Histological Contributions: The Blood Vessels ; The Alimentary Canal; The Urinary Excretory Passages; The Suprarenal Capsules; The Mammary Gland. BY EDMUND C. WENDT, M. D. REPRINT FROM JSatttrt&toaitts $ t s t o I o 3 g. New York, 1881. BIBLIOGRAPHY. 141 Ibid. Ueber einige Erscheinungen an den Muskeln lebendiger Corethra plumicomis- larven. Archiv. fur mikro. Anat. Bd. X. 1874. Kaufmann. Ueber Contraction der Muskelfaser. Reichert & Du Bois-Reymond’s Archiv. 1874. Thin. On the Minute Anatomy of Muscle and Tendon. Edinburgh Medical Jour- nal. Sept., 1874. Weber. Note sur les noyaux des muscles stries chez la grenouille adulte. Archives de physiologie. 1874. Ranvier. De quelques fait relatifs a l’histologie et a la physiologie des muscles stries. Archives de phys. 1874. Ibid. Note sur les vaisseaux sanguins et la circulation dans les muscles rouges. Archives de phys. 1874. Ibid. Traite technique d’histologie. Paris, 1875. Fredericq. Generation et structure du tissu musculaire. Bruxelles, 1875. Meyer. Ueber rothe und blase quergestreifte Muskeln. Reichert & Du, Bois- Reymond’s Archiv. 1875. Fredericq. Note sur la contraction des muscles stries chez l’hydrophile. Bulletin Acad. Roy. de Belgique. Tome XL. 1877. Renaut. Note sur les disques accessoires des disques minces dans les muscles stries. Compt. rend. Tome LXXXV. No. 21. 1877. Biedermann. Zur Lehre vom Bau der quergestreiften Muskelfaser. Wiener Acad. Sitzungsbericht. Bd. LXXXV. No. 21. 1877. Schaefer. Quain’s Anatomy. Eighth edition. New York: Win. Wood & Co. 1878. Nasse. Zur microscopischen Untersuchung. des quergestreiften Muskels. Pfliiger’s Archiv. Bd. XVII. 1878. Froriep. Ueber das Sarcolemm und die Muskelkeme. Archiv fur Anatomie und Entwickelungsgeschichte. 1878. Engelmann. Nouvelles recherches sur les phenomenes microscopique de la con- traction musculaire. Archives Neanderlaises des Sciences exactes et natu- relles. 1878. Flemming. Ueber Formen und Bedeutung der organischen Muskelzellen. Zeit- schrift f jir wissenschaftliche Zoologie. XXX. Supplement. 1878. Unger. Untersuchungen iiber die quergestreiften Muskelfasem des lebenden Thiers. Wiener medinische Jahrbiicher. 1879. (Largely pathological.) Newman. New Theory of Contraction of Striated Muscle, and Demonstration of the Composition of the Broad Dark Bands. Journal of Anatomy and Physi- ology. Vol. XIII. 1879. CniTTENDEN. Histochemische Untersuchungen iiber das Sarcolemm und einige verwandten Membranen. Untersuchungen aus der Physiol. Institut der Uni- versitat Heidelberg. Bd. III. 1879. Klein and Smith. Atlas of Histology. Part V. 1879-80. Ranvier. Lecjons d’anatomie generate sur le systeme musculaire. Paris, 1880. CHAPTER XI. THE BLOOD-VESSELS. Bt EDMUND C. WENDT, M.D., Curator of St. Francis’ Hospital, New York City, etc. In man, a closed circuit of branching tubes, which proceed from a central organ, the heart, and, ramifying throughout the body, return the blood to this central organ, constitutes the blood-vascular system, as it has been named. Of these vessels we recognize three different kinds : arteries, capillaries, and veins. The arteries convey the blood to the various capillary districts, whence it is again collected and car- ried back to the heart by the veins. The arteries, highly elastic throughout, are composed of three superimposed layers or tunics. The veins, less elastic, and consequently more flaccid and compressible, likewise con- sist of three coats or tunics. In both sets of vessels these coats have received the names of intima for the inner, media for the middle, and adventitia for the external layer. The capillaries, intervening between the two, form minute branch- ing tubules, which generally have but a single exceedingly thin and permeable membrane as the sole constituent of their walls. Of course, all these vessels merge into one another, so that a sharp line of demarcation can nowhere be drawn ; but in their typical forms they present clearly defined structural dif- ferences, necessitating a separate description of them. We begin with the simplest and yet most important class: The capillary blood-vessels.—They are composed, as we have already said, of a single layer of cells, arranged in tubu- lar form, and containing nuclei. These corpuscles are di- rectly continuous, on the one hand, with the inner coat of THE BLOOD-VESSELS. 143 the terminal arteries, and, on the other, with the intima of the veins, hence also with the lining membrane of the heart. They are called endothelia, and since they constitute the only struc- tural elements which enter into the composition of all blood- vessels, we will first consider them and their relations to these vessels. The vascular endothelium.—Histologists understand by the term endothelium a thin layer of flattened cells lining the free surface of various membranes, canals, sheaths, and cavi- ties, all belonging to the serous type. Epithelium, on the other hand, is found covering the skin and mucous surfaces. All endothelia, in common with the blood, the blood-yessels, and connective tissues, are derived from the mesoblast, or mid- dle of the three fundamental layers of the embryo. The epi- tlielia, it will be remembered, originate in the two other layers, called epiblast and hypoblast, respectively—the former being the superior and the latter the inferior layer of the embryo. In adult human subjects the vascular endothelia are made up of thin, polygonal, sometimes irregularly pentagonal, flat- tened cell-plates. Most of the elements are furnished with a rounded or ovoid nucleus, of central or more or less peripheral location (Fig, 58). Some have two nuclei. In general, the cells are somewhat elongated in the longitudinal direction of the ves- sel to which they belong. They also grow slightly narrower as the calibre of the vessel decreases. Their borders are serrated or scalloped, and dove-tailed into one another. An albuminoid substance, ordinarily invisible, cements their adjoining edges. This substance has the peculiar property of effecting an ener- getic reduction of silver nitrate. Hence, by proper manage- ment, the outlines of each individual cell may be made visible as a black zigzag surrounding a nucleus. Every cell represents a plate-like expanse of modified protoplasm. Remnants of this original substance may be seen to surround the nuclei of young vessels, where they appear in the shape of varying quantities of distinctly granular matter. Klein has described an intra- cellular network, formed by plexuses of minute fibrils, and associated with a second denser reticulum within the nucleus, called the intranuclear network. Whatever interpretation we choose to give these minute structures, the fact of their exist- ence is indisputable. In man, however, their presence is not as readily demonstrable as in animals. 144 MANUAL OF HISTOLOGY. An isolated endothelial cell, when tilted up on its edge, pre- sents the appearance of a straight or curved double contour, with a central thickening corresponding to its nucleus. Viewed en face, we observe the sinuous outline and the central or ec- centric nucleus, with its surrounding granules of protoplasm. The shape and contour of endothelial cells are subject to con- Flo. 58.—Endothelium of the carotid artery of man, after treatment with nitrate of silver: a, cells; b, clearer, c, darker intermediate spaces; d, intra-cellular circular and spotted markings. Eberth, siderable variations in tlie different vascular districts. Sucli differences also occur in the same district, with the varying de- gree of expansion or contraction of the particular vessel under observation. The capillaries proper.—In point of wideness of distribu- tion, this variety of blood-vessels greatly exceeds all others. Indeed, the capillaries occupy a rank, in this respect, second only to the connective-tissue group of histological struc- tures. As regards importance to the economy, it will only be necessary to advert to the vital processes of nutrition, secre- tion, respiration, and excretion, to recall the quality and extent of their physiological usefulness. Throughout the THE BLOOD-VESSELS. 145 body 1 capillary plexuses are interposed between arteries and veins, which constitute a series of conveying and returning tubes. Thereby the direct continuity of these blood-channels is established. It is in these intermediate territories, and in them only, that the blood serves its true function of giving and taking. True markets of exchange, then, these capillary districts, where the system is supplied with new material, and in return gets rid of useless or even deleterious by-products of tissue-life. Hence, the para- mount importance of these vessels in the maintenance of life and health. Hence, also, the direct practical utility of knowing their minute anatomy and physiological dignity. Every practitioner of medicine will see the important relation this branch of liistolog}r holds to pathology, and therefore to thera- peutics. At the same time we should not forget that the role played by the capillaries in the system is normally due to the inherent mechanical and physical properties of a fine- ly elastic animal membrane, rather than to any specific action of their cellular constitu- ents. Robin, following Henle’s example, dis- tinguishes several varieties of these vessels. It seems to me proper to limit the term capil- laries to those minute tubules which are entirely devoid of muscular elements. This corresponds to the classification adopted by Virchow, Kolliker, Eberth, Ranvier, Frey, and others. It is the one therefore that has generally been accepted, and is both simple and logical. The diameter of these tubules varies from 0.0045 to 0.0115 mm. Their structure is readily understood. Examined in the living animal with a high power, we see mere- ly a delicate, hyaline, double-contoured membrane, having an Pig. 59.—A rather large capillary from the hyaloid of the frog, presenting a membranous and nucleated tunica adventitia. Eberth. 1 Hoyer has shown that a direct communication of arterioles with venules occurs normally in the tips of the fingers, the matrix of the nails, the tip of the nose, and various other parts. 146 MANUAL OF HISTOLOGY. average thickness of 1 to 2 micro-millimetres (0.001—0.002 mm.). This membrane forms a tubule, the parietes of which are studded at intervals with rounded or oval nuclei, often containing one or more bright nucleoli. When oval, these nu- clei have their long axis parallel with the direction of the ves- sel. Their average size is 0.0056 to 0.0074 mm. They possess the property of eagerly imbibing most of the staining fluids employed in histology, and of resisting the action of dilute acids, alkalies, and other reagents. (See Fig. 59.) Besides nuclei, the capillary wall contains at various points peculiar granules, which indicate its protoplasmic nature. In addition, Strieker and Eberth have described lateral processes and pointed prolongations jutting out from the parietes of the Fio. 60.—Capillaries of the lungs of the frog, with irregularly dentated cells: a, vascular meshes. Eberth. capillary tubes. In growing tissue these are readily demonstra- ble, often forming tliread-like connecting bridges between neigh- boring vessels ; at a later period they are hollowed out into true capillaries. The shorter sprouts are also protoplasmic buds, capable of further development into similar vessels. (See Fig. Gl.) By employing weak solutions of silver nitrate, the capillary-wall may be shown to consist of variously shaped areas, each one corresponding to a nucleated cell. They are the endotlielia, and represent, as already stated, the sole essen- tial constituents of all capillaries. Their form varies with the calibre of the vessel, the smaller capillaries being composed of THE BLOOD-VESSELS. 147 corpuscles which are comparatively narrow, the larger vessels having broader cells. In man they have an average length of 0.0756—0.0977 mm., and an average breadth of 0.01—0.05 mm. The intercellular boundaries, brought out as dark lines by means of the silver salt, frequently exhibit little nodular swell- ings. (See Fig. 58.) In addition to the ordinary endotlielia, we find smaller areas, generally without nuclei; they have rounded or some- what dentate contours, and are interposed be- tween the other cells. Eberth believes that some of these intercal- ated areas, as Auerbach has called them, proba- bly correspond to por- tions of strangulated vas- cular cells. It is more logical to regard them as the remnants of an in- complete endothelial des- quamation, a process which is of physiologi- cal occurrence through- out the blood-vessels. These remaining bits are finally destined to be- come quite detached from the vascular wall, and are then swept away by the rush and flow of the blood-current. The detached portions of such endotlielia and their nuclei appear as free granules in the blood, where they have puzzled many observers, and have vari- ously called microcytes, hcematoblasts, etc. From this descrip- tion it is plain that Cohnheim’s view, that these spaces are openings or stomata, is not sustained. True, we find in serous membranes of certain animals real openings, but these always appear of rounded shape, and are, to say the least, not com- monly observed in human blood-vessels. This statement of the case does not militate against Cohnheim’s well-known views that the corpuscles emigrate through the vessels, for, remembering the protoplasmic nature of the endothelial tubes, Fig. 61.—A, A, stellate connective-tissue cells connected by B,B, delicate protoplasmic threads to C,C, sprouts of endothe- lial tubes ; D, protoplasm connecting two capillaries ; E, nu- cleus imbedded in a primitive sprout of protoplasm, budding from wall of capillary. Specimen prepared by silver nitrate. 148 MANUAL OF HISTOLOGY. we can readily account for the phenomena in question. The capillary-wall is elastic, extremely thin, and permeable. By virtue of these qualities, it may allow the passage of a leu- cocyte or colored globule through its substance without suf- fering a permanent breach of continuity. The writer’s views on endothelial desquamation as a normal process of physi- ological import may strike the reader as insufficiently substantiated by known facts. But when we remember that similar processes have been actually ob- served taking place under the microscope, all doubts as to the probability of this endothelial desquamation should vanish. The author refers to the recent observations of Altmann {Arch. f. mikros. Anat., Yol. XVI., p. 111). This his- tologist investigated the changes which take place in the serous epithelium (i.e., endothelium) of the exposed frog’s mesentery. Multiple swellings of the endothelia were seen to occur; then portions of these cells would become de- tached. Such detached bits were found to resemble in their appearance ordi- nary leucocytes. But, in spite of this apparent breaking up of the endo- thelia into these nucleated corpuscles, they often retained their individuality unaltered. The production of bodies resembling leucocytes from endothelia has, therefore, been actually observed in connection with serous membranes, and vascular desquamation is essentially the same process. The capillary blood-vessels occupy the interstitial connec- tive tissue of organs, without entering their parenchyma proper. Cartilage, the teeth, the hairs and nails, the cornea, and cer- tain structures of the nervous system and organs of special sense are devoid of capillary supply. Most of the larger tubes are invested by a delicate, exter- nal, sheath-like structure, called the capillary adventitia or vascular perithelium. It is composed of a rather close net- work of delicate connective-tissue librils. Prolongations of pe- culiar stellate cells, which clasp the capillary-tube, may some- times be seen to join these fibrils. (Fig. 62.) Such branching cells are also encountered at some distance from the capillaries. They show delicate processes, which may anastomose with the offshoots of the adventitial corpuscles. In other places we only find external plates of connective-tissue cells (Krause’s ino- blasts), which have become more or less fused with the capil- lary-wall. In many instances the perithelium is inseparable from the connective-tissue stroma surrounding the vessel. In reference to the manner of anastomosis, the forms and modes of ramification of different networks vary with the dif- ferent tissues and organs of the body. Hence, a simple in- THE BLOOD-VESSELS. 149 spection of capillary reticula will generally enable us to decide the nature of the tissue or organ in question. From a physio- logical point of view, we recognize a causal relation between high capillary development and great functional activity. Therefore, the abundance of capillaries will determine the physiological importance of an organ. The chief forms of ramification may be grouped as follows : 1. Loops (a), simple or compound; e.g., the skin and the hard Fig. 62.—Capillaries from the hyaloid membrane of the frog: a,a, capillary-wall; ft, 6, nuclei of the same; c,c. cells of the tunica adventitia ; d,d, processes of these cells clasping the capillary-wall; e, stel- late cell anastomosing with the cells of the tunica adventitia. Eberth. palate ; (b) reticulated (the intestinal villi). 2. Tufts (the kid- ney). 3. Irregularly polygonal networks (the glands and the mucous membranes). 4. Rounded reticula, with round or polygonal meshes (adipose tissue). 5. Reticula with elongated meshes (the muscles, bones, and tendons). There would be a certain satisfaction in knowing that this or that vessel had a precise breadth, and its coat a certain thickness. The precision would be apparent, however, rather than real, because such 150 MANUAL OF HISTOLOGY. measurements vary greatly at different times in the same ani- mal, and even more so in different animals. It may be stated, in general, that the calibre corresponds to the size of the largest blood-globules. In man, therefore, we have an average diam- eter of about 0.007 mm. The largest capillaries exist in the mucous membrane of the stomach and colon, the periosteum and bones, and the pituitary body. The smallest are found in the skin, the small intestine, the lungs, the muscles, the gray substance of the brain, and the retina (Valentin, Weber, and Henle). The genesis, reproduction, and regeneration of capillaries. —There is still much uncertainty about the mode in which blood-vessels are first formed in the embryo. My personal Pig. 63.—Growth and development of capillaries by nucleated sprouts of protoplasm : A, poly-nucle- ated large sprout with Aliform process ; B,B, blood-globules; C, branched cell; D, delicate protoplasmic tendril linking C with E, a smaller mono-nucleated sprout of endothelial wall. observations on this subject, while working recently under the supervision of Kblliker, appear to confirm the view held by Foster and Balfour. These authors’ account of the interesting process may be summed up as follows : About the second day of incubation in the chick, certain mesoblastic cells send out solid processes, which, uniting, form a protoplasmic network containing nuclei. A majority of the latter acquire a reddish tint, and are ultimately transformed into colored blood-glob- ules. Other nuclei, however, remain unaltered, and, receiving an investment of protoplasm, form walls inclosing the reddened THE BLOOD-VESSELS. 151 nuclei. The protoplasm of these central nuclei rapidly becomes liquefied, thus forming the blood-plasma. And now we have a system of communicating tubules, containing corpuscles float- ing in a plasma, their walls consisting of nucleated cells. Hence, the blood-vessels do not arise as intercellular spaces, but are hollowed out to form channels in an originally solid reticulum of protoplasm derived from mesoblastic cells. This explanation of the way in which vessels are formed aids us in understanding both how capillaries are reproduced in the adult, and their regeneration under pathological condi- tions. The capillary-wall itself, under the influence of favor- ing circumstances, begins to bud, as it were ; the delicate proto- plasmic sprouts send out more delicate filaments, which, uniting with similar offshoots from neighboring vessels, establish a connection between two capillaries. In due time these solid structures undergo the familiar process of hollowing out, and the newly formed vessel is complete. Frequently the proto- plasmic threads communicate, forming a reticulum which Ran- vier has called vasoformative network. This author also ob- served that capillaries develop from special cells, termed vasoformative cells. They resemble leucocytes, and form by their prolongations a network of solid protoplasm. This is originally quite independent of already existing capillaries. Subsequently, however, a consolidation is effected, and the blood then flows through these new channels in the usual manner. The author has been able to trace collections of emigrated leucocytes through various stages of progressive development, culminating in the formation of true capillaries. The experi- mental investigations on this subject were carried out in Pro- fessor v. Rindfieiscli’s laboratory, and have been fully described by his former assistant, Dr. Ziegler, of Wurzburg. The arteries.—If we follow the capillaries in a direction toward the heart, we soon find the endothelial tube receiving an investment of unstriped muscle-cells. These are wound transversely or obliquely around the capillary, thus forming a second tube, as it were, surrounding the first. External to the muscular layer there appears some connective tissue, mingling with which elastic elements may be observed. The direction of these additional fibres is mainly longitudinal. They form the third or external coat, called the adventitia, the second or 152 MANUAL OF HISTOLOGY. middle being represented by the muscle-cells, and the first or internal by the endothelial tube. The latter now receives the name of intima. When the layers of its walls are arranged in this simple manner the vessel is called an arteriole, and this constitutes the type of all arteries. Arterioles, however, commonly contain a few additional fibres between the intima and the media, as the first indication of what afterward becomes a special layer. This structure, known as the internal elastic coat, attains considerable devel- opment in the larger vessels. With the growth of an artery in calibre its individual coats are reinforced by additional layers. Hence the thickness of the entire wall increases at the same Fig. 64.—Minute artery showing optical section of alternate groups of muscle-cells, and an external nu- cleated membrane, representing the tunica adventitia. Fig. 65.—A. intima ; B, delicate internal elastic coat; E, media (as in Fig. 04); D, adventitia. Arteriole, from a child’s mesentery. Fig. 66.—Elastic internal tunic of the basilar aiteries. Fig. 64. Fig. 65. Fig. 66. time that its structure is rendered more complex. But new tissues never appear. Moreover, the increased thickness is not uniformly proportionate to the enlarged calibre ; neither does it take place by equal participation of the different tissues men- tioned. In vessels of small and medium size there is a prepon- derance of muscular over elastic elements. In the larger trunks the reverse condition obtains. It is, therefore, proper to dis- tinguish arteries of the muscular from those of an elastic type. The latter class is represented by the principal distributing trunks, all the remaining arteries belonging to the muscular type. There exist, however, no abrupt lines of demarcation between these main forms—the one merging gradually into the other. The interposition of the internal elastic coat between the THE BLOOD-VESSELS. 153 intima and the media marks the transition of a minute into a small artery. This new layer consists at first of delicate fibrils oi elastic tissue, or an apparently homogeneous membrane. Vascular contraction throws it into folds, which appear as longitudinal striae or a transverse series of continuous festoons. As the vessel grows larger this coat gets thicker, becomes dis tinctly fenestrated, and presents a reticulat- ed appearance. It is now made up of inter- lacing bundles of connective tissue and elas- tic fibres, with spaces left between them. The latter constitute the fenestree of this layer, which in the large vessels becomes a double or triple lamellated membrane. Be- tween it and the lining endothelium there appears still another structure, which has re- ceived various names from different authors. Thus, Kolliker has called it the striated in- ternal coat; Remak, the innermost longi- tudinal fibrous coat; and Eberth, the in- ternal fibrous coat. We shall employ the last term. The internal fibrous coat consists at birth of a granular substance, which be- comes distinctly fibrillated in the adult. Embedded in this membrane lie numerous branching corpuscles, containing large, con- spicuous nuclei. Besides these cells, smaller, so-called granulation-bodies are frequently seen. So far from regarding them as of path- ological origin (Eberth, in “Strieker’s His- tology”), I prefer to consider them as ma- trix-cells for the regeneration of desquamated endotlielia. My reasons for so doing are as follows: In the blood-vessels of young animals and newly born infants I have fre- quently noticed thick, dark, and granular bodies immediately below the endothelial lining. These subendothelial cell-plates were smaller and more polyhedral than ordinary endothelia, and invariably contained one or even two nuclei. They ap- peared to resemble germinating endothelial cells, such as Klein has described as occurring in serous membranes. They did not, however, occur in single layers, as Klein has seen them, Fig. 67. — Small artery from the brain of man : a, tunica adventitia ; a', a', nu- clei of the tunica adventitia; i>, muscle nucleus; c, elastic internal tunic ; d, membrane formed of fusiform cells. Eberth. 154 MANUAL OF HISTOLOGY. but in strata. They were observed in particular vessels of young animals. It seems likely that these cells disappear or shrivel with the growth of the individual, but their sudden reap- pearance in pathological processes leads the author to believe that at least some of them persist through life. Talma (Vir- chow's Arch., Yol. LXXVII., pp. 242-269) observed similar elements, but thinks they are derived from the ordinary en- dothelia, instead of rice versa. He is also convinced that the latter are merely modified leucocytes ; but this view has been shown to be erroneous by Yircliow {Archir f. jpath. Anat., Yol. LXXVII., pp. 380-383). Endothelial desquamation is probably, as already stated, a physiological process of constant Fig. 68.—Transver-e section through small artery and vein : A, artery; a, intima with bulging en- dothelial cells, the vessel being drawn in a state of contraction ; b, internal elastic coat, wavy for same reason; c, media; d, adventitia. B, vein, same denominations. occurrence, and in some respects analogous to the epithelial shedding from the surface of the skin and mucous membranes. The media musculosa, or middle coat, consists of superim- posed layers of smooth muscle-elements disposed in groups. Most of them lie transversely to the course of the vessel. The intervals between neighboring groups are occupied by connec- tive tissue and elastic fibres, arranged in networks. This inter- stitial substance becomes augmented with the increasing calibre of the artery. In the largest trunks it all but replaces the muscle-cells. Here, however, the elastic fibres also reach their maximum development, encroaching upon the connective-tissue elements until the latter become quite inconspicuous. Besides its principal transverse layer, the media also contains fusiform muscle-cells, placed in an oblique or longitudinal direction. THE BLOOD-VESSELS. 155 They are scattered irregularly throughout the middle coat. Sometimes the intima and the adventitia also contain sparsely distributed muscle-cells. The arterial muscular coat is dis- tinctly separated from the intima by the interposition of the internal elastic coat. Externally a sharp boundary is formed either by the adventitia or by the external elastic coat. The latter appears as a separate membrane in arteries of small and medium size. There are, however, exceptions to this rule. The external elastic coat consists of a close network of delicate Fig. 69.—Longitudinal section of pulmonary artery. Mounted in glycerine and acetic acid after de- siccation of the artery, a. Internal portion of intima ; b, external portion of intima ; c, internal elastic coat; d, media, showing cross sections of muscle fibres and elastic tissue; e, adventitia. elastic fibrils, anastomosing with similar adventitial-reticula. The adventitia is composed of interlacing bundles of connec- tive tissue, commingled with elastic lamellae of varying thick- ness. The veins.—From their origin in the capillaries to the point where they enter the trunk proper, the veins preserve through- out a uniform type of structure. But no sooner have they penetrated into the visceral cavities of the body than we find them undergoing considerable alterations, which may either increase or diminish the complexity of their structure (Ran- vier). The veins are far more numerous than the arteries. They are also, as a rule, wider and more dilatable, and have thinner coats. It is owing to the latter peculiarity that the 156 MANUAL OF HISTOLOGY. color of the blood is seen through their semitranslucent walls. Finally, they branch more frequently than the arteries. Three main coats or tunics enter into the composition of most veins. These resemble the corre- sponding arterial struc- tures, and have likewise received the names of in- tima, for the internal endo- thelial lining ; media, for the middle muscular ; and adventitia, for the external connective-tissue coat. Veins, however, differ from arteries in the feebler development of their mus- cular coat, in the compara- tive paucity of elastic ele- ments, a greater laxity of their intima, and the presence in some of valves. We may distinguish veins of smaller calibre, or venules, from the vessels of medium and large size. The venules, like the arterioles, in certain respects resemble the capillaries. As Fig. 70.—Portion of innominate vein of dog, after in- jection of a solution of silver nitrate. The endothelial cells and their nuclei are visible. The media shines through this layer. Pig. 71.—Arteriole and venule from child’s mesentery, treatment by acetic acid and glycerine: A, ar- tery ; a, nucleus of muscle-cell of media ; 6, same in transverse section (optical). B, vein ; c, nucleus of connective tissue constituting media, which in these minute veins contains no muscle-cells; d, nucleated connective tissue. it may become important to differentiate the minuter forms of vessels, we will here briefly indicate the main points of dis- tinction between full-sized capillaries, small veins, and arte- THE BLOOD-VESSELS. 157 rioles. In the latter, the endothelial cells are more nearly fusiform, longer, and somewhat narrower than in the venules. In the capillaries, their form and dimensions hold an interme- diate position between the arterial and venous types. The middle coat is entirely wanting in capillaries, and is much less conspicuous in the small veins than in the arterioles. In fact, under ordinary circumstances, the muscle-coat forms by far the most characteristic distinguishing feature between these ves- sels. Venules quite frequently have only a few sparsely scat- tered muscle-cells, in place of the continuous muscular layer which exists in minute arteries. The former also are either altoge- ther deficient in the in- ternal elastic coat, or the presence of this struc- ture is barely indicat- ed by delicate elastic fibres ; these latter usu- ally have a longitudinal direction. On the other hand, arteries of corre- sponding calibre are mostly furnished with a distinct elastic inner coat. Finally, with re- gard to the adventitia, we find it more highly developed proportionally in venous than in arterial vessels, whereas capillaries commonly have only a few faint fibres to denote the presence, in them also, of this coat. The internal elastic coat of the larger and largest veins is very feebly developed in comparison with that of the arteries. Distinct fenestrated membranes are scarcely ever encountered. Veins are likewise possessed of an internal fibrous layer, but here again we observe that comparatively feeble development of a coat which in the arteries is quite conspicuous. Among the many special characteristics of the various veins in different regions, we will only mention the following : the jugular veins show well-marked elastic reticula, the meshes of which contain sparse muscular elements. In the femoral, Fig. 72.—Longitudinal section of popliteal vein : a, intima; b, media ; c, adventitia. 158 MANUAL OF HISTOLOGY. brachial, and subcutaneous branches there is a media of con- siderable dimensions. The inferior vena cava has, in addition to a transverse layer of muscle-cells, a longitudinal one of greater thickness, and, besides these, contains muscle-cells, which are scattered through its elastic coat. The veins of the meninges of the encephalon and cord, the retina, the bones, and the muscles, and the jugular, the subclavian, the innomi- nate, and the thoracic portion of the vena cava are all entirely devoid of a true muscular coat. The veins of the gravid ute- rus have only longitudinal muscle-elements. In addition to an outer longitudinal layer, the vena cava, the azygos, the renal, the hepatic, the internal spermatic, and the axillary veins pos- sess an inner circular layer. The iliac, the femoral, the popli- teal, and several other veins contain a middle coat of transverse muscle-cells, between internal and external longitudinal layers. The valves of the veins consist of longitudinal bundles of connective tissue commingled with scanty elastic fibrils, and containing nucleated cells. The inner endothelial layer appears to be a direct continuation of the intima of the vein. That portion of the subendothelial tissue which does not face the blood-current is less developed than the part turned toward it; the elastic fibres of the latter are also barely visible. The at- tached valvular border frequently presents transversely dis- posed muscle-elements. Eberth has denied their occurrence, but they have been repeatedly observed by Ranvier and other competent histologists. Peculiar vascular structures.—The following structures are remarkable for the conspicuous and characteristic development of their blood-vessels the vascular membranes, tunica vascu- loses, such as the pia mater of the brain and spinal cord, and the choroid coat of the eye. In these we find that the excessive vascularity is intended to nourish, not the membranes them- selves, but the organs which they invest. Blood-vascular glands, vascular plexuses.—In man, two bodies of peculiar structure represent this group. They are the coccygeal gland of Luschka, and a rudimentary organ called the intercarotid gland. Both consist essentially of con- voluted blood-vessels and nerves, imbedded in a nucleated con- nective-tissue stroma. The coccygeal gland is a small, rounded, pinkish body, of rather firm consistence, and is connected by a pedicle with the middle sacral artery. This pedicle contains THE BLOOD-VESSELS. 159 blood-vessels and nerves. The arteries entering the gland-like body become convoluted, and show numerous tubular, fusi- form, or ampullar dilatations. Sometimes they have terminal sacculi, closely resembling minute aneurisms, and giving the organ its glandular appearance. Indeed, Luschka has called them gland-tubules and vesicles. After death they are com- Fig. 73.—Section of a naturally injected coccygeal gland : a, vessels ; 6, collection of cells. Eberth. monly found to be empty, but by proper management a good natural injection with blood may be readily obtained. Both capillaries and veins also present lateral varicosities, studding them in great number. All these vessels have the usual endo- thelial lining. External to this there appear aggregations of rounded or polygonal cells. They are furnished with nuclei, and receive an investment corresponding to the vascular ad- 160 MAXUAL OF HISTOLOGY. ventitia, but containing comparatively more nuclei than that structure. The intercarotid gland differs from the coccygeal in its larger size, and because it contains accumulations of ganglionic nerve-cells. These are derived from the carotid plexus. Here the vascular sacculi also more nearly resemble dilated capilla- ries, whereas in the other body they approach the arterial type. In all other respects the structure of these vascular plexuses is identical. Some authors regard the spleen and the supra- renal capsule as belonging to this group of blood-vascular glands. The author sees no necessity for so considering them, and the subject may therefore be dis- missed without fur- ther comment. Corpora caverno- sa.—They consist in great part of dilated blood-vessels, chief- ly of the venous type. These inter- communicate very freely, and when filled with blood cause the organ to assume the peculiar condition known as erection. The penis and the clitoris are supplied with caver- nous bodies. The urethra of the female and the vestibule also contain them. Interlacing bundles of muscle-fibres, together with similar bands of connective tissue, form a framework for the support of the vascular structures mentioned. The latter present the ordinary endothelial lining. Several years ago Dr. H. J. Bigelow succeeded in demon- strating the existence of cavernous tissue in the nasal fossae. In a letter to the author, Dr. Bigelow states that his point was “ the demonstration of an abundant and true cavernous structure and erectile tissue on and about the turbinated bones, occupying the place of what had been previously supposed to be only venous sinuses, the loops of Kohlrausch. The new re- sult obtained was due to a different mode of preparation. Kohl- Fig. 74.—A, cellular vascular sheath, from the coccygeal plexus: a, connective tissue with scattered cells and nuclei; 6, round and polygonal cells lying immediately upon the capillary wall, c; B, a capillary from the coccygeal plexus, with a vascular sheath very rich in cells. Beferences as in A. Eberth. BIBLIOGRAPHY. 161 rausch injected from the jugular vein ; I [Dr. Bigelow] inflated the tissue locally, as if it were in the penis.” Vasa vasorum, lymphatics, and nerves.—Nutrient ves- sels are found in the walls of all the larger arteries and veins, where they occupy the adventitia. Sometimes they are seen to dip down into the outermost portions of the media. Lym- phatics occur as clefts or spaces between the various tissues of all arterial and venous trunks. Some vessels are ensheathed by a lymphatic membrane, which is sometimes furnished with a lining endothelium. Such structures are called perivascular, or, better, circumvascular spaces. They may be fpund in connection with the omental and the mesenteric vessels, also the splenic and the hepatic arteries, as well as certain menin- geal vessels of the brain and cord. Nerve-fibres are seen to pass to many of the blood-vessels. They enter the adventitia, and at its internal boundary sud- denly appear to divide into numerous filaments, the ultimate distribution of which has not hitherto been satisfactorily ascer- tained. They seem to terminate in the muscle-cells of the media. Beale considers the presence of ganglion-cells in the vascular nerves as of constant occurrence. The author cannot admit the truth of this general statement, having discovered such cells in only exceptional instances. There is no discerni- ble difference of structure between the vaso-constrictor and the vaso-dilator nerve-fibres. BIBLIOGRAPHY. In addition to the well-known standard treatises by Bichat, Kolliker, Henle, Sappey, Krause, Frey, Leydig, Teichmann, Strieker, Klein, Ranvier, Donders, Vier- ordt, Luschka, Pouchet et Tourneux, the following may be consulted : Ludwig. De arteriarum tunicis. Lipsiae, 1739. Rauschel. De arteriarum et venarum structura. Vratisl., 1836. Robin. Sur la structure des arteres. Compt. rend. 1847. Sciiultze. De art. struct. Gryph., 1850. Remak. Hist. Bemerk. ueber d. Blutgefasswande. Muller’s Arch., p. 96. 1850. Segond. Syst. capillaire sanguin. Th£se. Paris, 1853. Remak. Entwickelung d. Wirbelthiere. Berlin, 1855. Remak. Klappend. Venen. Deut. Klinik. 1856. Hackel. Muller’s Arch. 1857. Luschka. Virch. Arch. XVIII., p. 106. 1860. 162 MANUAL OF HISTOLOGY. Hoyer. Arch. f. Anat., p. 244. 1865. Klebs. Virch. Arch. Vol. XXXII., p. 172. 1865. Aeby. Med. Cent. Zeit. No. XIV. 1865. Curzonszczewsky. Virch. Arch. Vol. XXXV. 1865. Eberth. Virch. Arch. Vol. XLIII., p. 136, and Centralblatt, p. 193. 1865. Auerbach. Virch. Arch. Vol. XXXIII. 1865. Med. Cent. Zeit. No. X. Gimbert. Structure et texture des arteres. These. Paris, 1865. Journ. de l’anat. et de la phys. Robin, p. 536. 1865. Fasce, Luigi. Istologia della arterie. Palermo, 1865. Langiians. Virchow’s Arch. Vol. XXXVI., p. 197. 1866. His. Die Haute und Hohlen d. Korper’s. Basel, 1866. Legros. Journal de l’anat. et de la phys. No. III., p. 275. 1868. ToIjUbew. Beitr. z. Kennt. d. Baues u. d. Ent. d. Capill. Arch. mikr. Anat., p. 49. 1869. Ziegler. Exp. Unt. ueber d. Herk. d. Tuberkelelemente. Wurzburg, 1875. Ziegler. Unt. ueber pathol. Bind. u. Gefassneubildg. Wurzburg, 1876. Kolliker. Entwickelungsgeschichte. Leipzig, 1876. Disse. Arch. f. mikros. Anat. Vol. XVI., p. 1. 1879. Illtmann. Arch. f. mikros. Anat. Vol. XVI., p. 111. 1879. BIBLIOGRAPHY. 385 Von Wrss. Ueber ein neues Geschmacksorgan auf der Zunge des Kaninchens. Centralblatt f. d. med. Wiss. Nr. 35. S. 548. 1869. Derselbe, Die becher- formigen Organe der Zunge. M. Schultze. Arch, fur mikroskop. Anat. VI. S. 238. Krause. Die Nervenendigung in der Zunge des Menschen. Gottinger Nachrichten. S. 423. 1870. Verson. Beitriige zur Kentniss des Kehlkopfes und der Trachea. Sitzgsbr. der wiener Acad. 1 Abth. LVII. S. 1093. 1868. Derselbe, Kehlkopf und Trachea in Strickers Handbuch der Lehre von den Geweben. I. S. 456. Leipzig, 1871. HOnigsciimied, J. Beitriige zur mikroskop. Anatomie der Gescbmacksorgane. Ztschr. f. wissenscb. Zool. XXIII. S. 414. Exner. Med. chirurg. Rundschau, Juni Heft. S. 400. Wien, 1872. Ditlevsen. Unders jgelse over Smaglogene paatungun bos patte dyrene og men- nesket. Kopenhagen, 1872. Referat in Hoffmann und Schwalbe Jahresb. I. Lib. S. 211. 1872. Honigsciimied. Ein Beitrag iib. die Verbreitung der becherformigen Organe auf der Zunge der Siiugethiere. Centralbl. f. d. med. Wiss. No. 26. S. 401. 1872. Henle. Handbuch der system. Anatomie des Menschen. II. 2. Aufl. S. 873. 1873. Von Ebner, Ritter. Die acinosen Driisen der Zunge und ihre Beziehungen zu den Geschmacksorganen. Gratz, 1873. Sertoli, E. Osservazioni sulle terminazioni dei nervi del gusto. Gazetta Medico- Veterinaria. IV. 2. Separatabdruck. Deutsch in Molesch. Unters. XI. 4. Heft. S. 403. 1874. Hoffmann, A. Ueber die Verbreitung der Geschmacksorgane beim Menschen. Arch. f. pathol. Anat. LXII. S. 516. 1875. Watson, W. Spencer. Diseases of the Nose and its Accessory Cavities. London, 1875. Von Brunn. Untersuchungen uber das Riechepithelium. Arch. f. mik. Anat. No. 11. 1875. .Krause, W. Allgemeine und mikroskop. Anat. Hannover, 1876. Voltolini. Address delivered December 15, 1876, before the Silesian Association for National Culture. Krause. Lehrbuch. Hannover, 1876. KOlliker. Ueber die Jacobson’schen Organe des Menschen. Festschrift zu Rineckers Jubilaum. Leipzig, 1877. Ponchet et Tourneux. Precis d’histologie humaine. 1878. Lusciika. Das Epithelium der Riechschleimhaut des Menschen. Centralbl. f. die med Wissenschaft. Nr. 22. 1877. Wundt. Lehrbuch der Physiologie des Menschen. Stuttgart, 1878. CHAPTER XXIV. THE ALIMENTARY CANAL. By EDMUND C. WENDT, M.D., Curator of the St. Francis’ Hospital, etc., New York City. The human alimentary canal is a tube of great length, ex- tending from the mouth to the anus. There are considerable variations of its calibre in the different regions of the body through which it passes. The two external openings of the digestive tract are continuous with the cutaneous surface of the body. Throughout its entire extent we find several super- imposed layers or membranes, which are from within outward : 1, a mucous membrane with its submucosa ; 2, the muscular coat; and 3, a fibrous layer. In addition to these fundamental strata, we encounter certain special structures, which charac- terize the various parts of the canal. The buccal cavity and pharynx are elsewhere described ; we begin, therefore, with a consideration of THE (ESOPHAGUS. The walls of this section of the tract are directly continuous with those of the pharynx, and have an average thickness of from three to four millimetres. In the oesophagus, in addition to the four pharyngeal coats, a new layer appears between the epithelial stratum and the submucous tissue. This new struc- ture has received the name of muscularis mucosae. Hence, the different layers of the oesophagus are from within outward : 1. The mucous membrane. 2. The muscularis mucosae 3. A submucous layer. 4. The muscular coat. 5. A fibrous envelope. The mucous membrane presents comparatively long, coni- THE (ESOPHAGUS. 387 cal papillae of more or less dense connective tissue, containing looped blood-vessels, and lined throughout by stratified pave- ment-epithelium. These papillae attain a marked degree of development in the adult only. In infancy their future pres- ence is indicated by a wavy outline at the internal attached border of the epithelial stratum. This latter portion of the mu- cous membrane contributes 0.22 —0.26 mm. toward the entire oesophageal thickness of about 4.0 millimetres. The muscularis mucosce con- sists chiefly of longitudinal, un- striped muscle-cells. They are disposed in bundles of differ- ent sizes, separated by varying amounts of connective tissue. Toward the inferior portion of the oesophagus these bundles approach each other, displacing the interposed tissue, and form- ing finally one continuous mus- cular layer. The thickness of this layer varies between 0.2 and 0.3 mm. The submucous layer is made up of fasciculated connective tissue and elastic fibres. It contains groups of fat-cells, and lodges the mucous glands. The latter closely resemble the glands found in the mouth. They consist of pyramidal or poly- gonal secreting-cells with conspicuous rounded nuclei, and ducts lined by cylindrical epithelia. The lower portion of the oesoph- agus contains smaller and more superficial acinous glands. In this region they are also found in greater abundance, and around the cardiac orifice they form almost a complete ring. The muscular coat has an inner circular and an outer longi- tudinal layer. In man it is formed of both varieties of muscle- cells, the striped and unstriped. The upper portion is composed of striped muscle only, whereas the lower half consists exclu- sively of the unstriped variety. Below the upper one-eighth of the oesophagus smooth muscle-cells first begin to be blended with the other variety; they rapidly increase as we proceed Fiq. 164.—TmnR-verse section through the lower part of the oesophagus of the newly-born child : a, a, epithelium ; 6, mucosa; c, muscu- laris mucosae ; d, submucous tissue ; e, layer of circular muscular fibres ; f longitudinal muscu- lar layer; y, external fibrous layer ; h, h, two of the ganglia of Auerbach. Klein. 388 MANUAL OF HISTOLOGY. downward, until at about the middle of its course the striped fibres entirely disappear, being replaced by continuous layers of unstriped muscle-cells. The fibrous envelope consists of connective tissue and elastic fibres, arranged so as to form a thin, peripheral, sheath-like membrane. Blood-vessels and lymphatics are found in less abundance in the oesophagus than in the mouth and pharynx. The for- mer are arranged in the shape of capillary networks in the mucosa. The papillary loops, already mentioned, take their origin from these reticula. The larger branches are found in the submucosa. The lymphatics occur as plexuses; one is situated superficially in the mucous membrane, and communi- cates by capillary vessels, with a second larger one, placed in the submucosa. The glands are said to have special lymphatics. Nerves.—An elaborate account of the mode of distribution of nerves in the oesophagus is given in Ranvier’s “ Legons d’ana- tomie generate,” 1880, p. 366 et seq. The following brief sum- mary gives the main points: Nervous filaments proceeding from the pneumogastricsfind their way to the striped muscles, where they terminate in the well-known eminences ordinarily found in that tissue. These terminal bodies are seen to be very numer- ous, a fact which corresponds to the importance and complex- ity of nervous action concerned in the process of deglutition. The terminal distribution in the unstriped muscle presents no striking peculiarity. Between the two layers of the muscle- coat we find an arrangement analogous to Auerbach’s gangli- onic plexus, but the ganglia and their nerve-cells are larger and appear to be more numerous than in the intestine. The nerve- fibres proceeding from the vagus are medullated ; those from the ganglionic plexus belong of course to the non-medullated variety. THE STOMACH. The serous covering of this organ has the same general structure as all visceral peritoneum, being composed of a con- nective-tissue membrane lined by flat endothelial cells. The muscular coat of the stomach is divisible into three layers, composed of, 1, external longitudinal fibres ; 2, middle circular; and 3, internal oblique fibres. All of these belong THE STOMACH. 389 exclusively to the unstriped variety of muscle-cells. A thickening of the inner circular layer constitutes the pyloric sphincter. The submucous layer is composed of loose connective tis- sue, and it is for this reason that the mucous membrane is so freely movable over the muscular coat. It is, moreover, owing to this peculiarity that, whenever and wherever muscular contraction takes place, the mucous mem- brane presents numerous folds, ridges, and eleva- tions. Thus, we may find in a perfectly healthy stom- ach appearances quite an- alogous to those described by pathologists as the so- called etat mamelonne of gastritis. The muscularis mucosae frequently presents two lay- ers of unstriped muscle- cells—an outer longitudinal and an inner circular one. In some regions we observe only one layer of longitu- dinal muscle-cells. The gastr ic mucous mem- brane is covered by a single layer of columnar epitheli- um, containing goblet-cells in greater or less abun- dance. These goblet-cells represent ordinary epitlielia, which appear to be bulged out by mucoid contents. At the cardiac extremity of the stomach there is a sharp, serrated line of demarcation between the oesophageal and gastric epithelial lining. The surface-epithe- lium forms one continuous stratum, and is continued down into the ducts of the gastric glands. The latter occur in two distinct varieties, viz., peptic glands and pyloric glands. The peptic glands, also called gastric glands, are cylindrical Pro. 165.—Transverse section through the fundus of the stomach in a child : a, a, cylindrical epithelium; b, b, peptic tubes ; c, c, muscularis mucosae ; d, d, sub- mucous tissue; e, circular muscular layer: /, longi- tudinal muscular layer ; g, peritoneum ; A, A, ganglion of Auerbach. Klein. 390 MANUAL OF HISTOLOGY. tubules, nearly straight or slightly tortuous, with often a single rounded caecal extremity. However, the latter is sometimes double by dichotomous division, or we find many such blind terminal branches. Hence, we may speak of simple peptic glands and compound peptic glands. They are all placed ver- tically to the surface, and consist of a homo- geneous basement-mem- brane with a lining of secreting epithelia. (Fig. 166.) The basement- membrane contains flat- tened nuclei, and at its inner aspect it is fur- nished with flat, branch- ing adventitial cells. Each gland is divisible into a duct and gland proper. The latter, again, consists of a neck, body, and fundus. Usually, two, three, or even more of these glands, have a common duct. The length of the entire structure varies in the different gastric re- gions from 0.4—2.0 mm., in accordance with the thickness of the entire mucous membrane in the respective parts. .The duct, amounting to about one-fourth of the whole length of the tube, is lined with one contin- uous layer of columnar epithelial cells, similar to the surface epithelium of the rest of the stomach. The neck, the thin- nest portion of the minute tube, has similar cells; but they appear shorter, darker, and have a smaller ovoid nucleus. As regards its breadth, the body stands about midway between Fig. 166.—A, simple gastric gland: P, parietal; and 0, chief cells B, compound gastric gland. Only the outline, denoting the membrana propria, is drawn. TIIE STOMACH. 391 the neck and the fundus, which latter is the thickest portion of the entire gland. In the neck we also tind, in addition to the cells already described, other corpuscles placed externally to the former. They are the parietal cells (Heidenhain), or delomorphous cells (Rollett), the former variety being termed chief cells (Heidenhain), or adelomorphous cells (Rollett), or simply peptic cells. The parietal cells occur as spheroidal, oval, or polygonal, rather opaque, sometimes very granular bodies, which lie beneath the basement-membrane, but com- monly outside the layer of ordinary chief cells. In the body of the gland-tube we again meet with these two forms of lin- ing-corpuscles. Here, however, the columnar or chief cells are longer than in the neck, and their bodies generally appear more transparent, while the nuclei, again spheroidal, are situ- ated nearer the external than the internal border. Klein de- scribes the substance of these cells as consisting of a delicate reticulum, with a small amount of a hyaline interstitial sub- stance in its meshes. The same author, also, invariably finds an intra-nuclear network. Others have been less fortunate in finding such appearances. The parietal cells of the body in all respects resemble those of the neck. As the fundus is ap- proached their number grows comparatively less. The pyloric glands, which some histologists insist on call- ing mucous glands, are lined throughout by a single layer of epithelium. This is composed of the ordinary columnar cells of the gastric surface. But the corpuscles here appear to be somewhat compressed, so that they seem less transparent than elsewhere. They are known to undergo certain changes dur- ing their passage from activity to rest. Examined in the latter condition, we find them more granular, and apparently smaller or shorter, than during and immediately after secre- tion. These glands have long ducts, each one serving for sev- eral secreting tubules. Their bodies are branched, and usually appear somewhat tortuous. When such glandules become somewhat more complex and grow larger (a change which nor- mally takes place in the duodenum), they are called Brunner’s glands. Dr. Edinger has recently (ArcMv f. mihr. Anat., Yol. XVII., p. 193) asserted that the gastric glands contain in reality only one kind of cellular element. He based his opinion on results obtained by treating the almost living mu- 392 MANUAL OF HISTOLOGY. cons membrane with osmic acid, after Nussbaum’s method. By him the chief cells are said to develop into parietal cells, through an increaS3 of their volume and a filling up with the gastric ferment. The considerations which led him to form this opinion are as follows : 1, the occurrence of bodies which represent transition-forms between chief cells and parietal cells ; 2, the analogy of this assumed metamorphosis of gas- tric corpuscles (i.e., the conversion of chief cells into parietal cells), with similar changes, known to occur in other glands during active secretion ; 3, the fact that many animals which secrete pepsin have only the parietal cells ; 4, the results of an examination of the mucous membrane of starving animals, which revealed only the chief-cell form of gastric corpuscles; and 5, the apparent discrepancy in the descriptions of these bodies by competent histologists—some observers regarding the chief cells, others the parietal cells, as exclusively pepsin- ogenous. Still more recently, Stolir has (Verhandl. d. phys.-med. Gesel. in Wurzburg, 1881, p. 101) studied the histology of the gastric epithelium. His specimens were derived from the fresh stomach of a criminal immediately after execution of the latter. The man had taken no nourishment for some hours before his death. The principal conclusions of Stolir are: 1, the epithe- lia of the mucous glandules are not destroyed during the pro- cess of secretion, but, like those of the true gastric glands, con- tinue their existence; 2, the parietal groups of cells represent those portions of the mucous corpuscles which have not un- dergone mucoid metamorphosis, being made up of unaltered protoplasm. From the above contradictory statements it appears that even to-day our intimate knowledge of the gastric mucous membrane, and especially its epithelia, is far from being in a satisfactory condition. It will have to be reserved for future investigations to dispel the uncertainty still existing with re- gard to some of the most interesting details of the pliysiologico- histological characteristics of the inner coat of the stomach. The blood-res sets of the stomach have an arrangement simi- lar to that of the oesophagus. In the mucous membrane, how- ever, we find abundant plexuses of capillary vessels surround- ing the gastric glands. These networks intercommunicate, and just beneath the surface-epithelium they become especially THE STOMACH. 393 close. From this point the veins take their origin. The ve- nous rootlets unite in a stellate manner to form larger branches, which descend almost vertically and empty into a venous retic- ulum situated between the glandular layer and the muscularis mucosae, and just above a similar arterial network. Lymphatics abound in the stomach. They appear to arise from superficial loops, which, anastomosing between the Fig. 167.—Lymphatics of the gastric mucous membrane of the human adult. Frey. glandular tubules, reach the fundal zone of these structures. There they form a network, and this is in communication with a plexus of larger vessels, situated in the submucous tissue. The distribution of the gastric nerves does not differ mate- rially from that of the small intestine, in the description of which this matter will receive more particular attention. Gan- glion-cells are frequently found both in the muscular layer and the submucosa; in the latter we have a tolerably distinct plexus of nerve-filaments and ganglion-cells. Of the normal occurrence in the walls of the stomach, of true lymphoid follicles, the author has been unable to find convincing evidence. Nevertheless some writers assert that they are always to be found there. 394 MANUAL OF HISTOLOGY. TIIE SMALL INTESTINE. The serous coat presents no structural characteristics pecu- liar to itself, closely resembling the gastric peritoneum. It encloses a muscular coat and the mucous membrane, which are held together by connective tissue. The average thickness of these layers does not, in man, exceed 1.0 mm., of which three-fourths belong to the muscular, and one-fourtli to the Fig. 108.—Longitudinal section of the small intestine of a rabbit: Z, Z, villi; J, crypts; Pp, a Peyer's patch; K, cap of a follicle; S, submucosa; m, m, muscularis mucosae; It, circular muscular layer; L, longitudinal muscular layer; P, peritoneum. Verson. mucous coat. Of course, the contracted or relaxed condition of the intestinal tube at the time of measurement will appre- ciably influence these figures. But they represent the general ordinary average. The muscular coat has an external longitudinal and an in- ternal circular layer. Between the two we find Auerbach’s THE SMALL INTESTINE. 395 plexus myentericus of flat nerve-fibres, which will be described farther on. The muscle-coat becomes gradually thinner as we pass from the duodenum to the ileo-csecal valve. In the for- mation of this thickened fold the longitudinal layer does not participate. The unstriped muscle-cells have an average length of 0.255 mm., and are about 0.005 mm. broad. They are arranged in bundles, surrounded by connective-tissue bands, with which elastic elements are abundantly interwoven. The mucous membrane is thrown into folds, and is studded with closely placed projections, called villi. The general di- rection of these folds, the valvules conniventes Kerkringii, is parallel to the transverse course of the circular muscle-layer. They run parallel to one another, or join at acute angles. The villi jut out into the lumen of the intestinal canal, as variously shaped projections, of an average length of 0.04—0.6 mm., and an average breadth of 0.06—0.12 mm. In general their form may be said to be conical or cylindrical: but we always en- counter a great variety of shapes, in accordance with the varying states of contraction in the mas- cularis mucosae. Each villus con- sists of a large-meshed reticulum of connective tissue, infiltrated, as it were, with leucocytes, and con- taining flattened corpuscles, which resemble endothelial cells. One or several spaces, situated in the cen- tre of every villus, constitute the origin of the lacteal tubes. Ac- cording to Briicke, these chyle- vessels are covered by thin, but not continuous bundles of smooth muscle-fibres. Their walls show only a single layer of ordinary endothelial cells, with clear oval nuclei. The free surface of the villi, like that of the stomach, is covered by a single layer of columnar epithelium. Each cell presents, in the recent state, a finel}r striated hyaline band at its unattached border. This structure has, at different times, received various interpretations, and even now opinions Fig. 169.—Section of a villus from the intestine of a rabbit: a, epithelium; 6, stroma; c, central cavity. Verson. 396 MANUAL OF HISTOLOGY. are much divided as to its true significance. Some histologists regard the strire as indicating so many minute pores for pur- poses of absorptive transmission; others believe that the jux- taposition of numerous delicate rods explains the peculiar ap- pearance ; and Klein has lately asserted them to be merely prolongations of the fibrils of the cell-substance composing the epithelia. These striae are always seen to run parallel to the long axis of the cells. Krause also described as of normal occurrence, a basal pro- cess extending at an obtuse angle from the attached surface of these bodies, and inserted into the delicately serrated border of the villi. Near its attached border each epithelium presents a bright ovoid nucleus, with one or more distinct nucleoli. Besides the ordinary corpuscles, we find interposed between them the so-called goblet-cells. These are derived from the former by mucoid infiltration of the cell-body, which is there- fore conspicuously bulged out. Lymph-corpuscles also occur between the epithelia. Immediately beneath this layer we find a delicate, homo- geneous basement-membrane, composed of flattened cells, re- sembling endothelia. The muscularis mucosce, or muscle of Briicke, is made up of a single or double layer of smooth muscle-cells. When double, an inner circular may be distinguished from an external longi- tudinal coat, both being always very attenuated. The submucous layer is formed of connective tissue, the supporting framework of which contains lymphatics, blood- vessels, nerves, and often groups of fat-cells. The glands of the small intestine are those of Brunner and the crypts of Lieberkiihn. In addition to these, however, there occur numerous lymphoid follicles, which, when found singly, are known as the solitary follicles, and, when grouped together, as agminated glands, or Peyef s patches. The solitary or closed follicles are real lymphoid glands, and, like these, con- sist of reticulated connective tissue, the meshes of which are replete with lymph-corpuscles. The jejunum, ileum, and colon all contain such follicles, but the agminated glands occur in the ileum, abounding especially at its lower part. Around each follicle we find a ring of villi and glands, which arrange- ment goes by the name of corona tubulorum (Muller). The follicles receive an enveloping layer of fibro-connective tissue. THE SMALL INTESTINE. 397 Brunner's glands lie in the submucosa, where they form closely crowded tubules, separated by a small amount of con- nective tissue. Smooth muscle-cells, starting from the muscu- laris mucosae, are often seen to pass between them. These con- voluted tubules resemble and correspond to the gastric glands, but have here attained a much greater degree of development. Fig. 170.—Vertical section thronerh a human Foyer's patch, with its lymphatics injected : a. intestinal villi with their lacteal : b. Lieberkiihnian fdands: c, muscular layer of the mucous membrane: d, apex of the follicle; e, middle zone of the follicle; /, basis portion of the follicle ; g, continuation of the lacteals of the intestinal villi into the mucous membrane proper: A, reticular expansion of the lymphatics in the middle zone; i, their course at the base of the follicle ; Ic, continuation into the lymphatics of the submu- cous tissue; I, follicular tissue in the latter. Frey. They also appear to have been pushed down, as it were, from the mucous into the submucous layer. An individual gland consists of its long duct lined by col- umnar epithelium, and the branched tubules, which frequently have terminal clusters, resembling true acini. They are, how- ever, only secondary or tertiary diverticula, so that Brunner’s glands really conform to the compound tubular type of secret- ing structures (Renaut). Each ultimate diverticulum has an external membrana propria composed of flattened endothelial cells, and a lining of cylindrical, columnar, or prismatic secret- ing epithelia, containing oval nuclei. Histologists have described minute capillary channels pro- ceeding from the central lumen of the gland, between the se- creting-cells, ending just underneath the membrana propria. The author believes these intercellular channels, as they have 398 MANUAL OF HISTOLOGY. been called, to be the artificially altered cement-substance al- ways present between such adjacent cells. Brunner’s glands abound only in the duodenum, but a few may occasionally be seen lower down the intestine. Their ducts, after traversing the muscularis mucosae, ascend almost vertically between the crypts, opening on the free surface of the mucous membrane. Fig. 171.—Crypts and interfollicular connective tissue, from the intestine of the rabbit: K, crypt; o, «, epithelium; d, adenoid tissue, from which the cells have been removed by pencilling; T, fibrous tissue on the opposite side. Verson. These crypts represent open spaces within the so-called follicles of Lieberkuhn, which are tubular glands placed verti- cally in the intestinal mucous membrane, existing throughout its entire extent. They form a continuous layer, except where the upward projection of a lymph-follicle creates an interruption. These glands open at the base of the villi, the epithelial covering of the latter being continued down into the tubular depressions which they constitute in the mucous membrane. The cells of this stratum naturally appear broader at their attached than at THE SMALL INTESTINE. 399 their free extremities. A continuation of the villous basement- membrane forms the membrana propria of the crypts of Lie- berkiihn. External to this we find the surrounding connective tissue, which is disposed in reticula, containing many leuco- cytes in its meshes. Hence it is also known as adenoid tissue. The blood-vessels enter and leave the intestine at the me- senteric margin. The arteries, generally accompanied by one or two veins, pierce the muscle-coat, giving off branches which form networks in those layers, then enter the submucosa, where they run parallel to the surface of the mucous membrane, and finally send off vertical arterioles at the base of the villi. The latter ascend on one side of the villus, and then-suddenly divide into a dense capillary network. This division takes place near the middle, the capillaries then spreading out to the apex and periphery. Here they become quite superficial, being covered by the epithelial lining only. The venous rootlets of the villus are generally two, or even three in number. About the glands and follicles we encounter special networks with variously shaped meshes. Lymphatics are found in all the layers of the intestinal canal. Those of the serous coat empty into the large mesen- teric trunks. In an inward direction we also find a network of lymph-capillaries between the two layers of the muscle-coat. The submucous layer contains the perifollicular lymph-sinuses situated at the base of these bodies, and a reticulum of larger channels, many of which are found provided with valves. The lymphatics of the mucous membrane are present in the shape of capillary networks surrounding the intestinal glands. In the villi we note, as already stated, one or more central lacteals, communicating at the base of these structures with the lymph-vascular networks situated around and between the glands. The nerves of* the intestine are known as the plexus of Auerbach, and of Meissner. The former, situated between the circular and longitudinal fibres of the musculosa, is com- posed of flattened nerve-branches, made up of numerous ulti- mate fibrils. Small nodules, containing characteristic gan- glion-cells, are also found, while little twigs are given off from the plexus myentericus, to be distributed to the layers of the musculosa. The plexus of Meissner is situated in the submucous tis- 400 MANUAL OF HISTOLOGY. sue. Its component nerves are less flattened, but are likewise provided with ganglia containing variously shaped ganglion- cells. This plexus also gives origin to the secondary networks of the muscularis mucosae, and is besides connected by certain branches with Auerbach’s plexus. THE LARGE INTESTINE. The histological structure of the colon, broadly speaking, very nearly resembles that of the preceding section of the ali- mentary canal. The lining epithelium of the mucous mem- brane presents the same characteristic appearances as in the Fio. 172.—Section of the large intestine of a rabbit: .7, crypts of Lieberkuhn : a, epithelium ; 6, mu- cosa ; m, muscularis mucosae ; s, submucosa: li, circular muscular layer; L, longitudinal muscular layer; p, peritoneum. Verson. small intestine. The mucosa of the colon is, however, devoid of villi; but it shows numerous crescentic folds. The muscu- laris mucosae will be found to answer to the description already given of that layer in the small intestine. The submucosa also shows the same morphological compo- sition, but appears to be much richer in deposits of fat-cells. Aggregations of lymph-follicles are not generally found, but large, conspicuous solitary glands abound throughout. The crypts of Lieberkuhn are identical with the glands of TIIE RECTUM. 401 the same name found in the small intestine. As we approach the rectum an increase in their length becomes apparent. In the vermiform appendix we find the collection of solitary lymph-follicles so closely placed that the space left between adjoining glands does not equal in diameter that of these struc- tures themselves. The longitudinal layer of the muscle-coat is quite thin be- tween the taeniae coli, or flat longitudinal bands of the large intestine. These bands themselves represent thickened layers of the musculosa. It appears that the circular fibres are espe- cially developed in the portions between the sacculi of the caecum and colon. The blood-vessels are arranged after the same plan as in the small intestine. In the submucosa are contained large trunks, running parallel to the surface. Capillaries arise from these, and ascend almost vertically between the crypts of Lieberkuhn, the capillary network surrounding those structures being only moderately developed. As regards the lymphatics, they have a distribution similar in all essential respects to that found in the small intestine. The nerves likewise imitate in their structure and arrange- ment those encountered in the small intestine. Meissner’s plexus appears to be provided with comparatively large gan- glia and relatively small component cells. The plexus of Auerbach also attains conspicuous development in the large intestine. THE RECTUM. The internal sphincter ani represents a thickening of the circular layer of the muscle-coat. In its upper portion the rectal mucous membrane is like the same structure of the large intestine. Lower down we find the columnar epithelium grad- ually replaced by stratified pavement-epithelium. The follicles of Lieberkiihn are large and long. Finally, the mucous membrane gradually passes into the ordinary in- tegument surrounding the anal orifice. The blood-vessels, lymphatics, and nerves resemble in their distribution those of the colon, and are devoid of characteristic peculiarities. 402 MANUAL OF HISTOLOGY. BIBLIOGRAPHY. Bceiim. De glandularum intest, struct, penit. Berol., 1835. Henle. Symbol, ad anat. vill. intest. Berol., 1837. , Bischopf. In Muller’s Archiv, p. 503, 1838. Wasmann. De digestione nonnulla. Berol., 1839. Middeldorpf. De glandulis Brunnianis. Vratisl., 1846. Brettauer and Steinach. Unt. iiber d. Cylinderepithel. Vienna, 1857. Leydig. Histologie. 1857. Auerbach. Ueber einen Plexus myentericus. Breslau, 1862. Auerbach. Virch. Arch., VoL XXXIII., p. 340. 1865. Letzerich. In Virchow’s Archiv, Vol. XXXVII., p. 232. 1866. Eimer. Zur Geschichte der Becherzellen. Berlin, 1868. Schwalbe. Arch. f. mikros. Anat., Vol. VIII., p. 92. 1872. Heidenhain. Arch. f. mikros. Anat., Vol. VIII., p. 279. 1872. Gerlach. Ber. d. sachs. Ges. der Wiss. Leipzig, February, 1873. Krause. Handb. d. menschl. Anat., Band I. 1876. F. Hoffmann. Die Follikel des Dunndarms beim Menschen. Munich, 1878. Sertoli. Contribuzioni all’ anatomia della mucosa gastrica. Arch, di med. veter. Fasc. 3, p. 15. 1878. Rudinger. Beitr. z. Morphol. d. Gaumenseg. u. des Verdauungsapp. Stuttgart, 1879. H. Sewall. Devel. and Regen. of the Gastric Gland, Epithel., etc. Journal of Phys., Vol. L, p. 321. 1879. Edinger. Zur Kenntniss d. Driisenzellen d. Magens. Arch. f. mikros. Anat., Vol. XVII., p. 193. 1879. Ranvier. Les muscles de l’oesophage. Journ. de micrographie, III., p. 9. 1879. Renaut, G. Note sur la structure des glandes a mucus du duodenum. Gaz. mod. de Paris, No. 41, 1879, and Progres mod., No. 23, p. 439. 1879. Ranvier. Leqons d’anat. generale. Paris, 1880. P. Stohr. Ueber das Epithel. des menschl. Magens. Verhandl. der phys.-med. Gesellschaft in Wurzburg, p. 101. 1881. THE THICK CUTIS VERA. 427 would aid the contraction of the muscle. In specimens where the muscle is found in a state of contraction, the liair-follicle is bent like a bow, the root being drawn through the arc of a circle. The presence of fat near the hair-bulb is made possible by this structure, a condition which is constant with all hairs. That the fat is not an incidental feature of their structure, which might be considered merely a cleft for the transmission of vessels, is rendered probable by the observation of rows of fat-cells beneath each hair in the lip of the rat, where no special channels exist, and, also, by the fact that such columns of fat do not accompany the nutrient vessels of the skin, in those parts where the hairs are not found. It seems, therefore, probable, that this structure has some bearing upon the nu- trition of the hair. Sweat-glands are found not only in these canals, but else- where in the thick cutis ; the coil of the gland is then usually situated at a level a little below the middle of the cutis vera, and not in the subcutaneous adipose tissue, as in thin skin. CHAPTER XXVII. URINARY EXCRETORY PASSAGES; SUPRARENAL CAPSULES. By EDMUND C. WENDT, M.D., New York City, Curator of the St. Francis Hospital, etc. Tiie renal pelvis, the calices, ureters, and bladder, all consist essentially of three layers, which are an inner mucous mem- brane, a middle muscular coat, and an external fibrous layer. In the EEXAL PELVIS we find the mucous membrane lined with stratified epithelium, the cells of which are large and variously shaped. Three dif- ferent forms are readily distinguished. The most superficial layer consists of flat or polyhedral cells of various sizes, each one containing a round or oval nucleus, or, as frequently hap- pens, two nuclei. Peculiar dark granules, often of large size, surround the nucleus, and are quite distinct from the finely granular protoplasm of these cells. Then comes a layer of conical or club-shaped bodies, each one again furnished with a round or oval nucleus. Every cell also possesses a long basal process, which appears to attach it to the subjacent tissue. The bulbous portion of these corpuscles is turned outward in the direction of the surface. Wedged in between the processes just mentioned we find the third variety of cellular elements. These are oval or rounded bodies contain- ing ellipsoid nuclei. At the renal calices we find a sharp line of demarcation between the cylindrical columnar epithelium of the papillary ducts and the stratified pavement epithelium of the pelvis. The epithelial layer has a thickness here of 0.045-0.09 mm. The connective-tissue portion of the mucous membrane is devoid of papillae, contains sparse elastic fibres, and is rich in THE URETERS. 429 fixed corpuscles, the inoblasts of Krause. There is no true basement-membrane. Below this stratum we find a submu- cous layer, which is abundantly furnished with elastic tissue, and contains a few simple acinous glands with ducts having a lining of cylindrical epithelium. The muscular coat is composed of bundles of smooth mus- cle-cells forming an inner layer, with a peripheral direction of its constituent anatomical elements, and an outer layer concen- trically arranged. The “papillary sphincter” is but a thick- ening of this latter layer. The external fibrous layer forms a thin connective-tissue membrane, not always clearly marked here, whereas in. the ure- ters and bladder it is found to be well developed. The blood-vessels of the pelvis are derived from the renal artery and vein, and form capillary networks characterized by polygonal meshes. The lymphatics and nerves are found to have the same distribution as in the ureters. THE URETERS have a structure which closely resembles that of the renal pel- vis. The mucous membrane shows the same varieties of epithe- lium ; its connective-tissue components are similarly arranged ; and the external investing membrane is composed of the same kind of tissue already described. But in addition to the two muscular layers, which here attain a greater development, we find a third muscle coat, so that we can now distinguish an in- ternal and external longitudinal from a middle circular layer of muscular elements. Engelmann has described a close reticulum of blood capil- laries lying immediately under the epithelial stratum, but its existence is made doubtful by the negative statements of other authors. Glandular bodies are not found in the ureters. The peri- pheral layer of fibrous connective-tissue possesses conspicuous elastic bundles in the lower portion of the ureters. The distribution of the blood-vessels is like that of the pel- vis already described. The lymphatics are well developed here, forming several networks in the different layers of the ducts. Nerves are likewise readily distinguished, some of the nerve- 430 MANUAL OF HISTOLOGY. fibres being also furnished with ganglion cells. Their mode of termination in the muscular layer is not definitely known, but may be assumed to resemble that of ordinary smooth muscu- lar-tissue. THE BLADDER lias the same type of structure as the ureters, but contains, in addition, a serous covering in its upper portion. The different coats of the bladder are, however, much thicker than the cor- responding layers in the other urinary excretory passages. The epithelial lining of the mucous membrane shows the three varieties of its cellular elements in a clearly defined man- ner. The connective-tissue stratum presents no noteworthy pe- culiarities, if we ex- cept the comparative abundance of simple acinous glands. The bundles of muscle-cells in the muscular-coat inter- lace, forming irregu- lar, long-stretched meshes. This irregu- lar arrangement pre- vents tlie distinct rec- ognition of successive layers, each with a largely prevailing di- rection. Nevertheless, we find in the external portion of the muscle-coat some pre- dominance of longitudinal bundles, together with an abundant supply of elastic fibres. The anterior wall and vertex of the bladder show this arrangement very conspicuously, in fact the muscle-fibres have here received a separate name, that of detru- sor urince. The vesical neck shows a tolerably distinct thicken- ing of its circular muscle-fibres, which is known as the sphincter vesicce. It should always be borne in mind that the arrange- ment of the muscular coat is apt to vary in different individuals, the description here given will, however, be found to apply to the majority of cases. Pig. 182.—Epithelium of the urinary bladder, a, a cell of the second layer ; 6, a cell of the first layer ; c, shows the first, second, and third layers of the epithelium in connection. Obersteiner. SUPRARENAL CAPSULES. 431 The blood-vessels form a capillary network in the mucous membrane, which is situated about midway between the epi- thelial stratum and the muscular coat. In other respects they present no peculiarity worthy of note. The lymphatics are less abundant in the bladder than in the ureters. They, also, lack noteworthy peculiarities or special features of interest. Plexuses of nerve-fibres are found in the subserous connec- tive-tissue, and also in the muscular coat. Microscopic ganglia and groups of ganglion cells are also met with. SUPRARENAL CAPSULES. The suprarenal capsules (glandules suprarenales) are small flattened bodies, two in number, situated somewhat above and Fig 183.—Cellular groups and trabeculae of the cortical substance, from the suprarenal capsule of the Frog. Eberth. iii front of the upper end of either kidney. They are usually triangular or semilunar in shape, although round and oval forms are also met with. In structure they resemble the so- 432 MANUAL OF HISTOLOGY. called blood-vascular glands, but their function is not known. They belong to the ductless variety of glands. Each suprarenal body consists of a capsule inclosing the paren- chyma, which shows a cortical and medullary substance. The cap- sule is formed of ordinary connec- tive tissue containing many deli- cate elastic fibrils. Externally it is surrounded by loose connective tissue, containing a greater or less proportion of adipose tissue, and internally it sends out trabecuhe, which traverse the entire organ, thus constituting and completing its frame-work. The cortical substance, as its name implies, occupies the exter- nal portion of the suprarenal body. It has an average thickness in man of 0.28 to 1.12 mm., is of a yellow- ish color, and may be divided into three layers or zones. The lim- its of demarcation between these layers are much less marked, however, than the corresponding boundary line between the corti- cal and medullary portions. In the human being the external layer of the cortex is distinctly separate from the middle one, but the latter shows no such sharp limit against the innermost layer. The cortex is a friable substance, and its broken surface presents a striated appearance. Owing to rapid post-mortem changes, the cortex in man is usually found to be separated from themedul- lary portion by a dirty brownish substance, containing modified blood and cortical corpuscles. Fig. 184.—Perpendicular section through the suprarenal capsule of man : 1. cortex ; 2, medulla; a, capsule; b, layer of outer cell- groups ; e, layer of cell-trabeculae (zona fasci- culata}; d, layer of inner cell-groups ; e, med- ullary substance; /, transverse section of a vein. Eberth. Fig. 185.—Single cells and cell-groups of the outermost cortical layer. Human suprarenal cap- sule. Eberth. 433 SUPRARENAL CAPSULES. The three layers of the cortex are an external one, or zona glomerulosa ; a middle one, or zona fasciculata / and an in- ternal one, or zona reticularis. The external layer consists of rounded or oval groups of cells, separated by delicate connective-tissue trabeculm, which spring from the capsule. Similar cells are found throughout the entire cortex. They have been called the parenchymatous bodies or cells, although a better name is cortex corpuscles. In structure they resemble ordinary cells, consisting of poly- Fig. 186.—Horizontal section through the outermost cortical portions of the suprarenal capsule of the Horse, a, blind termination of a cylinder ; b, groove-shaped and cylindrical cortical trabeculae; c, stroma. Eberth. liedral masses of protoplasm furnished with spherical nuclei and conspicuous nucleoli. Their protoplasm has a coarsely granular character, and, as a rule, contains more or less fat in greater or smaller droplets. The middle layer contains cortical corpuscles which are ar- ranged in almost parallel rows, and are so closely packed that this portion acquires a distinctly striated appearance. These cellular columns have received various names. By Ecker they were called gland tubules, Kolliker termed them cortical cylin- 434 MANUAL OF HISTOLOGY. ders, Eberth described them as cylindrical cell-trabeculae, or cortical trabeculae, and Krause named them cellular pillars. These cellular rows, columns, or streaks, are by no means always cylindrical, for on cross-section they frequently present a semilunar, oval, or bean-shaped appearance. Their inner and outer terminations have a rounded shape, and near the former place they seem to anastomose with one another. At T’ig. 1S7.—Vertical section through the the cortical portion of the suprarenal capsule of the Horse, a, capsule; 6, cell-trabeculae ; c, cell-groups. Eberth. the peripheral end they sometimes appear groove-shaped, or in liorse-slioe form. Connective-tissue processes communicating with the cap- sule are found between the cell columns, but the latter are not completely isolated by them. These connective-tissue streaks also send otf transverse or oblique fibres, so that occasionally the cells of the middle layer seem to be inclosed in basket-like meshes. In addition to fat-droplets, granules of pigment are SUPRARENAL CAPSULES. 435 found in the cells of the innermost portion of the middle layer. The external layer is made up of irregularly arranged cor- tical corpuscles. Nearly all the cells of this layer contain pigment granules. The connective-tissue here forms a reti- culum, with variously shaped meshes, which contain greater or smaller heaps of cells. The medullary substance has a whitish-gray appearance, and is of a more delicate consistency than the cortex. It consists Fig. 188.—Vertical section through the medullary substance of the suprarenal capsule of the Cow. a, blood-vessels; 6, trabeculfe of medullary cells. Strieker. of a network of connective tissue, which contains in its meshes the medullary corpuscles. These are pale cells with spherical nuclei and large nucleoli. They may assume various shapes. In man they are generally of an irregularly stellate or polyg- onal form. Their protoplasm is finely granular, and they con- tain, as a rule, much less fat and pigment than the cortical corpuscles. Kolliker finds that they resemble the nerve-cells of the central nervous system, but he adds that they cannot be regarded as such nerve-elements. The medullary cells assume a yellow or brownish color when treated with chromate of potash or chromic acid. Since the cortex corpuscles are not thus colored, this peculiarity may serve to distinguish one cellular variety from the other. The connective-tissue framework of the medulla is called its 436 MANUAL OF HISTOLOGY. stroma, and its meshes in man have an oval or rounded form, so that, as a rule, the cell-groups have a similar shape. On the whole, we find a smaller proportion of connective tissue in the medulla than in the cortex. The blood-vessels of the suprarenal capsules occupy the stroma, and are found in great abundance. The arterial vessels arise from the aorta, the phrenic and renal arteries, and the coeliac axis. About twenty small branches pierce the capsule, and are distributed mainly to the cortex. The medullary sub- stance is very rich in venous plexuses. Capillary networks are found in both cortical and medullary portions. The veins uniting form one principal branch, which passes out at the lii- lus of the organ. The right suprarenal vein empties its blood into the vena cava inferior, the left one into the vena renalis sinistra. Lymphatics were seen by most observers only at the sur- face of the suprarenal capsules. Klein, however, has recently asserted that there exists between the cells “an anastomosing system of narrower and broader clefts, channels, and lacunae, which belong to the lymphatic system.” This applies to the zona fasciculata. In the other portions of the organ the same writer also finds lympli-spaces, and lymph-sinuses, occupying the regions “between the septa and trabeculae of the frame- work on the one hand, and the cell-groups on the other.” The nerves occur in comparatively greater abundance in these organs than in any other glandular structures of the hu- man body. Kdlliker was able to count thirty-three branches in a single suprarenal capsule of a man. They are derived from the renal plexus, the pneumogastric and phrenic nerves, and semilunar ganglion. Very fine or medium-sized, dark-bor- dered fibres are commonly encountered, and they abound espe- cially in the medulla. Ganglion-cells are also frequently seen, and Virchow has traced them into the interior of the organ. In the cortical substances they are of rare occurrence. The terminal distribution of the nerves has not been hitherto ascertained, and it appears to be still a matter of doubt whether they ter- minate in the suprarenal body at all. Development.—In mammals the suprarenal capsule has an independent origin in a collection of tissue between the Wolff- ian bodies behind the mesentery and in front of the abdomi- nal aorta. (Kolliker.) The mesoderina at this point assumes BIBLIOGRAPHY. 437 a special structure. Certain of its cells form more or less cyl- indrical masses with a reticulated appearance. Between these cellular groups a network of blood-vessels is soon found, so that the whole structure is now not unlike embryonal hepatic tissue. In rabbits, Kolliker saw the first traces of these bodies about the twelfth or thirteenth day. On the sixteenth day they had already attained a length of 1.56 mm., and occupied a position along the vertebral column from the first to the fourth and part of the fifth lumbar vertebra. On cross sections of em- bryos sixteen days old, Kolliker found that the suprarenal cap- sules were distinctly separate at their upper borders, whereas their lower ends were joined together to form a single organ. The same writer also found a nervous ganglion at the coalesced central portions of somewhat older embryos. Behind the suprarenal capsules a second sympathetic ganglion was discovered. Remak and v. Brunn do not in all respects corroborate the statements of Kolliker. The latter was unable to ascertain any existing relationship between the nervous system and the suprarenal capsules. BIBLIOGRAPHY. Bergmann. De glandulis suprarenalibus. Diss. inaug. Gottingen, 1839. Ecker. Der feinere Bau der Nebennieren beim Menschen und den vier Wirbelthier- klassen, 1846. Article “ Blutgefiissdrusen ” in Wagner’s Handworterbuch der Physiologie, Bd. IV. 1849. H. Frey. Art. “ Suprarenal Capsules” in Todd’s Cyclopaedia of Anat. 1849. Remak. Untersucbungen ueber der Entwickelung d. Wirbelthiere. Berlin, 1853- 1855. Virchow. Zur Chemie der Nebennieren. Virchow’s Archiv, 1857. Leydig. Lehrbuch der Histologie, 1857. B. Werner. De capsulis supraren. Dorpat Dissertatio. 1857. Vulpian. Gaz. mod., p. 659. 1856; p. 84, 1857. Gaz. hebd., p. 665, 1857. G. Harley. The Histology of the Suprarenal Capsules. Lancet, June 5th and 12th, 1858. Barkow. Anat. Unters. ueber die Harnblase. 1858. Palladino. Estratto del bulletino dell’ ass d. natur e med. Anno I., No. 5. Napoli. BuRCKnARDT. Virchow’s Arch., Vol. XVII., p. 94. 1859. G. Joesten. Archiv fur phys. Heilkunde, S. 97. 1864. A. Moers. Virchow’s Archiv, Bd. XXIX., S. 336. Henle. Anatomie des Menschen. Bd. 2. 1866. 438 MANUAL OF HISTOLOGY. Arnold, Jul. Ein Beitrag zu der feineren Structur und dem Chemismus der Ne- bennieren. Virchow’s Archiv, Bd. 35, S. 64. 1866. Holm. XJeber die nervosen Elemente in den Nebennieren. Sitzungsberichte der Wiener Akademie. Ed. 53, 1. Abtheilung. 1866. Grandry. Structure de la capsule surrenale. Journal de l’anatomie et de la physi- ologie. 1867. KOlliker. Handbuch der Gewebelehre. 5. Aufl. 1867. Eberth. Strieker’s Archiv. Kisselefp. Centralblatt, No. 22. 1868. Bouvin. Over der bouw en de beweging der Ureteres. Utrecht, 1869. Engelmann. Zur Phys. d. Ureters. Pfliiger’s Arch., Vol. II., p. 243. 1869. Obersteiner, in Strieker’s Manual. Unruh. Archiv f. Heilkunde, p. 289. 1872. v. Brunn. Archiv f. mikr. Anat., Vol. VIII., p. 618. 1872. Egli. Arch. f. mikros. Anat., Vol. IX., p. 653. 1873. Hamburger. Zur Histol. d. Nierenb. u. d. Harnleiter. Arch. f. mikr. Anat., Vol. XVII., p. 14. 1879. See also the text-books of Frey, Krause, Kolliker, and Henle. Braun. Ueber Bau u. Entw. der Nebennieren bei Reptilien. Zool. Anzeiger, Vol. II., No. 27, p. 238. 1879; und Arbeiten aus d. zool.-zootom. Institut in Wurzburg, Vol. V., p. 1. 1879. Kolliker. Entwickelungsgeschichte des Menschen. Leipzig, 1879. Klein, and S. Noble Smith. Atlas of Histology. 1880. CHAPTER XXVIII. THE MAMMARY GLAND. BrW. H. PORTER, M.D., and EDMUND C. WENDT, M.D., of Netf York City. General considerations.—By virtue of its intimate associa- tion with the function of reproduction, this organ occupies a distinctly peculiar position among the glands of the body. In the male it persists through life in the same rudimentary form which characterizes the mamma of both sexes at birth. Only in the female, and in her only at certain times, does this organ attain its complete histological maturity. It may be borne in mind, however, that in a few anomalous cases, male beings sup- plied with fully, developed mammary glands have been ob- served. After conception, and as pregnancy advances, progressive evolution takes place within the mamma. This unfolding process at length culminates in exaggerated tissue-metamor- phosis, which in other organs we should scarcely hesitate to call pathological. In fact, Virchow and his followers all main- tain that the secretion of milk is the direct result of a fatty degeneration of mammary epithelium, and similar in all essential respects to the processes involved in the elaboration of the seba- ceous material from the cutaneous glands of that name. Bill- roth, indeed, calls the mammae cutaneous fat-glands {Hautfett- drusen), and he does this in consideration of the mode of their development, and because they are placed immediately be- neath the integument. In spite of these statements, however, we must maintain that the mammae are radically different from ordinary sebaceous glands, and that the processes of secretion in the two sets of glands are quite distinct. The grounds on which we base this opinion will be amplified farther on. The secretory activity of the gland, consisting in the elaboration of milk, is, as a rule, called into play only during the period 440 MANUAL OF HISTOLOGY. of rapid growth and development already alluded to. In ex- ceptional instances, however, lacteal fluid may be secreted during the extra-puerperal period. The mammae belong to the class of compound acinous or race- mose glands, and, like the other organs of this group, consist of a framework or stroma, and a proper secreting structure or parenchyma. As they appear to the naked eye, the bulk of the breasts is not their secreting parenchyma, but ordinary adipose tissue. This fills out the intervals between the lobes and lobules, and gives to the entire organ its smooth, round form. The different lobes have separate secretory ducts, which open upon the nipple. These ducts ramify throughout the substance of the gland tissue, and ultimately carry upon their terminal branches the clusters of secreting vesi- cles, called acini or alveoli. Accord- ing to Zocher and Hennig, the true glandular substance has not a rounded shape, but shows a grouping into three principal divisions, one of which ex- tends far up in the direction of the axilla. It is separated from the axillary lymphatic glands only by a small amount of adipose tissue. This would explain the ease, readiness, and frequency with which these glands become implicated in ma- lignant disease of the mamma. Since the glands at birth differ very widely from the mamma? of adult women, and still more widely from those of pregnancy, it will be convenient to consider the histology of the organ under different aspects. This will be necessary, however, only with regard to the acini and the epitlielia therein implanted, as these alone show such wide morphological divergencies in the dif- ferent phases of existence. The nipple (teat, mamilla, papilla mammce) is the one struc- ture belonging to the mamma which is least liable to modifica- tions of tissue due to age and sex. It generally assumes the shape of a pigmented conical or cylindrical projection, at the apex of which the galactophorous ducts have their terminal openings. It is composed principally of a rather loosely woven connective tissue, containing abundant corpuscles, and provided Fig. 189.—Terminal vesicles and stroma from the gland of a nursing woman. Langer. THE MAMMARY GLAND. 441 with elastic fibrils. This conjunctive tissue forms a supporting framework for the milk-ducts traversing the nipple. The latter show walls of rather dense fibrous tissue, with a large pro- portion of elastic elements, and are provided with a lining of one row of short cylindrical cells. As the external orifice is approached, these cells begin to take on the character of the ordinary epidermic corpuscles of the integument. Partscli has found in many animals that the secreting paren- chyma accompanied these ducts almost to their mamillary orifices. The occurrence of unstriped muscle in the nipple, accords with the fact of its erectile properties. But the exact mode of distribution of these elements is still a matter of controversy among histologists. From the researches of Winkler and Kolessnikow, recently confirmed by Partscli, it would appear that they occur not in the ducts themselves, but form an in- complete ring around and external to the same. In or around the smaller galactophorous ducts, muscle-cells cannot be unmis- takably recognized, though some authors have described their occurrence there. As regards the structure of these smaller galactophorous ducts (