COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX00025402 LIBkmki OF THE ASSOCIATION fFlli ALUMNI I OF THE OF THE OLLEGE OF ICIANS AND SURGEONS !N THE CITY OF NEW YORK SCHOOL OF MEDICINE OF COLUMBIA UNIVERSITY C^^^o^x THE LIBRARY V'?*'^ OF THE ASSOCIATION OF THE ALUMNI OF THE COLLEGE OF PHYSICIANS AND SURGEONS IN THE CITY OF NEW YORK SCHOOL OF MEDICINE OF COLUMBIA UNIVERSITY Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/elementsofhistolOOklei MANUALS Students of Medicine HIS T'©*'®'&«. BY E. KLEIN, M.D., F.R.S. LECTURER ON GENERAL ANATOMY AND PHYSIOLOGY AND J. S. EDKINS, M.A., MB. JOINT LECTURER AND DEMONSTRATOR OF PHYSIOLOGY IN THE MEDICAL SCHOOL OF ST. BARTHOLOMEW'S HOSPITAL, LONDON WITH 296 ILLUSTRATIONS REVISED AND ENLARGED EDITION LEA BROTHERS & CO., PHILADELPHIA AND NEW YORK, Co tl&f fHfmorg OF SIR WILLIAM BOWMAN, LL.D., F.R.S., THIS BOOK IS DEDICATED, IN ACKNOWLEDGMENT OP HIS MANY AND GREAT DISCOVERIES IN ANATOMY AND PHYSIOLOGY. PREFACE TO THE REVISED AND ENLARGED EDITION. Since the last edition of this book in 1889, consider- able additions have been made to the knowledge of minute structural anatomy. The progress in the knowledge of the structure and life of the cell and nucleus, the remarkable discoveries in the structure of the central nervous system and sense organs — introduced bv the method of Golo-i, and followed up by the brilliant work of Ramon y Cajal, Kolliker, Lenhossek, Retzius, and others — have made it neces- sary to revise and to make considerable additions to the chapters dealing with these organs. While care has been taken to correct and amplify other jmrts of the book, the chapters on the central nervous system have been practically rewritten. The task of rewriting and re-editing the chapters on the brain and medulhx and on the alimentarv canal has devolved upon my colleague Dr. Edkins, who is now associated with me as joint-author. While a large number of the illustrations of the former edition have been retained, a considerable number has been added ; these are either original photograms prepared by Mr. Norman from Dr. Edkins's and my own speciiiiens, or they are copied from Kolliker's " Handbuch," from Ramon y Cajal, from Schiifer (Quain's " Anatomy "), from Halli- burton (Kirke's " Physiology "), and from Klein and Noble Smith's " Atlas of Histoloijv." To our colleague Dr. Tooth our special thanks are due for the loan of some of the lantern slides illustrating the medulla. E. KLEIN. St, B.uiTHOLOMEw's Hospital, LONDOX. — 1S98. COXTENTS. CHAPTER I.— Cells . , . . . II.— Blood III. — Epithelium .... IV. — Endothelium .... V, — Fibrous Connective Tissues VI. — Cartilage VII.- Bone VIII. — Xon-strii:)ed Muscular Tissue . IX. — fStriped Muscular Tissue . X.— The Heart and Blood-Vessels . XI. — The Lymjjhatic Vessels XII. — Follicles or Simple Lymph Glands XIII.— Compound Lymphatic Glands . XIV. — Nerve Fibres .... XV. — Peripheral Xerve-Endings XVI.— The Spinal Cord XVII.— The Medulla Oblongata or Spinal Bulb XVJII. — Continuation of the Medulla Oblongata throu^ Pons Varolii and the Region of the Crura XIX. — The Cerebrum and Cerebellum XX. — The Cerebro-Spinal Ganglia XXI. — The Sympathetic System XXII. — General Considerations as to the Anatomical Con stitution and Nature of the Nervous System XXIII. -The Teeth XXIV.— The Salivary Glands XXV.— The Moutli. Pharynx, and Tongue . XXVI. — The (Esophagus and Stomach .... h the PAGE 1 19 30 40 46 63 68 86 90 10.5 117 126 134 140 155 170 202 216 235 253 2.58 268 275 286 298 307 xu Elements of Histology. . " CHAPTJER PAOE XKVIL— The Small and Large Intestine .... 317 XXTIIL — The Glands of -Brunner andthe Pancreas . . 328 XXIX.— The Liver 333 XXX.— The Organs of Respiration 3.30 XXXI.— The Spleen 3-51 XXXII.— The Kidney. L'reter and Bladder . 356 XXXIIL— The Male Genital Organs 372 XXXIV.— The Female Genital Organs . . . .386 XXXV.— The Mammary Gland 400 XXXVI.— The Skin 404 XXXVII.— The Coniuuctiva and its Glands . . .424 XXXVIII. — Cornea, Sclerotic, Ligamentum Pectinatnrn and Ciliary Muscle 429 XXXIX. — Iris, Ciliary Processes and Choroid . 436 XL.-— The Lens and Vitreous Body ... 442 XLI. -The Retina 44.5 XLIL— The Outer and Middle Ear .... 4-58 XLIIL— The Internal Ear . . \. . 460 XLIV. — The Xasal Mucous Membrane .... 47-") XLV.— The Ductless Glands 484 jprnpfrtn o( l\ft ^sjuciaiimi uf i^e ^^lumni of t^e CoUtgc of I^DS. & iurgs.. gfto fork, Elements of Histology. CHAPTER I. CELLS. 1. The ripe oviiiii (Fig. 1) of man and mammals is a minute spherical mass of a soft, gelatinous, trans- parent, granular-looking substance, containing nume- rous minute particles — yolk globules. It is invested by a radially striated delicate membrane called the zona pellucida. Inside this mass, and situated more or less excentrically, is a vesicle — the germinal vesicle — and inside this, one or more solid spots — the germinal spot or spots. The gela- tinous transparent substance of the ovum, containing a very large percentage of proteid material, is called protoplasm. Before and immediately after fertilisa- tion, the protoplasm of the ovum shoAv^s distinct movement, consisting in contraction and expansion. These movements are spontaneous — i.e. not caused by any directly visible external influence. The diameter of the ripe ovum in man and do- mestic animals varies between ^^^ and y^^ of an inch. But before it ripens the ovum is considerably V--^-c Fig. 1. — Ripe Ovum of Cat. a, Zona pellucida ; h, gerniinal vesicle; c, protoplasm. 2 Elements of Histology. smaller — in fact, its size is in proportion to its state of develo])ment. 2. Fertilisation causes marked changes in the contractions of the protoplasm of the ovum ; these Fig. 2.— From a Section through the Blastoderm of Chick, unincubated. a Cells foimiui,' ilie ectoderm ; b, cells forming the endoaerm ; c, larue formative cells ; /, segmentation cavity. {Handooolc.) lead to cleavage or division of its body into two jiarts, the germinal vesicle having previously split up into two bodies or nuclei ; so that we now find the ovum / Fig. 3.— From a Section through the Rudiment of the Embryo Chick, e, rrimitive groove ; /, dorsal laminae of epihlast : d, raesoblast. The thin layer of spindle-shaped cells is the hypoblast. (.Handbook.) has originated two new elements, each of which consists of protoplasm, of the same substance as that of the original ovum, and each contains one nucleus or kernel. ; The investment of the ovum rakes no Cells, part ill this process of division. Not long afterwards, each of the two daughter elements undergoes cleavage Fig. 4.— Vertical Section tlirough the Ovum of Bufo Cinereiis, in the early stage of the Embryo Development. a, Tegmental layer of epiblast ; 6, dorsal groove ; c, rudiiuent of central nervous system ; d, notochord ; e, deep layer of epiblast ; /, mesoblast ; g, hypoblast ; ft, cavity of alimentary canal— Rusconi's cavity ; h, central yolk ; A:, remainder of von Baer's or segmentation cavity. ^Handbook.) or division into two new elements, the nucleus having previously divided into two, so that each new offspring possesses its own nucleus. This process of division is continued in the same manner for 4 Elements of Histology. many generations (Figs. 2, 3, 4), so that after a few davs we find within the orioinal investment of the ovum a large number of minute elements, each consisting of protoplasm, and each containing a nucleus. 3. From these elements, which become smaller as the process of cleavage progresses, all parts and organs of the embryo and its membranes are formed. It can be easily shown that the individual elements possess the power of contractility. Either spontaneously or under the influence of moderate heat, electricity, mechanical or chemical stimulation, they throw out processes and withdraw them again, their substance flowing slowly but perceptibly along. Hence they can change their position. In this respect they com- pletely resemble those lowest organisms which are known as amceb?e, each of these being likewise a nucleated mass of protoplasm. Wherefore this move- ment is termed amoeboid movement. It can be further shown that they, like amoeb?e, grow in size and divide ■ — that is to say, the individuals of a generation grow in size l^efore each gives rise to two new daughter individuals. 4. Although for some time during embryonic life the elements constituting the organs of the embryo are possessed of these characters, a time arrives when only a limited number of them retain the power of contractility in any marked degree. At birth only the white corpuscles of the blood and lymph, many of the elements of the lymphatic organs, and the muscular tissues, possess this power; while the others lose it, or at any rate do not show it except when dividing into two new elements. Some of these elements retain their protoplasmic basis ; as a rule, each con- tains one nucleus (but some two or more), and is capable of giving origin by division to a new genera- tion. Others, however, change their nature altogether, Cells. 5 their protoplasm and nucleus disappear, and tliey give origin to material other than protopLism — e.g. collagenous, osseous, elastic, and other suljstances. As develojiment proceeds, and after birth of the fa3tus, different cells assume different functions, which for each kind are of a special character and constitute its specific character or its specific junction. 5. Beginning with the ovum, and ending with the protoplasmic nucleated elements found constituting the organs and tissues of the embryo and adult, we have, then, one uninterrupted series of generations of Fig. 5. — Amoeboid iiioveinent of a Wliite Blood Corpuscle of Man ; various phases of nioveiiient. (Handbook.) elements, which with Schwann we call cells and with Briicke elementary organisms. Of these it can be said that not only is each of them derived from a cell (Virchow : omnis cellula a cellula), but each consists of the protoplasm of Max Schultze (sarcode of Dujar- din), is without any investing membrane, and includes generally one nucleus, but may contain two or more. We can further say that each of these cells shows the phenomenon of growth, which presupposes nutrition and reproduction. A.11 of them in an early stage of their life-history, and some of them throughout it, show the phenomenon of contractility, or amoeboid move- ment (Fig. 5). In a recent work, and following the procedure of V. Sachs on the life and activity of vegetable cells, v. KoUiker systematises and summarises those of animal cells thus : The protoplasm and nucleus constituting 6 Elements of Histology. a vegetable cell is called by v. Sachs an energid; in the animal body it is represented by a nucleated protoplasmic cell without a cellulose membrane, and is called by v. Kolliker a protohlast (germinal matter of Beale). All protoblasts, as also all energids, are always derived from parent protoblasts ; they always propagate by division, and in this manner carry on the race from generation to generation ; they are the instruments of heredity. All growth of the protoblasts takes place by internal processes — that is, by intussusception. The active work of protoblasts consists in : («) formation of the typical organs ; (6) special move- ments of the protoplasDi — e.g. amoeboid movement ; (c) the formation of alloplasmatic organs (A. Meyer). These latter are derived from the livmg protoplasm, are organised, and are participating themselves in the living functions, but they are not capable of multipli- cation by division. Such alloplasmatic organs are : cilia, muscular fibres, nerve cells and nerve tibres, and the terminal cells in the sense organs, {d) The pro- duction of passive, partly non-organised, ergastic structures (A. Meyer), or formed matter (L. Beale) ; such are the cellulose membranes of vegetable cells, cuticular formations, fluids, and intercellular and other substances (collagenous, chondrinous, osseous, elastic, dental, etc.), cell-juices and granules of all kinds. Cells ditfer in shape according to kind, locality, and function, being spherical, irregular, polygonal, squamous, branched, spindle-shaped, cylindrical, pris- matic, or conical. These various shapes will be more fully described when dealing in detail with the various kinds of cells. Cells in man and mammals differ in size within considerable limits : from the size of a small white blood corpuscle of about tt/ou ^^ '"^"^ "^*^^^ to that of a laroe ganglion cell in the anterior horns of Cells. the spinal cord of about ^.^o of 'ii^ inch, or to that of multinucleated cells of the bone marrow — myeloplax — some of which suri)ass in size even the ganglion cells. The same holds good of the nucleus. Between the nucleus of a ganglion cell of about ^\-^ to yaVo ^^ ^^ inch in diameter and the nucleus of a white blood corpuscle of about -goVo ^^ tit wo ^^ ^^^ inch and less there are all intermediate sizes. 6. Pi-otoplasiii or cytoplasm is a transparent homogeneous or granular-looking substance. On very careful examin- ation with good and high powers, and especially ^vhen examined with c e r t a i n reagents, in many, but not in all, instances it shows a more or less definite structure (Fig. 6), composed of fibrils, more or less regular, and in some instances grouped into a honeycomhed re- ticulum, sjyongioplasm, in the meshes of which is a homogeneous substance, /njaloplasm (Leydig). The closer the meshes of the reticulum, the less there is of this interstitial substance, and the more regularly granular does the reticulum appear. In the meshes of the reticulum, however, may be included larger or smaller granules of fat, pigment, or other material. Water makes protoplasm swell up and ultimately this becomes disintegrated ; so also act dilute acids and alkalies. All substances that coagulate proteids have the same effect on protoplasm. Fig. 6. — Anictboid pale leucocyte of the newt, showing the nuclei embedded in the cell proto- Ijlasni— this latter consisting of spongioplasm and hyaloplasm. (After Scho/er.) 8 Elements of Histology. In arrangement of its elements the spongioplasm ditfers in different cells ; while in some — e.g. spheroidal or cubical ej^ithelial cells — it is as a rule uniform ; in columnar cells it is elongated in the direction of the long axis of the cell, hence the reticulum appears as an eminently longitudinally fibrillated substance ; in ganglion cells it is concentrically arranged. In some Fig. 7. — Cell with radially disposed reticulum from the intestinal epithelium of a worm. (After Carnoy, from Quain's "Anatomy.") mc. Cell iiiembraiie ; j)c, cell protoplasm ; mn, nuclear membrane ; pn, nuclear achromatin surrounding the convoluted chromatin filaments bn. cells in the outer portion the spongioplasm possesses a different arrangement from that in the middle portion, and then a division is made between ectoplasm and endoplasni (Fig. 7). The hyaloplasm differs in amount in different cells, and in the same kind of cells it varies according to different states of cell activity. Thus in gland cells during activity the amount of hyaloplasm is increased, containing in these instances more or less of jjranular matter. Cells. In amceboid cells, such as the white corpuscles of the blood, the hyaloplasm is the substance in which the spontaneous or amoeboid changes and movement are principally lodged, as has been shown by instan- taneous electric illumination by Strieker. In the protoplasm of many cells are lodged granules of various kinds, microsomes ; they differ in size, shape, colour, and chemical nature, and are, as a rule, the result of cell activity. Such are the zymo- gen granules in secreting gland cells ; eosinophil e, basopliile, and neutrophile or amphophile granules in leucocytes ; glycogen granules in the liver cells, cartilage cells, and leucocytes ; pigment granules in various kinds of jDigmented cells ; fat granules and fat globules in wandering cells, in connective-tissue cells, in liver cells, in the epithelial cells of the milk gland, etc. It is not justifiable to as- sume with Altmann that these microsomes or bio- blasts are living entities in the sense that the whole cell is. In the cell proto- plasm of leucocytes, of epithelial and other cells, certain granules and fibrils have been de- scribed by Flemming, Boveri, Heidenhain, and others, which being of a constant and definite nature play an important part in the division of the cell and its nucleus. This is the centrosome, and with its radiating fibrillse forms the attractionsjyJiere (Fig. 8). The centrosome is a granule surrounded by a hyaline Fig. 8.— Leucocyte of Salamandra con- taining two nuclei, and showing the attractionsphere : the centrosome is already divided into two. (After Dr. Martin Heidenhain.) ro Elements of IIistologv. spherical space ; through this pass the fibrillse radi- ating from the former, aod connect it with the spongioplasm of the cell body. The whole — Le // ' ' -»— ^-^^-i '— — '^^ Fig. 9. — Blastomeres of Bi-segmented 0\-um of Ascaris megalocephala {Ajter Boveri,from Kdllik'jr, I.) A : a, Attractionsphere ; v, nucleus in resting- state ; B : nucleus in stage of convolution: c, attractionsphere nearly divided; D, attract ionsphere divided: E. attractionspheres arranged at the poles, chx-omosomes forming tiiC eauaiorial plate. centrosome and radiating tibrilhe — represents the attractionsphere. Preceding the division of the cell nucleus, the centrosome divides into two, each daughter centrosome, with its own hyaline areola and system of radiating fibrillar, forming by - and - by a separate attractionsphere, which Cells. i i migrating towards op})Ositc pules of the cell- Itody become separate jjoints of attraction for the divided nuclear mitoma. [See division of nucleus.) So that the division of the attractionsphere would be the tirst, the division of the nucleus the second, and the division of the cell protoplasm the third and final stage in the division of a cell (Fig. 9). 7. The iiiicleiis, the size of which is generally in proportion to that of the cell, is usually spherical or oval. It is composed of a more or less distinct invest- ing cuticle and the nuclear contents ; the former is tlie membrane, the latter the nuclear substance, karyo- plasm, or nucleoplasm. This, again, is composed, in adult nuclei, of a stroma or network, mitoma, and the inter-Jibrillar suhsta^ice. The network consists of tibrils of various thickness, and trabecular or septa more or less irregular in thickness and length. In- timately connected with and lodged in the network are anijular or rounded masses called nucleoli. The number and size of these vary considerably ; in young nuclei they may be large and numerous, in adult or resting nuclei they are few, and in those about to divide they are altogether absent. Also the network is subject to great variation : while in adult or resting nuclei^ and particularly those about to divide, the network is of great uniformity and well developed ; it may be very imperfect in young nuclei, in which it is sometimes represented by a number of irregular masses joined by short bridges. The more perfect the nuclear network, the fewer are the nucleoli. Owing to the ready manner in which the fibrils of the nuclear network, i.e. the mitoma, take up certain dyes, their substance is called chromatin, and the fibrils are the chromosomes ; while the inter-tibrillar sub- stance not possessed of this character is called achromatin. Occasionally, also, the achromatin ap- pears composed of fibrils, and these are then called 1 2 Elements of Histology. secondary fibrils, as distinct from tlie chromosomes or })rimary fibrils. Rabl and with him Heidenhain maintain, however, that the achromatin in typical adult nuclei is ahvays composed of tine fibrils, and that both the chromatin and achromatin fibrils possess a definite unipolar arrangement and convergence, while Carnoy and van Gehuchten assume a bipolar arrangement. But this distinction holds good only for adult nuclei ; in young nuclei the whole nuclear contents may possess this aflinity for the same dyes, and in this case the whole nucleus becomes uniformly stained. The nuclear membrane is a condensed outer stratum of the nuclear network. At the commence- ment of the division of the nucleus the membrane disappears. In some instances it can be shown that the nuclear filjrils are in continuity with the fibrils of the cell substance. In the moving white blood corpuscles Strieker and linger have seen the nucleus becoming one with the cell substance, and again afterwards diti'erentiated by the apjDearance of a membrane. 8. During: division of the cell the nucleus generally divides before the cell i)rotoplasm. This division of the nucleus was formerly supj)osed to occur in the same manner as that of the cell proto- plasm — i.e. by simple cleavage. This mode is called the direct or amitotic division, or Remak's mode of division. In this division the nucleus is supposed to become constricted, kidney-shaped and hourglass- shaped and, if the division is into more than two, lobed. Nuclei of these shapes are not uncommon ; but they need not necessarily indicate direct division, because, being very soft structures, pressure exerted from outside, or the motion of the cell protoplasm, may produce these shapes ; and, further, the contrac- tility of the nucleus may, and occasionally has been observed to, cause these changes of shape. From the Cells. ^3 ol>s('r\ations of Schneider, Biitschli, Folil, Strass- burgor, Mayzel, van Beiieden, Schleicher, Fleniiiiing, liabl, and others, it is known that in the embryo and adult, in vertebrates and invertebrates, in all kinds of cells, both in the noi'nial as well as morbid condition, the division of the cell protoplasm is preceded by complex changes of the nuclear mitoma, leading to the division of the nucleus (Fig. 10). The sum-total of these Fig. 10. — Karyoinitosis. A, Ordinary nucleus of a columiiar opitlieli.al cell : b, c, the same nucleus in the stage of convolution ; D. the wreath, or rosette form; e, the aster, or single star; F, a nuclear spindle from the Desceiin't's endothelium of the frog's Cornea; G, H, I, diaster ; k, two daughter nuclei. changes is called indirect division, karyokinesis (Schleicher) or karyomitosis "^ (Flemming). Where this process occurs in its complete and typical form, the mitoma passes through the following phases (Flemming, Rabl) : — i. — Convolution or spireme or shein ; disappearance of the nucleoli, increase of the fibrils constituting the * Schleicher noticed that the fibrils duriuo; this process show movemeut ; hence the name Karyokinesis. Mitosis indicates the r- . grouping and changes of the fibrils (MtTos = fibril). 14 Elements of Histology. chromatic substance, at the same time the fibrils become free, as it were, and bent and twisted at first into a dense, afterwards into a loose convolution. The fibrils of the loose convolution are thicker than before, less twisted, and more like masses of loops. / "> c t ^ ^If ^?\r'.4\:^ '^^^ ■- .^^^'r>' ^ (" Fig. 11. — Eiiithclium of iiiouth of einbiyo salamander, showing nuclei in various stages of karyomitosis (Flemming). These latter Ijy cross division along the periphery of the mass increase in number, and thereby are con- verted into simple loops, arranged more or less like a wreath or rosette. The whole nucleus is larger than before, its membrane has disappeared, and it is sur- rounded by a more or less clear halo of cell proto- plasm (Fig. 11). ii. — Longitudinal division of the loops, each loop giving origin to a pair of sister loops; the whole, viewed from the surface, looks like a star of numerous fine fibrils, joined centrally so as to form single loops. Cells. 15 iii. — The nuclear sjnndle^ a spindle shaped ar- rangement of tine threads of (possibly) achromatin extending between two opposite points of the cell protoplasm ; these points are the poles, and the transverse line midway between them — i.e. at the c Fig. 12. — Karyomitosis. {Ajter KolUker.) A, Spireme ; b, diasier; c, ilie nucleus lias divuled, cUe prucoi'lasiu of the cell In tbe act. of dividing. broadest part of the spindle — is called the equator. At each pole the threads of the spindle are connected with a granule of the cell protoplasm, tlie pole cor- puscle or centrosome, mentioned on a previous pa^-e ; from the centrosome radiate numerous fine fibrillar, connecting the centrosome or pole corpuscle with the cell protoplasm, thus forming " the suns " or attraction- spheres, one at each pole (van Beneden). The above-named sister loops so arrange themselves about the equator of the spindle as to form a star — the motJier-star, monaster, or aster. In this arrange- ment the vertex of the loops is directed inwards, the open limbs outwards. Seen in profile the aster would appear like a narrow granular - looking plate of chromosomes — the nuclear plate. iv. — Metakinesis : Of each pair of sister loops form- ing the aster one loop is attracted by — i.e. migrates 1 6 Elements of Histology. towards one, tLe otlier towards the other pole of the spindle: that is, towards the attractionspheres, the vertex of the loops always leading. V. — Diaster : arrived at tlie pole, the loops form again an aster or daughter star for each pole (Fig. 12). \i. — Dispireme : the threads of each star become convoluted. ZS^ow follows usually the division of the cell proto- plasm in the line of the equator of the spindle. vii. — In the last phase all traces of the spindle are lost : a membrane appears around each of the two new nuclei, and the threads of the dispireme become branched and connected into a network. From the forecjoin^; it is clear that during division an intimate fusion Vjetween cell protoplasm and nucleus takes place : («) by the fusion of the nuclear interstitial suVjstance with the cell protoplasm after the disappearance of the nuclear membrane ; and (h) bv the connection of the nuclear spindle with the centrosomes and attractionspheres, the fibrils of the latter being part of the cell protoplasm. It ought to be mentioned, however, that some histolo^ists do not rec;ard the fibrils of the nuclear Spindle as part of and derived from the original nuclear substance (achromatin). Boveri regards the fibrils of the spindle as derived from the cell proto- plasm and as forming part of the attractionspheres — i.e. those fiVjrils which remain connecting the two attractionspheres, and which finally, after the nuclear division has Ijeen completed, by their transverse division, mark off and initiate the final stage — that is, the division of the cell body. While these various details and phases in the changes and division of the centrosome and attrac- tionsphere are well enough marked in the ovum, as is also their relation to the chromosomes of the dividing ovum nucleus, it is not sufficiently established that Cells. i 7 the above are of general occurrence in the division of adult cells; the attractionsphere and its division have ])een observed only in a few such instances — e.g. in the leucocytes of salamander and man. In some cases the process of karyomitosis has Vjeen found to be atypical, inasmuch as some of the above phases are left out, as it were ; while in other cases the nuclear division takes place already during the earlier phases — e.g. in the phase of the spireme. When the nucleus divides into two or three or more nuclei without the cell protoplasm also undergoing division, a cell with two, three, or more nuclei is the result. Multiplication of the nucleus by budding and direct fission has also been observed, but it is quite possible that this process is only as a sort of imper- fect and abnormal karyomitosis. This mode [)robably jDlays a more important part than the typical karyomitosis, whenever rapid multi- plication and rei^roduction are necessary. Thus, for instance, while in the epithelium cells covering the anterior surface of the normal cornea of the newt and frog here and there a nucleus can Ije seen which shows the process of typical karyomitosis, such forms cannot be found in cases of rapid regeneration of that epithelium. For example, after removing the whole thickness of the anterior epithelium from the middle part of the cornea, rapid multiplication of the epithelium cells takes place, starting from those immediately around the defect ; in consequence of this, in two or three days the defect becomes again quite covered with the new epithelium. Xow, ex- amining the epithelium cells at the margin of the defect, as well as those gradually pushed over and covering the defect, none of the nuclei are found in any of the phases of typical karyomitosis ; while a few days later, after the defect is covered by the new c 1 8 Elements of Histology. epithelium, there is no difficulty in finding nuclei in one or another ])lia.se of the typical kar3"omito.sis. Paranuclei and cell enclosures, — It was mentioned above that cells may and do include in their j^rotoplasm formed substances like granules of various kinds, fat globules, pigment, etc. ; but in addition to these, and distinct from the attraction- spheres mentioned on a former page, occasionally the cell substance includes corpuscles of an altogether different nature. These corpuscles, in size and staining power, resemble the cell nucleus or parts thereof, and as a matter of fact are derived from the cell nucleus. Balbiani has called such bodies in the ovum cell 'paranuclei^ and Griitzner has applied the same term to those that occur in the gland cells of the pancreas. Now it is a fact that preceding the segmentation of the ovum, and preceding the fusion of the sperm- and ovum-pronucleus, part of this latter is eliminated, and the same occasionally is observed to take place in other cells prior to the division of the nucleus, as also under various pathological conditions. The eliminated body or bodies, known as polar bodies, are part of the original nuclear substance, principally the chromatin. The paranucleus is as a rule smaller than the cell nucleus, lies close to this, and has similar affinit}'' to the dyes which stain the nucleus itself. 19 CHAPTER IT. BLOOD. 9. Under the microscope blood appears as a transparent Huid, the liquor sanguinis or plasina, in which float vast numl^ers of formed bodies, the blood corpuscles. The great majority of these are coloured ; a few of them are colourless. The latter are called ivhite or colourless blood corpuscles, or leucocytes ; the former are called red or coloured blood coryuscles, or blood-discs. They appear red only when seen in a thick layer ; when in a single layer they appear of a yellow-greenish colour, more yellow if of arterial, more green if of venous, blood. The proportions of plasma and blood corpuscles are sixty-four of the former and thirty-six of the latter in one hundred volumes of blood. By measurement it has been found that there are a little over five millions of blood cor- puscles in each cubic millimetre {y-^^o^y of ^ cubic inch) of human blood. There appears to be in healthy human blood, on an average, one white corpuscle for 600-1200 red ones. In man and mammals the re- lative number of blood corpuscles is greater than in birds, and in birds greater than in lower verte- brates. The number of red, and also of white, corpuscles is subject to variation, both in health and disease. After profuse haemorrhage, the number of red cor- puscles is temporarily greatly reduced, but in a short time, it may be even in twenty-four to forty-eight hours, they may approach again the normal number ; 2o Elemexts of Histology. in constitutional chronic diseases the number of red corpuscles is, as a rale, decreased ; so also in anj^mia, spontaneous or following acute infectious diseases, fevers, etc. The number of white corpuscles is always greater after a copious meal than during fasting. Certain diseases are associated with a decrease, others wi.th an increase, of the white corpuscles of the cir- culating blood ; the decrease when pronounced is spoken of as leucopenia^ the increase as leucocy- th(emia^ leucctmia, or leucocytosis. 10. The red blood corpuscles (Fig. 13) of man and mammals are homogeneous bi-concave discs (ex- cept in the camelida?, where they are elliptical), and do not possess any surroundmg membrane or nucleus. Being bi-concave in shape, they are thinner and more transparent in the centre than at the periphery. In other vertebrates they are oval, and more or less flattened from side to side, and each possesses a central oval nucleus. The diameter of Fig. 13. — ^arious kiuds of Red Blood i , i i i i Corpuscles. the human red blood A, Two human, one seen flat, the other COrpUScle is about edgeways ; b, a red corpuscle of the ■■ p " 1 ' camel; c, two red corpuscles of the solTo '^^^ mCll 111 frog, one seen from the liroad, the \ ■\,\ ■ i , other from the narrow side. DreaCltn, I.e. aOOUt 7 "8 ^. and its thick- ness about ^ ^QQQ of an inch. But there are always corpuscles present which are much smaller by about one-third to one-half than the others — microcytes. In normal blood these microcytes are scarce : but in certain abnormal conditions, especially in pernicious anfemia, they are conspicuous by their number. According to Gulliver, ^A'elcker, and others, tlie followinof are the averagfe diameters of the red blood corpuscles of various vertebrates : Man, -3-2V0 J ^^i 08 A "3 'sou ' ^"^j 4cFo^ y outc|7, 5 00^ } v.iv>^jii«.ij.v, :jTi 5" ^ 1 • cat, ^ J^ ; sheep, ^^W i elephant, Blood. 21 horse, j:^ 1 \ . 6 () O ' 10 4 3 ; "ewt, 1 1 1 -t 2 • 11 musk deer, y^i^ 5 ; pigeon, ^g^y ; toad, proteus, yl^ ; pike, ^-qVo ; ^li^^i'k, 1^ S 1 i In a microscopic specimen of fresh unaltered blood (Fig. 14) the red blood corpuscles form peculiar short or long rolls, like so many coins, from be- coming adherent to one another by their broad surfaces. Under various conditions — such as Avhen isolated, or when blood is diluted with a 7*5-l p.c. saUne solution or solutions of other salts (sulphate of sodium or magnesium) — the cor- puscles lose their smooth ^• circular outline, shrink- ing and becoming crenate (Fig. 15, a). In a further lose their discoid form, and become spherical, but beset all over their sur- face with minute processes. This shape is called the liorse-chestnut shaj^e (Fig. 15, b, c). It is probably due to the cor- puscles losing carbonic acid, as the addition of the acid brings back their discoid shape and smooth circular out- line. On abstracting the carbonic acid they return to the horse-chestnut shaj)e. , Water, acid, alcohol, ether, the electric current, and many other reagents, produce decoloration of the red blood Fig. 14. — Human Blood, fresh. Piouleaux of red corpuscles ; b, iso- lated red fdrpuscle seen in pr<5flle ; c, isolated red corpuscle seen flat ; D, •ttliite corpuscles. stage of shrinking smaller they and a o o Fi h ^' 15. — Human Red Blood Corpuscles. Crenate; b, c, horse-cbestnut- sliaped. corpuscles. the coloured matter — generally the combination of the blood-colouring matter with globulin, known as hcenioylohin — becoming dissolved in the plasma. 2 2 Elements of Histology. What is left of the corpuscles is called the stroma. In ne^^i;'s and frog's blood a separation of the stroma from the nucleus and haemoglobin can be effected by means of ^ ^ a'^ ^c^ boracic acid(Fig. 16, b); " Ai. ^i \^' ^8 ^F\ c ^^^^ former is called by O ^ {€^) Briicke the oekoid, the U^ B latter zooid. This stroma contains amongst other Fig. IG.— Red Blood Corpuscles of things mucll paraf'lobu- Man and Xewt. t mi j. c J.^ , ^ ^, . im. I he stroma or the A, Human red corpuscles after the action , i -i • of tannic acid; a, tbree red corpuscles, COrDUSCles Ot amplllljiaUS from which the hierauf^loliin is pass- . ■•■ •'• ing out: 5. Roberts's corpuscles. B, is scen, undcr Certain ^ewt s red corpusdesafter theaction ' of boracic acid; a, corpuscle. show- reao^ents, to be of a re- mg Briicke s zooid and cekoid ;&,."' corpuscle showing the reticulated tlCUlated StrUCture, but stroma ; c, corpuscle showins the • ^ c i reticulum in the nucleus; d, thenu- ]n the fresh state appears cleus passing out. ^^ homogeneous and pale. Decoloration of the blood corpuscles can also be observed to take place in blood spontaneously without the addition of any reagents or with that of indifferent fluids, such as the aqueous humour of the eye, hydro- cele fluid, etc. The number of corpuscles undergoing decoloration under these conditions is, however, small, When blood is dried on a glass in a thin tilm, the corpuscles, forming a single layer onh", dr}^ on before they shrink, and thus retain their natural size and outline ; their strouia can then be easily stained with aniline dyes. 12. The haeiiioglotoiii of the red blood cor- puscles forms crystals (Fig. 17), which differ in shape in various mammals. They are always of microscopic size, and of a bright red colour. In man and most mammals they are of the shape of prismatic needles or rhombic plates ; in the squirrel they are hexagonal plates, and in the guinea-pig they are tetrahedral or octahedral. The blood pigment itself is an amorphous dark- Blood. 23 brown or l)l;ick powder — the luematin ; but it can be obtained in a crystalline form, as liydrochlorate of hi\iinatin (Fig. 18). These crystals also are of micro- scopic size, of a nut-brown colour, of the shape of nari'ow rhombic plates, and are called lut^rnin cry- stals, or Teich- mann^s crystals. In extravasated hu- man blood, crystals of a bright yellow or orange colour are occasionally met with ; they are coverer, hctmatoidin. tical with bilirubin human bile. 13. The white or colourless cor- puscles, or leucocytes, are in human blood of about 2-5 00 ^^ 2"5Vo *^^ ^^ ^^^^ in diameter — i e. about 10 fi — and are spherical in the circulating blood or in blood that has just been removed from the vessels. Their substance is transparent granular-looking protoplasm, some containing larger or smaller distinct granules. These granules are not all of the same nature, as will presently appear. In some kinds of blood, notably horse's, they are of a reddish colour, and these corpuscles were supposed by some observers (Semmer and Alexander Schmidt) to be intermediate between red and white corpuscles. The protoplasm of the colourless corpuscles contains occasionally glycogen (Ranvier, Schiifer). In the blood of the lower verte- brates the colourless corpuscles are much larger than Fig. 17. — Hitmoglobin crystals. A, Of guinea-pig ; b, of siiuirrel ; c, D, buiuan. called by Yirchow, their dis- They are supposed to be iden- obtainable from Fig. IS.— Ha-miii crystals. 24 Elements of Histology. in mammals. But in all cases tliey consist of proto- plasm (spongioplasm and hyaloplasm), include one, two, or more nuclei, and show amoeboid movement. This may he observed in corpuscles without any addition to a fresh microscopic specimen of blood, but it always becomes much more jironounced on Fig. 19. —Phagocyte (with three nuclei) from the iieritoneal fluid of a guinea-pig, iireviously injected intraperitoneally with cholera culture. The interior of the phagocyte contains numerous degenerated comma bacilli. (Photo, highly magnified.) applying artificial heat of about the degree of mammals' blood. It is then seen that either they throw out longer or shorter filamentous processes, which may gradually lengthen or be withdrawn, or the corpuscle changes its position either by a flowing movement, or it pushes out a filamentous pro- cess and shifts its body into it. During this move- ment the corpuscle may take up granules from the Blood. 25 siuToiinding lluicl. Leucocytes, be they in the blood or in connective tissue or lymph glands {see below), that can, and in certain circumstances do, take up granules or similar matter are spoken of as phagocytes (eating cells) (Figs. 19, 20). Division by simple ^ Fig. 20. — Hyaline Leucocytes (pus cells) from purulent matter ; the leuco- cytes contain in their hyaline protoplasm two, three, or more nuclei two of the cells contain in their protoplasm a number of cocci, these cells acting as phagocytes. {Photo, highly magnified.) cleavage of leucocytes of the blood of lower verte- brates has been directly observed by Klein and Ranvier. 14. The white corpuscles or leucocytes in the same sample of blood differ in size and aspect. They may be classed into three groups : (a) The li/m2)hocyte, 2 6 Elements of Histology. a small cell possessed of a relatively large single nucleus surrounded by a narrow zone of protoj^lasm. (6) The typical leucocyte or liyaline leucocyte is larger than the former, contains two, three, or even four relatively small nuclei ; its cell protoplasm appears hyaline, but includes a spongy network. This leucocyte is Fig. "21. — Frog's Blood, showing red blood discs and one oxypliile white cell. (Photo, highly magnified.) as regards numbers by far the predominating white corpuscle, and its amceboid movement is very striking, (c) The gramdar leucocyte forms a small minority, it contains a single large nucleus, occasionally two, and its cell })rotoplasm contains conspicuous granules. The lymphocytes are identical with similar cor- puscles of the adenoid tissue of lymph glands, from Blood. 27 Nvliicli ill all probability they are derived. It is highly probable that they are young forms of the typical leucocytes. The grnnidar leucocytes — i.e. the white corpuscles that contain real gi'anules — behave dif- ferently when subjected to staining with aniline dyes. In some the granules stain readily with acid aniline dyes — e.g. eosin — so that they become bright red — eosinophile (Ehrlich) or o.vi/phile cells (Fig. 21); in others the granules stain only in basic aniline dyes — hasopJi He cells ; in still others they stain both with acid and alkaline aniline dyes — neutrophile or amjjho- phile. "What the exact relation of these different granule-cells amongst themselves and to the non- granular or hyaline cells is, is not definitely established. But it appears from the researches of Kanthack and Hardy that in the frog, at any rate, and probably also in the mammal, the oxyphile or eosinophile leucocyte does not act as a phagocyte, and that this function is mo- nopolised by the other or hyaline variety of leucocytes. 15. In every microscopic specimen of the blood of man and mammals are found a variable number of large granules, more or less angular, singly or in groups. According to f^ Max Schultze they are derivatives of e^\ broken-up white corpuscles ; but ac- ^S ^^ cording to Bizzozero, they are present ^ al read}' in the living and fresh blood, © o^ as pale, circular, or sliijhtly oval „. ,., „ T-i- ->-» 7\ rriiiii ; stratum luciduiii ; d, the stratum corneum. Laiiger- less flattened and more polyhed r al , and the deepest form a layer of more or less columnar cells, placed verti- cally on the surface of the subjacent co- rium. The sub- stance of the hairs, nails, claws, hoofs, consists of horny scales. {See chapter on Skin.) 22. The pavement liiiiii (Fig. Fig. 26. — From a Vertical Section tliroiigh the anterior layers of tlie Cornea. (Handbook.) a. The stratified pavement eiiithelium; b, the substantia propria, with the corneal corpuscles between its la- melht. Stratified epitlie- 26) lining the cavity of the mouth, the surface of the tongue, the pharynx and oeso- phagus of man and mam- mals, and the anterior surface of the cornea, etc., is, as regards tlie style and arrangement of the cells, identical with the stratum Mal- pighii of the epidermis. The cell protoplasm is more transparent in the former, and the granular cells of the stratum Epithelium. 35 granulosum are not always present, but they generally are in the e})itheliiini of the tongue and of the rest of the oral ca^•ity. The most superficial scales show more or less horny transformation. 23. Stratified roliiiiiiiai' €>|>itiic'iiiini is met with on the lining Hi('iiil)iane of the respiratory organs : in the larynx, trachea, and large bronchi. It consists of several layers of columnar cells ; a superficial layer of conical or prismatic cells, with a more or less pointed extremity directed towards the depth ; between these are inserted spindle-shaped cells, and finally inverted conical cells. The epithelium of the ureter and bladder is called transitional epitheUum. It is stratified, and the most superficial layer consists of j^olyhedral cells. Under- neath this is a layer of club-shaped cells, between which extend one or more layers of small spindle- shaped cells. Amongst the columnar epithelial cells occurring in man and mammals the ciliated cells and the gohlet cells, and amongst the squamous cells the jirickle cells, deserve special notice. 24. Ciliated cells are characterised by possess- ing a bundle of very fine longer or shorter hairs or cilia on their free surface. These cilia are direct prolongations of the cell protoplasm. More correctly speaking, the cilia are continuous with the filaments or striye of the cell protoplasm. The superficial layer of conical cells of the epithelium in the respira- tory organs, the columnar cells lining the uterur, and oviduct, and the columnar cells lining the tubes of the epididymis, possess such cilia. In lower verte- brates the ciliated cells are much more frequently observed ; in Batrachia the epithelial cells lining the mouth, pharynx, and (esophagus are ciliated. While fresh in contact with the membrane which they line, or even after removal from it, provided the 36 Elements of Histology. cells are still alive, the ciliated cells show a rapid synchronous whip-like movement of their cilia, the cilia of all cells moving in the same direction. The movement ceases on the death of the cell, but may become slower and may cease owing to other causes than death, such as coagulation of mucus on the surface, want of sufficient oxygen, presence of car- bonic acid, low temperature, etc. In these circum- stances, removal of the impediment, as by dilute alkalies, wdll generall}^ restore the activity of the cilia. Moderate electric currents and heat stimu- late the movement, strong electric currents and cold retard it. Reagents fatally affecting cell protoplasm also stop permanently the ciliary action. 25. CjJoblet or clialice cells (Figs. 24, 27) are cells of the shape of a conical cup. The pointed part is directed away from the free surface, and contains a compressed triangular nucleus surrounded by a trace of protoplasm. The body of the =^="^-='^-%nn goblet contains mucus. This latter P|'| -P< £' ^ -^' - J ^i"*^! ^^ ^^ various states of for- ^llim^^^ mation, and may at any time be Fig. 27.— From a Ver- poured out of the cell. Goblet tical Section throucrh n , i j. •-! the Epithelium on cclls are most commonlv met with the surface of the amon^jst the epithelium lining the mucous membrane . ^ ^ , , ^ ^ of the large intes- respiratory Organs, the surface 01 ^'"^* the stomach and intestines, and Three goblet cells are • n • i t • seenpourin^'oiit their especiallv HI mucous glands, m luucus. TliG r6st urt* "^ . . ordinary coiiuunar whose secretiuo- portion all cells cells. ® '- are goblet cells. The protoplasm of columnar cells facing a free surface, no matter whether in simple or stratified epithelium, ciliated or non-ciliated, may undergo such alteration as will lead to the transformation of the cell into a mucus-secretinfj goblet cell. This takes place during life, and corresjDonds to an im- portant function of columnar ejDithelial cells — viz. Epithelium. 37 the formation of iniicus. In mucus-secreting glands all the epithelial cells have this function permanently, but in ordinary columnar epithelium only a compara- tively small number of the cells, as a rule, undergo this change, and then only temporarily : for a cell subject to it at one time may shorth^ afterwards resume the original shape and aspect of an ordinary protoplasmic, cylindrical, or conical epithelial cell, and vice versa. If ciliyted cells undergo this change, the cilia are generally first detached. It can be shown that in this change of an ordinary columnar epithelial cell into a goblet cell the interstitial substance of the cell reticulum swells up and increases in amount, the meshes enlarging and distending the body of the cell. The middle and upper part of the cells then change, tirst into mucigen, and hnally into mucin, which is eventually discharged, leaving in the deeper part the compressed nucleus surrounded by a trace of protoplasm behind (see Fig. 34). 2G. Prickle cells (Fig. 25). — Amongst the middle and deeper la3^ers of the stratified pavement epithelium, such as is present in the epidermis and on the surface of the oral cavity and pharynx, we meet with a close, more or less distinct and regular striation, extending from the margin of one cell to that of each of its neighbours, by means of fine transverse short fibrils which, passing from proto- plasm to ])rotoplasm, connect the surfaces of the cells. 27. Pigmented epithelial cells — i.e. epithelial cells filled with black pigment pai'ticles (crystals) — are found on the internal surface of the choroid and iris of the eyeball. In coloured skins, and in coloured patches of skin and mucous membrane, such as occur in man and animals, pigment in the shape of dark granules is found in the protoplasm of the deeper epithelial cells, as well 38 Elements of Histology. as in branched cells situated between the epithelial cells of the deeper layers. Minute branched non- pig mented nucleated cells are met with in the interstitial or cement substance of various kinds of epithelium, simple and stratified — e.g. epidermis, epithelium of oral cavit}', cornea, etc. 28. Epitlielial cells undergo division, and by this means a constant regeneration takes place. In those parts where the loss of the superficial layers of cells is conspicuous, such as the epidermis, the stratified epi- thelium of the tongue and oral cavity, the sebaceous follicles of hairs, the regeneration goes on more copiously than at places where no such conspicuous loss occurs — as, for instance, in the stomach and in- testines, the secreting glands, or sense organs. In the stratified pavement epithelium it is the cells of the deepest layers which chiefly divide. As a rule, this division takes place transversely in the cylindrical cells, but may also occur longitudinally (A. Kollmann). The epithelial cells next to the deepest layer of columnar cells are to a great extent the result of the division of the latter, and as this proceeds there is a orradual shiftino; of the older cells towards the surface and a simultaneous flattening of the cell protoplasm as well as the nucleus. 29. The interstitial substance between, and the protoplasm of, the epithelial cells being a soft flexible material, the cells can change their shape and arrange- ment owing to pressure exerted on them by the con- traction or distension of the subjacent membrane. Thus the epithelium lining a middle-sized bronchus at one time apjDears composed of thin columnar cells in two layers ; at another, as a single layer ; or again, as a single layer of short columnar cells : in the first case the bronchus ig contracted, in the second in a medium state of distension, in the third much dis- tended. Similar changes may be noticed in the Epithelium. 39 epithelium lining tlu^ bladder and the, stratum Malpighii. The interstitial substance, being a soft, semi-fluid substance, represents the paths through whicli granules and formed particles may find their way from the free surface into the membrane beneath, or vice versa. Also leucocytes pass out in certain localities from the membrane underneath, between and into the sul)stance of epithelial cells, and may Anally be discharged on to the free surface — e.g. in the tonsils, in the fauces and pharynx and larynx. Epithelial cells may in this way include in tlieir substance various formed particles : granules, fat globules, leucocytes, nuclei of leucocytes, etc. Besides these cell enclosures and the paranuclei and chromatin granules mentioned in a former para- graph, in some localities [e.g. stratum Malpighii of the ef)idermis, epithelium of the oral cavity, pharynx and oesophagus) the epithelial cell substance undergoes a partial or total change into keratinous substance, keratohyalin, forming a mantle around the unchanged cell j)rotoplasm like a capsule. 40 CHAPTER lY ENDOTHELIUM. 30. The free surfaces of the serous and synovial membranes, and of those of the brain and spinal cord, the posterior surface of the cornea and anterior surface of the iris, the surfaces of tendon and tendon- sheaths, the lymph sinuses or lymph sacs of amphibian animals, the cavity of the heart, of blood-vessels and of lymphatic vessels, are lined with a continuous endothelial membrane, composed of a single layer of flattened trans- jjarent squamous cells, called endo- thelial cells (Fig. 28). Each contains an oval nucleus, situated as a rule excentrically. Just as in Fig 28 -Endothelium the case of epithelium, " the endo- of the Mesentery of ■,■,•■> n i ■ • Cat. thelial cell plates are joined by a The outlines of the endo- fluid or semi-fluid liomoifeneous in- thehal cells and tlie • • 7 7 nucleus of the latter terstitiat or Cement substance or the are well shown. „ , , , . nature oi globulin. \\ hen examin- ing any of the above structures fresh, the endothelial cells are not, as a rule, visible, owing to their great transparency; but by staining the structures with a dilute solution of nitrate of silver, and then exposing them to the influence of the light, the cement sub- stance appears stained black, whereby the shape and size of the cell plates become e^■ident. By various dyes also the nucleus of each cell plate may be brought into view. On careful examination, and with suitable re- agents, it can be shown that each endothelial cell En DO THELIUM. 41 consists of a homogeneous ground 'plate. Tii it lies tlie nucleus, and around it is a sul)staiicf* which ap- pears granular, but ^vhich is of a fibrillar nature, the fibril he being arranged in a network, and extending Fig. 20.— Network of Lymphatics in the Central Teudon of the Diaphragm of Rabbit, prepared with nitrate of silver, so as to show the outlines of the Endothelial Cells formiug the wall of the Lymphatics. {Handbook.) a. Large I^-mphatic vessels; b, Ivinphatic capillaries ; c, apparent ends of the capillaries. in many places up to the margin of the ground plate. The nucleus is limited by a membrane, and contains a well-developed reticulum. The tibrillje of the cell substance appear to be connected with the nuclear reticulum. 31. As regards shape, endothelial cells differ considerably. Those of the pleura, pericardium, peri- toneum, and endocardium of man and mammals are 42 Elemexts of Histology. more or less polygonal, or slightly elongated. Their outlines vary ; in the lining of the lymph sacs of the frog they are much larger, and of very sinuous out- line ; while those of the posterior surface of the cornea Fig. 30. — Onientum of Rabbit, stained with Nitrate of Silver. {Atlo.s.) (I. Ordiuaiy flat endothelial cells ; b, germinating cells. are very regular, pentagonal, or hexagonal, ha^^Ilg straight outlines in the perfectly normal and well-pre- served condition, but serrated and sinuous after they have been prepared with various reagents and in the abnormal state ; the endothelial plates lining the blood- vessels and lymphatic vessels (Fig. 29) are narrow and elongated, with more or less sinuous outlines. In the lymphatic capillaries the endothelial plates are polygonal, but their outline is serrated. 32. As a rule, the endothelial cells are flattened — - Endothelium. 4: i.e. scaly — but in some places they are polyhedral, or even short columnar. Such cells occur isolated or in small gi'oups, or covering large and small patches, nodular, \illous, or cord-like structures of the pleura Fig. 31.— Part of Peritoneal Surface of the Central Tendon of Diaphragm of Rabbit, prepared with Nitrate of Silver. (Handbook.) s, StoniRta; Z, lymph-channe!s ; f, tendon Inindles. The surface is covered witli endothelium.' The stomata are surrounded by geruunatiug endi)thelial cells. and omentum, on the synovial membranes, tunica vaginalis, testis, etc. They are especially observable in considerable numbers in the pleura and omentum (Fig. 30) of all normal subjects (in man, ape, dog, cat, and rodent animals) ; their number and frequency of occurrence are increased in pathological conditions (chronic inflammations, tuberculosis, cancer, etc.). These endothelial cells are tlie germinating endo- thelial cells, and they can be shown to be in an 44 Elements of Histology. active state of division. They thus produce small spherical lymphoid (amoeboid) cells, which ultimately are absorbed by the lymphatics, and carried into the blood system as white 1)1 ood corjiuscles. On the Fi.£ -Part of Omentum of Cat, stained with Nitrate of Silver. a, Feuestraj or holes ; />, tianecultB covert-a witli emloilielium. Ouiy tiie outliues (silver lines) of the endothelial cells are shown. surface of the serous membranes, especially the diaphragm (Fig. 31) and pleura, there exist minute openings, stomata, leading from the serous cavity into a lymphatic vessel of the serous membrane. These stomata are often lined by germinating cells. 33. In the frog, germinating cells occur in great abundance on the mesogastrium and the part of the peritoneum which separates the ])eritoneal cavity from the cisterna lymphatica magna. This part of Endothelium. 45 the peritoneum is called the septum cisternae lym- phaticji? magnsB, and on it occur numerous holes or stomata, by which a free communication is established between the two cavities. On the peritoneal surface of this septum the stomata are often bordered by germinating cells. In th(^ female frog, these and other germinating endothelial cells of the peritoneum (mesogastrium, mesenterium, septum cisternee) are ciliated. 34. The omentum and parts of the pleura are, in the adult human subject, ape, dog, cat, guinea-pig, rat, etc., of the nature of di. fenestrated membrane {¥\g. 32), bands of fibrous tissue of various sizes dividing and reuniting, and leaving between them larger or smaller holes, in shape oblong or circular. These holes or fenestras are not covered with anything, the endo- thelial cells adhering only to the surfaces of the bands without bridging over the fenestrse. On the peritoneal surface of the diaphragm the endothelial cells possess a different arrangement from that on the pleural side ; on the former surface a number of lymph channels (that is, clefts between the bundles of tendon and muscle) radiate towards the middle of the central tendon. The endothelium of the free surface over these lymph channels is composed of much smaller cells than at the places between, so that the endothelium of the peritoneal surface of the diaphragm shows numbers of radiating streaks of small endothelial cells. Many of these small cells are not flattened, but polyhedral, and of the nature of germinating cells (Fig. 31). The above-mentioned stomata occur amongst these small endothelial cells. 46 CHAPTER Y. FIBROUS CONNECTIVE TISSUES. 35. By the name of " connective tissues " we designate a variety of tissues which have in common with one another, that they are developed from the same embryonic elements ; that they all serve as sup- porting tissue or connecting substance, for nervous, muscular, glandular, and vascular tissues ; that they are capable of taking one another's place in the different classes of animals ; that in the embryo and in the growing normal and morbid condition one may be changed into the other ; that in the adult they gradually shade off one into the other ; and that they yield allied chemical products. Connective tissues are divided into the three great groups of (1) fibrous connective tissue; (2) cartilage; (3) bone, to which may be added dentine. Each of these is subdivided into several varieties, as will appear farther on ; but in all instances the ground substance, or matrix, or intercellular substance, is to be distinguished from tJie cells. In the fibrous con- nective tissue the matrix yields collagen or gelatin, and the cells are called connective-tissue cells, or con- nective-tissue corpuscles. In the cartilage the ground substance yields chonclrin, and the cells are called cartilage cells. In the third group the ground sub- stance contains inorganic lime salts, intimately con- nected with a fibrous matrix, and the cells are called hone cells. 36. The fibrous coiiiiertivc tissue, or white fibrous tissue, occurs in the skin and mucous Fibrous Connective Tissues. Al membranes, in tlie serous and synovial membranes, in tlie membranes of the brain and spinal cord, in tendons and tendon sheaths, in fascite and aponeuroses, in the intermuscuhir tissue, and in the tissue con- nectino; neiirhbourim'- organs, etc. It consists of microscopic band-like or cylindrical bundles or fasciculi of exceedingly tine homogeiuous tinrils (Fig. 33), which Fig. 33. — Plexus of Bundles of Fibrous Tissue from the Oiuentuiu of Rat. «, Capillary blood-v'cSi'cl ; ^, lumiilc:^ nr Hijidhs tissue ; c tue oouuectivc-tiiiu.: foi'iuiscles; c/, i)lasiii i ceils. {Atlas.) are known as the elementary connective-tissue fibrils. According to the number of these the bundles differ in size. The bundles, and also their constituent fibrils, may be of very great length — several inches. Where the fibrous tissue forms continuous masses — as in tendon, fascia, aponeurosis, skin, and mucous membrane — the microscoj)ic bundles are aggregated into smaller or larger groups, the trabeciilce., and these are again associated into groups. The fibrils are held together by an albuminous (globulin), semi-fluid, homogeneous cement substance^ which is also present between the bundles forming a trabecula. 48 Elements of Histology. The groups of bundles, and even the individual bundles, are in some localities invested with an elastic sheath — e.g. in the trabeculae of bundles in the subcutaneous tissue. On addincj an acid or an alkali to a bundle of fibrous tissue, it is seen to swell up and to become glassy-looking, homogeneous, and gelatinous. Sub- jected to boiling in water, or to digestion by dilute acids, the bundles of tibrous tissue vield collacjen or gelatin. 37. According to the arrangement of the bundles, the fibrous connective tissue varies in ditierent locali- ties. (1) In tendons and fasciae the bundles are arranged j^arallel to one another. (2) In the true skin and mucous, serous, and synovial membranes, in the dura mater and tendon sheaths, the trabeculse of bundles divide repeatedly, cross and interlace very intimately with one another, so that thereby a dense felt-work is produced. (3) In the subcutaneous, sub- mucous, or subserous tissue, in the intermuscular tissue, in the tissue connecting with one another different organs or parts of the same organ — i.e. inter- stitial connective tissue— the texture of the tibrous tissue is more or less loose, the trabecul^e dividing and reuniting and crossing one another, but leaving between them larger or smaller spaces, celluhe or areola?, so that the tissue assumes the character of a loose plexus, which is sometimes called " areolar " or " cel- lular tissue." Such tissue can be more or less easily separated into larger or smaller lamelhie, or plates of trabecul^e. (4) In the omentum and parts of the pleura of man, ape, dog, cat, and some rodents, and in the subarachnoidal tissue of the spinal cord and brain, the trabecule form a fenestrated membrane, with larger or smaller oval or circular holes or fenestra?. 38. The eoiiiiective -tissue cells or corpuscles occurring in white fibrous tissue are of several F/niwus C(hxXECTn'E T/ssu/:s. 49 varieties, {a) lii teiulon and faseiie tlie cells ai<' called tendon cells or tendon corpuscles ; they are flattened ^-3^^ Fig. 34.— Tendon of Mouses Tail. (£. A. Schu/er.) a, Chains of tendon-celJ!? seen broadways ; b, the same in profile. nucleated protoplasmic cells of a square or oblong shape (Fig. 34), forming continuous rows (single files), situated on the surface of groups of bundles of fibrous tissue. Between these groups are wider or narrower channels, the in- t erf CISC i culn r lymph spaces, running parallel with the long axis of the ten- don (Fig. 35). The cells in each row are separ- ated from one another by a nar- row line of allju- minous cement substance, and the round nucleus of the cell is generally situated at one end, in such a Fig. 3.J. — From a Transveix- Section through the Tendons of tlie Tail of a Mouse, stained with gold chloride. {Handbook.) Several fine tendons are shown here. The darfe branched corpnseies correspond to albuminous cement substance stained with srold chloride; they are the channels between the bundles of fibrous tissue, constituting,' the tendon, and seen here as the clear spaces in cross section. In each of these channels is a row of tendon cells— not discernible here, the Ion? axis of these rows beins parallel with the long axis of the tendon. ^o Elemexts of Histology. Fig. 36.— From the Tail of a Tadpole. c. Branched coDnective tissue cells ; m, a migratory cell. (Atlas^ way that in two adjacent cells of the growing tendon the nuclei face each other. This indicates that the individual cells undergo division. Corresponding to the martjin of each row, the cells j;>ossess minute processes. The cell plate is not quite riat, Ijut possessed of one, two, or even three membranous pro- jections l)y which it is wedged in between the individual bundles of the group to which the row of cells belongs. 39, (fe) In the serous meuibranes, cornea, subcu- taneous tissue, and loose connective tissues, the cells are flattened transparent cor- puscles, eac-li witli an oblong flattened nucleus, and more or less branched and connected by tlifir processes. In the cornea they are spoken of as the corneal corpuscles, and are ver}' richly branched (Fig. 37). They are situated between the lamellae of fibrous bundles of which the ground substance of the cornea consists. These corpuscles are also situated in the interfascicular lymph spaces, or spaces left between the bundles of the fibrous matrix, which are cavi- ties in the interstitial cement, cementing tlie Imndles and trabecuke together (von Recklinghausen). In the cornea and serous mem- branes these spaces possess the shape of branched Fig. 37. — Fi-om the Cornea of Kitten, showing the Networks of the Branched Corneal Corpuscles. a. The network of their pro- cesses ; b, nucleus of the corpuscle. (Atla^.') Fibrous Conxecth'e Tissues. 51 lymph V laciinne, eacli lacuna being the home of the body of the cell, while the branches or canaliculi contain its processes. These canaliculi form the channels by which neighbouring lacuna? anastomose with one another (Fig. 38). The cell and its processes do not fill up the lacuna and its canaliculi, but are bathed in the paraplasma or fluid contained in the canal system. In loose connective tis- v^^':m^'''"'^'m sue the lacuna may " ^ '^ be of considerable 7 size, and may contain several connective cells, which make as it were a lining for it. These in some places are very little branched, and almost form a continuous endotheloid mem- brane of flattened cells. Such is the subepithelial endotJie- lium ofDehove, occur- ring underneath the epithelium on the surface of the mucous membrane of the bronchi, bladder, and intestines. 40. (c) In the true skin and mucous membranes the connecti^'e-tissue cells are also branched flattened corpuscles, and by their longer or shorter processes are connected into a network (Fig. 36). Each cell has a flattened oblong nucleus. As a rule, some of the processes are membranous prolongations coming ofl" under an angle from the body of the cell, which is then called the chief plate, the processes being the secondarv plates. By the latter the cell is g. 38.— From the Cornea of Kitten, stained with Nitrate of Silver, show- ing the Lymph-canal System. fl. The lacuna?, each containiugthe nucleated cell-body just indicated here; b, the canaliculi for the cell procer^ses. (Atlas.') 52 Klemexts of Histology. wedged in between the bundles of the trabecula to which it belongs. This character of the cells (i.e. possession of secondary j)lates) is well shown Ijy the cells of the skin and mucous membranes, but only in a very limited degree by those of the cornea and serous mem- branes, and somewhat better by some of those of the subcutaneous and other loose connective tissues. In the skin and mucous membranes also the cells and their processes are bathed in the paraplasma contained in the interfascicular lymph spaces. 41. The connective - tissue corpuscles hitherto mentioned are fixed corpuscles : they do not show movement. Kiihne and Rollett ascriVje to the corneal corpuscles a certain amount of contractility, inasmuch as they are said to be capable of withdrawing their processes on stimulation. When this ceases they are said again to protrude them. According to Strieker and Norris, they acquire contractility when the corneal tissue is the seat of inflammatory irritation. It can be shown that the connective- tissue cells consist, like the endothelial plates, of a ground plate and a fibrillar reticulated (granular- looking) substance around the nucleus, and extending beyond the ground plate into the proces.ses of the cell. 42. Pigment cells. — In the cold-blooded verte- brates, fishes, reptiles, and amphibian animals, we find certain branched nucleated connective-tissue cor- puscles, distinguished by their size and by the proto- plasm both of the cell-body and processes (but not of the nucleus) being filled with pigment granules. The pigment is either grey or yellow, or more commonly dark brown, or even black. These cells are called pig- mented connective-tissue cells, or simply inijinent cells. They are very numerous in the skin of fishes, reptiles, and amphibian animals, and also around and between Fibrous Connective Tissues. 53 the blood-vessels of the serous membranes. They are also present in man and mammals, but then they are chieriy linuted to the eye-ball, where they occur in the Fig. 89,— Pigment Cells of the Tail of Tadpole. A, B, c, D represent variims states ; a heinar a cell in an uncontracted or passive stati'. D in a contracied or active state. proper tissue of the iris of all but albino and bright blue eyes, and in the tissue of the choroid membrane. In dark eyes of mammals a large number of these cells are found in the tissue between the sclerotic and choroid, as the lamina fusca, and also, but to a more 54 Elemexts of Histology. limited degree, in the sclerotic. As a rule, they appear to be of various kinds : sucli as are flattened, large plates perforated l>y a number of small and large holes and minute clefts : such as possess a more spindle- shaped liudy. and loni'. thin, not very richly branched processes : and intermediate forms between the two. But on careful examination it will be seen that these appearances are due to different .states of contraction of the same kind of cells (Fig. 39). 43. In the lower vertebrates the dark pigment cells show marked contractility, ina^mucli as they are capable of altogether withdrawing into their body the pigmented processes. Tn the passive state these are exceedino'lv numerous, anrl form a network so dense that the whole mass of the cells and their paraplasma resembles an extremely close network of pigment. In tlie maximum of activity the pigmented processes disappear, being withdrawn into the cell-body, which now looks like a spherical or oblong mass of black pigment. Between the states of passiveness and maximum activity there are various intermediate grades, in which the pigmented processes are of various numbers and lengths. 41. Owing to the great number of the pigment cells in the skin of fishes and amphibians, the state of contraction of these cells materially affects the colour of the skin. If the dark pigment cells of a particular part contract, the skin of this jiarticular part will 1)ecome lighter and brighter, the degree of liijhtness and brightness depending on the degree of contraction of the pigmented processes by the cells. Briicke has shown that darkne.ss is a stimulus to the pigmented cells : they contract and the skin becomes lifdit. Sunlidit leaves the piomented cells in the pas.sive state, their pigmented processes numerous and well branched, and the skin appears therefore of a darker colour. If previously they have been Fibrous Coxnective Tissues. 55 contracted by darkness, on being exposed to sunlight they again return to tlie passive state. Tlie contrac- tion of the pigment cells is under the direct influence of the nervous system (Lister). Pouchet proved that the contractility of the pigment cells of the skin of certain fishes is intiuenced as a reflex action by the stimulation of the retina by light. 45. Fat cells. — Fat cells in the ripe and fully-formed state are spherical, large vesicles, each Fig. 40. — From a Preparation of the Omentum of Guiuea-pig. {Atlas.) a, Artery ; v, vein ; c, young capillary lilooil-vesriel ; d, fat ceils?. consisting {a) of a thin protoplasmic membrane, which at one point includes an oval nucleus flattened from side to side, and (/>) of a substance, which is a fat globule filling the cavity of the vesicle (Fig. 40). These fat cells are collected together by fibrous connective tissue into smaller or larger groups, which in their turn form lobules ; these again form by means of thicker masses of fibrous connective-tissue lohes, and these are finally arranged as continuous masses. Each group and lobule has its afferent arteriole, one or two 56 Elemexts of Histology. efferent veins, and a dense network of capillaries between ; each mesh of the capillary network holding one, two. or three fat cells [see below). Such are the nature and arrangement of fat or adipose tissue in the subcutaneous and sul)mucous tissue, in the serous Fig. 41. — From a Section through the adipose layer of the Skin ; showing Lobules of Fat-cells. Magnifying jiower, 40. {From a Photograph by Mr. A. Pringle.) and synovial membranes, in the intermuscular tissue, in the loose tissue connecting organs or parts of organs. It can be shown that fat cells are derived from ordinary connective tissue cells. In some places — both in the embryo and adult — the protoplasm of the connective-tissue corpuscles, growing in size, becomes Fibrous Connective Tissues. SI tilled with small fat globules, wliicb, increasing in number, become fused with one another to larger globules ; as their size thus increases the cell nucleus becomes shifted to the periphery ; ultimately one larijje fat globule tills the cell, and what is left of the Fig. 42. — From a Section of Lobules of Fretal Fat, showing connective-tissue septa with vessels (surrounding the lobules) ; the spheroidal young cells, many of them containing globules of fat. {Photograph, moderately magnified.) cell protoplasm surrounds this fat globule like a mem- branous envelope. The cell as a whole has become in this process many times its original size (Fig. 41). 46. It can also be shown that where at one time only few isolated connective-tissue corpuscles are present, at another time, in the natural state of 58 Elemexts of Histology. growth, and especially under very fav-ourable con- ditions of nutrition, the connective-tissue cells become increased by cell-multiplication so as to form groups ; these groups continue to increase in size and to be srraduallv furnished with their own svstem of blood- vessels ; the individual cells constituting the group become then converted into fat cells, and their pro- cesses are thereby lost (Fig. 42). Isolated connective -tissue cells situated in the neighbourhood of small blood-vessels are converted into fat cells under favourable conditions of nutrition. In starvation the fat cells lose their fat globule, tliey become smaller and contain a serous fluid, which may ultimately also disappear. Finally, the fat cell may be reduced to a small, solid, ^protoplasmic, slightly branched cell. 47. In many places the fibrous connective tissue includes, besides the fixed cells, others which show amoeboid movement, u-andering cells. These are of various kinds, like tliose of the blood : (1) A majority are identical with the typical hyaline leucocytes of thf- blood, as regards size, shape, aspect, and general nature (Fig. 36, m). They wander about through the spaces of the fibrous tissue. They con- tain two or tViree nuclei. (2) Those of the second varietv possess a small amount of protoplasm, and one comparatively large nucleus : they correspond to the lymplwcytes mentioned in connection with the white blood corpuscles. The amoeboid movement of these cells is not so distinct as in the first variety. (3) Plasma cells of Waldeyer. They are larger than the former, less prone to migrating, being possessed of only slight amceboid movement, which is, however, sutiiiciently pronounced to be detected. They always contain granules, and correspond to the granular cells mentioned of the blood : also in regard to their predi- lection for acid and basic aniline dyes they may be Fibrous Connective Tissues. 59 distinguished as eosinopliile or oxypliile, basophile or neutropliile cells. The "grnnules" in some of the plasma cells may change into fat globules, and thus the plasma cell becomes convei-ted into a fat cell. 48. The wandering cells occur almost in all loose fibrous tissues, chiefly around or near blood-vessels ; they are not numerously met with in the healthy state, but increase greatly in the state of inflamma- tion of the part. Those of the larger kind — e.g. the granular wandering cells or plasma cells, are met with in certain localities onlv ; in the sub-linijual orland of the dog and guinea-pig they occur in numbers between the gland tubes or acini. They are also found in the mucous membrane of the intestine, in the trabecular of the lymphatic glands, and in the omentum. The " granules " of these cells under many conditions change into fat globules. Just like the hyaline leucocytes of the blood so also those of the connective tissues are capable of swallowing minute particles of extraneous matter — granules of living (bacteria) and non-living matter that accidentally find entrance into the connective tissue. These cells, when acting in this capacity, are called pliagocytes. 49. Development of fibrous tissue. — Fibrous connective tissue is developed from embryonic connec- tive-tissue cells — i.e. from spindle-shaped or branched nucleated protoplasmic cells of the mesoblast. The spindle-shaped cells are met with isolated or in bundles, as in the umbilical cord or embryonic tendon. The branched cells form a network, as in the foetal skin and mucous membrane. In both instances the p)'otoplasm of the embryonic connective-tissue cells increases rapidly in amount, and becomes gradually transformed into a bundle of elementary fibrils, with a granular-looking: interstitial substance. The nucleus of the original cell finally disappears, A modification 6o Elements of Histology. of this is when only part — generally unilateral — of the cell substance is converted into a bundle of con- nective tissue tibrils and inter-fibrillar cement sub- stance. A remnant of the protoplasm persists with the nucleus as a connective-tissue cell. The same modes of formation of connective tissue may be also observed in the achilt under normal and pathological conditions. 50. Fibrous connective tissue is in most places associated with elastic fibres or yellow elastic tissue. These are of bright aspect, of vari- able thickness and length, branching and anastomosing so as to form net- works (Fig. 43). They are some- times straight, but more often twisted and coiled. The latter condition maybe observed when the tissue is shrunk, the former when it is stretched. They do not swell up in acids or alkalies, nor yield gelatin on boiling, but contain a chemically ditferent sub- stance — viz. elastin. When broken their ends generally curl up. 51. Elastic fibres occur in great numbers as net- works extending on and between the bundles of tibrous tissue in the skin and mucous membranes, in the -From a Prei>aration of the Mesentery. of fibrim-; tissue; h, networks of elastic fibres. {Atlas.') F/BKOus Connect I \'E Tissues. 6i serous and synovial membranes, and in tlie loose in- terstitial connective tissues. They are not very com- monly met with in tendons and fasciae ; in the former they are seen as single fibres often twisting round the tendon bundles. Elastic fibres forming bundles, l)ut branched and connected into networks within the bundle, are to be found in large numbers in the walls of the trachea, l)ronchi, infundibula, and alveoli of the lung, in the ligamenta flava, in the ligamentum nucha? of the ox (in which the fibres are exceedingly thick cylinders), in yellow elastic cartilage {see below), in tlie mem- brane lining the cavity of the heart, and in the vascular system, particularly the arterial division. In the latter organs the intinia, and also to a great extent the media, consist of elastic fibrils densely connected into a network. 52. The following are special morphological modi- fications of the elastic fibres : (o) elastic fenestrated membranes of Henle, as met with in the intima of the big arteries ; these are in reality networks of fibres with very small meshes, and the fibres unusually broad and Hat. {h) Homogeneous elastic membranes, which surround, as a delicate sheath, the connective- tissue trabecules in some localities — e.^. subcutaneous tissue, (c) Homogeneous-looking elastic membranes iu the cornea, behind the anterior epithelium as Botv- 'nianHs anterior elastic membrane, and at the back of the cornea as elastica posterior, or Descemet's mem- brane ; in the latter bundles of minute fibrils haA'e been observed. Between the mucosa and submucosa of the stomach of the cat occurs an elastic membrane of considerable thickness, (d) Elastic trabeculae form- ing a network, as in the ligamentum pectinatum iridis. In the embryonic state the elastic fibres are nucleated, the nuclei beincj the last remnants of the cells from which the fibres develop, one cell generally giving 2 Elements of Histology. oricjiii to one fibre. These nucleated fibres are called Henle's nucleated fibres. 53. Special varieties of fibrous connective tissue are these : — (1) Adenoid retlcidum. This is a network of fine fibrils, or plates, forming the matrix of lymphatic or adenoid tissue. {!See Lymphatic glands.) The reti- culum is not fibrous connective tissue nor elastic tissue ; it contains nuclei in the young state, and is derived from a network of branched cells ; but in the adult state the reticulum itself possesses no nuclei. Those found on it do not form an essential part of it. (2) The iiearogUa of Virchow is a dense network of very fine homogeneous fibrils which form the sup- porting tissue for the nervous elements in the central nervous system. These fibrils are supposed to be elastic fibres (Gerlach). Embedded in, and inti- mately connected with, the network of these fibres are found branched, nucleated, flattened cell plates, which correspond to the fixed connective-tissue cells. (3) Gelatinous tissue. This occurs chiefly in the embiTO, being the unripe state of fibrous connective tissue (see above). It consists of spindle-shaped or branched connective-tissue cells, separated from one another by a homogeneous transparent mucoid sub- stance. It is met with in the umbilical cord and ill tlie cavity of the middle ear of the embryo, and in all places Avhere fibrous connective tissue is to be developed. After birth it is found in the tissue of the pulp of the teeth, where it persists through life ; in some places it is the precursor of fat tissue, its cells becoming: transformed into fat cells. 63 CHAPTER YI. CARTILACiE. 54. Cartilage consists of a firm ground sub- stance which yields diondrin, and of cells embedded in it. Most cartilages (except on the articulating surface) are covered on their free surface with a membrane of tibrous connective tissue with a few elastic fibrils. This membrane is supplied with blood-vessels, lymphatics, and nerves, and is of essential imjiortance for the life and growth of the cartihige. This is the perichondriiun. There are three varieties of cartila^je. 55. (1) Hyaline cartila§:e(Fig. 44).— This occurs on the articular surfaces of all bones ; on the borders of many short bones ; in the sternal part of the ribs, as costal cartilages : at the margin of the sternum, scapula, and os ileum : in the rings of the trachea, the cartilages of the bronchi, the septum and lateral cartilages of the nose ; and in the thyroid and cricoid cartilages of the larynx. The ground substance is hyaline — i.e. transparent, like ground glass, and firm. The cells are spherical or oval proto^^lasmic corpuscles, each with one or two nuclei. They undergo division, and although the two offsprings are at first close together (half moon-like in optical section), they gradually grow wider apart by the deposit of hyaline ground substance between them. The cells are con- tained in cavities, called the cartilage lacunce. Each cell generally occupies one lacuna, but, according to the progress of division, a lacuna may contain two. 64 Elemexts of Histology. four, six, or eight cartilage cells : the latter are those cases in which division proceeds at a more rapid rate than the deposition or formation ot hyaline ground substance between the cells. The jjart of the cartilage next to the perichon- drium shows most active growth; hence the cells are here smaller, closer together, and there is less ground substance. Each lacuna is liner] liy a delicate membrane, and, according to the state of the cell, is either completely or partially filled out bv it. This membrane is called the capsiiIe(Fig. 44). In many cartilages, espe- cially in growing cartilage, it is thickened by the ad- dition of a layer or layers of hyaline ground sub- stance. This is the most recently-formed j^art of the matrix; it stains differ- ently with dyes, and is dis- tinct from the older part of the ground substance. 56. In some places, especially in articular carti- lage (Tillmanns Baber), bundles of fine connective- tissue lil>rils may Ije noticed in the hyaline ground substance. 57. In some cartilages the protoplasm of the cell becomes filled with fat globules (Fig. 46). This fact may be observed in many normal cartilages ; some- times the fat globules become c(mfluent into one larjje drop, and then the cell has the appearance of a fat cell. In old age, disease, and deficient nutrition lime salts are deposited in the ground sul)stance, beginning from the circumference of the cell. The earthy matter a])})ears in the shape of opaque granules, or irregular Fig. 44.— Hyaline Cartilage of Hixiiian Trachea. In the hyaline ground substance are seen the cartilage cells enclosed in capsules. Cartilage. or anujular granult's. Tlie groiincl suljstance thereby loses its transparency, becomes o})Htic cai'tilag:e. this ^ji^?^?r^i^K:''^ii^^^o variety is also called reti- ^p ''^-^^^^^^i cular ; it occurs in the epi- •^, ^^.;''®^^ TO glottis, in the pinna of the ^ -■--«--—. ^ external ear, in the Eus- tachian tube, in the car- tilacrps of AVn\bp7-rr and ^ig. 4S.— From a Section through iiiages or » iisueig ana the Epiglottis. {AtUs.) Santorini in the larynx. «^ perichondrium; &, networks of In the early stages this eig^c^fltois sun-ounding the car- kind is hyaline. Gradually numbers of elastic tibrils make their appearance, growing into the cartilage matrix from the peri- chondrium in a more or less vertical direction, and branching and anastomosin^r with one another. The final stage is reached when the ground substance is permeated by f/^e/ise neiicorJxs of elastic Jibrils (Fig. 48), so arranged that spherical or oblong spaces are left, each of which contains one or two cartilage cells, surrounded by a smaller or larger zone of hyaline ground substance. 68 CHAPTER VII. BONE. 62. BoxE, or osseous substance, is associated with several other soft tissues to form a bone in the ana- tomical sense of the word. (a) The periosteiiiii. — Except at the articular surfaces, and where bones are joined with one another bv liiraments or cartilao;e, all bones are covered with a vascular membrane of fibrous connective tissue. This is the periosteum. It consists in most instances of an outer fibrous layer, composed of bundles of fibrous tissue densely aggregated, and an inner, or osteogenetic layer, which is of loose texture, consisting of a mesh- work of thin l^undles of fibrous tissue, in which numerous hlood-vessels and many protoplasmic cells are contained. The blood-vessels form hj their capil- laries a network. The cells are spheroidal or oblong, each with one spherical or oval nucleus. They have to form bone-substance, and are therefore called the osteoblasts (Gegenbaur). (b) Tlie carlilag-e is hyaline cartilage, and its distribution on and connection with bone have been mentioned on pp. 63 and 64. 63. (c) The marrow of l>oiie is a soft \'ascular tissue, filling up all spaces and cavities. It consists of a very small amount of fibrous tissue as a matrix, and in it are embedded numerous blood-vessels and cells. The few afierent arterioles break up into a dense network of capillaries, and these are continued as plexuses of veins, characterised by their compara- Bone. 69 lively large size and exceedingly thin walls. The cells are of the same size, aspect, and shape as the osteoblasts of the osteogenetic tissue, and they are called marrow cells. In origin and structure, the tissue of the osteo- genetic layer of tlie periosteum and tlie marrow are identical. In the embryo, the marrow is derived from an ingrowth of the osteogenetic layer of the periosteum {see below), and also in the adult the two tissues remain directly continuous. As will be shown later, the marrow at the growing ends of the bones is concerned in the new formation of osseous substance in the same way as the osteogenetic layer of the peri- osteum is in that of the surface ; and in both tissues the highly vascular condition and the cells (osteo- blasts of the osteogenetic layer, and marrow cells of the marrow) are the important elements in this bone formation. Marrow is of two kinds, according to the condition of the cells. If many or most of these are transformed into fat cells, it has a yellowish aspect, and is called yellow marroio ; if few or none of them have undergone this change, it looks red, and is called red marroiD. In the central^ or marrow, cavity of the shaft of tubular bones, and in the spaces of some spongy bones, the marrow is yellow ; at the ends of the shaft, in the -spongy bone substance in general, and in young growing bones it is red. Some of the cells, especially those of red marrow, the erythrohlasts, are the elements from which nor- mally vast numbers of red blood corpuscles are formed, as has been mentioned on a former page. In marrow, particularly in red marrow, we meet with large multinucleated cells, called inyeloplaxes of Robin. They are derived by overgrowth from ordin- ary marrow cells, and are of importance both for the absorption as also for the formation of bone [see below). According to Heitzmann, Malassez, and 70 Elements of HistoloCjY. others, they also have to do witli the formation of blood-vessels and blood corpuscles. NuQierous eosino- phile cells are present in the marrow, 64. The matrix of osseous substance is dense plexiform fil^rous connective tissue, i.e. a tissue yield- ing- gelatin on boiling. The cement substance between the fibrils is petrified, owing to a deposit of insoluble inorganic lime salts, chiefly carbonates and phosphates. These can be dissolved out by strong acids (hydro- chloric) and are thereby converted into soluble salts. Thus the orijanic matrix of osseous substance — called ossein — may be obtained as a soft flexible material, easily cut. In young bone the matrix or ossein is a plexus of trabecuLe of fibrous tissue (v. Ebner), and in it are also a few elastic fibres to be noticed. The bone substance is in the adult state generally lainellated, the lamellse being of microscopic thinness. Between every two lamellae are numbers of isolated, flattened, oblong spaces — the hone lacnnce (Fig. 49), which anastomose by numerous fine canals with one another, and also with those of the next lamella above and below (Fig. 50). The appearances are very similar to those presented by the lacunse and canali- culi containing the corneal corpuscles as described in Chapter V. The bone lacunte and their canaliculi are the lymph-canalicular system of osseous substance, for they Fig. 49. — Osseous Lanieihe ; oblong branched bone lacun;e and canaliculi between them. {Atlas.) Bone. 7 1 are in open and free communication with the lymphatic vessels of the marrow spaces and of the Haversian canals. 65. In the bone matrix, each lacuna contains also a nucleated protoplasmic cell, called the hone celi, which, however, does not fill it completely. In the Fig. 50. — From a Transverse Section through Compact Bone, showing systems of concentric lamelliB (with bone corpuscles between) around Haversian canals. (From a photogram by Mr. Pearce.) young state the cell is branched, the branches passing into the canaliculi of the lacunae ; but in the old state only traces of the original nucleated cell and very few processes can be detected ; this with its lacuna and canaliculi is called a bone corpuscle. 66. Accordinsf to the arrano^ement of the bone substance, we distinguish compact from spongy sub- stance. The former occurs in the shaft of tubular 72 Elemexts of Histology. bones and in the outer layer of flat and short bones. Its lamell?e are arranged as : («) concentric or Haversian lamella ., directly surrounding the Haversian canals (Fig. 51). These are narrow canals of varying lengths pervading the compact substance in a longitudinal a P'ig. 51.— Compact Bone Substance in Cross-section. (Atlas.) a. Concentric lamellae arranged around the Haversian canals, cut across; 6, in- termediate or ground lamellia The bone lacuna? are seen between the bone lamellas. direction, and anastomosing with one another by transverse or oblique branches. The Haversian canals near the marrow cavity are larger than those near the periosteum. In fact, those next to the marrow cavity become gradually enlarged by absorption of the concentric lamellse, until finally they are fused with the marrow cavity. Each Haversian canal con- tains a blood-vessel, one or two lymphatics, and a variable amount of marrow tissue. These canals open both into the marrow cavity and on the outer surface into the osteogenetic layer of the periosteum, and they form the means by which the latter remains in continuity with the marrow. Each canal is surrounded Bone. 73 by a series of concentric bone la?7iellcf, tvith the bone corpuscles between thein, and this is a system of con- centric lanielhe. Near the external surface of the compact substance the number of lamellae in each system is smaller than in the deeper parts, {b) ^'^^^mm^g Fig. 51a. — Sharjipy's fibres amongst the iiisterstitial lamella; of a transverse section of the human humerus ; the fibres run in a vertical direction, and surround spaces wliicli contain the bone-cells. {After KolUker, I.) Between these systems of concentric lamellae are the intermediate or ground lamelhe ; they run in various directions, and in reality fill the interstices between the systems of the Haversian or concentric lamellae. Near the external surface of long bones they have pre- eminently a direction parallel to the surface. These are the circumferential lamellce of Tomes and de Morgan, The ground lamellae are the earliest to be developed, being the matrix of the first-formed spongy bone, and they are the last to disappear where bone is 74 Elements of Histology. melted clown in the marrow cavity. The concentric lamellfe, on the other hand, are the last to be formed where spongy bone is converted into compact bone, and they are the tirst to become absorbed where com- pact bone is reduced again to spongy bone, as near the central marrow cavity. The lamellae of compact bone are perforated by perpendicular petrified fibres, the perforating fibres of Sharpey. They form a con- tinuity with the fibres of the periosteum, from which they are developed, through the lamellae of osseous substance deposited by the osteogenetic layer of the periosteum (Fig. 51a). 67. Spongy- bone substance occurs in the end of the shaft, in the apophyses, in short bones, and in the diploe of flat bones. The cavities or meshes of the spongy substance are called Haversian spaces or can- celli ; they intercommunicate with one another, and are filled with marrow, which in the vouncf and grow- inij state is fjenerallv of the red varietv. The firm parts form spicules and septa, called hone trahecuUt, of varying length and thickness, and are composed of lamellae of bone substance. According to the arrangement of the trabeculse, the spongy substance is a uniform honeycombed sub- stance, or appears longitudinally striated, as in the end of the shaft. In the latter case the marrow spacas are elongated and the trabeculse more or less parallel, but anastomosing with one another by transverse Ijranches. 68. Development of bone.— Bone is developed in the embryo, and continues to be fonned also after birth as long as bone grows, either in the cartilage or, independently of this, directly from the osteo- genetic layer of the periosteum. The former mode is called endodiondral, or intracartilagino^is: the latter periosteal^ or inter me mhranous formation. All the bones of the limbs and of the vertebral Bone. 7 5 column, the sternum, and the ribs, and the bones forming the base of the skull, are preformed in the early em])ryo as solid hyaline cartilage, covered with a membrane identical in structure and function with the periosteum, which at a later period it represents. This cartilage is eventually replaced by bone — endochondral hone. The tegmental bones of the skull, the bones of the face with the lower jaw, except the angle, are not preformed as cartilage at all. Only a membrane identical with the future periosteum is present, and underneath and from it the bone is gravlually deposited — i-)eriosteal hone. The same deposit of periosteal bone takes place on all bones, no matter what their origin, and this deposi- tion of layer after layer of bone by the osteogenetic layer of the periosteum represents the groivtli of the hone in thickness. 69. EiKlochoiiclral foriiiatioii. — The stage next to the one (1) in which we have solid hyaline cartilage covered with periosteum is the following : (2) Starting from the "centre, or point, of ossifica- tion," and proceeding in all directions, the cartilage l)ecomes permeated by numbers of channels (cartilage channels) containing prolongations (periosteal pro- cesses of Virchow) of the osteogenetic layer of the periosteum — i.e. vessels and osteoblasts, or marrow cells. This is the stage of the vascidarisation of the cartilage. In the next stage (3) the cartilage border- ing on these channels grows more transparent, the lacun{3e becoming enlarged and the cartilage cells more transparent. The latter gradually break down, while the intercellular trabeculse become calcified; the lacume, by absorption of the calcified trabeculfe, fusiuff witli the cartilaoje channels. These latter thereb}^ become transformed into irregidar cavities, which are bordered by trahecuhe of calcified cartilage. The cavities are the primary marroiv cavities, and 76 Elements of Histology. they are filled witli \\\^ jjrimary or j\4 '^'-^-f'^/'i',--, ^-- ■ Fig. 52. — Longitudinal Section through the entire Foetal Humerus of a Guinea-];)ig. fl, Periosteum ; 6, hyaline cartilage of the epiphysis ; c, intennediate cartilage at the end of the shaft ; d, zone of calcification ; t, i>eriostealbone, spongy ; /, endochondral bone, spongy. tilage gradually assumes the appear cartilage marroiv — i.e. blood-ves- sels and osteo- blasts, derived, as stated above, from the osteo- genetic layer of the periosteum. (4) The osteo- blasts arrange themselves by active multipli- cation in a special layer on the sur- face of the calci- fied cartilajje trabeculse pro- jecting into and bordering the primary marrow cavities. The osteoblasts form hone substance — osseous matrix and branclied bone corpuscles — and as this proceeds, the cal- cified cartilage trabecules become gradually en- sheathed and covered icitli a layer of osseous substance. Thus the original car- ance of a spongy Bone. 7 7 substance, in wliicli the cavities (primary marrow cavities) arc tilled with the primary marrow, and are of considerable size, while the trabecuhe bor- dering them are calcified cartilage covered with layers of new bone. The marrow cells, or osteo- blasts, continue to deposit bone substance on tlie free surface of the trabecul?e, while the calcified cartilage in the centre of the trabeculte gradually becomes absorbed. 70. The nearer to the centre of ossification, the more advanced is the process — i.e. the more bone and the less calcified cartilage is found constituting the trabecuhe, and the thicker the latter. At the " centre of ossification," i.e. whence it started, the process is farthest advanced ; away from it, it is in an earlier stage. At this period of embryo life, between the centre of ossification and a point nearer to the ex- tremity of the shaft of a long bone, all stages described above may be met with — viz. between the solid unaltered hyaline cartilage at the end of the shaft and the spongy bone with the unabsorbed remains of calcified cartilage in the middle of the shaft all intermediate stages occur (Fig. 52). 71. After birth, and as long as bone grows, we find in the end of the shaft, and also in the epiphysis, a continuation of the process of endochondral forma- tion described above. In fact, all bones preformed in the embryo as cartilage grom) in length before and after birth by endochondral formation of new bone. The hyaline cartilages at their extremities, the carti- lage of the epiphysis, the intermediate cartilai^e at the end of the shaft, are the cartilages at the expense of which the new bone of the epiphysis and of the end of the shaft respectively are formed by the marrow (blood-vessels and marrow cells or osteoblasts) in contact with the cartilage. As long as this cartilage continues to grow, so long is there new formation of 78 Elemexts of Histology. bone by the marrow encroaching on it, or, in other words, so long is there growth in length of the shaft. When at a certain period of adidt life the growth of the intermediate cartilage has come to an end, the cartilage is completely replaced by the spongy bone y^^M m:\\b « i (f^,^m rt^ Q)% /fiT ■* \i* it) 'W Fig. 53. — From a Transverse Section tlirough the Tibia of Foetal Kitten. a. Fibrous layer of the periosteum; b, osteogenetic Inyer of the periosteum; c. periosteal bone; d, calcifled cartilage not covered yet by bone; below this layer the tralieculte of calcified cartilage covered with plates of bone — sbaded darkly in the figure ; e, boundary between periosteal and endochondral bone. iAtlas.) Bone. 79 of the end of the shaft, and this is not capable of further lengthening. 72. Following the development of a tubular bone after the above mentioned stage 4, we find that the spongy bone once formed is not a permanent structure, Fig. 54.— From a Section through the Intermediate Cartilage of Femur of a Foetus. Low magnifjing power. {From a photogrcqjh by Mr. A. Pringle.) a, intermediate cartilajsre ; b, cartilage of the eiiiiihysis ; c, spongy bone of epiphysFs ; d, spongy bi>ne at the end of the shaft. but becomes gradually absorbed altogether, and this process also starts from the points of ossification. Thus a f;rc\dual enlargement and ultimate fusion of the marrow cavities of the spongy endochondral bone 8o Elements of Histology. into one continuous cavity takes place. This repre- sents the rudiment of the future central marrow cavity of the shaft. Simultaneously with, or some- what previous to, this absorption of the endochondral bone, new bone of the nature of spongy hone is deposited directly hy tlie osteogenetic layer of the periosteum on the outer surface of the endochondral hone. This also commences at the centre of ossifica- tion, and proceeds from here gradually to further l^oints. This is the tirst rudiment of the periosteal hone of the shaft (Figs. 52, 53). It is formed without the intervention of cartilage directly by the osteo- blasts of the osteogenetic layer. And as fresh masses of osteoblasts become developed l)y division, new layers of spongy bone are formed by the change of the former into bone matrix and bone cells, and the old trabecular become increased in thickness. In the meshes or Haversian spaces of this new spongy periosteal bone the same tissue is to be found that constitutes the osteogenetic layer of the periosteum, the one being derived from, and continuous with, the other. In these Haversian spaces concentric lamellai of bone substance become subsequently formed by the osteoblasts, while at the same time the Haversian spaces, being narrowed in by the deposit of the con- centric lamellae, are transformed into the Haversian canals. The original spongy bone represents, there- fore, the ground substance (primary, or ground lamella?), in which, or rather in the spaces of which, the secondary deposit of the concentric lamella} or Haversian systems of bone lamellae takes place, by which deposit the spongy bone becomes transformed into compact bone. This process is farthest advanced in the middle of the thickness of the shaft, and least near the periosteum. When this compact bone is again absorbed — e.g. that next the medullary cavity of the Bone. 8r sliaft of a long bone— tlie concentric lamella? are first absorbed, the Ha- be- way and versian canal ing in this widened out again transformed into a Haversian space. While, then, the bone first de- posited by the peri- osteum is of a spongy character, and gradually be- comes transformed into comi3act_, the reverse is ""oing on at the same time near the marrow cavity, inasmuch as compact bone is here changed into spongy bone, and this ultimately dis- a23pears and be- comes absorbed by the mari'ow. 73. At birth all the primary en- dochondral bone «. has already disap- peared by absorp- tion from the centre of the shaft, and the bone present is all of periosteal origin shaft Fig. 55. — From a Longitudinal Section Femur of Rabbit, through the part in which the intermediate cartiLige joins the end of the shaft. {Atlas.) a, Intermediate cartilage; 6, zone of calcified cartilage ; c, zone in which the calcified tra- heculEB of cartilage become gradiiRlly in- vested in osseous substance, shaded light in the figure; the spaces between the tral>e- cula3 contain marrow, and the cai>illar.v blood-vessels are seen here to end in loops ; d, in this zone there is more bone formed; the greater amount the farther away from this zone. At the extremity of the however, tlie spongy bone is all endochondral G 82 Elements of Histology. bone, and it continues to grow into the interme- diate cartilage as stated above, so long as the bone grows as a whole (Fig. 55). Of course the parts of this spongy bone nearest to the centre '^' \% ^^§)^ Fig. 5(3. — Small mass of Boiie Substance in the Periosteum of the Lower Jaw of a Human Foetus. [Atlas.) tt, Osteou'enetic liiyer of periosteum ; l>. luuliiuiicle.ired giuiit cells, inyeloiil.ixes. Tbe one in the midcile of the upper margin is an osteoclast, whereas the smaller one at the left upper corner appears concerned in the fornntion of bone. Above c the osteoiihist cells become surrounded by osseous substance and thus become converted into bone cells. of the shaft are the oldest, and ultimately dis- appear by absorption into the central medullary cavity. In the epiphysis the spongy bone is also endochondral bone, and its formation is connected with the deep layer of the articular cartilage, but more so with the hyaline cartilage separating the epiphysial spongy bone from the intermediate carti- lao-e (see c of Fisj. oi). Underneath the periosteum and on the surface of the spongy endochondral bone at the extremity of the shaft, the periosteal bone is represented only by a Bone. 83 thill liiyer, extending as far as the periosteum reaches — e.g. to tlie margin of the articular cartilage. 74. liiteriuoiiibrsiiioiis format ion. — All Fig. 57.— From a Longitudinal Section through the Spongy Bone of Shaft, near the intermediaiy cartilage, of Foetal Kitten, showing the formation of osseous substance on tlie calcilied cartilage. {Atlas.) a, Mhitow space, with bluud-vcssei ; 6, caicifled cartilage, covered with isolated or confluent zoues of new osseous substance, consisting of fibrillated bone matrix, bone lacuna, and in it a bone cell. 84 Elements of Hjstologv. Fig. 58. — From a Lolly itudiual Section of Femur of Rabbit, close to the intermecliate cartilage. a, Calcified cartilage, next to the inter- mediate cartilage; 6, calcified carti- lage covered with thin layer of bone ; c, uiari'ow spaces containing osteoblasts, forming bone on the calcified cartilage; d, niyeloplaxes (chondroclastsj. bones not preformed in the embryo as cartilage are developed directly from the osteogenetic layer of the periostemii in the manner of the i^eri- osteal bone described on p. 80. Here also the new l)one is at first spongy bone, which in its deeper or older layers gradually becomes converted into compact bone. In all instances dm'ing embryonic life and after birth the growth of a bone in thickness takes place after the manner of periosteal or intermem- hranous hone ; this is at first spongy, but is gra- dually converted into compact bone. 75. All osseous sub- stance is formed in the embryo and after bii th by the osteoblasts, or marrow cells (Gegenbaur, Wal- deyer) : each osteoblast oivino: orioin to a zone of osseous matrix, and re- maininof in the centre of this as a nucleated ^yo- toplasmic remnant, which gradually becomes branched and transformed into a bone cell. The Bone. 85 osseous matrix is at first a soft fil)nllar tissue, but is gradually and uuiformh^ impregnated with lime salts. This impregnation always starts from the centre of ossification (Fig. 57). 76. Wherever in the embryo or adult, in health or disease, absorption of calcified cartilage or of osseous substance is going on, we meet witli the multi- nucleated large protoplasmic cells called the myelo- plaxes of Robin. K()lliker showed them to be import- ant for the absorption of bone matrix, and called them therefore osteoclasts (Fig. 5Q). For cartilage they ma}" be called chondroclasts ( Fig. 58). When concerned in the absorption we find these myeloplaxes situated in smaller or larger pits, which seem to have been produced by them; these absorption pits or lacunae on the surface of l)ones are called Howships lacunce. They invariably contain numbers of osteoclasts. It can, however, be shown that myeloplaxes are also concerned in the formation of bone by giving origin to a number of new osseous zones with their bone cells. In the earliest stages of development of the ftetal jaw" this process is seen with great distinctness (Fig. 56). 77. Dentine forms the chief part of a tooth. It consists of a petrified matrix in which are numbers of perpendicularly arranged canals — the dentinal tubes — containing the dentinal fibres. It is in some respects similar to bone, although diftering from it in certain essentials. It is similar inasmuch as it is developed in like manner by some peculiarly transformed embryonic connective tissue — viz. by the tissue of the embryonic tooth papilla — and inasmuch as cells are concerned in the production both of the petrified matrix (impregnated with lime salts) and of the processes of the cells contained in its canals — the dentinal fibres. The details of structure and distri- bution will be described in connection with the teeth. 86 CHAPTER V]II. XOX-STRIPED MUSCULAR TISSUE. 78. This tissue consists of nucleated cells, which, unlike amoeboid cells, are contractile in one definite direction, becoming' shorter and thicker diirinc; con- traction. The cells are elongated^ spindle-shaped, or band-like (Fig. 59), and drawn out at eacli extremity into a lonuer or shorter, sfenerallv single, but occasionally Fig. 59.— Xon-striped Muscular Fibres, isolated. (Atlas.) The cross-markings indicate corrugations of the elastic sheath of the individual fibres. branched, tapering process. Each cell includes an oval nucUAis, which is flattened if the cell it belongs to is flattened. The cell substance is a pale, homo- geneous-looking or longitudinally striated substance. During extreme contraction the nucleus may be- come more or less plicated, so that its outline becomes wavv or zicj-zag. It lias been shown by Klein in certain preparations Non-striped Muscular Tjssue. 87 — e.y. the non-striped muscle cells of the mesentery of tlie newt — that each muscle cell consists of a delicate elastic shentJi, inside of which is a bundle of minute fibrils which cause the longitudinal striation of the cell. These fibrils are the contractile portion ; and they are contractile towards the nucleus, with whose intra- nuclear reticulum they are intimately connected. AVhen the cell is contracted its sheath becomes trans- versely corrugated (Fig. GO). 79. The non-striped muscular cells are aggregated into smaller or larger bundh>^ by an interstitial alV)U- Fig. 60.— Xon-stiipL'eminalis and j^rostate ; in the ^. , , 9 ^ - corj^ora cavernosa and spongiosa ; ■"''" ' ' .^ , _ ill the tissue of the ovary and in ' . . the broad ligament : in the mus- x^ -^ cular coat of the oviduct, the uterus and vagina ; in the pos- Fig.61.-From a Transverse terior part of the Wall of the Section through Bundles \y^r.\^r.^ . infhp Inrcrp and cimnll of Non-striped Muscular ^racnea , mine large ana small Tissue of the Intestine, bronchi, in the alveolar ducts '^%^l^l^Jt'. c'uT^, and infundibula of the lung ; in cor^cie"^of%=he'flga?l the pleura pulmonalis (guinea- ?{:^''irinre.^'^ril!e''et pig) ; in the peritoneum of the ceii"""(4itol)"'^ """'"^^ frog and newt, in the upper part of the upper eyelid, and in the fissura orbitalis ; in the sphincter and dilator pupilliTe, and the ciliary muscle ; in the capsule and trabecular of the spleen, and the trabecular of some of the lymphatic glands ; in the arrectores pilorum, and sweat glands of the skin, the tunica dartos of the scrotum ; in the tissue of the nipple of the breast ; in the larcfe ducts of the sali^'arv and pancreatic glands ; and in the muscular coat of the gall bladder, the hepatic and cystic duct. The aorta and the arteries have a large amount of non-striped muscular tissue, the veins and lymphatics less. 81. As regards length, the muscular cells vary within considerable limits (from ^\-^ to 0-5 millimeter), those of the intestine, stomach, respiratory, urinary. NoN-STKiPED Muscular Tissu/-:. 89 and genital organs being very long as compared with those of the blood-vessels, which are sometimes only twice or thrice as long as they are broad, and at tlie same time branched at their extremities. Non-striped muscular tissue is richly supplied with blood-vessels, the capillaries forming oblong meshes, though their number is not so great as in striped muscle. The nerves of non-striped muscle are all derived from the sympathetic ; their distribution and termination will be described in a future chapter 90 CHAPTER IX. STRIPED MUSCULAR TISSUE. 82. The striped muscular tissue is composed of long cylindrical fibres, some measuring in length as Fig. 02.— Striped Muscular Fibres of the Tongue of a Guinea-pig, of which the blood-vessels have been injected with carmine gelatine. Owing to the contracted state of the niuscular tibres the capillaries are much twisted and wavy ; in several places tlie " safety receptacles " are well show n. (From a microplwto. , moderatehi magnified.) mucli as 1.^-2 inches, others are much shorter; their thickness varies between ^-^o ^^ e^o ^^ ^^^ inch. The Striped Muscular Tissue. 91 til:) res are regularly transversely striated, and are therefore called the striped oi' striated muscular fil)res By fibrous connective tissue they are grouped together so as to form larijer or smaller bundles — muscular fasciculi ; the connective tissue surrounding the bundles is called the perimT/sium ; while the delicate connective tissue passing from the perimysium into the bundle, and separating the individual muscular fibres from one another, is called the endomysium. The perimysium is the carrier of the larger vascular and nervous branches, while the endomysium contains the capillaries and the terminal nerves. The capil- laries form very rich networks with elongated meshes, and are always situated between the individual muscle fibres. The capillaries and veins appear very wav^y and twisted in the contracted bundles, and straighter in the uncontracted bundles (Fig. 62). The small vessels are provided here and there with j)eculiar saccular dilatations, which act as a sort of safety receptacle for the blood when, during a sudden intense contraction, it is pressed out from some of the capillaries. 83. Each muscular fibre during contraction be- comes shorter and thicker. In the living uninjured muscular tibres, sjDontaneously or after the application of a stimulus, a contraction starts at one point and passes over the whole muscular fibre like a wave — contraction vxive — the progress of which is noticeable by the thickening rapidly shifting along the fibre, the part behind resuming its previous diameter. 84. A striped muscular fibre consists of (1) a delicate hyaline elastic sheath, the sarcolenima, and (2) the rnuscniar contents. It is the structure of the latter which has given origin to a variety of theories, owing to optical difficulties in examining fresh and living fibres, and owing to the varied changes it is liable to undergo when acted upon by many reagents. 92 Elemexts of Histology. jMJS8S»i»i*9f^^§i^f/ ;i^6siJ^aS 1; . »S24? ji ;t5J t " vC^S In the following we shall adopt the view enunciated by Rollett during recent years ; we think that his conclusions are based on extensive observations and study of muscular fibres in vertebrates and inverte- brates under the best conditions, and his conclusions harmonise best with the classical observations of Bowman, Briicke, Cohnheira, and Engelmann, and with observations which can g ---.,„.,,,,.,,.,,, 3 be verified by careful study f of fresh muscular fibres. S5. The contents of a mus- cular fibre consist of two prin- cipal parts (Figs. 63, G4) : {a) the fihrillce, or rhabdia of Kiihne ; and (h) the sarco- plas'/ii or intertibrillar sub- stance, a hyaline or faintly granular substance, having resemblances to protoplasm, and acting as the matrix for the tibrilhe. The fibrillar ex- tend in a longitudinal direc- tion parallel to the long axis of the muscular fibre, and they are grouped together into bands, strands, or tubes, called the muscle columns ; the latter larger groups. The sarco- plasm fills up all interstices between the groups of the muscle columns, between the columns of each group, and between the fibrillfe of each column. The amount of sarcoplasm between the groups of columns is generally greater than between the columns of each group. During growth and regeneration of mus- cular fibres in the adult the collections of nucleated sarcoplasm on the surface —i.e. underneath the sarco- lemma — become conspicuously increased in vertebrate Fig. 63. — Part of a Muscular Fibre of Geotruxjes sylva- ticus, showing its compo- sition of fibrillit. {Rollett.) I, Intermediate disc (Krause's membrane) ; s, sarcous ele- ments. are aorgresfated into Striped Muscular Tissue. 93 muscular tibres, both in number and size ; and they are the material from which muscular fil^rilhe are formed. Special collections of nucleated sarcoplasm are found at the termination of the motor nerve tiljre in the muscular fibre [see below). On observing a cross section through fresh or well-preserved muscular fibres, the sarcoplasm is seen as transparent lines sub- dividing the muscular contents, which appear dim like ground glass, into small more or less polyhedral areas, the areas of Cohnheim. These areas are the cross-sections of the muscular columns, and are therefore made up of a number of granules, the optical cross-sections of the constituent fibrillae. The mus- cular columns appear aggre- gated by larger accumulations of sarcoplasm into larger or smaller groups ; and between the groups the sarcoplasm is again greater than between the fibrillae of each column, and in this respect there exists the greatest variety between the different animals. In the per- fectly fresh condition tlie amount of sarcoplasm between the fibrilhe of a column is in some cases insignificant, and almost appears absent from place to place. Tlie sarco[)lasm shows also other differences of A'— \ jL Fig. 64. — Mu>;cul;ir Fibre, stained with hitmatoxy- lin, of Staphylinuscaesa- reus. {liollett.) I, Interniefliate disc (Krause's membrane or Dobie's layer); L, secondarj' disc (placed witliiii tlie lateral disc ur Floi-'el's layer) ; T, tranverss disc (sarcoiis eleiiieats); x, nucleus of muscle corpuscle. Q4 Elements of Histology. distribution ; in the muscular libres of many insects it generally forms a cylindrical accumulation in the centre of the muscular fibres, containing spherical nuclei ; from it thinner septa pass between the groups of muscular columns. In vertebrate muscular fibres the sarcoplasm forms small plate-like or angular col- lections on the surface of the muscular contents — i.e. immediately under the sarcolemma. These collections include spherical, or more generally oval, nuclei, and are called the muscle corpuscles. The whole sarco- plasm must be considered as a sort of protoplasmic basis, and the muscle corpuscles as the nucleated accu- mulations of it. 86. Each hbrilla shows along the whole length of the muscular fibre regular alterations, as regards both aspect and thickness of its sul)stance, and accordingly can be considered as consisting of different portions following each other endwise, and repeating them- selves uniformly and in regular manner throughout the whole length and thickness of the muscular fibre. These portions are the sarcous elements of Bowman, dim, homogeneous rods or prisms forming the chief parts ; between each tw^o successive sarcous elements of the saQie fibrilla, at equal distance, is a dark granule, sometimes double, to whicli the end of each sarcous element is joined by a thin bridge. In the fresh state the sarcous elements are prisms, and those of con- tiguous fibrilla?, almost touch each other at their sides, so that little or no sarcoplasm intervenes between them here ; but when the sarcous elements shrink — e.g. after death or after hardening reagents, or sometimes even duriiig life and during contraction — they are more or less hourglass-shaped, and are separated by thin layers of sarcophism from those of contiguous fibrillse. The bridge by which each end of a sarcous element is joined to the granule being much thinner than the latter, there is more sarco- Sir IP /CD Muscular Tissue. 95 granules of the plasm present in the layer containing the bridge; and since the sarcoplasm is more transparent than either the sarcous elements or the fibrilla^ the nmscnlar libre as a whole shows a con- s p i c u o u s transparent layer or disc between each layer of the dark granules and each layer of the sarcous elements. This causes the transverse striation. The layer of the dark granules corresponds to tlie line of Dohie, or the line of Amici, or the inter- mediate disc of Engelmann, or the yneinhrane of Krause. The layer or disc of sarcoplasm in which the bridges are placed, which join the sarcous elements to the granules of the intermediate disc, is the lateral disc. The layer or disc of sarcous elements corre- sponds to the transverse disc. In many muscular fibres of insects, notably in those of the crab (Ruther- ford), there occurs in each fibrilla witliin the lateral disc a short rod-like thickening midway between the sarcous element and the dark granule ; the layer or E Fis. 05.— Striped Muscular Fibres of the Water Beetle (Hydropliilns). {Atlas.) Sarcoleiuraa; b, Krause's menibrane. The sarcous eliiiient^; are well seen. In a the oblong nuclei of tlie muscle corpuscles nre shown. In b the sarco- lennua has become unnaturally raised from the mus- cular contents. The contractile discs are M^ell shown : so also are the sarcons elements. 96 Elements of Histology. y^-\ disc of these rods or grannies forms the secondary disc, or the Layer of Flcigel. cS7. A typical niuscnlar fibre shows then, owing to the differentiation of each fibrilla into the above portions, the following layers in regular alternation throughout the thickness of the fibre : (1) 27ie dark inter- mediate disc, Dobies line, or Kraiise's membrane ; (2) the transparent lateral disc ; (3) the dim transverse disc of sarcous elements. Then fol- lows another transparent lateral disc, and then again the intermediate disc. As stated above, in some fibres the line of Dobie is a double row of granules, and the transparent lateral disc contains a line of granules, Flugel's layer. The intermediate disc appears to be intimately connected with the sarcolemma ; hence Krause gave it the name of a membrane. When a muscular fibre contracts during life, or when it shrinks after death, the sarcolemma shows regular bulgings between each two Krause's mem- branes ; at these latter the sarco- Fig. 66. — Three Fibrilke of Crab's Muscle, showing the successive stages from complete relaxation (?•) to complete contraction (t). (From Rtither- foi'd's " .'itructui-e and Contraction of Striped Muscular Fibre.") b — 610, The various appearances of the sarcous ele- ments; d—(l9, the appearances of Dol>ie's granules ; /, Flogel's granules ; c, clear layer (lateral disc) between Flogel's granules and end of sarcous elements. STK/r/lD Ml'SCULAR TiSSi'E. 97 lemma is drawn in. The part of a muscular fihn; between two neighbouring Krause's membranes and the corresponding portion of the sarcolemma is Fij;-. t)7. — Semi-schematic representation of portions of Fibrils of Crab's Muscle, showing the appearances of the fibrillar segments in the several stages from complete relaxation at a to complete contraction at F. (After Eutherjord.) A.— &, Bowman's sarcous elements ; i, intermediate discs, comprising d, granules of Dobie ; /, granules of Fli5?el ; c, clear layer between it and end of sarcous element (lateral disc), b, I''frst stai,'e of contraction ; the clear layer be- tween Dobie's granules and Fliiiirers' granules on the one side, and Fliigel's granules and the end of the sarcous elements has disappeared. F, complete contraction, showing sarcous elements comjiletely shortened : accumulation of chromatic sulistauce at the ends, leaving the intervening shaft clear— Hansen's median disc. H yS Elements of Histology. spoken of as a muscular conipaitment of Krause {See Fig. 65, a). The lateral disc contains in some muscular fibres {see above) a layer of granules or rods, the secondary- disc, or Flogels layer ; but each of these granules or rods is ioined to a granule of the . 51 i intermediate disc, or Dobie's ^^^ |! I layer, on the one hand, and to 1 1 \ the end of a sarcous element on ,- »* \ the other ; so that in reality it is vL 11 I a thickening of the bridges con- V^ "-^ I necting the ends of a sarcous Vl \\ I element to the granule of the V 11 I intermediate disc. ^\\ • The transverse disc, or the - '* \ laver of sarcous elements, shows m VV^ \ hardening, or after treatment ^\\ \ "^^'i^^ reagents, a median trans- w\ 5 verse transparency, due to the in muscular fibres during con- traction (.y^e below) or after 1.1 \\\\8 substance of the sarcous ele- "Wfi ments being here thinner, as IllW i^'-Pi^tioned above. This corre- Fig. GS.-Primitive Mus- ^ponds to the median disc of euiar Fibriiia; from the Hensen. Eutlierford, however, Si'-^^S'f- ^''■^'"' pointed out that this appear- ance is due to the stainable or chromatic substance of each sarcous element accumu- lating at the ends (Figs. 66 and 67). In muscular fibres treated with alcohol, the con- nection between the sarcous elements and the rest of the fibrillse is not recognisable ; hence the muscular fibre seems split up into discs, apparently not con- nected with one another {see Fig. 60). The reticulation described by ^Nlelland, ^Marshall, and others is due to coagulation of the sarcoplasma Striped Muscular Tissue. 99 brought about by certain hardening reagents ; the sarcoplasma between the granules of the layer of Dobie or Krause would thus form a reticulated disc extendinoj transversely across the muscular fibre, and to it are joined lines of coagulated sarcoplasma ex- tending longitudinally between the sarcous elements of the tibrill^ (Fig. 69). 8''^. During contraction the transverse striation of the tibre becomes much narrower, the different discs becoming thinner in the long, broader in the trans- verse direction of the fibre. In the naturally contracted portion of a muscular fibre — i.e. at the point of the passage of the contraction wave — the stripes alter their character, inasmuch as at the end of the transverse and lateral discs the fibres become darker, while the middle of the discs of sarcous elements becomes lighter. Whether the former change — i.e. of the lateral discs — is due to compression, while the latter — i.e. of the sarcous elements —is due to an imbibition with water squeezed out of the sarcoplasma in the lateral discs, as is maintained by Engelmann, has not been fully established. Rutherford, on the other hand, points out, what appeal^ a good explana tion of this phenomenon — ^-iz. of the so-called re- versal of the stripes during contraction — that during contraction the chromatic substance of the sarcous elements, together with Flogel"s granules and Dobie's granules, forms one shortened mass ; hence the darkness of these portions in each fibrilla. We reproduce Fig. 69.— striped Muscular Fibres in Cross-section. {Altos.) Each fibre is limited by the sarco- lemiiia ; the luuscular substance is differentiated into Cohnheim's areas. loo Elemexts of Histology. here from Rutherford drawinus illustrating these points (Figs. 66 and 67). Rollett considers, with Briicke, Kolliker, Engel- mann, and many others, that the fibrillar are the contractile parts : while Klihne, Ramon y Cajal, and others, are inclined to think that the sarcoplasma — which Kiihne calls sarcoglia— is the contractile part, while the fibrillse — i.e. the rhabdia of Kiihne — or rather the sarcous elements, are elastic elements. The differentiation into intermediate, lateral, and transverse discs, possessing the above-named different structure and optical properties, produces the trans- verse striation of the muscular fibres ; but it must be also added that a fibre, though homogeneous but moniliform (by shrinking or naturally so), would show a transverse striation (Haycraft). 89. In the embryo the muscular tibres are developed from spindle-shaped nucleated cells (Remak, Weissmann. Kulliker). One spindle-shaped cell with "^--^.s^* Fig 70. — Striped Muscular Fibre of the Diaphragm of a Guinea-pig. {Atlas.) The muscle corpuscles are much increased iu size aud numbers ; tbey are probably used here for the new formation of muscular substance. an oval nucleus grows rapidly in length and thickness, its nucleus divides repeatedly, and the offspring become shifted from one another as the cell continues to grow in lengtli. Tlius a ]<»ng spindle-shaped mass of sarcoplasma, with iiunierous nuclei, is the result. Striped Muscular Tissue. ioi Tliis sarcoplasiiia in the middle of the cell becomes converted into fibrilhe, and this formation continues, while the sarcoplasma as a whole increases. The muscle corpuscles of the adult fibres are remains of this sarcoplasma (Fig. 70). At all times in adult life, when muscular fibres increase in thickness, as, for instance, when muscle is kept at constant work, this increase is due to increase of sarco})lasma, and joart-conversion of this into fibrillin. Paneth described in fishes, amphibia, birds, and mammals a mode of new formation of muscular fibres which supplements the one above described. While in the embryo the first muscular fibres develop from spindle-shaped cells in the manner stated above, muscular fil^res are also newly formed from spherical or oval cells — sarcoplasts ; in the interior of these cells, the protoplasm is converted into contractile substance, which is capable of enlarging and elon- gating, and becoming converted into striped muscular fil)res. According to Kdlliker and Weissmann, muscle fibres divide longitudinally also, so that one fibre is capable of giving origin to a bundle of thin fibres each of which continues to increase in thickness [see muscle spindles below). 90. The striped muscular fibres, taken as a whole, are, as a rule, spindle-shaped, becoming gradually thinner towards their ends. They are branched in some exceptional cases — e.g. in the tongue ; here the extremities of the muscular fibres, passing into the mucous membrane, become richly branched previous to their terndnation amongst the connective-tissue fibres of the mucosa. 91. Muscular fibres terminate in tendons, either by the whole fibre passing into a bundle of connective- tissue fibrils (Fig. 71), or by the fibre ending abruptly with a Ijlunt, conical end, and becoming here fixed to 102 Elements of Histology. from one end FS a bundle of cuunective-tissue tibrils. TJie individual fibres have only, as has been mentioned above, a limited lensth : so that, following an anatomical bundle to the other, we tind at many points along the fasciculus some muscle fibres terminating, others originating. This takes place in the following way : the contents of a fibre suddenly terniinate, while the sarcolemma, as a fine thread, becomes interwoven with the fine con- necti\'e tissue between the muscular fibres. Manv muscles contain peculiar spindle-shaped enlargements ; these are the muscle buds of Kolliker or the inascle spindles of Kiihne ; each spindle is a bundle of fine striped muscular til ires formed bv lencjth division of a mother fibre, and enclosed within a thickened connective - tissue sheath, which sheath is continuous with the laminated connective - tissue sheath (Henle's sheath) of nerve fibres — ^in fact, the sjfiiidles occur at the entrance of certain nerves into the muscle bundle [see nerve endings). 92. Tlie striped muscular fibres of the heart (auricles and ventricles) and of the cardiac ends of the large veins (the pulmonary veins included) differ from other striped muscular fil)res in the following respects : — -(1) They possess no distinct sarcolemma. (2) Their muscle corpuscles are in the centre of the fibres, and more numerous than in ordinary fibres. (3) They are very richly branched, each fibre giving oft" all along its course short branches, or continually dividinir into smaller fibres and forming a close / Fig. 71. — Two Striped Mus- cular Fibres passing into Bundles of Fi- brous Tissue. (Handbook.) (Termination in Tendon.) Striped Muscular Tissue. ro3 network (l^'ig. 72). A transverse section tlirough a bundle of such fil)res shows, therefore, their cross- sections irregular in shape and size. (4) Each nucleus of a muscle corpuscle occupies the centre of one lU'isuiatic portion ; each fibre and its branches thus appear composed of a single row of such prismatic portions, and they seem separated from one another — - at any rate in an early stage — by a septum of a trans- parent substance. 93. Some mus- cular fibres are either markedly pale or markedly red (Ranvier) ; in the former {(ijj. quadratus lumbo- rum, or adductor magnus femoris of rabbit) the trans- verse stria t ion is more distinct, and the muscular cor- puscles less nume- rous, than in the ^ ' latter (ejj. semi- tendinosus of rabbit, diaphragm). Here the longitudinal striation appears very distinct, but these differences are not constant in the same fibres of other animals or of man (E. jMeyer). 94. Briicke has shown that striped muscular fibres are doubly refractive, or anisotropous, like uniaxial positive crystals (rock crystal), the optical axis coincidini; with the lonsc axis of the fibres. The Z.— striped Muscular Fibres of the Heart. A, Showinfe' tlie liniuching of the fll)res and their anastomosis in networks; b, part of a thin filire, highly mairnifled, showing the raouili- forni primitive flbrillae; c, one inimitive tibrilla more highly magnified. I04 Elements of Histology. sarcoplasiiia is isotropous, tlie tibrilhr alone being anisotropoiis ; of these the sarcous elements were the first recognised by Briicke to be doubly refractive. They are, however, not the ultimate optical elements, but must be considered as composed of disdiaclasts, the real doubly refractive elements (Briicke). lo; CFI AFTER X. THE HEART AXD BLOOD-VESSELS. 95. (a) The heart consists of an outer serous covering, tJie visceral pericardium or exocard, an inner lining, the endocardium, and Ijetween the two the muscular suh- stance (Fig- 73). Underneath the pericardium is a thin layer of con- nective tissue called the subpericardial tissue. The free surface of both the peri- cardium and endo- cardium has an en- dothelial covering, like other serous membranes — i.e. a single layer of trans- parent nucleated cell plates of a more or less polygonal or irregular shape. The groundwork of these two membranes is tibrous connective tissue, forming a dense texture, and in addition there are many elastic fibres arranged as networks. Capillary blood-vessels, Fit 73. — Transverse Section through Auricle of the Heart of a Child. the a, Endotbelium lining the endocardium; h, en- docardium; c, muscular bundles cut trans- versely ; d, muscular bundles cut longitudi- nally ; e, pericardial covering ;/,endotlieliuui. io6 Elements of Histology. lymphatic vessels and small Ijranclies of nerve li))res are met with in the pericardial layer. The sub- pericardial tissue consists of trcibecula^ of tibrous connective tissue, which are continuous with the intermuscular connective tissue of the muscular wall of the heart. The former contains in many places groups of fat cells. 96. On the free surface of the papillary muscles, in some parts of the surface of the trabeculse carnese, and at the insertion of the valves, the endocardium is thickened by tendinous connective tissue. Each valve is covered with a prolongation of the endocard, but the main body of the valve is dense tibrous connective tissue ; on the surface of this connective-tissue matrix is a somewhat looser connective tissue, containing also a few elastic fibres. All the corda3 tendineie and the \alves are of course co\ ered on their free surfaces with endothelium. Special tracts of uiuscle fibies occur in the sub- endocardial tissue. The fibres of Furkinje are peculiar beaded fibres occurrinor in the subendocardial tissue in some mam- mals — e.g. the sheep and the horse — and birds (not in man). They are thin, transversely striped, muscular fil^res possessed of local thickenings ; the central part of each thickening is a continuous mass of protoplasm, with nuclei at regular intervals, as is the case with some skeletal muscular fibres of insects. These beaded fibres of Purkinje must not be confused with the inuscle spindles of Kiihne. 97. The muscular fibres forming the proper wall of the heart, the structure of which has been described in the previous chapter, are grouped in bundles separated by vascular fibrous connective tissue. In the ventricles the bundles are aggregated into more or less distinct lamella?. Like other striped muscular fi'hres, those of the Heart and Blood-vessef.s. 107 wall of the iieart are richly supplied with blood-vessels and lymphatics. The endocardium and valves have no blood-vessels of their own, but the pericardium possesses its own system of Idood- , '•.-^n C"^ '~^\ "^^v - — ~ /'^^ --^ tics form a peri- Wi ;j_j^' -.==^^=.^^i^ cardial and an ^^^^ _j;_^ _ ^.^^s^ """^^^^^^'^^ endocardial net- ^^^ fe— .^^ .=^^=s. "^^ work connected g ^--^ss - _ ^^ with the lym- phatics of the muscular tissue of the heart ; here there are lym- phatic clefts be- tween the mus- cular bundles, and also net- works of tubular 1 1 X- fig. 74.— i^roin a xransverse eectiou tiii< i_) inpuaiicb. ^jjg Inferior Mesenteric Artery of the Pig. Jg, inenerve <>, Endothelial lining; ?, elastic intinia; m, muscular l>.^Ti-./-l-.«c. ,^^ ■*-!.« media; a, adventitia with numerous elastic Dianciies Oi ine Ulinls, cut in transverse section. (Af/a.s.) l^lexus cardiacus torm rich plexuses. In connection with some of them are found numerous collections of ganglion cells or ganglia. These are very numerous in the nerve plexus of the auricular septum of the frog's heart (Ludwig, Bidder), and in tiie auriculo-ventricular septum of the frog (Dogiel). In man and mammals numerous ganglia are found on the auricular nerve branches, chiefly at the point of junction of the large veins with the heart, Remak's ganglia, and at the boundary between the auricles and the ventricles, Bidder's ganglia. 91). (b) The artoi-ieN (Fig. 74) consist of : («) an Fig. 74. — From a Transverse Section thiuugh [o8 Elemexts of Histology. endotheliaJ laijer lining the lumen of the vessel ; (6) an intima^ consisting of elastic tissue ; (c) a media, con- taining a large proportion of non-striped muscular cells arranged chiefly in a transverse, i.e. circular manner ; and [d) an adventitia composed chiefly of fibrous connective tissue, with an admixture of net- works of elastic fibres. («) The endothelium is a continuous single layer of flattened elon- gated cell plates. (6) The intima in the aorta and larcje arteries is a very com- plex structure, consist- ing of an innermost layer of fibrous connec- tive tissue, which is the " inner longitudinal fibrous layer " of Re- mak, outside of which ^^^ is a more or less longi- \^\ *~^^^^^^" tudinally arranged elas- tic membrane. This is laminated, and com- posed of fenestrated elastic meinhranes of Henle. {See page 61.) The larger the arte^^y the thicker the intima. In microscopic arteries the intima is a thin fenestrated membrane, the fibres having distinctly a longitudinal arranfjement. (c) The media is the chief layer of the wall of the arteries (Fig. 75). It consists of transversely arranged / ^ "^>*isa^> Fis. -Transverse Section through a Microscopic Artery and Vein m the Epiglottis of a Child. {Atlas. ) A, The artery, showing the nucleated en- dothelium, the circular muscular media, aud at a the fibrous-tissue ad- ventitia: V, the vein, showing the same layers ; the media is very Inuch thinner than in the arterv. Heart and Blood-vessels. 109 clastic laniellse (fenestrated membranes and networks of elastic tibres), and between thern^ smaller or larger Ijundles of circularly arranged muscular cells. The larger the artery the more elastic tissue is there present in the media, the smaller the artery the more muscular tissue. In microscopic branches of arteries the media consists almost entirely of circular non- striped muscle cells with only few elastic fibres, 100. In the last branches of the microscopic arteries the muscular media becomes discontinuous, inasmuch as the (circular) muscular cells are arranged not as a continuous membrane, but as groups of small cells (in a single layer) in a more or less alternate fashion. When the media contracts, the intima is thrown into longitudinal folds. The aorta has, in the innermost and in the outer- most parts of the media, numbers of longitudinal and oblique muscle cells. According to Bardeleben, all large and middle-sized arteries have an inner longitudinal muscular coat. 101. Between the media and the next outer la3'er there is^ in larger and middle-sized arterieS; a special elastic membrane, the elastica externa of Henle. (d) The adventitia is a relatively thin fibrous con- nective-tissue membrane. In large and middle-sized arteries there are numbers of elastic fibres present, especially in the part next to the media ; they form networks, and have chiefly a longitudinal direction. The larger the artery the more insignificant is the adventitia as compared ^^•ith the thickness of the media. In microscopic arteries (Fig. 76) the adventitia is represented by thin l)undles of fibrous connective tissue and branched connective-tissue cells. Large and middle-sized arteries possess their own I lO Elements of Histology. system of blood-vessels (vasa chiefly iu the adventitia and vessels and lymphatic clefts are these coats, 102. (c) vasorum), situated media: lymphatic also present in 771 i.e fli ^1 m 11 r^ 3 u '^ The veiiisi differ from the arteries in the greater thinness of their wall. The intima and media are similar to those of arteries, only thinner, both abso- lutely and relatively. The media con- tains in most A^eins circularly arranged muscular fibres ; they form a continu- ous layer, as in the arteries, and there is between them generally more fibrous connective tissue than elastic. The adventitia is usually the thickest coat, and it consists chiefly of fibrous con- nective tissue (Fig. 75). The smallest veins — i.e. before passing into the capillaries — are composed of a lining endothelium, and outside this are de- licate bundles of connective tissue forming an adventitia. The valves of the veins are folds, consisting of the endothelium lining the surface, of the whole intima, and of j^art of the mus- cular media. 103. There are many veins that have no muscular fibres at all — e.g. vena jugularis (interna and externa), the vena -ubclavia, the veins of the bones and retina, and of the membranes of the brain and cord. Those of the gravid uterus have only longitudinal muscular fibres. The vena cava, azygos, hepatica, spermatica interna, renalis and axillaris, possess an inner circular and an outer longitudinal coat. The vena iliaca, cruralis, poplitea, mesenterica, and umbilicalis possess an inner and outer longitudinal and a middle circular n I fl Jeconie lur^er holes, or *•^(J'/y<^(^^ Tlie passage of red bloofl cori)uscles (diapedesis) and the migration of wJiite corpuscdes in inflammation through the un- broken capillaries and small veins occur through these stigmata and stomata. 108. Yoiiii^: and g^row iiig^ capillaries, Ijoth of normal and pathological tissues, possess solid thread- like shorter or longer nucleated protoplasmic processes (Fig. 79), into which the canal of the capillary is Fig. 70. —From a Pi-eparation of Omentum of Rabbit, after staining with Xitrate of Silver. {Atkis.) V, Minute vein ; a, solid protoplasmic prolongations of the wall of a capillary, connected with connective-tissue corpuscles ; c, solid young bud. gradually prolonged, so that the thread becomes con- verted into a new capillary branch. Such growinor capillaries are capable of contraction (Strieker). All blood-vessels, arteries, veins, and capillaries. 114 Elements of Histology d fibrous connective-tissue both in the embryo and ill their early .stages, both ill embryonal and adult life, are of the nature of minute tubes, the wall of which consists of a simple endothelial membrane. In the case of the vessel becoming an artery or vein, cells are added to the outside of the endothelium, thus forming the material for the development of the elastic, muscular, and elements of the wall. 109. In the first ;• in the adult, the vessel is re^jresented by solid nucle- ated protoplasmic cells, spherical, elongated, spindle- shaped, or bran- ched — vasofor- iiiative cells. Such cells may be isolated and indej)endent of any pre-existing vessel, or they ma}^ be solid prot opl as mic outgrowths of the endothelial wall of existing capillarv vessels (Fig. 80). In both cases they become hollowed out by a process of vacuolation ; isolated vacuoles appear at first, but tliev oradu- ally become Oion- iiuent, and thus a young vessel is formed, at first very irregular in outline, but gradually acquiring more and more of a tulnilar form. In the case of so. — Developing Capillary Blood-vessels from the Tail of Tadpole. {Atlas.) V, Capillary vein with clumps of pigiueat in the ■wait :«, nucleated protoplasmic sprouc ; /.solid anastomosis between two neighbouring capil- laries. Heart and Blood-vessels. 11^ ail isolated cell, its protoplasmic processes grow l)y degrees to th(! nearest capillary, to the wall of which they become fixed, and the cavity of the cell finally opens through such processes into that of the capillary vessel. The islets or cysts of blood that appear early in the area vasculosa of the embryo are due to vacuolation of Fig. SI.— Cells from inesoblast of chick's blastoderm undergoing develop- ment into blood-vessels in the area vasculosa. (Handbook.) ", Cavitj- of cell; b, cell wall ; /, cells not yet hollowed out ; d, hlood corpuscles. spherical or elongated vasoformative cells of the meso- blast, the islets or cysts being composed of a central portion which are blood corpuscles, at first white, then red, and a joeripheral protoplasmic nucleated envelope, the future vascular wall. The central nucleated blood cells develop by a process of endogenous division from the original cell protoplasm. The blood cysts, at first isolated, afterwards become connected by protoplasmic processes with other cysts or other vasoformative cells, ultimately forming a network of vessels (Fig. 81). The. wall of young capillaries is granular-looking })rotoplasm (the original cell substance), and in it ii6 Elements of Histology. are disposed, in uiore or less regular fashion, oblong nuclei, derived Ijv multiplication from the nucleus of the orkdnal cell. In a later stai:e. a differentiation takes place in the protoplasmic wall of the capillary into cell plates and cement substance, in such a way that each of the above nuclei appertains to one cell plate, which now represents the linal stage in the formation of the capillary. Both in the embryo and in the adult a few isolated nucleated protoplasmic cells, or a few protoplasmic solid processes of an existing capillary, may by active and continued growtli give origin to a whole set of new capilkries (Strieker, Aftanasieff". Arnrild. Klein, Balfour, Ranvier, Leboucq). I T CHAPTER XI. THE LYMPHATIC VESSELS. 110. The larg^e lymphatic trunks, such as the thoracic duct, and the lymphatic vessels passing to and from the lymphatic glands, are thin-walled vessels, Fig. 82. — Lymphatic Vessels of the Diaphragm of the Dog, stained with Nitrate of Silver. (Atlofi.) The eadothelium foniiin',' tlie wall of tlie lymphatics is well shown ; V, valves. siaiilar in structure to arteries. Their lining endo- thelium is of the same character as that of an artery, and so are the elastic intima and the media with its circular muscular tissue ; but these latter are very much thinner than in an artery of the same calibre. ii8 Elements of Histology a Tlie ach entitia is an exceedingly thin connective- tissue membrane with a few elastic fibres. Tiie valves are semi-lunar folds of the endothelium and intima, 111. The lyiiipliatics in the tissues and organs form rich plexuses. They are tubular vessels, the wall of which is, like that of a capillary blood-vessel, a single layer of endothelial plates (Fig. 82). The lym- phatic is often many times wider than a blood capillary. Tlje endothelial plates are elon- gated, but not so long as in a Ijlood capillary, with more or less sinuous outlines : but this depends on the amount of shrinking of the tissue in which tlie vessel is embedded : when there is no shrinking in the tissue or in the vessel, the out- lines of the cells are more or less straight. The lymphatics are sup- ported by the tibrous connective tissue of the surrounding tissue, which does not, however, form part of their wall 112. The outline of the vessel is not straight, but more or less moniliform, owing to Fig. 83. -From silver-stained tlie slight dilatations present specimen of the mesentery l^elow and at the senii-lnnar of tne fro*" o. Artery; %. perivascular VfdceS: thcSC are folds of the iffendoibHiar'vaa "'"'''^ endothelial wall, and they are met with in great numbers. The vessel apjiears slightly dilated innnediately be- vond the valve — that is, on the side farthest from LvMPffAT/c Vessels. 119 the peripliery, or rootlet, whence the current of lymph starts. il3. Tracing the lymphatic vessels in the tissues and organs towards their rootlets, we come to more or less irregularly-shaped vessels, the wall of which also consists of a single layer of polygonal endothelial ])lates; the outlines are very sinuous. These are the IjimpJtatic capUJaries ; in .some places they are mere clefts and irregular sinuses, in others they have more the character of a tube, but in all instances they have a complete endothelial lining, and no valve.s. Sometimes a blood-vessel, generally arterial, is ensheathed for a shorter or longer distance in a lymphatic tube, which has the character of a lym- l»hatic capillary ; these are the perivascular hjm- pliatics of His, Strieker, and others (Fig. 83). 114. The rootlets of the lyiiiphatic!^ are situ- ated in the connective tissue of the different origans in the shape of an intercommunicating system of crevices, clefts, spaces, or canals, existing between the bundles, or groups of bundles, of the connective tissue. These rootlets are generally without a complete endo- thelial lining, but are identical with the spaces in which the connective-tissue corpuscles are situated ; N\here these are branched cells anastomosing by their processes into a network — such as the cornea, or serous membranes — we tind that the rootlets of the lymphatics are the lacunse and canaliculi of these cells — the typical lymph- canalicular system of von Recklinghausen (Fig. 84). The endothelial cells forming the wall of the lymphatic caj^illaries are directly continuous with the connective cells situated in the rootlets. In tendons and fascife the minute lymphatics lie between the bundles, and have the shape of continuous long clefts or channels ; in striped muscular tissue they have the same character, being situated l^etween the muscular fibres. I 20 Elements of HjsroLOGV. The passage of plasma from the minute arteries and capiUarv blood-vessels into the lymph-rootlets situated in the tissues, and thence into the lymphatic Fig. S4- From silver-stained preparation of the Central Tendon of the Rabbit's Diaphragm, showing the direct connection of the Lyniph- canalicular System of the Tissue with the Lymphatic Capillaries. a. LympUatlc vessel; h, lymphatic capillary lined wich "sinuous' endotheliom. (Handbook.) capillaries and lymphatic vessels, represents the natural current of Ivmph irrigating the tissues. 115. Lymph cavities. — In some cases the lym- phatic vessels of a tissue or organ are possessed of, or connected with, irregularly-shaped large sinuses, much wider than the vessel itself : these cavities are the lymph sinuses, and their wall is also composed of a Lymphatic Vessels. I 2 I single layer of more or less polygonal endothelial plates with very sinuous outlines. Such sinuses are found in connection with the subcutaneous and sub- mucous lymphatics, in the diaphragm, mesentery, liver, lungs, etc. On the same footing — i.e. as lymph sinuses — stand the comparatively large lymph cavities in the body, such as the subdural and subarachnoidal spaces of the central nervous system, the synovial cavities, the cavities of the tendon-sheaths, the cavity of the tunica vaginalis testis, the pleural, pericardial, and peritoneal cavities. In batrachian animals — e.g. frogs — the skin all over the trunk and extremities is separated from the subjacent fascipe and muscles by large bags or sinuses — the subcutaneous lynipJi sacs. These sinuses are shut off from one another by septa. Between the trunk and the extremi- ties, and on the latter, the septa generally occur in the region of the joints. In female froiifs in the mesoo-as- trium smaller or larger cysts lined with cili- ated endothelium are sometimes found. Be- hind the peritoneal cavitv of the fros:, on each side of the ver- tebral column, exists a similar large lymph si- nus, called the cisterna lyniphatica magna. 116. The lymph cavities are in all instances in direct communication with the lymphatics of the surround- ing parts by holes or open mouths (stomata), often Fi; . 8.J. — Stuinata, lined witli Gennina- ting Endothelial Cells, as seen froni the Cisternal Surface of the Septuni Cisternal I.yniphatici« Magnai of the Frog. (Hundboolc.) 122 Elements of Histology. surrounded by a special layer of polyLedral endothe- lial cells — germinating cells (Figs. 85, %^). Such stomata are numerous on the peritoneal surface of the central tendon of the diaphragm, in which are found straight lyn)ph channels between the tendon bundles, and these channels communicate by nu- merous stomata with the free surface. A similar arrangement exists on the costal pleura, the omentum, and the cisterna Ivm- phatica magna of the frog. {See Chapter IV.) 117. The serous uieiiibraiies con- sist of endothelium upon a layer of fibrous tissue with networks of line elastic fibres : they contain networks of ])lood capillaries and numerous lymphatic vessels arranged in (superficial and deep) plexuses. Plexuses of lymphatics are very numerous in the pleura costalis — or rather, intercostalis — in the diaphragm and pleura pulmonalis. They are important in the process of absorption from the pleural and peritoneal cavity respectivelv. Lymph and lymph corpuscles, and other solid particles, are readily taken uj:) by the stomata {see Fig. 31) and brought into the lymphatics. Here the respiratory movements of the intercostal muscles, of the diaphragm, and of the lungs respectively, pro- duce the result of the action of a pump. 118. There exists a definite relation between the lymphatics on the one hand and the epithelium on the Fig. 86. — Endotheliuia ami Stomata of tlie Peritoneal Surface of the Septum Cis- ternse Lj-mpbaticte Magnge of the Frog. {Hawlhook.) Lymphatic Vessels. 123 other, wliieli covers the mucous membranes and lines the various glands, and also between the endothelium covering serous membranes and that lining their vessels and lymph cavities — namely this: the albuminous semi- fluid cement substance {see former chapters) between the epithelial or endothelial cells is tlie path by which fluid and formed matter passes between the surfaces and the lymph-canalicular system — i.e. the rootlets of the lymi)liatics. 119. L.yiiii>li taken from the lymphatics of difl^er- ent regions differs in composition and structure. That from the thoracic duct contains a large number of colourless or white corpuscles (lymph corpuscles), each of which is a protoplasmic nucleated cell similar in structure to a white blood corpuscle. They are of various sizes, according to the stage of ripeness. The smaller lymphocytes contain one, some of the larger con- tain two and three nuclei corresjDonding to the typical leucocytes. The latter show more pronounced amoeboid movement than the former. Also "granular " oxyphile, basophile, and amphophile cells are met with amongst the leucocytes. A few red corpuscles are also met with. Granular and fatty matter is present in large (|uantities during and immediately after digestion. In the frog (and also in other lower vertebrates — e.g. reptiles) there exist certain small vesicular lymph cavities, about an eighth of an inch in diameter, which show rhythmic pulsation ; they are called lym^^li hearts. On each side of the os coccygis and under- neath the skin is a pulsating posterior lymph heart. The anterior lymph heart is oval, and is situated on each side of the processus transversus of the third and fourth vertebrae ; it is rather smaller than the posterior one. Each lymph heart has afferent lymphatics, by which it is in open communication with the lymph- atics of the periphery, and from it passes out an efferent vessel which opens into a large vein (a l)ranch of the 124 Elements of Histology. sciatic and jugular veins resiDeetively). A valve allows Ivmpli to flow out of the lymph heart into the vein, but pre\'ents regurgitation of blood from Fig. 87. — Developing Lyinph-capillaries in the Tail of Tadpole. {Atlas.) a, Solid nucleated protoplas iiic branches not yet hollowed out. the vein. The i?iternal surface of the lymph hearts is lined with an endothelium like the lymph sacs, and in their wall they possess plexuses of striped, branched, muscular fibres. The nerve fibres terminate in these striped muscular fibres in the same manner as in those of other localities. (Ranvier.) L YMPHA TIC Vessel s. 125 12U. Lvm})liatic vessels are developed and newly formed under normal and pathological conditions in precisely the same way as blood-vessels. The accom- panying woodcut (Fig. 87) shows this very well. AVe have also here to do with the hollowing out of (con- nective tissue) cells and their processes previously solid and protoplasmic. 126 CHAPTER XII. FOLLICLES OR SIMPLE LYMPH fiLAXDS. 121. Under this name ^ve include the blood glands, or the conglobate gland substance of Hewson, His, and Henle. or the lymph follicles (Kolliker, Huxley, Liischka). The ground sul)staneeof all lymph glands, simple as well as compound (see below), is the lymph- atic or o.denoid tissue, or leucocvtocrenous tissue. Like all other gland tissue, it is supplied with a rich network of capillaries derived from an afferent artery, and leading into ett'erent veins. 122. The elements constituting this tissue are : — («) The adenoid reticnlura (Fig. 88), a network of tine homogeneous fibrils, with numerous plate-like enlargements. (b) SiiiaU, transparent, fljif, endotlteloid cell phites, each with an oval nucleus. These cell plates are fixed on the reticulum, of which at first sight they seem to form part. Their oval nucleus especially ap[)ears to belong to a nodal ])oint — i.e. to one of the enlargements of the reticuluni : l>ut bv continued shaking of a section of any lymphatic tissue, the oval nuclei and their cell plates can be got rid of, so that onlv the n^riculum is left, without any trace of a nucleus. (c) Lymph rorpiLScles completely fill the meshes of the adenoid reticulimi. These can, however, be easily shaken out. They are of different sizes ; some^the young ones — are small cells, with a comparatively large nucleus ; others — the ripe ones — are larger, have a distinct protoplasmic cell body, with one or S/MFLK Lymphatic Glands. 127 two nuclei. Ill all lyini)hatic tissues, be they part li tubes (Fig. 89, a and b). 124. The tonsils (Fig. 90) are masses of lymph follicles anil diflfase adenoid tissue covered with a thin mucous membrane, which penetrates in the shape of • ■•'.**,■•'.'. ;'-'^i',\ /■' -^ ■^'^^^: --' III Fig. 90.— Vertical Sectiun through part of the Tuiisil of Dog. {AUo.s.) e. Stratified pavement epitbelluni covering tbe free surface of the raucous membrane. The tissue of the mucous membrane is infiltrated wiih adenoid tissue. /, lymph follicles ; m, raucous gland of tbe submucous tissue. longer or shorter folds into the substance within. Numbers of mucus-secreting cjlands situated outside the layer of lymph follicles discharge their secretion into the pits (the crypts) between the folds. The free surface of the tonsils and the crypts is covered or lined with similar stratified epithelium to that which lines the oral cavity. Xumbers of lymph corpuscles 130 Elements of Histology. constantly, in the perfectly normal condition, migrate through the epithelium on to the free surface, and are mixed with the secretions (mucus and saliva) of the oral cavity. The so-called mucous or salivary cor- puscles of the saliva, taken from the oral cavity, are such discharged lymph corpuscles (Stohr). They become swollen up by the water of the saliva, and assume a spherical shape. They finally disintegrate. Similar relations, only on a smaller scale, obtain at the root of the tongue. The pJuirynx tonsil of Luschka, occurring in the upper part of the pharynx, is in all essential respects similar to the palatine tonsil. Owing to large parts of the mucous membrane of the upper portion of the pharynx being covered with ciliated columnar epi- thelium, some of the cryptr: in the pharynx tonsil are also lined w4th it. 125. The lenticular g-laiitl*^ of the stomach are single lymph follicles. The solitary glands of the small and large intestine are single lymph follicles. The agniinated g-lands of the ileum are groups of lymph follicles. The mucous membrane containing them is much thickened by their presence. These groups of follicles are called a Peyer^s ixitcli or a Peyers gland (see Intestine). 126. In most instances the capillary blood-vessels form in the lymph follicles meshes, arranged in a more or less radiating manner from the periphery towards the centre ; around the periphery there is a network of small veins. A larger or smaller portion of the circumference of the follicles of the tonsils, pharynx, intestine, bronchi, etc., is surrounded by a lymph sinus leading into a lymj)hatic vessel. (See above.) The lymphatic vessels and lymph sinuses in the neighbourhood of lymphatic follicles or of diffuse adenoid tissue are almost always found to contain Simple Lymphatic Glands. 131 numerous lymph corpuscles, thus indicating that these are produced by the adenoid tissue and absorbed by the lymphatics. r27. The tliyiiiiiH ^laiid consists of a frame- '* ■" =« to '^ " Fig. 91.— Section through the Thymus Gland of a Fcetus. a. Fibrous tissue between the follicles; &, cortical portion of the follicles c, medullary portion. work and the gland substance. The former is fibrous connective tissue arranged as an outer capsule, and in connection with it are septa and trabeculae passing into the gland and subdividing it into lobes and lobules, which latter are again subdivided into the follicles (Fig. 91). The follicles are very irregular in shape, most of them being oblong or cylindrical streaks of adenoid tissue. Near the capsule they are well defined from one another, and present a polygonal outline ; farther inwards they are riiore or less fused. Each shows a central transparent medulla (germ centre) and a peripheral less transparent cortex (Watney). 132 Elements of Histology. At tlie places where two follicles are fused with one another the medulla of both is continuous. The matrix is adenoid reticulum, the fibres of the medullary part being coarser and shorter, those of the cortical portion of the follicle liner and longer. The meshes of the adenoid reticulum in the cortical part of the follicles are filled with lymph corpuscles like those occurring in the adenoid tissue of otlier organs, but in the medul- lary part they are fewer, and the meshes are more or less completely occupied by the enlarged but more transparent cells : in many of these mitotic division of the nucleus occurs. These conditions cause the neater transparency of the medulla and represent the germ centres above mentioned. Amongst the laro-e cells of the medullary portion, some are coarsely granu- lar and include more than one nucleus ; some are even multinucleated giant cells. 128. Amongst the cells of the medulla occur also larger or smaller, more or less concerTErically arranged nucleated protoplasmic ijiasses. which are the concentric bodies of Hassall (Fig. 92). They are met with even in the early stages of the life of the thymus, and cannot there- fore be connected with the involution of the gland, as maintained by Afanassief, according to whom the concentric corpuscles are formed in blood-vessels which thereby become obliterated. According to Watney they are concerned in the formation of blood- vessels and connective tissue. The lymphatics of the interfollicular septa and trabecular always contain numbers of lymph corpuscles. The blood capillaries of the follicles are more richly distributed in the cortex than in the medulla, and Fig. 92. — Two Concentric or Hassall's Corpuscles of the Thymus. Foetal Gland. S/MPf-F. LvMriiAric Glands. 133 they radiate from the periphery towards the central parts. 129. After birth the thymus begins to undergo involution, leading to the gradual disappearance of the greater portion of the gland, its place l)eing taken by connective tissue and fat. But the time when the involution is completed varies within very wide limits. It is not unusual to find in persons of tifteen to twenty years of age an appreciable amount of thymus tissue. According to Waldeyer, about 60 per cent, of adults examined had still a portion of thymus gland left. In some animals— e.^. guinea-i)ig — the involu- tion of the gland even in the adult has not made much progress. In the thymus of the dog Watney found cysts lined with ciliated epithelial cells. 134 CHAPTER XTII. COMPOUND LYMPHATIC GLAXDS. 130. The compound or true lymphatic glands are nodules, generally of an oblong shape, directly inter- ]>olated in the course of lymphatic vessels. Such are the mesenteric, portal, bronchial, splenic, sternal, cervical, culntal, popliteal, inguinal, lumbar glands. Afferent lymphatic vessels anastomosing into a plexus open at one side (in the outer capsule) into the lymphatic gland, and at the other (the hilum) emerge from it as a plexus of efferent lymphatic tubes. 131. Each true lymphatic gland is enveloped in a fibrous capsule which is connected with the interior and the hilum by traheculcn and septa of connective tissue. The trabeculse havincj advanced a certain distance, about one-third or one-fourth, towards the centre, branch into minor trabecular, which in the gland anastomose with one another so as to form a plexus with small meshes. Thus the peripheral third or fourth of the gland is subdivided by the septa and trabeculte into relatively large spherical or oblong compartments, while the middle portion is made up of relatively small cylindrical or irregularly-shaped com- partments (Fig. 93). The former region is the cortex^ the latter the meduUa of the gland. The compart- ments of the cortex anastomose with one another and with those of the medulla, and these latter also form one intercommunicating system. The fibrous capsule, the septa and trabecuhe are tlie carriers of the vascular trunks ; the trabeculse consist of fibrous connective tissue and of a certain Compound Lymphatic Glands. 135 amount of non-striped nuiscular tissue, which is con- spicuous in some animals — e.g. pig, calf, rabbit, guinea-pig^but is scanty in man. Sometimes coarsely granular connective-tissue cells (plasma cells) are present in considerable numl^ers in the trabecuhe. 132. The com})artments contain masses of adenoid Fig. 03.— From a Vertical Section through a Lj-mphatie Gland, the Lymphatics of which had been injected. {Atlas.) c, Outer capsule, with lymphatic vessels in section; «, corticallymph follicles; around them are the cortical lymph sinuses; b, medulla; injected lymph sinuses between the masses of adenoid tissue. tissue, without being completely filled with it. Those of the cortex contain oval or spherical masses — the lymph follicles of the cortex ; those of the medulla cylindrical or irregularly-shaped masses — the medullary cylinders. The former anastomose with one another and with the latter, and the latter amongst them- selves, a condition easily understood from what has been said above of the nature of the compartments containing these lymphatic structures. The follicles 136 Elements of Histology. and medullary cylinders consist of adenoid tissue with germ centres of exactl}^ similar character to that described in the previous chapter. And this tissue also contains the last ramifications of the blood- vessels — i.e. the last branches of the arteries, a rich netwoik of capillary blood-vessels, and the first or smaller branches of the veins. The capillaries and other vessels receive also here an adventitious envelope fiom the adenoid reticulum. 133. The cortical follicles and the medullaiy cylinders do not completely fill out the compartments made for them by the capsule and trabecular respec- tively, but a nar- row peripheral zone in each com- jmrtment is left free; these are the lymphatic sinuses. In the cortex they are spoken of as the cortical (Fig. 94), in the medulla as the medullary J lyinj)h sinuses (Fig. 95). The former is a space between the outer surface of the cor- tical lymph follicle and the corre- sponding part of the capsule or cortical septum, the latter between the surface of a medullary cylinder and the trabecuhe. From what lias been said of the n eT?:^'^^ Fi 04.— Fnnii a Section tlninigli a Lyiiiiiliatic Gland. (Atlas.) Outer caisiile; s, cortical lyiiii>li sinus; a, adenoid tissue of cortical follicle. Numerous nuclei, indicating lynijiL corpuscles. Com POUND Lymphatic Glands. 137 relation of the compartments, it follows that the cortical and medullary lymph sinuses form one inter- communicating system. These are not empty free spaces, but are filled with a coarse reticulum of fibres, much coarser than the adenoid reticulum ] to it are attached large transparent cell plates — endotheloid Fig. 95. — From a Section Uirough the Medulla of a Lymphatic Gland. a, Transition of the medullary cylinders of adenoid tissue into the cortical follicles; 6, lymph sinuses occupied by a reticulum; c, fllirous tissue trabe- culae ; d, medullary cylinders. plates. In some instances (as in the calf) these cell f)lates of the medullary sinuses contain brownish pigment granules, which give to the medulla of the gland a dark brown aspect. In the meshes of the reticulum of the sinuses are contained lymph cor- puscles, the majority of which consist of a compara- tively large protoplasmic body and one or two nuclei ; 138 Elements of Histology. they show lively amoeboid movement ; a few small lymphocytes are also amongst them. The surface of the trabeculse facing the lymph sinuses is covered with a continuous layer of endothe- lium (von Recklinghausen), and a similar endothelial membrane, but not so complete, can be made out on the surface of the cortical follicles and the medullary cylinders. The endotheloid plates, applied to the reticulum of the sinuses, are stretched out, as it were, between the endothelial membrane covering the surface of the trabecular on the one hand and that covering the surface of the follicles and cylinders on the other. In the mesenteric glands of the pig the distribu- tion of cortical follicles and medullary cylinders is almost the i-everse from that of other glands and in other animals : the cortical part having the arrange- ment of cylinders of adenoid tissue and trabeculai, while the medulla shows lymph follicles and longer septa between them. 134. The afferent lymphatic vessels having entered the outer capsule of the gland, and having formed within the capsule a dense plexus, open directly into the cortical lymph sinuses. The medullary lymph sinuses, on the other hand, lead into lymphatic vessels, which leave the gland at the hilum as the efferent vessels. Both afferent and efferent vessels are supplied with valves. 135. The course of the lymph through a lymphatic gland is this : From the afferent vessels, situated in the capsule, the lymph flows into the cortical lymph sinuses, from these into the medullary sinuses, and from these into the efferent lymphatics. Owing to the presence of the reticulum in the lymph sinuses the current of the lymph will flow very slowly and with difficulty, as if through a spongy Alter. Hence a Compound Lympi/atic Glands. 139 large number of formed corpuscles, pigment, inflam- matory or other elements, passing into the gland from the afferent vessels are easily arrested and deposited in the sinuses, and are there readily swallowed by the amre'boid corpuscles lying in the meshes of, or de- posited on the reticulum. Passing a stream of water by way of the afferent lymph vessels through the gland, the contents of the meshes of the reticulum of the sinuses — i.e. the lymph corpuscles — are of course the first things washed out (von Recklinghausen), and on continuing the stream some of the lymph corpuscles of the follicles and cylinders are also washed out. Probably also by the normal lymph-stream passing from the minute arteries and capillary blood-vessels of the adenoid tissue (follicles and medullary lymph cylinders) into the lymph sinuses, lymph cells are drained, as it were, from the follicles and cylinders into the sinuses. The amoeboid movement of these cells will greatly assist their passage into the sinuses. From here the cells are carried away by the lymph current into the efferent lymph vessels, and are ulti- mately carried into the big lymph-trunks discharging into the big veins — i.e. into the circulating blood — as white blood corpuscles. I40 CHAPTER XIY. NERVE FIBRES. 136. The nerve fibres conduct impulses to or from the tissues and organs on the one hand, and the nerve centres on the other, and accordingly we have to consider in each nerve fibre the peripheral and Fig. 9(3.— From a Transverse Section tlirough the Sciatic Nerve of Dog. ep, Epineurium ; }). periueuriuni ; n, nerve filires coustituting a nerve bundle in cross-section ; /, fat tissue surroundiug the nerve. {Athig.) central termination and the conducting part. The latter, i.e. the nerve fibres proper, in the cerebro- spinal nerves are grouped into bundles, and these afifain into anatomical nerve branches and nerve Each anatomical cerebro-spinal nerve con- trunks Nerve Fibres. 141 sists, therefore, of bundles of nerve fibres (Fig. 96). The general stroma b}^ which these bundles are held together is fibrous connective tissue called the epi- neurium (Key and Retzius) ; this epineurium is the carrier of the larger and smaller blood-vessels with which the nerve trunk is supplied, of a plexus of lymphatics, of groups of fat cells, and sometimes of numerous plasma cells. 137. The nerve bundles or faiiiculi (Fig. 97) vary in size according to the number and size of the nerve fibres they contain. They are well defined by a sheath of their own, called perineurium (Key and Retzius). This perineurium consists of bundles of fibrous connective tissue arranged in lamella?, every two lamella? being separated from one another by smaller or larger Ijmiph spaces, which form an inter- communicating system, and anastomose with the lymphatics of the epineurium wdience they can be injected. Between the lamella, and in the spaces, are situated flattened endotheloid connective-tissue corpuscles. The nerve bundles are either simple or compound. In the former the nerve fibres are not subdivided into groups within the bundle, in the latter the bundles are subdivided by thicker and thinner septa of fibrous connective tissue connected with the peri- neurium. When a nerve bundle divides — as when a trunk repeatedly branches, or when it enters on its peripheral distribution — each branch of the bundle receives a continuation of the lamellar perineurium. The more branches the perineurium has to supply, the more reduced it becomes in thickness. In some of these minute branches the perineurium is reduced to a single layer of endothelial cells. When one of these small bundles breaks up info single nerve fibres, or into small groups of them, each of these has also a continuation of the fibrous tissue of the 142 Elemexts of Histology. perineurium. In some places this perineural con- tinuation is only a very delicate endothelial membrane as just mentioned, in others it is of considerable thickness, and still shows its lamellated nature. Such Fig. 07.— Transverse Section through a Xerve Bundle in the Tail of Mouse. i^AtUs.) p. Perineurium ; c, endoneurium separating the medullated nerve fibres seen in cross-section ; i, lymph spaces in the perineurium; i, lymph spaces in the endoneurium. a lamellated sheath of single nerve fibres, or o a small group of them, represents what is called a He /lie's sheath. 138. The nerve fibresarehekl together or separated respectively within the bundle by connective tissue, called the endoneurium (Fig. 97 j. This is a homo- geneous crround substance in which are embedded tine bundles of fibrous connective tissue, and con- nective-tissue corpuscles, and capillary blood-vessels arranged so as to form a network with elongated meshes. Between the perineurium and the nerve fibres are found here and there lymph spaces ; similar spaces separate the individual nerve fibres, and have been injected by Key and Retzius. The endoneural lymph spaces communicate with those of the peri- neural sheath. A^ER VE Fibres . 143 When nerve trunks anastomose so as to form a plexus — e.g. in the brachial or sacral plexus — there occurs a division, an exchange and re-arrangement of nerve bundles in the branches. A similar con- dition obtains in the ganglia of the cerebro- spinal nerves. Nerve trunks and nerve branches passing through a lymph cavity, such as the subdural spaces, or the subcutaneous lymph sacs, or the cisterna lym- phatica magna in the frog, receive from the serous membrane an outer endothelial covering. 139. Most of the nerve fibres in the bundles of the cerebro-spinal nerves, with the exception of the olfactory nerve, are meduUatecl nerve fibres. These are doubly - contoured smooth cylindrical fibres, varying in diameter between ttoVo ^^ more and iToooo ^^ ^^^ inch. Within the same nerve, and even wdthin the same nerve bundle, there occur fibres which are several times thicker than others, and it is probable that they are derived from different sources ; this, for instance, is very conspicuous in the vagus nerve (Gaskell, Fig. 98). Schwalbe has shown that the thickness of the nerve fibre stands in a certain relation to the distance of its perijihery from the nerve centre and to its functional activity. A medullated nerve fibre in the fresh condition is a bright glistening cylinder, showing a dark double contour. Either spontaneously after death, or after reagents — as water, salt solution, dilute acids — or after pressure and mechanical injury, the outline of the nerve fibre becomes irregular; smaller or larger glistening dark-bordered droplets and masses appear, and gradually become detached. These droplets and masses are called myeline droplets^ and are derived from the fatty substance or myelin constituting the medullary sheath or white substance of Schwann (see below). When a nerve fibre within the bundle under- goes degeneration during life, either after section of 144 Elemexts of Histology. the ner\'e or after other pathological changes, or in the natural course of its existence (S. Maver), the medullarv sheath is the first to undergo cliange ; it breaks uj) into similar smaller or larger globules or Fig. 98. — From a Transverse Section through the Vagus Xerve, showing in the nerve bundles nerve fibres (in cross-section) which differ markedly in size, some being much larger than others. (Photo., highly imignified.) particle-, whicli gradually l)ec'ome granular and absorbed. Later also the axis cylinder dwindles away, and only the neurilemma with the nucleated corpuscles persist. 140. Each medullated nerve fibre (Figs. 99, 101) consists of tlie following parts : {a) the central axis cylinder, axon or neuraD:on. This is the essential part of the fibre, and is a cylindrical or band-like. Nerve Fibres. 145 pale, trans|>ureiit structure, which in certain locali- ties (near the terminal distribiiiion, in tlie olfactory nerves, in the centj'al nervous system), and especially after certain reagents, shows itself composed of very fine homogeneous or more or less beaded tibrilhe — the elementary or jjriniitive Jibrillfe (Max Schultze) — held together by a small amount of a faintly gianular in- terstitial substance The longitudinal striation of the axis cylinder is due to its being composed of primitive librillcV. The thickness of the axis C3dinder is in direct proportion to the thickness of the whole nerve tibre. The axis cylinder itself is enveloped in its own hyaline more or less elastic sheath — the axi- lemma (Kiihne), composed of neurokeratin. 1-1:1. (b) The medidlarij sheath, or myeline sheath, or white substance of Schwann, is also called the medulla of the nerve fibre. This is a olisteninff bright fatty substance surrounding the axis cylinder, as an insulating hollow cylinder surrounds an electric wire. The medullary sheath gives to the nerve fibre its double or dark contour. Between the axis cylinder and the medullary sheath there is a small amount of albuminous fluid, which appears greatly increased when the former, owing to shrinking, stands farther apart from the latter. 142. (c) The sheath of Scliicann, or the neurileinma, closely surrounds the medullary sheath, and forms the outer boundary of the nerve fibre. It is a delicate structureless membiane. Here and there between the neurilemma and the medullary sheath, and situated in a depression of the latter, is an oblong- nucleus, surrounded by a thin zone of protoplasm. These nucleated corpuscles are the nerve corpuscles (Fig. 99), and are analogous to the muscle corpuscles, situated between the sarcolemma and the striated muscular substance. They are not nearly so numerous as the muscle corpuscles. K 146 Eleisients of Histology 143. The neurilemma presents at certain definite intervals annular constrictions — the nodes or constric- tions of Rani-ier (Figs 99, 100, 101) — and at these nodes of Ranvier the medullary sheath, but not the axis cylinder and its special sheath, is suddenly inter- rupted, and sharply terminates at the constriction. The neurilemma is at the same time thickened by annular permanent, folds (see b in Fig. 101). The portion of the nerve fibre situated between two nodes is the internodal segment. Each in- ternodal seojment has orenerallv one, occasionally more than one, nerve corpuscle. The medullary cylinder of each internodal segment is made up of a number of conical sections (Fio-. 101, A) imbricated at their ends ¥W 99. -Two Nerve - ^ . Fibre's, showing the (Schmidt, Lantermann ; and each such section is again made uj) of a large number of rod-like structures (Fig. 102) placed vertically on the been dissolved axis cvlinder (MacCarthy). away. The deeply- „ - , ^ 1 ihese rods are, however, con- nected into a network. The net- work itself is verv likelv the neuro- keratin of Ewald and Kiihne, where- as the interstitial substance of the network is probably the fatty substance leaving the nerve fibre in the shape of myeline droplets, when pres- sure or reagents are applied to the fresh nerve fibre. 144. Medullated nerve fibres without any neuri- lemma, and consequently without any nodes of Ranvier, with a thick more or less distinctly laminated medullary sheath, form the entire white substance of nodes or constric tions of Ranvier and the axis cy- linder. The me- dullary sheath has stained oblong nuclei indicate the ner\'e corpuscles within the neuri- lemma. (Atlas.) Ner I'E Fibres. 147 the brain and spinal cord. In these organs, in the hardened and fresh state, numerous nerve fibres may be noticed, whicli show more or less regular f(iil//'i///(' l|-i N^I/f^PI varicosities, owing to ((allllamlmru il/^^ h local accumulations of /: M lUlnf/rnwi !Wm% fluid between the axis /J l////tl W^lJ ///j > ^^^^ cylinder and medullary jl B ni f'lJ'/^^iJf'liHwV^ sheath. These are called varicose nerve B \\\l^ Fig. 101.— Medullated Xerve Fibres. A, Medullated nerve fibre, show- ing the subdivision of tlie medullary sheath into cylin- drical sections imbricated with their ends ; a nerve corpuscle with an oval nucleus is seen between tlie neurilemma and the medullary sheath, b, me- dullated nerve fibre at a node or constriction of Kanvier ; the axis cylinder passes uninter- ruptedly from one se.L'inent into the other, but the medull- ary s sheath is interrupted. (Key. and Retzius.) Fig. 100.— Medullated Xerve Fibies, after staining with nitrate of silver. {Key and Retzius.) rt. Axis cylinder; h, Ranvier's constriction. fibres. They occur also in the branches of the sympa- thetic nerve. The nerve fibres of the optic and acoustic nerve are medullated, but without any neurilemma ; they are there- fore without any nodes of Ranvier. Varicose fibres are common in them. 145. Medullated nerve fibres occasionally in their course divide into two me- dullated fibres. Such divi- sion is very common in 148 Elements of Histology. medullated nerve libres supplying striped muscular tissue, especially at or near the point of entrance into the muscular fibres. (See below.) But also in other localities division of nerve fibres may be met witli. Tlie electric nerve of the electric fishes — e.g. malapterurus, gym- notus, silurus — shows such divisions to an extraor- dinary degree, one huge nerve fibre dividinc; at once into a bundle of minute fibres. Division of a medullated fibre takes place generally at a node of Ranvier. The branches taken together are generally thicker than the undivided part of the fibre, but in structure they are identical with the latter. 146. When medul- lated nerve fibres ap- proach their peripheral Medullated xen-e Fibres, termination, they change A, B. Showinc on a surface view the i x • 1 reticulated nature of the medullary SOOner Or later, inasmUCh sheath; c, two nerve fibres showintr ±a • in 1 ji the axis cylinder, the medullary aS their meOUJlary Slieath sheath with their vertically-arranged i i i i minute rods, and the delicate neuri- SUCluenlV CeaSCS ; and UOW lemma or outer hyaline sheath. i ' 77 {.Atlas.) Ave have a non-meam- lated or grey (trans- parent) nerve fibre of Remak. Each of these consists of an axis cylinder, a neurilemma, and between the two a nucleated nerve corpuscle from place to place. Xon-medullated nerve fibres alwavs show the fibrillar nature of their axis cylinder. The olfactory nerve branches are entirely made up of non-meduUated nerve fibres. In the branches of the sympathetic A^ER I 'E Fibres. 149 most tilnes arc iiou-medullated. Non-medullated til)res do not show Raiivier's constrictions. Bundles of non-medullated fibres are grey, bundles of medullated Hbres are white, when viewed in reflected light ; the former being without medullary sheath allo'.v light to Fig. 103. — View of the anterior surface of Gold-stained Cornea of Guinea- pig, showing the rich distribution of the terminal nerve tibrilhe and their ramifications in the anterior epithelium of the cornea. {Photo., highly magnified.) pass through them, while the latter owing to their medullary (fatt}') sheath reflect light strongly. In the extra-vertebral course of many branches of the cerebro-spinal nerves — e.g. those supplying the limbs, the wall of the chest and abdomen — there occur non-medullated fibres generally in small groups ; ISO Elements of Histology. these fibres are considered to be derived from the sympathetic system, haviiii;' joined the cerebro spinal nerves by the grey portions of the rami communi- cantes (Gaskell). Tiie non medullated fibres near their terminal distribution always undergo repeated divi- sions. They form plexuses, large fibres branching into smaller ones, and these again joining. Gener- Fig. 104. — Dendritic terminations— Demlrons of Xerve Fibres. Transverse section of the optic lobe of a binl prepared by Golgi's method. (R. y Cajal. from Quain.) a, Optic fibres; ft, c, rf, e, dendrons of same in the diifereiit layers of the optic lobe ; 6 and 7 are the sixth and .seventh layers respectively of the organ. ally at the nodal points of these plexuses there are triangular nuclei, indicating the corpuscles of the neurilemma. 147. Finally the non-medullated nerve fibres leav- ing tlie plexuses ultimately lose their neurilemma and l)reak up into tlieir constituent small bundles and even single primitive nerve fihrillce, which occasion- ally show regular varicosities (Fig. 105). Of course, of a neurilemma or the nuclei of the nerve corpuscles there is nothing left. The bundles of primitive fibrils Nerve Fibres. T51 and also single fibrils branch and interlace, whereby a more or less dense dendritic ramification — avhoriHa- tion or (/c?irfywi— is produced (Fig. 104). The indivi- Fig. 105. — Nerve Fibres of tlie Cornea. a, Axis cylinder near the anterior epithelium of the cornea splitting up into its constituent primitive flbrillaj ; &, primitive flbrillae. dual fibrils of the dendron are straight or twisted, and often provided with smaller or larger terminal knobs. In some localities — e.g. in the grey matter of the central nervous system — the number of fibrils con- 152 Elements of Histology. stituting a dendron is large, and hence the dendron is conspicuous, in other localities the number of tibrils is relatively scanty — e.g. in the anterior epithelium of the cornea — and hence the arborising character of the dendron is not very conspicuous (Fig. 103). Fig. 106. — Intra-epitlielialXerve-teriniuation in the Anterior Epithelium of the Cornea, as seen in an oblique section. (Handbook.) a. Axis cylindei' ; b, sub-epithelial nerve flbrillie ; c, iutra-epithelial i-amiflcatiou ; d, epithelial cells. Pronounced dendrons are found in the nerve termin- ation in muscle and tendon (the endplates) in the branched processes (dendrites) of the ganglion cells in the central nervous system, as will be described and illustrated later. In the skin, cornea and mucous membranes, the peripheral termination — ■ i.e. the primitive fibrils and their ramitications. are intra-epithelial (Fig. lOG), i.e. they are situated in the stratum Malpighii of the epidermis, in the epithelial parts of NeR VE FlBR ES. 153 the hair follicle, in the anterior epithelium of the cornea, or in the epithelium of the mucous mem- branes. The primitive nerve fibrils lie in the inter- stitial substance between the epithelial cells, and some of them have been observed to end with minute Fig. 107. — From gold-stained cornea of frog, showing the numerous beaded line nerve fibrils and the branched corneal corpuscles. [Photo., highly magnified.) knobs in the cell substance itself close to the nucleus (Pfitzner, Macallum). 148. Tracing then a nerve fibre, say one of com- mon sensation, from the periphery towards the centre, we have isolated primitive fibrils or their ramifications ; they form by aggregation simple axis cylinders, which vary in thickness according to the number of their 154 Elemexts of Histology. constituent primitive til)rils. These axis cylinders then become invested bv neurilemma and nuclei, and form plexuses. By association they form larger axis cylinders, and these form typical non-medullated nerve fibres with neurilemma, and with the nuclei of nerve corpuscles (Fig. 106). Lastly, if a medullary sheath makes its appearance between the neurilemma and the axis cylinder of each fibre we get a rneduUated nerve fibre. 155 CHAPTER XV. PERIPHERAL NERVE-ENDINGS. 149. In the preceding chapter we referred to the termination of the nerves of common sensation, .as iso- lated primitive fibrillre, and as ramifications and den- drons of these in the epitlielium of the skin and mucous membranes, in the anterior epithelium of the cornea, and in the grey matter of the central nervous system. Besides these there are other special terminal organs of sensory nerves, probably concerned in the per- ception of some special quality or quantity of sensory impulses. These are all connected with a meduUated nerve fibre, and are situated not in the epithelium of the surface but in the tissue, at greater or lesser depth. Such are the corpuscles of Pacini and Herbst, the end-bulbs of Krause in the tongue and con- junctiva, the genital end-corpuscles or end-bulbs in the external genital organs, the corpuscles of Meiss- ner or tactile corpuscles, in the papillae of the skin of the volar side of the fingers, the touch-cells of Merkel, the end-corpuscles of Grandry, in the beak and tongue of the duck. 150. The Paciiiisiii corpuscles. — These are also called Yater's corpuscles. They occur in large numbers on the subcutaneous nerve fibres of the jDalm of the hand and foot of man, in the mesentery of the cat, along the tibia of the rabbit, in the genital organs of man (corpora cavernosa, prostate). Each corpuscle is oval, more or less pointed, and in some places (palm of the human hand, meseutery of the cat) easily percej)tible to the unaided eye, the largest '56 Elemexts of Histology. beino; about T.^rrtli of an incli Ioiijt; and ^th of an inch broad ; in other places they are of microscopic size. Each possesses a stalk, to which it is attached, and which consists of a single medullated nerve fibre (Fig. 108), differing froin an ordinary medullated nerve fibre merely in the fact that outside its neuri- lemma there is present a thick laminated connec- tive-tissue sheath. This is the sheath of Henle — continuous with the perineural sheath of the nerve branch with which the nerve fibre is in con- nection. This medullated nerve tibre within its sheath possesses generally a very wavy outline. The corpuscle itself is com- posed of a large number of lamella, or capsules, more or less concentric- ally arranged around a central elongated or cylin- drical clear space. This space contains in its axis, from the proximal end — i.e. the one nearest to the stalk — to near the opposite or distal end, a continuation of the nerve tibre in the shape of a simple axis cylinder. But this axis cylinder does not fill out the central space, since there is all round it a space left filled with a transparent substance, in which, in some instances, rows of spherical nuclei may be perceived along the margin of the axis cylinder. At or near the distal end of the central space the axis cylinder divides in tico or Fig. lOS. — Pacinian Corpuscle, from the Mesentery of Cat. a, Medullated nerve fibre : b. concen- tric capsules. Per ipher a l Ner ve-endings. ^57 more branches, and these terminate in pear-shaped, oblong, spherical, or irregularly-shaped granular- looking enlargenients. 151. The concentric cajjsules forming the corpuscle itself are disposed in a different manner at the peri- phery and near the central space from that in which they are dis- posed in the middle parts, in the former localities being much closer together and thinner than in the latter. On looking, therefoi-e, at a Pacinian corpuscle in its longi- tudinal axis, or in cross-section, we alwaj^s notice the striation (indicating the capsules) to be closer in the former than in the latter places. Each capsule con- sists of — (rt) a hyaline, probably elastic, ground substance, in which are embedded here and there (b) fine bundles of connective- tissiie fibres; (c) on the inner surface of each capsule, i.e. the one directed to the central axis of the Pacinian corpuscle, is a single layer of nucleated endotJielifd plates. The oblong nuclei A'isible on the capsules at ordinary inspection are "• ^'"^''" u\;^a\vay.'''^ ^''''^ the nuclei of these endothelial plates. There is no fluid between the capsules, but these are in contact with one another (Huxley). Neighbouring capsules are occasionally connected with one another by thin fibres. 152. In order to reach the central space of the corpuscle, the medullated nerve fibre has to perforate the capsules at one pole ; thus a canal is formed in which is situated the medullated nervQ fibre, and Fig. 109.— Herbst's Cor- puscle, from the Tongue of Duck. 1:^8 Elements of Histology. as such, and in a very wavy condition, it reaches the proximal end of the central space. This part of the nerve fibre may be called the intermediate part. The lamellae of the sheath of Henle pass directly into the peripheral capsules of the corpuscle. Immediately before entering the central space, the nerve fibre divests itself of all pirts except the axis cylinder, which, as stated above, passes into the central space of the Pacinian corpuscle. In some cases a minute artery enters the corpuscle at the pole, opposite to the nerve fibre ; it penetrates the peripheral capsules, and supplies them with a few capillary vessels. loo!^ The corpuscles of Horbst are similar to the Pacinian corpuscles, with this difference, that they are smaller and more elongated, that the axis cylinder of the central space is bordered by a continuous row of nuclei, and tliat the capsules are thinner and more closely placed (Fig. 109). This applies especially to those near the central space, and here between these central capsules we miss the nuclei indicatinii the endothelial plates. Such is the nature of Herbst's corpuscles in the mucous membrane of the tongue of the duck, and to a certain degree also in tliose of the rabbit, and in ten- dons. 154. The tactile corpuscles, or corpuscles of ^leissuer, oc- cur in the }>apilhe of the corium of the volar side of the fingers and toes apes ; they are oblong, straight, or In man they are about —t, to Fig. IIO'.— Tactile Cor- puscle of Meiss- ner from the Skin of the Human Hand. (£. FiscUr awl W. Flemming.) Showing the convolu- tions of the nerve fibre. in man and in slightly folded. 1 3 pf an inch long, and 5 00 to -i- of 2 ^^ an inch broad. Per ip/fER A L Ner ve-endings. 159 They are connected with a medullated nerve fibre — generally one, occasionally, V)ut rarely, two — with a sheath of Henle, The nerve fibre enters the corpuscle, but usually before doing so it winds lound the cor- puscle as a medullated fibre once or twice or oftener, and its Henle's sheath becomes fused with the fibrous capsule or sheath of the tactile corpuscle. The nerve fibre ultimately loses its medullary sheath and pene- trates into the interior of the corpuscle, where the axis cylinder branches ; its branches retain a coiled course all along the tactile cor- puscle (Fig. 110), anastomose with one another, and ter- minate in slight en- largements, pear- shaped or cylindrical. These enlargements, according to ]Merkel, are touch-cells. The matrix, or main part of the tactile cor- puscle consists, be- sides the fibrous sheath with nuclei and numerous elastic fibres, of fine bundles of connective tissue, and number of nucleated small cf-lls. 155. The end-bulbs of Krauze. — These occur in the conjunctiva of the calf and of man, and are oblong or cylindrical minute corpuscles situated in the deeper layers of the conjunctiva, near the corneal margin. A medullated nerve fibre, with Henle's sheath, enters the corpuscle (Fig. 111). This possesses a nucleated capsule, and is a more or less laminated Fig. 111. — End-bulljof Kraii.sc. Medullated nerve fibre : b, caiisule corpuscle. )f the of a i6o Elemexts of Histology. (in man more granuLir-looking) structure, numerous nuclei being scattered between the lamina?. Of the nerve fibre, as a rule, only the axis cylinder is pro- longed into the interior of the corpuscle. Occasion- ally the medullated nerve fibre passes, as such, into the corpuscle, being at the same time more or less convoluted. Having passed to near the distal ex- tremity, it l)ranches, and terminates with small enlargements (Krause, Longworth, Merkel, Key and Retzius). The end-hidbs in the genital organs, or the genital corpuscles of Krause, are similar in structure to the simple end-bulbs. They occur in the tissue of the cutis and mucous membrane of the penis, clitoris, and vagina. 156, The €ori>ii«irIe«» of Graiidry, or tou.ch corpuscles of Merkel, in the tissue of the papill?e in the beak and tongue of birds, are oval or spherical corpuscles of minute size, possessed of a very delicate nucleated membrane as a capstile. aud consisting of a series (two, three, four, or more; of large, slightly- flattened, granular-looking, transparent cells, each with a spherical nucleus, and arranged in a vertical 71 A B -^ C Fig. 112. — Corpuscles of Grandry in the Tongue of Duck, {Iz2uierdo.) A, Composed of three cells : b. composed of two cells ; c, showing- the develop- ment of a Grandry's corpuscle from.tlie epithelium covering the papilla, p; e, epithelinra ; 'i, nerve fibre. row (Fig. 112). A medullated nerve fibre enters the corpuscle from one side, and losing its medullary Per ipheral Ner ve-endings. i6[ sheatl), the axis cylinder brandies, and its branchlets terminate, according to some (Merkel, Henle), in the cells of the corpuscle (touch cells of Merkel) ; accord- ing to others (Key and Retzius, Ranvier, Hesse, Izquierdo), in the transparent substance between the touch cells, thus forming the '• disc tactil " of Ranvier or the " Tastplatte " of Hesse. Neither theory seems to us to answer to the facts of the case, since we find Fig. 113.— Bundles of Non-striped Musenlar Tissue surrounded by Plexuses of Fine Xerve Fibres. (Hamlbook.) that the branchlets of the axis cylinder terminate, not in the touch cells, nor as the disc tactil, but with minute swellings in the interstitial substance between the touch cells, in a manner very similar to what is the case in the conjunctival end-bulbs. According to IMerkel, single or small groups of touch cells occur in the tissue of the papilhe, and also in the epithelium, in the skin of man and mammals. 157. In Jirtieiilatioiis — e rj. the knee-joint of the rabbit — Xicoladoni described numerous nerve branches, from which fine nerve fibres are given off. Some of these terminate in a network, others on blood-vessels, and a third group enter Pacinian cor- puscles. Krause described in the synovial membranes L l62 Elements of Histology of the joints of the human fingers medullated nerve fibres whicli end in peculiar tactile corpuscles, called by him '^ articular nerve corjiuscles.'" 158. The nerve branches snpplyiiig^ non- striped ninsenlar tissue are derived from the sympathetic system. They are composed of non- medullated fibres, and the branches are invested in an endothelial c 5 sheath (perineu- ^\"^ \ \\ \ » rium). The branches divide into single or small groups of axis cylinders, which reunite into a plexus — the ground plexus of Ar- nold. Small fibres coming oflf from the plexus supply the in- dividual bundles of non - striped muscle cells, and they form a plexus called the intermediary lilexus (Fig. 113). The fibres joining this plexus are smaller or larger bundles of primitive filu'illa? ; in the nodes or the points of meeting of these fibres are found angular nuclei. From the intermediate plexus pass oft' isolated or small groups of primitive fibrillar, which pursue their course in the interstitial substance between the muscle cells; these are the intermuscular Fig. 114. — Termination of Nerves in Xon-striped Muscular Tissue. {Atlas.) a, 3Cou-inPduUated flltre of the iutermediary plexus; b, fine intermuscular flbrils ; c, nuclei" of mus- cul;ir cells. Peri p HER a l Ner i 'e-end/xgs. 163 According to Frankenliaiiser and the the the fibrils (Fig. lU) Arnold, tlicy give oti' tiner tihrils, ending in nucleus (or nucleolus). According to Elischer, primitive fibrils terminate on the surface of nucleus with a minute swellinij. In many localities there are isolated ganglion cells in connection with the intermuscular tibres. 159. The nerves of blood-vessels are derived from the sympathetic, and they terminate in arteries and veins in essentially the same way as in non- striped muscular tissue, being chiefly present in those Fig. 115. — Plexus of Fine Xon-iiiedullated Xerve Fibres .surrounding Capillary Arteries in the Tongue of Frog, after staining Avith chloride of gold. (Handbook.) a, Blood-Tessel ; 6, connective tissue corpuscles ; c, thick non-medullated fibres rf, plexus of fine nerve fibres. parts (media) which contain the non-striped muscular tissue. But there are also fine non-medullated nerve fibres, which accompany capillary vessels — capillary arteries and capillary veins — and in some places they give off elementary fibrils, which form a plexus around the vessel (Fig. llo). In some localities the 1 64 Elements of Histology. vascular nerve brandies are provided witli small groups of ganglion cells. 160, In striped muscle of man and mammals, reptiles and insects, the termination of nerve fibres •^^^mfi'ID^-i^i-'K •^•^>^' 4 Fig. 116. — Nerve-endings in Striped Muscular Fibres. (Kindly lint by Professor Kiiline.) A, In fresh muscular fibre of Lacerta, x ^^ ; b, in gold-stained muscular fibre of lacerta, X ^^•, c, in gold-stained muscular fibre of flog, x ^-Y- ! m, medullated nerve fibre ; t, termination of axis cylinder underneath the sarcolemma of the muscular flv>re. takes place, according to the commonly accepted view of Iviihne, in the following manner (Fig. 116) : — A medullated nerve fibre, enclosed within a lamellated sheath (Henle's sheath) divides at a node of Ranvier, each branch — a medullated nerve fibre — enters under a variable angle a striped muscular fibre, the neurilemma Periphera l Ner ve-endings. becoming fused with the sarcolemuia, and the nerve fibre, either at tlie point of entrance or immediately afterwards, loses its medul- lary sheath, so that only the axis cylinder, with its axi- lemma, })asses on, and then forms on the sui'face of the muscular substance a ter- minal arborisation or den- dron, which is called the nerve endpJate. Each axon, on entering, gives off by division several branches like antlers : in amphibia these branches are rodlike, long, and of the form of baj^onets ; in mammals they are crooked, hook-like. In all instances, however, the divisions are unsymmetri- cal. In many cases the arborisation of the endplate is embedded in a granular mass of protoplasm con- taining oblong nuclei. This nucleated protoplasm is identical with the substance of the sarcoglia, or the sarcoplasm mentioned on a former page. When the muscular fibre contracts, this endplate naturally as- Fig. 117.— Muscle Spindle of the sumes the shape of a pro- ^'^l^^it treated with gold chio- t J i iide. (Kolliker, II.) mmence — Boyere s nerve „^ ^^^^,.^ q^,,,^ terminating' iu the Oiinoi'^if ^^'npl^ mnQpnlnr middle p;iit of the spiiidlt- us a lUOUlil. JLaCil mUbCUiai spiral endiDg of fine Hbrils. i66 Elements of Histology. libre has at least one nerve endplate, but occa- sionally has several in near pioximity. Each end- plate is generally supplied by one nerve fibre, some- times, however, by two. The contraction wave generally starts from the endplate. The muscle Fiy;. lis. — Termiuation of ilediillated Nerve Fibres in Tendon, near the Insertion of the Striped Muscular Fibres. (Golgi.) The nerve fibres terminate in peculiar arborising eudplates of primitive fibrillae huds of KoUiker or muscle spindles of Kiihne (mentioned on a former page) contain numerous medullated nerve fibres with lamellated Henle's sheath, and these nerve fibres terminate in the same manner, namely, by means of nerve endplates (Fig. 117). In these endplates the fine nerve fibres have a sj^iral arrangement (Ruffini). These are con- sidered to be sensorv end-organs. According to Kol- liker, from the primary nerve ending of the mother fibre — i.e. of the undiWded portion of the spindle — grow out the ner\e endings for the thin daughter fibres. PeRIPHERA L NeR I 'E- EN DINGS. 167 .-a Besides this iutra-musciilar termination, tliere is a plexus of tine nev\e fibres, many of them said to terminate with free ends, situated outside the sarcolemma — i.e. intermnscuh\r ; such free ends are described by Beale, Kolliker, Krause, and others. Kolliker and Arndt consider these intermus- cular fibres as sensory ,.:^:v -- :^ nerves, 161. Ten- dons are sup- plied w i t h special nerve endings, studied by Sachs, Rol- lett, Gempt, Rauber, and particularly G olgi, whose work on this subject is ex- tensive. These terminations are most numerous near the muscular insertion. They are of the follow- ing kinds : — («) A medullated nerve fibre branches repeatedly, and the axis cylinder, after having lost the medullary sheath, breaks up into a small plate composed of a dendritic ramification of fine primi- tive nerve fibrils (Fig. 118). Owing to the number of the fibrilla3 and their repeated crossing, it is difiicult to say whether the appearances as shown in Fig. 119 cor- respond to a real network or to a dendron. This end- plate is occasionally embedded in a granular-looking material, and thereby a similar organ as the nerve end- plate in muscular fibres is produced (Fig. 119). (6) In the tendons of man and many mammals Golgi has shown that nerve fibres terminate in peculiar spindle-shaped Fig. 119. — One of the Teriniual Ramitk-atioiis of the previous figure, more highly magnified. rt, Medullated nerve fibre ; ft, apiiareutly reticulated endplate. {Golgi.) i68 Vj^I <. I Fig. 120. — Two Tendon Spindles of Golgi in tlie rabliit, sliowing the distri- bution and spiral terniination ol' the nerve fibres ou the spindles. {After K oil Her.) Per I pn ERA l Ner ve-en dings. 169 enlargements of tendon Ijundles (Fig, 120). These tendon spindles of Golgi consist each of two, three, or more tendon bundk's within a common sheath ; a bundle of fine medullated nerve fibres enters the Fig. 121.— Termination of Metlnllated Nerve Fibres in Tendon. {Golgi.) a, End-lnilbs with couvoliited lueclullatecl nerve fibre ; b, end-bulb similar to a Herlist's corpuscle. spindle, their axis cylinders break up into primitive fibril he, which are arranged as a network and as spiral fibrillar. (c) A medullated nerve fibre ter- minates in an end-lmlb (Fig. 121), similar to those of the conjunctiva, or of a Herbst's corpuscle. 170 CHAPTER XVI. THE SPINAL CORD. 1 G2. The spinal cord is enveloped in three distinct membranes. Tiie outermost one is the dura mater. This is composed of more or less distinct lamellag of fibrous connective tissue with the flattened connective- tissue cells and networks of elastic fibres. The outer and inner surface of the dura mater is covered with a layer of endothelial plates. 163. Next to the dura mater is the extremely delicate arachnoid membrane. This also consists of bundles of fibrous connective tissue. The outer surface is smooth and covered with an endothelial membrane facing the space existing between it and the inner surface of the dura mater ; this space is the subdural lyniph space. The inner surface of the arachnoidea is a fenestrated membrane of trabeculse of fibrous connective tissue, covered on its free surface — i.e. the one facing the sub-arachnoidal lympli space — with an endothelium. 164. The innermost memVjrane is the pia mater. Its matrix is fibrous connective tissue, and it is lined on its outer surface with an endothelial membrane. Also the inner surface facing the cord j)roper has an endothelial lining, but this is not as complete and continuous as that of its outer surface. Between the arachnoid and pia mater extends, from the fenes- trated portion of the former, a spongy f)lexus of trabeculse of fibrous tissue, the surfaces of the trabeculse being covered Avith endothelium. By this Sr/NA L Cord. lyr spongy tissue — tho snh-araclinoidal tissue (Key and Ketzius) — the subarachnoidal space is subdivided into a labyrinth of areohe. On each side of the cord, between the anterior and posterior nerve roots, -•_» j^f J " -^■'^v*! Fig. 12-2.— Transverse section tlirougli the Cervical Cord of aeliild, 2 years old, sliowing well the anterior wliite commissure and the numerous nieduUated fibres passing horizontally through the grey matter (col- laterals) from and to the white columns. {Weigcrt.) z, Tract of Goll ; B, tract of Burdach ; l, tract of Lissauer. extends a spongy fibrous tissue, called ligamentuni denticidatiiin, between the arachnoidea and pia. By it the sub-arachnoid al space is subdivided into an anterior and posterior division. 165. The subdural and sub-arachnoidal spaces do not communicate with one another (Luschka, Key and Retzius). ^7 Elements of Histology. The dura mater, as well as the arachnoid, sends prolongations on to the nerve roots ; and the sub- dural and sub-arachnoidal spaces are continued into the lymphatics of the peripheral nerves. li.C, Fig. 123a. — Transverse section of the Spinal Cord in tlie Cervical region- {M icrophotog raph of Weigcrt-Pal specimen.) p. E. c, Postero-extenial column ;C.g., postero-niedian column or colmnu of GoU ; p. u., the issuing posterior root ; L. c. lateral column : a. f., anterior or ventral Assure. The white matter is more deeply stained than the more central grey. All three membranes contain their own system of blood-vessels and nerve fibres. 166. The cord itself (Fig. 122) consists of an outer or cortical part composed of medullated nerve fibres : the ichite matter, and an inner core of grey matter. On a transverse section through the cord the Spinal Cord. 17.3 contrast of colour between the white mantle and the grey core is very conspicuous. The relation between the white and grey matter differs in different parts ; it gradually increases in favour of the former as we P.E.C. L.H. L.C A.F. Fig. 123b. — Section of the Spinal Cord in the Dorsal region. {Micropliotograph of a IVeigert-Pal specimen.) Note the small aiii) a network of very Spinal Cord. 183 delicate fibrils — npurotjlia fibrils — which are similar in some respects, but not quite identical with elastic fibres. In the columns of the wliite matter the p.m. Cty.o. a.c. Fig. 129.— Cross-section of the central part of the Spinal Cord from tlie Lumbar region of an Adult, showing the central canal, its lining epithe- lium surrounded by neuroglia, forming the central grey nucleus, (After Schdfer.) /.a., Anterior median fissure; p.m.c, posterior white column ; ff.c, anterior white comniissure. fibrils extend chiefly in a longitudinal direction, in the gi'ey matter they extend uniformly in all directions, and in the septa between the columns 184 Elements of Histology. they extend for the most part radially, (c) Richly branched nucleated cells intimately woven into the network of neuroglia fibrils. These cells are the neuroglia cells or glia cells. Golgi was the first to show that though richly branched they do not anasto- mose with one another. The sweater the amount of ^^%f|^NiS»/ 1^ * Fig. 1:30a.— Cross-section tlii-ongh central canal of tlie cord, sbowiug the lining epithe- lium, from a child of sis. (After Schdfer.) Fig. 130b.— CUiated Epithe- lium lining the central canal of the cord in a child of six, more highly magnified than in Fig. 130a. {After Scha/er.) neuroglia in a particular part of the white or grey matter, the more numerous are these three elements (Figs. 127 and 128). In both the white and grey matter the neuroglia has a very unequal distribution ; but there are certain definite places in which there is always a considerable amount — a collection, as it were, of neuroglia tissue. These places are : («) underneath the pia mater — i.e. on the outer surface of the white matter : here most of the neuroglia fibrils have a horizontal direction ; near the grey matter there is a greater amount of neuroglia between the nerve fibres of the white matter than in the middle parts of this latter : in the septa between the columns and between the Spinal Cord. 18: divisions of columns of white matter ; at the exit of the anterior and the entrance of the posterior nerve roots. (6) A considerable accumulation of neuroglia is present immediately around the epithelium lining the Fig. 131.— Central C'aual of the Cord of a Child, 1^ year old ; the cells of ependyina are well shown, with their long filamentous processes. {Kdlliker, II.) central canal ; this mass is cylindrical, and is called the central grey nucleus of KoUiker (Fig. 129). The epithelial cells lining the central canal are conical, their bases facing the canal, their pointed extremity being drawn out into a fine filament intimately inter- woven with the network of neuroglia fibrils. In the embryo and young state (Figs. 130a and 130b), the free base of the epithelial cells has a bundle of cilia, but in the adult they are lost amongst the epithelial cells 1 86 Elements of Histology lining the central canal : some show in i:)reparations stained after Golgis method processes of extreme length (Fig. 131). (orising dendrons of the dendrites of ganglion cells or surround the hody of the ganglion cells. Owing to the great number of such collaterals, as mentioned on a former page, their arborisations or dendrons form a considerable por- tion of the grey matter. Sherrington sug- gests W.W the term of synapsis {avv and (tTr-w) as indicating the contiguous but not continuous re- lation of the arbo- rising terminations of axons surround- ing the arborising dendrites or the body of a ganglion ■m\^ cell. Such synapsis would then occur everywhere in the central nervous sys- tem (cord, brain, medulla, Sympa- t^ig- 137A.-Scheme of the Elements of the Conl , . ' T concerned in Reflex Actions. Longitudinal thetlC ganglia, re- view. (Kdlliker,II.) where .s- rj, Ganglion cell of a spinal ganglion ; s, sen- sory flhre coming from the periphery; sth, division of a posterior root fibre into sa, an ascending and descending fibre; sc, collaterals of same passing to motor ganglion cells, m ; m ('•, motor (anterior) root fibres being axons of anterior nerve cells. tina, etc. ) neuraxons and their collaterals of a near or distant ganglion cell arborise ( ter- minate) around dendrites or the cell body of a ganglion cell. A second, also considerable, portion of the grey 200 Elements of Histology. — L/is, Fibres of the crossed pyramidal tract in the cord ; these fibres had crossed (pyramidal crossing) m the medulla ; collaterals of these fibres pass into and terminate in the grey matter of the cord : p o, fibres of the direct pyramidal tract in the cord, collaterals cross in the cord ; m, nerve cells in the anterior grey horns; 7?i. if, axons of same forming the fibres of the motor (anterior) roots. Spinal Cord. 201 it is shown that tlie grey matter contains a really astonishing number of medullated nerve fibres, run- ning singly or in small bundles, horizontally and obliquely. All the above collaterals, as also the continuations of the fibres passing from the white columns into the grey matter, or vice versd, are medullated fibres {see Figs. 122 and 123a). 183. The large vascular branches enter the white matter of the cord from, or pass out by way of the pia mater, being invested in neuroglia continuous with the tissue of the pia mater. By continued division they resolve themselves into fine branches, which pass into, or pass from, the network of capillaries. The capillaries are more abundant and form a more uniform network in the grey than in the white matter. In the latter most of them have a course parallel to the nerve fibres, i.e. longitudinally. The blood-vessels and the orano^lion cells are ensheathed in lymph spaces (perivascular and pericellular spaces). 202 CHAPTER XVII. THE MEDULLA OBLONGATA OR SPIXAL BULB. 184. As the cervical portion of the spinal cord passes into the medulla oblongata its parts alter in position and relation. It is possible, to a large extent, to recognise in the bulb, regions which correspond to different areas of the cord. Many of the cord areas are, however, lost in the bulb, and on the other hand, many new areas appear. 185. The anterior or ventral fissure is continued as far as the bulb extends. The posterior or dorsal fissure of the cord is also continued for a certain distance along the medulla, but this widens out in the upper part of the bulb into the lower end of i\\e foui^th ventricle. The line of origin of the anterior roots of the spinal cord is continued into the medulla, being marked out by the exit of the roots of the hypoglossal nerve. In the upper portion of the medulla this line of origin develops into a marked fissure. The shallow groove existing dorsally between the postero-median and postero-external columns of the cord is even better marked in the bulb, and divides the funiculus gracilis (median) from the funiculus cuneatus (external). The postero-lateral groove into wliicli the posterior roots pass to the cord is continued up as the external boundary of the funiculus cuneatu.s and the internal boundary of yet another longitudinal projection, leading u]3 to a prominence, the tubercle of Rolando. In the upper portion of the cervical cord there project from the lateral columns the roots of the spinal Med ul la Oblo nga ta . 203 accessory nerve. The line of origin of these roots is continued up along the lateral surface of the bulb and there arise successively along this line the roots of Fig. 138.— Section through the Lower Eud of the Pyramidal Decussation. The section is slightly distorted. {Microphotograph of section stained with aniline Nue-blacl-.) A. F., Anterior or ventral Assure lying obliquely on accountiof fibres passing from crossed pyramidal tract on left side to anterior column on risht ; p. k., pos- terior Assure ; i. f., corresponds to septum l)etweenGoirs columnand postero- external column : p. li., posterior root of first cervical nerve ; on the left side at level a. h. the anterior horn is separated from rest of grey matter. The substantia gelatinosa at tip of posterior horn is increased, and the angle between the posterior horns is greater than below. the spinal accessory, the vagus, and the glosso- jyharyngpxd. At the junction of the bulb with the pons the seventh nerve passes out in the same line, and passing through the substances of the pons \\\q fifth nerve possesses a corresponding origin. 204 Elements of Histology. 186. It will be found most convenient in order to determine the relation of the different regions in the bulb with those of the cord, to examine the appearances presented by successive sections of the Fig. 139.— Section thi'ougli the Upper Part of the Pyramidal Decussation in the Medulla Oblongata. {Microphotograph of a Weigert-Pal specimen.) A.F., Remains of anterior Assure; the dark mass immediately above consists of the decussating pyramidal fibres ; at the level A. H. is a light mass on either side represeatinff the remains of anterior liorn; at tue level c. c. in the middle line is the grey matter round the central canal ; the posterior nuclei are not clearly distinguishable. bulb, cut in a dorso-ventral direction, and com- mencing at a level immediately above the cervical spinal cord. 187. The region of the pyraiiiiclal decus- sation (Figs. 138 and 139). — In this region the fibres Mrd ul l a Ob long a ta . 205 of the crossed pyramidal tract, lying in the dorsolateral portion of the cord, take on an oblique course and, passing across the middle line, again resume their direct course in what would correspond in the cord to the P.F. •c.c S D. M. A.F. Fig. 140.— Section through the Medulla Oblongata at the level of the Sensory Decussation. {Photograph of a Weigert-Pal specimen.) The section has not involved the olives ; the pyramids are completely formed and project at p, and extend inwards as far as the level sr, meeting in the middle line. At level of c.c. on middle line is the central canal, and at a short distance from this are seen numerous fibres arching round and decus- sating on middle line at level s.u. ; k, lies between funiculi gracilis and cuneatus. anterior or ventral column. In their passage across to the other side of the medulla these fibres separate oft' the head of the anterior horn so that the grey matter of the cajnit lies in the anterior area disconnected from the main mass of the grey matter. The angle formed by the median boundaries of the two posterioi^ 2o6 Elements of Histology. horns increases very considerably, so that these horns come to lie more transversely across each half of the medulla than was the case in the cord. There develop also from this inner margin of the posterior horns, in the iij)per part of the pyramidal decussation, certain protuberances of grey matter ; a median mass projecting into the funiculus gracilis and known as the mideus of the funiculus gracilis Rud a more externally situated mass, projecting into the funiculus cuneatus, and known as the nucleus of the funiculus cuneatus. The substantia gelatinosa at the tip of the posterior horn also becomes more conspicuous and causes the medulla to project in this region, forming the funiculus uf Rolando. Higher up this projection becomes even more conspicuous and is known as the tubercle of Rolando. In the region of the pyramidal decussation the substantia gelatinosa of Rolando is separated from the surface by a longitudinal mass of medullated fibres which pass to the origin of the fifth nerve. This mass of fibres is spoken of as the ascending root of the fifth nerve. 188. The region between the npper end of the pyramidal cleenssation and the eouiniencenient of the olives (Fisf. 140). — In this region the central canal is seen to lie more posteriorly corresponding to its gradual approach towards the posterior surface. The p3Tamids oc- cupy well defined positions on the ventral side of the bulb immediately abutting on the anterior fissure and bounded laterally by the fibres of the hypoglossal nerve coursing from the nucleus of the twelfth, across the medulla. There is to be seen lying in the lateral region between the substantia o^latinosa of Rolando and the fibres of the twelfth, a mass of cells, which correspond to some extent to the more dorsal portion of the separated anterior horn, but which in part is to be regarded as a new formation. Medulla Oblongata. 207 This mass of cells is spoken of as the lateral HKc/f'us. It is to be noticed tliat the ])Osterior white matter is gradually undergoing absorption, being invaded by the grey matter of the corresponding nuclei. The grey matter of these nuclei gradually becomes more marked, the nucleus of the funiculus gracilis early absorbing the white matter of the column and lying quite close to the surface. The nucleus of the funiculus cuneatus lies rather more deeply, but is gradually invading the white substance. The central portion of the medidla becomes broken up, and fibres are seen passing in an arched manner from the nucleus gracilis mainly, and, to some extent, from the nucleus cuneatus towards the middle line. These arched fibres on reaching the middle line, for the most part bend longitudinally, and thus form a mass of fibres lying dorsal to the pyramids, and spoken of, higher up, as the inter-olivary layer. This decussation of fibres passing from the gracile and cuneate nuclei is sometimes referred to as the supei'ior or sensory decussatior. 189. The region of the lower portion ol the olives (Fig. 141). — A few millimetres higher up than the last section the olives are seen to be distinctly formed, though they have not reached their greatest size and though the central canal is still closed. The central canal has at this level approached yet more closely to the posterior suiface. Each lateral half of the bulb may be more or less distinctly marked off into three areas : a median area lying between the middle line and the roots of the twelfth nerve as they coui^e across the bulb from the hypoglossal nucleus : a lateral area, lying between the roots of the twelfth and those of the eleventh, which issue more laterally ; and an area, posterior to the eleventh roots, which may be called the posterior area. The lateral nucleus lies in the dorsal portion of the lateral area. The main 2o8 Elements of Histology. mass of tlie olive lies of the lateral area. Imt in the ventral portion two additional masses, S.G. XI. N 3. A. M.H. Fig. 1-tl. — Section through the Medulla Oblongata at level of commence- ment of Olives. {Microphotograph of a specimen stained with aniline hlue-hlack.) The central canal is not yet opened out, and is at level of x.s. a. : the posterior grey matter is arranged iu three masses, >'. g., nucleus gracilis, x.c, nucleus ciineatus, and s. g.. the substantia gelatinosa of Rolando: with respect to grey matter round central canal, that at level x. s. a, has cells forming nuclei of the xi, that at level x. h. forming nuclei of xii ; xi is placed against the line of issue of the spinal accessory, xii against hyi>oglossal ; the grey matter lying slightly beneath surface at level l.x. is the lateral nucleus; o, is at level of the twisted dark 1>and, the olive; the large light areas at level of p are the pyramids : the area more dorsal at level R. f. is the reticular formation, in the middle line of which is the raphe (.above a. f. i. similar in structure to the olive, may also be seen, one lying in the lateral area, dorsal to the main olive, kno^vn as the dorsal accessory olives and the other lying in the median area, separated Medulla Oblongata. 209 from the iimin olive by the roots of the liypoglossal nerve and known as the menial accessory olive. The more central ]»ortion of the section is seen to be broken np by til)res passing horizontally, separating others which are proceeding longitudinally; and yet other strands are to be noticed intersecting both of these. Nerve cells are scattered through this area, and more conspicuously in its lateral portions, and these nerve cells with attendant neuroglia may be regarded as representing the much ditiiised grey matter of the ventral horn which was separated by the decussation of the pyramidal fibres. This broken tissue is spoken of as the reticular formation, the more lateral portion, which appears darker on account of the nerve cells being more numerous, being referred to as the grey reticular formation, and the central j^art as the ■?r/n", from a collection of cells in the course of the lateral fillet, known as the nucleus qftJie lateral jillet j (3) from longitudinal fibres lying against the superior olive, which increase in ntmiber on proceeding upwards; (4) possibly, from fibres derived from the striae acusticae, which have passed ventrally into the tegmentum and turned into the tract of the"^ fillet. The ^jo/is proper is made up of numbers of transverse fibres passing laterally from the middle peduncles of the cerebellum on one side to that on the other. In crossing ventrally upon what is the continuation of the substance of the bulb these fibres divide the pyramids into groups of longitudinal fibres. The more dorsal of these transverse fibres (those lying immediately adjacent to the upward con- tinuation of the formatio reticularis) are known by the special name of the trapezium. Amongst the transverse fibres of the pons are numerous scattered masses of grev matter with which manv of the loncjitudinal fibres become connected. 194. The reg^ioii of tlie posterior coi*pora qiiadri^eiiiina and upper part of tlie poii^>. — The first section taken is immediately below (distal) the posterior corpora quadrigemina. The fourth ventricle has here narrowed to form the commence- ment of the aqueduct of Sylvius. Surrounding the channel is the ependyma enveloped on all sides by a considerable thickness of ^rex matter. In that Med ulla Obl onga ta . 227 portion lying on the ventral side maybe seen masses of cells foi-mini: the commencement of the nuclei of S.C.P IV. I. IV. V. S.C.P. P.L.B L.F M.F Fig. 147. — Section throu<:li the Pons Varolii immediately below the Posterior Corpora Quadrigemina. {Fhotograph of a U'eigert-Pal specimen.) The main mass of the section forms the fibre? of the pons (P). The two large dark masses in the upiier part (under >s. c. p. », the lower ends meeting in middle line, are the superior cerebellar peduncles or lirachia conjunctiva. The area included between their lower halves forms tbe teirmentum. Tbe iiuadrangular space lielow i is the Sylvian aiiueduct. Decussating in the valve of Vieussens above are seen fibres of the ivth nerve, the two small dark masses below iv being the main trunks lying obli.iuely. Lying a short distance below the aqueduct at p. l. b. are two dark comma-shaped masses, the posterior longitudinal bundles. The twu elongated dark masses one lying against l. f.. the ntlier passing l)etween the pons fibres and the superior cerebellar peduncles opposite M. f. are the lateral and median fillets. The darkish mass lying below v, just on the median side of the upper part of the peduncle is the descending root df vth. the fourth nerve. Lying again ventral to thi.s grey matter are two prominent longitudinal bundles on 2 28 Elements of Histology. either side of the middle Une, tapering towards the lateral region. These are the posterior longitudinal bundles. Near the lateral tapering end of these bundles may be seen the desceitdiag root of the fifth nerve, separated by a mass of cells forming the substantia femiginea or locus cceruleus. Lying to the median side of the root of the fifth may be seen bundles of white fibres pa^^sing into the superior nieduUary velum or valve of Vieussens, decussating here (Fig. 1J:7) and issuing literally as the fourth nerve. Lying again ventrally and laterally to the posterior longitudinal bundles, and separated from them by what is an upward continuation of the reticular formation, are the upward prolongations of the superior cerebellar peduncles or brachia conjunctiva. There at the level of the nuclei of the fifth nerve, in section, two semicircular masses lie immediately lateral to the side of the fourth ventricle. Passing upwards, they gradually take a more venti-al position till, as in the present section, they commence to fuse in the middle line. At a short distance externally and ventrally to the superior cerebellar peduncle is seen another band of longitudinal fibres. This band is of considerable thickness between the peduncle and the lateral surface, then passing ventrally it narrows somewhat^ and widens again to a fairly broad band lying on the dorsal side of the pons proper. This is the fillet or lem- niscus, the lateral portion witli nerve cells forming its nucleus being the lateral fillet, that portion lying adjacent to the pons being the median fillet. Ventrally to this again is the substance of the pons proper, having the characters described in ^ 193. A section slightly higher would pass through the posterior corpora quadrigemina. Here, there would appear two protuberances, dorso - laterally to the aqueduct. The lateral fillet forms connections with Medulla Oblongata. 229 these bodies. Tlie pons pioper is here soinewliat smaller, the up])er limit being appruuched. The two superior cerebellar peduncles gradually lessen in width, their lateral extensions disappearing by degrees. The nucleus of the fourth nerve consists of a mass of large multipolar cells lying in the grey matter on the ventral side of the aqueduct and near the middle line, and reaching from the upper to almost the lower extremity of the posterior corpora quadrigemina. The fibres from these cells take a somewhat oblique backward course to the lower limit of the posterior corpora quadrigemina where they decussate, as already described. In the region of the posterior cor[)ora quadrigemina the posterior longitudinal bundle is very prominent. The basal ends of the ependyma lining the aqueduct are frequently continued into a set of fine fibres which pass through the grey matter (and even beyond) and give a radially striated appearance to the region adjacent to the aqueduct. 195. The region ot llie anterior eorpora quadrigemina and the cinra eei ebri. — At this level (Fig. 148) the pons has disappeared, and its position is occupied by two well-marked protuberances on the ventral side, spoken of as the crura cerebri. Lying dorsally to the crus on each side is a broad band of black pigmented cells, forming the substantia nigra. The grey matter around the aqueduct is considerable, the posterior longitudinal bundle is somewhat less con- spicuous than below and forms a narrow band lying at the ventral edge of the central grey matter. Large nerve cells lie in the ventral portion of this grey matter, forming the nuclei of the third nerve, the fibres of which can be seen passing ventrally in many bundles. In the middle line between these roots a well-marked raphe is visible. Lying midway between the central grey matter and the substantia 230 Elements of Histology nigi'a is a large mass of cells, known as the red nucleus. In man this nucleus consists of cells vary- ing in size from 20-7 5yu. These nuclei have some R.N Fi< 14S.— Section through the Anterioi- Corpora Quadrlgemina. graj^li of a Weigert-Pal preparation.) {Photo- The section is somewhat oblique, lieing slightly higher on the right side than the left. The symmetrical projections above are the anterior corpora quadrl- gemina. The openiii!.' between them is the Sylvian aqueduct. Tlie lighter substance around this is the grey matter surrounding the iter. The darker masses forming tlie lower Ijoundary of this L'rey matter arranged in discrete areas on right side are the posterior longitudinal bundles, lyins in which are cells forming the nucleus of the third nt- rve. The bundles of fibres passing in an arched manner downwards from the third nucleus are the fibres of the third nerve. At level r. x. on right side is a large dark mass lyin.L' in a still darker patch, having the tibres of the third passing throusrh its median region. This is the commencement of the red nucleus, which is not yet evident on the left side, where a corresponding dark mass consists of the decussated fibres of the suiierior cerebellar peduncle. On the left side lying below and laterally to this mass and light in shade is the substantia nigra, this forms the base of a projection (the cms cerebrii, in which the fibres of • thepyramids and other fibres pass longitudinally. The dark band somewhat arched passing upwards to the anterior corpus quadrigeminum from the dark mass of the superior cerebellar peduncle is the fillet. Medulla Oblongata. 231 connection with the superior cerebellar peduncles, which terminate liere in their uj)\vard course. Laterally, the tillet is seen passing dorsally towards the prominent e of the vago-accessory, the fifth and the acoustic (vestibular branch). Connections also exist with the sixth, fourth, and third nuclei. The posterior longitudind bundle furnishes, therefore, commissural connections between the different eye muscles. Connections of the third nucleus also exist with the optic nerves. The hracJiia passing to the corpora quadrigemina are spoken of as the superior or anterior and the inferior or posterior. The fibres of the superior pass to the lateral corpus geniculatum and to the occipital tract. The fibres of the inferior brachium are connected with the median corpus geniculatum and possibly may pass through the tegmentum by the internal capsule to the temporal region. That portion of a transverse section through the region of the corpora quidrigemina which projects ventrally into the two crura is sometimes S[)oken of as the crusta, being separated from the remainder (tegmentum) of the region ventral to the aqueduct by the substantia nigra. The crusta contains, in addition to the fil)res derived from the pyramids which occupy a central portion in each crus, other fibres derived 23 4 Elemexts of Histology. from the pons. Those on the median side pass to the frontal region, those on the lateral portion to the temporal and occipital regions. Some fibres on the median side are derived from the median fillet. 235 CHAPTER XIX. THE CEREBRUM AND CEREBELLUM. 196. The structure of the dura mater, araclinoidea, and pia mater of the brain is simihir to that of the same membranes of the cord. As has been shown by Boehm, Key and lletzius, and others, the deeper part of the dura contains peculiar ampullated dilatations connected with the capillary l)lood- vessels, and forming in fact the roots of the veins. The glanduhe Pacchioni^ or arachnoidal villi of Lnschka, are composed of a spongy connective tissue, prolonged from the sub-arachnoidal tissue and covered with the arachnoidal membrane. These prolongations are pear-shaped or spindle-shajDed, with a thin stalk. They are pushed through holes of the inner part of the dura mater into the venous sinuses of this latter, but are covered with endothelium. Injected material passes from the sub-arachnoidal sjiaces through these stalks into the villi. Tlie spaces of their spongy substance become thereby filled and enlarged, and finally the injection matter enters the venous sinus itself. The pia cerebralis is very rich in blood-vessels, like that of the cord, which pass to and from the brain substance. The capillaries of the pia mater possess an outer endothelial sheath. The plexus choroideus is covered with a layer of polyhedral epithelial cells, which are ciliated in the embryo and in the young subject. 197. As was mentioned of the cord, so also in the 236 Elements of Histology. brain the subdural lymph space does not commu- nicate with the sub-arachnoidal spaces or with the ventricles (Luschka, Key and Retzius). Nor does there exist a communication between the sub- arachnoidal space and a space described by His to exist between pia mater and brain surface, but doubted by others. The relations between the cere- bral nerves and the membranes of the brain and the lymph spaces of both, are the same as those previously described in the case of the cord and the spinal nerves. The pia mater ])asses with the larger blood-vessels into the brain substance by the sulci of the cerebrum and cerebellum. In the white and grey matter of the brain we find the same kind of supporting tissue that we described in the cord as neuroglia. In tlie brain also it is composed of a homogeneous matrix, of a network of neuroglia fibrils, and of branched, flattened neuroglia cells, called Deit^rss cells. In the white matter of the brain the neuroglia contains between the bundles of the nerve fibres rows of small nucleated cells ; tliese form s})ecial accumulations in the bulbi olfactorii, and in the cerebellum. Lymph corpuscles may be met with in the neuroglia, especially around the blood-vessels and ganglion cells. All the ventricles, including the aqueductus Sylvii, are lined witli a layer of neuroglia, being a direct continuation of that lining the fourth ventiicle, and this again being a direct continuation of the central grey nucleus of the cord. Like the central canal of the cord, also, the ventricles are lined with a layer of ciliated columnar, or short columnar epithelial cells. The blood-vessels form a denser capillary net- work in the grey than in the white matter ; in the Cerebrum and Cerebellum. 237 latter the network is pre-eminently of a longitudinal arrangement, i.e. parallel to the long axis of the bundles of the nerve fibres. In the grey cortex of the hemispheres of the cerebrum and cerebellum, many of the capillary blood-A'essels have an arrange- ment vertical to the surface, but are connected with one another by numerous transverse branches. The blood-vessels of the brain are situated in spaces, perivascular lymph spaces, traversed by fibres passing between the adventitia of the vessels, and the neuroglia forming the boundary of the space. There are no separate lymphatic vessels in the grey or white substance. 198. The white iiiaftei* consists of medullated nerve fibres, which like those of the cord possess no neurilemma or nuclei of nerve corpuscles, and no constrictions of Ranvier. The nerve fibres are of very various sizes, according to the locality. Divisions occur very often. When isolated the fibres show the varicosities mentioned in the cord. The grey iiiattei* consists, like that of the cord and medulla, of a basis of neuroglia in which are embedded nerve cells. The dendritic ramifications from the nerve cells, with medullated and non- medullated nerve fibres, form a large proportion also of the grey matter. With regard to the structure of the ganglion cells of the brain and medulla, what has been mentioned of the ganijlion cells of the cord holds good as to them. Like the former, those of the medulla and brain are situated in pericellular lymph spaces (Obersteiner). 199. We now proceed to consider in detail the structure of the different parts of the cerebellum and cerebrum. The cerebelliiiii is composed of laminated folds, or convolutions, and these again are composed of 238 Elements of Histology secondary folds, each of which consists of a central tract of white matter covered with grey matter. The tracts of white matter of neisfhhourinfr convolutions of one lobe or division join, and thus form the principal tracts of wdiite matter. The white matter of the cerebellar hemisphere is Fig. 149. — Photograiu through the grey matter of the cereliellmn of tlie dog, showing the hiyer of Purkinje's ganglion cells with their dendrites ramifying in the grey cortex. {Lov magnification.) connected (a) with the medulla oblongata by the corpus restiforme, this forming the inferior peduncle of the cerebellum ; (6) with the cerebrum by the processus cerebelli ad cerebrum, this forming the superior peduncle ; and (r) with the other cerebellar hemisphere by the tracts connecting with the pons Cerebrum and Cerebellum. 239 varolii ; these are the pedunculi cerebelli ad pontem, or the middle peduncles. 200. On a vertical section through a lamina of the cerebellum (Fig. 149), the following layers are seen: {a) the pia mater covering the general surface, and pene- trating with the larger blood-vessels into the superficial substance of the lamina ; (6) a thick layer of cortical grey matter ; (c) the layer of Purkinje's ganglion cells ; {d) the nuclear layer ; and (e) the central white matter. 201. The layer of ganglion cells of Purkinje is the most interesting layer ; it consists of a single row of large multipolar ganglion cells, each with a large vesicular nucleus. Each possesses also a thin axis- cylinder process, directed towards the depth, the cell sending out in the opposite direction — i.e. towards the surface — a thick process which soon branches like the antlers of a deer, the processes being all very long-branched and pursuing a vertical course towards the surface ; sooner or later they all break up into the fine nervous network of the grey cortex. The longest processes reach near to the surface. The layer (6) above mentioned — i.e. the cortical grey matter — is in reality the terminal nerve network for the branched processes of the ganglion cells of Purkinje. San key maintained, before the adoption of more modern methods of research, that in the human cerebellum there are also small multipolar ganglion cells connected with the processes of Purkinje's cells. 202. The connections and distributions of the different cells of the cerebellum have been exhibited to a considerable extent by the labours of observers who have followed the methods of Golgi. A scheme of the main points on these results is shown in Figs. 150 and 151. Fig. 150 indicates the appearance represented in a section across a lamina. Fig. 151 corresponds to a section taken in 240 Elements of Histology. the direction of a lamina. Purkinje first, they are extensive dendritic ramification, viewed transversely, Considering the cells of seen to possess a very '\^jn\ i~Ta ■ml Fig. 150.— Scheme of the Connectiou of the Cells in the Superficial Grey Substance of the Cerebellum. (After KoUiker.) p, Xeuraxons of Purkinje's cells with collaterals : k, tendril-like fibres with k^ their terminations; gU glia cells; /, nio^s fibres; m, small cells of the molecular layer; vi^, larare cells of the same layer (basket cells) forming synapses round Purkinje's cells, 3A-; gr, cells of the nuclear layer witli neuraxons passing into molecular layers, here turning horizontally and giving a punctated appearance in cross-section ; n, the luxuriant branching of a Gblgi's cell of the second type. passing through the whole thickness of the molecular layer, as the cortical grey matter is sometimes called. This ramification is less extensive viewed in the longi- tudinal section of a lamina (Fig. 150). The neuraxon Cerebrum and Cerebellum. 241 passes throu,<;li the uucle;ir layer oblkjuely, giving off collaterals which to some extent re-enter the molec- ular layer, then the axon passing fiom the nuclear layer enters the central white matter. There are also seen in the molecular layer other fairly conspicuous Fig. 151.— Longitudinal Section of the Grey Substance of the Ceiebelliun. {After Kolliker.) The restricted branching of the cells of Purkinje (v) is seen. Tbe nuclear cells below are seen sending axons upwards inio the luoleciilar layer which divide dichotomously, and run longitudinally. cells (m'), which are termed backet cells. These cells have dendrites Avhich ramify amongst those of the Purkinje's cells, and a neuraxon which gives off collaterals, and these again form arborescences around the Purkinje cells. Other smaller cells [in) have ])rocesses all of which i-amify in the neighbourhood of the cell. On the border line between the nuclear and molecular layers may be seen large multipolar cells Q 242 Elements of Histology (sometimes spoken cf as Goh/i's* cells), which exhibit a dendritic ramification in the nuclear laj^er, and in which the neuraxon, on entering the molecular layer, Ne - Fig. 152.— From a Transverse Section through the Edge of the Restiform Body, PC, and the Tuberculuia Acustieum of the new-born Cat. {Gofgi. Kolliker, II.) Xe, Xerve fibres of the coclilear nerve : Ne', the same fibres passing round the peduncle ; c, collaterals : T, large ganglion cells of the tuberculinu ; n, their axons becoming fibres of the stria? acustica'. divides up not far from the main cell. In the nuclear layer are numerous small cells (fjr), the dendrites dividing verv near to the cells, the neuraxons. * Though referred to frequently as ^^ cells of Golgi,'''' these are more correctly described as "alls of the, second tt/pe of Golgi.'" Some authors use the term "cells of Golgi" to refer to neu- roglia cells. Cerebrum and Cerebellum. 243 however, pass into the iiiolecuhir hiyer and bifurcate longitudinally (Fig. 150) at various levels. The so- called "molecular" condition of the cortical grey matter is largely due to the appearance of these fibres being cut across as well as to the sections of the processes of the cells of Purkinje. The central white matter shows other fibres than those representing the neuraxons of the Purkinje cells (Fig. 151). One set of these terminate in arborescent tufts in the nuclear layer, and are referred to as moss fibres {/). Another set pass into the molecular layer and break up on connection with the dendrons of the cells of Purkinje. These are spoken of as tendril fibres. These two sets of fibres are to be regarded as conducting to the grey matter of the cerebellum. In addition to the proper nerve cells already described, may be seen neuroglia cells (gl). These are also present in the central white matter (Fig. 152). 20.3. The structure of the cerebral con- volutions in g-eneral. — In a vertical section through a cerebral convolution one is able to see with the naked eye a central core of white matter sur- rounded by a cap of grey or reddish-grey matter, which again, on careful observation, can be seen to consist of several alternate strata of lighter or darker substance. The exact appearance of these dif- ferent layers varies in different parts of the cerebral hemispheres. In general, a vertical section of a convolution shows three main layers : (1) a superficial molecular layer, (2) a layer of pyramidal cells, (3) a layer of poly mor pilous cells. These layers are subdivisible into several others in different parts of the hemispheres (Fig. 153). 204. Structure of the cerebral convolu- tions in the reg^ion of the Rolandic fissure. — In this region one can distinguish six layers, showing Fig. 153.— Vertical Section through tlie Grey Cerebral Cortex in the Parietal Region. (KoUikcr, II.) a, .Superficial white layers : 6, onter layer of small pyramidal cells: c, outer laver of large pyramidal cells; d, inner layer of small pyramidal cells ; e, inner layer of large pyramidal cells ; /, polymorphous cells. Sir. zon. c.s.c. R.F. Fig. 154. — For description see next page. 246 Elements of Histology. different characters. Superficially is the stratum zonale or moJecidar layer (a), then the outer layer of small 2^y'i'<^'i>^^d^^ cells {b), then (c) the outer layer of large pyramidal cells, followed by (cZ) the inner layer of small iiyramidal cells, then (e) the inner layer of large lyyramklal cells, and, adjacent to the white matter (/"), the layer of polymorphous cells. These cells are, to some extent, separated into vertical columns by intercolumnar bundles of nerve fibres. There are also, running horizontally, following the contour of the gyrus, other more or less defined bundles of fibres. Some of these run in the super ficial molecular layer ; two other bands are disposed tan^fentially, in the pyramidal cell layer, the more superficial being the band of Vicq d'Azyr or Geunari, the deeper that of Baillarger. In general, the neuraxons of the cells descend towards, and finally, pass into the white matter (Fig. ISt). There are some cells in the cortex which do not conform to this rule. Amongst the pyramidal cells may be found cells known as Martinotti's cells, from which the neuraxons ascend towards the superficial molec- ular layer. Cells known as Golgi's cells are also to be found, with neuraxons passing towards the surface and dividing up not far from the cell. The general relation of the different cells and fibres is sliown in the accompanying scheme (Fig. 15-i) Description o/Fig. 154 [-f- --15). Fie. 154.— Scheme of the Connection of the Cells of the Cerebral Cortex. {After KoUiker.) Pj, Pi, Smaller aud larger pyramidal cells, the neuraxons passing downwards on their way to the inner capsule ; P3, pyramidal cells forming a termination in tlie corpus striatum ; at level M a cell of Martinotti with neuraxon passing upwards and terminating in stratum zonale ; at level G a Golgi cell (2nd order) with much-branched neuraxon immediately aliove it ; Ac, association cell, on inner side of G is a cell (Cc) with neuraxon passing into corpus c-allosum : C.S.C., a cell of corpus striatum with neuraxon passing into cortex ; R.F.. a fibre from the fillet passing up into the cortex, one of Ramon y Cajal's fibres ; Str. zon., stratum zonale, or superficial white layer. Fig. 155. — Pyramidal Cell of the Cortex of the Brain, its axon giving off unmerous collaterals. {Kollilcr, II,) Fig. 156. -Fascia Dentata and adjoining part of C-nim Amnionis of Human Embryo. (Aft'^r KoUiker.) ^^■'.^'ifL^^iK^^S'^^^^^ bundle, an accessory bundle pasMnsr out to the rights • ^^f. ■. ""i-'? ''■*^"'" radwtuni of fascia dentata: «. cell with ascendiiis axon (cell of Martinott.) : Pi/r.. pyramidal cells; F, flml.ria: K. nuclear laNer Cerebrum and Cerebellum. 249 from Kolliker. The pyramidal cells have a conspicuous apical process, which passes vertically, giving off lateral processes, and forms a system of dendrites in the superficial molecular layer. Other dendritic ramifications occur closer to the cell and the neuraxon passes towards the white matter, giving off collaterals as it traverses the grey substance (Fig. 155). Some of the pyramidal cells (Cc) have neuraxons which pass to the opposite hemisphere in the corpus callosum, and not towards the inner capsule, through which a large number of the neuraxons course. Some pyramidal cells again probably have their neuraxons ter- minating in connection with cells of the corpus striatum (P'*). The connections of a cell of Marti- notti are seen (M), and those of a Golgi cell (G). Fibres conducting towards the cortex are repre- sented by (1) Ramon y Cajal's fibi-es (R.F.), passing from the fillet and subdividing in the cortex ; (2) fibres from cells of the corpus striatum (C.S.C.) passing up into the grey matter of the cortex in a similar manner. 205. Structiii-e of the liippocaiiipus major and the fascia deiitata (Fig. 156). The hippocampus as it projects into the ventricle is invested beneath the ependyma with a layer of wdiite fibres called the alveus. Lying against the alveus are pyramidal cells, the neuraxons of which pass into it ; the conspicuous apical process passes through a large ):»ortion of the thickness of the hippo- campus, giving it a radiate appearance (the stratum radiatum), and forming a dendritic ramification above this in the stratum lacunosum. Tracing the sub- stance of the hippocampus towards the fascia dentata, these pyramidal cells become less conspicuous and are not to be regarded as forming any definite layer in this region. The fascia dentata has externally a superficial layer or stratum zonale into which pass the 250 Elements of' Histology. dendritic ramifications of a layer of small cells, the stratum (jranuJosum. From these small cells neuraxons pass to the central substance of the fascia olfc. Fig. 157. — Diagram of the Probable Connections of Cells and Fibres in the Olfactory Bulb. {After Schafer.) olf.c, Sensory cells of tlie olfactor.v epithelium ; olf.n., deepest layer of the liulb composed of the olfactory nerve fibres which are prolonsed from the olfac- tory cells ; f//., olfactory shjiueruli, containing dendrons of hoth the olfactory nerve fibres and the mitral cells; mc, mitral cells; tx. their axons ; J4.fr., nerve fibres of tlie bulb becoming continuous with the olfactory tract. dentata, and from this also many so called "moss fibres " issue, passing to the granular layer [Mf and 31/"). 206. Structure of tlie oHaetory bulb (Figs. 157 and 158). — A vertical section through the olfac- tory bulb indicates considerably more development on the side lying against the cribriform plate than Cerebrum and Cerebellum. 251 on the dorsal side. Passing from the surface lying on the ethmoid bone, one can make out the following la3^ers : (1) Bundles of olfactory nerve fibres; (2) the zone of olfactory glomeruli ; (3) a layer pervaded Fig. 158.— From the Olfactory Bulb of a Mouse 24 days old. {Highly magnified. Golgi. KoUiker, II.) C, Collaterals ; C;^ glomeruli ; M, mitral cells; J/', large brush cell ; .172, small ditto ; n, neuraxon. by many irregular fibres, giving it the character of a molecular layer, and containing the so-called ^nitral nerve cells ; (4) a nuclear layer composed of small cells ; (5) a layer of longitudinal nerve fibres ; (6) the neuroglia forming the central substance. The 252 Elements of Histology. connection of these mitral cells is indicated in Figs. 157 and 158. One or two processes pass horizontally and an axis-cylinder process passes through the nuclear layer towards the layer of longitudinal nerve fibres. One conspicuous process passes towards the glomeruli and, entering one of the masses, forms a dendritic clump. Similarly axons from the olfactory cells in the nose pass to these glomeruli and form dendritic clumps. These glomeruli are definite localities where connec- tions are established between cells of the olfactory bulb and the olfactory mucous membrane. 25. CHAPTER XX. THE CEREBRO SPINAL GANGLIA. 207. The ganglia connected with the posterior roots of the spinal nerves, and with some of the roots of the cere- bral nerves — Gas- serian, otic, genic- n 1 a t e, ciliary, Meckel's ganglion, the ganglia of the branches of the acoustic nerve, the submaxillary gan- glion, etc. — possess a capsule of fibrous connective tissue continuous with the epineurium of the afferent and efferent nerve trunks (Fig. 159). The interior of the ganglion is subdivided into smaller or larger divisions, contain- ing nerve bundles with their perineu- rium, or larger and smaller groups of c'an.a'lion cells In Fig- 1j9— Spinal Ganglion of the Lumbar ^, ° . , '■ ,. Region of a Puppy. {KoUiler, II.) the spinal ganglia c, Ganglion with its cells and their axons; Bp, fVlpop latter ^''^^ posterior; Ita, anterior branch ; M, motor ; S, are sensory root. 254 Elements of Histology. generally disposed about the cortical part, whereas the centre of the ganglia is chiefly occupied by bundles of nerve fibres. 208. The ganglion cells differ very greatly in size — YVj.. Ii30.— Transverse Section of the Spinal Cord of a Chick of the 9th day of incubation. {Afttr Ramon y Cajal, from Quain's " Aimtomy.") A, Axons— anterior root fibres— issuing from large ganglion cells of anterior horn. C : B, posterior root fibres passing from the bipolar ganglion cells (/), O of the spinal arangliou into the posterior white column Z>. where they bifur- cate to become longitudinal ; e,f,g, collaterals from these fibres : b, fibres of anterior white column in cross-section. some being as big, and bigger, than a large multipolar ganglion cell of the anterior horn of the cord, others much smaller (Fig. 162). Each cell has a large oval nucleus, including a network with one or two large nucleoli. Cerebrospinal Ganglia. 255 Its substance shows a distinct fibrillation. Each cell of the spinal ganglia in man and mammals is }inipolar (Fig. 1G2), tiask- or pear-shaped, and invested in a hyaline cajisule, lined with a more or less continuous Fig. 161. — From a Longitudinal Section tlirougli the Gasseiian Ganglion of the Calf. {Koinier, //.) layer of nucleated endothelial cell plates. The single process of the ganglion cell is finely and longitudi- nally striated, and is an axis-cylinder process. Im- mediately after leaving the cell body it is much convoluted (Retzius) ; it is then covered with a medullary sheath, and so becomes a medullated nerve fibre. The capsule of the ganglion cell is continued on the axis cylinder process, and, farther on, on the 256 Elements of Histology. meclullated ner\'e fibre, as the neurilemma ; the endothelial plates of the capsule pass into the nerve Fig. 1(32. — Large and Small Ganglion Cell of the Ganglion Gasseri of RabVdt. (A'ei/ and Retzhts.) The axis cylinder, after leaving the cell, becomes convoluted and transformed into a medullated nerve filire. which divides into two medulLited fibres. Fig. 163.— Lsolated Ganglion Cell of Spinal Ganglion of Toad. {Key and Retzius.) The axis cylinder process becomes transformed into a medullated nerve fibre. The capsule of the cell IS prolonged as the neu- rilemma of the nerve fibre. corpuscles linin^ the neurilemma, their number greatly diminishing (Fig. 162). 209. In the rabbit this medullated nerve fibre at its first node of Ranvier, which is not at a great dis- tance from the ganglion cell, divides into two medul- lated nerve fibres in the shape of T ; one branch Cer ebr 0-spina l Ga ngl I a. 257 passes to the cord as a posterior root fibre, the other to the peripher}^ (^ig- 1(^3). In man, this T-shaped division has also been observed by Retzius, but, though liighly proljable, it cannot be said to have been actually pro\ed that in rabbit or man every axis-cylinder process shows this T-shaped division. Retzius obser\'ed this T-shaped division also in the Gasserian, geniculate, and ^■agus ganglia in man. The ganglion cells are not unipolar in all cerebral ganglia ; in the ciliary and optic ganglia there are ganglion cells which are multipolar. 210. Numerous ganglia of microscopic size are to be found in the submaxillary (salivary) gland : they are of ditferent sizes, and are in reality ganglionic enlargements of larger or smaller nerve bundles. Each ganglion is invested in connective tissue con- tinuous with the perineurium, and the ganglion cells are unipolar, and of the same nature as those described above, each cell being possessed of an axis-cylinder process, which becomes soon a nerve fibre. At the back of the tongue there are similar small micro- scopic ganglia. R 258 CHAPTER XXI. THE SYMPATHETIC SYSTEM. 211. The sympathetic nerve branches exactly re- semble the cerebro-spinal nerves in their connective- tissue investments (epi-, ])eri-, and endoneurium)^ and Fig. 164.— Sympathetic Nerves. (Atlas.) A, Small Imndle invested in an endothelial sheatli, iierineurium ; b, one raediillated and three non-medullated nerve flbres of various sizes; the largest shows division ; c, two varicose nerve flbres. in the arrangement of the fibres in bundles (Fig. 164, a). Most of the nerve fibres in the bundles are non- medullated or Remak's fibres (Fig. 164a), each being an axis cylinder invested in a neurilemma, with 5 J -MP A TH E TIC SyS TEM. 259 oblong nuclei indicative of nerve corpuscles (Fig. 1G4, b). But there are some meJullated nerve fibres to be met with in each bundle, at least, of the hirger nei"ve trunks. These in some cases show the medullary sheath more or less discontinuous, and "with a vari- cose outline (Fig. lG-1, c), owing to a uniform local accumulation of fluid between it and the axis cyl- inder. The small or microscopic bundles of nerve fibres possess an endothelial (peri- neural) sheath. The small and large branches always form plexuses. 212. The gan- glia of the sym- pathetic chain (Fig. 16 5)— lateral gancjlia, as also the further sym- pathetic ganglia — the collateral ganglia like the ' - t-'^^ ;^;"' ^^;> /r.% ■ Fig. 164a.— Cross-Section through part of Branch of the Splenic Nerse of the Ox, showing bundles of non-medullated or Remak's fibres in cross-section ; the nerve fibres being com- posed of fibrillK appear granular in cross- section ; the nuclei here shown belong to the neurilemma of the fibres. {Kolliker, II.) semilunar and the cardiac ganglia, and the peripheral ganglia, like those on and in the abdominal viscera, are microscopic in size, but possess in a general way the same structure as the cerebro-spinal ganglia. The ganglion cells are bipolar, or more commonly multipolar. Such are the 26o Elements of flisroLOGV. microscopic ganglionic enlargements on many of the sympathetic nerve l)ranclies in the thoracic and abdominal organs. Thev occur in some organs very numerously — e.g. ,■7,,^,,^ alimentary canal, urinary bladder (Fig. 166 and Fig. 167), respiratory organs, salivary glands — and are of all sizes, from a few ganglion cells placed between, or laterally to, the nerve tibres of a small bundle, to oval, spherical, or irregularly - shayyed masses of ganglion cells placed in the course of a large nerve bundle, or situated at the point of anasto- mosis of two or more nerve branches ( Fig. 167). 213. The fjanglia in connection with the plexuses of nerve branches of the heart, the cjanwlia in the plexus of non-medul- lated nerve tibres ex- isting between the longitudinal and cir- cular coat of the exter- nal muscular coat in the aliuientary canal, known as the plexus myen- tericus of Auerbach, the ganglia in the plexus of fig. 165.— Sixth Ganglion Thoracicuni of the Left Sympathetic of the Rabbit. (KoUiker, //.) Re, Rami communicantes ; S, lirauch of sranslion containing two coarser and several finer fibres: Spl, srlanchnicus ; T, sympathetic trunk; 3, ganglion cells. Si -MPA THE TIC SVS TEM. 26t nerve Blanches of tlie submucous tissue in the aliiuent;iry canal, known as Meissner's plexus (Fig. 172), the ganglia in the nervous plexuses in the Fig. 166.— Group of Ganglion Cells interposed in a Bundle of Sympa- thetic Xerve Fibres ; from the Bladder of Rabbit. (Handbook.) outer wall of the Vjladcler, in the bronchial wall, and in the trachea, and lastly the ganglia in connection Fig. 1G7. — Small Collection of Ganglion Cells along a small Bundle of Sympathetic Nerve Fibres in the Bladder of Rabbit. {Atlas.) Each gangliou cell possesses a capsule. Tlie substance of the ganglion cell is prolonged as the axis cylinder of a nerve flljre. with the nerves supplying the ciliary muscle of the eye, all belong to the sympathetic .system. 262 Elements of Histology The ganglion cells (Fig. 170) are of very different sizes, each possessing a large oval or spherical nucleus with one or two nucleoli. Their sliape is spherical or ova], flask -shaped, club-shaped, or pear-shaped ; they Fig. 168.— Microscopic Ganglion in the Submaxillary GlaudofDog. i^AtUs.') c. Connective tissue surrounding tlie ganglion : g, tlie ganglion cells with their capsule ; n, nerve fibres. possess either one, two, or more processes, being uni-, bi-, or multipolar. The cell is invested in a capsule lined with nucleated cells, both being continued on the processes as neurilemma and nerve corpuscles respectively. 214. By the aid of Golgi"s method it has been definitely established (Golgi, Ramon y Cajal, Retzius) Sympathetic System. 263 that, like the ganglion cells in the cord, the cells in the ganglia of the sympathetic system possess one axis - cylinder process, axon or nenraxon, which remains unramified (R^Diun y Cajal, Van Gehuchten, Fig. 100.— Plexus of Auerbacli iu Rectum of Toad. {Atlas.) n. Xerve branches ; g, ganglion cell. L. Sala. Von Lenhossek, Kolliker), though sometimes it is possessed of nodose swellings (Fig. 171). It passes into the periphery as a non-medullated fibre (as, for instance, the non-medullated fibres passing from the lateral ganglia of the sym- pathetic back to the spinal nerves as the grey ramus communicans) ; or as a medullated fibre (as for instance, the medullated fibres passing from the ciliary ganglion into the ciliary nerves). The 264 Elements of Histology. 2)ost-ganglionic fibres of Langley are fibres which originate as the neuraxon of a sympathetic gan- glion cell (in the lateral, collateral or peripheral ganglia, as the case may be), and hence pass into muscle (wall of intestine, blood- vessels, the viscera). The ganglion cells in the microscopic peripheral ganglia are also multipolar, although there oc- cur amongst them bi- and unipolar cells (Ramon y Cajal, Dogiel, Kol- liker). Besides the neuraxou or axon the sympathetic ganglion cells pos- sess ramifying pro- cesses - — dendrites, which resolve them- selves like those of the cells of the grey matter of the cen- tral nervous system into fine fibres, some of them form- ing more or less distinct arborisa- tions or dendrons (Fig. 171). An interesting relation exists between the medullated nerve fibres which pass into a sympathetic gan- glion from a spinal nerve [motor fibres passing from Fig. 170.— Synipatlietic Gauglion Cell of Man. (Key and Itetzius.) The arnnarlion cell ii^ iiniltiiiolar : each proce.-s re- ceiving a iieiirileiunia from the eapsiile of the cell beeouies a iion-inediiUated aerve fibre. Sv^'ifPA THE TIC SyS TEM. 265 anterior roots, as also sensory fibres from the j)osterior roots and spinal ganglia], as, for instance, those passing from the motor roots by the white rami com- miinicantes into the lateral and farther into the collateral ganglia, i.e. the free - i/anc/ lionic fibres of Langley ; these fibres ter- m i n a t e (Van Gehuchten, L, Sal a, Dogiel, Von Lenhossek) as fine ramifications be- tween and around the ganglion cells, or they form curious, more or less dense, convolutions and plexus surrounding the body of the ganglion cell — circ II m c ellul a r plexus^ as is shown in Fig. 173 (Kol- liker). 215. By the observations of Beale, Arnold, Axel, Key and Retzius, it was known that in the ganglion cells of the sympathetic nerves of the frog, the ganglion cell substance passes on as a straight neuraxon wdiich continues its course peripherally as a non-medullated nerve fibre surrounded by a nucleated sheath or neurilemma — continued from the capsule of Fig. 171. — Three Multipolar Ganglion Cells with their Axon, n. From the Ganglion Semilunare of Dog one day old. {Kolliker, II.) 266 Elements of Histology. the ganglion cell. This straight process is entwined by a thin spiral fibre which, farther away from the body of the irancvlion cell, is a medullated fibre ; it ramifies on the substance of the ganglion cell (Fig. 174). Fig. 172. — Group of Ganglion Cells from the Plexus of Meissner of a Puppy ; amongst them a Multipolar and several Unipolar Cells. (Kolliker, II.) Arnold, then Ehrlich and further Retzius (the last two by ibjection of methylene blue into the blood- vessels of the living frog) have shown this spiral fibre (stained blue) to terminate on and around the sub- stance of the ganglion cell as an arborisation ; a condition which occurs in many parts of the central nervous system (anterior grey cornu, cerebellum, sympathetic ganglion cells, previously mentioned, SVMPATHETIC SvSTEM. 267 etc.), that is to say, the l)odj of a ganglion cell becomes surrounded and ensheathed as it were by a dendron of an afferent nerve fibre, the dillerence being Fig. 173.— Circunicellular Plexus from tlie Gauglioii Cervieale Supremuin of Calf. (KoUiker, II.) Fig. 174. — Sympathetic Ganglion Cell of Frog, showing the straight process and the spiral fibre ; the latter becomes a metlullated fibre, {Key and Eetzius.) tliat in the sympathetic cells of the frog this afferent (inedullated) fibre entwines as the spiral fibre the efterent axon (non-mednllated) of the ganglion cell. 26S CHAPTER XXri. GEXERAL COXSIDERATIOXS AS TO THE ANATOMICAL COXSTITUTIOX AND NATURE OF THE NERVOUS SYSTEM. 216. We are now in a position to summarise the general structure and relation of the constituent parts of the nervous system. The nervous system consists of nerve cells or ganglion cells and of nerve fibres — the cells forming the centres, the fibres the conducting paths. The ganglion cells form an integral part of the central nervous system — brain, medulla, and cord — as also of the ganglia of the sympathetic and of the peripheral collections and special nerve end-corpuscles in the various viscera and in the sense organs. The ner%e fibres, on the other hand, are all, as far as at present known, axons or neuraxons — that is to say, pro- longations of the substance of the ganglion cells : by these axons near and distant centres, or ganglion cells, are brought in relation to one another, as also by the peripheral terminations of the axons with muscles, skin, mucous membranes, glands, etc. The whole nervous svstem mav be considered as consistincr of a collection of units (Ramun y Cajal), each such unit being called a neuron (Waldeyer). A neuron, then, is a ganglion cell with all its processes, axon or axons, and dendrites — be they short or long — as well as all the ramifications and terminations of such axons and dendrites. While of many parts of the nervous SPINAL OAN&LION CELL MUITI POLAR CELL OF ANT. HORN 1 SMN Fie. 175.— Sr-heme of Relationship of Cells and Fibres of Brain and Cord, ° prepared by Halliburton and Mott. (From Kirke's " Physiology.") AB, Middle line tlirough brain medulla and cord; pyr. ijyraniidal ganglion cell of the cerebral cortex in the Uolandic area ; ax, axon of this same gangl on cell, a collateral of this axon passes in the cr)rpus callosum (c. call.) to terminate in the cortex of the other cerebral hemisphere ; c.stk., is the corpus striatum : K.a.c, s-'anulion cell in the cerebral cortex (nerve unit of associa- tion of Cajali, around which arborises an axon coming from a ganglion cell of the optic thalamus ; o.th., thalamus opticus ; f, mesial hllet ; s.g., nucleus gracilis of the meduUa ; i. a., axon ..f a ganglion cell in the nucleus f-'rac Us. passing to the other side as an internal arcuate hbre; v, ganglion cell ot Purkinje in the corte.x of cerebellum ; p.ax., its axon ; g.m., succession ot cell stations (units) in the erey matter of the cord to the optic thalanu. qc.fi,lc. Leu. clcuo ocuIoTaoLorU'.S 1 T Cbrtci CCrcV: Ficr 176.— Diagram of the probable Connections and Relations of the Optic Xerve Fibres between the Ganglion Cells of the Retina and the Cortex Cerebri. {After Schdfcr.) Between the ganffliou cells of the retina and the lateral corpus geniculatum or anterior corpus quadrit:eminura respectively is the rirst neuron ; between the corpus nuadritrennnum anterius and the nucleus oculomotorms is a second neuron, so also between the lateral corpus ireniculatum and the cortex cerebri ; between the nucleus oculomotorius and the cortex cerebri on the one hand and the axons of the tranarlion cells of the nucleus oculomotorms by the nerve tibres constituting the ocuhiraotor nerve terminating in the muscles supplied by this on the other hand is a third neuron. Of the Nervous System. 271 system the constituent units or neuronic are under- stood and traced out, tliere are other parts in which the constituent neurons have not been as yet fully worked out. Of the former it has been established by the new methods that the older theory as to anatomical continuity between different parts of the nervous system — i.e. the units or neurons — is not correct ; but, on the contrary, that the processes (axons as well as dendrites) of one ganglion cell form only contact with those of others, as also with peri- pheral organs, ivifhout direct contimdty (Fig. 175). Thus, for instance, it has been shown that there exists no direct or uninterrupted continuity between a motor (pyramidal) ganglion cell, say of the limb centres in the grey cortex of the brain, and the nerve fibres which terminate as motor end-plates or dendrons in the muscles of the limbs, but that the whole of this path is made up of a succession or chain of neurons or units ; and similarly beginning with a dendritic nerve termination in the epithelium of the skin of the limbs up to the arborising termination of nerve fibres in the sensory centres of the grey cortex of the brain, we have no anatomical continuity, but a succession or chain of units or neurons. In each case, a ganglion cell with its axon, in- clusive of its collaterals, and its dendrites, is possessed of arborisations or dendrons which do not form con- tinuity with, but are only in close contiguity to, the arborising axons, or dendrites respectively* of another unit or neuron (synapsis). A further point that has been established is this, namely, all nerve fibres, be they medullated or non-medullated, afferent or efferent fibres, be they of a relatively short course — e.g. those beginning and ending within the central nervous system — or do they extend over long dis- tances like those passing out from, or passing into, the cord, medulla, and brain as spinal and crainial 272 Elements of Histology. nerves respectively, are, in reality, axons or direct prolongations of the substance of ganglion cells, which, after a longer or shorter course, terminate as arl>orisations or dendrons in the periphery or in the central nervous system, as the case may be. 217. We will illustrate, by selecting a few from the many known examj)les, the nature and extent of such neurons : — (1) A motor neuron of the grey cortex cerebri con- sists of the following parts (Fig. 175) : («) the cell body of a pyramidal ganglion cell ; (6) its dendrites, with their arborisations in the grey cortex ; {c) the axon given off as the median basilar process and its col- laterals becoming medullated nerve fibres of the white substance of the cortex, passing further through the internal capsule, the pons, the anterior pyramidal tract of the medulhi, the direct or crossed pyramidal tract of the cord, and forming the tinal arborisations or dendrons of them and their collaterals in the anterior cornu around the body and dendrites of the ganglion cells in the grey matter of the cord. (2) A motor neuron of the grey anterior cornu of the cord consists of : («) a ganglion cell in the anterior grey cornu of the cord ; (6) its dendrites terminatinix in f^itu as arborisations or dendrons; («:) the axon passing out as a medullated nerve fibre through the anterior root, and further through a spinal nerve, and terminating finally in the periphery in a striped muscle fibre as a dendron — i.e. the nerve end-plate. (3) A sensory neuron : (a) a ganglion cell of the spinal ganglia ; {h) the afferent nerve fibre — i.e. the distal portion of the T-shaped division of the axon, coming from the periphery — e.g. the skin — by way of a medullated nerve fibre of a spinal nerve ; in the skin it terminates or originates either in or around special nerve end-corpuscles or as ramifying fibrillae in the Of the A^F.Ri'ous System. 273 epithelium of tlie smface ; (c) the efferent fibre — i.e. the proximal branch of the axon of the spinal •/•if"'^^^Nkf^)i /V---"-' Fig. 177.— Diagrniu showing the Mode of Termination of Sensory Nerve Fibres in 1, the auditory, 2, the gustatory, and 3, the tactile sense organs of vertebrata. Each of these represents one sensory neuron. (After Retzius,frorii Qnuin.) ganglion cell passes into the cord as a medullatecl fibre by way of a posterior root and farther into the 274 Elemexts of Histology posterior white colunni ; it or its collaterals finally enter into the grey matter of the cord or pass on into the nucleus gracilis of the bulb, terminating as dendrons around or close to a ganglion cell (body or dendrites) in such grey matter (Fig. 175). (4) A neuron of a special sense (Figs. 177, 178): (a) the fjcinolion cell in the san- glion cell laj^er of the retina ; (J)) its dendrites terminating as arborisations or dendrons in the inner molecular layer ; (c) the axon passing out in the opposite direction and forming a fibre of the nerve fibre layer and further pass- ing into the optic disc and optic nerve as a niedullated fibre, pursuing its course as such through the chiasma and optic tract, and terminating, finally, in an arborisation around cells in the corpus geniculatum or the anterior corpus quadrigeminum (Fig. 176). Fig. ITS. — Diagram of the Ar- rangement of the Sensory Xerve Fibres in the Olfactory Organ and Bixlb. {After Eetzius, from Quain.) n, Neuraxon : (il. glomerulus in the olfactory bulb. This repie- seuts two consecutive neurous. 275 CHAPTER XXIII. THE TEETH. 218. A HUMAN tootll, sists (Fig. 17!)) of (a) the (b) the denfine forming tiie bulk of the whole tooth, and surrounding the pulp cavity both of the crown and fangs, (c) the pulp cavity, and {d) the ceinent, or crusta petrosa. The cement covers the outside of the dentine of the fang or fangs, the enamel covers the dentine of the crown. The cement is covered on its outside by dense fibrous tissue acting as a 27eriosteuni to it, and is fixed by it to the inner surface of the bone forming the wall of the alveolar cavity. 219. The enamel (Fig. 180) consists of thin microscopic pris- matic elements, the enamel prisms placed closely, and extending in a vertical direction adult and milk-tooth, con- enamel covering the crown, Fiji 17*> — Loii„Mtu(linal Section till oUj^h the Piceniolai Tooth of Cat. {Waldeyer, in Strieker's Manual.) a, Enamel ; 6, dentine ; c, crusta petrosa; c/ande, periosteum ;/, bone of alveolus. 276 Elements of Histology. from the surface to the dentine. When view^ed in transverse section, the enamel prisms appear of a hexagonal outline, and are separated by a very fine interstitial cement substance. The outline of the enamel prisms is not straight, but wavy, so that the prisms appear varicose. The prisms are aggregated Fig. ISO.— Enamel Prisms. (Kdllikc,:) A, In longitiuliual view ; B.in eross-section. into bundles, which are not quite parallel, but more or Jess slightly overlap one another. On a longitudinal section through a tooth, the appearance of alternate light and dark stripes in the enamel is thus produced. Besides this there are seen in the enamel dark hori- zontal curved lines, the brown parallel stripes of Retzius, probably due to inequalities in the density of the enamel prisms produced by the successive forma- tion of layers of the enamel. The enamel consists of lime salts — phosphate, carbonate, and fluoride of calcium — with corresponding magnesium salts. In young teeth the free surface of the enamel is covered with a delicate cuticle (the cuticle of Nasmyth), a single layer of non-nucleated scales. In adult teeth this cuticle is wanting, having been rubbed off. Teeth. ^11 220. The €l«'iitiii«» is tlic principal part of the hard substances of the tooth, it forms a coniph^te invest- ment of tlie pnl[) cavity of the crown and fang, being sUghtly thicker in the former than in the latter region. The den- tine is composed of (Fig. 181): (l)a homogeneous matrix ; this is a re- ticular tissue of fine tibrils impregnated with lime salts, and thus re- sembling the matrix of bone ; (2) long fine canals, the dentinal canals or tithes, passing in a more or less spiral manner, and vertically from the inner to the outer surface of the dentine. These tubes are branched ; they open in the pulp cavity with their broadest part, and become smaller as they approach the outer surface of the dentine. Each canal is lined with a delicate sheath — the Fig. ISl.— From a Section through a 7 ,• 7 7 ,7 T •! Canine Tooth of Man. (Waldeyer, in dentinal, sheath. ^ Inside Strieker's Mamud.) the tube is a fibre, the ((.Crustapetrosa, with large bone corpus- 7 ,• 7 /•/ T 1 ties; b, interglobular substance: c, dentinal JlOre, a solid dentinal tubules. elastic fibre originatinsf with its thickest part at the pulp side of the dentine from cells lining the outer surface of the pulp, and called odontoblasts. 278 Elements of Histology. On the outer surface of tlie dentine, both in the region of the enamel and crusta petrosa, the dentinal tubes pass into a layer of intercommunicating irregular branched spaces, tlie interglohular spaces of Czermak, Fi"^. 18'2.— From Section through the Pulp and Dentine of Tooth of Guinea- pig. {Photograph, highly magnified.) Pulp tissue with vessels in cross-section; o, odontoblasts; d, dentine acci- ' dentally detached from odontoblasts. or the granular layer of Purkinje. These communi- cate with spaces existing between the bundles of enamel prisms of the crown, as well as with the bone lamina of the crusta petrosa of the fang. The inter- o-lobular s})aces contain each a branched nucleated cell. The dentinal fibres anastomose with the processes of these cells. The inrrempntal lines of Salter are lines more or less parallel to the surface, and are due to Teeth. 279 imperfectly calcilied dentine— the inter (jlohuhir anb- stance of Czerniak. The lines of Schreger are curved lines parallel to the surface, and are due to the optical eflect of simultaneous curvatures of dentinal fibres. Fig. 183.— Early Development of Tooth. (Photograph Inj ^[,•. A. Pringle.) l.Tonfrue in cross-section ; 2, bone of jaws; 3, rudiment of enamel organ and tooth papilla, the former still connected with the surface epithelium. 221. The eeiiieiit is osseous substance, being lamellated bone matrix with bone corpuscles. There are no Haversian canals. 222. The pulp is richly supplied with blood- vessels, forming networks, and extending chiefly in a direction parallel to the long axis of the tooth. Xumerous medullated nerve fibres forming plexuses are met with in the pulp tissue ; on the outer surface 2 So Elements of Histology. of the pulp they become non-mediillated fibres, and probably ascend in the dentinal tubes. The matrix of the pulp is formed by a transparent network of richly branched cells, similar to the network of cells forming the matrix of gelatinous connective tissue. 223. On the outer surface of the pulp — i.e. the one in contact ^vith the inner surface of the dentine — is a layer of nucleated cells, which are elongated, more or less columnar. These are the odontoblasts proper (Fig. 182). Between them are wedged in more or less spindle-shaped nucleated cells, the outer or distal pro- cess of which passes into a dentinal fibre. The odonto- blasts proper are concerned in the production of the dentinal matrix, according to some by a continuous growth of the distal or outer part of the cell and a petrification of this increment, according to others by a secretion by the cell of the dentinal matrix. Waldeyer, Tomes, and others consider the odonto- blasts proper concerned in the production both of the dentinal matrix and dentinal iibres. The odontol)lasts proper and the spindle-shaped cells are continuous with the branched cells of the pulp matrix. 224. Devolopiiieiit of teetli. — The first rudi- ment of a tooth in the embryo appears as early as the second month. It is a solicl cylindrical prolongation of the stratified epithelium of tlie surface into the depth of the embryonic mucous membrane. Along the border of the jaws the epithelium appears thickened, and the sul>jacent mucous membrane forms there a depression — the primitive dental groove. Into this groove the solid cylindrical prolongation of the surface epithelium takes place. This prolongation is the Y\\([\mQ\\t oi the enamel organ. While continuing to grow- towards the depth, it soon broadens at its deepest part, and the surrounding vascular mucous membrane condenses at the bottom of the prolongation as the rudiment of the tooth papilla. While the distal part & Teeth. 28r of the enamel organ continues to grow towards the depth, it grtidually embraces the tooth ])apilla in the shape of a cap — the enamel caj) (Fig 183). During this time the connection between the surface epithe- Fh 184. — From a Section tlirough the Tooth and Lower Jaw of Fatal Kitten. a, Epithelium uf the free surface of the gum {b, the raucous membrane of same; c, spongy bone of jaw: rf, papilla of tooth; e, odontoblasts:/, dentine; -r^ masses, being the demilunes of -. /: ^l) ': Q, Ileidenhain, or ; \; . ' Tl ■' ^^ the crescents of ■ • .' ^' , '7 . ^^- • ^ J ji>:; Gianuzzi (see 'i-^i-J- 'l-:'^ ' -^ -f Fig. 188). Each ^ ^^ "^ V, _ '^ is composed of >' '- A il-' -■;^^^ :: ^"1 several polyhe- dral granular- r--'(vi f \VT ^ - . -> ^ , •„^.-v lookmor cells, \^>§^' ^ -^-r- ■ O ^^- each with a Fig. 192.— From a Section through the Orbital spherical IIU- Gland of Dog, after prolonged electrical Stimu- „i„„„ . j.i,p ppil^ lation. The acini are lined with small granular ^it;u^5 , tiic ccjio cells. (Lavdovsid.) " at the margin of the crescent are, of course, thinner than those forming the middle. Heidenhain and his pupils, Lavdovski and others, have shown that, during prolonged exhausting stimulation of the submaxillary and orbital of the dog, all the lining cylindrical mucous cells become ref)laced by small polyhedral cells, similar to those con- stituting the crescents, while at the same time the acini become smaller (Fig. 192). These observers maintain that this change is due to a total destruction of the mucous cells, and a replacement of them by new ones, derived by multiplication from the crescent cells. This is improbable, since during ordinary conditions of secre- tions there is no disappearance of the mucous cells as such ; they change in size, becoming larger during Salifakv Glands. 295 secretion, and tboir contonts are converted into perfect mucus. It is prol)able that, on prolonged exhaustive stimulation, the mucous cells collapse into the small cells, seen by Heidenliain and his pupils. 238. (iii.) The acini of the sublingual of the dog are again different in structure both from those of the submaxillary of the dog and of the sublingual of the guinea-pig, for the acini are there lined either with mucous cells or with columnar albuminous cells, or the two kinds of cells follow one another in the same alceolus. This gland is a sort of intermediate form between the sul)lingual of man and the submaxillary of man and ape (Fig. 191). These are the mixed or muco- salivary glands. In these the great number of acini are serous— ■i.e. small — with small lumen, and lined with albuminous cells, whereas there are always present a few acini exactly like those of a mucous gland. The two kinds of acini are in direct continuity with one another. In some conditions there are only very few mucous acini to be met with within the lobule — -so few sometimes that they seem to be altogether absent ; in others they are numerous, but even under most favourable conditions they form only a fraction of the number of the serous acini. In the sublingual of man they are much more frequent, and for this reason this gland possesses a great resemblance to the sub- lingual of the dog. What appear to be crescents in the mucous acini of the human gland are an oblique view of albuminous cells lininof the acini at the transition between the mucous and serous part of the same gland-tube. 239. The columnar salivary cells lining the acini of the submaxillary of the guinea-pig in some condi- tions show two distinct jjortioiis : an outer homogeneous or slightly and longitudinally striated substance, and an inner, more transparent, granular-looking part, and 296 Elements of Histology. in this respect the cells resemble those of the pancreas. {See pp. 330-2.) 240. Langley has shown (Fig. 193) that during the period preparatory to secretion the cells lining the acini of the serous salivary glands become en- larged and tilled with coarse granules : during secretion these granules become used up, so that the Fig. 193. — Acini of Serous Gland. (Langley.) A, At rest ; B, first stage of secretion ; c, prolonged secretion. cell-substance grows more transparent, beginning from the outer part of the cell and gradually advancing towards the lumen of the acini. These granules may be seen in the fresh gland, but reagents very rapidly destroy them. Salivary glands hardened by the usual reagents, though not themselves showing the granules, may, however, present appearances corre- sponding to the removal of the granules from the outer zone of the alveolus. It is found that in such cases the outer zone stains more deeply (Fig. 102), an appearance frequently met with in the pancreas. AYhen the outer part of the alveolus is devoid of granules, the alveolus is said to be active or partially exhausted; when the granules reach practi- cally to the outermost part of the cells, the alve- olus is said to be resting. Under normal conditions Salivary Glands. 297 secretion in the salivary glands never approaches ex- haustion, though in the pancreas it is not uncommonly the case. 241. Blood-vossels and lyiiiplialics.— The lobules are richly supplied with blood-vessels. The arteries break up into numerous capillaries, which with their dense networks surround and entwine the acini. Between the interalveolar connective tissue carrying the capillary blood-vessels and the membrana ju'opria of the acini exist lymi^h spaces surrounding the greater part of the circumference of the acini and forming an intercommunicating system of spaces. They open into lymi-iliatic vessels accomjoanying tlie intralobular ducts, or at the margin of the lobule directly empty themselves into the interlobular lymphatics. The connective tissue between the lobes contains rich plexuses of lymphatics. 242. The iierve-braiiclies form plexuses in the interlobular tissue. In connection with them are larger or smaller ganglia (Fig. 168). They are very numerously met with in the submaxillary, but are absent in the parotid. Some ganglia are present in connection with the nerve-branches surrounding the chief duct of the suljlingual gland. Pfliiger maintains that the ultimate nerve fibres are connected with the salivary cells of the acini in man and mammals, but this remains to be proved. 298 CHAPTER XXV. THE MOUTH, PHARYNX AND TONGUE. 2-43. The jflaiids.— Into the cavity of the mouth and pharynx open very numerous minute glands, which, as regards structure and secretion, are either serous or mucous. The latter occur in the depth of the mucous membrane covering the U[)S, in the ]:)uccal mucous membrane, in that of the hard palate, and especially in that of the soft palate and the uvula, in the depth of the mucous membrane of the tonsils, at the Ijack of the tongue, and in the raucous membrane of the pharynx. The serous glands are found in the back of the tongue, in close ])roximity to the parts containing the special organs for the perception of taste — the taste goblets or buds (see below). All the glands are very small, but when isolated the}^ are perceptible to the unaided eye as minute whitish specks, as big as a pin's head, or bigger. The largest are in the lips, at the back of the tongue and soft palate, where there is something like a grouping of the alveoli around the small branches of the duct, so as to form little lobules. 244. The chief duct generally opens with a narrow mouth on the free surface of the oral cavity ; it passes in a vertical or oblique direction through the superficial part of the mucous membrane. In the deeper, looser part (submucous tissue) it branches in two or more small ducts, which take up a number of alveoli. Of course, on the number of minute ducts and alveoli depends the size of the gland. Mouth, Pharyxx and Tongue. 299 In man, all ducts are lined with a single layer of columnar epitliclial cells, longer in the larger than in the smaller ducts ; in mammals the epithelium is a single layer of polyhedral cells. No fibril lation is noticeable in the epithelial cells. At the transition of the terminal ducts into the acini there is occasionally a slight enlargement, called the infundibuhtm ; here the granular- looking epithelial cells of the duct change into the co- lumnar transparent mucous cells lining the acini. 245. The acini of these glands are identical with those of the mucous glands described above (Fig. 194) — e.g. the sub- lingual gland as regards size, tubular branched nature, the lining epithelium, and lumen. In some instances (as in the soft palate and tongue) the duct neir the opening is lined with ciliated columnar epithelium. The stratified epithelium of the surface is generally continued a short distance into the mouth of the duct. 246. The serous glands at the root of tlie tongue (von Ebner) differ from the mucous chiefly in the epithelium, size, and lumen of the acini. These Fig. 194. — Part of a Lobule of a Mucous Gland iu the Tongue of Dog. {Atlas.) «, Gland tubes (alveolii viewed in various directions : they are lined with transparent ■'mucous ceils" ; d, duct lined with small polyhedral cells. 300 Elements of Histology. are of exactly the same nature and structure as those of the serous or true salivary glands. 247. Saliva obtained from the mouth contains numbers of epithelial scales detached from the surface of the mucous membrane, groups of bacteria and micrococci, and lymph corpuscles. Some of these are in a state of disintegration, while others are swollen up by the water of the saliva. In these there are contained numbers of granules in rapid oscillation, called Brownian molecular movement. 248. The mucous nionibrane lining the cavity of the mouth consists of a thin membrane covered on its free surface with a thick stratified pavement epithelium, the most superficial cells being scales, more or less changed into horn. Underneath the epithelium is a somewhat dense feltwork of fibrous connective tissue, with numerous elavstic fibrils in networks. This part is the corium or mucosa, and it projects into the epithelium in the shape of cylindrical or conical papilla. According to the thickness of the epithelium, the papillae differ in length. The longest are found where the epithelium is thickest — e.g. in the mucosa of the lips, soft palate, and vivula. Numerous lymph corpuscles are found in the mucosa of the palate and uvula. Sometimes they amount to diffuse adenoid tissue. The deeper part of the mucous membrane is the suhmucosa. It is looser in its texture, but it also is composed of fibrous con- nective tissue with elastic fibrils. The glands are here embedded ; adipose tissue in the shape of groups of fat cells or continuous lobules of fat cells are here to be met with. The large vascular and nervous trunks pass to and from the sub mucosa. 249. Striped uiiiscular tissue is found in the submucosa. In the lips, soft palate, uvula, and palatine arches it forms a very conspicuous portion : Mouth ^ Pharynx and Tongue. 301 namely, the sphincter orbicularis, with its outrunners into the mucous membrane of the lips, the muscles of the })alate, uvula (levator and tensor palati), and the arcus palato-pharyngeus and palato-glossus. 250. The last branches of the arteries break up in Fig. 195.— Section through the Tongue of Cat ; the Blood-vessels injected. The lower part of the figure shows the injected muscular tissue, in the middle part the mucous membrane with large vessels ; the ui)per part shows the papillae filiformes, with their capillary blood-vessels. (Photograph by Mr. A. Priiuilc.) a dense capiUary net 1 cork on the surface of the mucosa, and from it loops ascend into the papillae. Of course, fat tissue glands and muscular tissue receive their own supply. There is a very rich i^lexus of veins in the superficial part of the mucosa. They are con- spicuous by their size and the thinness of their wall. 302 Elements of Histology. Tlie lymjohatics form networks in all layers of the mucosa, including the papilla^. The large efferent trunks are situated in the submucosa. The last out- runners of the nerve-hranches form a j^^^^ris of notv- meduUated fibres in the superficial layer of the mucosa, whence numerous primitive fihrilUe. ascend into the epithelium to form networks. Meissner's tactile cor- puscles have been found in the papillae of the lips and in those of the tongue. 251. In the pharynx the relations remain the same, except in the upper or nasal part, where we find many places covered with columnar ciliated epithelium. As in the palatine tonsils, so also here, the mucosa is infiltrated with difiiise adenoid tissue, and with lymph follicles in great numbers. This forms the pJuiryngeal tonsil of Luschka. In the palatine tonsil and in the pharyngeal tonsil there are numerous crypts leading from the surface into the depth. This is due to the folding of the in- filtrated mucosa. Such crypts are, in the pharynx, sometimes lined all through with ciliated epithelium, although the parts of the free surface around them are covered with stratified pavement epithelium. 252. The tongue is a fold of the mucous mem- brane. Its bulk is made up of striped muscular tissue (genio-, hyo-, and stylo-glossus ; according to direction: longitudinalis superior and inferior, and transversus lingupe). The lower surface is covered with a delicate mucous membrane, identical in structure with that lining the rest of the oral cavity, whereas the upper part is covered with a membrane, of which the mucosa projects over the free surface as exceedingly numerous fine and short hairdike processes, the papiUct jilijormes, or as less numerous, isolated, somewhat longer and broader mushroom-shaped papiUce fungiformes. The papilla?, as well as the pits between them, are covered with stratified pavement epithelium. Each has numbers MOUTH^ F/fARVNX AND ToNCUE. ;o3 of minute secondary papillne. Their substance, like the mucous membrane of the tongue, is made up of fibrous connective tissue. Tlie mucous membrane is on the whole thin, and is firmly and intimately connected /*»»!». Fig. 196. — Section through the Papilla Foliata of Rabbit, showiug the Taste Buds amongst the Epithelium. In the depth are Imndles of muscular libres and glands. Magnifying power, 40. {Photograph by Mr. A Pringlc.) with the fil3rous tissue forming the septa between the muscular bundles of the deeper tissue. It contains large vascular trunks, amongst which the plexus of veins is very consj^icuous (Fig. 195). On the surface of the mucosa is a rich network of capillary blood-vessels, extending as complex loops into the papillse. Lym- phatics form rich plexuses in the mucosa and in the deep muscular tissue. Adipose tissue is common 104 Elements of Histology. between the muscular bundles, especially at the back of the toncfue. 253. There are two varieties of glands present in the tongue, the mucous and serous. The latter occur only at the back, and in the immediate neighbourhood Fig. 197.— Section through Taste Organ (Papilla Foliata.) From same preparation as Fig. 196, more magnitied, to show the taste buds. {Photogrcq^h by Mr. A. Pringle.) of the taste organs ; the mucous glands are chiefly present at the back ; but in the human tongue there are small mucous glands (glands of Xuhn) at the tip. All the glands at the back are embedded between the bundles of striped muscular tissue, and thus the move- ments of the tongue have the effect of squeezing out the secretion of the glands. About the glands Mouth, Pharynx and Tongue. 305 numerous nerve bundles are found connected with minute ganglia. At the root of the tongue the mucous membrane is much thicker, and contains in its mucosa numerous lymph follicles and diffuse adenoid tissue. Thus numerous knob-like or fold-like prominences of the mucosa are produced. There are also minute pits or crypts leading into the depth of these prominences. 254. The psipilltii! circiiiiivallatae are large papill?e fungiformes, each surrounded by a fold of the mucosa. They contain taste goblets or buds — i.e. the terminal taste organs. At the margin of the tongue, in the region of the circumvallate papillae, there are always a few permanent folds, which also contain taste goblets. In some domestic animals these folds assume a definite organisation — e.g. in the rabbit there is an oval or circular organ composed of numbers of parallel and permanent folds, jiainlla foliata (Fig. 196). 255. The papillae fungiformes of the rest of the tongue also contain in some places a taste goblet. But most of the taste goblets are found on the papilla? circum- vallatae and foliatse. In both kinds of structures the taste goblets are placed in several rows close round the bottom of the pit, separating, in the papillae circumvallatae, the papillae fungiformes from the fold of the mucosa surrounding it : in the papilla foliata the pits are represented by grooves separating the individual folds from one another. 256. The taste jfoblets or taste buds are barrel- or llask-shaped structures (Fig. 197) extending in a vertical direction through the epithelium, from the free surface to the mucosa. Each is covered with flat- tened, elongated epithelial cells, forming its periphery ; these are the tegmental cells. The interior of the goblet is made up of a bundle of spindle-shaped or staff-shaped taste cells. Each includes an oval nucleus, and is drawn out into an outer and an inner fine extremity. u ;o6 Elements of Histology. The former extends to the free surface, projecting just through the mouth of the goblet, and resembles a tine hair ; the latter is generally y)ranched, and passes towards the mucosa, where it probably becomes connected with a nerve fibre. The mucosa of these parts contains rich plexuses of nerve fibres. Accordmtr to Eetzius the meduUated nerve fibres Pig. 198.— Ending of Nerve Fibres in and around Taste Buds of Rabbit. {G. SetziiiSffrom Quain.) n, Xerve fibres; 5. taste bud ; i, iutrabulbar ramification of nerve fibrils; p, peribulbar ramification of nerve fibrils ; s, sulcus between two adjacent folds of the papilla f oliata. entering from the mucosa lose their medullary sheath and continue their course, either as peribulbar ramifications between the tegmental cells, or as iutra- bulbar fibres between and amongst the taste cells. Both sets of fibres terminate with free knoblike endings (Fig. 198). Into the pits surrounded by taste goblets open the ducts of the serous glands only (von Ebner). 3° 7 CHAPTER XXVI. THE (ESOPHAGUS AND STOMACH. 257. I. Tlic €BSO|>liag^ii§. — Beginning with the cesophagiis, and ending with the rectum of the large intestine, the wall of the alimentary canal consists of an inner coat or mucous membrane, an outer or muscular coat, and outside this a thin fibrous coat, which, commencing with the cardia of the stomach, is the serous covering, or the visceral peritoneum. The epithelium lining the inner or free surface of the mucous membrane of the oesophagus is a thick, stratified, pavement epithelium. In Batrachia, not only the oral cavity and pharynx, but also the oesophagus, are lined with ciliated columnar epithelium. The mucous membrane is a fibrous connective- tissue membrane, the superficial part of which is dense — the mucosa; this projects, in the shape of small papillae, into the epithelium. The deeper, looser portion of the mucous membrane is the suh mucosa ; in it lie small mucous glands, the ducts of which pass in a vertical or oblique direction through the mucosa, in order to open on the free surface. In man these glands are comparatively scarce ; in carnivorous animals (dog, cat) they form an almost continuous layer (Fig. 199). 258. Between the mucosa and submucosa are longitudinal bundles of non-striped muscular tissue. At the beginning of the oesophagus they are absent, but soon make their appearance — at first as small 3o8 Elements of Histology. bundles sejDarated from one another by masses of con- nective tissue ; but lower down, about the middle, thej form a continuous stratum of longitudinal bundles. This is the miiscularis mucosce (Fig. 200). re-^^*^ —^^n Fig. 199.— From a Longitudinal Section througli the Mucous Membrane of the ffidopliagus of Dog. {Atlo.s.') c, Stratified pavement epithelium of the surface; m, muscularis mucosa; between the two is the mucosa ; g, mucous irlands ; d, ducts of same. Outside the submucosa is the muscularis externa. This consists of an inner thicker circular and an outer thinner loncjitudinal coat. And outside this is the outer, or limiting, fibrous coat of the oesophagus. In man the outer muscular coat consists of non-striped muscular tissue, except at the beginning (about the upper third, or less) of the oesophagus, which is composed of the striped variety ; but in many (Esophagus. 309 mammals almost the whole of the external muscular coat, except the part nearest the cardia, is made up of stripe* I tihres. 259. The large vessels pass into the submucosa, Fig. 200. — Ti'ansverse Section through the (Esophagus of a Newly-born Child. {Photograph. Lovj magnification.) 1, Stratified epillieliura of the inner surface; 2, mucosa containing cross-cut hundles of non-striped muscle, muscularis raucoss ; 3, outer muscular coat. whence their liner branches pass to the surface parts. The superficial part of the mucosa and the papillae contain the capillary networks. The outer muscular coat and the muscularis mucosae have their own vascular supply. There is a rich plexus of lymphatics in the mucosa, and this leads to a plexus of larger vessels in the submucosa ^Teichmann). The nerves form rich 3IO Elements of Histology. plexuses in the outer fibrous coat ; these plexuses include numerous ganglia. A second plexus of non- medullatecl fibres lies between the longitudinal and circular muscular coat ; a few ganglia are connected with this plexus. In the submucosa are also plexuses of non-medullated fibres. Now and then a small ganglion is connected also with this plexus. 260. II. The istoniacli. — Beginning with the cardia, the mucous membrane of the stomach is covered with a single layer of beautiful thin columnar epithelial cells, most of which are mucus-secreting goblet cells. On the surface of the mucous membrane of the stomach open numerous fine ducts of glands, placed very closely side by side. These extend, more or less vertically, as minute tubes, into the depth of the mucous membrane. In the pyloric end, where the mucous membrane presents a pale aspect, the glands are called the i^yloric glands : in the rest of the stomach, the mucous membrane presents a reddish or red-brown appearance, and here the glands have a different character. This second variety of gland is typical of the cardiac end of the stomach as distinct from the pyloric, and hence is described as the cardiac gland. 261. The part of the mucous membrane containing the glands is the mucosa ; outside this is a loose connective tissue containing the large vessels — this is the submucosa. Between the two, but belonging to the mucosa, is the muscularis mucosce, a thick stratum of bundles of non- striped muscular tissue, arranged in most parts of the stomach as an inner circular and an outer longitudinal layer. The tissue of the mucosa contains the gland tubes, arranged more or less in small groups. Between them is a delicate connective tissue, in which the minute capillary blood-vessels pass in a direction vertical to the surface. Numerous small l)undles of non-striped muscular fibres pass from the muscularis mucosae towards the surface — up Stomach. ;ii to near the epitheliuin of the surface — forming longitudinal muscular sheaths, as it were, around the gland tubes. The plicce villos?e of the suj)erficial part of the Fig. 201.— Cardiac Glands. A, Under a low power ; d, duct ; n^ neck, b, part of the fundus of a gland tube under a high power ; Pi parietal cells ; c, chief cells. mucosa contain fibrous connective tissue and numerous lymphoid cells. 312 Elements of Histology. 262. The car[iicous membrane; b. summits of the lymph follicles reaching the free surface; c, body of the lymph folliclfs iu the submucous tissue: d, outer muscular coat. {PItoto. Loic Maynijication.) submucous plexus, while passing through the outer muscular coat in order to reach the mesentery, take up the efferent vessels of the plexus of the lymphatics of the muscular coat. 324 Elements of Histology. L'74. The cliyle, composed of granules and fat globules of different but minute sizes, passes from the inner free surface of the mucous membrane of the small intestine through the epithelium into the spaces Fig. 211.— Vertical Section through the Mucous Membrane of the large Intestine. {Micropliotograph.) Some six elands are shown occupying almost the full height of the photograph. Ihe luiuen of the ^land is large, the glands being hardened in the distended condition. The epii helium lining is seen to include a very large number of roundish, clear, and but slightly staining cells, these being goblet cells. The nucleated cells of the sub-epithelial reticular tissue are seen between the glands. of the reticulum of the villi, and from here into the central chyle vessels. The plasma-corpuscles in the reticulum of the matrix may, and sometimes do, take up chyle globules : but it is a mistake to ascribe to these lymph cells an important role in Small and Large Intestixe. 3^5 passing chyle gloljules from the epitheliuin into the central chyle vessel (Fig. 214). Owing to the peripheral disposition of the capillaries in the villi, and owing to the greater tilling with blood of the capillaries during digestion, .p ^^ ^. ■.ch .^ i.i r-/..''/t?'*» ^r N '^. #M^ r**** Fig. 212. — From a Horizontal Section through the Mucous Membrane of Large Intestine of Pig, showing the gland tubes of Lieberkiihn in cross-section, their lining columnar epitlielium with numerous goblet cells amongst them. Between the gland is the tissue of the mucosa. (Photo. Moderately magnified.) the villi are thrown into a state of turgescence during this period, in consequence of which the central chyle vessels are kept distended. Absorption is thus greatly supported. The contraction of the muscular tissue of the villi and of the muscular coat of the in- testine greatly facilitates the absorption and discharge of the chyle. 326 Elemenis of Histology. 275. The non-medullated nerves form a rich plexus, called the i^lexus myentericus of Auerhach (Fig. 215), with groups of ganglion cells in the nodes ; this plexus lies between the longitudinal and circular muscular coat. Another plexus connected %% Fig. 213. — Transverse Section through the Human A]ipendix Verniiforiuis ; showing the mucous membrane with the densely arranged glands of I.ieberkiilin, the subuiucous layer with the cross-cut large vessels, and the outer muscular coat covered by the peritoneal layer. {Photo. Low poicer.) with the former lies in the submucous tissue ; this is the plexus of Meissner, with ganglia. (Fig. 172.) In both plexnses the branches are of a very variable thickness ; they are groups of simple axis cylinders, held together by a delicate endothelial sheath. Small and Large Intestine. 3^7 Fig. 214.— Part of a Villus filled with Chyle, from the intestine of a puppy- four days old. (ReidenJui.in.) rt, Epithelium of surface of villus; b, tissue filled with chyle globules. rMmmM^ ^... Fig, 215. — Plexus Myentericus of Auerbaeh of the small intestine of a newly-born child. (Atlas.) The minute circles and ovals indicate sranglion cells. .28 CHAPTER XXVITI. THE GLANDS OF BRUNNER AND THE PANCREAS. 276. At the passage of the pyloric end of the stomach into the diiodeniini (Figs. 'JOS, 216), and in the P.G. <^- ;;-sO^U^T,f^ MM. M.C. Fig. 216.— Section througli the Gastro-duodeiialJunction. (Microphotograph.) A bandisseen runninf,' across from m.m. to m.m., the muscularis mucosa?. In tlie suljimicoiis coat beneath on the right side are seenBrunuers glands, B.G. In the mucous coat pyloric ghands are seen on left side, p.g. ; villi, v., and crypts of Lieberkuhn, c.l., on right side. A small piece of muscular coat is seen at Ji.c. Glands of Brunwkk. 329 first part of tlie latter, is a continuous layer of gland tissue in the submucosa, composed of convoluted, more or less branched tubes grouped into lobules, and permeated by bundles of non-striped muscular tissue. ^» M fti»^ Fig. 217. — Section tlirougli Pancreas of Cat. {Micropliotogrwph.) Three lobules are cut across. In the middle of the small lobule on the right a lighter patch is seen; this is an interlobular clump. Similar clumps are seen on the other lobules. outrunners of the muscularis mucosae. These are the glands of Brunner. Numerous thin ducts lined with a single layer of columnar epithelial cells pass through the mucosa and open with the crypts of Lieberkiihn between the bases of the villi. The gland tubes of Brunner's glands are identical in structure tvith the pyloric glands, with ichich they form a direct ana- tomical continuity. 35^ Elements of Histology. 111. The pancreas (Fig. 217) is in most respects identical in structure with a serous or true salivary gland. The distribution of the blood-vessels and lymphatics, and the arrangement of the connective tissue, so as to separate the ghmd tissue in lobes and lobules, with the corresponding inter- and intra-lobular Fig. 218. — From a Section through Pancreas of Dog. {Atlas.') a. Alveoli (tuhes) of the gland; the liuin? cells show an outer homogeneous and an inner granular-looking portion ; d, minute duct. ducts, are simihxr in both cases. The epithelium lining the latter ducts is only faintly striated, not by any means so distinctly as in the salivary tubes. The alveoli or acini are much more elongated than is the case in the serous salivary glands, and in section the tubular character of the alveoli is marked (Fig. 218). The intermediate part of the duct leading to the alveolus resembles the ductule of the salivary gland. The cells of the alveolus are somewhat pyramidal, and show in specimens hardened by ordinar}^ reagents an outer more deeply staining zone varying in width. Pancreas. 331 and an inner less deeply staining area (Fig. 218). Tiiis lighter zone represents the part of the cell in which tlie secretory grannies are collected (Fig. 219). The outer more deeply staining zone may Fig. 219.— Section througli Pancreas. { Micro-photograph of specimen hardened in osrnic acid.) Several alveoli are seen, the darker masses in the centre of each being accumu- lations of secretory granules. sometimes show a radial striation. In some animals the cells lining the ductule appear to be continued as an internal lining into the alveolus. These constitute the so-called centro-acinous cells of Lancjerhans. There are also to be seen in the pancreas of most animals masses of cells possessing no alveolar arrange- ment, staining less deepl}"", but having large oval 2>2>^ Elements of Histology. nuclei, which masses lie here and there between the alveoli. These groups of cells are very well ":^.. '^L.- ^ Fig. 220. — Seetior. through the Pancreas of Cat. (Micropliotograph.) In the central lobule is seen a large, slightly-stained mass, which is an inter- tiihiilar clump. supplied witli blood-vessels, and are spoken of as intertiihii.lar chimjj.'i, or iiiteralveolar cell islets (see Fig. 220). 333 CHAPTER XXIX. THE LIVER. / 278. The outer surface of the liver is covered with a delicate serous membrane,, the peritoneum, which, like that of other abdominal organs, has on its free surface a layer of endothelium. It consists chiefly of fibrous connective tissue. At the liilum or porta hepatis this connective tissue is continued into the interior, where it joins the connective tissue of the GJisson's ccqysuh, or the in- terlobular connec- tive tissue (con- nective tissue of the portal canals). This tissue is fibrous, and more or less lamellated ; by it the substance of the liver is subdivided into numerous, more or less polyhedral, solid lobules or acini (Fig. 221), each about 2V of than inch in diameter. According to -A ^s Fig. 221.— From a Section through the Liver of Pig. Five lobules are shown. " They are well separated from one another by the inter- lobular tissue. {Atlas.) .*, Interlobular connective tissue, containing the interlobular blood-vessels, i.e., the branches of the hepatic artery and portal vein. and the inter- lobular bile ducts ; i, intralobular or central vein. 334 Elements of Histology whether the interloltular tissue forms complete boundaries or not, the acini appear well defined from one another (pig, ice-bear), or more or less fused (man and carnivorous animals and rodents). AVithin each acinus there is only very scanty connective tissue, in the shape of extremely delicate Fig. 222.— From a Vertical Section through the Liver of Rabbit ; the blood- vessels and bile-vessels injected. i^Atlo.s.) a. Interlobular veins sun-ounded by interlobular bile ducts ; these latter take up the network of fine intralobular bile capillaries ; the mesbes of this net- work correspond to the liver cells ; h, Intraloliular or central vein. bundles and flattened connective-tissue cells. Occa- sionally, esjDecially in the young li\'er, lymph cells are to be met with in the acini and in the tissue between them. 279. The vena portie having entered the hilum gives off' rapidly numerous branches, which follow the interlobular tissue in which they are situated, and they form rich flexuses around each ac.invs : these are the interlohdar veins (Fig. 222). Xumerous LlVEK. 335 large capillary blood-vessels are derived from these veins. These capillaries pass in a radiating direction to the centre of tlie acinus, at the same time anastomosing with one another by numerous transverse branches. In the centre of the acinus the capillaries become confluent into one vein, the cen- tral or intralohular vein. The intralo- bular veins of se- veral neighbouring acini join so as to form t\iQ sublohular veins, andthe-e lead into the efterent veins of the liver, or the hepatic veins, which finally pass into the vena cava inferior. 280. The sub- stance of each acinus — i.e. the tissue Fig. 223. — From a Lobule of the Liver of Rabbit, in Avhicli blood- and bile-vessels had been injected, more highlv magnified than in Fig. 222. (Atlas.) b, Bile capillaries between the liver cells, which are well shown as nucleated polj'gonal cells, each with a distinct reticulum ; c, capillary blood-vessels. between the capillary blood-vessels — is composed of uniform polygonal protoplasmic epithelial cells, of about jQ^j-yth of an inch in diameter ; these are the liver cells. Owing to the peculiar, more or less radiating, arrangement of the capillaries, the liver cells appear to form columns or cylinders, also more or less radiating from the periphery towards the centre of the acinus. The cells contain particles of glycogen in various amounts. According to Brunton and Delepine, the amount gradually increases in the rabbit's liver after a meal, and reaches its maximum between the third and eighth hour. They also contain pigment granules, which, being derived from the disintegration of haemoglobin in the spleen, include 336 Elements of Histology. iron. Each liver cell shows a more or less fibrillateJ protoplasm (Kupfer), and in the centre a spherical nucleus with one or more nucleoli. The liver cells are joined by an albuminous cement substance, in which are left fine channels ; these are the hile capillaries (Figs. 223 and 2'2-i). In a successfully injected preparation the liver cells appear separated everywhere from one another by a bile capillary, and these form for lite ivhole acinus a continuous inter- cominunicating network of minute channels. Where the liver cells are in contact with a capillary blood- vessel, there are no bile capillaries. 281. At the margin of the acinus the bile capil- laries are connected with the lumen of minute tubes ; these jDOssess a membrana propria and a lumen lined with a single layer of transparent polyhedral epithelial cells. These are the small interlobular hile ducts (Fig. 222). Their epithelial cells are in reality continuous with the liver cells. These ducts join and form larger interlobular hile ducts, lined with more or less columnar epithelium. The first part of the bile duct lined with polyhedral cells corresponds to the intermediary part of the ducts of the salivary glands. The interlobular bile ducts form networks in the interlobular tissue. Towards the hilum they become of great diameter, and their wall is made up of fibrous tissue, and in it are bundles of non-striped muscular cells. Small mucus-secreting glands are in their wall, and open into their lumen. The wall of the hepatic duct, and of the gall bladder, are merely exaggerations of a large bile duct. 282. The hepatic artery follows in its ramification the interlobular veins. The arterial branches form plexuses in the interlobular tissue, and they supply the capillary blood-vessels of the interlobular connective tissue, and especially of the bile ducts. The capillary blood-vessels of the bile ducts join so as to form Liver. 337 small veins, wliicli finally empty themselves into the hepatic veins. The anastomoses between the capillary blood - vessels, derived from the arterial branches, and the capillary blood-vessels of the acini, Fig. 224.— From a Section tlirougli the Liver of Rabbit, of which the bile ducts had been injected ; showing the distribution of the bile capillaries and their branchlets between the liver cells. (Fhotograpli. Moderately magnified.) are insignificant (Cohnheim and Litten). The serous covering of the liver contains special arterial branches — rami capsulares. Networks of lymphatics — deep lymphatics — are present in the interlobular connective tissue, forming plexuses around the interlobular blood- vessels and bile ducts, and occasionally forming a perivascular lymphatic around a branch of the hepatic vein. Within the acinus, the lymphatics are repre- w ^T,S Elements of Histology. sented only by spaces and clefts existing between the liver cells and capillary blood-vessels ; these are the intralohidar lymphatics (Macgillivray, Frey, and others). They anastomose at the margin of the acinus with the interlobular lymphatics. In the capsule of the liver is a special network of lymphatics called the superficial lyinphatics. Numerous branches pass between this network and the interlobular lymphatics. 539 CHAPTER XXX. THE ORGANS OF RESPIRATION. 283. I. The larynx — The supporting frame- work of the larynx is formed by cartilage. In the epiglottis the cartilage is elastic and reticulated — i.e. the cartilage plate is perforated by numerous smaller and larger holes. The cartilages of Santorini and Wrisbergii, the former attached to the top of the arytenoid cartilage, the latter enclosed in the aryteno- epiglottic fold, are also elastic. The thyroid, cricoid, and arytenoid cartilages are hyaline. All these are covered with the usual perichondrium. A small no lule of elastic cartilage is enclosed in the front part of the true vocal cord. This is the cartilao^e of Luschka. The mucous membrane lining the cavity of the larynx (Fig. 225) has the following structure : — The internal or free surface is covered with ciliated stratified columnar epithelium : the most superficial cells are conical cells with cilia on their free surface ; then between the extremities of these cells are wedged in spindle-shaped and inverted conical cells. Numerous goblet cells are found amongst the superficial cells. The two surfaces of the epiglottis and the true vocal cords are covered with stratified pavement epilheli^im. Underneath the epithelium is a basement mem- brane separating the former from the mucous mem- brane proper. 284. Themucojs membrane is delicate connective ;4C Elements of Histology. tissue with numerous lymph corpuscles. In the pos- terior surface of the epiglottis, in the false vocal cords, and especially in the ventricle of the larynx, this 7n — \ ^^^ >- ^ ^ In ^-S2> ^^*'.\ „H(^ Fig. 225.— From a Longitudinal Section through the Ventricle of the Larvnx of a Child. (Atlas.) a, True vocal cord ; b, false vocal cord ; c. nodule of elastic cartilage (cartilage of Luschka): d, ventricle; I, lymphatic tissue ; m, bundles of the thyro- arytenoid muscle in transverse section. infiltration amounts to diffuse adenoid tissue, and even to the localisation of this as lymph follicles. In both surfaces of the ej^iglottis, and in the true vocal cords, the mucosa extends into the stratified pavement epithelium in the shape of minute papillae. In the lower part of the larynx the mucous mem- brane contains bundles of elastic fibres connected into Larvnx.\ 341 networks, antl running in a longitudinal direction. Those elastic fibres are found chieHy in the superficial parts of the mucous membrane. Tn the true vocal X 40. {Photograph by Mr Fig. 226. — Section through Trachea of Foitus. A. Pringle.) 1, Ciliated columnar epithelium of internal surface; 2, mucous membrane with its glands ; ?,, cartilage ; 4, outside this the thyroid gland. cords the mucosa is entirely made up of elastic fibres extending in the direction of the vocal cords. 285. The deeper part of the mucous membrane is of loose texture, and corresponds to the submucosa ; in it are embedded numerous mucous glands, the ducts of which pass through the mucosa and open on the free surface. The alveoli of the glands are of the nature of mucous alveoli — i.e. a considerable lumen lined with a layer of mucous goblet cells. There are, 342 Elements of Histologw however, also alveoli lined with columnar albuminous cells, and such as have Ijoth side by side, as is the case i^t^-^'iVmrr/r-^i^'-r-i-'. g»y'.;?j7-^[7f^| m •^ wn V. iV^ ^^ I Fig. 227.— From a Longitudinal Section tlirougli the Trachea of a Child. {Atlas.) a. Stratified columnar ciliated epitheMum of the internal free surface: ft, base- ment nienihrane ; c, mucosa ; d. networks of longitudinal elastic tihres ; the oval nuclei bL-tween them indicate connective-tissue corpuscles; e, sub- mucous tissue containing mucous glands; /, large blood-vessels; g, fat cells ; h, hyaline cartilage of the tracheal rings. in the sublingual dand of the dof?. The ciliated epithelium of the surface in some places extends also for a short distance into the ducts. The true vocal cords have no mucous glands. The Ijlood-vessels terminate with the capillary net- Trachea. 343 work in the superficial — i.e. &u)>epithelial — layer of the mucosa ; where tliersj are papilla; — i.e. in the epiglottis and true vocal cords — these receive a loop of capillary blood-vessels. The lymphatics form super- ficial networks of fine vessels and deep submucous networks of large vessels. These are of enormous width and size in the membrane of the anterior surface of the epiglottis. The finer nerves form superficial plexuses of non-medullated fibres, some of which ter- minate, according to Luschka and Boldyrew, as end bulbs. Taste buds have been found in the epithelium of the posterior surface of the epiglottis (V( rson, Schofield, Davis), and also in that of the deeper parts of the larynx (Davis). 286. II. The trachea — The trachea is very similar in structure to the lower part of the larynx, from which it differs merely in possessing the rings of hyaline cartilage, and in containing, in the posterior or membranous portion, transverse bundles of non- strijoed mnscrdar tissue, extending horizontally between the ends of the rings. Its com])onent parts are (Figs. 226,227, 228):— {a) a stratified columnar ciliated epithelium ; {Jj) a basement membrane ; (c) a mucosa, with the terminal networks of capil- lary blood-vessels, and infiltrated with adenoid tissue ; {d) a layer of longitudinal elastic fibres connected into networks ; (e) a loosely textured submucous tissue, contain- ing the large vessels and nerves and small mucous glands. Occasionally the gland or its duct is em- bedded in a lymph follicle. 287. III. The bronchi and the lung: The bronchi ramify within the lung dendritically into finer and finer tubes. The finest branches are the terminal bronchi. In the bronchi we find, instead of rings of hyaline cartilage, as in the trachea, larger 344 Elements of Histology. and smaller oblong or irregularly-sliaped plates of hyaline cartilage distributed more or less uniformly in the circumference of the wall. Towards the small microscopic bronchi these cartilage plates gradually diminish in size and number. The epithelium, the Fig. 228.— From a Section througli the Traclieal Mucous Membrane of a Newly -born Child. {Photo. Highly magnified.) e. Ciliated columnar epithelium ; amongst the ciliated cells are numerous goblet cells ; m, mucosa ; ulum or alveolar duct in cross-section ; b. groups of polyhedral cells lining one part of the infundibulum, the rest being lined with fliittened transparent epithelial scales ; c, alveoli lined with flattened epithelial scales ; here and there between them is seen a polyhedral trranular epithelial cell. with the coDiieetive tissue accompanying the bronchial tubes and large vascular trunks, and with these is traceable to the hilum. On the other hand, the inter- lobular connective tissue of the superficial parts of the lung is continuous with the fibrous tissue of the Brlwchi axd Lung. 347 surface called the pleura pulmonalis. This membrane contains numerous elastic libres, and on the free surface is covered with a hiyer of endothelium. In some instances (guinea-pig) the pleura pulmo- nalis contains bundles of non-striped muscular tissue. The lobes of the lung are separated from one another by large septa of connective tissue— the liga- menta pulmonis. 291. The teriiiiiial bronchi contain no cartilage or mucous fflands in their wall. This is made up of three coats : («) a delicate epithelium — a single layer of small jxjhjhedral (jranular-Jooking cells ; (h) a circular coat of non-striped muscular tissue ; and (c) a tine ad\entitia of elastic fibres, arranged chiefly as longitudinal networks. 292. Tracing the elements constituting the wall of a terminal bronchiole into the infundibula and air cells (Fig. 229) we find the following changes : {«) the polyhedral granular-looking epithelial cells forming a continuous lining in the terminal bronchiole are traceable into the infundibulum only as larger or smaller groups : between these groups of small poly- hedral granular-looking cells large, flat, transparent, homogeneous, nucleated, epithelial scales make their appearance. The farther away from the terminal bronchiole, the fewer are the groups of polyhedral granular-lookinf; cells. In all infundibula. however, the transparent scales form the chief lining. This becomes still rnoie marked in the air cells. There the small polyhedral granular-looking cells are traceable only singly, or in groups of two or three (Elens), the rest of the cavity of the fir cells being lined with the large transparent scales. In the foetal state all cells lining the infundibula and air cells are of the small polyhedral granular- looking variety (Kuttner). With the expansion of the lungs during the first inspiration many of these 348 Elements of Histology. cells change into the large transparent scales, in order to make up for the increment of surface. A lung expanded ad maximum shows much fewer or none of the small polyhedral cells ; while a lung that is col- lapsed shows them in groups in the infundiljula, and isolated or in twos or threes in the alveoli. Fig. 230.— Network of Capillary Blood-vessels surrounding the Alveoli of the Human Lung. (Photograph by Mr. A. Pringle.) 293. (b) The circular coat of non-striped muscular tissue of the terminal bronchiole passes as a continuous circular coat — but slightly thinner — on to the alveolar ducts or infundibula, in their whole extent, but not beyond them, i.e. not on to the air cells. (c) The adventitia of elastic networks is continued on the infundibula, and thence on the air cells, where Bronchi and Lung. 349 it forms an essential part of the wall of the alveoli, being its framework. Amongst the network of elastic fibres forming the wall of the alveoli is a network of branched connec- tive-tissue cells, contained as usual in similarly-shaped branched lacun?e, which are the radicles of the lym- phatic vessels. 294. The blood-vessels and lyiiipliatics. — The branches of the pulmonary artery and veins are contained within the connective tissue separating the lobes and lobules, whence they can be traced into their finer ramifications towards the infundibula and air cells. Each of these latter is surrounded by a sort of basket-shaped dense network of capillary blood- vessels (Figs. 230 and 231). The capillary networks of adjacent alveoli are continuous with one another, and stand in communication on the one hand with a branch of the pulmonary artery, and on the other with branches of the pulmonary vein. The branches of the bronchial artery belong to the bronchial walls, which are supplied by them with capillary networks. The lacunse and canaliculi in the wall of the alveoli, mentioned above, are the rootlets of lymphatic vessels, which accompany the pulmonary vessels, and form a network around them ; these are the deep lymphatics, or the "perivascular lympJtatics. They are connected also with the networks of lymphatics sur- rounding the bronchi, i.e. the peribronchial lymphatics. The rootlets of the superficial air cells empty them- selves into the siib-j)leural j^le.mis oflymj^hatics., a rich plexus of large lymphatics with valves. All these lymphatics lead by large trunks into the bronchial lymph glands. 295. Between the flattened transparent epithelial cells lining the alveoli are minute openings, stomata (Fig. 229), leading from the cavity of the air cells into the lymph lacunae of the alveolar wfiU. These stomata. 350 Elements of Histology. are more distinct during expansion, i.e. inspiration, than in the collapsed state. Inspiration, by its ex- panding the lungs, and consequently also the lym- phatics, greatly favours absorption. Through these stomata, and also throuirh the interstitial cement Fig. 231.— Injected Lung of Cat. (Photograph.) substance of the lining epithelium, formed particles — such as soot particles of a smoky atmosphere, pigment artificially inhaled, cellular elements, such as mucous or pus corpuscles, bacteria, etc. — find their way into the radicles of the lymphatics, thence into the perivascular and sub-pleural lymphatics, and finally into the bronchial glands. The cellular elements just mentioned, containing particles of soot, are spoken of as " dust cells." .53 CHAPTER XXXI. THE SPLEEX. 296. The capsule enveloping the spleen is a serous membrane — the peritoneum. It is a connec- c i 0* '0 , Tig. 232.— From a Vertical Section through the Spleen of Ape. (Atlas.) a. Capsule; b, rrabeculEe; c. Malpighian corpuscle: d, artery ensheathed in a Malpit'hian corpuscle ; e, pulp tissue. tive-tissue membrane with networks of elastic fibres, and covered on its free surface with an endothelium. v5D- Elemexts of Histology. The deep part of the capsule contains bundles of non- striped miLscuIar tissue forming plexuses. In man the bundles are relati\ely thin, but in some mammals - — e.g. dog, pig, horse — they are continuous masses arranged sometimes as a deep longitudinal and a superficial circular layer (Fig. 232). In connection with the capsule are the trahecuhe- (Fig. 232). These are microscopical, thicker or thinner cylindrical bands branching and anastomosing, and thus making a framework in which the tissue of the spleen is contained. Towards the hilum the trabeculye are larger, and they form there a continuity with the connective tissue of the hilum. They are the carriers of the large vascular branches. The trabecul^e in the human spleen consist chieflv of fibrous tissue with an admixture of longitudinal non-striped muscu- lar tissue. This is more pronounced in the dog, horse, pig, guinea-pig, in which the trabeculae are chiefly composed of non-striped muscu- lar tissue. Folio v\-- ingasmalltrabecula after it is given off from a larger one, we tind it branch- ing into still smaller ones, winch ulti- mately lose them- selves amongst the spleen tissue called Fig. 233.— From a Section through the Pulip of the Spleen of Pig. ( Atlas. ) a. Last outrunners of the muscular trabecule ; b, flattened cells forming the honevcomhed matrix of the pulp: in the meshes of this matrix are contained lymphoid cells of various sizes. of the elements of that part spleen pulp (Fig. 233). Tlie meshes of the network of the trabecular are filled up with the parenchyma. This consists of two Spleex. 353 kinds of tissues : {a) the Malpighian corpuscles ; and (Jj) the pulp tissue. 297. The .llal|ii;:liiaii corpuscles are masses of adenoid tissue connected with the branches of the splenic artery. Following the chief arterial trunks as they pass in the big trabeculfe towards the interior of the spleen, they are seen to give off numerous smaller l>ranches to the spleen parenchyma ; these are ensheathed in masses of adenoid tissue, which are either cylindrical or irregularly-shaped, and in some places form oval or spherical enlargements. These sheaths of adenoid tissue are traceable to the end of an arterial branch ; and in the whole extent the adenoid tissue or ^Malpighian corpuscle is supplied b}^ its artery with a network of capillary blood-vessels. 298. The rest of the spleen parenchyma is made up of the pulp. The matrix of this is a honeycombed, spongy network of fibres and septa, which are the processes and bodies of large, flattened, endotheloid cells, each with an oval nucleus. In some, es^^ecially young, animals, some of these cells are huge and multinucleated. The spaces of the honeycombed tissue are of different diameters, some not larger than a blood corpuscle, others large enough to hold several. All spaces form an intercommunicating system. The spaces contain nucleated lymph corpuscles, more or less connected with and. derived from the cell plates of the matrix. But they do not fill the spaces, so that some room is left, large enough to allow blood corpuscles to pass. The spaces of the honeycomljed pulp matrix are in communication, on the one hand, with the ends of the capillary blood-vessels of the Malpighian corpuscles, and, on the other, they open into the venous radicles or sinuses (Fig. 234), udiich are oblong spaces lined with a layer of more or less polyhedral endothelial cells. These sinuses form networks, and lead into the large 354 Elements of Histology. venous branches passing in the big trabeculse to the hihun. The venous sinuses in man and ape possess a special adventitia formed of circular elastic fibrils. Not all arterial branches are ensbeatlied in -AL Fig. 234. — From a Section through the Spleen of a Guinea-pig ; the blood- vessels had been injected. {Atlas ) a, Artery 'of Malpighian corpuscle; h. pulp; hetween its cells are the minute blood-ctiannels opening into c, the radicles of the veins. Malpighian corpuscles; some few fine arterial branches open directly into the veins of the pulp matrix, being invested in a peculiar reticular or concentrically arranged cellular tissue (not adenoid). These are the capillary sheaths of Schweigger Seidel. 299. The blood passes then from the arterial branches through the capillaries of the ^Malpighian Spleex. 355 corpuscles, whence it travels into the labyrinth of minute spaces in the honeycombed pulp matrix ; thence it passes into the venous sinuses, and finally into the venous trunks. The current of blood on its passage through the pnlp tissue becomes, therefore, greatly retarded. Under these conditions numerous red blood-corpuscles appear to be taken up by the cells of the pulp, some of which contain several in their interior. In these corpuscles the blood discs become gradually broken up, so that finally, only granules and small clumps of blood pigment are left in them. The presence of blood pigment in the corpuscles of the pulp is explained in this way ; and it is therefore said that the pulp tissue is a destroyer of red blood-corpuscles. The pulp tissue is most probably the birthplace of colourless blood-corpuscles; and according to Bizzozero and Salvioli it is also the birthplace of red blood- corpuscles. The hjmphatics form plexuses in the capsule (Tomsa, Kyber). These are continuous with the plexus of lymphatics of the trabecul^e : and these again with the plexus of lymphatics in the adventitia of the arterial trunks. Xon-meduUated nerve fibres have been traced along the arterial branches. 356 CHAPTER XXXII. THE KIDNEY, URETER AXD BLADDER. 300. A. The framework. The kidney possesses a thin investing capsule com- posed of fibrous tissue, more or less of a lamellar arrangement. Bundles of fibrous tissue pass with blood-vessels between the deeper part of the capsule and the parenchyma of the periphery. According to Eberth, a plexus of non-striped muscle cells is situated underneath the capsule. The ureter entering the hilum enlarges into the pelvis of the kidney, and with its minor recesses or prolongations forms the calices. Both the pelvis and the calices are limited by a wall which is a direct con- tinuation of the ureter. The internal free surface is lined with stratified transitional epithelium. Under- neath the epithelium is a fibrous connective- tissue membrane (the mucosa), containing the networks of capillary blood-vessels and fine nerve fibres. Outside the mucosa and insensibly passing into it is the loose-textured submucosa, with groups of fat cells. There are present in the submucosa bundles of non-striped muscular tissue, continued from the ureter, in the shape of longitudinal and circular bundles. In the pelvis of the kidney of the horse small alands (simple or branched tubes), lined with a single layer of columnar epithelial cells, have been observed by Paladino, Sertoli, and Egli. The last-named mentions also that in the pelvis of the human kidney Kidney, Ureter and Bladder. 357 there are gland-tubes similar in structure to sebaceous follicles. 301. The large vascular trunks enter, or pass from the tissues of the calices into the parenchyma of the kidney between the cortex and medulla, and they are accompanied by bundles of fibrous connective tissue and a few longitudinal bundles of non-striped muscular tissue, thereby separating the individual Malpighian pyramids. The parenchyma itself contains ver}^ scanty fibrous connective tissue, chiefly around the Malpighian cor- puscles and around the arterial vessels, especially in the young kidney. In the jDapilhe there is relatively a great amount of fil>rous tissue. On the surface of the papillae (facing the calices) there is a continuous layer of tibrous tissue, and this on its free surface is covered with stratified transitional epithelium. The parenchyma of the kidney consists entirely of the urinary tubules and the intertubular blood-vessels, and there is an interstitial or intertubular connective- tissue framework in the shape of honeycombed hyaline membranes with flattened nucleated branched or spindle-shaped cells. The meshes of the honeycomb are the spaces for the urinary tubules and blood-vessels. 302. B. The pareiicliyma. — I. The urinary tubules (Fig. 235). — In a transverse or longitudinal section through the kidney we notice the cortex, the houndary layer of Ludwig and the papillary j)ortions, the last terminating in the conical ^;«^?j<7/rti in the cavity of the calices. The boundary layer and the papillary portion form the medulla. A papilla with the papillary portion and boundary layer, continuous with it, constitutes a MalpiyJiian pyramid. The medulla of the human kidney contains about a dozen of such Malpighian pyramids. 303. The cortex contains vast numbers of 358 Elements of Histology. Fig. 235. — Diagram showing the course of the Uriniferous Tubules in the difterent parts of the cortex and medulla. {Atla&,) (For description of this Fig. see foot of next page.) Kidney, Uri:ti:r and Bladder. 359 convoluted tubules with their c.ecal origin in the Malpighian corpuscles ; this is the lahnrinth separated into numerous divisions of ecjual breadth by regulai-ly- disposed straight stria? originating a sliort distance from the outer capsule, and ratliating towards the boundary layer through which they pass. Each of these stria3 is a bundle of straight tubules, and represents a mednUary ray. The boundary layer shows a uniform vertical striation, in which opa(pie and transparent strife alternate with one another. The opacpie stria^ are continuations of the medullar}^ I'ays, the transparent striae are bundles of blood-vessels. The papillary portion is uniformly and vertically striated. Tracing a medullary ray from the boundary layer into the cortex, it is seen that its breadth gradually diminishes, and it altogether ceases at a short distance from the outer capsule. A medullary ray is, con- sequently, of a conical shape, its apex being situated at the periphery of the cortex, its base in the boundary layer. Such a pyramid is called a pyramid of Ferrein. 304. All urinary tubules commence as convoluted tubules in the part of the cortex named the labyrinth, but not in the medullary rays, with a Cfecal enlargement called a Malpighian corpuscle^ and terminate — having previously joined with many other tubules into larger and larger ducts— at one of the many minute openings or mouths at the apex of a papilla. On their way the tubes several times alter their size and nature. Ai Cortex limited on it* free surface hy the capsule; a, subcapsular layer not containing Malpitfliian corpuscles ; a' inner stratum of cortex without Malpighian corpuscles ; b, lioundary layer : c. papillary part next the boundary layer; 1, Bowman's capsule; 2, neck of capsule; 3, proximal con- voluted tube; 4, spiral part; 5, descending limb of Henle's loop-tube; 6, the loop itself ; 7, 8, and 9, the ascending linil) of Henle's loop-tube ; 10, the irreu'ular tubule ; 11, the distal convoluted tul)ule ; 12, the first part "f the collecting tube; 13 and U, larger collecting tube; in the papilla itself, not represented here, the collecting tube joins others, and forms the duct. 360 Elements of Histology From \X> >tart to it^ end there is a continuous fine memhrana propria forming the boundary wall of the urinary tubule, and this memhrana propria is lined with a single layer of ejnthelial cells differing in Fig. 236. — From a Section through the Cortical Substance of the Kidney of a human Foetus, showing a 3Ialpighian corpuscle. (HandbooJ:.) a.Glomemlu* ; 6. tissue of the glomerulus : c. epithelium covering the glomer- ulus ; d, flattened epithelium lining Bowmans capsule ; e, the capsule itself ; /, uriniferous tubules in cross section. size, shape, and structure from place to place : in the centre of the tubule is a lunifn, differing in size according to the size of the tubule. 305, (1) Each Mcdpigldan corpuscle (Fig. 236) is composed of the capsule — the <-apsv.le of Bou-man — and the glomerulus, or Malpighian tuft of capillary blood-vessels. The capsule of Bowman is a hyaline membrana propria, supported, as mentioned aljove, by a small amount of connective tissue. On its inner surface Kidney, Ureter and Bladder. 361 there is a continuous layer of nucleated epithelial cells, in the young state of polyhedral shape, in the adult state squamous. The glomerulus is a network of convoluted capillary blood-vessels separated from one another by scanty connective tissue, chiefly in the shape of a few connective-tissue corpuscles. The capil- laries are grouped together in two to five lobules. The whole surface of the glomerulus is lined with a delicate membrana propria, and a continuous layer of nucleated epithelial cells, polyhedral, or even columnar in the young, squamous in the adult state. The membrana propria and epithelium dip in, of course, between the lobules of the glomerulus, and represent in reality the visceral layer of the capsule of the Malpighian corpuscle, the capsule of Bowman being the parietal layer. The glomerulus is connected at one pole with an afferent and efferent arterial vessel, the former being the larger of the t^vo. Between Bowman's capsule and the glomerulus there is a space, the size of which difiers according to the state of secretion, being chiefly dependent on the amount of fluid present. The Malpighian corpuscles are distributed in the labyrinth of the cortex only, with the exception of a thin peripheral layer near the outer capsule, and a still thinner layer near the boundary layer. The Malpighian corpuscles near the boundary layer are the largest, those near the periphery the smallest ; in the human kidney their mean diameter is about -^^-^ of an inch. 306. (2) On the side opposite to that where the afferent and efferent arterioles join the glomerulus, the capsule of Bowman passes through a narrow neck into the cylindrical urinary tubule in such a way that the membrana propria and epithelium of the capsule are continued as the membrana proj^ria and 36; Elements of Histology lining epithelium of the tubule respectively, an»•/ -J . .,- '/• -. . ^. * •.■■•• '■% .. ■ . . (. , « ,, / * .1 •' 1' Fig. 239. — Vertical Section through the entire Kidney (injected) of a Rat. {Photo. Low Power.) (I, Cortex ; b, papilla ; c, boundary layer. "fibrillated^' epithelium. He maintains that this excretion is effected through the cell substance ; but, in the case of carmine being used as pigment, I have not found the excretion to take place through the substance of the epithelial cells, but through the homogeneous interstitial or cement substance between the epithelial cells. 315. 11. The blood-vessels. (Figs. 238 and 239). 568 Elements of Histology. The large branches of the renal artery and vein are situated in the submucous tissue of the pelvis, and they enter, or pass out respectively from, the part of the parenchyma corresponding to the junction of the cortex and boundary layer, where they follow a more or less horizontal course, and give off, or take up respectively, smaller branches to or from tlie cortex and medulla. (1) In the cortex the arterial trunks give off to the cortex small branches, which singly enter the lahijrinth in a direction vertical to the surface of the kidney. These are the interlohidar arteries. Each of these, on its way towards the external capsule of the kidney, gives off, on all sides of its circumference, shorter or longer lateral branches : these are the afferent arterioles for the Malpighian corpuscles, each one entering a Malpighian corpuscle and breaking up into the capillaries of the glomerulus. On their way towards the external capsule, the arteries become greatly reduced in size, and finally enter the capillary network of the most peripheral part of the cortex ; but some of these arterioles may be also traced into the outer capsule, where they become connected with the capillary networks of this latter. The efferent vessel of a Malpighian glome- rulus at once breaks up into a dense network of capillary blood-vessels, which surround in all direc- tions the urinary tubules of the labyrinth. This network is continuous with that of the capillaries of the medullar}^ I'ays, the meshes being here elongated, and the capillary blood-vessels, for obvious reasons, more of a straight arrangement. The capillaries of the whole cortex form one continuous network. 316. The veins which take up the blood from this network are arranged in this manner : — ^There are formed venous vessels underneath the external capsule, taking up like rays on all sides, minute Kidney, Urkter and Bladder. 369 radicles connected with the capillaries of the most peripheral ^Axt of tlie cortex. These are the venoi steUata; ; they pass into the labyrinth of the cortex, where they follow a vertical course in company with the interlobular arteries. On tliis passage the}?" com- municate with the capillaries of the labyrinth, and ultimately open into the large venous branches situated between cortex and boundary layer. 317. (2) In the medulla. From the large arterial trunks short branches come off, w^hich enter the boundary layer, and there split up into a bundle of minute arterioles, which pass in a straight direc- tion vertically through the boundary layer into the papillary portion. These are the arterim recUt (Fig. 238). The number of vessels of each bundle is at the outset increased by the efferent vessel of the Malpighian corpuscles nearest to the boundary layer. On their way through the boundary layer, and through the papillary portion of the medulla, these arterioles give off the capillary netw^ork for the urinary tubules of these parts, the network, for obvious reasons, possessing an elongated arrange- ment. From this network originate everywhere minute veins, which on their way towards the cortical margin increase in size and number ; they form also bundles of straight vessels — vence rectca — and ultimately enter the venous trunks situated between the boundary Jayer and cortex. The bundles of the arterise rectae and venae rectse form severally, in the boundary layer, the transparent striae mentioned on a previous page as alternating with the opaque striae, these latter being bundles of urinary tubules. At the apex of each papilla there is a network of capillaries around the mouth of each duct. J) / Elements of Histology. 318. The outer capsule of the ki(hiey contains a network of capillary blood-vessels ; the arterial branches leading into them are derived from two sources : («) from the outrunners of the interlobular Fig. 240.— From Transverse Section through Urinary Bladder of Dog. {Photo. Low Pov:er.) a, Inner surface of folded mucous membrane, covered with stratified transitional epithelium ; b, raucous membrane : c, outer coat of non-striped muscle. arteries of the cortex, and (b) from extra-renal arteries. The veins lead [a) into the vena? stellatie, and (b) into extra-renal veins. The li/mpJtatic vessels form a plexus in the capsule of the kidney. They are connected with lymph spaces between the urinary tubes of the cortex. The large blood-vessels are surrounded by a plexus of lym- phatics, which take up lymph spaces between the KlDNKV, UrKTER and B LADDER. 37 1 urinary tubules, both in the cortex and the boundary layer. oil*. The ureter is lined with stratified transi- tional e]>itlieliam. Underneath this is the mucosa, a connective-tissue membrane with capillary blood- vessels. The submucosa is a loose connective tissue. Then follows a muscular coat composed of non- striped muscular tissue, arranged as an inner and outer longitudinal and a middle circular coat. Then follows an outer limiting thin tibrous coat or adventitia. In this last have been observed minute cjanfjlia in connection with the nerve-branches. 320. The bladder is similar in structure, but the mucous membrane and muscular coat are very much thicker. In the latter, which consists of non- striped fibres, can be distinguished an inner circular, a middle oblique, and an outer longitudinal stratum. The last is best developed in the fundus (Fig. 2-10). Xumerous sympathetic ganglia, of various sizes, are found in connection with the nerve-branches underneath the adventitia (peritoneal covering), and in the muscular coat (F. Darwin). The epithelium lining the bladder is stratified transitional, and it greatly varies in the shape of its cells and their stratification, according to the state of expansion of the bladiler. 172 CHAPTER XXXIII. THE xMALE GENITAL ORGANS. 321. (1) The testis of man and mammals is en- veloped in a capsule of white fibrous tissue, the tunica adnata. This is the visceral layer of the tunica vaginalis. Like the parietal layer, it is a serous membrane, and is therefore covered with endo- thelium. Minute villi are occasionally seen pro- jecting from this membrane into the cavity of the tunica vaginalis. These villi are generally covered with germinating endothelium. Inside the tunica adnata, and firmly attached to it, is the tunica cdbnginea, a fibrous connective-tissue mem- brane of lamellar structure. Towards the posterior maro-in of the human testis its thickness increases, and forms there (Fig. 241) a special accumu- lation — in cross section more or less conical, with posterior basis — the mediastinum testis, or corpus Highmori. Between the tunica adnata and tunica albuginea is a rich plexus of lymphatics, which, on the one hand, takes up the lymphatics of the interior, and on the other leads into the efferent vessels that accompany the vas deferens. The testis of the dog, cat, bull, pig, rabbit, etc., have a central corpus Highmori ; that of the mole, hedgehog, and bat a peripheral one ; while that of the rat and mouse have none (Messing). 322. The framework. — From the anterior margin of the corpus Highmori spring numerous Male Genital Organs. 373 septa of connective tissue, which, passing in a radiat- ing direction towards the alhuginea, with which tliey form a continuity, sul)divide the testis into a large a^ Fig. 241.— Passage of Convoluted Seminiferous Tubules into Straight Tubules and into the Rete Testis. {Mihalkovics, Quain's " Anatomy.") ^ a, Seminiferous tubules ; b, fibrous tissue : c, rete testis. number of more or less conical compartments, or lobules, the basis of which is situated at the tunica albuginea, the apex at the corpus Highmori. Kolliker 374 Elements of Histology. mentions that non-striped muscular tissue occurs in these se[)ta. From these septa thin connective-tissue lamellte pass into the compartments, and they form the supporting tissue for the blood-vessels, and also represent the interstitial connective tissue between the seminal tubules. This intertubular or interstitial tissue is distinctly iamellated, the lamella? being of different thicknesses, and consisting of thin bundles of fibrous connective tissue — arranged more or less as fenestrated mem- branes — and endotheloid connectixe plates on their surface. Between the lamella? are left spaces, and these form, through the fenestra? or holes of the lamellae, an intercommunicating system of lymph spaces — being, in fact, the rootlets of the lymphatics (Ludwig and Tomsa). AVithin the lamellae are found peculiar cells, which are much larger than lymph cells, and which, in some instances {e.g. guinea-pig), include pigment granules. They contain a spherical nucleus. In man, dog, cat, sheep, especially in the boar, these cells form large, continuous groups — plates and cylinders — and the cells are polyhedral, and exactly similar to epithe- lial cells. They are separated from one another within the grouj:) by a thin interstitial cement substance. Their resemblance with epithelium is complete. They are remnants of the epithelial masses of the Wolffian body of the fcetus. 323. The seminal tiibiile!^ (Fig. 242). — Within each compartment, above mentioned, lie numerous seminal tubules, twisted and convoluted in many ways, and extending from the periphery to near the corpus Highmori. The tubules, as a rule, are rarely branched ; but in the young state, and especially towards the periphery, branching is not uncommon. Male Genital Organs. 375 Each seminal tubule consists of a membrana propria, a lining epith(4iuin, and a lumen. The membrana propria is a hyaline membrane, with oval nuclei at regular intervals. In man it is thick and lamellated, several such nucleated membranes being Fig. 242.— Section of parts of three Seiniuiferous Tubules of Rat. (£. A. ScMfer.) a, "With the spermatozoa least advanced in development; &, more, and c, most advanced. Between the tubules are strands of interstitial cells. superimposed over one another. The lumen is in all tubes distinct and relatively large. The lining epithelium, or the seminal cells, differ in the adult in ditferent tubules, and even in different parts of the same tubule, being dependent on the state of secretion. 324. Before puberty all tubules are uniform in this respect, being lined with two or three layers of polyhedral epithelial cells, each with a spherical 376 Elements of Histology. nucleus. After puberty, however, the following different t3qies can be distinguished. (a) Tubules or parts of tubules similar to those of the young state — viz. several layers of polyhedral epithelial cells lining the menibrana propria. These are considered as («) the outer and ih) the inner seminal cells. The former are next to the membrana Fk '243 -From a Section through the Testis of Dog, showing portions of three seminal tubules. {Atlas.) j», Seminal epithelial cells and mimerous small cellt- loosely arranged ; B, small cells or sperniatohlasts becoming converted into spermatozoa; c, groups of these in a further stage of development. propria ; they are ])olyhedral in shape, transparent, and the nucleus of many of them is in the process of karyomitosis or indirect division (see par. 8) ; in some the nucleus is oval transparent, but containing a distinct network. The inner seminal cells generally form two or three layers, and are more loosely con- nected with one another than the outer seminal cells, and therefore possess a more rounded appearance. Male Genital Oh cans. 377 Between these a nucleated reticuluiii of fine fibres is sometimes noticed, the i^erm reticulum of von Ebner. But this is merely a supporting tissue, and has nothing to do with the germination of the cells or the spermatozoa (Merkel). The inner seminal cells show very abundantly the process of indirect division of the nucleus, almost all being seen in one or another phase of it. 325. The division of the inner seminal cells yields numerous small spherical cells ; these lie nearest the lumen, and are very loosely connected vi^ith one another. It is these which are transformed into spermatozoa, and hence are appropriately called spermatoblasts (-t'ig. 242). Amongst the seminal cells, especially of cat and dog, are found occasionally, but not very commonly, large multinuclear cells, the nuclei of which are also in one or other stage of karyomitosis. (b) The innermost cells — i.e. the spermatoblasts — - become pear-shaped, the nucleus being situated at the thinner extremity, becoming at the same time flattened and homogeneous (Fig. 24.')). The elongation of the spermatoblasts gradually proceeds, and in consequence of this we find numerous elongated, club-shaped spermatoblasts, each with a flattened nucleus at the thin end. These are the young spermatozoa, the nucleated extremity being the head. (c) At the same time these young spermatozoa become grouped together by an interstitial granular substance, in peculiar fan-shaped groups : in these groups the head — i.e. the thin end containing the flattened homogeneous nucleus — is directed towards the inner seminal cells, while the opposite extremity is directed into the lumen of the tube. Meanwhile the inner seminal cells continue to divide, and thus the groups of young spermatozoa get more and more buried, as it were, between them. 378 Elements of Histology. 326. The original cell-body of the spermatoblasts goes on elongating until its protoplasm is almost, but not quite, used to form a rod-shaped middle -piece (Schweigger Seidel) of the spermatozoa; from the distal end of this, a thin long hair-like filament, called the tail., grows out. Where this joins the end of the middle piece, there is present, even for some time afterwards, a last remnant of the granular cell-body of the original spermatoblast. Some of the inner seminal cells not used for the formation of spermatozoa dis- integrate and yield the granular substance between the spermatozoa of the groups, and also between these latter. When the granular interstitial substance holding together the spermatozoa of a group has become dis- integrated, the spermatozoa are isolated. \\'hile this development of the spermatozoa goes on, the inner seminal cells continue to produce spermatoblasts, some of which are converted into spermatozoa. 327. Spermatozoa (Fig. 24-4). — Fully formed spermatozoa of man and mammals consist of a homo- geneous flattened and slightly con\-ex-concave head (the nucleus of the original spermatoblast), a rod- shaped middle 2nece (derived directly from the cell- body of the spermatoblast), and a long hair-like tail. While living, the spermatozoa show very rapid oscilla- tory and propelling movement, the tail acting as a Hagellum or cilium ; its movements are sj^iral. In the newt there is a tine spiral thread attached to the end of the long, curved, spike-like head, and by a hyaline membrane it is fixed to the middle piece ; it extends beyond this as the tail. Also in the mam- malian and human spermatozoa, a similar spiral thread, closely attached to the middle piece, and terminating as the tail, has been observed (H. Gibbes). 328. The seminal tubules of each lobule pass into a short straight tubuU-. the vas rectum. This is Male Genital Organs. 379 narrower than tlie seminal tubule, and is lined with a single layer of polyhedral or short columnar epithelial cells. The vasa recta form, in the corpus Highmori, a dense network of tubular channels, which are irregu- lar in diameter, being at one place narrow clefts, at Fig. 244. — Various Kinds of Spermatozoa. A, Spennatr)zoon of guinea-pig not yet completely ripe; b, the same seen side- ways, the head of the spermatozoon is flattened from side to side; c, spermatozoon of h(jrse ; d, spermatozoon of newt. another wide tuljes, but never so wide as the seminal tubules ; this network of channels is the rete testis. 329. (2) The epidid.vnii«». — From the rete testis we pass into the rasa eferentia, each being a tube wider than those of the rete testis, and each leading into a conical network of coiled tubes. These are the coiii vascalosi. The smn total of all the coni vasculosi forms the globus major or head of the epididymis. 330. The vasa efferentia and the tubes of the coni •So Elements of Histology. vasculosi are about the size of the seminal tubules, but, unlike them, are lined with a layer of beautiful columnar epithelial cells, with a bundle of cilia (Fig. 245). Outside these is generally a layer, more or less continuous, of small polyhedral cells. The sub- stance of the columnar cells is distinctly longitudinally tibrillated. The membrtaia propria is thickened by the presence of a circular layer of non - striped muscular fibres. The rest — i.e. the globus minor, or tail of the epididymis — is made up of a continuation of the tubes of the globus major, the tubes diminishing gradually in number by fusion, and thereby at the same time becoming larger. The columnar epithelial cells, facing the lumen of the minor, are possessed of cilia Fig. 245.— Tubule of the Epi- didymis in cross-section. The wall of the tubule is made up of a thick layer of roncentrically ar- ranged n(tn-:.? -^ Fig. 257. — From a section through Human Scalp, showing a degen- erating hair. (Atlas.) a. Epidermis ; b, hair ; c, outer root- sheath of hair follicle ; d, sebace- ous follicle; f, arrector pili ; /, cyst grown out of the outer root- sheath; g, hair-kuob ; h, new out- growth of the outer root-sheath ; /, new papilla. 4i6 Elements of Histology. is left only the uj^per part uf the follicle, and in the centre of this is the remainder — i.e. non-degenerated portion — of the hair-root. The fibres of this are at the extremity fringed out and lost amongst the cells of the outer root-sheath of the follicle. This repre- sents the hair-knoh (Henle). Xow, from the outer root-sheath a solid cylindiical outgrowtli of epithelial cells into the depth takes place ; against the extremity of this a new papilla is formed. In connection with this new papilla, and in the centre of that cylindrical outgrowth, a new hair-bulb and hair are formed, and as the latter gradually mows outwards towards the surface, it lifts, or rather pushes, the old hair — i.e. the hair-knob — out of the follicle. The outer part of the follicle of the old hair persists. Thus we find in all parts of the skin where hairs occur complete or j^apillarv hairs side by side with degeneratincT hairs or hair-knobs. 388. Developiiieiit of liair. — In the human fcetus the liair-follicles make their first appearance about the end of the third m.onth, as solid cylindrical outgrowths from the stratum INIalpighii. This is the rudiment of the outer root-sheath. After having pene- trated a short distance into the corium, this latter becomes condensed around it as the rudiment of the hair-sac. and at the distal extremity forms the papilla 2:rowinc( against the outer root sheath and invajicin- ating it. On the surface of the papilla a rapid mul- tiplication of the epithelial cells of this extremity of the outer root-sheath takes place, and this forms the hair-bulb, by the multiplication of whose cells the hair and the inner root-sheath are formed. As growth and multij^lication proceed at the hair bulb, so the new hair, with its pointed end, gradually reaches the outer surface. It does not at once penetrate the epidermis, but remains growing and burrowing its wav for some time in the stratum corneum of the Sa'/.v. 417 epidermis in a more or less horizontal direction, till it finally lifts itself out of this beyond the free surface. 3iS9. In many mammals occur, amongst ordinary hairs, special large hairs, with huge hair-follicles planted deeply into the subcutaneous tissue ; such Fig. 25S.— Section througli the «kiii nf tlie Lip of a Rabbits Mouth. (Fhotorjraph. Loiv power.) Small ordinary hair-follicles, one hirge tactile hair and hair-follicle. Tlie dark thick hoiindarj- is the tissue of the hair-sac. the clear parts in.side are the masses of blood spaces, the dark line next to the hair itself is the outer root-sheath. are the big hairs in the skin about the lips of the mouth in the dog, cat, rabbit, guinea-pig, mouse and rat, etc. These are the tactile hairs (Fig. 258). Their hair-follicle possesses a thick hair-sac, in which are contained large sinuses intercommunicating with one another and with the blood system ; these sinuses are separated B B 41 8 Elemexts of Histology. \)\ trabecul?e of non-strined muscular tissue, and represent, therefore, a cavernous tissue. The papilla is large, and so is the outer root-sheath and the hair-root in all its parts. There are vast numbers of nerve-fibres, distributed and terminating amongst the cells of the outer root-sneath (Arnstein). 390. With each hair- follicle are connected one or tvro sehaceous foUirles. These consist of several fiask- shaped or oblong alveoli, joined into a common short duct opening into the hair-follicle near the surface — i.e. that part called the neck of the hair-follicle. The alveoli have a limiting membrana propria ; next to this is a layer of small polyhedral, granular- looking epithelial cells, each with a spherical or oval nucleus ; next to this, and filling the entire cavity of the alveolus, are large polyhedral cells, each with a ■-spherical nucleus : the cell substance is filled with minute oil globules, between which is left a sort of honeycombed reticulated stroma. The cells nearer to the centre of the alveolus are the largest. Towards the duct they become shrivelled \\\} into an amorphous mass. The duct itself is a continuation of the outer root-sheath. As multiplication goes on in the marginal layer of epithelial cells — i.e. those next the membrana proprise — the products of this multiplication are gradually shifted forward towards the duct, and through this into the neck and rnoutli of the hair-follicle, where they constitute the elements oi sehuin. There is a very characteristic misproportion be- tween the size of the hair-follicle and that of the sebaceous gland in the embryo and newly-ljorn, the .sebaceous cjland Ijeing there so larije that it forms the most conspicuous part, the minute hairs (lanugo) being situated, as it were, in the duct of the sebaceous follicle. 391. In connection with each hair-follicle, espe- Sa'/jv. 419 daily where they are of good size — as in the scalp — there is a bundle, or rather group of bundles, of non- sti-iped muscular tissue ; this is tlie arrector pili. It is inserted in the liaii--sac near the bulbous portion of the Fig. 259. — Vertical Section through the Human Xail and Nail-bed. a. Stratum Malpigbii of uail-bed; I), stratum .arrauulosuin of uail-bed • c Aeev layers of nail sulistaucc ; d, superfieiallayers of same. ' ' hair- follicle, and passes in an oblique direction towards the surface of the coriuni, grasping, as it were, on its way the sebaceous follicle, and terminating near the papillary layer of the surface of the corium. The arrector pili forms with the hair-follicle an acute angle — this latter being planted into the skin in an 42 o Elements of Histology. oblique direction, as mentioned above — and conse- quently, when the arrector contracts, it has the effect of raising the hair-follicle and hair (cutis anserina — "goose's skin '), and of making the hair assume a more upright position (causes it, as we say, to " stand on end "). At the same time, it compresses the sebaceous follicle, and thus facilitates the discharge of the sebum. 392. The corium of the scrotum, of the nipple of the breast, of the labia pudendi majora, and of the penis, contains numbers of bundles of non-striped muscular tissue (Kolliker), independent of the hairs ; these run in an oblique and horizontal direction, and form plexuses. 393. The nails (Fig. 259).— We distinguish the hody of the nail from the free margin and from the root ; the body is the nail proper, and is fixed on to the nail-bed, while the nail-root is fixed on the nail- matrix — i.e. the posterior j)art of the nail-bed. The nail is inserted, with the greater part of its lateral and wdth its posterior margin, in the nail-groove, a fold by which the nail-matrix passes into the surrounding skin. 394. The substance of the nail is made up of a large number of strata of homogeneous horny scales — the nail-cells — -each with a staff-shaped remnant of a nucleus. The corium of the nail-bed is higlily vascular : it is firmly fixed by stifi" bands of fibrous tissue on the subjacent periosteum ; it is covered with a stratum ]\Ialpighii of the usual description, except that the stratum irranulosum is absent in the nail-matrix, but is present in a rudimentary state in the rest of the nail-bed. The nail itself rej^resents the stratum lucidum, of course of exaggerated thickness, situated over the stratum Malpighii of the nail-bed. There is no stratum corneum over the nail. The stratum Malpighii and coriuni of the nail-bed are placed into permanent minute folds, and the nail possesses on its lower surface corresponding linear indentations. 395. In the foetal nail-bed the stratum Malpighii is covered with the usual stratum lucidum and stratum corneum, but the former is the larger : by a rapid multiplication of the cells of the stratum Malpighii, and a conversion of its superficial cells into the scales of the stratum lucidum. the fcetal nail is produced. At this early stage the nail is covered by stratum corneum. By the end of the fifth month the nail marcrin breaks throuijh this stratum corneum. and bv the seventh month the greater part of tlie nail has become clear of it. 306. Till' bIood-ves«»eIs of the »kiii. — The blood-vessels are arranged in diflerent system < for the different parts of the skin (Tomsa) : — {(() There is. fir^^t, the vascular sy.stem of the adipose tissue, diflering in no way from the dis- tribution of blood-vessels in fat tissue of other places. (6) Then there is the vascular system of the hair- follicle. The papilla has a capillary loop, or rather a minute arteriole, a capillary loop, and a descending vein, and the fibrous ti.ssue of the hair-sac possesses capillaries arranged as a network with elongated meshes, with its afferent arteriole and eflerent vein. (c) The sebaceous follicle has its afferent arteriole and eflerent vein, and capillary networks surrounding the alveoli of the gland. The arrector pili and other bundles of non-striped muscular tissue possess capil- lary networks \\ ith elongated meshes. (d) The sweat glands have an afferent arteriole, from which proceeds a veiy rich network of capil- laries, twining and twisting round the gland-tube. The duct possesses its separate aff'erent arteriole and capillaries, forming elongated meshes. 42 2 Elements of Histology. (e) The last arterial branches are those that reach the surface of the corium, and there break up into a dense capillarv network with loops for the papillae. In connection with these capillaries is a rich plexus of veins in the superficial layer of the corium. Fig. -260. —Skin of the Web of Frog of which the lymphatics had been in- ° jected, showing the dense plexus of lympliatic vessels. {Photograph. Lov: poi'-er.) (/) In the nail-bed are dense networks of capil- laries, with loops for the above-named folds. 397, The lysiipliatics (Fig. 260). — There are net- works of lymphatic vessels in all strata of the skin ; they are, more or less, of horizontal expansion, with oblique branches passing l^etween them. Their wall is a sinfde laver of endothelial cells, and some of them possess valves. Those of the surface of the corium Sa'/x. 4-3 take up lyiuplKitics of the papilla?. The subcutaneous lymphatics are the biggest. The fat tissue, the sweat- glands, and the hair-follicles possess their own lym- phatic clefts and sinuses. The interfascicular spaces of the corium and subcutaneous tissue are directly continuous with the lymphatic vessels in these parts. 398. The iierve^». — The nerve-branches break up into a dense plexus of fine nerve fibres in the super- ficial layer of the corium. This plexus extends hori- zontally, and gives ofi" numerous elementary fibrils to the stratum Malpighii, in which they ascend verti- cally and in a more or less wavy fashion towards the stratum lucidum (Langerhans, Podkopaefi", Eberth, Eimer, Ranvier, and others). According to some, they teraiinate with a minute swelling ; according to others, they form networks ; according to more recent observations, some of the fibrils terminate also in the substance of the deep epithelial cells {see Chap. XIV.). The subcutaneous nerve-branches of some places — palm of hand and foot, and skin of penis — give off' single niedullated nerve fibres, terminating in a Pacinian corpuscle, mentioned in a former chapter. In the volar side of the fingers and toes there occur in some of the papillfe of the corium the tactile or Meissner's corpuscles, each connected with one or two meduUated nerve fibres, as described in a previous chapter. The outer root-sheath of the hair-follicles contains the terminations of fine nerve fibres, in the shape of primitive fibrillte (Jobert, Bonnet, and Arnstein). According to Jobert, the nerve fibres entwine the hair-follicle in circular turns. The tactile hairs possess a greater supply of nerves than the ordinary hair-follicles. 424 CHAPTEE XXXVII. THE CONJCXCTIVA AXD ITS GLANDS. 399. (1) The eyelids (Fig. 261).— The outer layer of the eyelids is skin of ordinary description : the inner is a delicate, highly vascular membrane — the conjunctiva palpehrcn. This includes a firm plate — the tarsal plate. — which is not cartila^re, but very dense, white, fibrous tissue. In it lie embedded the Meibomian glands. These extend in each eyelid in a vertical direction from the distal margin of the tarsal plate to the free margin of the eyelid : in the posterior angle of this margin lies the opening or mouth of each of the Meibomian glands. The duct of a Meibomian gland is lined with a continuation of the stratified pavement epithelium, lining the free margin of the lid : it passes in the tarsal plate toward its distal margin, and takes up on all sidi-s sliort minute ducts, each of which becomes enlarged into a spherical, saccular, or llask-shaped alveolus. This is identical in structure and secretion icith the alveoli of the sebaceous follicles of the skin. 400. The conjunctival layer is separated from the subcutaneous tissue of the skin layer of the eyelid by the bundles of the sphincter nrbicidaris — striped mus- cular tissue. Some bundles of this extend near the free margin of the lid, and represent what is known as the musculus ciliaris Riolani. This sends bundles around the mouth of the ^Meibomian ducts. 401. At the anterior angle of the free margin of the lid are the evelashes or cilia, remarkable for their Conjunctiva and its Glands. 425 thickness and rapid reproduction. Xear the cilia, Viut towards the ^leiboniian ducts, open the ducts of .9 \iT&, - ^® "P^^- yh *:■$• Y-^ K. "=S^ Fig. -261.— Vertical Section through the Upper Eyelid. (Waldeger.) 1 CoDfunetiva • 2, skin ; 3. permanent folds of the conjunctiva ,- 4, bundles of ' the sphincter orbicularis; 5, eyelashes : 6. mouth of the gland of ilohl ; 7, duct of the Meibomian gland : >, tarsal gland>. peculiar large glands — the glands of Mold. Each of these is a wavy or spiral tul>e, pa^^sing in a vertical 426 Elements of Histology. direction from the margin of the lid towards its distal part ; it comjdetely coincides in structure with the large portion of a sweat gland — i.e. that part contain- ing a columnar epithelial lining, and between this and the membrana propria a longitudinal layer of non- striped muscular cells. The free margin is covered, as mentioned above, with stratified pavement epithelium, into which the mucous membrane extends in the shape of minute papillae. In the conjunctiva palpebral the epithelium is a thin stratified pavement epithelium ; there are no papilhe, but the sub-epithelial mucosa — that is, the layer situated between the epithelium of the surface and the tarsal plate — contains a dense network of capillary blood-vessels. 402. Passing from the eyelids on to the eyeball, we have the continuation of the conjunctiva palpebrse — i.e. the fornix conjunctivae — -and, further, the con- junctiva fixed to the sclerotic, and terminating at the margin of the cornea — the conjunctiva l)ul])i. The epithelium covering the conjunctiva fornicis and con- junctiva bulbi is stratified epithelium, the superficial cells being short columnar ; next to the fornix the superficial cells are beautiful columnar, and the mucosa underneath the epithelium is placed in regular folds (Stiedn, Waldeyer). Towards the cornea the epithelium of the conjunctiva assumes the character of stratified pavement epithelium, and minute papillae extend into it fi-om the mucosa. 403. The mucous membrane is fibrous tissue, con- taining the networks of capillary blood-vessels. Into the fornix lead minute mucous glands, em- bedded in the conjunctiva fornicis; they are the glands of Krause. Similar glands exist in the distal "portion of the tarsal plate. 404. The blood-vessels of the conjunctiva terminate as the capillary network of the su])erficial Conjunctiva and its Glands. 427 layer of the mucosa, and as capillaiy networks for the Meibomian glands, Krause's gland, etc. Around the corneal margin the conjunctival vessels are particu- larly dense, and loops of ca})illaries extend from it into the very margin of the cornea. 405. The lyiii|>liafic«» form a superficial and deep network. Both are connected by short branches. The deep vessels are possessed of valves. The super- ficial plexus is densest at the limbus cornese, and they are in direct connection with the interfascicular lymph clefts, both of the sclerotic and cornea. In the margin of the lid the superficial lymphatics of the skin anastomose with those of the conjunctiva. Lymph follicles occur in groups in the conjunctiva of many mammals about the inner angle of the eye. In the lower eyelid of cattle they are very conspicuous, and known as the glands of Bruch. They are also well marked in the third lid of many mammals. According to Stieda and Morano, isolated lymph follicles occur also in the human conjunctiva. 406. The nerves are very numerous in the con- junctiva ; they form plexuses of non-medullated fibres underneath the epithelium. From these plexuses fine fibrils pass into the epithelium of the surface, between whose cells they terminate as a network (Helfreich, Morano). End bulbs of Krause occur in great numbers in man and calf. They have been mentioned in a former chapter. 407. (2) The lacliryiiial g-laiids are identical in structure with the serous or true salivary glands. The arrangement of the connective-tissue stroma, the nature and structure of the ducts — especially of the intralobular ducts— and alveoli, the distribution of blood-vessels and lymphatics, are exactly the same as in the true salivary glands. Reichel has found that the epithelial cells lining the alveoli are well defined, conical or cylindrical, transparent, and slightly 428 Elements of Histology. granular during rest ; but during secretion they grow smaller, more opaque and more granular, their outlines are not well defined, and the nucleus becomes more spherical and placed more centrally. 408. In most mammals there is in the inner angle of the eye, and closely placed against the surface of the eyeball, a gland called Harder's (jiand. Accord- ing to Wendt, this is either a true serous gland, like the lachrymal — as in the ox, sheep, and pig — or it is identical in structure with a sebaceous gland, as in the mouse, rat, and guinea-pig ; or it consists of two portions, one of which (white) is identical with a sebaceous, while the other (rose-coloured) is a true serous gland ; such is the case in the rabbit and hare According to Giacomini, a rudiment of Harders gland exists also in the ape and man. 429 CHAPTER XXXVIII. CORNEA, SCLEROTIC, LIGAMENTUM PECTINATUM AND CILIARY MUSCLE. 400. T. The roriiea (Fig. 262) of man and many mauiDials consists of the following layers, counting from front to back : — (1) The epithelium of the anterior surface [see Fig. 26). This is a very transparent, stratified pave- ment epithelium, such as has been described in par. 22. It is directly continuous with the epithelium of tlie conjunctiva, but it is more transparent; in dark pigmented eyes of mammals the epithelium of the conjunctiva is also pigmented. In these cases the pigment, as a rule, does not pass beyond the margin of the cornea. 410. (2) Next follows a homogeneous elastic mem- brane, Bowman^s 'ineinhrane, or elastica anterior. It is best shown in the human eye, but is present, even though only rudimentary, in the eye of mammals. (3) Then follows the ground suhstaiice, or sub- stantia propria, of the cornea. This is composed of iamelhe of bundles of fibrous connective tissue. Neiofhbourinor lamellse are connected with one another by oblique bundles. The fibre bundles within each lamella run parallel to the surface of the cornea, but may cross one another under various angles. In the anterior layer of the ground substance some of the bundles pass through several lamellae in an oblique manner ; they represent the librse arcuatse. 43° Elements of Histology. The fibrils within the bundles, and the bundles, and the lainelhv of bundles are held together by an interstitial, albu- ;g7 niinous, semi-fluid ce- ment sul)stance, which, like other similar in- tei'stitial substances, belono's to the globu- lins, and is soluble in 10 per cent, saline solution (Schweigger Seidel). A few elastic tibrils are seen here and thei'e. Between the lamellae are left the lacunas and canal iculi for the branched, flat- tened, nucleated, cor- neal corpuscles^ de- scribed in a previous chapter (Figs. 37, 38). They anastomose with one another within the same plane, and also, to a limited degree, with those of neigh- bouring planes. 411. (4)Thenieni- l>i'aiia Desceiiioti, or elastica posterior, is a resistant elastic membrane, conspic- uous by its thickness in all corne?e, (5) The posterior surface of this mem- l^rane is covered with Fig. 2(32. — From a Vertieal Section through the Membranes of the Eve of a Child. {Atlas.) a. Cornea; b, sclerotic : c. \v\> ; d, processus ciliaris; e, ligameunnn pectinatiiui : /, ciliary imisck", Its meridional bundles; n choroid membrane; h. retina of the nra serrata; i, sphincter piipilla^ in cross- section. Cornea. 431 a mosaic of ])eautit'vil pohjijomd endotlielidJ ceUs^ eacli with an oval nucleus — the endotheliuiii of Descemet's membrane. Under stimulation these cells contract. At first they appear slightly and numerously branched, but gradually their processes become longer and fewer, and ultimately they are reduced to minute clumps of nucleated protoplasm, each with a few long processes. There are no blood-vessels in the normal cornea, except in fretal life, when there is underneath the anterior epithelium a plexus of capillaries. The lymphatics are represented as the intercom- municating lymjih-canalicular system — i.e. the lacun?e and canaliculi of the corneal corpuscles ; and in con- nection with these are lymph channels lined with a continuous endothelium and containing; the nerve bundles. 412. The nerves (Figs. 103, 105, 106) are distri- buted as the nerves of the anterior layers, and as those of the Descemet's membrane. The first form rich plexuses of tibrillated axis cylinders, with trian- gular nodal points (Cohnheim), in the anterior layers of the ground substance ; from this plexus pass obliquely through Bowman's membrane short branches — the rami perforantes (Kfilliker) — and these imme- diately underneath the epithelium break up into their constituent primitive fibrils, the latter coming off the former brush-like (Cohnheim). These primitive fibrilhe ultimately ascend into the anterior epithelium (Hoyer, Cohnheim, and others), where they branch, and nearly reach the free surface. They always run between the epithelial cells, and are connected into anet\Aork. According to some observers, they ter- minate w^ith free ends, pointed or knobbed : but according to others these apparent free ends are not in reality free endings (Figs. 107, 263 and 264). 43 2 Elemests of Histology 413. The nerves of Descemet's membrane form also a j^lexus of non-medullated fibres in the posterior lavers of the o-round substance : from them come off vast numbers of primitive fibrilla?, running a more Fi'^'. 263. — From a Horizontal .Section through the Gokl-stained Cornea of " Rabbit ; the corneal (branched) cells are faintly indicated, but the nerve tibrillse are well marked, also their lateral branchlet.s, terminating apparently with a minute knob. {Photograph. Moderate magnification.) or less straight and long course, crossing one another often under right angles : they give off very fine fibrils, which are closely associated with the corneal corpuscles, without, however, really becoming con- tinuous wdth their protoplasm. 414. II. The sclerotic consists of lamella? of tendinous tissue. The bundles of fibrous tissue are opaque as compared with those of the cornea, although SCLEKDl^IC. 433 they pabs insensibly into them. There are lymph clelts bet^veen the lamella? and trabeculse, and in them lie the flattened connective-tissue corpuscles, which, in the dark eyes of some mammals only, contain Fig. 264. — From the same preparation as in ijrecediiig tigiue, shuwing tlie tine Nerve Fibrils jiassing along the processes and bodies of the branched corneal corpuscles. (Pliotograph. Moderate magnification.) pigment granules. Numerous elastic fibrils are met with in the inner layers of the sclerotic. 415. Between the sclerotic and choroid membrane is a loose fibrous tissue, which acts also as the sup- jjorting tissue for the blood-vessels passing to and from the choroid. The part of this loose tissue next to the sclerotic, and forming part, as it were, of the sclerotic, contains, in dark eyes of mammals, numerous pigmented connective-tissue corpuscles ; it c c 43+ Elements of Histology. i« then called lamina Jusca. The rest — i.e. next to the choroid membrane — is the supra-choroidal tissue. 416. There H re blood-vessels in the sclerotic, whicli belong to it ; they are arterioles, capillaries, and veins : in addition to these are the vascular branches passing to and from the choroid. 417. III. The li»Jiiii«*iitiii" pec tiiiatuiii iridic [see Fig. 262) is a conical mass of spongy tissue joining hrndy the cornea and sclerotic to the iris and ciliary processes. It forms an intimate connection, on the one hand, with the junction of cornea and sclerotic, and on the other, withtliat of the iris and ciliary pro- cesses. This ligament is composed of trabeculse and lamella? of stiff elastic fibre-, forming a continuity, on the one hand, with the lamina Descemeti of the cornea and the elastic fibres of the sclerotic, and on the other with the tissue of the ciliary border of the iris. The trabecular anastomose, so as to form a honeycombed plexus, and the spaces in this plexus are lined with a layer of flattened endothelial cells, directly continuous with the endothelium of Descemet's mem- brane on the one hand, and with the layer of endo- thelial cells covering the anterior surface of the iris on the other band. In some mammals, the sjiaces in the ligamentum pectinatum near the iris are very considerable, and are called the spaces of Fontana. The interlamellar and interfascicular lymph spaces of the sclerotic form an intercommunicating system. The nerves form a dense plexus of non-medullated fibres in the tissue of the sclerotic (Helfreich). At the point of junction of the cornea and sclerotic, but belonging to the latter, and in the immediate neii^hbonrhood of the ligamentum pectinatum iridis, is a circular canal — the canal of Sclilemni ; this is Ciliary Muscle. 435 lined with (nidotheliuin, and is considered Ijy some (Schwalbe) as a lymphatic canal ; Ijy others (Leljer) as a venous vessel. 418. IV. The <'iliar.v muscle (Fig. 2G-J), or tensor choroideie, is tixed to this ligamentum pecti- natum ; it is composecl of bundles of non-striped muscular tissue. This muscle consists of two parts : {a) one of circular bundles nearest to the iris — this is the portio Miilleri ; {h) the greater part is composed of radiating bundles, passing from the ligamentum pectinatum in a meridional direction for a consider- able distance backwards into the tissue of the choroid membrane. It occupies the space between the liga- mentum pectinatuDi, sclerotic, ciliary processes, and the adjoining portion of the choroid membrane. The bundles of the muscle are arranged more or less in lamellpe ; within each lamella they form plexuses. A rich plexus of non-medullated nerve fibres, with groups of ganglion cells, belongs to the ciliary muscle. 436 CHAPTER XXXIX IRIS, CILIARY PROCESSES AND CHOROID. 419. I. The ii'is consists of the following layers : — (1) The endothelium of the anterior surface : trans- parent, flattened, or polyhedral cells, each with a spherical or slightly oval nucleus ; in dark-coloured eyes of man and mammals brown pigment granules are contained in the cell substance, (2) A delicate hyaline basement membrane : it is continuous throucjh the trabecule of the lisramentum pectinatum with the membrana Desceraeti of the cornea. (3) The substantia propria : this i-, the ground substance ; it consists of fibrous connective tissue in bundles, accompanying the blood-vessels, which are very numerous in the tissue of the iris. Many connective-tissue corpuscles are found in the sub- stantia propria : they are more or less branched, and many of them CDntain, in all but albino and blue eyes, yellowish-brown pigment granules. The depth of the colour varies according to the number of these pigmented connective-tissue cells, and to the amount of the pigment granules present in them. (4) A hyaline delicate basement membrane limits the substantia propria on the ])osterior surface ; this is an elastic membrane, and is continued over the ciliary processes and choroid as the lamina vitrea. 420. (5) The last layer is the epithelium of the posterior surface : this is a layer of polyhedral cells, filled with dark pigment granules, except in albinos, JRIS. 437 where there are no pigment granules This enchj- theliuiu is called the uvea, or iapetum nigrum. The interstitial cement substiince between the cells is not pig- mented, but transparent. The name "uvea" is some- times applied to the whole of the iris, ciliary processes, and choroid membrane. In blue eyes the posterior epithelium is the only pigmented part of the iris, and so it is also in new-born children, whose iris appears blue. In all cases where the iris appears blue, this is due to the dark back — i.e. the pigmented epithelium of the posterior surface — being viewed throutjh a dull layer — i.e. the substance of the iris. 421. Near the pupillary border the posterior section of the substantia propria contains a broad layer of circular bundles of non-striped muscular tissue : this is the spliincter pupiUct. In connection with this are bundles of non-striped mus- cular fibres, passing in a radi- ating direction towards the ciliary margin of the iris : these are the bundles of the dila- tator pupiUc(;, forming a sort of thin membrane near the posterior surface of the iris (Henle and others). At the ciliary margin the bundles take a circular direction and form a plexus (Ivanoff). Fi-; I - vessels I injected) uf the Iris and Choroid Membrane of the Eye of a Child. {Kolliker, after Arnold.) a, Capillaries of the choroid ; b, era serrata; c, iilood- vessels connected with, d, those of the ciliary pro- cesses, and with e, those of the iris; /, capillary network of the pupillary sphincter. 43^ Elements of Histology. 422. The blood-vessels (Fig. 265) of the iris are very numerous. The arteries are derived from the eirculus arteriosus iridis major, situated at the ciliar}" margin of the iris, and from the arteries of the ciliary processes. These arteries run in a radi- ating direction towards the pupillary margin, where they terminate in a dense network of capillaries for the sphincter pupilla?. But there are also numerous capillary blood-vessels of a more or less longitudinal direction near the posterior surface of the iris. The veins accompany the arteries, and both are situated in the middle stratum of the substantia propria. In the sheath of the Ijlood -vessels are lymplt clefts and lympli sinuses; there appear to be no other lymphatics. 423. The nerve fibres are very numerous (Arnold, Formad), and in the outer or ciliary portion of the iris form a rich plexus, from which are derived : [a) networks of non-medullated fibres for the dilator pupilla3 : (h) a network of fine non-medullated fibres for the anterior surface ; and (c) a network of non- medullated fibres for the sphincter pupilhe. The capillary blood-vessels are also accompanied by fine nerve fibres (A. Meyer), and, according to Faber, there exist ganglion cells in these nerve net- works. 424. TI. The miliary processes are similar in structure to the iris, except, of course, that they do not ])0ssess an anterior endothelium or an anterior basement membrane. The suhstantia propria is fibrous tissue with elastic fibres and numerous branched cells, pigmented in dark (but not in blue) eyes. The posterior basement membrane is very thick, and is called the lamina vitrea ; in it may be detected bundles of fine fibrils. It possesses perma- nent folds arranged in a network (H. Muller). The inside of it is covered with a layer of pigmented poly- Ciliary Processes. 439 licdral v\\\\\\v\\w\\\^W\(^ inpotu))i nigriDii : the cells are polygonal when viewed from the surface. The in- divkliial cells are separated by thin lines of a trans- parent cement substance. This pigmented epithelium is covered with a layer of transparent columnar %M Y'v^. 2(i(l — Fi-()iii a Vertical Section thr()uc;li the Ciliary Processes of the Ox's Eye. {Atlas.) u. Fil)roiis tissue with iiigiiiented cells; 6, loose niirons tissue fciniiiiiLr the proiier ineiiihi-ane of the ciliary process ; c. iiigiiieiited epithelium rovermg the posterior sui-fac-e of the ciliaiy process; (/, epitheloid cells, lorniiug the j>ars ciliaris rctiiuv covering the l)ai-l\ of the ciliary jirocesses; e, Zonula Zinnii, with laindles of lilircs. epitheloid cells, each w^ith an oval nucleus. These are closely fixed on the tapetum nigrum, and are the continuation of the retina over the ciliary processes : this is thenars ciliaris retince (Fig. 266). 425. The arterial branches for the ciliary processes 440 Elements of Histology. and muscle are cliieliy derived from the ciivulus arteriosus iridis major, and fnrn a dense network of capillaries for the former ; eacli ciliar}^ process pos- sesses a conical group of capillaries (Fig, 'l^o). 426. III. The €lioi"oi)^j ■^^)/ A jj^ - - Fig. 2(iS. — From a Section through the Lens of Dog. (Atlus.) Sliciwing four lamellse ; in each the component lens filires are cut across ; they appear as flattened hexa"- u'ons. 444 Elements of Histot.ogy didereiitiuted by clefts, conct-ntric in the })Hripberal, radiating in the central part (Briicke, Hannover, Bowman, Ivanoff, Schwalbe). But these do not con- tain an}' distinct membranous structures (Stilling, IvanofF, Schwalbe). The canalis hyaloideus, or canal of Stilling, extends from the papilla nervi optici to the posterior capsule of the lens, and is lined with a continuation of the membrana hyaloidea. 433. In the substance of the corpus vitreum occur isolated nucleated cells, possessed of amoeboid move- ments, and some contain vacuoles, indicating com- mencinjj desfeneration. Thev are all identical with white blood-corpuscles (Lieberklihn, Schwalbe). Fine V)undles of fibrils are occasionally seen in the substance of the vitreous body. 445 CHAPTER XLT. THE RETINA. ±iJj±ULH SMAlAAl~---{ -A 434. The retina (Fig. 269) consists of the follow- ing layers, counting from inwards towards the choroid membrane : — (1) The membrana li- mit ans interna, wliich is next to the membrana hya- loidea of the vi- treous body ; (2) the nerve fibre layer ; (3) the layer of c(anglion cells ; (4) the inner gi-an- ular or inner mole- cular layer ; (5) the layer of inner nuclei ; (6) the outer granular, or outer molecular, or internuclear layer : (7) the layer of outer nuclei; (8) th e m em br ana limitans externa ; (9) the layer of rods and cones ; and (10) the pig- mented epithelium of the retina, or the tapetum nigrum mentioned above (p. 439), which forms, at the ^ ,- o . ; o oo o ^3 Oa 3 3 o a tt_ 5-— 771 Fi fihrps ■ 1 •'in^'lion ceUs:4, inner molecular layer; 5. inner nuclear - ';lver:^6.omermole6u^rl^y^ riourernuclearlaver ; 8. membranahmitans externa ; 9, rods and cones. (Jfojc Schultze.) papiUa nervi optici, (b) the macula lutea and fovea centralis retinae, and (c) the ora serrata of the retina. (a) The papilla nervi optici, or the blind spot of Retina. 447 the retina, represents the entrance of tlie optic nerve fibres into the retina; thence, as from a centie, they spread out in a radiating direction into the sancer- sliaped retina, of which they form the internal layer. No other elements of the retina are present at the papilla, except a continuation of the limitans interna. At the papilla nervi optici the arteria and vena centralis nervi optici also enter, and spread out with their branches in the inner layers of the retina. A large lymph space is also found there. (6) The macula lutea and fovea centralis will be considered after the various layers of the retina have been described. (c) At the ora serrata all circular and nuclear elements of the retina — except the pigmented epithe- lium — and the nerve fibres, come to an end ; but the limitans interna, with its peculiar radial or Miiller's fibres, is continued over the ciliary processes in the shape of columnar epitheloid nucleated cells men- tioned above : this is the pars ciliaris retime. 436. Structure of the layers of the retina (Figs. 270, 271). (1) The iiieiiibraiia liiiiitaii!^ iiiteriia is composed of more or less }jolygonal areas, which are the ends or bases of pyramidal, finely-striated fibres — the radial fibres of JlilUer. Each radial fibre passes from the limitans interna in a vertical direction through all lavers to the limitans externa, and on its way gives off numerous lateral branchlets, fibrils and membranes, which anastomose with one another so as to form a honeycombed stroma or matrix for all cellular and nuclear elements of the retinal layers. In the nerve fibre layer the radial fibres are thickest, this being, in fact, the pyramidal basis ; in the inner nuclear layer each possesses an oval nucleus. 437. (2) The layer ol nerve fibres. — The optic nerve fibres at their entrance into the eyeball 448 Elements of Histology. lose their medullary sheath, and only the transparent axis cylinder is prolonged into the retina. In man, medullated nerve fibres in the retina are very excep- tional : in the rabbit there are two bundles, whose libres retain their medullary sheath in the retina Fk jectiou of Retina of Dog. \\Aflei " Anatomy.") Cajal, from Quain's u. Cone rtbre ; h, rod fibre aud nucleus ; c, d, bipolar cells ■with inner nuclei, with vertical ramifications to receive the knobbed ends of the rod fibres, e,f, with flattened ramifications for the arborising ends of the cone fibres ; g. gan- glion cell sending an axon to the outer molecular layer; /), spongioblast ; 1, nerve fibres passing to the outer molecular layer ;], centrifugal nerve fibres passing into, and terminating in, inner molecular layer : m, nerve fibres passing toinner molecular layer ; n, ganglion cells ; a, outer molecular layer; B, inner molecular layer; c, nerve fibre layer. (Bowman). The nerve fibres remain grouped in bundles in the retina, and even form plexuses. For obvious reasons, the number of nerve libres in the nerve fibre lay^n* diminishes towards the ora serrata. 438. (3) Tlie layer of g^sin^l ion cells. — There is one stratum of these cells only, except in the macula lutea, where they form several strata. Each Retina. 449 cell is multipolar, and possessed of a lar^e nucleus. One process is directed inwards and Ijeconies the axon, being a fibie of the nerve fibre layer. Several branched processes or dendrites pass from the opposite side of the cell into the next outer layer — i.e. the inner molecular layer. From the researches of Eamon y Cajal, it is clear Fig.273. — From the Retina of Dog. i^Afttr Ca}al,fTom Quaiiis ''Anatomy. A, Small amacrine (spougiuhlast) of the inner molecular layer : c, large ganglion cell ; /,g,h, i, small ganglion cells arborising in the inner molecular layer. that the dendrites terminate by arborisations or den- drons in the next or inner molecular layer (see Figs. L'72, 27:3, and 274). The ganglion ceils are separated from one another by the radial fibres of Miiller. 439. (4) The inner nioleciilai' layer is a fine and dense reticulum of fibrils, with a small amount of granular matter between. The fibrils are connected with lateral branchlets of the radial fibres of ^luller. This layer is, on account of its thickness, a conspicuous part of the retina. In lower vertebrates it a])pears stratified. As mentioned just now, it contains the terminal arborisations of the dendrites of the ganglion cells. 440. (5) The inner nnrlear layer contains in a honeycombed matrix of a hyaline stroma numerous nuclei, in two. three, or four layers. In the am- phibian retina these form a larger number of layers. Some oblong nuclei of this layer belong, as has been mentioned above, to the radial fibres of Miiller. D D 45° Elements of Histology Js^ext to the molecular layer are small nuclei belonging to flattened branched cells (Vintschgau). the spongio- hh.sts of W. Miiller. These cells have been shown by Golgi's method to be possessed of rich arborisations, ^vhich extend horizontallv into the outer and inner Fig. 274— Section of Retina of Bird. {After Cajal,/rom (^uain's ^'Anatomy."\ A, B. Large sponsioljlasts of inner nuclear layer; c. small spongioblast; d. bipolar cell of inner nuclear layer wirh a and b arborising in inner mole- cular layer and also terminating at k at the limitans externa ; f, g, rod and cone nuclei ; H, i, cells with arborisations in outer molecular layer ; j, radial fibre of Muiler. molecular layers (see Fig. 272). Ramon y Cajal desicrnates them as amacrines. But the ofreat majority of the nuclei of this layer are slightly oval, with a reticulum in their interior. Each belongs to a spindle-shaped cell, with a small amount of proto- plasm around the nucleus : it is, in fact, a bipolar Retina. 451 ganglion cell (Max Scliultze), of which ono i)rocess (the innei") ))asses as a fine varicose fibre into the inner molecular layer, where it terminates as a delicate den- dron, while the other or outer process passes into the next outer layer of the retina — i.e. the outer molecu- lar layer, to terminate here by a rich arborisation or dendron (Fig. 272). (6) Tlie outer iiiolenilai* layer is of the same structure as the inner molecular layer- — i.e. a fine reticulum of fibrils — but is considerably tliinner than the latter. It also contains the dendrons of cells inside and outside it (Fig. 272). 441. (7) The outer uuclear layer contains, in a honeycombed matrix, a large number of oval nuclei. In the retina of man and mammals these nuclei are always present in considerably greater numbers or layers than those of the inner nuclear layer, but in the amphibian animals the reverse is the case. They are smaller than the nuclei of the inner nuclear layer, and show often a peculiar trans^'ersely-ribbed differ- entiation of their contents (Henle, Krause). The honeycombed matrix of this layer is in connection with lateral branchlets of the radial fibres of Miiller, with which it forms a sort of limiting delicate mem- brana propria at the outer surface of the layer; this is 442. (8) The liuiltaus externa — The nuclei of the outer nuclear layer next to this limitans externa are connected, in the retina of man and mammals, with the cones, while the nuclei farther inwards from the limitans externa are connected with the rods. In both instances the connection is established throuorh holes in the limitans externa. Each nucleus of the outer nucleai- layer is, in reality, that of a spindle-shaped cell with a minute amount of proto- plasm ; this is prolonged outwards, as the outer part of the rod- or cone-fibre, to become connected with a 452 Elements of Histology. rod or cone respectively, while inwards it passes into a longer, more conspicuous fibre, the inner part of the rod- or cone-fibre (Fi,cj. 272). According to Ramon y Cajal, the cone-fibre terminates as a flat dendron in contact witli the tufty arborisation of the outer process of the cells of the inner nuclear layer— f 6". in the outer molecular layer : the rod-fibre on the other hand terminates in the outer moleculai- layer as a small knob (Fig. 272) in tlie outer dendron of the same cells 443. (*.)) The rods and cones. — Each rod is of cylindrical shape, Avith rounded or conical outer extremity : it con.sists of an outer and inner member, joined by linear cement. Its substance is bright and glistening, and that of the outer member is composed of the neurokeratin of Kiihne and E^vald. In the fresh state the outer member shows a more or less fine and longitudinal striation, due to longitudinal fine ridges and furrows (Hensen, Max 8chultze). After certain reagents, such as serum, liquor potass^e, the outer rod-member disintegrates into numerous transverse, thin, homogeneous-looking discs (Hannover). The inner member in tlie human rods is slightly broader than the outer : it is pale or tinely and longitudinally striated, and contains in many instances a peculiar lenticular structtire : in the human and mammalian retina this is aljsent. but in its stead is a mass of lono-ittidinal fibrils (^fax ►"^cliultze). The inner member passes through a hole in the limitans externa, and becoming thiniif-r. represents the outer part of the rod -fibre. 4-4-1:. Each cone is composed of an outer, short, pointed, conical member, and an inner larger member with convex surface : this is the hody of the cone. The outer member of the cone separates under certain conditions also into thin transverse discs. The body of the cone is longitudinally and finely striated. The Rktina. 453 outer extremity of tlic body birds, reptiles, and amphibia contains a spherical corpuscle of red, orange, yellow, green, or even Ijlue colouration. The cones are shorter than the rods, the pointed end of the former not reaching much farther than the junction be- tween the outer and inner members of the rods. In the macula lutea and fovea centralis of man and most mammals there are pre- sent cones only, and towards the peripheral portion of the retina they gradually decrease in numbers ; in the peripheral part there are only rods. But in birds the cones exceed the rods everywhere. In the bat and mole the macula lutea possesses no cones, and in the owl, rat, mouse, guinea-pig and rabbit they are few and small. 445. The outer members of the rods (only) show in the fresh and living state a peculiar ditiuse purplish colour (Leydig, Boll, Kiihne) : this is the visual purple or Rhodopsin of Kiihne. When exposed to sunlight it passes through red, orange, and yellow, and finally disappears altogether — becomes bleached. There is of the cones in many Fig. 275. — Vertical Section through Ketiiia of Frog. (Atlas.) a. Pigmented epitbeliiim of retina or tapetum nigrum; 5, outer nieml>ers of rods, those of cones l)etween them ; c, inner mem tiers of rods and cones; d, liniitaus externa; e, outer nuclei ;/, outer mole- cular layer ; ace : and also between these various sheaths are lymph spaces — the subdural or sub vaginal space of Schwalbe, and the subarachnoidal space. The supravaginal and suit- vaginal spaces anastomose with one another (Michel). 452. Around the sclerotic is a lymph space limited bv a tiVji'ous membrane — the Tenonian co.ps.ii.le : the space is called tlie Tenonian space. The supravaginal space anastomoses with this Tenonian space, and into it pass also the lymph clefts in the suprachoroidal tissue (Schwalbe), by means of the lymph canalicular system of the sclerotic (Waldeyer). The snpra- choroidal lymph spaces communicate also with the subarachnoidal space of the optic nerve. 458 CHAPTER XLII. THE OUTER AXD MIDDLE EAR. 453. The meatus auditorius externus is lined with a delicate skin, in structure identical with, but thinner than, the skin of other parts. The ceruminous glands have been mentioned and described before. The cartilage of the auricula and its continuation into the meatus auditorius externus is elastic cartilage. 454. The in em bran a tyinpani sej^arating the outer from the middle ear has for its matrix a firm stratum of stiff trabecuhe of fibrous connective tissue, with numerous elastic fibrils and elastic membranes. This is the middle and chief stratum of the membrane : outwards it is covered with a delicate continuation of the skin of the meatus auditorius externus, and inwards M'ith a continuation of the delicate mucous membrane lining the cavum tympani. In the middle stratum of the membrana tympani the trabecule^ radiate more or less from the junction of the manubrium mallei with the membrane ; but towards the periphery many are also arranged in a circular direction. The former belong to the outer, the latter to the inner, portion of the middle stratum. The mucous membrane lining the tympanic surface of the memljrane is delicate connective tissue, covered with a single layer of polyhedral epithelial cells. The blood-vessels form capillary networks for all three layers — i.e. a special network for the skin layer, a second for the middle stratum, and a third one for the mucous layer ; the lymphatics are also arranged in Outer and Mmni.E Ear. 459 this way. An intercommunicating system of lym- phatic sinuses and ck^fts (Kessel) is left between tlie trabeculiu. The non-medullated nerve fibres form plexuses for the skin and mucous layer ; from these pass ott' fine fibrils, which form a sub-epithelial net- work, and from this the tilji'ils pass into the epithelium. 455. The tuba E:ii«itsicliii is lined with a uuicous meml)rane, which is a continuation of that lining the upper part of the phar^'nx, and therefore, like it, is covered on its inner or free surface with columnar ciliated epithelium. As in the pharynx, so also here, we find a good deal of adenoid tissue in the mucous membrane. The cartilage of the tuba Eustachii in the adult approaches in structure the elastic cartilages of other parts. 456. The caviiiii tympaiii, including the cellulte mastoidese and the surface of the ossicula auditus, is lined with a delicate connective-tissue membrane. Its free surface is covered with a single layer of poly- hedral epithelial cells in the following regions : on the promontory of the inner wall of the cavity, on the ossicula auditus, on the roof of the cavity, and in the cellulae mastoidea3 ; in all other parts it is columnar cili- ated epithelium, like that lining the tuba Eustachii. 457. The three ossicula auditus are osseous substance covered with periosteum, which is covered with the delicate mucosa just described. The liga- ments of the bones are, like other ligaments, made up of straight and parallel bundles of tiV)rous connective tissue. The articulation surface of the head of the malleus, of the incus, of the extremity of the long process of the incus, and of the stapes, are covered with hyaline (articular) cartilage. 460 CHAPTER XLTII. THE INTERNAL E A K. 458. The osseous labyrinth consists of the vesti- bule, prolonged on one side into the cochlea, and on the other into the three semicircular canals, each of which possesses an am^^ulla at one extremity. The vestibule shows two divisions — the fovea hemispherica next to the cochlea, and the fovea hemi-elliptica next to the semicircular canals. The cochlea consists of two and a half turnings twisted round a bony axis — the modiolus. From this a bony lamina extends towards the outer wall for each turn, but does not reach it : this is the lamina spiralis ossea. It extends through all turns, and it subdivides tlie cavity of each turn into an upper passage, or scala vestibuli, and a lower, or scala tympani. At the top of the cochlea the two seal* pass into one another by the helicotrema. The scala vestibuli opens into the fovea hemispherica, while the scala tympani at its commencement — i.e. at the proximal end of the first turn — would be in communication, by the fenestra rotunda, with the cavum tympani, were it not that this fenestra rotunda is closed by a membrane — the secondary membrane. 459. The semicircular canals start from, and return to, the fovea hemi-elliptica of the vestibule. The fenestra ovalis leads from the cavum tympani into the vestibule — its hemispheric division ; and this fenestra ovalis is, in the fresh condition, filled out by a membrane, in which the basis of the stapes is fixed, the circumference of this being nearly as great as that of the fenestra. Internal Ear. 461 460. Tilt' osseous labyi-inth in all parts consists of ordinary osseous suUstaiice, with the usual periosteum lining its outer surface and its inner cavities. These cavities contain the albuminous fluid called perilymph. But they ;ire not tilled out by this, since, in each of the two divisions of the vestibule, in each of the semicircular canals, and in the cochlea, is a mem- branous structure, analogous in shape to the corre- sponding division of the labyrinth. These membranous structures possess a cavity filled with the same albu- minous fluid as above, called the endolymph. These structures are disposed thus : in the fovea hemispherica is a spherical sac, called the saccule ; in the fovea hemi-elliptica is an ellij^tical sac, the lUi^icle ; in each of the three semicircular canals is a membranous semi- circular tube, which jiossesses also an ampulla corre- sponding to the ampulla of the bony canal. 461. In the cochlea is a membranous canal, tri- angular in cross-section — the scala media or cochlear duct — -which also twists two and a half times from the basis to the apex of the cochlea, and is placed against the end of the lamina spiralis ossea so as to occupy a position between the peripheral part of the scala vesti- buli and scala tympani. 462. The different divisions of the menil)ranous labyrinth are connected - with one another in this manner : the three semicircular (membranous) canals open into the utricle ; this does not form a direct con- tinuity with the saccule, but a narrow canal comes off both from the saccule and utricle ; the two canals join into one minute membranous tube situated in the aqueductus vestibuli. At its distal end it enlarges into the saccus endolymphaticus, situated in a cleft of the dura mater, covering the posterior surface of the petrous bone. The saccule is in communication with the cochlear canal, or scala media, by a short narrow tube — the canalis reuniens of Reichert. Thus the 462 Elements of Histology. cavity of the whole membranous labyrinth is in direct communication throiigliout all divisions, and it represents the inner lymphatic space of the labyrinth. There is no communication between the perilymph and endolymph, and the cavity of the membranous labyrinth stands in no direct relation to the cavum tympani, since the fenestra ovalis and fenestra rotunda both separate the perilymphatic space, or the cavity of the bony labyrinth, from the cavum tympani. The vibrations of the membrana tynjpani, transferred by the ossicula auditus to the fenestra ovalis, directly affect, therefore, only the perilymph. The fluctuations of this pass from the vestibule, on the one side, towards and into the perilymph of the semicircular canals ; and on the other side, through the scala vestibuli, to tlie top of the cochlea, then by the heli- cotrema into the scala t3^mpani, and find their conclu- sion on the membrana secundaria closing the fenestra rotunda. On their way they affect the membrane of Reissner, which separates the scala media from the scala vestibuli, and also the membrana basilaris separ- ating the scala media from the scala tympani ; the vibrations of these membranes affect the endolymph, and therefore tlie nerve-endings {see below). 463. Sti'U€tiire of seiiiicirciilai* canals, utricle and saccule. — The memhranous semi- circular canals are fixed by stiff bands of fibrous tissue to the inner periosteum of the one (convex) side of the osseous canal, so that towards the concave side there is left the space for the perilymph. A similar condition obtains with regaid to the saccule and utricle, which are fixed by the inner periosteum to one side of the bony part. The structure of the wall is the same in the semi- circular canals, utricle and saccule. The above-men- tioned fibrous ligaments of the periosteum form an oute7' coat ; inside this is a glassy-looking tunica I.XTEKNAL Ear. 463 propria. At one side (the one away from the bone) this tunica propria forms numerous papillary projec- tions. The internal surface of the membrane is covered with a single layer of polyhedral epithelial cells. 464. Each of the branches of the nervns vestibuli — i.e. one for the sac- cule, one for the utricle, and three for the three ampullae — possesses a ganglionic swelling. The nerve - branch, having passed through the mem- branous wall, enters special thickenings of the tunica propria, on that part of the mem- branous wall next to the bone : in the saccule and the utricle the thicken- ing is called macula acustica, in the ampullae crista acustica ( Fig. - 7 7) (M. 8chultze). This thickenin*^ is a lar^je villous or fold-like pro- jection of the tunica })ropria, into which pass the nerve fibres of the several branches. These tibres are all meduUated nerve fibres, and, ascending towards the internal or free surface of that pro- jection, form a plexus. In this plexus are in- terspersed numerous nuclei. From the medullated fibres pass oS minute bundles or primitive fiVjrillse, which enter the epithelium that covers the free surface of the projection. 465. This epithelium is composejcl of a laver of Fig. 277.— From a Transverse Section through the Macula acustica of the Utricle of the Labyrinth of Guiuea- pig. {Atlas.) a, Medullated nerve fibres, forming plex- uses ; b, nuclei of the membrane ; c, sensory epithelium (diagrammatic); the spindle-shaped sensory cells possess long auditory hairs projecting between the conical epithelial cells beyond the free surface. 464 Elements of Histology. columnar or conical cells, between which are wedged in spindle-shaped cells ; V^oth kinds possess an oval nucleus. According to Max Schultze and others, each of the spindle-shaped cells is connected by its inner process with the nerve fibrillse coming from under- neath : whereas, towards and beyond the free surface, Fig. 278. — Xerve Terminations in the Epithelium of tlie Macula acustica. The nerve fibres form denclrons in the epithelial layer. (After Betzius, from Quain.) its outer process is prolonged into a long, thin, stiff, auditory hair. Max Schultze, therefore, calls the columnar cells epithelial; the spindle-shaped ones, sensory. Retzius, on the other hand, maintains that, in the case of fishes at any rate, the epithelial cells are those which are connected each with a bundle of nerve fibrillse, and that each sendi^ . The coc'lilca (Fig. 279), as has been men- tioned above, consists also of a bony shell and a membranous canal, the former surrounding the latter in the same way as the bony semicircular canal does the membranous — i.e. the latter is fixed to the outer or convex side of the for-mer. The difference between the cochlea and the semicircular canals is this, that in the cochlea there is a division of the perilymphatic space by an osseous projection — the lamina spiralis ossea — and bv the scala media into two scalse, viz. the (upper) scala vestibuli and the (lower) scala tympani. 467. In the osseous modiolus are numerous parallel canals for bundles or groups of the fibres of the cochlear branch of the auditory nerve : these canals open into the porus internus, in which lies a large c^ansflion connected with the nerve. Coo The nerve bundles are situated in the canals of the modiolus, and opposite the lamina spiralis ossea are connected with ganglionic masses — composed of bipolar ganglion cells — called the ganglion spirale of Corti. From this ganglionic mass the nerve fibres (all niedul- lated) can be traced into the lamina spiralis ossea, in which they form rich plexuses extending to its outer E E Fig. 279.— From a Vertical Section through the Cochlea of Ear of Guinea- pig, seen in the long axis of the Modiolus. (Atlas.) a, Scala vestibuli ; b, scala tympani ; c, srala media ; d, membrana tectoria ; e, cells of Claudius ; /, upper outer angle of scala media ; g, region of outer hair cells nn membrana basilaris : /*, membrane of Reissner; ?, epithelium linintr «ulcus spiralis (internus) ; j, tunnel of Corti's arch ; k. stria vascularis ; ?, ligamentum ppirale : ?», crista spiralis; n, nerve Hbres in lamina spiralis ossea • o gansliun spirale; p, nerve fibres in modit)lus ; q. channels in bone containing blood-vessels ; r, masses of bone in modiolus ; s, outer bony capsule. Internal Ear. 467 margin — l.p. as far as the membrana basilaris of the scala media {see below). -4G(S. From the margin of the himina spiralis ossea to the external bony shell extends the membrana basi- laris (Fig. 279), forming the lower and chief wall of the scala media, while the upper wall of the canal is formed by the membrane of Reissner, extending under an acute an^le from near the marcrin of the O o lamina spiralis ossea to the outer bony shell. On a transverse section through the scala media we see the following structures : — 469. (1) Its outer Avail is placed close against the periosteum lining the internal surface of the bony shell ; it consists of lamellar fibrous tissue, with numerous stitf elastic bands, and is the vestibular part of a peculiar ligament — the ligamentuTti spirale (Kulliker) — semilunar in cross-section, and with its middle angular })rojection tixed to the outer end of the membrana basilaris. 470. (2) Its inner wall is represented by an exceedingly delicate membrane — the membrane of Reissner : this is also its upper wall, extending under an acute angle from the upper outer angle of the scala media to the lamina spiralis ossea. But here it is not tixed on the osseous substance, but on a peculiar pro- jection on this latter — the crista spiraUs (Fig. 279, m) — which is a sort of tissue intermediate between tibrous and osseous tissue, and is added to the vestibular surface of the lamina spiralis ossea. This crista spiralis has on one surface — i.e. that directed towards the scala media — a deep sulcus, called the sulcus spiralis, or sulcus spiralis internus ; so that of the crista .spiralis there are two labia to be distinguished — the labium vestibulare and the labium tympanicum ; the former being the upper, the latter the lower, boundary of the sulcus s})iralis (Fig. 279). 471. (3) The lower wall of the scala media 468 Elemexts of Histology. is the memhrana hasilaris, extending in a straight line betAveen the labium tynipanicum of the crista spiralis and the above-mentioned projection of the ligamentum spirale. The scala media is lined on its whole internal surface with epithelium, this only being derived from the epithelium forming the wall of the auditory vesicle of the embryo, peculiarly modified in certain places. The scala tympani and scala vestibuli are likewise lined with a continuous layer of flattened cells — an endothelium, which on the lower or tympanic surface of the mernbrana basilaris is somewhat modified, being composed of cjranular-lookinof irre^cnlar cells. 472. As regards the scala media, the epithelium lining its internal surface is of the following aspect :— Starting with the lower outer angle — i.e. Avhere the mernbrana basilaris is fixed to the ligamentum spirale — we find a single layer of polyhedral or short columnar transparent cells, lining this outer angle — the cells of Claudius ; ascending on the ligamentum spirale, the cells become shorter, more squamous ; as such they are found over a slight projection on the outer wall — i.e. the ligamentum spirale accessorium — caused by a small blood-vessel, the vas prominens. 473. Then we come to the stria vascularis, lining nearly the up[)er two-thirds of the outer wall of the scala media. It consists of a layer of columnar and spindle-shaped epithelial cells, between which extend capillary blood-vessels from the liga- mentum spirale, and in some animals (guinea-pig) clumps of pigment granules are found between them. 474. Then we pass from the upper angle of the scala on to the membrane of Eeissner. This consists of a homogeneous thin mernbrana propria, covered on its outer vestibular surface with a layer of flattened endothelium, and on its inner surface — i.e. that facing Internal Ear. 469 the scala media — with a layer of less flattened, smaller, poljdiedral epithelial cells. 475. We come next to the vestibular labium of the crista spiralis, on which are found cylindrical horizontal projections anastomosing with one another : these are the auditor y teeth (Huschke). The epi- thelium of Reissner's membrane is continued into the grooves and pits between the auditory teeth as small polyhedral cells, but over the teeth as large, flattened, squamous cells, which, passing on, line the sulcus spiralis and cover also the tympanic labium of the crista spiralis. Xow we arrive at the membrana basilaris, on which the epithelium l)ecomes modified into the organ of Corti. 476. The me 111 bra 11 a basilaris consists of a hyaline basement membrane, on which the organ of Corti is fixed : underneath this is the tunica propria^ a continuation of the tissue of the ligamentum spirale, composed of fine parallel stiff fibrils (Hannover, Henle) stretched in a very regular and beautiful manner in the direction from the ligamentum spirale to the crista spiralis (Nuel). On the tympanic side there is also a hyaline basement membrane. The endothelial cells covering this on the tympanic surface haA'e been mentioned above. 477. The org:aii of Corti (Fig. 280). — Passing outwards from the epithelium lining the sulcus sjiiralis, we meet with small polyhedral epithelial cells in the region of the termination of the lamina spiralis ossea, next which are columnar-looking cells — the inner supporting cells ; next to these is the inner hair-cell — a columnar, or conical, epithelial cell, with a bundle of stitf hairs, or rods, extending beyond the surface. The inner hair-cells form a sina^le file alonsr the whole extent of the two and a half turns of the scala media. 478. Xext to the inner hair-cell is the inner rod, or inner pillar, of Corti, and next to this the outer rod, 470 Elements of Histology or outer -pillar, of Corti. Each forms a single file for the whole extent of the two and a half turns of the scala media. The two rods are inclined towards one another, and in contact with their upper extremity, Fig. 2S0.— Organ of Corti of the Cochlea of Guinea-pig. (Atlas.) a. Outer rod or pillar of Corti : b, inner rod or pillar of Corti ; c, tunnel of arch of Corti ; d, oucer hair-cells ; e, inner hair-cell ; /, outer supporting cells containing fat globules; g, inner supporting cells; /*, cells of Claudius; i, epithelial cells lining the sulcus &i>iralis internus ; j. nerve fibres ; fc, part of crista spiralis. or head : whereas the opposite extremity, the foot, rests under an acute angle on the membrana basilaris, on which it is firuily fixed. The rest of the rod is a slender, more or less cylindrical, piece — the body. The outer rod is larger and longer than the inner, the latter being slightly bent in the middle. Owing to the position of the rods, the two files form an arch — the arch of Corti. Between it and the corresponding part of the basilar membrane is a space— the tunnel of the arch, triangular in cross-section. 479. The substance of the rods, or pillars, of Corti is bright, highly refractive, and slightly and longitu- dinally striated. The head of the inner rod is triangular, a short process extending inwards towards the inner hair-cell, a long process extending outwards over the head of the outer pillar. Outwards, the triangular head possesses a concave surface grasping the convex surface of tiie head of the outer rod. This latter Internal Ear. 471 possesses a process directed outwards, which is tirnily applied to the outer process of the head of the inner rod, the two together forming part of the niein))rana reticularis {see below). The relation in size between the outer and inner rods is such that the head of one outer rod fits into those of about two inner rods. 480. At the foot, each rod has, on the side directed towards the tunnel, a granular, nucleated mass of protoplasm, probably the remnant of the epithelial cell from which the lower half of the rod is derived ; the upper part sometimes has a similar nucleated remnant, proving that this also has been formed b}^ an ei3ithelial cell, so that each rod is in reality derived from two epithelial cells (Waldeyer). 481. Next follow^ three or four rows of outer hair - cells, similar in size and structure to the inner hair- cells. Each of the outer hair-cells seen in a section belongs to a file of hair-cells, extending on the mem- brana basilaris along the whole extent — i.e. two and a half turns — of the scala media. Each hair-cell possesses an oval nucleus and a number of stifl: rods, or hairs, disposed in the shape of a horseshoe in the outer jjarb of the free surface of the cell. Four, and even five, rows or files of hair-cells (Waldeyer), arranged in an alternating manner, are found in man. The outer hair-cells are also called the cells of Corti ; they are conical, and more or less firmly con- nected with a nucleated spindle-shaped cell — the cell of Deiters. The two cells are more or less fused to- gether in their middle part (Nuel). The cell of Corti is fixed by a branched process to the membrana basilaris, while the cell of Deiters sends a process towards the surface, where it joins the memhjrana reticularis {see below). 482. Farther outwards from the last row of outer 472 Elemexts of Histology. hair-cells are columnar epithelial cells, called the outer supporting cells of Hensen : they form the transition •s 5f •- f^ Si ss S 5 i i §t ^•3 ^ CO ... Internal Eak. 473 to the epitlu'lium lininij tlie outer angle of the scala media — i.e. to the cells of Claudius. In the guinea-pig, the outer suppDi-ting cells include fat globules. 483. The iii€», zona glonierulosa ; r. zona fascicu- lata; d, zona reticularis; e, medulla: /, large vein. m in of the will be sently. The medulla gland, as seen pre- cortex of the n;land consists of an outer, middle, and inner zone, ail three being di- rectly contin n o u s with one anothei-. The outer one is the zona rjlomerv- losa ; it contains numerous sphe- rical, or, more com- monly, elongated, masses of epithelial cells. The cells are polyhedral or cylindrical, each with a spherical or oval nucleus. In some animals — as the dog, horse — the cells are thin and columnar, and arranged in a t ran s verse man ner. Occasionally a sort of lumen can be discerned in some of these cell masses. Ductless Glands. 487 501. Next follows the middle zone, or zona fascicvlata. Tliis is the most conspicuous and broadest part of the whole gland. It consists of vertical columns of polygonal epithelial cells, each with a spherical nucleus. The cell substance is trans- parent, and often contains an oil globule. The columns anastomose with their neighbours. Between the columns are tine septa of connective tissue carrying blood capillaries. Between the cell columns and the connective septa are seen here and there lymph spaces, into which lead fine channels, grooved out between some of the cells of the columns. 502. Next follows the inner zone, or zona reticu- laris, composed of smaller or larger groups of poly- hedral cells, with more or less romided edges. These cell groups anastomose with one another. The indi- vidual cells are slightly larger, and their substance is less transparent than those of the zona fasciculata. In the human subject tliey are slightly pigmented. 503. In the medulla we find cylindrical streaks of very transparent cells ; the streaks are separated by vascular connective tissue. The cells are polyhedral, columnar, or branched. These cell streaks anasto- mose with one another and are directly continuous with the cell groups of the zona reticularis of the cortex. 504. The cortex is richly supplied with dense networks of caj)illary blood-vessels ; their meshes are polyhedral in the outer and inner zone, elongated in the middle zone, or zona fasciculata. In the medulla numerous plexuses of veins are met with. In the centre of the supra-renal body lie the large efferent venous trunks. In the capsule (Kolliker, Arnold), and in the connective tissue around the central veins, are plexuses of lymphatic tubes with valves. The nerves are very numerous and composed of non- / 4SS Elemexts of Histology. medullated fibres ; in the medulla they form rich plexuses. In connection with these and with those of the outer capsule are smill ganglia (Holm, El)9rth). 505. IV. The g^laiidiila coccygea and iiiter-rarotic-a. — The lirst of these is a minute corpuscle situated in front of the apex of the os coccygis, and was discovered by Luschka. The glandula carotica of Luschka (ganglion inter-caro- ticum) is of exactly the same structure as the glandula coccygea. 506. Its framework is of about the same nature as that of other glands — a fibrous capsule and inner fibrous septa and trabecular. The septa and trabeculae contain in some placs-s bundles of non striped muscular tissue (Sertoli). 507. The spaces of the framework are occupied by the parenchyma. This consists of spherical or cylin- drical masses of cells connected into networks. The individual cells are polyhedral epithelial cells, each with a spherical nucleus. According to Luschka, in the newly-born child they are ciliated. In the centre of each of the cell masses lies a capillary blood-v^essel, much convoluted and wavy. Numerous non-medullated nerve fibres forming a plexus are situated in the framework of the gland. I X D E X Alxlneens, 222 Absorption {see Lymphatics) Accessory nucleus, 210 Achruiiiatin, 11 Acini of glands, 292 of liver, 333 of pancreas, 330 Acoustic ganglion, 219 Adenoid reticulum, 62, 126 tissue, 126 A' 1 maxillary glands, 289 Adveutitia of arteries, 108 of capillaries. 111 of veins, 110 lymphatic vessels, 118 Agminated glands, 130 Air cells, 345 Alje nasi, 63 Albuginea of ovary, 3S7 of testis, 372 Albumin membrane of Ascherson, 402 Albuminous cells, 293 Alloplasmatic organs, 6 Alveolar ca\'ity, 275 ducts, 345 Alveoli of glands, 292 of lung, 345 of pancreas, 330 Alveus, 249 Amacrines, 450 Amitotic division, 12 Amwboid corpuscles, 4 ■ movement, 4, 5, 24, 58 Amphophile cells, 27 Ampulla, 460 Anterior column of cord, 17<'> corpus quadrigeminura, 231 grey commissure. 174 horn of cord, 173 lateral tract, 179 nerve-roots from cord, 187 white commissure, 187 Aorta, 109 Aponeurosis, 47 * of spinal Aqueduct us Sylvii, 220 vestibuli, 461 Arachnoid membrane cord, 170 of brain, 235 Arachnoidal villi, 235 Arborisation, 151 Arenate fibres of medulla, 213 Areolar tissue, 48 Arrector pili, 419 Arteriaj ciliares breves, 440 recurrentes, 440 helicinte, 385 rectse, 369 Arteries, 108 Arterioles, Afferent, 55 of uterus, 397 Articular cartilage, 63, 82 nerve-corpuscles, 161 Arjiienoid cartilage, 339 Ascending degeneration, 180 loop-tube, 364 root of glosso-pharyngeal nerve, 210 of the eighth nerve, 215 of the fifth nerve, 224 Aster stage in nucleus, 15 Attraction sphere, 9 Auditory hairs, 464 nen'e. Origin of, 217 , Division of, 219 teeth, 469 Auerbaoh's plexus, 326 Auricle of heart, 107 Aiiriculo-ventricular valves, 106 AxUemma, 145 Axis cylinder, 144 process of sympathetic ganglion cell, 263 Axon, 144 Bartholin's glands, 399 Basement membranes of skin, 405 490 Elements of Histology. Basilar membrane of cochlea, 46ft Basket cells of cerebellum, 241 Basophile cells, 27 Bellini's ducts, 305 Bile-duets, 330 Bile capillaries, 336 Bilirubin, 23 Bioblasts, 9 Bladder, S7, 371 Blastoderm of chick, 2 Blood, 19 corpuscles, 19 , their origin, 2S cysts, 115 islets, 115 glands of His, 126 platelets of Bizzozero, 27 -vessels, 105 Bone, 6S cartilage, 6S cells, 71 corpuscles, 71 , Development of, 74 trabecultf , 74 Bowman's capsule, 360 elastica anterior, 42!' glands, 481 membrane, 429 sarcous elements, 94 Brachia, 233 Brain membranes, 235 structure, 243 Bronchi, 343 BrowTiian molecular movement. 300 Bruch, Glands of, 427 Briicke's elementary organisms, 5 oikoid and zooid, 22 tunica nervea, 456 Brunner's glands, 328 Buccal glands, 298 Bulbus olfactorius, 250 Biitsclili's nuclear spindle, 15 Calcification of bone, So of cartilage, 65 • of dentine, 283 Calices of kidney, 356 Canal of Schlemm, 434 of Stenson, 482 of Stilling, 444 Canalis hyaloideus, 322, 444 Petiti, 443 reuniens, 461 Canaliculi in bone, 70 in cartilage, 65 Capillaries of marrow-bone, 111 Capillaries of nerve system, 111 Capillary bile-ducts, 336 blood-vessels. 111 • lymphatics, 119 network in mucosa, 801 sheaths, 354 Capsule of Bowman, 360 of ganglion cells, 255 of Glisson, 333 of kidney, 356 of the spleen, 351 Cartilage, 63 , Articular, 64 capsule, 64 cells, 63 , Elastic, 67 , Fibrous, 66 , Hyaline, 63 , Lacun*, 63 of Jacobson, 482 of Luschka, 339 Cavernous tissue in tactile liairs, 418 in organ of Jacobson. 483 tissues in genital oigans, 384 Cavities of tendon sheaths, 121 Cavum tympani, 459 Cell enclosures, 9 protoplasm, 7 Cells, 5 , Muscular, of blood-vessels, 88 , of intestine, 88 , of respiratory organs, 88 -, of stomach, 88 , of urinary organs, 88 in tadpole's tail, 50 of Claudius, 468 of Corti, 471 of Deiters, 236. 471 of Golgi, 242 of Martinotti, 246 of Purkinje, 239 Cellulai mastoide*, 4.59 Cellular tissue, 48 Cement of teeth, 279 substance, 30 of endothelium, 40 of epithelium, 30 of fibrous tissue, 47 Central canal, 185 grey nucleus, 185 Centroacinous cells, 331 Centrosome, 9 Cerebellum, 237 Cerebrum, 243 Ceruminous glands, 409 Cer\ix of uterus, 395 Chalice cells, 36 Chondrin, 46, 63 l.VDEX. 491 Chondroclasts, S:'> Choroidal portion of ciliary muscle, 87 Choroid lueinbrane, 440 Chromatic granules in ganglion cells, 1H4 Chromatin, 11 Chromosomes, 11 Chyle, S-M vessels, 31i> Ciliary muscle, 435 nerves, 43S processes, 438 Cilia, 404 Ciliated eells, 3o Circulus arteriosus in iris, 438 Circumanal glands, 409 Circumcellular plexus, 265 Cisterna lymphatica magna, 1-21 Clarke's columns, H»2 Cleavage of ovum, 2 of white blood corpuscles, 25 Clitoris, 309 Cochlea, 465 Cohnheim's areas, 93 Colloid, 4S5 Colostrum corpuscles, 403 Coloiu-ed blood corpuscles, 19 Colourless blood corpuscles, 23 Columnar epithelial cells, 30 Commatract, 179 Commissure, Grev, of spinal cord, 173 , Wliite, of spinal cord, 187 Compound lymphatic glands, 134 Concentric bodies of Hassall, 132 lamellie, 72 Cone fibre, 451 Cones of retina, 452 Coni vasculosi, 379 Conjunctiva, 424 blood-vessels, 426 bulbi, 426 lymphatics, 427 nerves, 427 palpebrse, 424 Connective tissue, 46 Contractility of corneal corpuscles, 52 of pigment cells, 54 Contraction of muscle, 99 wave, 99 Convolution of brain, 243 in nucleus, 13 Corda? tendinete, 106 Cords of adenoid tissue, 127 Coriuni, 404 Cornea, 50, 429 nerves in, 431 Corneal cells, 50 corpuscles, 50, 430 Cornuain cord, 173 Cornua uteri, 396 Corpora cavernosa, 384 geniculata, 270 quadrigemina, 226 striata, 249 Corpus callosum, 249 Highmori, 372 luteum, 391 restiforme, 209 spongiosum, 384 Corpuscles, Malpighian, 353, 359 of blood, 20, 23 of bone, 71 of connective tissue, 48 of Grandry, 160 of Herbst, 158 of lymph, 123 of Meissner, 158 of muscle, 94 of nerve, 145 ■ of Pacini, 155, 423 of Vater, 155 , Tactile, 158, 423 Corti's arch, 470 cells, 471 ganglion, 465 organ, 469 rods, 469 Cortical layer of ovary, 387 lymph-sinus, 136 Costal cartilages, 63 pleui-a, 122 Cowper's glands, 383 Cremaster internus, 381 Crenate blood corpuscles, 21 Crescents of Gianuzzi, 294 Cricoid cartilage, 339 Crista acustica, 338 spiralis, 342, 347 Crus cerebri, 229 , Crusta of, 233 Crusta petrosa, 463 Crypts, 129 of Lieberklihn, 318 Cuticle of Xasmyth, 284 Cutis anserina, 420 ■ vera, 404 Cystic duct, SS Cytogenous tissue, 126 Cytoplasm, 7 Deiters' cells, 236, 471 phalanges, 473 Demilunes of Heideuhain, 294 492 Elements of Histology, Dendrite, 197 Dendron, 151 Dentinal canals, 277 fibres, 277 sheaths, 277 tubes, 85 Dentine, So Descemet's membrane, ijl, 430 Diapedesis. 113 Diaphragm, 44, 122 Diaster stage in nucleus, 16 Diffuse adenoid tissue, 127 Dilatator puiiiUte, 437 Direct division, 12 "Disetactil," 161 Discus p>roligerus, 390 Disdiaclasts, 104 Dispireme, IG Distal convoluted tubes, 365 Division, Remak's mode of, 12 Doyere's nerve-mount, 165 Ductless glands, 484 Ducts of pancreatic gland, 330 of salivary gland, 291 Ductus ejaculatorii, 381 Dui-a mater, 170 Dural sheath, 457 Ear, External, 458 , Internal, 460 Ectoplasm, 8 Eosinophile cells, 27 Efferent lymphatics, 138 medullated nerve-fibres, ISS veins, 56 Elastic fenestrated membrane of Henle, 61 Elastin, 60 Electric nerve, 14S Eleidin, 33 Elementary fibrill*, 145 fibrils, 47 organisms, 5 Enamel, 275 cap, 281 cells, 281 organ, 280 • prisms, 275 End-bulbs of Krause. 159 Endocardium, 105 Endochondral formatio of bone, 75 EndoljTQph, 461 Endolympliangial nodules, 128 Endomysium, 91 Endoneurium, 142 Endoplasm, 8 Endothelial cells, structure, 40 membrane, 40 Endothelium, 40 Endotheloid ceU-plates, 126 Energid, 6 Engelmann's intermediate disc, 95 Ependvma, 211 Epidermis, 33, 404 Epididvmis, 379 Epiglottis, 67, 339 Epineurium. i41 Epithelial cells, 30 , Division of, 38 , Regeneration of. 38 Epithelium, 30 Ergastic structures, 6 Erythi-oblasts, 28 Eustachian tube, 459 External arcuate fibres, 213 Eyeball, 426 lashes. 424 lids, 424 Fascise, 48, 49 Fascia dentata, 249 Fascicles, 91 Fasciculus cuneatus, 178 of Goll, 179 of Lissauer, 179 pjrramidal, 177 Fat cells, 55 and starvation, 58 Fenestra ovalis, 460 rotunda, 460 Fenestrated membrane, 45, 48 of Henle, 61 Fertilisation of ovum, 2 Fibrfe arcuat«, 213 Fibres. Connective tissue, 46 , Elastic tissue, 60 of muscle, 86, 91 of nerves, 140 of Puikinje, 106 Fibrillie of connective tissue, 47 of muscle, 92 of nerve, 145 Fibro-cartilage, Q() Fibrous tissue development, 59 Fillet, 225 Fissura orbitalis, 88 Fissure of Rolando, 243 Fissures of spinal cord, 175 of medulla, 202 Foetal tooth papilla, 280 Follicles, Hair, 409 , Lieberklihn's, 318 Index. 493 Follicles, Lyinpb, 12ti , 8ebac»'oiis, 418 , Thyiuus, 131 Fornix conjunctivae, 426 vatdna?, 3'.»S Fossa glenoidalis, 66 navicularis, 383 IKJtcllari.s, 443 Fovea centralis, 455 hemielliptica, 460 hemispherica, 460 Fuhilus of peptic gland, 312 Funiculus cuneatus, 202 gracilis, 202 Gall-bladder, 336 Ganglia, Cerebro-spinal, 253 , Svmpathetic, 25tt Ganglion ceUs, 191, 239, 243, 253 Gasserian ganglion, 253 Gelatinous tissue, 62 Geniculate ganglion, 270 Genital coq>uscles of Krause, 160 end-corpuscles, 1 55 organs (male), 372 (female), 386 Germ reticulum of von Ebner, 377 Germinating cells, 44 endothelial cells, 43 epithelium, 387 spots, 1, 388 vesicle, 1, 388 Giralde's organ, 380 Gland, Prostate, 382 Glunds. agminated, 130, 321 , Bartholini, 399 , Bionchial, 349 , Brunner, 328 , Buccal, 298 , Carotic, 488 , Ceruminous, 409 , Coccygeal, 4SS , Harder, 428 , Krause, 426 , Laclirymal, 427 -. Lieberkiihn's, 318 . Littre's, 383 , Lymphatic, 126, 134 . Meibomian, 424 . Mohl, 425 , ilucous, 287, -298 . Peptic. 312 . Pever, 321 , Pyloric, 313 , Salivary, 286 , Sebaceous, 418 , Serous, 286, 299 Glands, Solitary, 130 , Submaxillary, 286 -: , Sweat, 407 , Thynuis, 131 , Thyroid, 484 Glandulie agminat^e, ISO lenticulares, 315 Pacchioni, 235 uteri nte, 396 Glans clitoridis, 399 penis, 384 Glassy membrane, 411 Glissons capsule. .333 Globulin, 21 Globus major, 380 Glomeruli. 251, 360 Glycogen, 9, 23, 335 Goblet cells. 36 Golgi's eeUs, 242 method, 182 tendon spindles, 167 Goll's tract, 179 Graafian follicles, 388 Grandry's corpuscles, 160 Granular leucocytes, 26, 58 Granules in blood, 27 Granulosa, membrana, 388 Grey commissure, 174 Ground lamelhe, 73 plexus of Arnold, 162 substance, 46 Growing capillaries, 113 Habenula X'erforata, 473 Hajmatin, 23 Haematoidiu, 23 Hsematoplasts, 27 Hiemin crystals, 23 H*nioglobin, 22 cnstals, 23 Hah-, 414 bulb, 412 , Development of, 416 fibres, 413 foUicles, 409 knob, 416 , Marrow^ of, 413 , Xew formation of, 415 l>apilla. 411 , Root of. 413 sheath of, 412 sac. 411 , Shaft of, 414 Harder's gland, 428 Haversian canals, 72 lamellie, 72 spaces, 74 494 Elements of Histology. Heart anrl blond-vessels, 105 Helicotrenia, 469 Henle. Fenestrated membranes of, •51. lOS , Fibres of, 62 , Sheath of, 142 . Stratum nervemii of, 456 , Tulies of, 364| Hensen's cells, 472 median disc, 9S Hepatic cells, 335 duct, 336 lobules, 333 veins, 335 Herbst, Corpuscles of, 158 Hilum of lymph glands, 134 of salivarj- glands, 291 of spleen, 352 Hippocampus, 249 Homogeneous elastic membranes, 61 Howship's lacunse, 85 Huxley's layer, 414 Hyaline cartilage, ii3 leucocyte, 26 Hyaloid membrane, 443 Hyaloplasm, 7 Hypophysis, 484 Ileum, 321 Incremental lines of Salter, 278 Incus, 459 Indirect division, 13 Infundibula, 88 of bronchiole, 345 of gland, 299 Inner molecular layer, 449 nuclear layer, 449 Interarticular cartilages, 66 Interfascicular spaces, 49 Interglobular spaces of Czermnk. 278 Interlobar ducts, 291 Interlobular bile-ducts, 336 connective tissue of liver, 333 ducts, 291 Intennediate cartilage, 66 disc, 96 plexus, 162 zone, 315 Intermembranous formation of bone, S3 Intermuscular fibrils, 163 Internal arcuate fibres, 213 cajjsule of brain, 233 Intervertebral discs, 66 Intestine, Large, 317 Intestine, Small, 317 Iiitima of arteries, 108 Intralobular bile-capillaries, 336 veins, 335 Intranuclear network, 11 Iiis, 436 . Blood-vessels of, 438 ; Lymph-clefts of, 438 , Lymph-sinuses of, 438 , Nerve-fibres of, 438 Jacobson's organ, 482 Karyokinesis, 13 Karyomitosis, 13 Karyoplasm, 11 Keratin, 33 Kidney, 356 , Afferent arterioles of, 368 blood-vessels, 367 glomerulus, 360 lymphatics, 370 parenchyma, 357 vessels, 367 Killliker's muscle buds, 102, 166 muscle spindle, 102 osteoclasts, 85 tract cells, 197 Kilhne's nerve-ending in muscle, 164 rhabdia, 92 rhodopsin, 453 sarcoglia, 100 Labia pudendi majora, 420 Labium tymjianicum, 467 vestibulare, 467 Labyrinth, Osseous, 460 Lachrj'mal glands, 427 Lacunfe Morgagni, 383 of bone, 70 of cartilage, 63 — — of lymphatics, 51 Lamellai of bone, 70 of cornea, 429 of lens, 442 Lamina cribrosa, 456 elastica of cornea, 429 fusca, 434 reticularis, 473 spiralis ossea, 460 vitrea, 438 Langerhans' gi'anular layer, 34 Index. 495 Larvnx, 330 r Lateral fillet, 228 horn, 174 nucleus, 211 tract, 175 Lemniscus, 214 Lens. 442 tibres, 442 stars, 443 Lenticular plands, l.iO Lencajmia, 20 Leucocyte, 23 Leucocj-tosis, 20 Leucopenia, 20 Ligamentuni denticulatum, 171 latum, 386 pectinatum, 434 pulmonis, 347 spirale, 4(57 suspensory of lens, 443 Liniitans, externa, 451 interna, 447 Lines of Salter, 278 of Schreger, 279 Liquor folliculi, 390 sanguinis, 19 Littre's glands, 388 Liver, 333 , Vessels of, 335 Lobes of pancreas, 330 of salivary gland, 200 of thymus gland, 131 of lung, 346 Lobules of liver, 333 of lung, 346 of salivary glands. 290 of thymus gland, 131 Locus ccenileus, 228 Lung, 346 blood-vessels, 349 Ivmphatics, 349 Lymph, 123 Lvmphatic capillaries. 119 ^— clefts, 119 glands, 126, 134 rootlets, 119 sinuses, 120 tissue, 62, 126 vessels, 117 Lymphatics, 117 in mucosa, 302 Lymph-canal system in cornea, 51 -canalicular system, 119 cavities. 120 corpuscles, 123 follicles, 126 hearts, 123 Lymphocyte, 25, 58, 123 Lymiihoid cells, 25 Macula acustica, 463 lutea, 454 Malleus, 459 Malpighian corpuscles of kidney, 359 of spleen, 353 pyramids of kidney, 357 stratum of skin, 33 Mammary gland, 401 Manubrium mallei, 459 Marchi's method, 182 Marrow of bone, 68 Matrix of osseous substance, 70 ^Meatus auditorius extemus, 458 Meckel's ganglion, 253 Media of arteries, 108 Median fillet, 228 lateral fissure, 176 ^fediastinum testis, 372 Medulla oblongata, 202 of gland, 134 Medullary cylinders, 135 lymph-sinus, 136 ray, 359 sheath of nerve-fibres, 145 Medullated nerve-fibres, 143 Meibomian glands, 424 Meissner's corpuscles, 158, 423 plexus, 261, 266, 326 Membrana basilaris, 469 • chorio capillaris, 441 Descemeti, 430 granulosa, 388 hyaloidea, 443 reticularis, 473 secundaria, 460 supra-choroidea, 434 tectoria, 474 tympani, 458 Membrane of Krause, 96 Mesencephalon, 229 Mesentery, 122 Mesogastrium, 45 Metakinesis, 15 Microcytes, 20 Microsomes, 9 Migratory cells. 44 Milk, 403 • globules. 402 tooth, 283 Mitoina, 11 Mitral cells, 251 Modiolus, 465 Monaster, 15 Motor ganglion cells, 197 Moss fibres, 243 Movement of cilia, 35 Mucin, 37 Mucosa, 300 496 Elements of Histology. Mucosa, Lymph follicles of, 128 Mucous cells, 2'.)3 glands, 2Sr, 298 membrane, 300 Miico-salivary glands, 288 Mucus, Formation of, 36 Miiller's fibres, 447 muscle, 435 Muscle bundles, 87, !)1 — — buds, 102 cells, 86 column, 92 corpuscles, 94 libres, 86, 90 librillEe, 92 sheath, 87 spindle, 102 tissue, Striped, 90 . Non-striped, 86 Muscular compartments, 98 Muscularis externa, 308 mucosEe, 308 Musculus ciliaris Riolani, 424 Myeloplax, 7, 85 Myeloplaxes of Robin, 85 Xail, 420 cells, 420 groove 420 substance, 420 Xasal mucous membrane, 475 sei)tum, 63 Nerve bundles, 141 corpuscles, 145 end plate, 16o endings, 155 fibres, 140 plexus, 143, 150 unit, 268 Network of fibrill*, 153, 167 Neurilemma, 145 Neuroglia, 182 cells, 184 fibrils, 183 of Virchow, 182 • tissue, 62 Neuraxon, 144 Neuron, 268 Neurokeratin, 146 Neutropliile cells, 27 Nipple, 401 Non-medullated nerve-fibres, 148 Nuclear layer in bulbus olfae- torius, 251 membrane, 11 substance, 11 zone, 442 Nucleoli, 11 Nucleoplasm, 11 Nucleus, .Structure of, H Nucleus ambiguus, 215 arciformis, 213 cuneatus, 206 gracilis. 206 Nuclei, Inner, of retina, 449 , Outer, of retina, 451 Nymphae, 399 Odontoblasts, 277, 280 0']sophagus, 307 Olfactory bulb, 250 cells, 478 glomeruli, 251 nerves, 148, 480 Olivary bodies, 206, 207 nucleus, 207 Omentum of cat, 44 of frog, 122 of guinea-pig, 45 of rat, 45 , Structure of, 48 Optic chiasma, 270 lobes, 231 nerve, 456 nerve-fibres, 447 tract, 270 ■ vesicle, 455 Ora serrata, 447 Organ of Corti, 469 of Giralde, 380 of Jacobson, 482 Ossein, 70 Osseous labyrinth of ear, 460 lamella;, 70 substance from osteoblasts, 85 Ossicula auditus, 459 Ossifying cartilage, 77 Osteoblasts forming bone, 84 Osteoclasts, 85 Osteogenetic layer, 68 Otoliths, 339 Oval nucleus, 41 Ovary, 386 , Development of, 392 , Lymphatics of, 282 , Nerves (jf, 282 Oviduct, 394 Ovum, 1, 388 Oxyntic cells, 312 Oxj-phile cells, 27 Pacinian corpuscles, 155 Palate, 298 Index. 497 Palmiii plicata\ 305 Pallicbni', 4-24 Pancreas, 330 Papilla oircimivallata, 305 liliJormis, 30-' foliata, .•i05 fmi^iformis, 302 iiervi optiri, 44t) Papillary hair ofUiiiia, 410 muscle, ItiC. Paraglobiilin, 22 Paraiiuck'i, IS Paraplasm, 51 Parenchyma of kidney, 357 Parenchymatous cartilage, 66 Parietal cells, 312 Pars ciliaris retiuic, 430 niembranacea, 3S3 prostatica, 383 Pedunculated hydatid of .Alor- gagni, 380 Pedunculus cerebelli, 238 Penis, 384 corpora caveinosa, 3S4 nerve-endings, IGO Peptic glands, 312 Peribronchial lymphatics, 340 Pericardial cavity, 121 Pericellular space, 201 Pcrichimdriuni, ti3 Perilymph, 401 Perilynjphangial nodules, 128 Perimysium, 01 Perineurium, 141 Periosteal bone, 75 f(jrmation, 84 j)tocesses of Virchow, 75 Periosteum, 68 Peripheral nerve-endings, 155 Peritoneal cavity, 121 Peritoneum, 41 Perivascular lymphatics, 110 lymph spaces, 201 Peyer's ulands, 321 - - pat'rh, 130 Phagocvtes, 25, 50 Pharynx, 208 tonsil, 302 Pia mater, 170, 235 Pial sheath, 456 Pigment cells, 52 Plasma, 10 cells, 50 Pleura pulmonalis, 347 Pleural cavities, 121 Plexus choroideus, 235 myentericus, 326 Meissner, 326 venosus vaginalis, 308 Plica} villosa?, 311 Polar bodies, 18 Pons Varolii, 226 Porta, hepatis, 333 Portio iMiilleri, 435 vaginalis uteri, 305 Posterior nerve roots from spinal cord, 188 Postganglionic libres, 2r)4 Pricganglionic fibres, 265 Prickle cells, 37 Primitive dental groove, 280 tibrilhe, 15U fibrils, 02 ova, 393 Prostate, 382 Protoblast, 6 Protoplasm, 1, 7 , ^5tructure of, 7 Protoplasmic memlirane, 55 Proximal convoluted tubule, 362 Pulp tissue, 270 Purkinje's ganglion cells, 239 Pyloric glands, 313 Pyramid of Ferrein, 350 Pyramidal decussation, 204 tracts, 177 Rami capsulares, 337 Ranii'm y Cajal's discoveries, 182, 180, 440, 450 Ranvier's constrictions, 146 nodes, 146 Raphe, 209 Red blood corpuscles, 20 Red nucleus, 230 Reissner's membrane, 46 Eemak's fibrous layer, 108 nerve-fibre, 148 Rete Malpighii, 33 mucosum, 33 testis, 370 Reticular cartilage, 67 formation, 200 Restiform body, 200 Retina, 445 , Blind spot of, 446 , Blood-vessels of, 456 , Ganglion cells of, 448 , Lymphatics of, 456 Rhabdia of Kiihne, 92 Rhodopsin of Kiihne, 453 Rods and cones, 452 Rollett's secondary substance, 03 Rosette stage in nucleus, 13 Rugse, 30S 49S Elements of Histology. Rutherford's scheme of ir.uscle contr.iction, 99 Saccules, -k52 Saccus endolvmphaticus, 461 Saliva, 300 Salivary cells, 293 • glands, 2S6 . Blood-vessels of. 297 , Ducts of, 291 . Lobes of, 290 : Lobules of, 290 , Lnnphatics of. 297 , Xenes of. 297 Sarcode of Dujardin, .j Sarcoglia, 100 Sareolemma, 91 Sarcoplasma, 92 Sarcoplasts, 101 Sarcous elements, 94 Scala tAiupaui, 465 vestibuli, 335, 465 Schultze's protoplasm, 5 Schwann's cells. 5 Sclerotic, 432 Scrotum, S7 Sebaceous follicles, 41S Semicircular canals, 462 Seminal cells, 375 tubules, 374 Sensory decussation, 207 end-organs in muscle, 166 in tendon, 16S ganglion cells, 197 Septum cistenise lymphatiese. 45 Serous glands, 2S6, 299 membranes, 122 Sesamoid cartilages, f>*^ Sharpevs perforating fibres, 74 Sheath" of Henle, 142 of Schwann, 145 Simple axis cylinders, 153 Ivmphatic glands, 126 Skin, 404 -, Blood-vessels of, 421 , Lymphatics of, 422 . Nerves of, 423 Solitarv glands. 130 lymph follicles, 321 Spaces of Foutana, 434 Spermatoblasts, 377 Spermatozoa, 37S Sphincter pupillae, 437 Sphincters, SS Spinal accessor^-, 203 conl, 170 ! grey matter, 191 .Spinal cord white matter, 186 Spiral fibre. 267 tubule, 363 Spireme, convolution, 13 Spleen, 3jl , Capsule of, 351 , L^Tiiphatics of, 355 , Xerve-tibres of, 242, 355 . Parenchyma of, 352 , Pulp o.^'353 . Red blood corpiLScles of, 2S , Trabecule of, 352 Spongioblast, 450 Spongioplasm, 7 Spong'y bone substance, 74 Squamous epithelial ceils, 32 Sternal cartilage, 63 Stigmata, 112 Stomach, 310 Stomata, 112, 121, 349 Stratified columnar epithelium, 35 pavement epithelium, 32 Stratum adiposmn. 406 cinereum, 231 comeum, 33 ■ glomerulosum, 251 granulosum, 34, 250 lacunosum, 249 lemnisci, 231 liicidum, 33 Malpighii, 33 optieum, 232 radiatum, 249 zonale, 231 Strife acusticte 220 Stria vascularis, 468 Stroma, 22 Subarachnoidal spaces, 121, 170 tissue, 171 Subcutaneous lymphatics, 422 tissue, 406 Subdural spaces, 121, 170 Subendocardial tissue, 105 Subepithelial endothelium of De- l)Ove, 51 Subhyaloid ceUs, 443 Submaxillary ganglion . 253 Submucosa, 300 Submucous lymphatics, 121 Subpericardial nerve branches, 107 ti.ssue, 106 Substantia ferruginea, 225 gelatinosa, iS6 nigra. 229 Subvaginal space, 457 Sudoriferous canal. 407 Sulcus hippocampi, 249 spiralis, 467 Superior pedunculus cerebelli, 22S Index. 499 Suprachoroiilal tissue, 434 .Suprarenal bodies, 480 Supravaj^iiial space, 457 Suspt'usory ligament, 443 Sweat glan< Is, 407 Sympathetic system, "258 Synapsis, ]9f> Synovial cavities, 121 Tactile eurpuscles, 1-38, 423 hairs, 417 Tapetuni nigrum, 43!>, 454 Tarsal plate, 424 Taste buds, 305 cells, 305 goblets, 305 Teeth, 275 cement, 279 develoimient, 280 pulp. 279 Tegmental cells, 305 Tegmentum, 231 Teichmann's crystals, 23 Tendon cells, 49 spindles, 167 Temlons, 49 Tendril fibres, 243 Tenoniau capsule, 457 space, 457 Tensor choroidete, 435 Ternainal bronchi, 347 Testis, 372 Thoracic duct, 117 Thymus fullicles, 131 ■ gland, 131 Thyroid cartilage, 63 gland, 484 Tongue, 302 , Serous glands of, 304 Tonsils, 129 Touch-cells of Merkel, 161 corpuscles of Merkel, 169 Trabecule carne*, 106 of lymphatics, 134 of sjileen, 352 Trachea, 343 Tracts of white matter in cord, 17 Tract cells, 197 Transitional epithelium, 35 Transverse disc, 95 Trapezoid nucleus, 218 Trapezium, 218, 226 Tuba Eustachii, 459 Tubercle of Rolando, 202 Tnberculuni acusticum, 219 Tubes of epididymis, 379 Tunica adnata, 372 Tunica albuginea, 37 dartos, 88 fibrosa. .390 prnpriii, 4i>9 • vaginalis, 372 Tyson's glands, 384 Ureter, 371 Urethra, Female, 399 , Male, 383 Urinary tubules, 361 Uterus, 395 Utricle, 462 Uvea, 437 Vagina, 397 Varicose nerve-fibres, 147 Vas deferens, 381 rectum, 378 Vasa etferentia, 379 Vascularisation of cartilage, 75 Vater's corpu.scles, 155 Veins, 110 , Intima of, 110 , Media of, 110 of the bones, 110 Veins of the l)rain, cord, gravid uterus, membranes, and retina, 110 , Valves of, 110 Vena axillaris, azygos, cava, cru- ralis, hepatica, intima, iliaca, mcsenterica, jtoplitea, I'enalis, spermatica, and umViilicalis, 110 jugularis, and subclavia, 110 Venae rectie, 369 stellatfce, 370 vorticosse, 441 Venous radicles, 353 sinuses, 353 Ventricle, Fourth, 211 Ventricles, 106 Ve.sicula; seminales, 381 Vestibulum of labyrinth, 460 Virchow's crystals, 23 Visceial pericardium, 105 peritoneum, 333 Visual purple, 453 Vitreous body, 443 Wandering cells, 58 Weigert's method, 182 White blood corpuscles, 23 500 Elements of Histology. White commissure, 187 fibrous tissue, 40 substance of brain, 237 of cord, ISiJ of Sclnvann, 145 Wolffian body, 374, 3S7 Wreath arrangement of nucleus, 14 Yellow elastir cartilai Yellow elastic tissue. 00 Zona fasciculata, 487 glomerulosa, 486 pel In ei da, 1, 388 reticularis, 487 vasculosa, 386 Zonula ciliaris, 443 Zinnii, 443 I'rintedbyC'AssKLL & Company. LnnTED. La Belle Sau\aye, Louilon, E.G. \ K67*^ 1698 lamdb