ajipearances (Call-E.\ncr bodies) in the stratum granulosum have been ascribed to cells undergoing liquefaction, and also to spaces containing a dense liquor. The structure of the egg cell within the cumu- lus will be considered under oogenesis. Oviilalion aitdlhc corjyiislulciiiii. Around the mature vesicular follicle the tunica interna becomes very thick and cellular, forming elevations toward the stra- tum granulosum. .\t this stage the follicle is large, being about 12 mm. in diameter, and one surface of it is so close to the ovarial ^'- 333. — C)\'AR\', Cut .\clmss, Slighllv Reduced. .Aperture through wliicli tlu' ovum escaped; c. a., corpus al- hicaus; cl., blood ciot in a cor- pus luteuni of o\'ulalion ; th., tlR-ca lolliculi : V. f., \esicidai follicle. I.Mlcr RiclTcLl Digitized by Microsoft® OVULATION. 291 epithelium as to cause it to bulge macroscopically and then to rupture. Through the opening thus made the liquor folliculi and the egg cell, sur- rounded by more or less of its corona, are expelled into the peritonaea! cavity. The discharge of the o\'um from the follicle is knoAvn as ovula- tion. Blood escapes from the tunica interna and forms a clot within the empty foUicle (Fig. 333). On all sides the clot is surrounded b}' prolifer- ating cells which contain a yellow fatty pigment; thus they form a corpus luteum. The lutein cells increase in size and number and the clot which may show haematoidin cr}'stals, is gradually abscjrbecl. Between the lutein cells there are strands of vascular connective tissue as shown in Fig. 334. If pregnancy does not occur the corpus luteum attains its maximum development in 12 days and degenerates within a few weeks. Connective tissue septa. Fibrous conneeti\'e tissue. Lutein cells. ^t A B Fig. 334. — A, Portion <.'V a CoRPt_-s Luteum of a Rabbit. B, Portion of a Corpus Luteum of a Cat. X 260. In B the lutein cells lia\'e become fatty and contain lartce and small vacuoles. Connective tissue increases anrl the lutein cells disintegrate; the newly formed vessels are obliterated and the mass becomes a nodule of dense "scar tissue," the corpus albicans. If however, ovulation is followed by pregnancy the corjjus luteum enlarges even to a diameter of from 1.5 to 3 cms., reaching the height of its development in five or six months. It persists until the end of pregnancy. Thus the coqtus luteum of preg- nancy must be distinguished from the coqaus luteum of ovulation. As to the origin of the granular, \'acuolated lutein cells there is a cHfferencc of opinion. Some consider that they arise from the stratum granulosum, and others from the tunica interna. They have been com- pared with the interstitial cells of the testis, and there is experimental evidence that they produce an internal secretion without which an embryo cannot develop within the uterus. Digitized by Microsoft® 292 HISTOLOGY. Many follicles degenerate wilhout discharging their egg cells. Cells from the stratum granulosum and leucocytes are said to invade them and after absorbing the egg protoplasm they disintegrate. The zona pellucida, a clear layer around the egg cell, becomes conspicuously folded and per- sists for some time (Fig. 331). The basement membrane of the stratum granulosum has been said also to thicken and become convoluted. These degenerating or atretic joUiclcs are finally reduced to inconspicuous scars or they disappear. After the menopause the degeneration of the egg cells becomes general. CI zp IIP- ^i,,,' //J (pw.- ^''IG. 335. — Till': 0\fM AS DlSCHARCFD FRf>M A VESICULAR FOLl-lCLF- OF AN EXCISED OvARV OF A \\'(iMAN 'J"niRT\ \'FARS UF Age. ExaiTiiiietl Iree-h in liquor fnlliculi. (Nagel.) C. r., Corona TLidiala : n., luicleus ; p., ^^ranular protoplasm ; p. s., perixilelline space ; y., yolk ; z. p., zniia pell Lie iU a. (From McMurrieh's " E!nbr\ oloi;y.") Oogenesis. The maturation of the ovum is comparable with that of the spermatozoon. Just as an indefinite number of generations of spermatogonia produced by ordinary mitosis, terminates in primary sper- matocytes, so the oogonia terminate in primary oocytes. Both the primary spermatocyte and oocyte give rise by tAvo reduction divisions, in which one half the somatic number of chromosomes is involved, to four mature sexual cells. In case of the OAum, howcA'cr, only one of the four is capable of fertilization. The sexual cells in tlie germinal ejiithclium and in the islands of the Digitized by Microsoft® OOGENESIS. 293 ovary are chiefly oogonia. The vesicular folhcles contain oocytes which may be recognized by their great size (about 200 /-/ in diameter). As seen in Fig. 335, the nucleus is large and vesicular [and is often caUed the germinative vesicle]. It contains a nucleolus [germinative spot] which in fresh Uquor folhculi exhibits amoeboid movements. The nucleus has a distinct membrane; usually it is near the center of the cell, but it may migrate to the periphery. The central part of the protoplasm contains coarse granules of yolk derived from the follicular cells; it is surrounded by a finely granular zone, and this is followed by a very narrow layer free from granules. The protoplasm of oocytes may contain a "yolk nucleus," a structure formed by the centrosome and archoplasm or idio- zome. Yolk nuclei are not found in mature ova. The oocytes probably possess no distinct cell wall. They are surrounded by a broad, clear, radially striated band, the zona pelliicida. The striations are said to be canals containing processes of the follicular cells. It is still doubtful whether the zona is a product of the oocytes or of the folhclc. The egg cell may become separated from it by a narrow perivitclliiie space as shown in Fig. 335. When the pjrimary oocyte di^'ides into the , . 1 . ^"^ 3^6.— 0\ UM OF White secondarv oocytes the nuclear material is equally M'.hsk. S' rkul-ni.kd ^ liv Zona PI'.i^li.icida. distributed between them. One of them, how- Aboxe the omuh are t«-o polar globules; within ever, receives nearly all the protoijlasm; conse- '' are two nuclei, one ^ belonli-iiig; to the ovuin, quentlv the other is a small cell and is known as the other being derived ^ •' rrom the head or the the first polar globule. In becoming a mature ovum ru™'''°so°bi'.tta ^' 1.™ the secondary oocyte divides for the second and m mot's ■■Embry- ( Alter Sobiitta, fiom Mi not' ology.") last time, thus giving rise to the ovum and second polar globule. The first polar globule may divide in two. Thus the pri- mary oocyte produces a mature ovum, and three polar globules which from their lack of p)rotoplasm are generall)' functionless. As they occur in the mouse they are shown beneath the zona pellucida in Fig. 336. It is unknown when the polar globules are formed in man, whether in the ovary before ovulation, or later. In the mouse one forms in the ovary and the other in the uterine tube. Feiiilizalioii. The ovum passes from the peritonaeal ca^-ity into the fimbriated end of the uterine tube, and in the upper part of the tube it may be fertilized. The process in man is unknown, Ijut from observations in other ani- mals it is probable that several spermatozoa enter the zona pellucida, and that only one passes into the protoplasm of the ovum. It loses its tail piece as it enters. The head is resolved into twelve (?) chromosomes which become ar- ranged beside the twelve (?) in the nucleus of the ovum. The centrosomes' Digitized by Microsoft® 294 HISTOLOGY. of the fertilized ovum may be derived from that of the spermatozoon, or from that of the ovum, or arise anew; the evidence is conflicting. Each of the two cells into which the fertilized ovum divides, receives one half of each of the twenty-four chromosomes, twelve from either parent, and in all subsequent mitoses 24 (?) chromosomes appear. This remarkable distribution of chromatin has caused it to be considered the bearer of hereditary qualities. The spermatozoon, however, contributes protoplasm to the fertilized ovum and possibly the centro- some also. Vessels and nerves. Branches of the ovarian and uterine arteries follow a tortuous course from the hilus to the capillary networks of the tunica interna. They branch freely in the stroma. The veins form a dense plexus at the hilus. Thin walled lymphatic vessels arise in the tunica externa of the corpora lutea and larger follicles, and become more numerous toward the hilus. Their course is independent of the blood vessels, peri- vascular lymphatics being absent. There are no lymphatics in the albu- ginea. MeduUated and non-meduUated nerves supply chiefly the vessels, but they form terminal nets in the thecae. It is uncertain whether any extend among the follicular cells. Ganglion cells have been recorded near the hilus, but in man the existence of an ovarian ganglion is denied. The principal nerve supply is the plexus of the ovarian artery. Epoophoron. The tubules of the epoophoron presumably vary in structure. They have been described as cords of cells and as tubules lined with simple cuboidal or columnar epithelium, sometimes ciliated. A layer of circular muscles may surround them and internal longitudinal fibers have been found. The epoophoron is of interest as a source of cysts of the broad ligament. Peritonaeal cysts may also occur. Uterine Tubes. Each uterine tube is about 5 inches long and extends from its orifice in the abdominal cavity to its outlet in the uterus. It is divided into the fimbriated funnel or infundibuluni; the ampulla or distensible outer two thirds, the lumen of which is about a quarter of an inch in diameter; the isthmus or narrow inner third, not sharply separated from the ampulla; and the uterine portion which extends across the musculature of the uterus to the uterine orifice. The tube includes a tunica mucosa, (submucosa), muscularis, and serosa. The mucous membrane is thrown into folds which are low in the isthmus but are tall and branch in the ampulla, the lumen of which they seem to fill (Fig. 337). The branches may anas- tomose; glands are absent. The ampulla has been compared with a ■seminal vesicle; in it the ovum is probably fertilized normally and the Digitized by Microsoft® UTERINE TUBES. 295 development of large embryos A\-ithin it is not a rare occurrence. epithelium is chiefly simple columnar and ciliated, the stroke of the being toward the uterus. Small areas of flat non-ciliated cells may occur near the infundibulum and non-ciliated cells ha\'c been found in the isthmus. The tunica propria is a vascular tissue often containing lymphocytes. It extends into the folds. In some j^laces the presence of strands of longitudinal smooth muscles (a muscularis mucosae) separates the mucosa from a sub- mucosa. The muscularis consists The ciha A Fig. 337. — The Mucosa of the ITtkrink Tube A, Near its Fimbriated End ; B, Near the Uterus. (After OrLhmanii.) of a thick inner layer of circular fibers and a thin outer longitudinal layer. The layers are thin toward the infundibulum where the longitudi- nal fillers may be absent. The loose inner tissue of the serosa is sometimes called the adventitia. Abundant elastic fibers occur in it, and n t/ , ■ ; 4^h T r I ^\U\ linariiiiiscles. ri od -\ tss^K "■ IHMj.ua , c, ■^kiiul iiLir l.nur; ;, (niU I, iinifv muscular uiscular la\er. Digitized by Microsoft® UTERUS. 297 and circular, and an outer longitudinal. The uterine muscles arc smooth sometimes branched. During pjregnancy they increase in number and in length to three or four times their ordinary dimensions. Except in the peripheral part of its lower half the uterus contains little elastic tissue. There the elastic elements are at right angles with the course of the muscle fillers. They increase during the lirst half of pregnancy and decrease in the latter half ("except in the outer connective tissue). There is no submucosa; epithelial pits or uterine glands extend to the muscle layer and occasionally enter it. They are vertical tubes, some- times branched, which have a tortuous course in their deeper part. Often two or three unite so as to have a common outlet. Their distance from one another, the extent of their flexures and their relation to the muscu- laris are features sub- ject to pathological changes. Cystic dila- tations are common especially in older persons. The glands produce no specific secretion. They are lined with simple col- u m n a r epithelium sometimes cihated, in all respects Uke that of the uterine cavity. Often ciha are absent from the uterine epithelial cells, which is said not to be due to faulty preservation but to the fact that the ciliated cells occur singly or in groups. According to a recent estimate only y- or ttV of the cells are ciliated; and from observations on certain animals it is suggested that ciha are present only in certain functional conditions, at other times being absent. In the cervix, mucus-producing cells occur, especially in the out- pocketings of epithehal pits, thus forming the branched cervical glands. Thev discharge a secretion which occludes the canal of the cervix during Fig. 341.— Mi/cous MRMBRANii ok thk Rks \'oL'NG Woman. X 35- (After Buliiii an CT THRI'S IIP A 1 Davuloff.) Digitized by Microsoft® 298 HISTOLOGY. pregnancy. Often they produce macroscopic retention cysts, due to the accumulation of secretion [ovules of Naboth, named for the Leipzig/ anatomist who mistook their nature in 1707]. When empty of secretion the cervical glands are said to resemble the uterine glands. Toward the external orifice of the uterus the epithehum becomes stratified, resting on papillae and having its outer cells squamous. Such epithehum is foimd in the vagina, and after the first child-birth it may extend into the lower half of the cervix. The tunica propria of the uterus is a very vascular reticular tissue with abundant nuclei. It contains many free lymphocytes and its lym- phatic vessels form a wide meshed network with bUnd extensions. They empty into a network of larger vessels in the subserous tissue. Medul- lated nerves are said to extend to the epithehum and many nonmedul- lated fibers supply the muscularis. Ganglion cells detected within the uterus by the Golgi method are beUeved to be not more ganglionic than those of the intestinal villi found by the same method. In the utero-vagi- nal plexus which is the source of the sympathetic nerves of the uterus, ganghon cells have been found in the vicinity of the cervix. Menstruation. Menstruation is the periodic degeneration and removal of the super- ficial part of the mucosa of the uterus, accompanied by haemorrhage from the vessels of the tunica propria. For four or five days before the discharge occurs, the thickness of the mucosa increases due to the conges- tion of its vessels and the proUferation of the reticular tissue. The glands become wider, longer, and more tortuous, opening between irregular swelhngs of the superficial epithelium. Red corpuscles pass out between the endothelial cells of the distended vessels and form subepithelial masses. This stage of tumefaction is followed by one of haemorrhage and des- quamation lasting about four days. The epithehum of the surface and outermost parts of the glands becomes reduced to granular debris, or it may be detached in shreds. The underlying vessels rupture and add to the blood which had escaped by diapedesis. In the stage of regeneration which requires about seven days, the epithehum spreads from the glands over the exposed reticular tissue, the congestion diminishes, and the mucosa returns to its resting condition. In about twelve days the cycle begins anew. The cervix takes no part in menstruation except that the secretion of its glands may increase during the stage of congestion. Beginning at puberty (12-15 years) menstruation takes place normally once in 28 days for 33 years, more or less. During pregnancy it is interrupted, although the time when it should occur may be indicated by slight uterine con- Digitized by Microsoft® ilENSTKUATION. 299 tractions and also by those which cause tiie dehvcn- of the child. Thus the duration of pregnancy is described as ten menstrual' c}-cles. The significance of menstruation is still obscure. In mammals generally, a period of congestion accompanied by uterine changes ^^'hich are sometimes closely comparable with those of menstruation, precedes sexual intercourse and ovulation. Ovulation ordinarily occurs at that time, independently of coitus. (In the rabbit and ferret, also in pigeons, ovulation may fail to occur in the absence of the male.) In the bitch ovulation takes place when the external bleeding "is almost or quite DisintesrraliTiE^ _*_ ' J - "'- ' ::■ , epithehuiii. Blood \-esseI. V.!-"~'-^C' 'Xi, '';■' ■-■■ -^ '■.'':-[ Supcrilcial eniU-njliuin. -lb< Excretory duct. --^^^^frl^fTh-'vi''-:J?>'-^\f-'^ i;^--i vJ'.'i - - IJisinteijrating ■C^^'.''' E vV'S J^'.^V...' ,.',^V--:5' S-.A.":"'.'^ X. epithelium. * -^ J ' '■'■ S- ■' 'f- ^-''.'l \.":>V!') '-. '."'■^- ^' '^i\';*'''--"T( Y' Pit-like depression. -^'■■'■'^ -^s;... '?^:':;?v^?i' ',.['?if .-^t^.V^-^iL^^;'-",t^_..,-r^V.j.', t " - ':; .f ^- ..;/,T:;^,r^'r'--tt^ — M.xcretor\- duct. ,- 1 !*■ . .-- ".\ W .V"^' ■■ '..V ■?.":■ . ■ /■ . ■. : ■. -" , - ' 'i-- Claud tubule. Dilated tubule. i^-- -■,= ;-.;.■,-'.■ ' ,■' ■;■ ■.' "''--■''i\ '.'■V -''-"■--?■;■'-- Bloodvessel. Blood ^-essel. Fig. 342. — Mucous Memi3ranh of a Virgin I^krus DtrRiNC the First Day OF Menstruation. X 30. (Schaper.J over," and this is the time of coitus. Domestication in ^-arious animals causes an increased frequency of flie congestive cycles, sometimes unaccompanied by ovulation. It is generally accepted that human ovulation is independent of coitus and to some extent of menstruation. The spermatozoa of rabbits retain their activity and are capable of fertilizing the ovum for about ten days, and it is perhaps true that if human ovulation takes place within some such period after coitus, fertilization may occur. The ovum is said to take four days in the rabbit and eight or ten in the bitch to pass through the tube to the uterus. The Digitized by Microsoft® ;oo HISTOLOGY. condition of Uie mucosa of tlie luiman uterus wlien tlie fertilized ovum enters it is unlinown. Tlie stage of development of many young human embryos sug- gests that their growth began nearer the time of the first menstruation vi'hich lapsed than the" last which occurred. This may be due to the frequency of human menstruation, which may still fje preparatory to coitus as in other mammals. The Development oe the Decidual Membranes. Before describing the mucosa of the uterus during pregnancy, it is necessary to consider the membranes of the embryo which are in contact with it. Fig. 343, A, represents a blastodermic vesicle in which the three germ layers are present. (The formation of such a vesicle by the seg- mentation of the ovum has been Ifgured on page 19.) In a thickened portion of the outer layer of the vesicle a cleft occurs, which in B has widened and become the amniotic cavily. It is bounded below by the Fig. 343. — TuRHK Diagrams np ti-ii- I-I\ i'dthiitical Dk\ KLOrMi:NT ci" i'\\\\ Himw r>i':ciDliAL Mkmbranp.s. (After Minot.) al., .\ll;niliiis ; am., nniiiioii ; am. c, anmiotic ca\'ity i cho., chorion ; coe.,coelom; y. s.. >"o]k sac. The iiu SM o has ]jeen exposed by cutting; away most of the chorion, cho., and pari of the amnion, am.: u.c, nmhihcal cord ; v., cliorionic villi ; y.s., > oik sac. chorion laeve, beginning at the placental margin, continues clear around the cavity of the uterus and, as before mentioned, the amnion adheres to it. The amniotic cavity is hUed with fluid in which the embryo is immersed. Shortly before birth the cervix dilates and the membranes thus exposed, rupture. The amniotic fluid escapes and the child follows, Digitized by Microsoft® DECIDUAL MEMBEAXES. 303 its uml;ilical cord extending througli the vagina to tlie placenta. In tlie course of lialf an liour tlie placenta and membranes are expelled, the sac which they form being inverted in the pjrocess. Thus the smooth or amniotic surface of the placenta is exposed. The very thin membranes attached to its margin consist of amnion, chorion and fragments of decidua ^•era. The denuded uterine mucosa is gradually restored to its normal condition, as after menstruation. E])ithelium spreads over its surface from the bases of the glands. In the following account the histology of the decidua vera and adjacent membranes will be considered first, then the placenta and Irnally the cord. d.br Fig. 346.-— Thi-: C'tkrus a.nd DecidI'Al Mi-:mbranes in EARL^■ Prkgn-ancv, A, and in Lati-. Prkg- NANCV, B. Thk Cord has bkk.n Cut and ti-lk EMBR^'o Removhd b'rom B. am., Amnion; am. c, amniotic cavity; c, cervix; ch., chorion ; c. u., cavity of the uterus; d. b., dcciaua hasalis; d.c, decidua capsularis; d. v., decidua vera ; m., amnion and chorion laeve drawn as one Hne ; pi., placenta ; u. c, umbihcal cord ; y. s., \'oll< sac. Decidua Vera, Amnion, .\:s'd Chorion Laeve. On the upper surface of the section Fig. 347, is seen the amnion, having its simple cuboidal or flat epithelium toward the embryo, and its mesodermic connective tissue toward the chorion. Adhesions in the form of slender strands bind it to the connective tissue of the chorion. The chorionic epithelium forms a layer over the surface of the vera; it presents slight iAegularities but is Avithout \illi. The superficial uterine epithehum has degenerated; it chsappeared in an earlier stage. The mofli- fied mucosa or decidua vera is divisible into a superficial compact layer and a deep cavernous layer. After the epithelium of the glands in the compact layer degenerated and was resorbed, the connective tissue came together obhterating the gland cavities. The compact kn'cr is therefore Digitized by Microsoft® 304 HISTOLOGY. Amnion ff^l!5^«'"!?'»5°?? Compact I. i^er. iS^'fJ^-'::^-'— ^<^ ^,<^^^~a^Z - „ Muscniaris. < Fig. 3-17 — \*i,RrrcAi, Shction thkough thf-. ^^'ALL hf a I'l iirl's about Si-:\'I'N Months Prhcnant, wijn thk Fetal Membrani-:s in Situ. Hetwefii aiiinnui and chorion arc tlireads ol" gelatinous connectn'e tissue. X 30. (Schaper.j without glands. The cells of the tunica propria have enlarged, and become decidual cells (Fig. 34S). These cells Avhich occur only in pregnancy are flattened, round, oval or branched structures of large size (.03 to 0.1 mm.). Usually they contain a single nucleus but often there are two or more, and in giant forms there may be 30 or 40. The cavernous layer of the mucosa contains slen- der clefts parallel with the muscularis. These are glands which have been stretched laterally; some of them retain areas of normal epithehum, but in many the epithelium has degenerated and from some it has wholly disappeared. The con- nective tissue is but slightly modified. Fig. 34S—DliciDUAl. Cells FR05I THr: i -i , '' ' ■ n • Mucous memhkanh OF a Human i hroughout the ciccidua Dut cspccialiy m Uti-;rus AROirr Seven Months ^ Pregnant. Below a" giant-cell," the Superficial porllon, the vcsscls ai'C ahovetothe rignta cell with a kar\- ^ ^ okinetic figure. X 250. (Schapei".) oveatlv distcndcd. Digitized by Microsoft® PLACENTA. 30s Placenta. The chorionic vihi, the interlacing branches of which form the fetal portion of the placenta, are shaped as sho\Yn in Fig. 349. The hnding of such structures in a uterine discharge or curetting is diagnostic of pregnancy. The villi in the earliest stages are composed entirely of epi- thehum, but they soon acquire a core of the chorionic mesenchymal tissue in which are the terminal branches of the umbihcal vessels. The epithe- lium is very early divisible into two layers. The outer layer consists of densely staining protoplasm containing dark round or flattened nuclei. Since cell boundaries are lacking, this is called the syncytial kivcr. Mitoses are seldom seen in it. Generallv its nuclei are in a single laver but thev m/\^ifMh^^ Fig. 349. — Isolated Thkminm- Branchf-"S of Chorimxh- \'ii.r.i; THAr o\" rni: I i:ft is irom an EiMBR^'o ov TwEiA'i-: Weeks; on the Right at Full Ti..Ri^l (Mini.t.) may accumulate in "knots" or "proliferation islands," especially in late stages. The knots project from the surface of the villi so that in certain planes of section they appear completely detached and suggest multinu- cleate giant cells. The syncytial layer perhaps completely in\-ests the \'illi at hrst, but later it is interrupted in many places. The deeper layer of the chorionic epithelium consists of distinct cells with round nuclei and clear protoplasm. Although this is a single layer at the base of }'oung villi, it produces great masses of cells at their tips. These columns or caps of cells in which the villi terminate, fuse with one another ne.xl the decidua, and the uterine tissue seems to be dissolved as this mass of epithelium proliferates. All the superficial epithehum of Digitized by Microsoft® 3C6 HISTOLOGY. the decidua basalis degenerates and disappears, and the distal parts of ■ S\ nc) tiuni. clal cells of the basal layer. Connective tissue. Filood vessel containinj^ nucleated red corpus- cles. f.lhlique section of the epitlielium. Fig. 350.— Cross Section of ^ Hl^man Chorionic \'ilh s oi' thi: Foirth Wkek of Prhgnanxv. the blood vessels in the tunica propria are dcstro^yed. The uterine blood escapes into the intervillous spaces, bounded by the syncytium, or where this is deficient, by the basal cells. The maternal blood circulates in the %^1 {^ %-)'Lf^\Sd X'^--^^^ "^^^y ) Chorionic v,ll,. .-Vj \^isvr } V- Inter\ilk'us spaces, ^^.^ Compact la\ er. (_ a\ernotis r la>er. ] C /fk\v'&^ ^^^ Floating \-illus. Attached villi. Miiscidaris. Fig. 3sI•~l>lACKA^r uK Tin.. Human Tiacknia at the Close of Trki.n.vncn . (Schaiiur). intervillous spaces as shown in the diagram Fig. 351, and does not clot. Digitized by Microsoft® PLACENTA. 307 So extraordinary is this that attempts have been made to detect an endo- thelial covering for the villi, but without success. (The syncytial layer has been considered endothelial or otherwise of maternal origin, but this view is not accepted.) The placenta at birth, being an inch thick, presents in cross section a vast number of the branches of villi cut in various planes. In the villi of Fig. 352 it is seen that the epithelium is in places hardly distinguishable from the connective tissue. This thin portion may represent the basal layer and the dark clumps of nuclei scattered over its surface may arise from the syncytium, but the reverse relation of the two types of epithe- lium to the original layers is sometimes stated. Within the villus are the blood vessels of the embryo; their blood never mixes with the maternal Epithelium. Epithelial nucleus. - Capillaries. « h^ iC^ ^S'?'*^^^^^-''.^^^^''"'^^"*^^ ^— "^^^ ■^'■^ ^J— .Vniniolic epittie Honio,<^eneous l:i\er. eliuni. Umbilical Coed. The umbihcal cord is a translucent glistening while or pearly rope of tissue about two feet in length, extending frt)m the umbilicus to the placenta. It consists of mucous tissue (p. 37) co\-ered with epithelium and containing at birth three large blood vessels, two arteries and a \'ein (Fig. 355, B). The parallel arteries gcneralh' wind around the vein making sometimes forty re\-olutions. The surface of the cord shows corre.s])onfhng s])iral markings and often irregular protuberances called Digitized by Microsoft® UMBILICAL CORD. 309 false knots. (True knots, tied by the intrauterine nio\-enients of the embryo, are very rare.) There are no lymphatic ^•essels or capillaries ^ '.or'*- . o- " li ^ ^4i no,' We« ■«a rounectn-e Li&sue. ■^■^fJ , Cell knots. 1 w^ . 354. — From -a Cross Section of a M\ti*re Human' PlaciiNta. X 260. in the cord and the vessels do not anastomose. The arteries contain many muscle fibers but very little elastic tissue and they are usually found Fig. 355. — Cross Sections of TImrtmcal Cortis. A, ' 20, from an embr\o of 2 mos. ; B, ■' 3, al birth. al., Allantois ; art., arteiA' ; coe., coelom ; v.. \ein ; y, s., >olk stalk. collapised in sections; their contraction is of interest since nerves have been traced into the cord for only a very short distance. The vein generally remains open. Digitized by Microsoft® 3IO HISTOLOGY. The uml)ilical arteries arise within the embr^'o as the principal ter- minal branches of the aorta; parts of them in the adult are called the common iliac and hypogastric [internal iliac] arteries. They end in the capillaries of the chorionic \-illi. The single umbilical vein is due to a fusion of two; within the body only the left remains, passing from the umbilicus along the under surface of the li\-er fas the ductus venosus) to the vena cava inferior. The alhvilois which the umbilical vessels accompany, extends the entire length of the cord as a slender tube or strand of cells. At birth it is rudimentary but may be found usually between and ecjuidistant from the arteries. It is more conspicuous when Mallory's stain is used. Within ^H53]23S^'' Fig 356.-V0LK Sac AND PERSISTENT pic. 3^7.— Part of a Human Am- VlTELI.lNK VeSSKIS, EXPOSED BY NIOTIC VlLLUS. X I30. Reflecting THE Amnion at thk _ ^ . . , . „ ^ Distal End of the Cord. EP" Epitnchmm ; S. C, stratum cor- (Lonnbere) iieiim : S.g., stratum o^r.TnuIosuni ; * S. Cstraliuii jiiriminativum ; M.B.. lioiiiotienenus la\er; F. T., tibrous tissue; A. T., areolar tissue. the body the allantois dilates to make the bladder, and if its prolongation into the cord remains tubular, urine may escape at the umbilicus (through a "urinary fistula"). The yolk stalk, surrounded by an extension of the body ca\-ity, is found in young umbihcal cords (h'ig. 355, A). The loop of intestine from which the yolk stalk S])rings may also extend into the cavity of the cord, and if it has not been drawn into the abdomen at birth, umbilical hernia results. If the ca^'ity of the yolk stalk remains pervious the intes- tinal contents may escape at the umbilicus (fecal fistula). Ordinarily the stalk and its vitelline vessels, together with the coelomof the cord, have been obliteratcfl before birth and no trace of them remains in sections of the cord. Digitized by Microsoft® VAGINA. 3 1 I The yolk sac may be found with almost every placenta, as a very small cyst adherent to the amnion in the placental area. If the distal end of the cord is gently stretched a wing-like fold appears (Fig. 356), differing from all others by containing no large vessels ; the fold indicates the direction of the yolk sac which may be exposed by stripping the amnion from the chorion. It may be beyond the limits of the placenta. Amniotic villi are irregular, flat, opaque spots on the amnion near the distal end of the cord. They are often present and may suggest a diseased condition. As seen in Fig. 357 they are areas of imperfectly developed skin; since epithelial elevations occur abundantly over the cords of certain mammals, these structures of unknown significance are probably normal. Vagina and External Genital Organs. The vagina consists of a mucosa, (submucosa), muscularis and fibrosa. Its epithelium is thick and stratified, its outer cells being squamous and easily detached. It rests upon the papillae of the tunica propria, and is thrown into coarse folds or rugae. Glands are absent. The tunica propria is a deHcate connective tissue with few elastic fibers, containing a variable number of leucocytes. Occasionally there are solitary nodules, above which numerous leucocytes wander into the epithelium. The sub- mucosa consists of strong elastic and looser white fibers. The muscu- laris includes an inner circular and a small outer longitudinal layer of smooth muscle. The fibrosa is a firm connective tissue, well supplied with elastic elements. Blood and lymphatic vessels are found in the connective tissue layers, and wide veins form a close network between the muscle bundles. There is a ganglionated plexus of nerves in the fibrosa. The mucous membrane of the vestibule differs from that of the vagina in possessing glands. The numerous lesser vestibular glands, 0.5-3 ^™- i'^ diameter, produce mucus; they occur chiefly near the clitoris and the outlet of the urethra. The pair of large vestibular glands [Bartholin's] also produce mucus; they correspond with the bulbourethral glands in the male and are of similar structure. The hymen consists of fine fibered, vascular connective tissue covered with mucous membrane. The chtoris is a somewhat erectile body, resembhng the penis. It includes two small corpora cavernosa. The glans chtoridis contains a thick net of veins. It is not, as in the male, at the tip of a corpus cavemosum urethrae which begins as a median bulb in the perineal region; the bulbus in the female exists as a pair of highly vascular bodies, one on either side of the vesti- bule. Each is called a bulbus vestibuli. The labia minora contain seba- ceous glands, 0.2-2.0 mm. in size, which are not connected with hair follicles; they first become distinct between the third and sixth years. The labia majora have the structure of skin. Digitized by Microsoft® ^12 HISTOLOGY. SKIN. The skin (citlis) consists of an ectodermal epithelium, the epidermis, and a mesodermal connective tissue, the eorium (Fig. 358). The ecto- derm is at first a single layer Ixit soon it Ijecomes double, the outer cells staining more deeply, and being notably larger than the inner cells. Their char- acteristic dome shape is seen in the figure. The . is uu. ,■/„/, ,.t,n„„ ^^^^^^ ^^^,^^ j^,^g 1^^,^^^ named the epilrichi'um since the hairs which grow up through the under- lying epithelium do not penetrate it, but cause it to be cast oil. The epitrichium has been found on the umbilical cord and in jjlaces on the amnion. It may possibly be related with the chorionic syncytium. The Fig. 35S.— Skin from thm Ocrii'ii-i- oi' an Emi!Rvo OF 2'2 Months. ( .Mlcr Bowc-ii.) The outer ]a\ei' of dark cell ^. Stratum conieiini Stratum lucidum Epi- dtrmis Stratum ,i;-ranii!osum Stratum L;frmiuati\uui Duct of a sweat -laud. -fe Coil of a sweat •Aand. St rat u til papillare Stratum 7"eticulare / Corium '(^f^ .■\rter>-. Fal tissue. Stratum subcutaucuni Fig, 351].— Vfrticai. Section from THti Solk of the Foot of an Adgi.t. X 25. deeper layer of ectoderm becomes stratified, and it gives rise to the hairs, nails, and enamel organs. It also produces two tj^jes of glands, the sebaceous glands which arc usually connected with hairs, and the sweat Digitized by Microsoft® SKIN. 212 glands. These are widely distributed througli tlie sl-cin; locally the ecto- derm forms the mammary glands, ceruminous glands of the ear, ciliary glands of the eyehds, and other special forms. The greater part of the surface of the skin presents many little furrows which in- a b c d tersect so that they bound rectangular spaces. On the palms and soles the furrows -Epidermis. are parallel for considerable distances, being separated from one another by slender ridges along the summits of which the sweat glands open. The ridges are most highly developed over the pads of tis- sue at the finger tips and in the interdigital spaces at their bases. Here the tactile func- tion is most perfect. The pads are very prominent in m &• 't:Mtm Pajiillae 01 A. Tactile corpuscle. ol" D. I'^iG. 360. — Vertical Section prom the Sole of the Foot of an Adult, showing Four Ridgks (A-D) "WITH A Pair of Papillae beneath Each. Bet\\'t:en the papillae of D is the duct of a sweat gland. X 25. the embryo and correspond with the "walking pads" of carnivora. Similar structures occur on the soles. Corium. The corium is a layer of densely interwoven bundles of connective tissue extending from the epidermis to the fatty, areolar suh~ W'-: Depressions whicli were occupied by papillae. Ridge corresponding to a furrow of the corium. '~'t^'^^iM^^^=^^h,^,.^^.-yr- ■ Portion of the duct of a sweat .inland. Fig. 361. — Epidermis i-rom the Skin of the Dorsum of thk Hcman Fo(jt, si--mn FROM Tin-: LdWitK Si_'R!'\\.ci-:. X 120. cutaneous tissue (Fig. 359). Its epidermal surface exhibits papillae which are tallest and most numerous on the palms and soles. Their height may be 0.2 mm. In the skin of the face they are poorly developed and in old Digitized by Microsoft© Part (if the stratum Lunieum. 314 HISTOLOGY. a^e llu'v k'lid (0 ilisappear entirely. y\s seen in Fit;. 360 they may be definitely arranged beneath the ridges of the linger tips, forming a double row under each; the grooves between the ridges corrcsjjond with epithe- lial dej)ressions bet\\'een the papillae. In Fig. 361, which rejjresents the under surface of the epidermis, the relation of the papillae to the rect- angular markings may be seen. The papillae are former] of tunica propria, a cellular connective tissue; and each papilla contains terminal capillarv loops or a tactile coqaiscle (Fig. 126, p. 105). The corpuscles are most numerous in the ^^-^_ sensitive linger tips where they may occupy one pa]jiUa in every four. Beneath the papillae the connec- tive tissue bundles ire closely inter- «'oven but toward t h e subcutaneous ,^ h ' m . \ ^y -''•^ -t , Tuuii a prop thr rMriui ,.@ 5 -> ' > ''>^ / ' .fi> ^ / _f if - v"" SKIN. 315 scrotum, and in the nipple. Striated muscle fibers in the skin of the face represent the insertions of the muscles of expression. The vessels and nerves of the corium are described on page 327. Epidermis. The epidermis is stratified epithelium, the many layers of which are divisible into a stratum germinativum and a stratum corneum. The former includes a basal row of columnar cells without membranes, which rest on the papillae of the corium. Although mitoses are seldom seen, these cells multiply and produce the several layers of polygonal cells which overiie them. The latter are connected by numerous slender inter- cellular bridges, as seen in Fig. 31, p. 30. Because of this striking feature the stratum germinativum was formerly called the stratum spinosum [and rete Malpighii]. The transition to the stratum .corneum or outer layer of horny flat cells is quite abrupt, except in the thick skin of the palms and soles. An incomplete layer of coarsely granular cells may intervene. In the corneum the cells acquire a horny exoplasmic mem- brane; the bridges become short stiff spines; the protoplasm and nucleus are dried and shrunken and in the outermost cells the nucleus may wholly disappear. The cells become flatter toward the surface, from which they are constantly being desquamated. The process of cornification presents a more elaborate picture in sections of the palms and soles. Passing outward from the stratum ger- minativum there is a darkly staining, coarsely granular layer, one or two cells thick, which is followed by a clear somewhat refractive band in which the cell outlines are indistinct. This layer seems saturated with a dense fluid formed by dissolution of the underlying granules. In haema- toxyHne and eosine specimens the granular layer or stratum granulosum is followed by a pink and then by a bluish band, which are subdivisions of the clear stratum lucidum. They are followed by a thick stratum corneum. ■ Except in the palms and soles the granulosum is thin and the lucidum is absent. Chemically the coarse granules of the stratum granulosum resemble keratin (from which they differ by dissolving in caustic potash); they are therefore called kerato-hyahn granules. Their diffuse product in the stratum lucidum is named eleidin. In the corneum it becomes pareleidin, which, Hke fat, blackens with osmic acid, but the reaction occurs more slowly. The pareleidin is not due to fat entering the skin from oily secre- tions on its outer surface. The color of the skin is due to fine pigment granules in and between the lowest layers of epidermal cells; a few smaller granules occur in the corium. Pigmented connective tissue cells are found near the anus, but they are generally infrequent and are absent from the palms and soles. The possibiUty of the mesenchymal origin of epithelial pigment Digitized by Microsoft® 3i6 HISTOLOGY. is stated on page 46. It is proljaljle that the epidermal pigment arises in the cehs in which it occurs. The origin of the granules found between the epithelial cells is obscure. Nails. The nails arc areas of modihcd skin consisting of corium and epi- thelium. The corium consists of fibrous and elastic tissue, the bundles Coriimi. Straumi geriiiinatj\ 111! Bone of third ]ihalaiix. Fig. 303 — DtiKS-M. H\i.f <>i- \ Cross Skciion of thk Third Ph.\i-\nx The ridgL'S of the nad bed in cross section appear like papi OF ..V llae. of which in part extend vertically from the periosteum of the phalanx to the epithelium, and in part run lengthwise of the linger. In place of papillae the corium of the nail forms narrow longitudinal ridges which are low near the root of the nail but increase in height toward its free distal border; there they abruptly give place to the papillae of the skin. At the proximal end or root of the nail the corium has tall papillae. The epithelium consists of a stratum gcnuinativiim and a stratum corneum, but the latter corresponds with a thick stra- tum lucidum. In the embryo the horny substance is entirely covered by a looser layer, the cponycJiium, and this name is applied in the adult to the skindike tissue which overlaps the root and sides of the nail (Fig. 363). The eponychium is the stratum corneum of the adjoining skin. Although the nail cells are formed by the entire underlying stratum germinati- vum, as is shown by the increasing thiclmess of the nail toward its distal edge, yet the principal production is at its proxi- mal root jjcncath the cresccntic white area, the lunula. The opacity of the nail at the lunula has been attributed to keratohyalin; an imper- fect stratum granulosum occurs there. The jiink color of the outer por- tion is due (o blood beneath, wdiich is seen through the transparent stra- tum lucidum. The cells of the nail may be separated by heating to fIG 304. Ilr.MAN N \ Digitized by Microsoft® HAIR. 317 boiling a fragment placed in a strong solution of caustic potash. The cells retain their nuclei as is seen in Fig. 364. The forward movement of the nail is due to the production of new cells from behind. Hair. The hairs arise as local thickenings of the epidermis. They soon become round columns of ectodermal cells extending downward into the corium (Fig. 365). As the columns elongate the terminal portion Ijecomes enlarged, forming the bulb of the hair, and a mesodermic papilla occupies the center of the bulb. On that side of the epithelial column which from its obliquity may be called the lower surface, there are found two swell- ings (Fig. 366 and 36S). The outer is to become a sebaceous gland dis- charging its secretion into the epithelial column; the inner or deeper swelhng is called the hair matrix and its cells, wliich increase by mitosis- Epidermis. Epuhdiai column, contribute to the growth of the col- umn. (The lower swelhng is often described as the place of insertion of the arrector pill muscle.) Beginning near the bulbus the core of the column separates from the peripheral cells; the latter become the oiilcr sliealh of the hair. The core forms the iiiiier sheatli and the shaft of the hair. The MesciiclT\ ma. cells of the shaft become cornihed just p,^, .^^ _ v,,rt,cal sect.on op the sk.k above the bulbus, and they are sur- Fn„[ montSs. % .Ic"'^"'''"' """"' °" rounded by the inner sheath as far as the sebaceous gland. Be3'ond this point the inner sheath degen- erates so that in later stages the distal pjart of the shaft is imme, diately surrounded by the outer sheath. As new cells are added to the hair from below, the shaft is pushed toward the surface. The central cells in the outer end of the column degenerate, thus producing a "hair canal" which is prolonged laterallv in the epidermis (Fig. 360). The shaft enters the canal, breaks up the o\'crlving epitrichium, and projects from the surface of the body (Fig. 370). That portion of the hair which remains beneath the epidermis is called its roof. In addition to the epi- thehal sheaths, the root of all larger hairs possesses a con net live tissue shealh derived from the corium. This serves for the insertion of a bundle of smooth muscle fibers which arise in connection with the elastic elements of the superficial part of the corium. Since this muscle by contraction causes the hair to stand on end it is called the arreclor pili. Its insertion Digitized by Microsoft® lipidui nn^. Cl'IIs uf tlie hair Laiial. ^ v: "^ :# •/ Papilla, *K I'lN'l-: Months. '/ 2^0. Fig. 367. — \'ki ,-'i#'.-«':<'«e»"' ^* ,^,^ ( Huxley's la>er ; .^ ^ ;. ^.^. J?'' . -.'"..-rl-' ^ .th. |„ :>",''?' 1 "" ■ ••'•f''.^ -^ -'^*:g-'2'-'' *-"" Anector muscle. I Heule slayer ,^ . 'i*'' " /A'^KS- , ^--' ^^'^^/■'■^*i' :''.■--"' Hau-tuatrix. .*'."- . , ,. .,.' ■ — Vl-K 1 ICAI, Sl-:CTION OF TH1-: SkiN OF THE FoREHEAD OF A HuMAK Fill US OF Fi\K Months. X 230. Din'ereiitialioii ol the sheaths of the hair. 318 Digitized by Microsoft® HAIR. 319 m^y^-- t.lit:;ali. I lair nialiix. Ouler sliealll is always below the sebaceous gland and on the lower surface of the hair as shown in Fig. 370. p,iocHUc..se The hairs which cover the body of the embryo and which to a variable extent persist after birth, arc soft and do'svny; they arc known as lan- ugo. Arrector muscles are absent from the lan- ugo of the nose, cheeks and hps, and also from the eyelashes (cilia) and nasal hairs (vibrissae). In describing the de- velopment of hairs it has been stated that a hair consists of apapilla, bulb, and shaft; and that the part of the shaft beneath the epidermis is covered with a connective tissue sheath, an outer epithelial sheath, and below the sebaceous gland, with an in- ner epithelial sheath. The finer structure of the shaft and its sheaths is shown in the cross section, Fig. 371, and the Fig. 369. — Vertical Skction of thi-: Skin oI' tiik Eack of a Human Fetus of Five and a Half Months. / 120. 'I he stainiii.a: with iron liaeniato.x\liii lias made the iiorny parts so black their details are iii\'isihle. Sebaceous gland Arrector pi nuiscle. longitudinal sec- tion. Fig. 372 ; it is described in the following p a r a - graphs. The connective tissue sJieatJi is de- rived from the co- rium. It is found about the larger hairs where it may be divisible into three layers. The Hpilhcli; sheaUis. CoDiiective tissue shtiath. Bulb. Papilla. I'HL cells_ Fig. 370.— From a Thick Skction of thk Hl"M\.n Scalp. Digitized by Microsoft© 3 JO HISTOLOGY. outer layer is a loose connective tissue with longitudinal bundles, con- taining elastic libers and numerous vessels and nerves. The middle layer, which is thicker, consists of circular bundles of connective tissue without elastic libers. The inner layer together with the basement membrane of the outer epithelial sheath may form a single, transparent hyaline mem- brane. The connective tissue portion of the membrane is sometimes longitudinaUy fibrous; the epithehal part is homogeneous and provided with small pores. The outer epilhelial sheaili is an inpocketing of the epidermis. The stratum corneum extends to the sebaceous glanrl; the stratum granu- losum continues somewhat deeper, but only a thinned stratum germina- tivuni can be followed to the bulb. "TNf. Longitudinal iibti laj'er. CoiinecUve I Circular fiber la\ tT tissue sheath. | Outer epithelial sheatli ^_ii_ i -' \l \ \i, e„lesla>er \^ . g,|j, K^ * 1 I n aline mem brant H Inner e,„thelialj ^ ® " (■ • sheath. I 1^ 'i-' '; I Huxle\ 's la\ ei — ' f Sheath and hair cutie J^ I ulae. , , ^ . ^' •' Hair. ■! Cortical substance "^ -^ -^ ^ "^ - \\ ^ ~ '^ i V Medullary substance ^ v S.""- ' Fk".. 371.— Fr^ciM A lIoRizoNTAi. Skction of the Hpman Scam'. X 2\0. Cross section of a hair and its sheaths in the Ir^wer half of the r.iot The /;;;;(■;• epilhelial sheatli extends from the sebaceous gland to the bulb. It begins as a laj'cr of cornified cells below the termination of the stratum granulosum; it is, however, not a continuation of that layer. Toward the bulb the inner sheath is divisible into three layers. The outer or Henle's layer consists of one or two rows of cells with occasional atrophic nuclei; for the most part they are non-nucleated. The middle or Huxley's layer is a row of nucleated cells, and the inner layer or cutic- ula of the sheath is formed of non-nucleated cornilied scales. Toward the bulb both the cuticule and Henle's layer are nucleated and the three layers become indistinguishable as seen in Fig. 372. Kerato-hyalin granules wliich occur in Huxley's and Henle's layers extend nearer the papilla in the latter. Digitized by Microsoft® HAIR. 321 Hair cuticle. Conical substance. I I I , Medullary substance I Han !j Loiig:itudiiial fiber -fl/yft? layer. .('-•' «\ Circular fiber la !• » ^«iio .'as 8«ia , 1 « \i\.fr ', H.ali.,e,.e™b.ane, -i{|aV ^..^ ^^ ^J ' i^^^ ^? » ^.S .'f ; H^'.^lf:^ Connective tissue. Outer epithel sheath. Huxley's layer, - ^JML.1>:^ *V*^e S^'^ '^' ^^ U*^ ^'."*^.*' '^ ^f/m Hetile's la>er, Fig. 372. — LoNcniDiNAL Skction of the Lowest Division of 'ii-ie Root of k Hair; the kerato- hyaline i^ranules are colored red. From a \'ertical section ol the human scalp. :■ 200. Digitized by Microsoft® :;2 2 HISTOLOGY. The sluijl of the hair is cnlircly epithehal Its surface is covered by a tliin iiiliciila which is formed of transparent scales directed from the cen- ter of the shaft outward and upward, and overlapping like shingles. These are non-nucleated cornified cells. The greater portion of the shaft is inckided in the cortex. Toward the bulb the cortex consists of soft ceUs, but distal]}- theA" Ix'comc cornified, elongated and compact; their nuclei are then linear. Except in white hairs pigment occurs both between and in these cells. Very small intercellular air spaces are found in the cortex of full\- dcA'cloped hairs. The medulla when present, occupies the center Cortical siili^tance. McdulUu\' suhsla Cuticle. ''I'l;', ■ ■''.-''1 / ,:' Fig. 373- — Ri_KMtiNTS ni-- a Htman H.air and its SutTATH. \ 240. 1, White hair; 2. scales of the cuticle , 3. cells ol the cortical substance of the shaft ; 4, cells of Huxley's la\er; 5,cell>of Henle's !a\ er, havitig the appearance of a fenestiatcLl membrane: 6, cells of the cortical sulistance of the root. of the shaft. It is generalh' a double row of cells containing kerato- hyalin granules and degenerate nuclei. .V medulla is found only in large hairs and it terminates before reaching their tips. The shedding of hairs. Shortly before and after birth there is a gen- eral shedding of hair. In the adult the loss and renewal of hairs is not periodic jjut constant. The life of a hair in the scalp ma\- last lOoodays. The process of removal begins with a thickening of the hyaline membrane and circular liber sheath. The matrix ceases to produce the inner sheath and consecpiently the cuticula and hair. The bulbus l.iecomes cornified, forming a solid frayed end of the shaft as seen in Figs. 375 and 376. The Digitized by Microsoft® HAIR. 323 increase of undifferentiated cells in the outer sheath and matrix forces the degenerating hair with its inner sheath outward (Fig. 376). The cornified bulb remains near the sebaceous gland at the outer sebaceous ^lands. Old Imi,-. New hair. hmit of the matrix; after a ~-i—. — ..— • • — ^--, • —<—■ variable time the hair falls out. The deep portion of the i„„er sheaih. -\\ v: .^/' ,,- -,C /.^* outer sheath, emptied of its W '"',(' ■''K/-. -". ; ■/ Iv hair, collapses and shortens, , ' i; drawing the atrophic papilla j^iif. upward. The matrix cells pro- liferate causing the epithelial 375 376 Manix. 1 , , J. ',„ I ^^^^ r'iG. 574. — Four Stages i.m thi^: ShI'^ddint, hf a Hair, cord to return to its toimer piJ^*j, ^ section .,f the nasa., skin of 7b , ,, 1 I'll Months Emhrvo, ' '. so. depth and a new hair develops y, be;n,ui„g nf the new hair. in the old sheath. This hair in growing toward the surface may complete the expulsion of its predecessor. ^ ^.j'^3^. Remains of inner ^ ' \ .'^-^■^... ,-■'' slieatli. / ■'. Cornified / .^\ ^ ^^^ bulb Remains of inner ' f, A ^-^ ^"^'v sheath. A'^fsa' ' -'^^ ■• ■• " Ma'ri.x. W: \,\ Coniified V • ijs, '^-.; 7?X :•*'« ,% •3 li' y bulb. V. .V<^' V 'a^- - ■-, Thin hyaline \ .^"^/r ' ' 1^*^ membrane. Epithelial curd. r" .^J ^ "„, > .■'' ^;i 1 Thick hyaline /' '1^ 5® ® %. , " membrane S 4 Epithelial '5) (^\ q ^ cord. - ,?i'" ^^If, V alia. ---^^^^/ Alniphic papilla. Matrix cells. Papilla - '^ \ Connective tissue. "" |. ':^ 3„,_LowKR Part of Fig. 374, A. ?' = ■ 376.-LOWER Part of Fig. 374, 8. ,■: 2,0. ■< ^30. Digitized by Microsoft® 324 histology. Sebaceous Glands. The sebaceous glands are simple, branched or unbranched alveolar structures situated in the superficial layer of the corium and usually appen- ded to the sheath of a hair (Fig. 370). In connection with the lanugo, a large gland may be associated with a very small hair (Fig. 377), and in exceptional cases as at the margin of the lip or on the labia minora, thev occur independently of hairs. They vary in size from 0.2 to 2.2 mm., the largest being found in the skin of the nose where the ducts are macro- scopic. None arc found in tlie palms or soles where hairs also are absent. The short duct is a prolongation of the outer sheath of the hair and is formed of stratilied epithchum, the number of layers of which decreases toward the alveoli. The alveoli consist of small cuboidal basal cells, and Kpidu CtU witli shrunken nucleus. Cell villi well de\'el- coT-ium, / :''•'' -i -T-^i — ' op^d J'ops of ^s^- cretion. Cell \\ith de\elopnij (Irups of secretion. Cubical cell Fig. ,^77, — A, Fkum .\ \'|h:kticm. Skction through thk Al.^ Na.si of a Child. >: 40. C, Stratum corueuni ; M, stratum j.jerminativum ; t, sebaceous gland consisting of four sacks, a, duct oi the same; w, lanugo liair, about to be shed, h, sheath of the same, at the base of which a new hair, x, is forming. B, From a Vkrtical Sf.ction of the Skin of the Ala Nasi of an Infant. X 240. Sack of a sebaceous gland containing gland cells in \'arious stages of secretion. of large rounded inner cells in all stages of fatt}' metamorphosis. As the cell becomes full of vacuoles the nucleus degenerates, and the cell is cast otl with its contained secretion. This in life is a semi-ffuid material com- posed of fat and broken down cells. Glandulae praeputiales are sebaceous glands without hairs which are sometimes, but not always, found on the glans and praeputium penis. The designation "Tyson's glands" is not justitied since Tyson described the epithelial pockets ^ to i cm. long which regularly occur near the fren- ulum praeputii. Praeputial glands and crypts are not found in the em- bryo. The praeputium is united to the outer surface of the glans by an epithelial mass, which often persists after birth and is broken up by the formation of concentric epitheUal jicarls. Glands and crypts are absent from the praeputium and glans clitoridis. Digitized by Microsoft® GLANDS OF THE SKIN. 325 Sweat Glands. The alandidae siidoriparae are long unbranched tubes termina- ting in a simple coil (described by Oliver Wendell Holm;s as resembling a fairy's intestine, Fig. 378). The coil is found in the deep part of the corium or in the subcutaneous tissue (Fig. 359). The duct pursues a straight or somewhat tortuous course to the epidermis which it enters between the connective tissue papillae. Within the epidermis its spiral wind- ings are pronounced; it ends in a pore which may be detected macroscopicalh'. The epithelium of the ducts consists of two or three layers of cuboidal cells; it has an inner cu- ticula, and an outer basement membrane covered by longitudinal connective tissue fibers. With- in the epidermis its walls are made of cells of the strata through which it passes. The secre- tory portion of the gland (3.0 mm. long according to Huber) forms about three-fourths of the coil, the duct constituting the remainder. The secretory epithelium is a simple layer of cells, varying from low cuboidal to columnar according to the amount of secretion which they contain. Those filled with secretion present granules, some of which arc pigment and fat. The product is eliminated through intra- and intercellular secretory capillaries. l''ic 37S. — MijDELDi- "I III'. Con,i-:D Part of a Sweat Gland FROM THK Sole of the Foot. (After HubtT.) MembrciTia prnpria. Ciiticula Miisele rtliers. A. Duct ill irtiss section. Xuclei of ^land cells. Musi libc-i D. Low epillK'lium iKjm a coiled Liibule. Menibraiia jiropria. Muscle Fibers. ucleiis. B. Columnar epithelium from the coiled tubuk*. C. Surface \"iew of the coiled tubule. E. Cross section of coiled tubule. Fig. 379.— A-D. irom a Section of the Skin ok the Axill.\; E, from the mnger Tipoi' a Man OE 23 Years. '/_ 230. E is not a tiue cross section. It is ordinarily a fatty fluid for oiling the skin, but it becomes the watery sweat under the influence of the nerves. The gland cells arc not destroyed by either form of activity. The secretory tubule is surrounded by a distinct basement membrane, within which there is a row of small longi- tudinally elongated cells described as muscle fibers. They do not form Digitized by Microsoft© 326 HISTOLOGY. a complete membrane, and they appear as a continuation of the basal layer of cells of the ducts. Sweat glands are distributed over the entire skin except that of the glans and the inner layer of the praeputium penis. They are most numer- Epidermis. CoriLini. Branches of the subpapil- lary ailerial network. -Veins of Ihe secoTid super- ficial plexus, \"eins aloiisT the duct of a sweat gland. Sul.icutane- ous tissue. Lai^^e \-CTii Vessel to the X'es.'^el to the fat tissue sweat L;land. Fig, ^Su — 1'art o}- a \'iiRricAi Shctiun iH' 'ii-ik Injected Sicin of tin-; Solm of thk Foot. X 20. Tlie \ein5 are not coinpleteh- filkd by the i iijection. OUS in the palms and soles. In the axilla there are large forms with 30 mm. of coiled tube. They acquire their large size at puberty and have been considered as sexual "odoriferous" glands. In the vicinity of the anus there are branched sweat glands, and large unbranched ''circum- anal glands" together with other modihed forms. Digitized by Microsoft© SKIN. 327 Vessels and Nerves of the Skin. The arteries proceed from a network above the fascia and branch as they ascend toward the surface of the skin. Their branches anastomose, forming a horizontal plexus in the lower portion of the corium. From this plexus branches extend to the lobules of fat and to the coils of the sweat glands, about which they form "baskets" of capillaries. Other branches pass to the superficial part of the corium where they again anas- tomose before sending terminal arteries into the papillae. The super- ficial plexus is called subpapillary, and from it the branches to the seba- ceous glands and hair sheaths are derived. The papilla of a hair receives an independent branch. The veins which receive the blood from the superficial capillaries form a plexus immediately beneath the papillae, and sometimes another just below the first and connected with it. The veins from these plexuses accompany the arteries and the ducts of the sweat glands to the deeper part of the corium, where they branch freely, receiv- ing the veins from the fat lobules and sweat glands. Larger veins con- tinue into the subcutaneous tissue where the main channels receive specific names. The lymphatic vessels form a fine meshed plexus of narrow vessels beneath the subpapillary network of blood vessels. It empties into a wide meshed subcutaneous plexus. There are lymphatic vessels around the hair sheaths and both sorts of glands. The nerves form a wide meshed plexus in the deep subcutaneous tissue, and secondary plexuses as they ascend through the skin. The sympathetic, non-meduUated nerves supply the numerous vessels, the arrector pili muscles, and the sweat glands; an epilamellar plexus out- side of the basement membrane sends branches through the membrane to terminate in contact with the gland cells. MeduUated sensory nerves end in the various corpuscles already described (page 105), and in free terminations, some being intraepithelial. MeduUated fibers to the hairs lose their myelin and form elongated free endings with terminal enlarge- ments in contact with the hyahne membrane. (The nerves to the tactile hairs of some animals penetrate the hyaline membrane and terminate in tactile menisci among the cells of the outer sheath.) There are no nerves in the hair papilla. The corium beneath the nails is rich in meduUated nerves, the non-meduUated endings of which enter the Golgi-Mazzoni type of lamellar corpuscle (having a large core and few lamellae), or they form knots which are without capsules. Elsewhere the skin contains tactile corpuscles in its papillae and lamellar corpuscles in the subcutaneous tissue, together with free endings in the corium and epidermis (as far out as the stratum granulosum). Digitized by Microsoft® 325 histology. Mammary Glands. In young mammalian embryos generally, the mammary glands are first indicated by a thiclvcned line of ectoderm extending from tlie axilla to the groin. Later much of the hne disappears, leaving a succession of nodular thickenings corresponding with the nipples. In some mammals this row of nipples remains, in others only the inguinal thickenings, and in still others only those toward the axilla. Thus in man there is normally only one nipple on each side. In an embryo of 25 cms. (Fig. 381) several sohd cords have gro^vn out from the ectodermal proliferation. There are ultimately from 15 to 20 of these in each breast and they branch as they extend through the connective tissue. At birth the nipple has become everted, making an elevation, and at that time the glands in either sex may discharge a little milkv secretion similar to the colostrum which .. •'" Z>.. Fig. 3S[. — Section T hroi'gh tiik Mammar\- Gi.and ov an Emhrn-o ok 25 cms. 1, Connective tissue of tlie fflanj. (.Mter Bascli. Iiom McMiirrioh.) precedes lactation. The glands grow in both sexes until puberty, when those in the male atrophy and only the main ducts persist. In the female enlarged terminal alveoh are scarcely evident until pregnancv. The glands until then are discoid masses of connective tissue and fat cells, showing in sections small scattered groups of duct-like tubes. Toward the end of pregnancy each of the 15 or 20 branched glands forms a mammary lobe and its alveolo- tubular end pieces are grouped in lobules. The secretory epithelium is a simple cuboidal or flattened layer in which fat accumulates at the seventh or eighth month. It first appears as granules at the basal end of the cell, where it is received in combination from the surrounding tissue. This fat is not produced by the gland cell. The lumen of the alveoli contains leucocytes which have passed between the epithelial cells, from the connective tissue. Some of them degen- erate; others receive fat from the gland cells, either in combination, or in drops which are devoured by phagocytic action. The fatty leucocytes Digitized by Microsoft® MAMMARY GLANDS. 329 grow to considerable size and are called colostrum corpuscles. Beneath the alveolar epithelium there are basal or basket ceUs which have been compared with the muscle fibers of sweat glands. A basement membrane separates them from the connective tissue ^\'hich contains many mono- nuclear leucocytes and eosinophilic cells. After the birth of the child the gland cells become larger and are filled with stainable secretory granules and fat droplets; the latter are near the lumen and are often larger than the nucleus (Fig. 3S3). After two days of lactation some of the gland cells are Hat and empty of secre- tion. Others are tall columnar, with a rounded border toward the lumen; Branch ot an excretory duct. Coniiecti\'e tissue. "-I'V-Cr-'t'- ■ - ■ 'I'uhule. Alveolo-Lubular end piece. 1: V^i ■''!'■'.■■-■'; ■'■:-;■■••.'<■ v'-\". '■..■■■-'■-■ ■■'■■. -■■;■■■-. .•'■• ;.;;,'•.:>.. 3r .■?: ''(.Jl:^^^^ fi^^^jS^. p-){fS^.: {%-^:---^H'<-:: '>i ^^' /■'•••/; -r ' Fig. 3S2.— Section of a Hu.ma.n- Mammary Gland at thk Period of Lactation. X 50- often they contain two nuclei. The fat within them is not a degeneration as in sebaceous glands, nor a secretion produced by the nucleus; it is a product of protoplasmic activity, and may fill the cell several times before it perishes. Transitions between the low empty cells and the columnar forms occur, but mitoses are absent from the lactating gland. Mitotic divisions are numerous during pregnancy. Milk consists of fat droplets, 2-5 ,« in diameter, floating in a clear fluid containing nuclein derived from degenerating nuclei, and occasion- ally a leucocyte or colostrum corpuscle. The interstitial connective tissue, greatly reduced by the enlarged glands, also contains very few leucocytes and eosinopliilic cells. Digitized by Microsoft® 3:: '5 cates a radical dift'erence between the cortex and medulla. In the sharks these components form separate organs. The interrenal gland which corresponds with the cortex, consists of cords of mesodermal cells and has apparently a sinusoidal circulation. The medulla is represented Ijy a peculiar development of the sym- pathetic ganglia. In mammals the meduUa likewise arises by the development of chromaffine cells in relation with the sympathetic nerves. The position of the involved nerves, between the aorta and the Wolfiian body, is shown in Fig. 276, C, page 245- The sympathetic portion of the gland becomes surrounded by dense mesenchyma in which the cords of the cortex are differentiated. Opinions are divided as to whether this mesen- chyma is derived from the Wolflian body or from the coelomic epithehuni. < As the kidneys attain their permanent position the suprarenal glands are found above them; they are structurally as independent of the kidneys as are the liver and spleen. Digitized by Microsoft® \ 332 HISTOLOGY. The cortical substance consists of cuboidal cells which in the outermost zone are arranged in rounded masses; in the middle zone they form cyhn- drical columns; and in the deepest layer the cords unite in an irregular network. The cortex is therefore divided into a zona glomerulosa, zona jasciculata and zona reticularis (Fig. 3S7J. The cells of the cortex are about 15 /'- in diameter and contain fat droplets causing the macroscopic yellow appearance. The drops are especially large in the zona fasciculata (Fig. 388), and are small or even absent in the zona reticularis. The rJark brown color of the latter is due to pigment which becomes con- Zona glomerulosa Tt*,*Y~ """^ /• Ca])Su]e. Zona fasciculata, Zona reticularis. Cell cords of Uu medulla. Nerve in cross section. Ganglion celk. Bundles of smooth muscle libers in crrtss section. Wans. P Cortex. Fic. j'^;. — Skction of a Human Stfrarenai. Gland. >^ 50. spicuous only in the adult. Besides vacuoles the protoplasm of the outer cells contains granules; the nuclei of the glomerular zone may be denser than those of the fascicular layer. The cell columns are in close relation with the endothehum of the blood vessels. They have no basement membrane, and are separated from the vessels by a very slight amount of reticular tissue. The medullary substance consists of chromafhne cells arranged in 'elongated strands which unite and form a network. The cells are very dehcate and easily become stellate by shrinkage even in well fixed prepara- tions. They have round nuclei and granular protoplasm but their specific Digitized by Microsoft® SUPRARENAL GLANDS. 133 3S8. Cell of the medulla. FrO.M a SkCTION' of the SrPRARKN.AL IW.AND OF .\N Alil'LT. 360. characteristic is an altinity for chromic acid or chromium saUs, b)- which they are colored brown. Similar cells occur in some sympathetic ganglia and in the glomus carot- icum. The capsule of the supra- renal glands is connective tis- sue, said to contain smooth mus- cle libers, blood and lymphatic vessels, nerves and small gang- lia. It sends prolongations into the interior. Elastic fibers are found in the medulla but they are very few or absent in the cortex. The arteries divide in the capsule into many small branches which penetrate the cortex and there form a long-meshed cap- illary network; toward and within the medulla the meshes become round. Some arteries pass directly from the capsule to the medulla, without branching in the cortex. The larger of the numerous veins which arise in the medulla are accompanied by longitu- dinal bundles of smooth muscle libers. Before leaving at the Jiiliis they unite to form tlie supra- renal vein. Lymphatic vessels have been record- ed in the capsule and medulla. The numerous mostly non - medullated nerves, of which a human suprarenal gland receives about thirty small bundles, proceed chiefly from the coeliac plexus and pass with the arteries from the capsule Artery Lon^ meshed capdlary net of the cortcr.x. Jound meshed net ol the nieiltilla. Fig. 389 - -From an Lnjected Section oI'^ i fie Suprarenal Gland of a Child. X 50. Digitized by Microsoft® 334 HISTOLOGY. into the medulla. Branches from the plexus in the capsule descend between the cell groups of the cortex and terminate on the surface of the cells in the two outer zones; they do not enter between the separate cells. The plexus in the zona reticularis is more abundant, but here also only groups of cells are supplied. In the medulla the nerves are extraordinarily abundant and each cell is surrounded by fibers. Groups of sympathetic gangHon cells may be found, but these rarely occur in the cortex. A part of the nerves terminate in the walls of the vessels. In the vicinity of the ductus deferens and in the broad Ugament of the uterus, suprarenal bodies may occur, consisting only of cortical substance. Groups of chromaffine cells have been found in relation with the paro- ophoron and paradidymis. BRAIN AND SENSE ORGANS. Brain. Development and General Anatomy. In a previous section the formation of the medullary tube from the primitive ectoderm has been described, and it has been stated that the posterior portion of the tube becomes the spinal cord and that the anterior portion forms the brain. In a human embryo of 4.0 mm., the tube still opens freely through a large anterior neuropore, the extent of its connection with the epidermal ectoderm being indicated in Fig. 390, A. The tube has become bent in two places; the posterior or neck bend is near the junction of the cord and brain, the line of separation between which must be arbitrarily drawn both in the embryo and in the adult; the anterior or head bend occurs in a part of the tube called the mid-brain (mesencephalon). In front of the mid-brain is the fore-brain (prosencephalon) and behind it is the hind-brain (rhombencephalon). The entire brain is therefore divided into fore-brain, mid-brain, and hind-brain. In an early stage the fore- brain, produces two lateral outpocketings, one on either side, called the optic vesicles. Each expands distally to form the retina of an eye and its connection with the fore-brain becomes reduced to a slender stalk. In later stages the depression on the inner wall of the brain which marks the position of the stalk is called the optic recess. The hind-brain soon becomes rhomboid or kite-shaped as seen from its dorsal surface. This is due to a widening of the cavity of the medullary tube; its lateral walls spread apart and the roof plate becomes thin and transparent. The dilated cavity of the hind-brain is called the fourth ventricle; the cavity of the mid-brain in the adult is a slender passage caUed the aqueduct [of Sylvius]; it becomes vertically expanded in the Digitized by Microsoft® DEVELOPMENT OF THE BRAIN. 335 fore-brain to form the tliird ventricle. These two ventricles and the aqueduct are continuous witla the central canal of the spinal cord and represent the original cavity of the medullary tube. In an embryo of lo mm. (Fig. 390, B) the hind-brain maybe subdi- vided into the myelcnecphalon posteriorly and the meienceplialon anteriorly. The constriction between the hind-brain and mid-brain is called the isthmus. The mesencephalon remains undivided; the fore-brain is rejjre- sented by the diencephalon posteriori}- and the telencephalon anteriorly. Thus there arc six funda- mental subdivisions of the brain. Their further de- velopment is illustrated in the mechan sagittal sections of the brain, Figs. 392 and 393, and may be briefly de- scribed as follows. The myelencephalon becomes the medulla oblon- gata. It transmits the fibers passing between the cord and the brain; it re- ceives the sensory roots of the vagus and glossopJiaryn- geal nerves and contains the groups of cell bodies from which their lateral roots arise [the lateral root of the vagus being called the accessory nerve]. It also contains the cell bodies from which arise the ven- tral roots which make the hypoglossal nerve. (These nerves are shown in Fig. 113, p. 96, and in Fig. 391, B.) The medulla also includes groups of cell bodies, the pro- cesses of which do not leave the central nervous system. Such groups are called nuclei; the gray substance in most of the ventral portion of the brain is in the form of separate nuclei and not in continuous columns as in the cord. The metencephalon produces the pons \'entraUy and the cerebellum dorsaUy. The pons receives the sensory roots of the trigeminal, inter- mediate and acoustic nerves; it gives rise to the lateral roots of the tri- FlG. 3qo — A, Thi-: Brain of a 4 o mm Htman EMBR^o (niter Breincrl; B, the Brain ok a 10.2 ^^M. E.mkrno (after His). Except the isthmus, is., the principal subdivisions of the brain are indicated bv prefixes of tlie term ciiCi'phalon\ sp.c, spinal cord ; h., hemisphere ; 0. v., optic vesicle ; r., rliiiien- cephaluii ; v., roof of the fourth \'cntricle. Digitized by Microsoft® 330 HISTOLOGY. geminus and intermedius (facial) and to the ventral root which makes the abducciis. The pons transmits the ascending and descending fibers between the cord and the anterior portion of the brain, together with fibers to and from the medulla. Many fibers of the pons pass through the lateral wall of the brain-tube into the cerebellum, forming a large bundle on each side, called the brachium ponlis (Fig. 391). The cerebellum also receives on each side a bundle from the anterior part of the brain, the bracliiiijii coiijunclivuin, and another from the medulla, the reslijorui body. These three bundles not only contain fibers to the cerebellum but also those passing from it. The cerebellum (Fig. 393) is a large lobular mass inf Fig. 391,— a, Dorsm, and B, Vhniral \'ih\v Ol' the Posiukiok Paki hk thk AuiLr Bkain. Thk Ct- iophysis (posterior lobe); isth., isthmus; med.; med iilla oblongata ; mes., mesencephalon; ol. b., olfactury bulb; puieal body ; p. s., pars subthalamica ; th., thalamus. 0. r., optic recess ; p. b Fig. 393.— Median Sagittal Section of an Adult Brain. cbl., Cerebellum; c. c, corpus callosum ; c. q., corpora quadrigemina ; hy., posterior lobe of the hypoph- ysis; med., medulla oblongata; 0. b., olfactory bulb ; 0. r., optic recess ; p., pons , p. b., pineal body; p. s.. pars subthalamica ; th.. thalamus. Digitized by Microsoft® 338 HISTOLOGY. the optic tract, and gives rise to some which connect with the motor cells of the nerves to the eye muscles; others pass down the spinal cord close beside the median ventral fissure. Thus the anterior corpora are centers of optic reflexes. The posterior or inferior corpora, which are smaller, are in relation through an intervening group of neurones, with the acoustic nerves; thus they are centers of auditory reflexes. The mesencephalon gives rise to the ventral root which forms the oculomotor nerve. The cerebral peduncles which begin in the isthmus extend under the mesen- cephalon. The diencephalon has on its median dorsal surface the pineal body [epiphysis]. This is a small nodular structure which is thought to represent a rudimentary median eye, such as is more clearly indicated in reptiles. The upper part of the lateral walls of the diencephalon are each thickened by a mass of nerve tissue called the thalamus. The thalami of the two sides bulge inward so that their most prominent parts adhere across the third ventricle. Fibers from the retina connect with nerve cells in the thalamus, the latter sending their processes to the hemispheres; thus the thalami have an important relation with the optic tracts. The walls of the diencephalon below the thalamus form the pars mamillaris hypothalami. This part of the hypothalamus includes the two mamillary bodies found side by side on the ventral wall of the diencephalon (Fig. 391, B). Telencephalon. The fibers from the posterior part of the brain pass outside of the thalami to terminate in the dorso-lateral walls of the telen- cephalon. As seen in Fig. 390, B, this part of the fore-brain forms a hemispherical outpocketing on either side,' into each of which a pro- longation of the third ventricle extends; the extensions are called lateral ventricles (and are counted as the first two). The hemispheres enlarge, growing back so as to cover the posterior portion of the brain. Their walls, which externally are subdivided by grooves into convolutions, constitute the pallium of the hemispheres. The olfactory bulb is the expanded termination of the part of the hemispheres which receives the olfactory nerves. The entire olfactory tract is called the rhinencephalon. The corpus striatum is a deep portion of the hemisphere found outside of the thalamus; anteriorly it forms the outer wall of the beginning of the lateral ventricle. The hemispheres are connected with one another by a great transverse commissure, the corpus callosum, through which fibers pass from one to the other. The principal subdivisions of the hemisphere are therefore the pallium, rhinencephalon, corpus striatum and corpus callosum. Besides the hemispheres, the telencephalon forms the pars optica hypothalami. This includes the optic recess in front on either side, and Digitized by Microsoft® DEVELOPMENT OF THE BRAIN. 339 the infundibulum in the mid-ventral line. The infundibulum terminates in an expansion which is the posterior lobe of the hypophysis. This body, together with the anterior lobe derived from the oral ectoderm but later severed from it, is lodged in the sella turcica of the sphenoid bone. The development of the brain is summarized in the following table (after His). Hind-brain . Medulla oblongata. Pons. Myelencephalon Metencephalon { cr^bellum Isthmus Isthmus Mid-brain . Mesencephalon . Diencephalon. . \ Fore-brain Telencephalon. Cerebral peduncles. Corpora quadrigemina. Mamillary part of the hypothal- amus. Thalamus. Pineal body. Optic part of the hypothalamus. Hypophysis (posterior lobe). Hemisphere : Pallium. Rhinencephalon. Corpus striatum. Corpus callosum. Medulla Oblongata. Before considering the medulla the student should review the arrange- ment of fiber tracts in the spinal cord (Fig. 147, p. 121). The cerebro- spinal fasciculi, both ventral and lateral, consist of the fibers which descend from the hemispheres. These four fascicuh of the cord arise from two in the medulla, which there produce a pair of ventral swellings (pyramids) shown in Fig. 391, B. In the section, Fig. 395, it is seen that the pyramids are in the position of the ventral cerebro-spinal tracts of the cord. In the lower or posterior part of the medulla the greater number of fibers in each pyramid crosses through the ventral commissure to the opposite side; thence they proceed across the gray substance to the lateral cerebro-spinal fasciculus, which they form (Fig. 394). The crossing is called the decussation of the pyramids, or, since these fibers terminate about motor cells, it is called the motor decussation. The relatively small number of pyramidal fibers which do not decussate in the medulla, form the ventral cerebro-spinal fasciculi of the spinal cord. The fibers from the spinal gangha ascend to the medulla in the cimeate and gracile fascicuh. Within the medulla their fibers terminate, but their course toward the hemispheres is prolonged by a second group or "relay" of nerve cells, the bodies of which form four nuclei. These nuclei Digitized by Microsoft® 340 HISTOLOGY. appear as additional columns or horns on the dorsal jjart of the gray H (Fig. 395); the inner pair are the nuclei oj Ihe gracile jasciculus, and the outer ones are nuclei oj Ihe ciineale jasciculus. In them the fibers from the cord terminate and others arise which cross beneath the central canal to the opposite side of the medulla (Pig. 395J. Then they pass forward in right and left bundles knouai as lemnisci or fillets. The decussation oj the lemnisci occurs higher up in the medulla (that is, more anteriorly) than that of the pyramids; and, after crossing, the fillets remain internal to the pyramids. With the sensory and motor decussations the resemblance between f.c.L Fir.. 3g4. — Section of the Cdrd \t thk I.KVEL OK THIi FlRST CKk\-ICAL N|-:K\'H. The riglit half of the suction shows tlie effect of \Veigert's slain, the m\'ehnated portions being dark; the left half shows the gray substance stippled and the white i.s blank. f. c, Fasciculus cuneatus; f. c. I., fascicu- lus cerebro-spinalis lateralis; f. c. v., fascic- ulus cerebro-spinalis \entralis; f. g., fascic- ulus gracilis; d. c, dorsal column, d. p., decussation of the pyramids; d.r., dorsal root of lirst cervical ner\e ; v. c, ventral colnum. t s n t -/ Fig. 395 — Section ot the Medi'lla. (.After Dejerine.) d. u.. Dorsal column; d. I., decussation of the lemnisci, f. c.. fasciculus cuneatus; n. ace. nucleus of theacctssor\' portion of the\agus; n. c, cuneatc nucleus , n. g., gracile nucleus ; py., p\ ramid ; t. S. n. t., spinal tract of the tri- geminal ner\e , v. c, Neutral column. the medulla and spinal cord is lost. The gray substance no longer forms an H, and the dorsal fiber tracts have become ventral; the central canal expands to make the fourth \entricle, as seen in Fig. 396. The lemnisci form vertical bands of white substance on either side of the median ventral raphe. The pyramids cause protrusions of the ventral surface. Dorsal to each there is a large nucleus, the olive, which also makes an external elevation (Fig. 391, B). Its gray substance forms a convoluted capsule; it receives fibers from the cord and cerebellum, and gives rise to some which cross through the median raphe and ascend to the cerebellum in the restiform body. The restijonit body, which forms the dorso-lateral portion of sections of the ujjjjer part of the medulla, contains olivary fibers, those Digitized by Microsoft® MEDULLA OBLONGATA. 341 is. n.h of the ccrebello-spinal fasciculus of Ihe cord, some from the gracile and cuneatc nuclei, anrl some from other nuclei in relation with the sensory roots of the cranial ner\-es. The cerebral ner\'es of the medulla (and jjons also) are arranged in general as follows. The \-entral roots arise from groups of cell bodies, — tire nuclei of the ner\'es, situated beneath the tloor of tlie \'entricle near the median line. The nucleus of the hypoglossal nerve is seen in Fig. 396. The lateral roots arise from nuclei more deeply placed and further from the median line; their tilx-rs ma}' pass ujtward and in\vard toward the ventricle before turning downward and outward to leave the brain. The nucleus ambiguns (Fig. 396) gi\'es rise to the lateral roots of the vagus and glossopharyngeus. Like the motor cells of the spinal cord, those of the brain are also in connection with descending libers of the pyramidal tract. The dor- sal roots on entering the brain generally divide into a short ascending branch and a longer descending one. The iractus soUtari- us (Fig. 396) contains the descending fibers of the vagus and glossopharyn- geus; the large spinal tract composed of the descend- ing libers of the trigeminus is shown in Figs. 395 and 3q6. The dorsal root fibers end in nuclei corresponding with the gracile and cuneate nuclei of spinal nerves. Fibers from the internal nuclei of the cerebral sensory ner\-es join the lemniscus and proceed toward the hemispheres. V\G. 396.— Section '«''\'*>-'4',''''i'''. ^.•k'KI'-'^o. :f- -:^■v.:■iv4,.^*^^.- ■■/•V'^i^^tff.^; L_^-2ji^. Fig. 404. Fins. 10', and 404 are from vertical sections of the ™'''^^ ' (central couvolulion) ol an adult. Fig. 403 is a \Uigcn ineparalion; Fig. 404 is from a section stained wiin ' cniatoxyline and eosine. ;< 45. ^VtetMiM^*'«#^^^' ^rt4 Digitized by Microsoft® HEMISPHERES. 349 branched neiiraxons limited to the vicinity of the cell body are foxmd in this layer and in the pyramidal layers also. The neuraxon may branch in the molecular layer (Fig. 402, 6). Many meduUated fibers are found in the deeper pyramidal and polymorphous layers. They are grouped in tapering radial bundles which are resolved into separate fibers toward the layer of small pyramidal cells (Fig. 403). The bundles include the descending meduUated neu- raxons of the pyramidal cells, and the ascending meduUated fibers from the white substance, which end after branching repeatedly in the supra-radial and tangential networks. The meduUated collaterals of the pyramidal cells run at right angles with the radial bundles; they form an inter-radial network, or a band of fibers which near the calcarine fissure is macroscopic. A similar supra-radial band may be detected elsewhere in thick sections. In the gyrus hippocampi and its hook (uncus) the tangential fibers are so abimdant as to form a considerable layer, the substantia reticularis alba. The hippocampus [Ammon's horn], olfactory bulb, and some other areas of the cortex, differ in details from the central region which has been described; these pecuUarities are considered in the larger special works on the nervous system. The neuroglia of the hemispheres, like that of the cord, is at first a syncytium with strands extending from the ventricle to the periphery. Later, the syncytium is divisible into short-rayed neuroglia cells found chiefly in the gray substance, long-rayed ceUs found chiefly in the white, and ependymal cells lining the ventricles. The ependymal layer is con- tinuous through the aqueduct with that of the fourth ventricle and central canal. In early stages its cells have cilia-Hke processes which are in part retained in the adult. The short-rayed ceUs, which are characterized by knotted, branching processes, are often in close relation with the blood vessels; they may serve to transfer the nutritive and myeUn-forming material from the vessels to the nerve fibers. The periphery of the cerebral cortex is particularly rich in neurogha fibers. Hypophysis. The development of the two lobes of the hypophysis [pituitary body], the anterior from the oral ectoderm and the posterior from the telencephalon, has ahready been described (Fig. 185, p. 165). The smaller posterior lobe, which is at the tip of the infundibulum, contains fine branching nerve fibers which form a delicate network, together with cells closely resembling bipolar and multipolar gangUon cells, and many blood vessels. The nature of the cells is, however, uncertain. The larger anterior lobe consists of loose connective tissue with many blood Digitized by Microsoft® :;50 HISTOLOGY. vessels and nerves, and of solid branched epithelial cords varying in caliber and frequently anastomosing. Near its border toward the posterior lobe a few of the columns are hollow, and sometimes they contain masses similar to the colloid of the thyreoid gland. This does not come from the granules which occur in varying quantity in all the epithelial cells, giving them sometimes a lighter and sometimes a darker appearance. The granules in some cells are eosinophilic; most of them are not, and a portion may be fat. Ciliated epithelial cells have been recorded. (The part of the anterior lobe which is near the posterior is sometimes called "medullary substance" ; in children it may be represented by a cleft-like cavity con- taining colloid). From the relation of the hypophysis to certain diseases, it is quite certain that it produces an important internal secretion. ^^ Epithelial cord. anlcnoi lube, i -r -- 'f.,i.:„,„ follicle. v.. Poi'Lion of the Iiustcrioi" lobtj. h^.2>~^-~ ■ >'\ ^^^j' Blood vessel con- ^^^""^ taining blood corpuscles. " Colloid" substance. Multipolar cell. -Connective tissue fibers. I-i(;..to5 — Portion of a Horizontal Srction of a Human H^'POPn^■sl.s, sbowiiig tbe boundary line between the anterior and the posterior lobes. Two gland follicles on tbe left e.ich contain a dark epithelial cell. X -^o. Pineal Body. The pineal body [epiphysis] is a median dorsal outpocketing of the diencephalon, which has preserved its original epithelial character. It consists of a layer of neuroglia cells thrown into folds and is covered by a connective tissue capsule sending prolongations between the folds. In the pineal body there is found generally "brain sand," accrvulns cerebri, which consists of round or mulberry- like concretions 5," to i mm. in diameter. In specimens preserved in glycerin or balsam they show distinct concentric layers. They consist of an organic matri.x containing calcium carbonate and magnesium phosjjhate, and are sometimes surrounded by a thick connective tissue capsule. Not infrequently, especially in old age, there are found in the brain sub- stance round or elongated bodies distinctly stratified, which are colored Digitized by Microsoft® MENINGES. Qcj violet by tincture of iodine and sulphuric acid, and therefore are related to amyloid. These corpuscula amylacea are found almost always in the walls of the ventricles of the brain, and also in many other places both in the gray and white substance and in the optic nerve. They have a homo- geneous capsule with occasional processes, composed of neuroglia cells transformed by amyloid infiltration. Meninges. The meninges are connective tissue membranes investing the central nervous system. They are usually divided into three layers, the dura mater, arachnoid, and pia mater. The dura mater spinalis, or dura mater of the cord, consists of com- pact fibrous connective tissue with many elastic fibers, flat connective tissue cells and plasma cells. Its inner surface is covered by a layer of flat cells forming a mesenchymal epithehum. It has few nerves and blood vessels. The dura mater cerehralis or dura mater of the brain, includes the periosteum of the inner surface of the i;^-, cranium and consists of two lamellae. The inner is hke &5v the dura mater of the cord but contains more elastic ""' _- fibers; the outer corresponds with the periosteum of the vertebral canal and consists of the same elements as the inner layer, but its fibers run in a different direc- tion. It contains many blood vessels, some of which extend into the cranial bones. The very large thin- fig. 406. - acervulus walled veins of the dura are called 5OTMje5. The dura body o™ wo^'man i_ J. J- 1 1 ,1 1 Seventy Years has many nerves, some endmg freely and others supply- old. x 50. ing the vessels. The arachnoid of the cord and brain is but loosely connected with the dura, being generally limited externally by a mesenchymal epithehum. Between the arachnoid and the dura there is a capillary cleft containing a very small amount of fluid. This subdural space in the rabbit and dog is in communication with the deep cervical lymphatic vessels and glands, with the lymphatic spaces around the peripheral nerves, with the lymphatic vessels of the nasal mucosa, with the tissue spaces in the dura, and with those around the arachnoid granulations. The arachnoid granulations [Pacchionian bodies] are elevations or outpocketings of the arachnoid in definite places, especially along the sides of the superior sagittal sinus. Covered by a thin portion of the dura and by the endothehum of the vessel, they project into the cavity of the sinus. The subarachnoid space between the arachnoid , and the pia mater, is traversed by strands and layers of tissue and bounded by mesenchymal Digitized by Microsoft® 0.1^ HISTOLOGY. c])ithelium. It connects with the lymph spaces of the ];eripheral nerves, with the Ivmph vessels of the nasal mucosa, and with the ventricles of the brain through apertures in tire roof of the fourth ^•entricle. It contains an abundant fluid called the liquor cerchrospinalis. (The direct con- nection of the suljdural and subarachnoid spaces with hotli lymphatic \-essels and tissue spaces, is not in accord with recent embryological studies and requires further investigatirjn.) The ])ia mater of the cord and Ijrain is a delicate vascular connective tissue which extends into their substance along with its blood vessels. Its ner\-es may remain outside. Pericellular lymphatic spaces around the ner\e cells, and the epicerebral sjjace between the pia and the brain, do not comnnmicate directly \\\\}\ the l}'mpliatic \'essels. The blood vessels form narrow-meshed capillaries in the gray substance and coarser ones in the white. Cajjillaries in the cerebral corte.x empty into veins which i'.loiKl \es'^els KpiUielinii Fig. 407. — Portion of ti-ik Plhxus Chorioidkus of-" an .^dllt Man. >; .So. I'.lood \ essel m optic:il section. Ttie larj^e dots in tlie epilhcliuiii are not nuclei, but pigment and arise in the white substance beneath, and from there pass through the cortex to the pia ; the blood in the capillaries therefore passes through the entire cortex before emptying into the veins. The blood vessels generally have a second so-called "adventitial sheath" consisting of a mesenchymal epithelium. Within the sheath is an "adventitial lymph space" con- necting with the subarachnoid space; outside of it is a perivascular tissue space. Chorioid plexuses. In certain places where the wall of the medullary tube is very thin, as in the roof of the fourth ventricle, it becomes invagi- nated into the central ca\'ity by the \'ascular pia, thus forming a chorioid plexus. The epithelial cells of the brain covering the plexus, contain pigment granules and sometimes fat droplets. The chorioid plexuses extending into the third, fourth, and Ijotlr lateral ventricles, are essentially similar in structure. A jiarl of the network of blood vessels within them is shown in Fig. 407. Digitized by Microsoft® DEVELOPMENT OF THE EYE. 353 EYE. Development and General Anatomy. The eyes first appear as a pair of optic vesicles, which are lateral out- pocketings of the fore-brain. They are shown in the model, Fig. 390, A (p. 325) and in section in Fig. 409, A. The vesicles are connected with the brain by the optic stalks, which become relatively slender as the vesicles enlarge. The epidermal ectoderm immediately overlying the vesicles, thickens and becomes invaginated (Fig. 409, B and C). The invaginated portion then becomes detached in the form of a vesicle, the inner wall of which is distinctly thicker than the outer; this "lentic vesicle" becomes the lens of the eye. Meanwhile, as seen in B and C, that layer of the optic vesicle which is toward the surface is- pressed in, transforming the vesicle into the optic cup. At first the cup is not complete, being deficient on its lower side (Fig. 408). The arteria centralis retinae is seen passing through the indentation, which begins on the lower surface of the stalk and extends to the free margin of the cup ; the cleft is sometimes called the "chorioid fissure." Distal to the point of entrance of the artery into the optic cup the edges of the fissure fuse; the artery then appears to perforate the base of the cup, and it retains this relation in the adult. ^^''■^f:~°lV': '^^l^^l J- ' bTALK OF A rlUMAN The artery is shown in section in Fig. 409, D. f^irLZ^^rS^.r' The two layers of the optic cup, the inner of which is toward the lens, are normally in contact with one another, al- though in sections they are often more or less separated. They constitute the retina-, which includes a thin outer pigmented layer, and a thick inner visual layer composed of several strata of nerve cells and fibers. The stimulus of Ught is received by tapering projections extending from the outer surface of the visual layer toward the pigmented layer; to reach them the rays of hght must traverse the strata of the visual layer. In explanation of the fact that the sensory processes are turned away from the hght it is stated that the outer surface of the skin ordinarily receives stimuh, and that through the infolding which makes the medullary tube and the outpocketing which makes the optic vesicle, the sensory sur- face of the retina is seen to be continuous with the outer surface of the skin. Since in mammals the optic vesicles begin to form before the rela- ted portion of the medullary groove has closed, they appear as depressions in a thickened epidermal ectoderm. Nerve fibers grow from the inner surface of the visual layer toward 23 Digitized by Microsoft® 354 HISTOLOGY. the central artery and vein of the retina, around which they pass out of the optic cup (Fig. 409, D). They grow beneath and among the cells of the optic stalk to the brain, which they enter. These fibers which constitute the optic nerve, cause the obliteration of the optic stalk. It is shown in the figure that the optic nerve at its origin interrupts the retinal layers, pro- ducing a "blind spot." The part of the nerve which forms the blind spot, with the vessels in the center, is called the papilla of the optic nerve. The lens (Fig. 409, D) loses its central cavity by the elongation of the cells in its posterior layer. These become the fiers of the lens. The anterior layer remains throughout life as a simple epithelium, called the epithelium of the lens (Fig. 410). The lens becomes covered by an elastic capsula lentis and in embryonic life it possesses a vascular capsule Fig. 409, E) containing branches of the central artery. The vascular layer covering the anterior surface of the lens is designated the pupillary membrane, and it disappears shortly before birth. Its occasional persistence interferes with vision. Between the lens and the retina there is a pecuhar tissue, mucoid in appearance and resembhng mesenchyma in form. Since processes from the retina and from the lens have been found extending into it, it is con- sidered to be essentially ectodermal. Its blood vessels become obliterated and it forms the vitreous body of the adult, consisting of a stroma and a humor. Extending through it, from the papilla of the optic nerve toward the lens, is the hyaloid canal, which in the embryo lodged the hyaloid artery (a prolongation of the central artery). Sometimes this artery is repre- sented in the adult by a strand of tissue. The vitreous body is surrounded by a fibrous layer called the hyaloid membrane. A cavity forms in the tissue in front of the lens and becomes filled with a watery tissue fluid (aqueous humor). It is bounded by a mesenchymal epithelium. The portion of the cavity which is anterior to the retinal cup and lens is called the anterior chamber of the eye; the smaller part within the retinal cup but in front of the lens and the fibrous covering of the vitreous body, is the posterior chamber (Fig. 309, E, c.p). The retinal cup is surrounded by two layers of mesenchymal origin. The inner tunica vasculosa corresponds with the pia mater and forms the chorioid coat of the eye; the outer tunica fibrosa corresponds with the dura and forms the sclera, into which the muscles of the eye are inserted. The portion of the retinal cup which forms a curtain, circular in front view, between the anterior and posterior chambers, is called the iris. It consists of the tunica vasculosa together with a thin pigmented prolongation of the retina over its posterior surface (Fig. 410). This pars iridica retinae is Digitized by Microsoft® DEVELOPMENT OF THE EYE. 335 rudimentary and without \-isual function. The iris is co\-ercd by the mesen- chymal epithelium of the chambers. At the attached border of the iris the vascular coat contains important muscle hbers and is there thickened to form the ciliary body. This is also covered fjy a rudimentary pigmented layer on its inner surface, the pars ciliaris retinae. At the ora serrata (Fig. 425) an abrupt thicl^ening of tlic \-isual layer f)f the retina marks the boun- conj. l.nPMI-.NT OF THK En'K A.q'j da\s, Fig. 40Q, — Sfxtioxs of Rabbit F.mbrvo', to show ihf Dkvi-,..... ■■ ■ ,,,■■■--,„,,; ■ ; B.io;.^ days, 5,4 mm.; C,ll days, 5.0 mm.; D, M days, 18 hours, l^.o (') mm.; E, 20 da> s, 29 mm. \ o mm.; „ Arteiia centralis retinae ; c, cornea ; c. a., anter.or chamloer , con .. conjunctu a C p., V<^'f<^™\ amber; c. v., corpus vitreum ; e. I., eyelid ; f. b., fore-bra.n ; I., lens ; I, e.. lens epithel.um . f ens .ers- oc. optic cup; 0. n., optic nerve ; 0. v.. optic vesicle; r. p., pigmented la>er of the icUna, a. c. r rh; lil r. v.. \-isual la\er of the retina. dary Ijetwecn its ciliary and optic portions. The pars optira rcliiiac^ extends from the ora to the optic nerve, covered successively l:«y the chorioid and sclera. The cornea is the tissue in front of the anterior chamber, consisting of a non-\-ascular mesenchvmal tissue bounded posteriorly by mesenchymal Digitized by Microsoft® 356 HISTOLOGY. cpilliclium and anlcriorly hy the epidermal ectoderm. The cornea is extremely transparent. The epidermal ectoderm extends from the cornea oAcr two folds which form the eyehds. They have met in Fig. 409, D, and fused temporarily. Externally the lids are covered by skin, internally by the coujuiicliva palpcbranini, or conjuncti^'a of the lids. The latter is continuous with the coiijunciiva hiilhi which forms the opaque, vascular EpiUieliuin .ViUcritM' ha^al lamina SLilislaiilia ])K)pria PosttT"i(.ir basal l.imiiia MeseiicliN mal tjiitlicliLiiii I of the cornea. P])liiiieLer muscle '] '-^lTClma -ol Uie iris. l'ais indica retinae) ,\n,icr 1 Gangliiin cell la\ er iS'erve fiber Ia\ ei Memlnana limitan interna. Ba c of a cone fiber. ^ clevis or a radial fiber. ^ ^ inakriiie cell. \ 3 x^ > /Sbii P raniidal base of a W ,^ radial fiber. »j.J^wmfciH».l..M.A.rtWL..^* »TiiiiJw.»^fj"3v^ =fe=^ i^ Bl 1 \css Is Fig. 411.— \'ERTiCAr SrXTiON of a Hl'Man Retin.\. X 36. remaining portion is a dense network of the branching processes from underlying nerve cells. Occasionally a cell body is displaced outward from the deeper layer and comes within the reticular layer. One of such "subepithelial ganglion cells" is seen in Fig. 412, x. The nervous ele- ments are supported by a fibrillar network derived from non-nervous ectodermal cells, corresponding with neuroglia. Some of the supporting cells found in the reticular layer are concentrically arranged (Fig. 412, 00). The inner nuclear layer, which underlies the outer reticular layer, contains the cell bodies of both nerve and sustentacular cells. The nuclei of the latter belong chiefly with radial fibers [Miiller's filjcrs]; these extend from the inner surface of the retina to the membrana hmitans externa. Digitized by Microsoft® RETINA. 359 which Ihey form. Slender fibers which arise from the outer surface of this membrane and surround the bases of the rods and cones in the form of basicets, may be regarded as prolongations of the radial fibers. The inner ends of the radial libers form pyramidal expansions which unite with one another to make a memhvana limilaus in/enia,~ihQ innermost layer of the retina. Throughout their course the radial fibers gi\-e off latc'ral expansions and processes, for the support of the ner^•ous elements; these are especially numerous in the outer nuclear layer. Their nuclei are among those of the inner nuclear layer. The nerve cells of this layer are chiefly small bipolar ganglion cells constituting tlie ganglion retinae. The dendritic process of each extends into the outer reticular layer, where Cone Rod .SiiJi! Stellate ganglion cell. Bipolar cells. Aniakriiie cells. Centril"u,£,'al iier\e fiher. Multipolar ganglion cell. I^nn nUl l niemnranalimuans lUW externa. JrvnOQ, > Outer nuclear la\er VV9 { llilul / Heme's fibre laser Layer of rods and cones ]\rcmbrana limiians Ciuler reticular la\er. « O^Oe^ ' Inner nuclear layer. C Inner reticular la\ er ion cell la\'cr Nerve fiber layer Collateral. Fig. 412. — DrxciRAM of Hlutax Rftin.\. Supporting Sr'PSiANXE Rrd. Pyramidal bases of radial fibers. by forking it breaks up into very fine fibers parallel with the surface. They form a subepithelial feltwork and have been said actually to anas- tomose. All the bipolar ganglion cells send their longest dendrite between the visual cells where it ends in a little thickening near the mcmbrana limitans. The neuraxons of the bipolar cells pass into the underlying inner reticular layer and there break up in fine varicose branches. The inner nuclear laver near its outer boundary contains stellate cells, sometimes large, which send many dendrites into the subepithelial felt- work where they anastomose. Their neuraxons extend horizontally, and may pass inward to join the fibers of the optic nerve (which is denied by some) or they may terminate in horizontal branches which ascend to the Digitized by Microsoft® 360 HISTOLOGY. bases of the visual cells (Fig. 412, '). Toward the inner surface of the inner nuclear layer there are large ganglion cells which send branched processes into the inner reticular layer. Neuraxons of these "amakrine cells" have not been found. Some libers extenchng out from the brain through the optic ner-\-c terminate in free endings within the inner nuclear la)'er. The inner reiiciihir layer consists of a very fine supporting network, lodging the processes of the Ijipolar and amakrine cells, together with the dendrites of large multipolar cells of the ganghon layer beneath. The ganglion cell layer or ganglion of tJie optic nerve consists of a single layer of large multipolar cells containing Nissl bodies. Giant forms " Fiber basket. Nucleated part of the fiber. ^- Easal pyramid. *^ Precipitate. Fig. 413.— Got. ci Prkp.-vr.^tion ok R..\ui.-\l Fiiiers in .\ Tmci.: Section of the HfM.KN Rktina. Ttie fine processes of tlie fibers in ttie outer nuclear la\'er appear as a compact mass. X 360. occur at quite regular intervals. "Twin cells" have been described as joined by a short bridge, only one of the pair having a neuraxon. The branched dendrites of these ganglion cells extend into the inner reticular layer; their neuraxons pass toward the papilla of the optic nerve and except for the internal limiting membrane which covers them, they form the innermost layer of the retina. Collaterals have been detected returning from this nerve fiber layer to branch about the cell bodies of the ganghon layer. The nerve fiber layer also contains the centrifugal fibers which terminate in the inner nuclear layer. The fibers are all non-meduUated. Summary. The elaborate subdivision of the retina into eleven layers should not be allowed to obscure the essential features, namely, that it Digitized by Microsoft® MACULA LUTEA AND lOVEA CENTRALIS. 36] %\?/"S 5. f '<•> Q r- ®> ^ ® r, 5j = : Digitized by Microsoft® 362 HISTOLOGY. consists of an outer pigmented and an inner visual layer. The latter includes an outer layer of visual cells, — rod cells and cone cells. The bipolar cells of the ganglion retinae receive dendritic fibers which have free endings between the visual cells. They give rise to branching neu- raxons which communicate with the ganglion cells of the optic nerve. The neuraxons of the latter converge at the papilla of the nerve and extend to the brain. The retina also receives fibers from the brain. It contains an ectodermal supporting tissue, blood vessels in its inner layers, and nerve cells perhaps commissural, the significance of which is still obscure. Macula lutea and fovea centralis. When vision is centered upon a particular object the eyes are so directed that the image of the object falls upon the macula lutea or yellow spot of the retina, within which there is a depression, the fovea centralis. The macula receives straight slender fibers from the papilla of the optic nerve which is close by on its median side; other coarser optic fibers diverge as they pass the macula, forming an ellipse around it. The retinal layers of the macula are arranged as show in Fig. 414. At its border the number of rod cells diminishes and within the macula they are entirely absent. The nuclei of the numerous cone cells, which are here somewhat smaller than elsewhere, form an inner nuclear layer of twice the usual thickness. The basal portions of the cone cells make a broad Henle's fiber layer and slope away from the fovea. The bipolar cells of the ganglion retinae are so numerous that their nuclei may form nine rows. The ganghon cells of the optic nerve are also abundant. All of these strata become thin toward the fovea, the deepest part of which contains scarcely more than the cone cells. In some individuals the slope of the sides of the fovea is less steep than in the figure; its depth is variable. The macula and fovea are saturated with a yellow pigment soluble in alcohol. Pars ciliaris retinae. The optic nerve fibers and their ganglion cells disappear before reaching the ora serrata. The cone cells extend further than the rods, but the last of them appear to lack outer segments. By the thinning of the reticular layer the nuclear layers become confluent (Fig. 415). Near the ora serrata large clear spaces normally occur in the outer nuclear layer and they may extend into the deeper layers (Fig. 415). The radial sustentacular cells form a simple columnar epitheKum as the other layers disappear, and they constitute the visual layer of the pars ciliaris. The pigmented epithelium is apparently unmodified as it extends from the optic to the ciliary portion. Along the inner surface of the visual layer of the ciliary retina the cells produce horizontal fibers closely packed, which form a refractive hyahne membrane. Zonula ciliaris. Some fiberg arising from the pars ciliaris immedi- Digitized by Microsoft® o 2 S u o IJ n! jD IX rt X; C rt rt ■u o 60 = ri \«f ^ :o o^"o _lo* ",;;OOo 9 -V 'ft? --* m R;itlial fihei ol Midler. -7 ma3 V »_.■■ t:2-4 1. %. ; : ° ' ?S 1 Pars Lili:iris retinae. h o ^6.^, Digitized by Microsoft® 3^4 HISTOLOGY. ately in front of the era serrata enter the vitreous body, but a much larger number pass between the cihary processes to the lens. They are attached to the borders of its capsule, overlapping slightly its anterior and posterior surfaces. Thus they form the zonula ciliaris [suspensory ligament] which holds the lens in place (Fig. 410). The zonula is not a continuous layer, nor does it consist of two laminae, one to the anterior and the other to the posterior surface of the lens with a space between them. It con- sists rather of numerous bimdlcs, between which and the vitreous body, and among the bundles themselves, there are zonular spaces [canals of Petit] which communicate with the posterior chamber. Optic Nerve. In its intraorbital portion the optic nerve is surrounded by prolonga- tions of the meninges. On the outside is the dural sheath, consisting of Central arter}'. Fibers of the lamina Cl'ilirosa. | Central vein. I-I\at' zone. — Choriocapillaiis. frrf Basal membrane. Piijrnent la>"er of the retina. Fig. 419.— Vi;RTrc.\L Section through a part of the Hu.man Sci-iiRA and the ENTu^i OF thf: Chorioid. X too. g. Large \e^^cls ; p, pigment cells ; c, cross sections of capillaries. The ciliary body encircles the eve as a muscular band, attached to the inner surface of which there are from 70 to 80 meridional folds, the ciliary processes (Fig. 410). The ecjuator of the eye is vertical, like that of the lens, and the meridians are antero-posterior. The processes begin Ioav at the ora serrata and rise graduallv to a height of 1 mm., terminating abruptly near the border of the lens. luich process consists of fibrillar connective tissue containing numerous elastic fibers and blood ax-sscIs, and is bounded toward the pars ciliaris retinae bv a continuation of the lamina basahs which forms intersecting folds. The ciliary processes, which are com- pressible, may ser\-e to prevent the increase of intraocular pressure during the contraction of the ciharv muscle. The ciliarv muscle is a band of Digitized by Microsoft® 36S HISTOLOGY. smooth muscle Tiljcrs about 3 mm. broad and 0.8 mm. thick anteriorly; it arises beneath the sinus venosus of the sclera and tapers toward the ora serrata (Fig. 410). It consists of two sets of fibers, the meridional and circular. The meridional fibers as seen in section (p. 356), form a triangular group con- verging toward the sinus veno- sus. Their numerous outer- most bundles mixed with elas- tic tissue are apphed to the scleral surface. Anteriorly the bundles become gradually shorter and more radially l)laced so that those in the front of the muscle are perpen-. dicular to the sclera. The radial fibers are classed as a separate group by Professor Stohr. The circular fibers which vary in number indifferent individuals form that part of the ciliary muscle which is nearest to the equator of the lens. The iris consists of its slro)iia anteriorly and the pars iridica retinae Fig. 420.— a, From a Teased Preparation of a Hu- man Chorioid. X 240. p, Pigment cells ; e, elastic fibers; k, nucleus of a flat iion-pigmenteil cell ; the cell budy is im'isihle. B, Portion of a Hi/man Choriocafillaris and the .Adherent Lamina Basalis. X 240 c, Wide capil- laries, some of wfiicb contain fbl blood corpuscles ; e, lamina basalis, sliowiiig-a fine " lattice work " Loose coniiecti\e tissue. ' \'ascular la>er. Spindle cell layer. <T-^5">f''S^ r'ars iridica Fig. 42t— Vertical Si'ci ion oe the Puptliary Portion oe a Huim.vn Iris. X 100. About one- filth of the entire witlth of the iris is shown, g, Blood vessel, with thick connective tissue sheath; m, sphincter pupillac muscle cut transverselv ; p, piipillaiN- border of the ins. posteriorly, and is covered by the mesenchymal epithelium of the chambers of the eye. The anterior ei)ilheliura is a simple layer of flat polygonal cells [unfortunately named endolheliuni]. The stroma consists anteriorly Digitized by Microsoft® IRIS. 369 of a network of stellate cells in part pigmented. It is followed by a vas- cular layer of fine loose connective tissue with few elastic fibers. Its stellate cells, which in blue eyes are not pigmented, form elongated polyg- onal meshes. The vessels are radial, and have a thick connective tissue externa but a very weak circular musculature. Among the vessels near the free border of the iris, there are smooth muscle fibers which form a band i mm. wide encircling the pupil. This is the sphincter muscle of the pupil. A few radial muscle fibers also occur among the vessels. The dilator muscle of the pupil is behind the vascular layer. It is a con- , tinuous layer of radially arranged smooth muscle fibers, beginning near the pupil and extending to the ciKary body. The contractile portion of the spindle shaped muscle cells forms a membrane-hke layer resting against the pars iridica retinae, with which the pigmented nucleated portion of the cells seems to unite. These muscle cells have been thought to arise from the outer layer of the retinal cup. Except in albinos both layers of the retina are here heavily pigmented, and apart from their embryo- logical development they would be regarded as a single layer. Tunica Fibrosa. The sclera consists of interwoven bundles of connective tissue, chiefly meridional and longitudinal. Elastic tissue accompanies the bundles and is especially abundant at the insertions of the ocular muscles. The flat irregular cells of the connective tissue are surrounded by tissue spaces as in the cornea. Next to the chorioid, the sclera forms a pigmented lamina fusca which has already been described. The sclera becomes thinner anteriorly where it is absolutely continuous with the transparent cornea. The corneal boundary is obhque, being bevelled at the expense of its anterior surface. The cornea (Fig. 422) consists of an outer epitheUum, external basal membrane, substantia propria, internal basal membrane, and mesen- chymal epithelium bounding the anterior chamber. The corneal epithe- lium, about .03 mm. thick, is stratified and consists of a basal layer of clearly outlined columnar cells followed by three or four rows of cuboidal cells and several layers of flattened superficial cells. The outer cells retain their nuclei. Peripherally the epithelium is continuous with that of the conjunctiva bulbi. The anterior basal membrane [Bowman's] is an almost homogeneous layer, sometimes as much as .01 mm. thick. Superficially it connects with the epithehal cells by bands and processes. Beneath it blends with the substantia propria, of which it is a modification. Since it is not formed of elastic substance the name "anterior elastic mem- brane" is not justified. 24 Digitized by Microsoft® 37° HISTOLOGY. The substantia propria consists of delicate straight connective tissue filjrils which are united in Ijundles of an almost uniform thickness by a El Anterior basal m lembranc. - __ -. !!££«««,# 'j.„(IS!? M31IH; Substantia jin.ipria. - Posteiior basal membrane. Mcscnch\-mal epillielium. '' ^?'sv.^^x-«vv.,v, '■;■■:>- Fic. 422.— \'kk'iicai. Si-xrn>N of a Human Corni-:a. X 100. CuiiifLiI can; <4c ■~>_ Corneal I I'^iG 42^^— CoRNK\L Sp\crs \n'ii (■\^Ul^^rl (IN Fig 424. — Corni-. \l Cr:i ls rROM a Horizontal Wi-iiiiO rRoM A HoRi?iiNi\i Smmon or Si-;cTiON or- rrn-: CoRNr.A ok a Rabbit. Tiir: CoRNKA OK an Ox. SiKer iMipaialinn \ 240 X 240- fHuid?) interTibrillar cement. The bundles are cemented together, form- ing superposed tlat lamellae jjarallel with the surface. The layers are Digitized by Microsoft® CORNEA. 371 connected by an interlamellar cement substance, and by occasional oblique fiber-bundles. The latter so-called arcuate fibers are to be found especially between the anterior layers. In the cement substance, there is a system of branched canaUculi, dilated in places to form oval spaces. The latter are between lamellae but the canaliculi extend among their constituent fiber- bundles. Within the spaces there are flat stellate anastomosing cells, the branches of which extend into the canals and tend to unite with those of neighboring cells at right angles. The cells and their processes are more or less surrounded by tissue fluid. Leucocytes enter the canals and are normally foimd in the cornea; if the cornea is inflamed they become, abun- dant. Blood vessels and lymphatic vessels are absent. The posterior basal membrane [Descemet's membrane] is a clear elastic lamina, 6 n thick. Its inner surface in the adult shows hemispher- ical elevations. The mesenchymal epitheUum is a simple layer of flat polygonal cells. The iris sends connective tissue prolongations over the peripheral part of the inner corneal surface. Collectively they are called the ligamentum pectinatum of the iris. As compared with those of the ox and horse, in man they are rudimentary. Blood Vessels. The central vessels of the retina supply a part of the optic nerve and the retina; the ciliary vessels supply the rest of the eye. These two sets of vessels anastomose with one another only at the entrance of the optic nerve (Fig. 425). The ciliary arteries are (i) the short posterior ciliary arteries to the chorioid; and (2) the long posterior ciliary arteries which with (3) the anterior ciliary arteries supply chiefly the ciliary body and iris. The three groups will be considered in turn. 1. After supplying the posterior half of the surface of the sclera, some twenty branches of the short posterior ciliary arteries penetrate the sclera around the optic nerve. They form the capillaries of the lamina choriocapillaris. At the entrance of the optic nerve they anasto- mose with branches of the central artery of the retina (c) and thus form the circulus arteriosus nervi optici. At the ora serrata they anastomose with recurrent branches of the long posterior ciHary and the anterior ciliary arteries. 2. The two long posterior cihary arteries also penetrate the sclera near the optic nerve (z). They pass, one on the nasal and the other on the temporal side of the eye, between the chorioid and sclera to the cihary body. There each artery divides into two diverging branches extending along the Digitized by Microsoft® 372 HISTOLOGY. ciliary border of Ihe iris. By the anastomosis of these four branches a vascular ring is formed, the circuhis iridis major (^), from which numerous branches proceed to the ciliary processes fj) and to the iris (^), Near Bi"a:)ches Brandies to the to the Sinus corneal coiijuncti\"a \enosus border biillTi. Cornea. sclerae. ^■-. V '-■— . Conneainn a\ itli tlic iainnia cliuriocapillaris. ciliaris anterior. \'enouy ] Episcleral branches of the ■ anterior Arterial J ciliary ^'essels. Capillaries of the lam ma t hoi kh ajullai \'ena vorticosa. WnoLis 1 Episcleral branches Aitcii il j of the short posterior ciliary \-essels. ciliaris posterioris brevis. \-essflsof the sheath. Short^postcrioi mIiiin uteins \'i_-na ArKTi cenlrali^- retinae- Eit;, 4:"^.— Bi,o<-i)i \'i'..ssi..j.s <■})■ ini-. Evt . ( Alter Leber.) The retina, ^optic iicn c, and Umica fibrosa are stifipled ; the tunica vasculosa is blank. V, Connection of the anterior ciliar\' nrler\ \\ illi llie circnlus iridis major. the pupillary border of the iris the arteries form an incomplete ring, the circuhis iridis minor. 3. The anterior cih'ar}- arteries arise from those supplying the recti Digitized by Microsoft© BLOOD VESSELS OF THE EYE. 373 muscles, penetrate the sclera near the cornea, and in part join the circulus iridis major, in part supply the ciliary muscle, and in part through recurrent branches, connect with the lamina choriocapillaris. Before penetrating the sclera the anterior cihary arteries give off posteriorly branches for the anterior half of the sclera, and anteriorly branches for the conjunctiva bulbi and the corneal border. The cornea itself is without vessels, but at its border, between the anterior lamellae of the substantia propria, there are terminal loops. The veins generally proceed toward the equator, uniting in 4 (less often in 5 or 6) venae vorticosae. These pass directly through the sclera and empty into one of the ophthalmic veins. Besides the venae vorticosae there are small veins accompanying the short posterior and the anterior ciliary arteries. The short ciliary veins receive branches from the ciliary muscle, the episcleral vessels, the conjunctiva bulbi and the periphery of the cornea. The episcleral veins also connect with the venae vorticosae. Within the sclera near the cornea there is a circular vein receiving small branches from the capillaries of the ciliary muscle. This sinus venosus sclerae [canal of Schlemm] connects with the anterior ciliary veins. Arteria centralis retinae. From 15 to 20 mm. from the eye the central artery of the retina passes to the axis of the optic nerve and proceeds to the optic papilla. There it divides into two branches directed upward and downward respectively, and these by further subdivision supply the entire pars optica retinae. The branches are chiefly in the inner layers but may extend into the' outer reticular layer; they are absent from the fundus of the fovea centralis. Within the optic nerve the artery sends out numerous Httle branches which anastomose with small vessels which have entered the sheaths from the surrounding fat; and also with branches of the short posterior cihary arteries (Fig. 425, h). The central vein of the retina receives two main branches at the optic papilla and follows the artery along the axis of the optic nerve. Chambers and Spaces of the Eye. The eye contains no lymphatic vessels but is provided with communi- cating tissue spaces, bounded by mesenchymal cells or epitheha. These include the canaUcuH of the cornea and sclera; and the anterior chamber of the eye which through the capillary interval between the lens and iris connects with the posterior chamber, and the latter is prolonged into the zonuiar spaces. Irregular extensions of the anterior chamber, associated with the pectinate ligament of the iris, are called spaces of the angle of the iris [spaces of Fontana]. They are but shghtly developed in man. Pos- Digitized by Microsoft® 374 HISTOLOGY. teriorly the tissue spaces include the hyaloid canal of the vitreous body; the very narrow perichorioideal space between the chorioid and sclera; the subdural and subarachnoid spaces of the optic sheaths, named the intravaginal spaces; and finally the interfascial space [of Tenon] which surrounds most of the sclera and is prolonged as a supradural space around the optic nerve. These spaces may be filled from the subarachnoid of the brain. They contain a "filtrate from the vessels." The interfascial and perichorioideal spaces hold but little fluid; acting as bursae, they may facilitate the movements of the eye. Nerves. Apart from the optic nerve, the eye is supplied by the short ciliary nerves from the cihary ganghon, and the long ciliary nerves from the naso- ciliary branch of the ophthalmic nerve. The cihary nerves penetrate the sclera near the optic nerve and send branches containing gang- lion cells to the vessels of the chorioid. The nerves pass for- ward between the chorioid and sclera to the ciliary body, where they form a circular ganghonated plexus, the plexus gangliosus Fig. 426.-FROM A Section of the Human Cornea. ciUaris. ItS branches extend tO n, A dividing nerve ineTrating the anterior basal i^) ^^6 ciliary body, (2) the irfs membrane; s, subepithelial plexus beneath the c-nA /''^^ fVio /^/-^tt-ioo cylindrical cells; a, fibers of the intraepithelial °-^^ \6) ^"^^ COrned. plexus ascending 4.^w«. the epithelial cells. ^j^g ^^^^^ ^^ ^^^ ^jy^j.^ body form a dehcate network on its scleral surface; they supply its muscle fibers and 'those of the vessels with slender motor endings, and between the ciliary muscle bundles they have branched free endings, perhaps sensory. The medullated nerves of the iris lose their myehn and form plexuses as they pass toward the pupillary margin. A sensory plexus is found just beneath the anterior surface, and motor fibers supply the sphincter, dilator and vascular muscles. The existence of ganghon cells in the human iris is denied. The nerves of the cornea enter it from the plexus annularis in the sclera just outside. The annular plexus also sends fibers into the conjunc- tiva, where they end in networks, and in bulbous corpuscles (Fig. 128, p. 106) situated in the connective tissue close to the epithelium. Such corpuscles may be found i or 2 mm. within the corneal margin. The corneal nerves become non-medullated and form plexuses between the Digitized by Microsoft® ■ EYELIDS. one lamellae throughout the stroma. They extend into the epithehum and there form a very deHcate plexus with free intercellular endings. Eyelids. The eyehds or palpebrae (Fig. 427) are covered with thin skin pro- vided with fine lanugo hairs; small sweat glands extend into the corium. The latter contains pigmented connective tissue cells, which are rare else- where in the corium. The subcutaneous tissue is very loose, having many elastic fibers and few or no fat cells. Near the edge of the lid there are two or three rows of large hairs, the eyelashes or cilia, the roots of which extend obHquely, deep into the corium. Since they are shed in from 100 to 150 days they occur in various stages of development. They are pro- vided with small sebaceous glands, and the ciliary glands [of Moll] open • close beside or into their sheaths. The cihary glands are modified sweat glands with simpler coils which may show successive constrictions; "a branching of the tubules has been observed." The central portion of the eyehds is muscular. Beneath the sub- cutaneous tissue there are striated bundles of the orbicularis palpebrarum extending lengthwise of the hd. A subdivision of this muscle found behind the roots of the ciha is called the musculus ciliaris Riolani. Posterior to the orbicularis muscle are found the terminal radiations of the tendon of the levator palpebrae. A part of these are lost in connective tissue ; another part associated with smooth muscle fibers, is inserted into the upper border of the tarsus and forms the superior tarsal muscle. This occurs in the upper Ud, but correspondingly in the lower hd the radiations from the inferior rectus muscle contain smooth muscle fibers, forming the inferior tarsal muscle. The inner portion of the hds consists of the conjunctival epithehum and the underlying connective tissue including the tarsus. This is a plate of dense connective tissue which gives firmness to the lid. It begins at the free edges and extends over the adjacent two-thirds of the lid close to the conjunctiva. Imbedded in its substance in either hd there are about 30 tarsal glands [Meibomian], which consist of a wide excretory duct opening along the palpebral border and of small acini with short stalks which enter it from aU sides. In structure they resemble sebaceous glands. At the upper end of the tarsus and partly enclosed in its substance, there are branched tubular accessory lachrymal glands. They occur chiefly in the medial (nasal) half of the hd. The tunica propria of the palpebral conjunctiva contains plasma and lymphoid cells; the latter invade the epithehum beneath which in some animals they form nodules. The stratified epithelium of the skin gradually Digitized by Microsoft® 376 HISTOLOGY. changes to that of the conjunctiva, which has several basal layers of cu- boidal cells and a superficial layer of short columnar cells. The latter are Supei ior tarsal musclf. Radiations fiom the tendon Orbicularis I il e 1 \atoi [ alpebi ie palpebrarut SI. liu 11 Tun 1 IM-opr taisc s cxti^rnus T-iibU I "? ^ I mis. *"'^ '^'' '^ ratuni i^ ^ f^/ subcula- - 4 }p neum. A' * b p-5, 10 mm. a., Ectodermal eiiillie- Hum \\ hich forms ttie membranrms internal ear ; a. bas., basilar artery : ch. t., chorda t\"mpani ; d. c, cochlear duct : d. e., endoh mphatic duct ; d. s. 1., lateral semicircular duct : d. s. S., superior seniicii - cular duct; ep., epidermis ; fa., facial uer\"e; meten., meteiiceijhalon , m. t., niedullar\' tube; ph., phar\"nx. The two ducts in question are the superior and posterior semicircular duds respecti\-ely. The third or lateral semicircular duct forms soon afterwards. In Figs. 429 D and 430 B it is a horizontal shelf-like projection of the \'esicle, the center of which is to become perforated so that its rim forms the duct. The portion of the vesicle which receives the terminal openings of the three semicircular ducts is called the utrieulus. Since at one of their ends the superior and posterior ducts unite in a single stalk before entering the utrieulus, there are but five openings for the three ducts (Fig. 430 D). Near one end of each duct there is a dilatation or ampulla, Avhere nerves terminate. Digitized by Microsoft® ;So HISTOLOGY. While the formation of the semicircular ducts is occurring in the upper part of the vesicle, the lower portion elongates and its end becomes coiled, eventually making two and a half revolutions. The coiled tube is the ductus cochleae; its distal end is the caecum cupitlare and at its proximal end is the caecum veslibulare (Fig. 430 D, c. v.). A dilated sac formed at its proximal or upper end opposite the caecum vestibulare is the saccuhts; in the adult the connection between the sacculus and ductus cochleae is relatively narrow and is called the duclus reuniens (Fig. 439). The portion of the original vesicle between the sacculus and utriculus, from which the endolymphatic duct arises, becomes a comparatively slender tulje, the duclus utriculo-saccularis (Fig. 439). dss A Fir. 430. — Lathrai, or Extkknal Suri-'aces of IModkls of thi-^ Mkmbrvnois Portion ok thi-: Li-:ft l.NTERNAL Ear 1'"rom Human Embrvos. Uiffercnt eiilargemenls. (After His, Jr.) A. from ail embr\o of 6 9 mm.; B. 10.2 mm.; C. 135 mm ; and D. 22 mm. am., ampllll'^ : c. v.. caecum \ estibulare of d. c, coclilear duct ; d. e., etiflolx-mpliatic duct , d. s. I., d. S. p.. and d. s. S.. lateral, posterior, and 5ii[ierior semicircular ducts ; sac. sacculus ; ut., ntriculns. The ectodermal vesicle thus produces a complex system of connected epithelial ducts, which are the superior, posterior, and lateral semicircular ducts, the utriculus, the utriculo-saccular duct with the endoh'mphatic duct connected with it, the sacculus, ductus reuniens and ductus cochleae. They all contain a fluid called endolympJt. The acoustic nerve terminates in branches between the epithelial cells in certain pxrrts of the ducts. Round areas of neuro-epithelium are called maculae acuslicac; there is one in the sacculus and another in the utriculus. Elongated areas are crislae and there is one in each of the three ampullae. The axis or modiolus, about which the cochlear duct is wound, contains the nerves which send terminal hirers to the spiral organ of the adjoining epithelium. In this they form a line of terminations along the medial wall of the cochlear duct, following its windings from base to cupula. The mesenchyma immediatch' surrounding the system of ducts Digitized by Microsoft® DEVELOPMENT OF THE EAR. 381 becomes mucoid in appearance and ca\'ities lined with mesenchymal epithelium are formed within it. They contain a tissue fluid called peri- lymph, x^round the semicircular ducts the perilymph spaces are so large that the tissue between them is reduced to strands as shown in Fig. 431; these are sometimes cahed ligaments. The perilymph spaces around the semicircular ducts are irregularly arranged and communicate with one another at various points, but those around the cochlear duct form a single tube. It arises from the other spaces at the base of the cochlea and covers the lateral or outer surface of the ductus cochleae as it ascends to the S^iii II irculiir iliKl. Blood vesst Wall of the ^emi- cii Lular durt. LigaineiiL. Perilymph sparts- -■ „_ EpiLlK-iiuni r.f ilie duct. l-i-anu'TU of the .liut. 5|$Vi^^} . I'one of fhe semi- ^'■i \ ' / ( ircular canal. I'.lood \cssel. Fig. 431. — Ckoss SKcrioK of \ Skmii iKcri \k Dii. r anh 'iiii-. AnjAi GKTHHR WITH THI. SEMICIRCULAR CAX.AL OI E'.m: IN WHICH IH I ■^■ adult. ■: Vj. (Bolim and von Da\ idoff.) I Pkrii'i.mpii Si'\cks to l.nDGi.H. J'roni a liuniai cupula; there it turns and descends along the medial or inner surface of the ductus cochleae, ending blindly at the base not far from its origin. The ascending perilymph space excavated in the mesenchyma around the coch- lear duct is the scala vestibiili. The descending space with which it con- nects at the cupula is the scala tympani. The arrangement of the cochlear duct and its scalae is shown in the section through the axis of the spiral, Fig. 432. The upper side of the figure is directed forward and outward in relation to the body. The temporal bone develops from the mesenchyma surrounding the Digitized by Microsoft® 382 HISTOLOGY. ducts and their perilymph spaces, so that when the membranous labyrinth which they form is removed by maceration, the bone still contains a corresponding arrangement of cavities and canals. These constitute the bony labyrinth. Casts of it made in soft metal may be seen in all anatom- ical museums. Instead of subdivisions to correspond with the utriculus, sacculus, and utriculo-saccular duct, the bony labyrinth has a single space called the vestibule. Into it the semicircular and cochlear canals open. The middle and the external ear arise in connection with the first or spiracular gill cleft. In common with the other clefts this includes an entodermal pharyngeal out])ocketing (Fig. iS8, p. i66) and an ectodermal depression (Fig. 187, sp.), which meet one another. The latter becomes surrounded bv several nodular elevations which coalesce in a delinite Modioli Scala veslibuli. Ganglion _ ^ Sc.ilci t\ mpani. Rniniis > chlearis of the f ntr\us >^f""'^ . 1 acusticus. \ostibularis ) M)_aLiis acusticus iiiLenuis. Fig. 432. — Horizontal ShcnoN ok thk Cochlka of a Kittkn. ^; S, The wiiidiu):,' ductus cochlctiris, x, crossed the plane of section five times. Above it in e\'eiv case is the .^cala vestihuli, and below it is the scala lyuipani. manner to make the projecting auricle [pinna] of the external ear. Its depression deepens, Ijccoming the external auditory meatus, the ectoderm at the bottom of which passes over the tympanic membrane, thus forming its outer layer. The entodermal portion of the spiracular cleft becomes in the adult an elongated outpocketing of the pharynx, known as the auditory tube [Eustachian tube]. As seen in the section Fig. 433, the tube is sepa- rated from the bottom of the meatus by a \'cry thin layer of mescnchvma. In the mesenchyma behind the spiracular cleft a chain of three small bones (the malleus, incus, and stapes) develops; it extends from the bottom of the meatus to the vestibule. The bony wall of the vestibule is deficient at the small oval area where tlie stapes reaches it, so that the chain of bones comes directly in contact with the fibrous covering of the jjerilymph space. Digitized by Microsoft® DEVELOPMENT OF THE EAR. This area of contact is the fenestra vestihuli (fenestra meaning window). When the chain of bones vibrates baclv and forth, tlie motion of the stapes is transmitted through the fenestra vestibuU to the perilymph, and waves may pass up the scala vestibuh and down the scala tympani, stimulating the nerves of hearing in the cochlear duct. The bhnd termination of the scala tympani rests against the lateral wall of the vestibule where also the bone fails to develop; the round fenestra cochleae is thus produced. Its fibrous membrane may yield somewhat to the perilymph waves, thus reheving tension in the cochlea. str _^cl sp ,i h Fi(";. 433. — Horizontal Section through the Ear of a Human Embryo of about 5 Cm^. au., rVuricle; au.t., auditory tube; ch.t., chorda tympani; d.c, coclilear duct; d.S.I. and d.S.p., lateral and posterior semicircular ducts; e.a.m., external auditory meatus; fa., facial nerve; f.c., fcucbtra cochleae ; p.s., perih inphatic space; St.. stapes ; s.tr.. transverse sinus; t.b., tempoial bone. In Fig. 433 the fragments of the chain of bones together with neigh- boring nerves are imbedded in a mass of mesenchyma. In a later stage the outer end of the auditory tube expands, filling all the space between the vestibule and the bottom of the meatus. Thus it forms the tympanic cavity. It encounters the chain of bones and the chorda tympani, and wraps itself around them so that they he in its folds or plicae. Thus all structures which extend into the tympanic cavity, or appear to cross it, are covered with a layer of entodermal epithelium derived from the audi- tory tube. The original contact between the ectoderm and entoderm of the spiracular cleft forms only an insignificant part of the tympanic membrane. The latter becomes greatly enlarged, extending somewhat along the upper surface of the ectodermal auditory meatus. The portion Digitized by Microsoft® 384 HISTOLOGY. of the malleus lying near it becomes imbedded in its mesenchymal layer, and its inner entodermal layer is made by the expansion of the tympanic cavity. The enlargement of the tympanic cavity continues after birth when it invades the spaces formed within the mastoid part of the temporal bone. In spite of these modifications the course of the spiracular cleft is retained in the adult. The ectodermal depression and its surroimding elevations constitute the external ear; the pharyngeal outpocketing persists as the auditory tube and the tympanic cavity of the middle ear. It opens freely into the pharynx and contains air. Sacculus, Utriculus, and Semicircular Ducts. The walls of all these structures consist of three layers. On the out- side there is connective tissue with many elastic fibers and occasional pig- ment cells. This is followed by a narrow basement membrane said to form small nodular elevations toward the third and innermost layer, the simple flat epithelium. Near the maculae and cristae the connective tissue and the basement membrane become thicker; the epithehal cells are columnar with a cuticular border. In the neuro-epithelium of these areas there are two sorts of cells, sustentacular and hair cells. The sustentacular or fiber cells extend clear across the epithelium and are some- what expanded at both ends; they contain oval nuclei. Hair cells, which receive the stimuH, are columnar cells limited to the is? superficial half of the epitheUum; they have large ^0 spherical nuclei near their rounded basal ends, and a ^, ^ ^ clump of fine agglutinated filaments projecting from ^ ^ their free surface. The nerves lose their myeHn as "^ U they enter the epithelium and ascend to the bases of ''"^fro'm the^sacci^- ^^ ^^^^ cells. There they bend laterally, forming a x'560.'' ^'^ ''~"'^''''^- dense network which appears as a granular layer in or- dinary preparations; the granules are optical sections and varicosities. The horizontal fibers terminate like their occasional branches, by ascending between the hair cells, on the sides of which they form pointed free endings. They do not reach the free surface of the epithelium. This surface is covered by a continuation of the cuticula, a "membrana hmitans," which is perforated by the hairs. Over the two maculae there is a soft substance containing very many crystals of calcium carbonate, 1-15 ,« long, which are named otoconia. (Large "ear stones" of fishes are called otoliths.) Over the cristae of the semicircular ducts there is a gelatinous substance, transparent in fresh preparations, but coagulated and rendered visible by reagents. Digitized by Microsoft® COCHLEA. 38s The "ligaments" of the ducts, the thin jK-riosteura of the bon)' semi- circular canals, and the perilymph spaces lined with mesenchymal epithe- lium are seen in Fig. 431. Cochlea. The relation Ijetween the ductus cochleae and the scalae tympani and ^•estibuli is shown in Fig. 435. The ductus is triangular in cross section, being bounded on its peri[)heral surface Ijy the thick periosteum of the bony wall of the cochlea; on its apical surface (toward the cupula) by the meiiihrana vestibularis [Reissner's membrane]; and on its basal or medial surface by the lamina spiralis. These three walls may be described in turn. The peripheral wall of the cociilear duct is formed by the dense fibrous periosteum attached to the bone, together with a large mass of looser tissue Blood % essels. Limltiis jMi.'ii]bi;iii.i spiralis. \ usLihularis. Scala x'ustibuli. s pr'jniiiieiis. Lamina sjiiralis ossca. Lamina spiralis nieiiil.r.macca. Flu. 435.— The Portion oi- Fi.,uke.132 marki.;i. " Scala vestibuli" anh " Slala iv.mi'V.m." X 50. crescentic in cross section, the Ugamcnium spiralc (Fig. 435). The spiral ligament is covered by a layer of cuboidal epithehal cells belonging to the cochlear duct. Close beneath the epithehum there are blood vessels which are said to give rise to the endoh'mph. The thick plexus which they form is described as a band, the stria vascularis, which terminates more or less distinctly with the vas prominens. The latter occupies a low elevation of tissue which has its maximum development in the basal coil of the cochlea (Fig. 435). Digitized by Microsoft® 386 HISTOLOGY. The apical wall or mcnihrana vcslihularis consists of a thin layer of connective tissue bounded on one side by the mesenchymal epithehum of the scala vestibuli, and on the other by the simple flattened ectodermal epithelium of the cochlear duct. The basal wall or lamina spiralis extends from the modiolus per- ipherally to the bony wall of the cochlea. Near the modiolus it lies between the two scalae but peripherally it is between the ductus cochleae and the scala tympani. Toward the modiolus it contains a plate of bone perforated for the passage of vessels and nerves; this part is the lamina spiralis ossea. The peripheral portion is the lamina spiralis mcmbranacea* Both parts Lattiiiiii ^■estibu]art Sulcus spiral \ Ca|iillarics nf Ihe slria Nevxe bundle. Laluuiii Itiiier Outer tinipaiiicum.^^ -^ ._^ Pillar cells. Deiters's Membraiia Connective cells. basilaias. tissue. Fig ^,6 -r.u;Ti.)\. O].- Fir.i,Ki.; 435. X 240. », Intercellular " tunnel " trave.sed by nerve fibers. are covered below by the mesenchymal epithelium of the scala tympani, and above by the epithelium of the cochlear duct including its complex ncuro-epithelium known as the spiral organ [of Corti]. W^iere the membrana vestibuli meets the osseous spiral lamina there is an elevation of tough connective tissue called the limbus spiralis (Fig. 435). It consists of abundant spindle-shaped cells and blends below with the periosteum of the spiral lamina. Superlicially it produces irregularly hemi- * Ttic familiar term laiiiiiia spiralis iiiaiihraiuuca employed tw Professor Stohr is not included among the Nomina Analamica. In place of it is lamina hasi.laris. Whether the laller should be considered synonymous with the former, or should refer to the entire basal la\a-r mio a portion of which a lamina spiralis ossca projects, is not apparent. Digitized by Microsoft® -f COCHLEA. og^ spherical painllae found within the cochlear duct near the vestibular membrane. Further within the ductus cochleae there is a row of flat elongated forms directed from the modiolus toward the periphery; these are sometimes called Huschke's auditory teeth (Fig. 43S). The papillae are covered by a simple layer of flat epithelium. As the hmbus extends from the vestibular membrane toward the peripheral part of the cochlea, it terminates abruptly in an overhanging lahiiim vestibulare beneath which is an excavation, the sulcus spiralis (Fig. 436). The basal wah of the sulcus is the labium tympanicum, found at the pcripjieral edge of the osseous spiral lamina. As the epithehum of the limbus passes over the labium vestibulare into the sulcus, it becomes cuboidal. A remarkable formation, non-nucleated, soft and elastic, projects from the labium ves- tibulare over the neuro-epithelium of the membra- nous spiral lamina. It is called the mcmhrana iccloria UWmi'i and is considered to be a cuticular formation of the ^yi<^$0r labial cells to which it is attached. ^a;-; The lamina spirahs membranacea, or lamina basil- aris (?), consists of four layers. The mesenchymal -^'■^'^■hrLi «_/>?'/ /;?//;/;« of the scala tympani is followed by a layer :. tV;,,:3jj| of dehcate connective tissue prolonged from the neri- i- O I h IG. 437. — S U R F A C E osteum of the scala. Its spindle cells are at right ][Im,'L "spir^^lis angles with the fibers of the overlying memhrana T^'"'''y'' :^. basilaris. This membrane, which is beneath the °fo"""'''' '''""»" epithelium of the cochlear duct, consists of coarse '' ^/-iaud'us) 'if\hl straight fibers extending from the labium tympanicum infocus; uibtSof ,,11. ^ .1 ri-n . tlie niembv:-iiia basil- to tlie hgamentum spirale. I hey cause it to appear aris in focus; b, ^ , . , nuclei of the under- fanely striated (Fig. 437). Peripherally (beyond the uingconnecii^eiis- bases of the outer pillar cells) the fibers are thicker and are called " auditory strings " ; they are shortest in the basal part of the cochlea and longest toward the apex, corresponding in length with the basal layer of the cochlear duct. These fibers have been thought to vibrate and assist in conveying sound waves to the nerves. The epithelial cells covering the basilar layer, present rows of highly modified forms extending up and down or lengthwise of the cochlear duct, and constituting the spiral organ [of Corti]. Next to the cuboidal epithelium of the sulcus spirahs there is a single row of inner hair cells (Fig. 436). These are short columnar cells which do not reach the bottom of the epi- thehum; each has about forty long stifl" hairs on its free surface. The inner hair cells are followed peripherally by two rows of pillar cells, the inner and outer, which extend the whole length of the cochlear duct. As seen in cross section they are in contact abo\'e, but are separated below Digitized by Microsoft® 38S HISTOLOGY. by a Irian^i^ulai- inlcrccUular space or "tunnel." The space is filled with soft intercellular suljstance. Thus they rest upon the basilar membrane in A-form. The inner pillar cells are said to jje more numerous than the outer. Both forms are stiff bands with triangular expanded bases, which are associated with nucleated masses of proto])lasm within the "tunnel." The "heads" or upper ends interlock, since the inner pillars are concave to receive the con\-ex surface of the outer pillars. From the superficial surface of both, plates extend ]jeripherally or outward, that of the inner pillar partlv covering the head-plate of the outer pillar (Fig. 4381. The lirale Oilier Mcmbrana Niiel's IJeilers's Viasilaris. space. cells. \iniiaii.' lainella Fit.. 43S.— DlAC.RAIM (iir luv. SlKI'CTURl'; OK THK I'.XsM. W\l I- OK lllh DlXT 01.~ THE CoCHLE.\. A, X'icw from Ihe side B. \'icw frmn the suii'acc In Ihe latter the free surface is in focus. It is evident tliat the epittielinni "\ Ihc suU ns spiralis, l\iiis iii another plane, as well as the cells of Claudius, can he seen distincth' onK- li\- lnwciint; the tube. The membrana tectoria is not drawn. The spiral iier\e bundles are indicated b\ duts. dark bodies in the heads of both pillars, and in the basal ])art of the outer ones, are not nuclei. On tlie peripheral side of the outer ])illars there arc several rows (usually four) of outer hair cells separated from one another by siisteiitae- iilar cells (Deiters's cells). The outer hair cells have shorter hairs than the inner ones, which otherwise the\' resemble. They do not extend to the basilar membrane, thus lea\'ing unoccu])ie(l the communicating inter- cellular (Nuel's) .spaces between the deeper ])(irtions of the sustentacular cells. Nuel's s])aces ciinnect with the tunnel. The sustentacular cells Digitized by Microsoft® COCHLEA. ,89 are slender bodies each containing a stiff filament. They have a cap- like cuticular border so that they remotely resemble the distal phalanges of the fingers. The spaces between the "phalanges" are occupied by the outer hair cells. The cuticular expansions connect with one another forming a reticular membrane, into the apertures of which the hair cell processes extend. The sustentacular cells resemble the pillar cells, but their transformation into stiff fibers has not proceeded so far; the cutic- ular border is comparable with the head plate. The most peripheral of the sustentacular cells are followed by elongated columnar cells (cells of Hensen) which gradually shorten and pass into the undifferentiated epi- thelium of the cochlear duct. The low cells following Hensen's cells are the cells of Claudius. They are said to have branching bases which extend deep into the underlying tissue. In both the columnar and the low forms there are single stiff filaments which are less developed than in the susten- tacular cells. The centrosomes of all these cells he near their free surfaces. Nerves and Vessels of the Labyrinth. The acoustic nerve is a purely sensory nerve passing between the pons and internal ear through a bony canal, the internal auditory meatus. It is divided into vestibular and cochlear portions (Fig. 432). The vestibular nerve proceeds from the vestibular ganglion and has four branches; the utricular nerve and the superior, lateral, and posterior ampullary nerves. Their terminations have already been described (p. 384). The cochlear nerve, which has a saccular branch, proceeds from the spiral ganglion lodged within the modiolus at the root of the lamina spirahs (Figs. 432 and 435). The ganghon cells remain bipolar like those of embryonic spinal ganglia. The neuraxon and the single peripheral dendrite. are meduUated except near the cell body. The peripheral fibers extend through the lamina spirahs ossea, within which they form a wide meshed plexus, and after losing their myelin they emerge from its free border through the foramina nervosa. In continuing to the spiral organ they curve in the direction of the cochlear windings, thus producing spiral strands. Those nearest the modiolus are on the axial side of the pillar cells; the middle ones are between the pillars, in the tunnel; and the outer ones are beyond the pillar cells. From these bundles delicate fibers pass to the hair cells, on the sides of which they terminate. The internal auditory artery is a branch of the basilar artery. It arises in connection with branches which are distributed to the under side of the cerebellum and the neighboring cerebral nerves, and passes through the internal auditory meatus to the ear. It divides into vestibular and cochlear branches. The vestibular artery supplies the vestibular nerve Digitized by Microsoft® 390 PIISTOLOGY. and the upper lateral portion of the sacculus, utrieulus and semicircular ducts. The cochlear arlery sends a vestibulo-cochlcar branch to the lower and medial portion of the sacculus, utriculus, and ducts. This branch also supphes the first third of the iirst turn of the cochlea. The capillaries formed b}^ the Ax-stibular branches arc generally wide meshed, but near the maculae and cristae the meshes are narrower. The terminal portion of Artena auilii-l\'a J idleriia i Artei ia \'csiibularis Aitfi la eocliU-ari-^. us scmicircularis SLipei lor. LiUa lateralis. na aquaeductus vestibuli. ctus seniicircularis lateralis. Diutus st'inicircularis ixisterior. Blood A'kssels of the Right Hi'man LAB^■Rl^:Tn. iMfpt al ano Pos- terior Aspect. S., sacculus ; U., utriculus ; i, (Uictiis iciiniens; The saccus eudohmpliaticLis is cut off. tnciiio-saccularis. the cochlear artery enters the modiolus and forms three or four spirally ascending l^ranches. These give rise to about thirty radial branches distributed to three sets of capillaries (Fig. 440); i, those to the spiral ganglion; 2, those to the lamina spiralis; and 3, those to the outer walls of the scalac and the stria vascularis of the cochlear duct. The veins of the labyrinth form three groups, i. The vena aquae- Digitized by Microsoft® BLOOD VESSELS OF THE INTERNAL EAR. 391 ductus veslibull receives blood from the semicircular ducts and a part of the utriculus. It passes toward the brain in a bony canal along with the ductus endolymphaticus, and empties into the superior petrosal sinus. 2. The vena aquaeductus coclileae receives blood from parts of the utriculus, saccu- lus and cochlea; it passes through a bony canal to the internal jugular vein. Within the cochlea it arises, as shown in Fig. 440, from small vessels including the vas prominens (a) and the vas spirale (b). Branches derived from tliese veins pass toward the modiolus. (There are no vessels in the ScLila t\!np;uii. Sualci \-cslihLili. Stria \-ascularis ,- Cross secUijii of a spiral arler>' ol' lliu niodiulus. \'ena laminae spiralis. '^ - Ganglion spirale. -Vena spiralis superior. Crrtss section bai \*nx. i» V / Fig. 4.(1 —Cross Si-;ctio_x oi- iiii-: C m; in m.'m.i s P \kt oi' nii- Ai i.itory Tiiii . X : (Btjhni and \uii IlaxiLlull.) Middle E,a.r. The tympanic cavity, which contains air, is lined with a mucous membrane closely connected with the surrounding jjcriosteum. It consists of a thin layer of connecti\'e tissue covered generall)' willi a simple cuboidal epithelium. In places the epithelial cells may be Hat, or tall with nuclei in two rows. Cilia are sometimes widely distribuleil and are usually to be Digitized by Microsoft® MIDDLE EAR. 39:; found on the floor of the cavity. In its anterior part, smah al\'eolar mu- cous glands occur very sparingly. Capillaries form wide meshed networks in the connective tissue, and lymphatic vessels are found in the periosteum. The auditory tube includes an osseous pari toward the tympanum, and a cartilaginoits pari toward the pharynx. Its mucosa consists of librillar connective tissue, together with a ciliated columnar epithelium which be- comes stratified as it approaches the pharynx. The stroke of the cilia is toward the pharyngeal orifice. In the osseous portion the mucosa is without glands and \'ery thin; it adheres closely to the suri'ounding bone. Along its floor there are pockets containing air, the cellular piicu- malicae. In the cartilaginous part the mucosa is thicker; near the pharynx it contains many mucous glands (Fig. 441). Lymphocytes are abundant in the surrounding connective tissue, forming nodules near the encl of tlie tube and blending with the pharyngeal tonsil. The cartilage, which only partly surrounds the auditory tube, is hyaline near its junction with the bone of the osseous portion; it may contain here and there coarse fibers which are not elastic. Distally the matrix contains thick nets of elastic tissue, and the cartilage is consequently elastic. External Ear. Between the middle ear and the external ear is the lympank membrane, which consists, from without inward, of the following strata: the ctitaneum, radialum, circulare and mucosnm (Fig. 442). The stratum cutaneum is a thin skin without , papiUae in its corium, except along the handle -^^A or mainibriuni of the malleus. There it is a thicker layer containing the vessels and ner\'es which descend along the manubrium and spread from it radially. In addition to the \-enous plexus which accompanies the arterv in that ^ , . -, l~ii-.. 442.— Cross Shctkin or^ situation, there is a plexus of vems at the per- tuh mkmbrana tvm- ^ . l-ANI BELOW THE MaNU- ipherv of the membrane. The latter recen'es |;ri™. x 450. (After vessels both from the stratum cutaneum and a. siraLum cuLaneum (sho\\-- ins; the corneuiii ami the less vascular stratum mucosum. The radiate j,'erminatwum ),; ^b, strat- and circular strata consist of compact bundles of ^Sf'I^'l'u."".-- fibrous and elastic tissue arranged so as to sug- >-°='"'"- gest tendon. The fibers of the radial la}-er blend with the {jerichondrium of the hyaline cartilage covering the manubrium. Peripherally the fiber layers form a fibro-cartilaginous ring which con- nects with the surrounding bone. The stratum mucosum is a thin layer of connective tissue covered with a simple non-ciliated flat epithelium Digitized by Microsoft® 304 HISTOLOGY. continuous with the h'ning of the tympanic cavity. Peripherally, in children, its cells may Ijc taller and ciliated. As a whole the tympanic membrane is divided into tense and //acc/(i portions. The latter is a rela- tively small upper part in which the fibrous layers are deficient. The external auditory meatus is lined with skin continuous with the cutaneous layer of the tympanic membrane. In the deep or osseous portion the skin is very thin, without hair or glands except along its upper wall. There and in the outer or cartilaginous part eeruminous glands are abun- dant. ''They are branched tubulo-alveolar glands" (Huber) which in many respects resemble large sweat glands. Their ducts are lined with Epidermib / Hair sheath Coriani E.\crctor>' duct Membraiia propria. Nuclei of smoi>lli muscle I'lhers. Secretion. Gland cells. - Cuticular border. Vouughaii _ , ^^-J ' r-#iaiii5,=^.,-{l^ Gland cells. [qVo\qu2j^._ JNuclei of smooth muscle r- ., t 1 1 ^— i--v« *. •^-r — .3:^Ss=;^5uif^ fibers. Cod of ceiummous gland -(f^^^.^iT^ i ^^^^^Ss:^- Membrana |.ropria. m Fig 443,— From a X'ertic.al Sf.ction through Fig. 444. — Tubules of the Chruminous Glands. THE Skin of the Extern.al Auditory A, Cross section, from an infant, B, longitu- Meatus of an Infant. X so. The excre- dinal Election, from a boy 12 ;-ears old. tory duct opens into the hair follicle. stratified epithelium. The coils consist of a single layer of secreting cells, general cuboidal, surrounded by smooth muscle fibers and a well defhied basement membrane. They difl'er from sweat glands in that their coils have a very large lumen especially in the adult, and their gland cells, often with a distinct cuticular border, contain many pigment granules and fat droplets. Their narrow ducts in adults end on the surface of the skin close beside the hair sheaths; in children they empty into the sheaths (Fig. 443). Tlie secretion consists of pigment, fat, and fatty cells, the latter de- rived probably from the hair sheaths. The cartilage of the external auditory meatus and of the auricle is elastic. Digitized by Microsoft® THE NASAL CAVITIES. 395 pa p NOSE. The nasal cavities are formed Ijy the invagination of a pair of epi- dermal thickenings similar to those which give rise to the lens and auditory vesicle. The pockets thus produced in the embryo are called "nasal pits" (Fig. 1S7, 11, p. 166). Their external openings remain as the narcs of the adult. Temporarily, from the third to the iifth month of fetal life, they are closed by an epithehal proliferation. Each nasal pit acquires an internal opening, choaua, in the roof of the pharynx. The choanae are at first situ- ated near the front of the mouth, separated from one another by a broad nasal septum (Fig. 445). As the latter extends posteriorly it is joined by the palate processes which grow toward it from the sides of the maxillae. Thus the choanae recede toward the back of the mouth while the em- bryonic condition of cleft palate is being removed. The lateral walls (not the mechal) of the nasal cavities produce three curved folds one above another; they are concave below, and in them the conchae [turbinate bones] develop. The nasal mucosa covers these and extends into the sphe- noid, maxillary, and frontal sinuses, and the ethmoidal cells. The boundary between the epithelium of the nasal pit and that of the phar}Tix early disappears, and the extent of each in the adult is uncertain. Presumably the olfactory neuro-epithehum is derived from the nasal pit. In man the olfactory region is limited to the superior and middle concha and the part of the septum which is opposite them. This regio oljactoria is co\-ered by a yellowish-brown membrane which may be distinguished macroscopically from the reddish mucosa of the regio res- piraloria. The latter includes the remainder of the nose. The two re- gions may be considered in turn. The vestibule or cavity of the projecting cartilaginous portion of the nose is a part of the respiratory region which is lined with a continuation of the skin. Its stratified epithelium has squamous outer cells and rests upon a tunica propria with papillae. It contains the sheaths of coarse hairs ivibrissae) together with numerous sebaceous glands. The extent of the squamous epithelium is variable; frequently it is found on the middle concha, less often on the inferior concha. The remainder of the respiratory mucosa consists of a pseudo-stratified epithelium with several rows of nuclei. It may contain few or many F:g. 445. — The Roof of thi" Mouth of a Human Em- )3RVO OF 8 Wfkks. X 4- (After Kollmaiiu.) na, Naris ; ch, clioana ; al. p., i. p., and pa. p., alvccilar, interma.xillary. and jialaU- proct;sses. Digitized by Microsoft® 39'J HISTOLOGY. "olilet cells. The Uinica [H'ojjria is well de\'elo])ed, Ijeing even 4 mm. thick on the inferior concha. It consists of ilbrillar tissue with many elastic elements especially in its deeper la3-ers. Beneath the epithelium it is thick- ened to form a homogeneous membrana propria perforated with small holes. Lymphocytes are present in \'arialjle quantity, sometimes forming solitary nodules and often entering the epithelium in great numbers. Branched m^ M M ^§* m-M mm..-. ^:'.&:\-' ■ '•■.'■Si.'-'-:-:- 1.: ' I •■'.■■:-'s' fc^:-'i\''''\fc •-/..'■ -JiC>»->jl«-' -^t--:. -V:;; *■ ' '^--.-■-■' ■ . ••/..>y.v^ ■:•, ^V,;yy^^);i:-ffr:jiir^^'-^p': ■^^■\ • • t' "j ^ - ■*•«-■.■.■ I ' ■ — 1 -.:;■■ ■■*! ..A.»vi'A'^ ' '.■■■ft*. •■ ^ !■> . ;»'."■: -- ■"' — Epithelium. Tunica proitria. .„ ^'c^1 Mucous cells. berous cc=lls. „^.^i^;:^,,. c^-j:'- £.- Fic. 446.— Vertical Skctkin thr( Oti tlie left iba funnel-shapeil de)i e-eLlion of a iai.t^e vein. I\Ticiis\ (JF 'ini-: TnfI' :i-ei\in,!j; an excrelor\- du )R CoNTii \ ob~ Man. X 4S. , ntaib\' un tlie iiylit is tlie alvcolo-tubular mixed glands extend into the tunica propria. Their serous portions ha\'c intercellular secretory capillaries. Both mucous and serous cells contain a trophospongium. The glands often empt}^ into funnel shaped dejuTssions which are macroscopic on the inferior concha, and are lined with the superficial epithelium. The mucosa of the several pnranasal sinuses is thin ( — 0.02 mm.), with less elastic tissue and luit Digitized by Microsoft© NOSE 397 few small glands. A pocket which extends into the lower part of the median septimi and is named the vomcro-nasal organ [Jacobson's organ], is in man the rudimentary remnant of an important sense organ supjdied I'^k;. 447.— Isoi.ATi^D Cki.ls of rill-: Oi,- FACTonv Mucosa oi' a Rabi;it. , 560. St. Supporting cells; s,extriK!ed mucus re- suiiibling- cilia; r, olfactory cells, from r'. the lower process has been torn off; f, ciliated cell ; b, cells of ollactory -lands. ^'^ ^ ^J — l{[jitliLliuin. V ar- h- teirm .^^^ 1 ccL I'jrupria. Fig, 448 — \ L Si- N H Olfactory M c t- A K LR 50. zo, Zone of oval ; zr, zone of round nuclei ; dr. olfac- tory glands; a, excretory duct, k, body; g, tnn- tlus; n, sections of the olfactory nerves; v, vein; ar, artery ; b. coiniecti\-e tissue. I Ei.itl: by the olfactory ner\x's. From the fifth month of fetal hfe it is lined with a tall columnar epithelium which is not olfactory. In the rcgio oljactoria the mucosa consists of a tunica propria and an olfactory epithelium. The latter consists of sustenlacular cells and oljaclory cells. The super- ficial halves of the susten- lacular cells are cylindrical, and contain yellowish pig- ment together with small mucoid granules often ar- ranged in vertical rows (Fig. 447j. The more slen- der lower halves have den- tate or notched borders, and branched basal ends which unite with those of neighboring cells thus form- ing a protoplasmic network. Their nuclei, generallv oval, are in one ])lane and in \-ertical sections they form a narrow "zone of oval nuclei" (Figs. 44S and 450). The olfactory cells generally have round nuclei containing nucleoli. The}- occur at different levels and so form a broad "zone of round nuclei." From the protoplasm which is gathered immediately about the nucleus. Fibers of the olfactor\' nei\"e. P^iG. 449- -GOLCI Pkkfmration o)- a Vci > UlI J>I IK CSS illuLtorv cell. Ol.l'ACJORV R Digitized by Microsoft© 398 HISTOLOGY. each olfactory cell sends a slender c_ylindrical process towards the surface, where it terminates in small hairs. Basally the olfactory cells pass directly into the axis cylinders of the olfactory nerves (Fig. 449). Thus they are ganglion cells, their basal processes being neuraxons. Cells intermediate between the olfactory and suslentacular forms may be found. At the free surface of the olfactory epithehum there are terminal bars, and small masses of mucus sometimes suggesting cilia. The mucus is the product of the sustentacular cells. Near the tunica propria there is a network of so-called "basal cells" (Fig. 450). The tunica propria is a network of coarse iibrous tissue and fine ■'^■■'"^ "' '' Pigment granule (_)\-al iniuleus of a >usu-ntacu]ar cell. Rijutnl nucleus of an olfactor\ cell. — Basal cell. ^'.'^, Dil Fin. 450 Sections of olfactory glands, (ted duct. Mucus. — \'l..RTIC.\L St'XllOX "ItlROL'GII THK Ol-l- AC la ) R\' Rl^GlO-X OI-"" .\N .Al>t_LT, >' 4OO. elastic fibers associated with many connective tissue cells. In some animals (for example, the cat) it forms a structureless membrane next to the epi- thelium. It surrounds the numerous oljactory glands [Bowman's glands]. In man these are branched cavities consisting of excretory ducts extending through the epithehum, and of gland bodies beneath. Oblique sections of the ducts have been mistaken for "olfactory buds." The glands in man appear to be serous but they sometimes contain mucus in small quantity. They are found not only in the olfactory region but also in the adjoining part of the respiratory region. Digitized by Microsoft® NOSE. 399 The nerves of the nasal mucosa consist of groups of non-medullated oKactory fibers, which unite in larger bundles in the tunica propria, and pass through the lamina cribrosa of the ethmoid to enter the olfactory bulb. They are covered by prolongations of the dura. MeduUated branches of the trigeminal nerve occur both in the olfactory and respiratory mucosa. After losing their myelin they form terminal ramifications in the tunica propria and may ascend into the epithehum. Thus they differ from the olfactory fibers which generally do not branch. The arteries are found in the deeper layers of the tunica propria, and they form a thick capillary network just beneath the epithehum. The veins are very numerous, especially at the inner end of the inferior concha where the tunica propria resembles cavernous tissue. Lymphatic vessels form a coarse meshed network in the deeper connective tissue. Injec- tions of the subarachnoid space follow the perineural sheaths of the olfactory nerves into the nasal mucosa. Digitized by Microsoft® PART II. THE PREPARATION AND EXAMINATION OF MICROSCOPICAL SPECIMENS. The following directions are limited to those of fundamental import- ance which are likely to be employed by students who are beginning their histological studies. Further information may be obtained from "The Microtomist's Vade-mecum" by A. B. Lee (3d ed., 1903, Blakiston, Philadelphia) and from Mallory and Wright's "Pathological Technique" (3d ed., 1904, Saunders, Philadelphia). The latter is particularly adapted to the needs of medical students. Fresh Tissues. Certain transparent tissues may be studied advantageously in a fresh condition. They are merely spread in a thin layer upon a clean glass shde, and after a drop of tap water and then a clean cover glass have been placed upon them, they are ready for the miscrocope. (The glass sHdes and covers are to be washed with water, using soap if necessary, and sometimes alcohol or strong acids, but all trace of these must be removed. Linen cloths, because of their small quantity of hnt, are the proper towels for drying the glassware. Covers and shdes as received from the dealers are never ready for use, and some which remain hazy after thorough wash- ing are worthless.) The fresh tissue is spread upon the slide with needles, being 'teased' into small fragments or drawn out into a thin film. Pure water causes some swelling of the tissue so that dilute solutions of common salt are preferable. A 0.6 per cent, solution has recently been found to cause less distortion than the somewhat stronger solutions formerly recom- mended. The tissue having been spread in the center of the slide and a drop or two of salt solution placed upon it, the cover glass is lowered so that air bubbles are not caught beneath it. Especially with the larger shdes which are to be preserved permanently this should be done as follows. The square or oblong cover glass is held over the specimen and its left edge is first brought in contact with the shde; a needle held in the left hand keeps this edge in position. Another needle held in the right hand with its 400 Digitized by Microsoft® FRESH TISSUES. 40I point beneath the right edge of the cover enables one to have perfect con- trol of it while it is being lowered. The contact between the cover and the mounting medium (salt solution in this case) spreads gradually from left to right as the cover is lowered, expelling the air as it advances. If bubbles are caught in the medium, the cover may be alternately raised and lowered a little until they escape, but once the cover is flat upon the specimen it should not be hfted. Connective tissue, meduUated nerves, fat, desquamated epithelial cells and blood should be examined in the fresh state by every student as showing certain features better than the preserved specimens. Chorionic villi may be identified in this way, and the cells in urine are studied un- stained. A drop of acetic acid (from i to 5 per cent.) placed upon connective tissue causes the white fiber to swell and disintegrate, but renders the elas- tic tissue and the nuclei more distinct. A few drops of stain may be placed upon the tissue for some minutes and then washed off in order to bring out the nuclei. Methylene blue (i per cent, aqueous solution) and methyl green (i per cent, solution in 20 per cent, alcohol) or the haematoxyline solutions may be used for this purpose. If sections are overstained a more dilute solution or shorter application is indicated, but if the section is pale, prolonged staining or stronger solutions are required. Thus the time limits given with the various dyes are only approximate as the response of different tissues is not uniform, and different samples of a given solution vary in their staining capacity. Isolation. Some tissues cannot properly be separated into their elements in the fresh condition but may be shaken or teased apart after prehminary treatment. EpitheHal cells become separable after remaining from 5 to 24 hours in 33 per cent, alcohol (40 cc. of 95 per cent, alcohol and 60 cc. of water). The pieces of epitheUum used should be small (5-10 mm. square). The same treatment prolonged for one or two weeks is employed in isolating the nerve cells of the spinal cord. Muscle cells may be pulled apart after remaining some hours in a fresh 35 per cent, solution of potas- sium hydrate. The muscle fibers should be examined in a few drops of the same solution, since they disintegrate if it is diluted. They may however be transferred to solutions of potassium acetate which neutrahzes the potash and prevents further maceration. The elements of nails may be scraped off from fragments boiled in a test tube containing a concentrated solution of potassium hydrate. Immersion in cold concentrated sulphuric acid is recommended for the same purpose. Another solvent for the intercellular subtances of muscle is a saturated 26 Digitized by Microsoft® 402 HISTOLOGY. solution of potassium chlorate in nitric acid. (About 5 gr. of potassium chlorate should be added to 20 cc. of nitric acid.) The muscle fibers should be separable in from i to 6 hours. They should be washed in distilled water for an hour or a few days so as to remove the acid, and then may be examined in water or in glycerine. Other macerating fluids are 10 to 20 per cent, nitric acid, diluted either , with water or with salt solution; ^ww to -5- of i per cent, of chromic acid; and water, by which the pulpy portion of organs may be removed from the connective tissue framework. Complex but valuable methods for demon- strating the connective and reticular networks have been described by Mall and Flint. They involve digestion of the tissues with pancreatic extract. Sectioning Feesh Material. Since the cutting of freehand sections of fresh tissue held between pieces of pith is no longer practised, the most rapid method for obtaining sections is by means of the freezing microtome. Small blocks of fresh tissue not over 5 mm. thick are moistened with water and placed upon the carrier of the microtome, where they are frozen by a jet of carbon dioxide pro- ceeding from a cyhnder of the liquefied gas. Sections 10-15 /^ thick may be chiselled from the frozen l:issue and placed in a dish of water, in which they unroll. Then they are fioated upon a sKde and may be stainedby ordinary methods. Frozen sections may be made from tissue hardened in formaline as well as from fresh material. In some cases this method is of special value in studying normal tissue; for rapid diagnbsis of pathological conditions it is indispensable. Descriptions of the freezing and other microtomes with full directions for their use will be found in Mallory and Wright's "Pathological Tech- nique." The use of the instruments, however, is seldom learned except by personal demonstration in the laboratory. Fixation. The fixation of tissues is the process by which post mortem changes are prevented, mitosis, for example, being checked at once and the mitotic figure permanently preserved. The hardening of the tissue is completed subsequently by immersion in alcohol. Small blocks of the desired tissue (about I cc. in volume and preferably less than i cm. thick) should be dropped without handling into a considerable quantity of the fixing fluid. Contact between the fingers and the peritonaeum is sufiicient to destroy the thin mesothelium. It is often advisable to place a piece of absorbent cotton beneath the tissue so that the fixing fluid may have access to its Digitized by Microsoft® FIXING FLUIDS. 403 lower surface. Tubular organs should be cut open before being put in the fluid, and their contents together with blood upon the surface of the block may be washed away with salt solution. Membranes may be kept flat and smooth by being tied across the end of a short tube or a detached bottle neck. After being used once the fixing fluids should be thrown away, ex- cept alcohol, which can be put to other uses. The following mixtures are those most frequently used. Zenker's Fluid is kept m stock as glacial acetic acid and the following solution, in preparing which the water is heated and the ingredients are stirred with a glass rod. (Metal instruments should not be put iii Zenker's fluid.) Bichromate of potassium 25 gr. Sodium sulphate 10 gr. Mercuric chloride (corrosive sublimate) 5° gr- Water 1000 cc. Shortly before using, Zenker's fluid is to be completed by adding 5 cc. of glacial acetic acid to 100 cc. of the solution. The blocks of tissue placed in it should be from 4 to 6 mm. thick; after remaining in the fluid from 10 to 24 hours they are to be placed in running water (or in water frequently changed) for the same length of time. Then they are transferred to 80 per cent, alcohol. The transfer of tissues from water to alcohol or vice versa is one of the commonest procedures. The abrupt change from water to strong alcohol causes violent diffusion currents which may distort the tissues; therefore graded percentages of alcohol are used, 50 per cent., 70 per cent., 80 per cent., 95 per cent., and absolute alcohol being always at hand. (Sometimes 90 per cent, also is used.) These may be prepared from the commercial 95 per cent, alcohol by adding water in the following proportions : Ninety per cent., — 475 cc. of 95 per cent, and 25 cc. of distilled water. Eighty per cent.,— 425- " " " " 75 " Seventy per cent., — 370 " " " " 130 " " " Fifty per cent.,— 265 " " " " 23S " Tissues may generally be transferred between water and 50 per cent, al- cohol without injury. In passing from 50 per cent, to absolute they may be placed successively in 70 per cent., 80 per cent., and 95 per cent., remaining in each only long enough to become saturated. Stains may be rated accord- ing to the alcohol they contain; the transition from 80 per cent, to an aque- ous stain should be graded as from 80 per cent, to water. It is a general principle that all these transfers should be gradual for the best results. Nevertheless abrupt transitions are often made, and ordinarily the tissue preserved in Zenker's fluid and washed in water is next immersed in 80 per cent alcohol. Digitized by Microsoft® 404 HISTOLOGY. The chief fault of Zenker's fluid is its tendency to form a precipitate of mercuric chloride (corrosive subhmate) within the tissue. The precipitate is dissolved out by the addition of enough tincture of iodine to the 80 per cent, alcohol to give it a mahogany color. The color fades as the iodine combines with the sublimate and it should be renewed imtil for two days there is no perceptible change in its color. This may require a week or more. Then the tissue is transferred to 80 per cent, alcohol which is renewed as long as it becomes discolored by the iodine. In 80 per cent, alcohol the tissue may remain for months but it gradually deteriorates. The pro- longed action of iodine causes some loss in staining capacity; nevertheless the treatment with iodine is an essential routine part of this method of fixation, and it should be thorough enough to remove the precipitate. The latter appears in sections as dark blotches resembling pigment. They may be dissolved after sections have been cut and attached to the slide by immersing the slide in the iodine solution and then rinsing it in 80 per cent, alcohol. Telly esnizcky's Fluid is employed hke Zenker's fluid but since it con- ' tains no mercuric chloride, the after-treatment with iodine is unnecessary. This fluid is a 3 per cent, aqueous solution of bichromate of potassium to which glacial acetic acid should be added shortly before using (5 cc. of acetic acid to 100 cc. of the solution). Tissues may remain in it for two or more days. The reagent is washed out in rurming water, and the tissue is transferred to 80 per cent, alcohol. Formaline is a 40 per cent, aqueous solution of formaldehyde gas. Ten per cent, aqueous solutions of formahne, which are 4 per cent, solu- tions of formaldehyde, are used for the preservation of small embryos and of various tissues. Small human embryos obtained by practitioners should be placed at once in 10 per cent, formaline and forwarded to an embryological laboratory. Tissues should remain in the 10 per cent, formahne for 24 hours or somewhat longer, and then are transferred to 80 per cent, alcohol in which they generally shrink. (Frozen sections may be made from the material taken directly from formahne and rinsed in water.) Instead of transferring the tissue from the formaline to 80 per cent, alcohol, some histologists recommend placing it at once in absolute alcohol for 2 days, after which it is immersed in 80 per cent. Formaline is used as a fixing agent in many solutions, especially the following. Orth's Fluid is Muller's Fluid with the addition of formaline. Miiller's fluid is a slow fixing solution, in large quantities of which objects may be left from i to 6 weeks; after washing 4 to 8 hours in rxmning water they are put through graded alcohols in which the tissue is hardened; or the tissue may be both fixed and hardened by remaining in the fluid for six months. Digitized by Microsoft® DECALCIFYING FLUIDS. 405 It is a solution of 30 grains of sodium sulphate and 60 grams of potassium bichromate in 3000 cc. of water. To make Orth's fluid, 10 cc. of formaline are added to 100 cc. of Miiller's fluid shortly before using. Small blocks of tissue should remain in it for 3 or 4 days, when, after washing thoroughly in running water, they are put in 80 per cent, alcohol. Alcohol. The higher grades of alcohol are important fixing fluids, although for most purposes inferior to Zenker's fluid or formahne. Tissue may be put directly into 95 per cent, or absolute alcohol, a piece of ab- sorbent cotton being under it. The alcohol should be changed after 3 or 4 hours, and after 3 or 4 days the tissue is transferred to 80 per cent. Some histologists recommend passing the fresh tissue through graded alco- hols before putting it in absolute; this causes less shrinkage but is said to fix imperfectly. One may begin with 80 per cent. Specimens should be kept in 80 per cent, or 90 per cent, alcohol after they have been preserved. They macerate in the weaker alcohols and lose their staining capacity in those which are stronger. Decalcification. Specimens which contain bone or calcareous material cannot be sectioned until they have been decalcified, which can be done only after they have been fixed, and hardened for a few days in alcohol. They are then placed in considerable amounts of dilute nitric acid (3 to 5 cc. of con- centrated nitric acid in 100 cc. of water). This should be renewed for 3 or 4 days, until the bone can be cut with a scalpel or be penetrated easily with a needle. The acid is removed from the tissue by immersion in running water for a day, and the block is returned to the alcohol. Phloroglucin is sometimes added to the decalcifying fluid to protect the tissue, and the nitric acid may be diluted with alcohol. The following solution has been recommended: Phloroglucin i Nitric acid 5 Alcohol 7° Water 3° A slight addition (i or 2 per cent.) of nitric or hydrochloric acid to 80 per cent, alcohol may be used in decalcifying emaU embryos. Imbedding. Imbedding is the process by which blocks of fixed, hardened, and decalcified tissues are prepared for sectioning. Sometimes the tissue is stained before bemg imbedded, as will be described later; often all the staining is done after the sections have been cut. Imbedding consists in Digitized by Microsoft® 406 HISTOLOGY. surrounding and infiltrating the tissue with a firm substance which can readily be cut into thin sections. Celloidin and parafiEin are used, each having its pecuhar advantages. To imbed in celloidin one needs graded alcohols, a mixture of equal parts of ether and absolute alcohol, a thin and a thick solution of ceUoidin, and vulcanized fiber blocks of such size as can be clamped in the carrier of the microtome. Thick ceUoidin consists of 30 grams of Schering's dry granular celloidin dissolved in from 200 to 250 cc. of an equal mixture of ether and absolute alcohol. It has a thick syrupy consistency and becomes constantly denser as the ether evaporates. It should be kept in a tightly closed preserve jar. Thin ceUoiden contains twice as much "ether and absolute" as the thick. The piece of hardened tissue is trimmed to the size and shape desired and is put successively in 95 per cent., absolute, and absolute and ether, remaining 24 hours in each. Then it is immersed in thin celloidin and finally in thick celloidin, in each of which it stays from 24 hours to a week or even longer. The success of the process depends largely upon the thorough penetration of the celloidin into the tissue. The time required in the celloidin varies with the penetrability of the tissue and the size of the piece. After remaining in the thick celloidin long enough the tissue is taken out with a mass of adherent ceUoidin and is pressed gently against the roughened surface of a block of vulcanized fiber. The ceUoidin should cover the tissue and spread out at its base upon the block. As soon as a film has formed over its siurf ace, the block and attached specimen are dropped into 80 per cent, alcohol in which the mass becomes firm. It is ready for sectioning in 6 hours. While the block is clamped in the sUding microtome with which sections from 10 to 15 // should be cut, it is kept moistened with 80 per cent, alcohol; the knife also should be wet with the same. Sections are immediately transferred to a dish of 80 per cent, alcohol in which they unroll, and where they remain until it is desired to stain them. Each sec- tion is surrounded by celloidin which it is not desirable to remove; the sections would then be too fragile. Therefore they are not to be placed in absolute alcohol. In case the tissue was not properly imbedded it may be returned to ether and absolute, and again be put through the celloidins. To imbed in parafjin the block of hardened tissue is immersed for from 6 to 12 hours in the following fluids successively: 95 per cent.; ab- solute; a mixture of equal parts of chloroform and absolute; chloroform. Then it is transferred to chloroform saturated with paraffin, which may be kept warm by placing on top of the paraffin bath; in this mixture it re- mains about 4 hours and then is put in melted paraffin. Hard paraffin which melts at 50° is ordinarily used, but if this is brittle when cut into the Digitized by Microsoft® IMBEDDING. 407 microscopic sections at the temperature of the room, a grade with a lower melting point should be used. The melted paraffin should be in a parafi&n bath or in a thermostat maintained at a temperature but slightly above the melting point of the paraf&n. The tissue should not remain in hot parafi&n longer than is required; it is generally left 2 hours in one cup and then is transferred to another in which it remains for two hours longer. The purpose of this transfer is to free the tissue from chloroform, most of which remains in the first cup. The imbedding frame in which the parafiSn is to be cooled, is a box the bottom of which is made by a glass plate and the sides of which are of metal in two L shaped pieces. By sUding the latter back and forth in relation to one another, the size of the space which they enclose can be varied. Before using the frame the inside surfaces of the metal pieces together with that surface of the glass on which they rest are rubbed with glycerine and the frame is warmed by placing it for a few minutes on the top of the parafi&n bath. Melted parafi&n is then poured into it, and the tissue, removed from ■ the cup by means of a spatula, is added. It sinks to the bottom and may be placed in any desired position by means of needles warm enough to prevent the paraffin from solidifying over their surface. The parafi&n is then quickly cooled by lowering the frame into a basin of cold water so that the latter surrounds the metal pieces. Water must not reach the upper surface of the parafl&n imtil it has solidified; then the frame is placed under water and in a few minutes the glass plate and metal pieces may be detached from the solid parafl&n. As soon as it is thoroughly cool it may be sec- tioned. Before the imbedded object is attached to a block of vulcanized fiber, superfluous paraffin is cut away leaving the tissue rising from a broad base of parafi5n and completely surrounded by a thin layer. The base is placed upon a heated spatula which rests upon the fiber block. When the parafl&n has melted somewhat, the spatula is withdrawn and the base is pressed down upon the block, to which it adheres securely when the par- afl&n has sohdified again. The fiber block is then clamped in a "precision" microtome. If a rotary microtome is used the paraflGn is attached to a metal disc in place of a fiber block. Sections should be from 6 to 10 ;/ thick, but under favorable conditions they may be made 2 [J- thick. If the paraffin on both sides of the tissue is trimmed parallel with the knife blade, the succes- sive sections adhere to one another by their edges forming ribbons. Thus the sections may easily be kept in order. The first one cut is attached to the upper left hand comer of the slide, and the others follow like fines upon a printed page. Sections mounted in this way are called serial sections. Paraffin sections, as they are taken from the microtome, are laid Digitized by Microsoft® 408 HISTOLOGY. in shallow boxes. Before being stained they must be attached to slides as follows. To attach paraffin sections to a slide, a mixture of equal parts of glyc- erine and white of egg is used, which may conveniently be called albumen. Its^^two ingredients should be stirred together thoroughly and filtered, after which a small lump of camphor is added as a preservative. It is kept in a capped bottle with a glass rod for a dropper. A drop or two are placed upon a clean shde and rubbed evenly with the finger over all that area upon which sections may be placed. It should be free from bubbles and should make a layer thick enough to allow the finger to glide easily over the surface of the shde. Then a few drops of water are placed upon it, forming a layer over the albumen deep enough to float the paraffin sections, strips of which are placed upon the water. The shiny side of the ribbon should rest upon the water. The slide is then held for a moment over the flame of an alcohol lamp so that the water is heated and the sections become flat and smooth. The paraffin must not be melted. This manipulation with a large shde bearing several rows of serial sections, requires some skill; the water should not come in contact with the fingers holding the slide and if the albumen layer ends abruptly before reaching the border of the slide, the water will not spread beyond it. Surface tension is such that enough water can be put upon the shde to float the sections freely. After the flattening process the water is cautiously drained off by a moist sponge held at the comer of the slide. The sections settle down upon the albumen and may be arranged in straight lines with needles applied to the paraffin but not to the sections themselves. After this the slide is held vertically in contact with filter paper to drain off any water which may remain. The slide is then placed in a drying oven which is not warm enough to melt the paraffin. It is well to let the sections remain there over night but a few hours may be sufficient to dry them thoroughly. In preparing large numbers of slides, each bearing only one or two paraffin sections, fragments of the ribbon containing the desired number of sections are floated in a basin of water warm enough to flatten but not to melt them. Slides rubbed with albumen are dipped into the water beneath the sections which are held in place upon them with a needle. The slides are drained and dried in the usual way. Stmning and Mounting. The staining of paraffin sections is accomplished by placing the slides to which the sections have been attached, in pairs back to back, in tube- like vials containing stains. One should have a dozen such vials containing various alcohols, xylol, stains, etc., the sections being passed from one to the Digitized by Microsoft® STAINING AND MOUNTING. 409 Other. The reagents are kept tightly corked and can be used for some time before being renewed. The separate stains are to be described in the following section. For staining large numbers of parafi&n sections pans have been made with vertically grooved sides, resembling wooden sUde boxes. In these 25 or 50 sUdes may be stained at once, one fluid being poured out of the pan and another substituted. Staining solutions can be used repeatedly and are not to be thrown away. Before paraffin sections are stained, the paraffin is to be removed by immersing the slide in xylol; it is then transferred in turn to a mixture of equal parts of xylol and absolute alcohol, then to absolute, 95 per cent., and through graded alcohols to that which corresponds with the solvent of the stain. After being stained the sections must be dehydrated, cleared and mounted. They are dehydrated in 95 per cent., and then in absolute alcohol. They are transferred to the mixture of xylol and absolute, and then into xylol in which they should become perfectly clear. Since the sections are thin and easily penetrated, they need to remain only a few minutes in each of these reagents. After the section has been cleared the xylol is drained from the shde, the borders of which (up to the specimen) may be wiped dry; the section itself should not become dry before a drop or two of damar is placed upon it and the cover glass is lowered as described under fresh tissue. The sHde may be used at once although the damar does not become solid for some time. Damar is a resin derived from trees of the genus Damara; for mount- ing microscopic objects is should be dissolved in xylol and filtered. The solution should be perfectly clear and nearly colorless. By evaporation of the xylol it thickens, but it may be diluted at any time by adding more xylol. When ready for use it should have the consistency of rather thin syrup. Damar is preferable to balsam since the latter gradually becomes yellow after it has been used. The staining of celloidin sections is performed in a series of small shallow staining dishes. The sections are taken from 80 per cent, alcohol and transferred through graded alcohols to water or the solvent of the stain. Then they are immersed in the stains, washed in alcohol or water, dehy- drated, cleared, and mounted. They are transferred from dish to dish with bent metal or glass needles. Because celloidin is dissolved in the strongest alcohols, the sections are dehydrated in 95 per cent. Since this extracts stains the sections are passed through it rapidly and are placed in the clearing fluid, either oil of bergamot or oil of origanum (oleum origani cretici). In this they should quickly become clear; if opaque spots remain, the section may be returned to 95 per cent, for further dehydration. The clearing oils may be used repeatedly and are not to be thrown away; the Digitized by Microsoft® 4IO HISTOLOGY. alcohol cannot be used twice. The section is mounted by taking it from the oil upon a spatula, and transferring it to the center of a slide upon which it should be spread out flat. The oil around it is wiped away and several layers of filter paper are placed directly upon the section; the finger is rubbed over them so that the section is further flattened. Remove the filter paper, and mount in damar as with paraffin sections. The handling of large numbers of celloidin sections is facihtated if they are placed in a perforated cup which fits into another ordinary cup. The ordinary cups contain the various reagents and the sections are trans- ferred from one to the other in the perforated cup. The latter may be obtained as Hobb's tea infusers, and the solid lemonade cups are of proper size to receive them. General Stains. Haematoxyline and eosine. Haematoxyline is a dye obtained from logwood, which stains nuclear structures blue. Eosine is an anihne dye staining protoplasm red. This and aU aniline dyes used in histological stains should be prepared by Griibler in Germany. There are many solutions of heamatoxyline among which is the fol- lowing: Haematoxyline crystals '. i gr. Saturated aqueous solution of ammonia alum loo cc. Water 300 cc. Dissolve the crystals in the water, which may be heated, and add the alum solution. Put the mixture in a bottle and drop in a crystal of thymol to prevent the growth of mould. A loose plug of cotton is used for a stopper and in this condition the solution is kept in the fight for 10 days to ripen. It changes color during this process of oxidation, after which it is ready for use and is kept tightly stoppered. It deteriorates in a few months. If a strong solution is desired the amount of water may be reduced. Another haematoxyhne solution in common use is Delafield's. It is made by dissolving 4 gr. of haematoxyline crystals in 25 cc. of 95 per cent, alcohol, and then adding 400 cc. of a saturated aqueous solution of ammonia alum. This is kept unstoppered for 3 or 4 days and then is filtered. 100 cc. each of 95 per cent, alcohol and of glycerine are added. It should not be used until it has become dark colored by remaining in the light for several days. Then it is to be filtered and tightly stoppered. Eosine is sold in two forms, one soluble in water, the other in alcohol. In connection with the haematoxyline stain, a y-j- to i per cent, aqueous solution may be used; or a i per cent, solution of alcoholic eosine, made in 60 per cent, alcohol. To stain with haematoxyline and eosine the sections are placed in the Digitized by Microsoft® GENERAL STAINS. 41I haematoxyline solution from 2 minutes to an hour. They are then placed in water changed repeatedly for half an hour or longer (they may remain in it over night) . As seen under the microscope the nuclei should be deeply stained but the protoplasm should be nearly free from color. Stain in eosine for i to 5 minutes; . dehydrate, clear, and mount. For paraffin sections this means treatment with 95 per cent., absolute and xylol, xylol, and damar. For celloidin sections, 95 per cent., oil of origanum, and damar. Methylene blue and eosine is highly recommended, especially for tissues fixed in Zenker's fluid and sectioned in paraflEin. Stain in a 5 or 10 per cent, aqueous solution of eosine for 20 minutes or longer, overstaining the tissue since the eosine is partly lost in the subsequent treatment. Wash out the excess of stain in water, and transfer to Unna's alkaline methylene blue diluted with three or four times as much water. Unna's blue is made by dissolving i gr. of methylene blue and i gr. of potassium carbonate in 100 cc. of water. Sections should be stained in the diluted solution for 10 to 15 minutes. Then they are washed in water and dehydrated and decolor- ized in 95 per cent, alcohol, moving the section about so that the stain may be washed out evenly. The pink color returns and when, as seen under the microscope, the blue is hmited to the nuclei the section is cleared in xylol and mounted in damar. Borax carmine and Lyons Hue is perhaps the best general stain for embryos. Dissolve 4 gr. of borax in 100 cc. of hot distilled water. When cool stir in 6 gr. of the best carmine and then add 100 cc. of yp per cent, alcohol. After 24 hours, filter. The Lyons blue may be used in i per cent, alcoholic solution, made with 50 per cent, or 95 per cent, alcohol. Generally it is desirable to dilute it somewhat with alcohol before using. Before imbedding the tissue, it is stained in borax carmine from 24 to 48 hours, larger blocks of tissue requiring more time than small ones. After being placed in water for 5 minutes (a step which some omit), the tissue is transferred to acid alcohol (0.5 cc. of hydrochloric acid in 100 cc. of 70 per cent, alcohol). In this the excess of stain comes out but the tissue acquires a deeper color. After remaining in the acid alcohol from 15 minutes to an hour the tissue is washed thoroughly in 70 per cent, alcohol and is imbedded and sectioned in paraffin in the ordinary way. After the sections have been attached to the shde they are stained in Lyons blue, rinsed in alcohol, dehydrated, cleared and mounted. Special Stains. An attempt to present all of the important histological stains would exceed the desired Hmits of this book. The four modifications of Golgi's Digitized by Microsoft® 412 HISTOLOGY. method, the very important but complex Weigert stain for myelin, and the iron haematoxyline stain for cytological details are omitted with many others. Since they are so well described in Mallory and Wright's Tech- nique, which the medical student who intends to understand bacteriological and histological methods should possess, it seems best to hmit this account to the stains which the beginner may employ. Elastic -fibers are stained dark purple or almost black with Weigert's resorcin-fuchsin. Other parts of the tissue should be nearly colorless. The stain is prepared by heating until it boils, in an evaporating dish, 2 gr. of fuchsin and 4 gr. of resorcin in 200 cc. of water. Then 25 cc. of Hquor ferri sescjuichlorati are added and the mixture is boiled for 5 minutes. It is cooled and filtered in order to collect the precipitate. The dish in which the boiUng took place is dried, together with whatever precipitate remained in it, and after the precipitate upon the filter paper is also dry it is placed with the paper in the dish. 200 cc. of 95 per cent, alcohol are added and boiled to dissolve the precipitate; the paper is removed. When the solution has cooled it is again filtered to collect the filtrate. 4 cc. of hy- drochloric acid, and enough 95 per cent, alcohol to make up 200 cc. of stain, are added. In this solution parafiBn or celloidin sections may be stained from 20 minutes to an hour; then they are washed in alcohol, dehydrated, cleared, and moimted. If the stain has affected other parts of the tissue than the elastic fibers, the sections should be washed in alcohol containing "a few crystals of picric acid," or in alcohol containing i per cent, of hydrochloric acid. White fibers of connective tissue may be stained by Mallory's aniline blue. Fibrils of connective and reticular tissue, amyloid, and mucus stain blue; nuclei, protoplasm, muscle, nerves and neurogUa fibres stain red; red corpuscles and myehn stain yellow. Paraffin or celloidin sections of material fixed in Zenker's fluid are stained 5 minutes or longer in a x^r per cent, aqueous solution of acid fuchsin. They are transferred directly to a stain consisting of 0.5 gr. of anihne blue soluble in water, and 2 gr. of orange G, dissolved in a 100 cc. of a i per cent, aqueous solution of phos- phomolybdic acid. In this they remain 20 minutes or longer. They are washed in several changes of 95 per cent, alcohol, cleared, and mounted. Fat may be stained red in frozen sections of fresh material or of that hardened in formaline, by means of a saturated solution of Scharlach R. in 70 per cent, alcohol The frozen sections are transferred from water to the stain, which has been filtered and is kept tightly stoppered, since evaporation of the alcohol causes a precipitation of the stain. The sections remain in the stain from 15 minutes to over night; then they are washed in Digitized by Microsoft® SPECIAL STAINS. 413 water, stained with haematoxyline and mounted in glycerine which clears them. They are not dehydrated in alcohol since strong alcohol dissolves the fat and its stain. Osmic acid in i per cent, aqueous solution stains fat in fresh tissues dark brown or black; myelin responds like fat both to osmic acid and Scharlach R. The fat is blackened in tissues preserved in a mixture of 2 parts of Miiller's fluid (p. 404) and i part of the i per cent, osmic acid solu- tion. Tissues should remain in it for about a week, after which they are transferred to dilute alcohol (50-70 per cent.) for a few days. They may then be imbedded in paraffin in the usual way, since the stained fat is rendered insoluble in alcohol; it dssiolves in xylol however, so that the sections should be cleared in chloroform and mounted in damar dissolved in chloroform. Blood may be stained for the study of leucocyte granules and blood plates with Wright's stain which should be prepared as follows: After eg" gr. of sodium bicarbonate has been completely dissolved in 100 cc. of dis- tilled water, add i gr. of Griibler's methylene blue (either the form called BX, Koch's, or EhrHch's rectified). "The mixture is next to be steamed in an ordinary steam sterilizer at 100° C. for one hour, covmting the time after steam is up. The heating should not be done in a pressure sterilizer, or in a water bath, or in any other way than as stated." After the steaming the mixture is taken from the sterilizer and allowed to cool, the flask being placed in cold water if desired. When cold it is poured into a large dish or flask. To ICO cc. of the mixture add about 500 cc. of a y q- per cent, solution of Griibler's yellowish eosine soluble in water. The amoimt of the eosine solution should be determined by the appearance of the mixture which it forms, the whole being stirred if in a dish, or shaken if in a flask, while the eosine is added. The color changes from blue to purple, and a yellowish metalHc scum forms on the surface, "while on close inspection a finely granular black precipitate appears in suspension." The solution is then filtered and the precipitate is allowed to become perfectly dry upon the filter paper. The stain is made by dissolving 0.5 gr. of the precipitate in 100 cc. of pure methyl alcohol. The stain need not be filtered, and hke the precipitate it keeps indefinitely. If by evaporation of the alcohol it becomes too concentrated, as is shown by the formation of precipitates when it is used, it should be filtered and a small quantity of methyl alcohol added. Blood is obtained usually from a needle puncture in the lobule of the ear. Two cover glasses, perfectly clean and dry, should be at hand. When the blood is flowing freely, the center of one of the covers is touched to a small drop as it emerges, and is then immediately inverted and dropped upon the other cover. The blood should spread evenly between the two Digitized by Microsoft® 414 HISTOLOGY. cover glasses, forming a film which cannot be too thin. The covers are then drawn rapidly apart, sliding over one another, and the blood dries from exposure to the air. It remains stainable for weeks. To stain the blood film, the cover glass may be held in the forceps devised for this purpose (cover-glass forceps), with the film uppermost. Stain sufiicient to cover it is poured upon it, and after one minute several drops of distilled water are added to the stain, imtil a delicate metallic scum forms upon the surface. The stain should not be so diluted as to become transparent. After two or three minutes, the stain is washed off. The preparation appears. blue. Distilled water is placed upon it to extract the excess of stain and the color changes to orange, or pink if the decolorization proceeds further. The general color of the specimen is due to that of the the red corpuscles which at first are blue. When they have become orange or pink as is desired, the water is removed by applying several layers of filter paper, and the preparation is mounted in damar. The process of decolorizing may be watched through the microscope by placing the cover glass (with the film side up) on a slide. Thicker portions of the film which remain blue when the thiimer parts are orange, should be disregarded. The leucocytes are figured on page 147. Intercellular cement spaces and the boimdaries of endothehal cells may be blackened by a ^ to i per cent, solution of silver nitrate, which acts chiefly upon free surfaces. The fresh tissue should be kept flat, the mesentery for example being tied over a bottle neck, while it is immersed in the solution for from i to 10 minutes. Then it is placed in distilled water and exposed to direct sunhght. As soon as it becomes brown (usually in 5 or 10 minutes) it is washed in dilute salt solution and slowly hardened in graded alcohols. Larger blood vessels may be injected through glass tubes with the silver solution, and after sections have been made and exposed to the light, the endothehal cell outUnes become dark. The courses of blood and lymphatic vessels and of ducts are studied by means of injections. Colored fluids, usually such as harden by cooHng or otherwise, are forced into them by pressure from a syringe. The syringe is connected by a short rubber tube with a tapering glass tube or cannula; the latter is inserted into the vessel which is then tied securely around it. Pressure may also be obtained by having the injection mass in a receptacle which connects with the cannula by a long flexible tube; pressure is in- creased by elevating the receptacle. The organs to be injected must be fresh; they may be left within the body or removed and injected separately. To avoid undue distension of the vessels and to allow the injection to flow more readily, the efferent vessels may be cut, so that the blood escapes. Sometimes the vessels are washed out by a preliminary injection of salt Digitized by Microsoft® INJECTIONS. 415 solution. The efferent vessels may be tied to cause the smaller side branches to be filled. After the injection has been finished, the tissues may be hardened in alcohol or Miiller's fluid, and sectioned in the usual way; thick sections are necessary in order to follow the course of the vessels. Solutions of BerHn blue or India ink are the simplest injection fluids. Carmine may be prepared by dissolving i gr. in the required amount of ammonia and adding 20 cc. of glycerine. The solution is completed by adding i gr. of common salt dissolved in 30 cc. of glycerine (or 20 drops of hydrochloric acid in 20 cc. of glycerine). The second solution is to neutral- ize the first solution, since the ammoniacal fluid tends to spread through the vessel walls. Gelatin injection masses are used while warm and fluid, and the tissues which receive them must be kept warm in a water bath. Clean sheets of the best French gelatin are soaked in water for several hours, until soft and swollen. Then they are melted over a water bath and an equal quan- tity of an aqueous solution of BerHn blue, saturated or dilute as desired, is stirred in. The mass is filtered through flannel wrung out in hot water, and is injected while warm. A carmine mass may be prepared by dissolving from 2 to 4 grs. of the best carmine in the required amount of ammonia. The solution is filtered and stirred into filtered melted gelatin prepared as already described. The amount of gelatin may be from 10 to 50 grs. Twenty-five per cent, acetic acid is then added drop by drop, until the mass becomes bright red and loses its anmioniacal odor. If too much acetic acid is added a pre- cipitate forms and the mass is spoiled. During the process the mixture is kept warm over a water bath and is constantly stirred. It is filtered through warm flannel and may be used at once or allowed to cool and heated when needed. Prepared injection masses are sold by Griibler. Many ingenious injection methods have been devised, such as the in- jection of small Uving pig embryos by allowing ink to enter the umbilical vein and be distributed through the body by the heart's action; or the injection of vessels with milk and staining the frozen sections with Scharlach R. The Microscope. It is unfortunate that the price of a microscope is prohibitive to many medical students, and that some who would otherwise purchase instru- ments at the beginning of their work, wait tmtil an official position entitles them to a discount. The price of microscopes is not always quite as high as is listed, and sometimes when several students buy microscopes at one time they may secure lower rates by having one of their number act as agent. Digitized by Microsoft® ^j6 histology. Within the past ten years the cost of a good instrument has been so reduced Eye-pieoe (Ocular) Eick aud pinion adjustment Triple revolver Objective Stage - • Iris diaphragm Mirror Micrometer Screw that an increasing proportion of students can enjoy the advantage of having a microscope of their own. Digitized by Microsoft® MICROSCOPES. 417 Microscopes of a certain grade are required, and if they cannot be afforded, no instrument should be bought. The necessary equipment, as shown in the figure, is a stand with fine and coarse adjustment ("microm- eter screw" and "rack and pinion") and a large square stage. The more expensive round and mechanical stages are not necessary. There should be an Abbd condenser (with iris diaphragm), a triple revolver, a high and a low eye- piece or ocular, and the following objectives: a f inch and a J or ^ inch, which must be parfocal, together with a -^ oil immersion for cytological and bacteriological work, and a 2 inch (very low power) for embryological work. The -^ oil immersion is an expensive objective, and its purchase may be postponed. The 2 inch is a cheap objective which is very useful in obtaining a view of an entire section, and for embryological reconstructions it is essential. The price of such an outfit, including the oil immersion objective, is from $70.00 to $90.00. Satisfactory microscopes of American manufacture are made by the Bausch & Lomb Company. A sample submitted by the Spencer Lens Company to the Harvard Embryological Laboratory is also quite satis- factory. The Leitz microscopes, made in Germany, are preferred by some to the American instruments just described; they are not much more ex- pensive. All agree that the Zeiss microscopes (German) are the best (and most expensive). It is undoubtedly true that any of these instruments will fill the requirements of medical students and physicians. If the micro- scope is purchased by a student unf amilar with its use, it is well to have the lenses examined by a disinterested microscopist. For a description of the nature and use of the microscope, the student is referred to the 9th edition of "The Microscope, " by Professor S. H. Gage, (Comstock Pub. Co., Ithaca, N. Y.). For the sake of emphasis it may be said that the microscopist works with his right hand upon the fine adjustment and his left hand upon the slide. As the latter is moved about, bringing different fields into view, the focussing is done with the adjustment and not with the eyes. Both eyes should be open (as wiU be natural after becoming accustomed to the instrument). Often one acquires the habit of using only the right or the left eye for microscopic work, but it is better to learn to use both. Always examine a specimen first with a low power and then with a high power objective. In focussing the microscope, have the objective drawn away from the slide and focus down. This should be done cautious- ly, with a portion of the specimen actually beneath the lens; if there is only cover glass and damar there, the objective wiU probably be driven down upon the sUde. Unless one is sure that stained tissue is in the field, the slide should be moved back and forth as the objective is being lowered. 27 Digitized by Microsoft® 4l8 HISTOLOGY. In working with the Abb^ condenser the flat surface of the mirror should be uppermost. The objectives must never be scratched. Lens paper or fine linen should be used to wipe them. If they are soiled with damar they should be wiped with a cloth moistened with xylol. Since the lenses are moimted in balsam, xylol must be applied to them cautiously. In lifting the microscope it should never be taken by any part above the stage; the pillar should be grasped below the stage. Drawings. Drawings should be made of all the significant structures observed; the structure should be observed however, before any drawing is attempted. In other words a thorough study of the specimen should precede the draw- ing. The nondescript character of many drawings seems due to the fact that the student had nothing definite in mind to portray. It is true never- theless that the repeated observation made while a careful drawing is in progress, reveals many details which would otherwise be overlooked. The drawings should be simple but exact, made and shaded with a hard (6 H) lead pencil having a sharp point. They should not be encum- bered with surrounding circles. The parts are to be labelled in one's plainest handwriting (not printing); and the terms should be explicit. A Kne proceeding from a mass of chromatin within a cell nucleus ought not to be labelled either cell or nucleus but chromatin. Some knowledge of drawing is very desirable although perspective is scarcely involved in histo- logical work. The lightly colored structures should be made hghter and the dark ones darker than they appear, to preserve the contrasts of the stains. The hnes should be few and made with assurance, — not pieced out as if one were feehng his way. Every line should correspond with some structure; if a cell has no wall, the even or granular shading representing its protoplasm should end abruptly, but without a bounding line. Reconstructions. There is an important arrangement of mirrors (Abba's camera lucida) for drawing the outlines of sections. It is attached to the microscope so that the image of the section beneath the objective appears spread upon the drawing paper. The paper is on the table beside the base of the microscope. On looking through the camera into the microscope one can see the pencil point, as it is made to trace the outhne on the paper. In this way a suc- cession of serial sections may be drawn with uniform magnification. The magnification is determined by substituting a stage micrometer for the slide of sections. The micrometer is a sHde upon which i mm., with subdivisions Digitized by Microsoft® RECONSTRUCTIONS. 419 into twentieths or hundredths, has been marked off by scratches in the glass; the subdivisions may be drawn with the camera under the same conditions as the sections, and the enlargement of the subdivisions may then be measured. From the camera-drawings of serial sections, wax reconstructions of adult glands or embryonic organs may be made. If the sections are 10 fi- thick and alternate sections have been drawn, magnified 50 diameters, then on the scale of the drawings these alternate sections are i mm. apart. Wax plates imm. thick are therefore to be made, either by roUing the wax, or by spreading a weighed amount of melted wax in a pan of hot water. It floats and spreads in an even layer, soHdifying as the water cools. The outlines of the drawings are then indented upon the wax plates, and the desired portions are cut out and piled up to make the model. In this way reconstructions hke those of the ear (p. 380) may be made. The details of the process should be learned from demonstrations in the laboratory. Graphic reconstructions are usually side views of structures, made from measurements of their transverse sections. Fig. 161, p. 138, is from such a re- construction. A camera drawing of the side of an embryo (or other struc- ture) is made before it is sectioned. The outline of this drawing is en- larged, and parallel Unes equally spaced are ruled across it, corresponding in number and direction with the sections into which it was cut. Often only every other section or every fourth section is used for the reconstruc- tion, and the number of hnes to be ruled across the drawing is correspond- ingly reduced. Camera drawings of a lateral half of every section used in the reconstruction are made, and across each drawing two hnes are rulied. The first follows the median plane of the body; and the second is at right angles with it, being drawn so as to touch the dorsal or ventral surface of some structure to be included in the reconstruction. Provided that the camera drawings and side view have been enlarged to the same extent, the perpendicular distance from the middle of the back to the junction of the .two hnes is marked off on the side view, on the hne corresponding with the section in question. The perpendicular distances from the second line to the dorsal and to the ventral surfaces of all structures to be reconstructed are also marked off upon the hne in the side view. The same is done in the following section, and the points belonging with a given structure are con- nected from section to section. Thus the outhnes of the organs are pro- jected upon the median plane; two dimensions are accurately shown but the third is lost. Often it is undesirable to attempt to make the magnification of the sections and of the side view identical; the measurements may be en- larged or reduced as they are transferred for plotting, by means of the draughtsman's proportional dividers,— an indispensable instrument for Digitized by Microsoft® 420 HISTOLOGY. this method of reconstruction. The corrections for unequal shrinkage of the sections in parafhn and other details can best be explained in the labora- tory with the drawings at hand. Digitized by Microsoft® INDEX. Abducens nerve, 96, 336 Absorption, intestinal, 209 Accessory lachrymal glands, 375 nerve, 96, 335 parotid glanc&, 187 thyreoid glands, 173 Acervulus cerebri, 350 Acetic acid, action on connective tissue, 401 Acidophiles {eosino-philes) , 148 Acinus, 36 Acoustic nerve, 97, 335, 389 Adamantoblasts, 70 Adelomorphous cells {chief cells), 200 Adenoid tissue {lymphoid tissue), 39, 154 Adipose tissue, 41 Adrenal glands {suprarenal glands), 331 Aggregate nodules, 156, 214 Agminated nodtiles {aggregate nodules), 156 214 Albumen, for attaching sections to slides, 408 Alcohol, for dehydrating tissues, 409 for fixation, 405 for hardening tissues, 403 Allantois, 193, 310 Alveolar ducts, 240 periosteum, 77 sacs, 240 Alveoli of the lungs, 236, 240 Alveolus, 36 Amakrine cells, 359, 360 Ameloblasts {adamantoblasts), 70 Amitosis, 14 Ammon's horn {hippocampus), 349 Amnion, 300, 303 Amniotic fluid, 244, 302 villi, 311 Amoeboid motion, 8 Amphiaster, 13 Amphipyrenin, 5 Ampulla, of the ductus deferens, 278 of the semicircular ducts, 379 of the uterine tubes, 294 AmpuUary nerves, 389 Anal plate, 2 1 Anaphase, 12 Angioblast, 23 Anisotropic substance, 82 Annuli fibrosi, 134 Anterior neuropore, 23 Anus, 193, 217 Aorta, 130 Appendices epiploicae, 217 Appendix epididymidis, 280 Appendix testis, 80 vesiculosa, 286 vermiform {processus vermi/ormis), 215 Aquaeductus cerebri, 334 cochleae, 391 vestibuli, 390 Aqueous humor, 355 Arachnoid, 351 granulations, 351 Archoplasm, 6 Areola, 330 Areolar glands, 330 tissue, 41 Arrector pili, 317 Arteria centralis retinae, 353, 373 Arteries, 127 Arterioles, 127 Articular cartilage, 64 corpuscles, 105 Astrosphere, 9 Atretic follicles, 292 Atria, of the heart, 133 of the lung, 241 Auditory groove, 166 tube, 116, 382, 393 vesicle, 353, 378 Auerbach's plexus {myenteric plexus), 95, 215 Auricle, 382 of the heart {atrium), 133 Axial filament, 271 Axis cylinder, 98 Axolemma, 99 Axon {neuraxon), 93, 94 B. Bartholin's ducts {sublingual), 190 glands {major vestibular), 311 Basal body, 31 Basement membrane, 30 Basket cells, of cerebellum, 344 of mammary gland, 329 of pancreas, 233 Basophile cells, 47, 148 Bergamot oil for clearing sections, 409 Berlin blue for injections, 415 Bertini, columns of {renal columns), 251 Bile, 226 Bile capillaries, 226 ducts, 219, 229 Bipolar cells, 109 Bladder, 261 development, 193 Blast, 54 421 Digitized by Microsoft® 422 INDEX. Blastodermic vesicle, i8, 300 Blood, 140 arteries, 127 capillaries, 126, 127 crystals, 144 destroying organs, 152 development of cardinal veins, 220, 246 of pulmonary veins, 235 of umbilical veins, 220, 316 of vitelline veins, 24, 220 of veins of liver, 220, 247 forming organs, 152 heart, 133 injections of, 414 islands, 23 pigments, 46 plasma, 151 plates, 150 red corpuscles, 140 sinus, 159 sinusoids, 125 stains for, 413 veins, 131 vessels, 124 white corpuscles, 145 Bone, S3 blood vessels of, 59 cartilage replaced by bone, 61 ceUs, SS compact, 57 corpuscles, 55 decalcification of, 403 development of, 54 lamellar, 57 marrow, 152 function of, 153 red, IS4 yellow, 154 membrane, 61 primary, 61 secondary, 61 spongy ,_ S7 Borax carmine, 411 Border fibrils, 78 Bowman's glands {olfactory glands), 398 capsule {capsule of the renal glomerulus') , membrane {anterior basal membrane of cornea), 369 Brachium conjunctivum, 336 pontis, 336 Brain, 91, 334-3S2 cerebellum, 342 development of, 334 hemispheres, 345 hypophysis, 349 medulla oblongata, 339 meninges, 351 pineal body, 350 pons, 341 Branchial arches, 176 clefts, 165 Bridges, intercellular, 30 Bronchi, 239 Bronchial arteries, 235 veins, 23s Bronchioles, 239 respiratory, 240 Brunner's glands {duodenal glands), 204 Bulbous corpuscles, 106 Bulbourethral glands, 282 Bulbus urethrae, 283 vestibuli, 311 Bursae, 50 Caecum, 216 cupulare, 380 vestibulare, 380 Calcification of dentine, 74 Calcified cartilage, 52 Calyces of kidney, 249 Camera lucida, 418 Canaliculi, of bones, 55 of the cornea, 82 Capillaries, blood, 127 secretory, 36 Capillary circulation, 125 Capsule, of cartilage cells, 50 of Glisson {capsule of liver), 220 of kidney, 252 of lens, 3S4, S^S of liver, 220 of Tenon (interfascial space), 374 Cardiac ganglion, 94 glands, of stomach, 200 oesophageal, 197 muscle, 80 development, 80 fibrils, 81 intercalated discs, 83 nuclei, 84 striations, 82 veins, 220, 246 Carmine, for injections, 415 Carotid gland {glomus caroticum), 176 Cartilage, 50 articular, 64 elastic, 52 epiphyseal, 64 fibrous, S3 hyaline, 52 Caruncula lacrimalis, 377 Cell, I amoeboid motion of, 8 differentiation, 15 direct division, 14 form, 7 formation, 9 indirect division, 9 size of, 7 vital phenomena of, 7 wall, 6 Celloidin, imbedding in, 406 Cells, amakrine, 3S9, 360 basket, 233, 329, 344 basophile, 47 centroacinal, 233 chromaffine, 114 chief, 200 commissural, 91 decidual, 304 Digitized by Microsoft® INDEX. 423 Cells, Deiters' {sustetUacular cells of cochlea), 388 egg, 288 eosinophilic, 47, 148 ependymal, 11 J epithelial, 27 fat, 43 fiber-producing, 46 follicular, 268, 289 giant, 152 glia, 115 goblet, 34 Henson's, 389 lutein, 291 mast, 47, 148 mucous gland, 185 neuroglia, 115, 349 of Claudius, 389 of Kupffer {stellate cells oj hepatic sinusoids), 228 of Paneth, 207 of Purkinje, 344 of Retzius, 346 of Sertoli {sustentacular of testis), 268 olfactory, 397 parietal, 200 pigmented, 45 plasma, 47 polarity of, 33 polymorphonuclear, 146, 148 pyramidal, 346 resting wandering, 47 serous gland, 185 sexual, 267, 288 squamous, 29 supporting, 179 sustentacular, 267, 384, 388, 397 tactile, 103 taste, 181 vegetative {sustentacular) of the testis, 268 visual, 357 Cellulae pneumaticae, 393 Cement substance, 16 Central nervous system, 91 Centroacinal cells, 233 Centriole, 6 Centrosome, 5 Cerebellum, 336, 342 development of, 335 Cerebral hemispheres, 345 nerves, 95 of medulla and pons, 336, 341 Cerebrum {includes fore-brain and mid-brain) , 334 Ceruniinous glands, 313, 394 Cervical glands of the uterus, 297 Chief cells, 200 Choriocapillaris, 367 Chorioid coat of eye, 355, 366 plexuses, 352 Chorion, 300 frondosum, 301 laeve, 301, 303 Chorionic villi, 300 Chromaffine cells, 114 of suprarenal glands, 331, 332 Chromatic bodies, 120 Chromatin, 5 Chromium, 14 Chromosomes, 10 Chyle, 209 Chyme, 208 Cilia, 30 (eyelashes), 375 Ciliary body, 355, 367 glands, 375 muscle, 367 nerves, 374 processes, 367 Circumanal glands, 326 Circumvallate papillae {vallate papillae), 177 Cisterna chyli, 138 Clarke, column of {dorsal nucleus), 117 Claudius, cells of, 389 Clasmatocytes, 47 Clearing sections, 409 Clitoris, 287, 311 Cloaca, 193 Coccygeal gland {glomus coccygeum) , 114. 176 Cochlea, 385 scala tympani, 385 scala vestibulae, 385 Cochlear artery, 390 duct, 380 nerve, 389 Cohnheim's areas, 87 Coelom, 20 Coil glands {sweat glands), 325 Collagen, 41 Collateral nerve fibers, 93 Collecting tubtiles of kidney, 249, 2*57 Colloid, 173 Colon, 216 Colostrum, 328 Columnar epithelium, 27 Columns of spinal cord, 115 Commissural cells, 91 fibers, 91 Commissure of spinal cord, 115, 117 Common bile duct, 219 Conchae, 395 Cone cells, 357 Conical papillae, 117 Conjunctiva bulbi, 356, 377 corneae,. 377 palpebrarum, 356, 375 sclerae, 377 Connective tissue, 40 " cells, 43 fibers, 41 intercellular spaces, 47 stains, 43, 412 Contour lines, 72 Convoluted tubules, of kidney, 252 of testis, 273 Corium, 212, 213 Cornea, 369 development of, 355 Corona radiata, 290 Coronary sinus, 134 Corpora cavernosa (in female), 311 penis, 284 Digitized by Microsoft® 424 INDEX. Corpora quadrigemina, 336 Corpus albicans, 291 callosum, 338 cavernosum urethrae, 286 luteum, 290 spongiosum, 262 striatum, 338 Corpuscles, articular, 105 bone, ss bulbous (of Krause), 106 colostrum', 329 cylindrical, 106 genital, 106 Golgi-Mazzoni, 243 Hassall's, 172 lamellar (Pacinian), 107 Malpighian, 253 nerve, 105 red blood, 140 renal, 253 tactile (of Meissner), 105 thymic, 172 white blood, 145 Corpuscula amylacea, 351 Cortex, 156 Corti, organ of {spiral organ), 387 Cotyledons of placenta, 307 Cowper's glands {bulbourethral glands) , 282 Cranial nerves {cerebral nerves), 95, 341 Crescents of serous cells, 186 Cristae, 380 Crusta, 30 Crypts of Lieberkuhn {intestinal glands), 203 Cumulus oophorus, 290 Cuboidal 'epithelium, 27 Cuticula, 6 dentis, 73 Cuticular border, 30 Cutis {skin), 312 Cuvier, duct of, 247 Cylindrical corpuscles, 106 Cystic duct, 219 Cytomorphosis, 15 Cytoplasm, 2 D. Damar, 409 Decalcification, 405 Decidua basalis, 301 capsularis,3oi reflexa {capsularis), 301 serotina {basalis), 301 vera, 301, 303 Decidual cells, 304 membranes, 300 relation to uterus, 301 Decussation of the lemnisci [sensory], 340 of the pyramids [motor], 339 Dehydration of sections, 409 Deiters' cells {sustentacular of cochlea), 388 Delafield's hematoxyline, 410 Demilune, 186 Dendrite, 93, 94 Dental canaliculi, 73 cavity, 67 fibers, 73 Dental groove, 68 papilla, 68, 73 pulp, 74 ridge, 68 sac, 76 Dentine, 73 calcification of, 74 Dermatome, 86 Dermis {corium), 312, 313 Descemet's membrane {posterior basal mem- brane of cornea), 371 Diapedesis, 141 Diaphragm, 219 Diaphysis, 64 Diarthrosis, 64 Diencephalon, 335, 338 Digestive tube, 193 development, 193 Dilatator muscle of pupil, 369 Diplosome, 6 Direct cell division, 14 Dispireme, 12 Diverticulum of the intestine, 218 Division of cells, direct, 14 indirect, 9 Drawing of specimens, 418 Ducts, 36 Bartholin's {sublinguaVj , 190 cochlear, 380 common bile, 219, 229 cystic, 219, 229 ejaculatory, 279 endolymphatic, 370 Gaertner's, 287 intercalated, 96 Miillerian, 263, 285 of Cuvier, 247 of Santorini {accessory pancreatic), 230 of Wirsu'ng {pancreatic), 230 perilymphatic, 392 semicircular, 379, 384 Stenson's {parotid duct), 187 utriculosaccular, 380 Wharton's {submaxillary duct), 191 Wolffian, 245, 285 Ductulus efferens, 266, 276 Ductus aberrantes, 265 arteriosus, 234 cochleae, 380, 385 deferens, 265, 278 epididymidis, 265, 277 reuniens, 380 venosus, 222 Duodenum, 203 Dura mater cerebralis, 351 spinalis, 351 Dyaster, 12 Ear, 378-394 development, 778 external, 393 internal, 384-392 middle, 392 nerves, 389 vessels, 389 E. Digitized by Microsoft® INDEX. 425 Ectoderm, 18 Efferent ducts of testis, 266, 276 Egg cells, 288 Ejaculatory ducts, 279 Elastic fibers, 40, 41 stain for, 412 Elastin, 42 Embryos, preservation of, 404 Enamel, 69 development, 68 prisms, 70 Enamel cells, 69 organs, 68, 69 pulp, 69 End bulb of Krause {cylindrical end bulbs), 106 End organs of Ruffini {terminal cylinders) , 106 Endocardium, 126 Endochondral bone, 63 Endolymph, 380 Endolymphatic duct, 379 sac, 379 Endoneurium, loi Endoplasm, 2 Endosteum, 57 Endothelium, 25, 27 Entoderm, 18 Entodermal tract, 165 Eosine, 410 Eosinophiles, 47, 148 Ependyma, 115, 117, 122 Epicardium, 126 Epidermis, 312, 315 Epididymis, 276 Epithelia, 26-34 layers, 28 origin, 27 shape of cells, 27 Epithelioid glands, 35 Epithelium, 24 basement membrane, 30 bridges, 30 cilia, 30 crusta, 30 cuticular border, 30 differentiation of cells, 29 false, 27 glands, 3i goblet cells, 34 membrana propria, 30 neuro-, 31 pseudostratified, 28 simple, 27 secretory processes, 32 stratified, 29 terminal bars, 29 Epitrichium, 312 Eponychium, 316 Epoophoron, 286, 294 Erectile tissue, 284 Ergastoplasm, 33 Erythroblast, 141, 153 Erythrocytes, 140 Eustachian fobs {"vditory tube), 382 Excretions, 32 Axoplasm, 2 External auditory meatus, 382, 394 External ear, 393 Eye, 353-378 blood vessels, 371 chambers, 354, 373 development, 353 lachrymal glands, 377 lens, 365 nerves, 374 optic nerve, 364 retina, 357 spaces, 373 tunica fibrosa, 369 tunica vasculosa, 366 vitreous body, 366 Eyelids, 375 Facial nerve, 96, 336 Falciform ligament, 279 Fallopian tubes {uterine tubes), 286 Fasciculi, cerebrospinalis, 121, 239 cuneate, 122, 340 gracile, 122, 340 lateral cerebrospinal, 122, 339 superficial, ventro-lateral, 122 ventral cerebrospinal, 122, 339 Fat cells, 43 crystals, 44 pigments, 46 stains for, 412 tissue, 41 Female genital organs, 285 Fenestra cochleae, 383 vestibuli, 383 Fenestrated membrane, 42 Ferrein, pyramids of {pars radiata), 251 Fertilization,' 293 Fiber cells of ear, 384 of Retzius, 346 layer of Henle, 358 tracts, 121 Fibers, elastic, 41 of Muller {radial fibers of the retina), 358 of Sharpey, 56, 76 muscle, 79 nerve, go, 97 white, 41 Fibrin, 150 Fibroblasts, 46 Fibrocartilage, 53 Fibroglia, 43 Filar mass, 3 Filiform papillae, 177 Fillets {lemnisci), 340 Fimbria ovarica, 287 Fixation of tissues, 402 Flagellum, 31 Foliate papillae, 177 Follicle, 37 Follicles, atretic, 292 formation in ovary, 288 Graafian {vesicular follicles), 289 lymph of ovary (see lymph nodules), 289 Follicular cells, 268, 289 Digitized by Microsoft® 426 INDEX. Fontana, spaces of {spaces of the angle of the »>"). 373 Formaline, 404 Foramen caecum, 166 epiploicum, 221 of Winslow {epiploicum), 221 Fore-brain, 334 Fossa of Rosenmiiller, 167 Fovea centralis, 362 Fresh tissues, examination of, 400 Freezing tissues, 402 Fundamental tissues, 24 Fundus glands, 200 Fungiform papillae, 177 Funiculi of spinal cord, 116, 122 Fuscin, 3S7 G. Galea capitis, 271 Gall bladder, 219, 229 Ganglia, 91, 109 cardiac, 94, 137 ciliary, 97 coeliac, 95 of Wrisberg, 137 otic, 97 semilunar, 95 sphenopalatine, 97 spinal, 92, no submaxillary, 97 sympathetic, 112 Ganglion cells, 109 bipolar, 109 multipolar, 109 unipolar, 109 Gastric glands, 200 Gelatin, 41 injection masses, 415 Gelatinous substance of spinal cord, 118 Genital corpuscles, 106 folds, 266 organs (female), 285 decidual membranes, 300, 303 development, 285 epoophoron, 294 external, 311 ovary, 288 placenta, 305 umbilical cord, 30S uterine tubes, 294 uterus, 296 vagina, 311 organs (male), 263 appendices, 280 development, 264 ductus deferens, 278 ejaculatory ducts, 279 epididymis, 276 paradidymis, 280 penis, 266, 281 prostate, 280 scrotum, 266 seminal vesicles, 279 testis, 267 urethra, 266, 281 Genital papilla, 193, 266 ridge, 264 Germ layers, 20 origin of tissues from, 26 Germinal epithelium of ovary, 288 Giant cells, 152 Gill clefts, 165 Glands, 32 • alveolo-tubular, 36 anterior lingual, 190 areolar, 330 Bartholin's {major vestibular), 311 biliary, 229 Bowman's {olfactory), 398 bronchial, 239 buccal, 190 bulbourethral, 282 cardiac, 200 ceruminous, 313, 394 cervical, of uterus, 297 ciliary, 375 circumanal, 217 classification, 34, 37 compound, 34 Cowper's {bulbourethral), 282 cytogenic, 34 duodenal, 204 ducts of, 36 epithelial, 35 epithelioid, 35 end pieces of, 37 fundus, 200 gastric, 200 genital, 264 intestinal, 203 labial, 190 lachrymal, 377 lingual, 182, 189 lumen of, 36 lymph, 154 mammary, 313, 328 Meibomian {tarsal), 375 mixed, 186, 190 molar, 190 mucous, 32, 189 mucous bile, 229 oesophageal, 197 cardiac, 197 of Brunner {duodenal), 204 of Littre {urethra^, 282 of Moll {ciliary), 375 of Montgomery {areolar) ,330 of the oral cavity, 185 olfactory, 398 palatine, 189 peptic, 200 praeputial, 324 pyloric, 200 sebaceous, 324 secretory capillaries of, 36 serous, 32, 187 simple, 3S sublingual, 190 submaxillary, 191 sudoriparous, 325 sweat, 323 Digitized by Microsoft® INDEX. 427 Glands, tarsal, 375 tubulo-acinar, 36 Tyson's, 324 unicellular, 35 vestibular, 311 von Ebner's {serous glands of the tongue), 187 urethral, 262, 282 Glans penis, 260 Glia cells, 115 Glisson's capsule {capsule of the liver), 220 Glomerulus, 126 of kidney, 252 of mesonephros, 245 Glomus caroticum, 114, 167, 176 coccygeum, 114, 176 Glossopharyngeal nerve, g6, 335 nuclei of, 341 Glycogen, 51 Goblet cells, 34 Golgi-Mazzoni corpuscles, 243 Gowers' bundle, 342 Graafian follicles, 289 Grey substance of spinal cord, 119 types of cells in, 120 Ground substance, 16 Gubernaculum testis, 267 Gustatory organ {taste buds), 179 Gyrus hippocampi, 349 H. Haematoidin, 144 Haematoxyline, 401, 410 Haemin, 144 Haemoglobin, 140 derivatives, 46 Haemolymph glands, 159 Haemosiderin, 144 Hair, 317 bulb, 317 connective tissue sheaths, 319 epithelial sheaths, 320 lanugo, 319 papiUa, 317 root, 317 shaft, 322 shedding of, 322 Hair cells, 384, 387 Hardening tissues, 402 Hassall's corpuscles {thymic corpuscles), 172 Haustrum, 217 Haversian canal, 56 Heart, 133 development of, 133 epicardium, 134, 135, 136 myocardium, 134, 136 muscles, 135, 136 nerves, 137 pericardium, 135 valves, 134, 135 Heidenhain, ground membrane of, 82 Hemispheres, 338, 345 Henle's fiber layer, 358 layer, 320 loop, 252 Henle's sheath, loi Henson's cells, 389 Hepatic arteries, 125, 222 cells, 224 duct, 2ig, 222 trabeculae, 218 Hind-brain, 334 Hippocampus, 349 Horns of spinal cbrd {columns), 115 Howship's lacunae, 57 Huxley's layer, 320 Hyaline cartilage, 52 Hyaloid artery, 355 canal, 354 membrane, 366 Hyaloplasm, 3 Hydatid of Morgagni, 280 sessile, 280 stalked, 280 Hymen, 285 Hypoglossal nerve, 96, 335 nucleus of, 341 Hypophysis, 349, 389 Idiozome, 6, 271 Ileum, 205 Incisures, 99 Inclusions, 4 Incus, 382. India ink for injections, 415 Infundibulum of the fore-brain, 339 of the lungs, 241 of the uterine tubes, 294 Injections of vessels and ducts, 414 Intercalated discs, 83 Intercellular bridges, 30 secretory capillaries, 36 substance, 16 Interfascial space, 374 Intermedius nerve, 96, 335 Internal auditory meatus, 389 secretions, 35 Interstitial cells of testis, 275 Intestinal absorption, 209 glands, 203 villi, 204 Intestine, large, 215 small, 203 Involuntary muscle, 77 cardiac, 80 smooth, 77 Iris, 368 development, 355 Islands of Langerhans, 231 Isolation of tissues, 401 Isotropic substance, 82 Isthmus, 33S, 336 Jacobson's organ {vomero-nasal organ), 397 Jejunum, 207 Joint cavity, 65 Joints, 64 Digitized by Microsoft® 428 INDEX. K. Karyokinesis, g Karyoplasm, 2 Keratohyalin, 184 Kidney, 249-259 blood vessels, 257 connective tissue, 256 convolute part of the cortex, 253 cortex, 250 development, 249 labyrinth {pars convoluta), 253 lobes, 257 lymphatic vessels, 258 medulla, 250 medullary rays (pars radiata), 251 nerves, 259 pyramids, 250 radiate part of cortex, 251 renal columns, 251 renal tubules, 250-256 structural units, 257 Krause's corpuscles (bulbous corpuscles), 106 cylindrical end bulbs (cylindrical cor- puscles), 106 ground membrane, 82 Kupffer's stellate endothelial cells, 228 Labia majora, 287 minora, 287 Labium tympanicum, 387 vestibulare, 387 Labyrinth, bony, of the ear, 382 membranous, of the ear, 382 of the kidney (pars convoluta), 253 Lachrymal glands, 377 accessory, 375 ducts, 378 sac, 378 Lacteals, 151, 213 Lactiferous sinus, 330 Lacunae, of bone, 55 of cartilage, 50 Howship's, 57 urethral, 282 Lamellae of bone, 56 Lamellar corpuscles, 107 Lamina cribrosa, 365 chorio-capillaris, 367 fusca, 366 spiralis, 385 suprachorioidea, 366 Langerhans, cells of (deeper layer of the chorionic epithelium), 305 islands of, 231 Lantermann's segments, 99 Lanugo, 319 Large intestine, 215 development, 195 nerves, 217 vessels, 217 Larynx, 237 Lemniscus, 340 Lens, 365 development, 353, 354 Lentic vesicle, 353 Lesser omentum, 219 Leucocytes, 140, 145 granules of, 147 varieties of, 149 Lieberkiihn, crypts of (intestinal glands) , 203 Ligament, 65 pectinate, 371 suspensory, of lens (zona ciliaris), 364 liver (falciform ligament), 219 Limbus spiralis, 386 Lines of Retzius, 72 Lingual glands, 182, 189 papUlae, 177 tonsil, 169, 184 Linin, 5 Lipochromes, 46 Lips, 184 Liquor amnii, 244, 302 cerebrospinalis, 352 foUiculi, 290 Littr^, glands of (urethral glands), 282 Liver, 218 bile capUlaries, 226 capsule, 222 connective tissue, 222 development, 218 ducts, 228 hepatic cells, 224 ligaments, 219 lobules, 223 perivascular tissue, 227 secretory units, 229 sinusoids, 125, 220, 227 veins, 220 Longitudinal duct, of epoophoron, 286 Lumen of glands, 36 Lungs, 234 alveoli, 240 atria, 241 development, 234, 236 lobules, 236, 243 nerves, 243 pigment, 243 pleura, 235, 242 respiratory bronchioles, 240 structural units, 243 vessels, 235, 243 Lunula, 316 Lutein cells, 291 Lymph, 15 follicles, 154 glands, 154 function, 158 nodes (lymph glands), 154 sinus, 156 vessels, 157 nodules, 154 solitary, 154 aggregate, 156, 214 vessels, 137 development, 138 injections of, 414 stomata, 140 valves, 139 Lymphocytes, 47, 146 Digitized by Microsoft® INDEX. 429 Lymphoid tissue, 34, 154 Lyons blue, 411 M. Macula lutea, 362 acustica, 380 Malleus, 382 Mallory's connective tissue stain, 412 Malpighian corpuscles {renal corpuscles), 253 corpuscles {splenic nodules), 160 Mamillary bodies, 338 Mammary glands, 313, 328 areola, 330 development, 328 Margarin crystals, 44 Marrow, bone, 152 Mast cells, 47, 148 Meckel's diverticulum, 195 Mediastinum of the ovary, 288 of the testis, 275 of the- thorax, 235 Medulla, 156 oblongata, 335, 339 spinalis {spinal cord), ir4 Medullary groove, 18, 91 plate, 9 1 tube, 20, 91 MeduUated nerve fibers, loi Megakaryocyte, 152 Megaloblasts, 141 Meibomian glands {tarsal glands), 375 Meissner's corpuscles {tactile corpuscles), 105 plexus {submucous plexus), 215 Melanin, 45 Membrana basilaris, of the cochlea, 387 limitans externa, of the retina, 357, 358 propria, in general, 30 limitans interna, of the retina, 359 vestibularis, of the cochlea, 385 Membrane, bone, 61 Bowman's (anterior basal membrane of the cornea), 369 Descemet's (posterior basal membrane of the cornea), 371 hyaloid, 366 pupillary, 355 Reissner's {membrana vestibularis), 385 tympanic, 382,' 393 Meninges, 351 Menstruation, 298 Mesencephalon, 334, 336 Mesenchyma, 23, 25 Mesenchymal epithelium, 28 tissues, 38 Mesentery, 211 Mesoderm, 19 Mesodermic segments, 22 Mesonephros, 244 Mesothelium, 25, 27 Mesovarium, 288 Metaphase, 11 Metencephalon, 335 Methyl green, 401 Methylene blue, 401 and eosine, 411 Micrometer, 418 Micron, 7 Microscope, 415 Microsome, 2 Microtome, 402 Mid-brain, 334 Milk, 329 Mitome, 3 Mitosis, 9 anaphase of, 12 atypical, 14, heterotypical, 12, 270 metaphase of, 11 prophase of, 9 Mixed glands, 190 Modiolus, 380 Moll, glands of {ciliary glands), 375 Monaster, 11 Mononuclear leucocytes, 146 Monospireme, 10 Montgomery's glands {areolar glands), 330 Morgagni, hydatid of {appendix testis), 280 sinus of, {ventricle of larynx), 237 Morula, 18 Motor cells, 91, 120 nerves, 90 endings, 107 Mounting sections, 408 Mouth, 184 development of, 165 Mucins, 40 Mucoids, 40 Mucous bursae, 50 glands, 33, 185 tissue, 39 Mucus, 33 Miillerian duct, 263, 285 Miiller's fibers (of the retina), 358 preserving fluid, 404 Muscle tissue, 25, 77 cardiac, 80 comparison of the three types, 85 contraction, 82 involuntary, 77 smooth, 77 striated, 85 voluntary, 77 Myenteric plexus, 95, 198, 215 N. Naboth, ovules of, 298 Nails, 316 Nasal cavity, 357 septum, 395 Nasolachrymal ducts, 378 Nasmyth's membrane {cuticula dentis) , 73 Nephrotome, 22 Nerve cells, 90 commissural, 91 motor, 91 sensory, 90 Nerve corpuscles, 105 Nerve endings, 102 free, 102 Digitized by Microsoft® 43° INDEX. Nerve endings, motor, 107 motor plates, 108 sensory, 102 tactile menisci, 102 Nerve fibers, 90, 97 afferent, 90 axis cylinders, 98 commissural, 98 motor, 90 neurolemma of, 98 non-medullated, 98 of central nervous system, 122 reflex path, 94 Remak's, 98 sensory, 90 sheaths of, 98 fibrils, 97 plexus, 94 tissue, 25, 90 development of, 91 Nerves, loi Nervous system, central, 91 peripheral, 91 sympathetic, 94 Neumann's membrane, 73 Neural groove, 91 Neuraxon, 93, 94 Neuroblasts, ri5 Neuroepithelium, 31 Neuroglia cells, 115 Neurokeratin, 99 Neurolemma, 98 Neurone theory, 123 Neuroplasm, 97 Neutrophils, 148 Nissl's bodies, 120 Nodes of Ranvier, 99 Nodules, aggregate, 156, 214 solitary, 154 Nodulus thymicus, 167 Normoblasts, 141 Nose, 395 development, 395 nerves, 399 olfactory glands, 398 vessels, 399 vestibule, 395 Notochord, r9, 21 Nucleolus, 5 Nucleoplasm, 2 Nucleus of cells, 4 of the nervous system, 117 Nuel's spaces, 388 O. Oculomotor nerve, 96, 338 Odontoblasts, 73 Oesophagus, 196 Odoriferous glands, 326 Oils for clearing sections, 409 Olfactory bulb, 338, 349 cells, 397 epithelium, 397 glands, 398 Olive, 340 Omental bursa, 221 Optic cup, 353 nerve, 354, 3^4 recess, 334 stalk, 353 vesicle, 20, 334, 353 Oocytes, 292 Oogenesis, 292 Oogonia, 292 Ora serrata, 355 Oral plate, 20, 165 Organ of Corti {spiral organ), 387 of Rosenmiiller (epoophoron), 286 Organs, 25 Orth's fluid, 404 Osmic acid, 413 Ossification, 53, 61 Osteoblast; 54 Osteoclast, 57 Otoconia, 384 Otocyst, 378 Otoliths, 384 Ovary, 288 development of, 287 follicles, 288 vessels and nerves, 294 Ovulation, 290 Ovum, mature, 290 P. Pacchionian bodies {arachnoid granulations) , 3SI Pacinian corpuscles {lamellar corpuscles), 107 Palate processes, 395 Palatine glands, 189 tonsils, 167 Pallium, 338 Palpebrffi, 375 Pancreas, 230 dorsal, 230 islands, 231 ventral, 230 Paneth, cells of, 207 Panniculus adiposus, 314 Papilla, duodenal, 205, 230 genital, 193 of hair, 317 of optic nerve, 354 renal, 250 Papillae, epidermal, 313 of the tongue, 177 Paradidymis, 280 Paraffin, imbedding in, 406 Paraganglia, 114 Paramitome, 3 Paranucleus, 4 Parathyreoid glands, 167, 175 Parietal cells, 200 Paroophoron, 286 Parotid gland, 187 Parovarium {epoophoron), 286 Pavement epithelium, 28 Peduncles of the cerebrum, 336 Pelvis of kidney, 249 Digitized by Microsoft® INDEX. 431 Penis, 266, 281 Peptic glands, 200 Pericardium, 135 Perichondral bone, 61 Perichondrium, Ji Peridental membrane {alveolar periosteum), 77 Perilymph spaces, 381 Perilymphatic duct, 392 Perineum, 193 Perineurium, loi ^Periosteal bone, 61 Periosteum, 56, 59 Peritonaeum, 211 Petit, canal of {zonular spaces), 364 Peyer's patches {aggregate nodules), 156, 214 Phagocytes, 8 Pharyngeal recess, 167 tonsil, 169 Pharynx, 184 development, 165 Pia mater, 118, 351 Pigment cells, 45 Pinguecula, 377 Pineal body, 338, 350 Pillar cells of spiral organ, 387 Pinna (auricle), 382 Pituitary body (hypophysis), 349 Placenta, 301, 305 Plasma, 151 Plasma cells, 47 Plasmodium, 6 Plates, blood, 150 Pleura, 236, 242 Pleural villi, 243 Jlexus annularis, 374 Auerbach's, 215 cardiac, 94, 137 chorioid, 352 coeliac, 95 gangliosus ciliaris, 374 Meissner's, 215 myenteric, 95, 198, 215 myOspermaticus, 278 pulmonary, 243 solar, 95 submucous, 95, 215 Plica semilunaris of the eyelid, 377 Plicae adiposae, of pleura, 243 circulares of small intestine, 205 palmatae, of uterus, 296 semilunares, of the large intestine, 217 transversales, of rectum, 217 villosae, of stomach, 198 Polar globule, 293 Polarity of cells, $3 Polymorphonuclear leucocytes, 146 Pons, 335, 341 Porta hepatis, 229 Portal veiri, 220 Praeputial glands, 324 Precartilage, 50 Premyelocytes, 153 Primary bone, 61 follicles, 287 Primitive streak, 18 Prisms, enamel, 70 Processus vaginalis, 267, 288 vermiformis, 215 Proliferation islands of the placenta, 305 Pronephros, 248 Prosencephalon, 334 Prostate, 280 Proteid absorption, 279 Protoplasm, 2 Protovertebrae, 22 Pseudostratified epithelium, 28 Pulmonary arches, 234 plexus, 243 veins, 235 Pulp, of teeth, 68, 74 Pupil, of dilatator muscle, 369 sphincter muscle, 369 Purkinje's cells, 344 fibers, 8s, 13s Pyloric glands, 200 Pylorus, 198 Pyramids of Ferrein {pars radiata), 251 of the medulla oblongata, 339 Pyramidal cells, 346 tracts {cerebrospinal), 122, 339, 342, 345 Pyrenin, 5 R. Radial fibers of the retina, 358 Ranvier, nodes of, 77 Raphe of the scrotum, 266 of the medulla oblongata, 340 Reconstructions, 418 Rectum, 217 Red corpuscles, 140 color, 143 number, 144 shape, 142 Reduction division, 14 Reflex path of spinal cord, 94 Reflexa {decidua capsularis), 301 Reissner's membrane {membrana vestibu- laris), 385 Remak's fibers, 98 Renal columns, 250 corpuscles, 253 pelvis, 260 pyramids, 250 tubules, 250 Respiratory bronchioles, 240 tract, 234 Restiform body, 336, 340 Resting wandering cells, 47 Rete Malpighii {stratum germinativum) , 315 testis, 265 Reticular tissue, 38 Reticulin, 39 Retina, 357 cones, 357 development, 353 ■ fovea centralis, 362 ganglion retinae, 359 macula lutea, 362 pars ciliaris, 355, 362 pars iridica, 355, 368 Digitized by Microsoft® 432 INDEX. Retina, pars optica, 355, 357 pigment layer, 353, 357 rods, 357 Resorcin-fuchsin, 412 Retzius, cells of, 346 lines of, 72 Rhinencephalon, 338 Rhombencephalon, 334 Rhomboidal sinus, 20 Rosenmiiller, organ of {epoophoron) , 286 Ruffini's terminal cylinders, 104 Saccus endolymphaticus, 392 Sarcolemma, 79 Sarcomeres, 82 Sarcoplasm, 79 Scala media {cochlear duct), 380, 385 tympani, 381, 385 vestibuli, 381, 385 Schlemm, canal of {sinus venosus sclerae), 373 Schreger's lines, 72 Schwann's sheath, 98 Sclera, 355, 369 Sclerotome, 86 Scrotum, 266 Sebaceous glands, 312, 324 Secretion, 32 ■ internal, 35 Secretory capUlaries, 36 Sectioning, 402 Segmentation, 18 Semicircular ducts, 384 development, 379 Seminal fluid, 272 vesicles, 279 Sensory decussation, 340 nerve cells, 90 fibers, 90 endings, 102 Septula testis, 275 Septum transversura, 218 Serotina {decidua basalts), 301 Serous glands, 32, 187 Sertoli's cells (sustentacular cells of the tes- tis), 268 Serum, 150 Sexual cells, 267, 288 Scharlach R, 412 Sharpey's fibers, 561 76 Silver nitrate, 414 Simple epithelium, 27 Sinus, coronary, 134 lactiferous, 330 urogenital, 193, 265, 287 venosus, 134 sclerae, 373 Sinuses, blood, in haemolymph glands, 159 lymph, 156 of the dura, 351 Sinusoids, 125, 227, 247 Skin, 312 corium, 313 epidermis, 315 Skin, hair, 317 nails, 316 nerves, 327 sebaceous glands, 324 sweat glands, 325 vessels, 327 Small intestine, 203 blood vessels, 211 duodenum, 204 glands, 206 ileum, 205 jejunum, 205 lymphatic vessels, 213 lymphoid tissue, 213 mesentery, 211 nerves, 215 villi, 204 Solitary nodules, 154 Spermatic cord, 278 Spermatid, 270 Spermatocytes, 270 Spermatogenesis, 270 Spermatogonia, 268 Spermatozoon, 269 Spermium, 270 Spinal cord, 114 cell bodies, 120 central canal, 117 columns, 115 commissures, 115, 117 dorsal median septum, 116 dorsal nucleus, 117 ependyma, 122 fasciculi, 122 funiculi, 122 gray substance, 119 neuroglia, iij, 118, 122 pia mater, 118 substantia gelatinosa, 118 sulci, 116 ventral median fissure, 116 white substance, 118 zona spongiosa, 118 zona terminalis, 118 Spinal ganglia, 92, 109, no nerves, 93 Spiracle, 165 Spiral organ, 380, 386 Spireme, 12 Splanchnic nerves, 95 Spleen, 159 capsule, 163 nerves, 163 nodules, 160, 163 pulp, 160, 162 Spongioplasm, 3 Squamous cells, 29 Stains, general, 410 Special, 411 Staining of celloidin sections, 409 of paraflSn sections, 408 Stapes, 382 Stenson's duct {parotid duct), 187 Stomach, 198 glands, 200 Stratified epithelium, 29 Digitized by Microsoft® INDEX. 433 Striated muscle (cardiac, 80), voluntary, 85 Stroma ovarii, 288 / Subarachnoid space, 351 Subcardinal veins, 220 Subcutaneous tissue, 313 Subdural space, 351 Sublingual glands, 190 Submaxillary glands, 191 Substantia adamantina, 67 alba, 118 eburnea, 67 gelatinosa, 118 grisea, 119 lentis, 365 ossea, 67 Suprarenal gland, 331 Sustentacular cells, of ear, 38^, 388 of nose, 397 • of taste buds, 1 79 of testis, 267 Sweat glands, 312, 325 Sylvius, aqueduct of, 334 Sympathetic ganglia, 112 nervous system, 91 Synapsis, 270 Synarthrosis, 64 Synchondrosis, 64 Syncytium, 6 Syndesmosis, 64 Synovia, 67 TactUe cells, 103 menisci, 102 Taeniae, 217 Tapetum cellulosum, 367 fibrosum, 367 Tarsal glands, 375 Taste buds, 179 cells, 181 Teeth, 67 cement, 76 dentine, 73 enamel, 69 pulp, 74 Telencephalon, 335, 338 Tellyesnizcky's fluid, 404 Tendon, 48 spindles, 103 Tenon's capsule {interjascial space), 374 Terminal bars, 29 corpuscles, 105 menisci, 102 Testis, 267 atrophy, 275 cells, 267 connective tissue, 274 convoluted tubules, 273 crescent of, 267 interstitial cells, 275 nerves, 276 rete, 274 vessels, 276 Thalamus, 338 Thebesius, veins of {venae minimae), 136 Thoracic duct, 148 Thymus, 167, i6g Thymic corpuscles, 172 Thyreoid gland, 166, 173 Tissues, 18 examination of fresh, 400 Tomes's fibers {dental fibers), 73 processes, 71 Tongue, 176 Tonsils, lingual, 169 palatine, 167 pharyngeal, 169 Top plate, 30 Trachea, 238 Triangular ligaments of the liver, 219 Trigeminus nerve, 96, 335 Trochlear nerve, 96, 336 Trophoblast, 300 Trophospongiurh, 4 Tympanic cavity, 385, 392 membrane, 382, 393 Tyson's glands, 324 U. Umbilical cord, 301, 308 vein, 220, 316 Umbilicus, 193 Unna's methylene blue, 4 1 1 Urachus, 193 Ureter, 260 Urethra, 193 female, 262 male, 265, 281 Uriniferous tubules, 254 Urogenital sinus, 193, 265, 2S7 Uterine tubes, 286, 294 Uterus, 296 menstruating, 298 pregnant, 300 Utriculus, 379, 384 V. Vacuoles, 4 Vagina, 311 Vagus nerve, 96, 335 Valves, of the heart, 135 of the lymph vessels, 139 of the veins, 132 Valvulae conniventes {circular /olds), 205 Vas deferens (ductus deferens), 265, 278 prominens, 385 Vasa aberrantia of the liver, 229 vasorum, 130 Vascular tissue, 25, 124 Vasomotor nerves, 130 Vegetative cells {sustentacular cells), 26S Vena cava inferior, 220, 247, 248 Veins, 131 cardinal, 220, 246 portal, 220 pulmonary, 235 umbilical, 220, 316 vitelline, 24, 220 Ventricles, of the brain, 91, 334, 335, 338 of the heart, 133 28 Digitized by Microsoft® 434 INDEX. Vermiform process, 215 Vesicular follicles, 289 Vestibule, of labyrinth, 382 of nose, 385 of vagina, 287 Vibrissae, 395 Villi, amniotic, 311 chorionic, 300, 305 pleural, 243 intestinal, 241 synovial, 67 Visual cells, 357 Vitreous body, 354, 366 humor, 366 Volkmann's canals, 56 White fibers, 41 substance, of the spinal cord, 118 Winslow's foramen {foramen epiploicum) , 221 WolflSan body, 244 duct, 24S, 285 tubules, 265, 286 Xylol, 409 Yolk sac, 193, 311 stalk, 194, 310 W. Wax reconstructions, 419 Weigert's elastic tissue stain, 412 Wharton's duct (submaxillary duct), 191 jelly (mucous tissue of the umbilical cord), 39 White corpuscles, 143 Z. Zenker's fluid, 403 Zona pellucida, 293 spongiosa, 118 terminalis, 118 Zonula ciliaris, 362, 364 Zymogen granules, 201, 233 Digitized by Microsoft® Digitized by Microsoft® Digitized by Microsoft® Digitized by Microsoft®