Book - A textbook of histology, including microscopic technic (1910) Special Histology 5
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Böhm AA. and M. Von Davidoff. (translated Huber GC.) A textbook of histology, including microscopic technic. (1910) Second Edn. W. B. Saunders Company, Philadelphia and London.
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- 1 V. The Genitourinary Organs
- 1.1 A. The Urinary Organs
- 1.2 B. The Suprarenal Glands
- 1.3 C. The Female Genital Organs
- 1.4 D. The Male Genital Organs
- 1.5 Technic
V. The Genitourinary Organs
A. The Urinary Organs
1. The Kidney
THE kidney is a branched tubular lobular gland, which in man consists of from ten to fifteen nearly equal divisions of pyramidal shape known as the renal lobes. The apex of each pyramid (the Malpighian pyramid) projects into the pelvis of the kidney. The kidney is surrounded by a thin but firm capsule consisting of fibrous connective tissue a ta^- Artery containing a few elastic fibers and, in its vein.
deeper portion, a thin layer of nonstriated muscle-cells
Fig< 2 ^ 9 ' Kidne y of new-born infant, showing a distinct separation into reniculi ; natural size. At is seen the consolidation of two adjacent reniculi.
The Secreting portion is composed of a
large number of tubules twisted and bent in a definite and typical manner, the uriniferous tubules. In each one of these tubules we distinguish the following segments : (i) Bowman's capsule, or the ampulla, surrounding a spheric plexus of capillaries, the glomerulus, which, with the capsule of Bowman, forms a Malpighian corpuscle ; (2) a proximal convoluted portion ; (3) a U-shaped portion, consisting of straight descending and ascending limbs and the loop of Henle ; (4) a distal convoluted portion or intercalated portion ; and (5) an arched collecting portion ; from the confluence of a number of these are formed the larger straight collecting tubules, which, in turn, finally unite to form the papillary ducts or tubules of Bellini, which pass through the renal papillae and empty into the renal pelvis. Besides the uriniferous tubules the kidney contains a complicated vascular system, a small amount of connective tissue, etc.
In a longitudinal median section the kidney is seen to be composed of two substances, the one, the medullary substance, possessing relatively few blood capillaries and containing straight collecting tubules and the loops of Henle ; the other, the cortical substance, richer in blood-vessels, and containing principally the Malpighian corpuscles and the proximal and distal convoluted tubules. In each renal lobe we find these two substances distributed as follows : The Malpighian pyramid consists entirely of medullary substance, which sends out a large number of processes, the medullary rays, or pyramids of Ferrein, toward the surface of the kidney. The latter do not, however, quite reach the surface, but terminate at a certain distance below it ; they are formed by collecting tubules which extend beyond the medullary substance. The entire remaining portion of the kidney is composed of cortical substance ; between the medullary rays it forms the cortical processes, and at the periphery of the kidney, where the medullary rays are absent, the cortical labyrinth. Those portions of the cortical substance separating the Malpighian pyramids are known as the columns of Bertini, or septa renis.
Fig. 260. Isolated uriniferous tubules : A and B, from mouse ; C, from turtle. In all three figures a represents the Malpighian corpuscle ; b, the proximal convoluted tubule; c, the descending limb of Henle's loop; d, Henle's loop; e, the straight collecting tubule ; f, the arched collecting tubule.
The various segments of the uriniferous tubule are characterized by their shape and size and by their epithelial lining.
The Malpighian corpuscle has a diameter of from I2O// to 220 p. The capsule surrounding the glomerulus consists of two layers, which are to be distinguished from each other when its relation to the glomerulus is taken into consideration. The capsule forms a double-walled membrane around the glomerulus ; a condition which is easily understood by imagining an invagination of the glomerulus into the hollow capsule. Between the inner wall covering the surface of the glomerulus (glomerular epithelium) and the outer wall (Bowman's capsule) there remains a cleft-like space which communicates with the lumen of the corresponding uriniferous tubule. In the adult the glomerular epithelium is very flat, with nuclei projecting slightly into the open space of the Malpighian corpuscle. The epithelium of the outer wall is somewhat higher, but still of the squamous type. The capsule of Bowman communicates with the proximal convoluted tubule by means of a short and narrow neck. Its epithelium passes over gradually into
Fig. 261, Median longitudinal section of adult human kidney ; nine-tenths natural size. In the peripheral portion the limits between its renal lobes are no longer recognizable.
the cubical epithelium of the neck, which, in turn, merges into that of the proximal convoluted tubule.
The proximal convoluted portion is from 40 [i to 70 // in diameter and is lined by a single layer of irregular columnar cells, the boundaries of which are made out with difficulty. The structure of these cells has been studied in recent years by a number of investigators, among whom may be mentioned Disse, whose account is here followed. In the epithelial cells of the proximal convoluted portion there may be recognized an outer or basal portion of the cells, in which there is found a spongioplastic network with rectangular meshes, with cytoreticular fibrils running parallel and at right angles to the basement membrane. In the meshes of this network there is found hyaloplasm. The cytoreticular fibrils which are at right angles to the basement membrane contain numerous granules, giving the basal portions of the cells a striated appearance. The inner portions of the cells contain a cytoreticulum and hyaloplasm; the reticular fibrils do not, however, contain granules,
Fig. 262. From section of cortical substance of human kidney ; X 2 4 : a Epithelium of Bowman's capsule; b and d, membrana propria ; c, glomerular epithelium; g, blood-vessels ; f, lobe of trie glomerulus ; g, commencement of uriniferous tubule ; A, epithelium of the neck ; i, epithelium of proximal convoluted tubule.
the inner portions of the cells presenting, therefore, a much less striated appearance than the outer portions. In tissues not well fixed there is often observed in the cells a free border which presents the appearance of being made of stiff fibrils or coarse and short cilia, which has been interpreted as a distinctive structure. Such a striated border is in all probability a result of partial disintegration or maceration of the cells. The nucleus of these cells is of nearly spheric shape and is situated in the inner part of the basal portions of the cells. The cells, especially in their inner non-striated regions, are so intimately connected that the cell limits are not always distinguishable. In the guinea-pig the basal regions of the lateral surfaces of the cells constituting the epithelium of the proximal convoluted portion present numerous projections which interlock and give to a surface view an irregular fringe-like outline. In crosssection the cells appear to be striated from their bases upward to the middle of the nucleus. Here, however, the striation is without doubt due to the outlines of the irregular ridges. (Fig. 264.) These structural relations have lately been confirmed in the case of the guinea-pig, and also found to hold true for man (Landauer). This striation is much coarser than that found in the basal portions of the cells, but both are, under certain circumstances, seen together.
Fig. 263. Section of proximal convoluted tubules from man ; X S% The proximal convoluted portion of the uriniferous tubule, before it terminates, passes over into a straighter portion, which gradually becomes smaller in diameter, and is situated in the medullary rays. This portion of the uriniferous tubule, which is sometimes designated as the spiral segment of Schachowa, or again as the end segment of Argutinski, is lined by an epithelium which is similar to that of the proximal convoluted portion, as above described. The attenuated end of the spiral segment is continuous with the descending limb of Henle's loop.
The descending limb of Henle's loop, from g/j. to 15^ in diameter, is narrow and possesses flattened epithelial cells, the centers of which, containing the nuclei, project into the lumen of the tubule. These central projections of the cells are not directly opposite those of the cells on the opposite wall, but alternate with the latter, thus giving to the lumen a zigzag outline corresponding to the length of the cell. The thick portion of the loop, for the most part represented by the ascending limb, but generally embracing the loop itself, from 23 fi. to 28 fji in diameter, possesses a columnar epithelium similar to that of the proximal convoluted portion. Here, however, the basal striation of the cells is not so distinct, the lumen is somewhat larger than that of the descending limb, and by treatment with certain reagents the epithelium may often be separated as a whole from the underlying basement membrane.
Fig. 264. Epithelium from proximal convoluted tubule of guinea-pig, with surface and lateral views (chrome-silver method) ; X 59 : a > a > The irregular interlacing projections.
Fig. 265. From cortical portion of longitudinal section of kidney of young child.
The distal convoluted or intercalated portion (segment of Schweigger-Seidel), from 39 /j. to 45 f* in diameter, is only slightly curved (2 to 4 convolutions). Its epithelium is relatively high, though not so high as that lining the proximal convoluted portion and not so distinctly striated, though containing numerous granules. The cells are provided with large nuclei and their basal portions are joined by interlacing projections.
Fig. 266. Section of medulla of .human kidney; X about 300: a, 0, a, Ascending limb of Henle's loop ; b, l>, b, blood-vessels ; c, c, c, descending limb of Henle's loop.
The next important segment is the short arched collecting portion, which has nearly cubical epithelial cells and a lumen somewhat wider than that of the intercalated tubule. The smaller straight collecting tubules have a low columnar epithelium with cells of somewhat irregular shape, the basal portions of which are provided with short, irregular, intertwining processes, which serve to hold the cells in place. The diameter of the collecting tubules measures from 45 // to .
In the larger collecting tubules the epithelium is more regular and becomes higher as the tube widens. These tubules gradually unite within the Malpighian pyramid and the regions adjacent to the columns of Bertini to form 1 5 to 20 papillary ducts from 200 fj. to 300 // in diameter. The latter have a high columnar epithelium, and empty into the pelvis of the kidney at the apex of the papilla, forming the foramina papillaria in an area known as the area cribrosa.
Besides the epithelium, the uriniferous tubules possess an apparently structureless membrana propria, that of the collecting tubules being very thin. This membrane may be isolated, as has been shown by F. P. Mall, by macerating frozen sections in a cold saturated solution of bichromate of soda for several days. This membrane is digested in pancreatin.
Fig. 267. From longitudinal section through papilla of injected kidney ; X 4 : a > Epithelium of collecting tubule under greater magnification.
Between the Malpighian pyramids are found the columns of Bertini, presenting a structure similar to that of the cortex of the kidney, and extending to the hilum of the kidney.
Between the uriniferous tubules and surrounding the bloodvessels of the kidney there is found normally a small amount of stroma tissue, consisting of white fibrous and reticular fibers, elastic fibers being found in connection with the blood-vessels (F. P. Mall, Riihle). Between the convoluted portions of the tubules this is present only in small quantity, the fibrils being felted to form sheaths for the tubules ; a somewhat greater amount being found in the neighborhood of the Malpighian corpuscles, in the boundary zone between the cortex and medulla and between the larger collecting tubules in the apices of the Malpighian pyramids.
From wrmt has been said concerning the uriniferous tubule it must be evident that its course is a very tortuous one. Beginning with the Malpighian corpuscles, situated in the cortex between the medullary rays, the tubule winds from the cortex to the medulla and back again into the cortex, where it ends in a collecting tubule, which passes to the medulla to terminate at the apex of a Malpighian pyramid. The different portions of the tubules have the following positions in the kidney : In the cortex between the medullary rays are found the Malpighian corpuscles, the neck, the proximal and distal convoluted portions of the uriniferous tubule, and the arched collecting tubules. The medullary rays are formed by the cortical portions of the straight collecting tubules and a portion of
Fig. 268. Section through junction of two lobules of kidney, showing their coalescence ; from new-born infant.
the descending and ascending limbs of Henle's loops. The medulla is made up mainly of straight collecting tubules of various sizes and of the descending and ascending limbs and loops of Henle's loops, the latter being often found in the boundary zone between the cortex and medulla. (See Fig. 266.) The ascending limb of Henle's loop of each uriniferous tubule, after it enters the cortex, comes into close proximity with the Malpighian corpuscle of the respective uriniferous tubule.
The blood-vessels of the kidney have a characteristic distribution, and are in the closest relationship to the uriniferous tubules.
The renal artery, as has been shown by Brodel, divides at the hilum on an average into four or five branches, about three-fourths of the blood-supply passing in front of the pelvis, while one-fourth runs posteriorly. The portion of the kidney supplied by the anterior branches is in its blood-supply quite distinct from that supplied by the posterior branches ; the one set of branches do not cross over to the other. The two ends of the kidney are supplied by an anterior and a posterior branch, each of which generally divides into three branches, which pass respectively, one anteriorly, one posteriorly, and one around the end of the uppermost and the lowest calyx.
The main branches of the renal artery give off lateral branches to the renal pelvis, supplying its mucous membrane and then breaking up into capillaries which extend as far as the "area cribrosa." The venous capillaries of this region empty into veins which accompany the arteries. Besides these, other arteries originate from the principal branches, or from their immediate offshoots, and pass backward to supply the walls of the renal pelvis, the renal capsule, and the ureter. The main trunks themselves penetrate at the hilum, and divide in the columns of Bertini to form arterial arches (arteriae arciformes) which extend between the cortical and medullary substances. Numerous vessels, the intralobular arteries, originate from the arteriae arciformes and penetrate into the cortical pyramids between the medullary rays. Here they give off numerous twigs, each of which ends in the glomerulus of a Malpighian corpuscle. These short lateral twigs are the vasa affcrcntia. Each glomerulus is formed by the breaking down of its afferent vessel, which, on entering the Malpighian corpuscle, divides into a number of branches, five in a glomerulus of a child three months old reconstructed by W. B. Johnston, each in turn subdividing into a capillary net. From each of these nets the blood passes into a somewhat larger vessel constituting one of the branches of the efferent vessel which carries the blood away from the glomerulus. Since the afferent and efferent vessels lie in close proximity, the capillary nets connecting them are necessarily bent in the form of loops. The groups of capillaries in a glomerulus are separated from each other by a larger amount of connective tissue than separates the capillaries themselves, so that the glomerulus may be divided into lobules. In shape the glomerulus is spheric, and is covered by a thin layer of connective tissue over which lies the inner membrane of the capsule, the glomerular epithelium. On its exit from the glomerulus the vas efferens separates into a new system of capillaries, which gradually becomes venous in character. Thus, the capillaries which form the glomerulus, together with the vas efferens, are arterial, and may be included in the category of the so-called arterial retia mirabilia. Those capillaries formed by the vas efferens after its exit from the Malpighian corpuscle lie both in the medullary rays and in the cortical pyramids. The meshes of the capillary networks distributed throughout the medullary rays are considerably longer than those of the networks supplying the cortical pyramids and labyrinth, the latter being quadrate in shape. The glomeruli nearest the renal papillae give off longer vasa efferentia which extend into the papillary region of the Malpighian pyramids (arteriolae rectae spuriae) and form there capillaries which ramify throughout the papillae with oblong meshes.
Artery cf capsule.
Fig. 269. Diagrammatic scheme of uriniferous tubules and blood-vessels of kidney. Drawn in part from the descriptions of Golubew.
Arterial retia mirabilia also occur in the course of the vasa afferentia between the intralobular arteries and the glomeruli, but nearer the latter. Each is formed by the breaking down of the small afferent vessels into from two to four smaller branches, which then reunite to pass on as a single vessel. In structure these retia differ greatly from the glomeruli in that here the resulting twigs are not capillaries and have nothing to do with the secretion of urine (Golubew).
From the vasa afferentia arterial twigs are occasionally given off, which break down into capillaries within the cortical substance. Other arteries originate from the lower portion of the intralobular arteries or from the arciform arteries themselves and enter the medullary substance, where they form capillaries. These vessels constitute the so-called "arteriolae rectae verae." Their capillary system is in direct communication with the capillaries of the vasa afferentia and "vasa recta spuria." The intralobular arteries are not entirely exhausted in supplying the vasa afferentia which pass to the glomeruli. A few extend to the surface of the kidney and penetrate into the renal capsule, where they terminate in capillaries which communicate with those of the recurrent, suprarenal, and phrenic arteries, etc. Smaller branches from these latter vessels may penetrate the cortex and form glomeruli of their own in the renal parenchyma (arteriae capsulares glomeruliferae). These relations, first described by Golubew, are of importance not only in the establishment of a collateral circulation, but also as a partial functional substitute in case of injury to the renal arteries. The same author also confirms the statements of Hoyer (77) and Geberg, that between the arteries and veins of the kidney, in the cortical substance, in the columns of Bertini, and at the bases of the Malpighian pyramids, etc., direct anastomoses exist by means of precapillary twigs.
From the capillaries the venous blood is gathered into small veins which pass out from the region of the medullary rays and cortical pyramids and unite to form the "intralobular veins." These have an arrangement similar to that of the corresponding arteries. The venous blood of the labyrinthian capillaries also flows into the intralobular veins, and as a result a peculiar arrangement of these vessels is seen at the surface of the kidney where the capillaries pass radially toward the terminal branches of the intralobular veins and form the stellate figures known as the vence stellatce. This system is also connected with those venous capillaries of the capsule which do not empty into the veins accompanying the arteries of the capsule. The capillary system of the Malpighian pyramids unites to form veins, the "venulae rectae," which empty into the venous arches (venae arciformes) which lie parallel with and adjacent to the corresponding arteries. The larger veins are found side by side with the arteries and pass out at the hilum of the organ.
Lymphatics of the kidney may be divided into superficial lymphatic vessels, situated in the capsule, and deep ones, found in the substance of the kidney. The deep lymphatic vessels need to be investigated further. They form a network of closed lymphatic vessels throughout the cortex. These empty, according to Rindowsky, into larger lymphatics, which follow the intralobular vessels ; and, according to Stahr, into larger vessels situated in the medullary rays. The lymphatic vessels of the kidney proper (deep vessels) leave this organ at the hilum.
The kidneys receive their innervation through nonmedullated and medullated nerve-fibers. The former accompany the arteries and may be traced along these to the Malpighian corpuscles. From the plexuses surrounding the vessels small branches are given off, which end on the muscle-cells of the media. According to Berkley, small nerve-fibrils may be traced to the uriniferous tubules, which pierce the membrana propria and end on the epithelial cells. Smirnow has also traced nerve-fibers to the epithelial cells of the uriniferous tubules and the Malpighian corpuscles. Dogiel has shown that medullary (sensory) nerve-fibers terminate in the adventitia of the arteries of the capsule.
The secretory processes of the kidney can be considered only briefly in this connection. The theories concerning uriniferous secretion may be grouped under two heads : namely, the theory of C. Ludwig, who believed that all the constituents of the urine
Fig. 270. A, Direct anastomosis between an artery and vein in a column of Berlin of child ; B, bipolar rete mirabile inserted in the course of an arterial twig. Dog's kidney (after Golubew).
leave the blood through the glomeruli, entering the uriniferous tubules as a urine containing a large percentage of water, which is concentrated in its passage through the uriniferous tubule by the absorption of water ; while according to the theory of Bowman, and later Heidenhain, only the water and inorganic salts leave the blood through the glomerulus, and that in the proportion found in the urine, while the urea is secreted by the epithelial cells of the uriniferous tubules, and mainly in those portions of the tubules possessing a striated epithelium. The majority of writers who have considered the question of urinary excretion have directly or indirectly expressed themselves as adherents to one or the other of the above theories. A number of recent observers have departed somewhat from either of the above theories, and of these we may mention especially the careful researches of Cushny, who brings forth strong proof to show that with the fluid passing through the glomerular epithelium there are carried certain salts and urea, the salts and urea in the proportion in which they occur in the bloodplasma, and that in passage through the uriniferous tubules a certain percentage of the fluids and certain salts are again absorbed, the salts in proportion to their diffusibility or their permeability of the renal cells.
The permanent kidney is developed as early as the fifth week of embryonic life. The renal anlagen, from which the epithelium of the ureter, renal pelvis, and a portion of the uriniferous tubules is formed, originate from the median portion of the posterior wall of the Wolfrian duct. These buds grow with their blind ends extending anteriorly, and are soon surrounded by cellular areas, the blastema of the kidneys. After the renal bud has become differentiated into a narrow tube (the ureter) and a wider central cavity (the renal pelvis) hollow epithelial buds are developed from the latter. These extend radially toward the surface of the renal anlagen, where they undergo a T-shaped division. These latter are the first traces of the papillary ducts and collecting tubules. The ends of these T-shaped divisions are surrounded by a cellular tissue, derived from the mesoderm, which is known as the renal blastema or the nephrogenic tissue. In this tissue there are differentiated spheric masses of cells, which in their further growth differentiate into S-shaped structures one end of which unites with the ends of the epithelial buds, developed as above described. The S-shaped structures acquire a lumen and form the anlagen of the uriniferous tubules, from the arched collecting tubules to and including Bowman's capsule. The ducts of the kidneys, from the papillary ducts to the collecting tubules of the medullary rays, have their origin from the epithelial buds which develop from the side of the Wolfrian ducts, while the uriniferous tubules proper have their origin in the nephrogenic tissues.
2. The Pelvis of the Kidney, Ureter, and Bladder
The renal pelvis, ureter, and urinary bladder are lined by stratified transitional epithelium. Its basal cells are nearly cubical ; these support from two to five rows of cells of varying shape. They may be spindle-shaped, irregularly polygonal, conical, or sharply angular, and provided with processes. Their variation in form is probably due to mutual pressure. The superficial cells are large and cylindric, a condition characteristic of the ureter and bladder. Their free ends and lateral surfaces are smooth, but their bases present indentations and projections due to the irregular outlines of the underlying cells. The superficial cells often possess two or more nuclei.
The mucosa often contains diffuse lymphoid tissue, which is more highly developed in the region of the renal pelvis. Here also there are found folds or ridges of mucosa which extend into the epithelium and present the appearance of papillae when seen in cross-section. A few mucous glands are also met with in the pelvis and in the upper portion of the ureter in certain mammals; in man, however, no typical glands are found, although solid epithelial buds, which extend into the mucosa for a distance, have been described. The ureter possesses two layers of nonstriated muscle-fibers the inner longitudinal, the outer circular. From the middle of the ureter downward a third external muscular layer is found with nearly longitudinal fibers.
Fig. 271. Section of lower part of human ureter ; X I 4
The urinary bladder has no glands, and its musculature apparently consists of a feltwork of nonstriated muscle bundles, a condition particularly well seen in sections of the dilated organ. But even here three indistinct muscle layers may be distinguished, the outer and inner layers being longitudinal and the middle circular. A remarkable peculiarity of these structures is the extreme elasticity of their epithelium, the cells flattening or retaining their natural shape according to the amount of fluid in the cavities which they line (compare London, Kann). The terminal blood-vessels of the mucosa of the pelvis of the kidney deserve special mention. The capillaries arise from arterioles which are situated in the ridges of the mucosa above mentioned. The capillaries are peculiar in that they are not completely surrounded by connective tissue, but are in part embedded in the epithelium, the epithelial cells resting on the endothelial wall of the capillaries (Disse). The blood-vessels of the bladder anastomose in the tunica adventitia, smaller branches pass to the muscular tissue. The main stems of the vessels form a plexus in the submucosa, from which arise the capillaries of the mucosa. The veins form submucous, muscular, and subperitoneal plexuses (Fenwick). Lymphatic vessels are found only in the muscular coat and not in the mucosa.
Fig. 272. Transverse section of the wall of the human bladder, giving a general view of its structure. X 1 5- e Pi Epithelium; tp, tunica propria or mucosa; sw, submucosa ; ilm, inner longitudinal layer of muscle ; rin, circular layer of muscle ; aim, external longitudinal layer of muscle ; fa, tunica adventitia.
The nerve supply of the bladder has been studied by Retzius, Huber, and Griinstein in the frog and a number of the smaller mammalia. Numerous sympathetic ganglia are observed, situated outside of the muscular coat, at the base and sides of the bladder. The neuraxes of the sympathetic neurones of these ganglia are grouped into smaller or larger bundles which interlace and form plexuses surrounding the bundles of nonstriated muscle-cells. From these plexuses nerve-fibers are given off, which penetrate the muscle bundles and end on the muscle-cells. The cell-bodies of the sympathetic neurones are surrounded by the telodendria of small medullated fibers, which terminate in the ganglia. Passing through the ganglia large medullated fibers (sensory nerves) may be observed which pass through the muscular coat, branch repeatedly in the mucosa, and lose their medullary sheat'hs on approaching the epithelium in which they end in numerous telodendria, the small branches of which terminate between the epithelial cells.
The ureters are surrounded by a nerve plexus containing nonmedullated and medullated nerve-fibers. The former end on cells of the muscular layers ; the latter pass through the muscular layer, and on reaching the mucosa branch a number of times before losing their medullary sheaths. The nonmedullated terminal branches form telodendria, the terminal fibers of which have been traced between the cells of the lining epithelium (Huber).
B. The Suprarenal Glands
The suprarenal gland is surrounded by a fibrous-tissue capsule containing nonstriated muscle-cells, blood- and lymph-vessels, nerves, and sympathetic ganglia. The glandular structure is divided into a cortical and a medullary portion. In the former are distinguished three layers, according to the arrangement, shape, and structure of its cells an outer glomerular zone, a middle broad fascicular zone, and an inner reticular zone. According to Flint, who worked in F. P. Mall's laboratory, and whose account will here be followed, the framework of the gland is made up of reticulum. In the glomerular zone this reticulum is arranged in the form of septa, derived from the capsule, which divide this zone into more or less regular spaces of oval or oblong shape. In the fascicular zone the reticulum is arranged in processes and fibrils running at right angles to the capsule. In the reticular zone the fibrils form a dense network, while in the medulla the reticular fibrils are arranged in processes and septa which outline numerous spaces.
The gland-cells of the glomerular zone are arranged in coiled columns of cells found in the compartments formed by the septa of reticulum above mentioned. The cells composing these columns are irregularly columnar, with granular protoplasm and deeply staining nuclei. In the fascicular zone the cells are arranged in regular columns, consisting usually of two rows of cells, and situated between the reticular processes, which run at right angles to the capsule. The cells of this zone are polyhedral in shape, with granular protoplasm often containing fat droplets and with nuclei containing little chromatin. Similar cells are found in the reticular zone, but here they are found in small groups situated in the meshes of the reticulum. The cells of the medullary substance are less granular and smaller in size than those of the cortex, and are grouped in irregular, round, or oval masses bounded by the septa of reticulum. These cells stain a deep brown with chromic acid and its salts are therefore known as chromaffin cells ; the color cannot be washed out with water a peculiarity which shows itself even during the development of these elements, and which is possessed by few other types of cells. Numerous ganglion cells, isolated and in groups, and many nerve-fibers occur in this portion of the organ.
Fig. 273. Section of suprarenal cortex of dog ; X 12O '
The blood-vessels of the suprarenal glands are of special interest, since it has been shown that the secretion of the glands passes directly or indirectly into the vessels. The following statements we take from Flint : The blood-vessels, derived from various sources, form in the dog a poorly developed plexus, situated in the capsule. From this plexus three sets of vessels are derived, which are distributed respectively in the capsule, the cortex, and the medulla of the gland. The vessels of the capsule divide into capillaries, which empty into a venous pldxus situated in the deeper portion of the capsule. The cortical arteries divide into capillaries which form networks, the meshes of which correspond to the arrangement of the cells in the different parts of the cortex, encircling the coiled columns of cells in the glomerular zone, while in the fascicular zone the capillaries are parallel with occasional anastomoses. These capillaries form a fine-meshed plexus in the reticular zone and unite in the peripheral portion of the medulla to form small anastomosing veins, from which the larger veins are derived. The latter do not anastomose, and are therefore terminal veins. The arteries of the medulla pass through the cortex without giving off any branches until the medulla is reached, where they break up into a capillary network surrounding the cell masses situated here. The blood from this plexus may be collected into veins of the medulla which empty into the terminal vein or some of its larger branches, or .may flow directly into branches of the venous tree. The endothelial walls of the capillaries rest directly on the specific gland cells, with the intervention here and there of a few reticular fibrils. According to Pfaundler, the walls of the blood-vessels of the entire suprarenal body consist solely of the tunica intima.
Fig. 274. Arrangement of the intrinsic blood-vessels in the cortex and medulla of the dog's adrenal (Fig. 17, Plate V, of Flint's article in " Contributions to the Science of Medicine," dedicated to Professor Welch, 1900).
The nerves of the suprarenal glands have been studied recently by Fusari and Dogiel (94) ; the description given by the latter will here be followed. Numerous nerve-fibers, both nonmedullated and medullated, arranged in the form of a plexus containing sympathetic ganglia, are found in the capsule. From this plexus numerous small bundles and varicose fibers enter the cortex, where they form plexuses surrounding the columns of cells or groups of cells found in the three zones of the cortex and about the vessels and capillaries of the cortex. The nerve-fibers of these plexuses are on the outside of the columns and cell groups and do not give off branches which pass between the cells. The nerve supply of the medullary substance is very rich, and is derived mainly from large nerve bundles which pass from the plexus in the capsule to the medulla, where they divide and form dense plexuses which surround the groups of gland-cells and veins ; from these plexuses fine varicose fibers pass between the gland-cells, forming intercellular plexuses. In the medulla there are found in many animals large numbers of sympathetic cells, some isolated, others grouped to form small ganglia. Pericellular networks surround the cellbodies of certain of these sympathetic cells. (For further information concerning the suprarenal glands consult Gottschau, Weldon, Hans Rabl, C. K. Hoffmann (92), Pfaundler, Flint, and Dogiel.)
Kidney. The arrangement of the cortical and medullary portions of the kidney is best seen in sections of the kidney of small mammalia, cut in the proper direction, and, if possible, embracing the whole organ. If, on the other hand, the finer epithelial structures are to be examined, small pieces are first fixed in osmic acid mixtures or in corrosive sublimate.
Impregnation with silver nitrate (method of Golgi or Cox) reveals some points as to the relation of the cells of the uriniferous tubules to each other.
In order to isolate the tubules, thin strips of kidney tissue are treated for from fifteen to twenty hours with pure hydrochloric acid having a specific gravity of 1.12 (for this purpose kidney tissue is used taken from an animal killed twenty-four hours previously). It is then washed, teased, and examined in glycerin (Schweiger-Seidel). Fuming nitric acid (40%), applied for a few hours to small pieces of tissue, occasionally isolates the uriniferous tubules very extensively. The further treatment is then the same as after hydrochloric acid. A 35% potassium hydrate solution may also be employed. The isolated pieces are, however, not easily preserved permanently.
The epithelium of the uriniferous tubules may be isolated either in YI alcohol or, according to R. Heidenhain (83), in a 5^ aqueous solution of neutral ammonium chromate. The latter method shows clearly the striation of the epithelium.
The autophysiologic injection with indigo-carmin, applied as in the case of the liver, fills the uriniferous tubules, which may then be further examined in sections.
The blood-vessels are examined in injected specimens (injection of the kidney is easily accomplished). In larger animals the injection is made into the renal artery, while in smaller ones the whole posterior half of the body is injected through the abdominal aorta.
The ureter and bladder are cut open, fixed, and then sectioned. In this way the organs are shown in a collapsed condition, in which the arrangement of the epithelium is totally different from that found in the distended organs. In order to observe them in the latter condition the fixing agent is injected into the ureter or bladder, when, after proper ligation, they are placed in the same fixing agent.
The usual fixing fluids are employed in the demonstration of the suprarenal capsule; but mixtures containing chromic acid, whether Flemming's fluid, chromic acid, or its salts, are of special importance in the examination of the organ, since the medullary substance of the suprarenal capsule stains a specific brown when treated by these mixtures (a condition only reduplicated in certain cells of the hypophysis). This brown staining also occurs when the cortical and medullary portions are entirely separated, as is the case in certain animals and during the development of the suprarenal capsule. The fat found in the cells of the suprarenal cortex is not identical with that of the rest of the body, as it may be dissolved by chloroform and oil of bergamot out of tissue fixed with osmic acid (Hans Rabl).
C. The Female Genital Organs
1. The Ovum
The product of the ovaries is the matured " ovum," or egg, having a diameter of from 0.22 to 0.32 mm. It forms a single cell with a thick membrane, from 7 /j. to 1 1 // in thickness, known as the zona pellucida. The ovum consists of a cell-body known as the yolk or vitellus, and a nucleus, from 30^ to 40 /J. in diameter, termed the germinal vesicle. The vitellus consists of two substances a protoplasmic network, with a somewhat denser arrangement at the periphery of the cell and in the neighborhood of the germinal vesicle, and of small, highly refractive, and mostly oval bodies imbedded between the meshes of the protoplasm the yolk globules. These latter, as a rule, are merely browned on being treated with osmic acid, although occasionally a true fatty reaction may be obtained. The germinal vesicle is surrounded by a distinct membrane having a double contour. In its interior we find a scanty lining framework containing very little chromatin, and one or two relatively large false nucleoli, or germinal spots, from 7// to lOfJt in diameter, due to a nodal thickening of the chromatin. In the latter a further very distinct differentiation is sometimes seen in the shape of a small body (vacuole?) of doubtful origin, which has been called Schron's granule. The germinal vesicle and spot were formerly known as " Purkinje's vesicle" and "Wagner's spot," respectively, from their discoverers.
2. The Ovary
The ovaries are almost entirely covered by peritoneum. The mesothelial cells of the latter, however, undergo here a differentiation, to form the germinal epithelium. At the hilum the peritoneal covering is absent, and it is here that the connective -tissue elements of the ovarian ligament penetrate into the organ to form its connective-tissue framework, the so-called stroma of the ovary. At an early period in the development of the ovaries, the germinal epithelium begins a process of imagination into the stroma of the ovary, so that at the periphery of the organ a zone is soon formed which consists of both connective tissue and epithelial (mesothelial) elements. This zone is called the cortex, or parenchymatous zone. That portion of the organ in the neighborhood of the hilum (aside from the rudimentary structure known as the epoophoron) consists of connective tissue containing numerous elastic fibers and unstriped muscle-cells, and is known as the medullary substance, or vascular zone. This connective tissue penetrates here and there into the cortex, separates the epithelial elements of the latter from each other, and is in direct continuation with a stratum immediately beneath the germinal epithelium, called the tunica albuginea. This latter layer of connective tissue is generally distinct in the adult ovary, although its structure and thickness vary to a considerable extent. In young ovaries it is irregular, but shows in its highest development three layers distinguishable from each other by the different direction of the fibers. In the medullary substance the connective-tissue fibers are long, in the cortex short, and in the zone containing the follicles (see below) are mingled with numerous connective-tissue cells. Nonstriated muscle-fibers occur exclusively in the medulla. Here they are gathered in bundles which accompany the blood-vessels, and may even form sheaths around the latter. They are especially prominent in mammalia. The germinal epithelium is distinguished from that of the remaining peritoneum by the greater height of its cells, which are cubic or even cylindric in shape. At an early period in the development of the ovaries this epithelium pushes into the underlying embryonic connective tissue in solid projections, to form the primary egg tubes of Pfluger, the cells of which very soon begin to show differentiation. Some retain their original characteristics and shape, while others increase in size, become rounded, and develop into the young ova. Those retaining their indifferent type become the follicular cells surrounding the egg. This differentiation into ova and follicular elements may even occur in the germinal epithelium itself, in which case the larger round cells are known as the primitive or primordial ova. In the further development of the ovarian cortex the primitive egg tubes are penetrated throughout by connective tissue, so that each egg tube is separated into a number of irregular divisions. In this way a number of distinct epithelial nests are formed, which lose their continuity with the germinal epithelium and finally lie imbedded in the connective tissue. According to the shape and other characteristics of these epithelial nests, we may distinguish several different groups: (i) The primitive egg tubes of Pfluger ; (2) the typical primitive follicles i. e., those which contain only a single egg-cell (present in the twenty-eighth week of fetal life) ; (3) the atypic follicles i. e., those containing from two to three egg-cells ; (4) the so-called nests of follicles, in which a large number of follicles possess only a single connective-tissue envelope ; (5) follicles of the last-named type which may assume the form of an elongated tube, and which are then known as the constricted tubes of Pfliiger. The fourth, fifth, and possibly the third types are further divided by connective-tissue septa, until they finally form distinct and typical follicles (Schottlander, 91, 93).
Fig. 275. Section from ovary of adult dog. At the right the stellate figure represents a collapsed follicle with its contents. Below and at the right are seen the tubules of the parovarium (copied from Waldeyer).
Fig. 276. From ovary of young girl ; X I9
In the adult ovary true egg tubes are no longer developed. Isolated imaginations of the germinal epithelium sometimes occur, but apparently lead merely to the formation of epithelial cysts (Schottlander). The theories as to when the formation of new epithelial nests or follicles ceases are, however, very conflicting, some authors believing that cessation takes place at birth, others that it continues into childhood and even into middle age.
The typical primitive follicle consists of a relatively large eggcell surrounded by a single layer of smaller cubical or cylindric follicular cells. The growth of the follicle takes place by means of mitotic division in the follicular cells and increase in size of the ovum. The egg-cell is soon surrounded by several layers of cells, and gradually assumes an eccentric position in the cell complex. At a certain distance from the ovum and nearly in the center of the follicle one or more cavities form in the follicular epithelium. These become confluent, and the resulting space is filled by a fluid derived, on the one hand, from a process of secretion and, on the other hand, from the destruction of some of the follicular cells. The cavity is called the antrum of the follicle, and such a follicle has received the name of Graafian follicle. Its diameter varies from 0.5 to 6 mm. The follicle increases in size through cell-proliferation, the cavity increasing and gradually inclosing the egg together with the follicular cells immediately surrounding it, although the latter always remain connected with the wall of the vesicle at some point. The egg now lies imbedded in a cell-mass, the discus proligerus, which is composed of follicular epithelium, and projects into the follicular cavity. The follicular epithelium forming the wall of the cavity is known as the stratum granulosum, the cavity as the antrum, and the fluid which it contains as the liquor folliculi. Those follicular cells which immediately surround and rest upon the ovum are somewhat higher than the rest and constitute the egg epithelium, or corona radiata.
During the growth of the follicle the connective tissue surrounding it becomes differentiated into a special envelope, called the tJicca folliculi. In it two layers may be distinguished the outer, the tunica externa, consisting of fibrous connective tissue, is continuous with the inner, or tunica interna, rich in blood-vessels and cellular elements. The follicle gradually extends to the surface of the ovary, at which point it finally bursts (see below), allowing the ovum to escape into the body cavity and thus into the oviduct.
During the growth and development of the ovarian follicles the ova undergo certain changes of size and structure which may receive further consideration. These have been described for the human ovary by Nagel (96), whose account will here be followed. The ova of the primitive or primordial follicles attain a size (in fresh tissue teased in normal salt solution) varying from 48 /* to 69^. They possess a nucleus varying in size from 20 fi to 32^, presenting a doubly contoured nuclear membrane, and containing a distinct chromatin network with a nucleolus and several accessory nucleoli. The protoplasm shows a distinct spongioplastic network containing a clear hyaloplasm. The primitive ova, until they undergo further development, retain this size and structure, irrespective of the age of the individual. They are numerous in embryonic life and early childhood, always found during the ovulation period, but not observed in the ovaries of the aged. Changes in the size and structure of the ova accompany the proliferation of the follicular cells in the growing follicles. As soon as the follicular cells of a primitive follicle proliferate, as above described, the ovum of the follicle increases in size until it has attained the size of a fully developed ovum. The zona pellucida now makes its appearance, and after this has reached a certain thickness, yolk granules (deutoplastic granules) develop in the protoplasm of the ovum. In a fully developed Graafian follicle the ovum presents an outer clearer protoplasmic zone and an inner fine granular zone containing yolk granules ; in the former lies the germinal vessel. Between the protoplasm of the ovum and the zona pellucida is found a narrow space known as the perivitelline space. The germinal vesicle (nucleus), which is usually of spheric shape, possesses a doubly contoured membrane and a large germinal spot (nucleolus), which shows ameboid movements.
Figs. 277, 278, 279, and 280. From sections of cat's ovary, showing ova and follicles in different stages of development ; X 22 5 a i a > a -> a > Germinal spots ; />, i>, b, 6, germinal vesicles ; t, c, c, c, ova ; </, d, d, zonx pellucidse ; e, e, e, e, corona radiata ; f,f,f,f, tbecse folliculorum ; g, beginning of formation of the cavity of the follicle.
Fig. 281. Transverse section through the cortex of a human ovary ; X 5 : ^ Tunica albuginea ; ep, follicular epithelium, zona granulosa ; y^primordial follicles ; ov, ovum in the discus proligerus ; the, thecaexternafolliculi ; thi, theca interim folliculi with blood-vessels (Sobotta, "Atlas and Epitome of Human Histology").
The origin of the zona pellucida has not as yet been fully determined. It probably represents a product of the egg epithelium, and may be regarded in general as a cuticular formation of these cells. At all events it contains numerous small canals or pores into which the processes of the cells composing the corona radiata extend. These processes are to be regarded as intercellular bridges (Retzius, 90) ; and, according to Palladino, they occur not only between the ovum and the corona radiata, but also between the follicular cells themselves. In the ripe human ovum the pores are apparently absent (Nagel), and it is very probable that they have to do with the passage of nourishment to the growing egg. Retzius believes that the zona pellucida is derived from the processes of the cells composing the corona radiata, which at first interlace and form a network around the ovum. Later, the matrix of the membrane is deposited in the meshes of the network, very probably by the egg itself.
Further developmental changes are, however, necessary before a fully developed ovum (ripe ovum) may be fertilized. These are grouped under the head of maturation of the ovum. They have in part been described in a former section (p. 71), but may receive further consideration at this time. During maturation the chromosomes are reduced in number, so that the matured ovum presents only half the number found in a somatic cell of the same animal. The manner in which this reduction takes place has been described for many invertebrates and vertebrates, and in all ova studied with reference to this point essentially the same phenomena have been observed. In this account we shall follow the process as it occurs in the Copepoda (Riickert, 94).
During the period of growth the cells composing the last generation of oogonia (primitive ova) increase in size, and are then known as " oocytes " (the ripe ova). These then undergo mitotic division, and in each a spirem is formed which divides into 12 chromosomes, and not into 24 as in the case of the somatic cells. These 12 chromosomes split longitudinally, so that the germinal vesicle is seen to contain 12 pairs of chromosomes, or daughter loops. By this process the oogonia have become egg mother cells (O. Hertwig, 90) or oocytes of the first order. The loops now begin to shorten and each soon divides crosswise into two equal rods, thus giving rise to 12 groups of 4 chromosomes, or 12 tetrads. The mother cell now divides into 2 unequal parts, the process consisting in a distribution of the rods composing the tetrads in such a way that the pairs of rods derived from one set of daughter loops pass to the one daughter cell, and those derived from the other set to the second daughter cell. In this manner are formed the large egg daughter cells (O. Hertwig) or oocytes of the second order, and a smaller cell, the first polar body. From this it is seen that the daughter cell still retains 12 pairs of rods. A second unequal division immediately follows without a period of rest, but in this case the component parts of the pairs of rods are so divided that each separate rod moves away from its fellow, although they both originated from the same daughter loop. In this manner a cell of the third generation is formed, the oocyte of the third order, or mature ovum, as well as a second polar body. The second division in the period of maturation is peculiar in that here daughter chromosomes are formed, not by a longitudinal splitting of the chromosomes, but by a transverse division.
Fig. 282. Schematic representation of the behavior of the chromatin during the maturation of the ovum (from Riickert, 94). Instead of 12 chromosomes we have drawn, for the sake of simplicity, only four : a, a, a, First, and (b) second polar body.
In the process of development of the ova, three periods are therefore distinguishable. The first, or period of proliferation, represents a stage of repeated mitotic division in the oogonia, during which the latter become gradually reduced in size. In the second, or period of growth, the oogonia increase in size and are then ready for the third, or period of maturation. In the latter, by means of a modified double mitotic division, uninterrupted by any resting stage, the matured ovum and the polar bodies are formed. These several periods are represented in figure 283.
The manner in which the fully developed Graafian follicle bursts and its ovum is freed is still a subject of controversy ; the following may be said regarding it : By a softening of the cells forming the pedicle of the discus proligerus, the latter, together with the ovum, are separated from the remaining granulosa, and lie free in the liquor folliculi. At the point where the follicle comes in contact with the tunica albuginea of the ovary, the latter, with the theca folliculi, becomes thin, and in this region, known as the stigma, the blood-vessels are obliterated and the entire tissue gradually atrophies ; thus a point of least resistance is formed which gives way at the slightest increase in pressure within the follicle, or in its neighborhood.
Fig. 283. Scheme of the development and maturation of an ascaris ovum (after Boveri) : P. B., Polar bodies. (From " Ergebn. d. Anat. u. Entw.," Bd. I.)
The part of the Graafian follicle which remains after the ovum has been released forms a structure known as the corpus luteum, a structure which passes through certain developmental stages and then undergoes degeneration. The regressive metamorphosis is much slower in a corpus luteum whose ovum has been fertilized and is in process of further development than in those whose ova have not been impregnated ; the former is known as the corpus luteum verum, the latter as the corpora lutea spuria. There is as yet difference of opinion as to the mode of development of the corpora lutea, certain observers maintaining that the cells ofthezona granulosa contribute largely to the development of these structures, while others trace their origin to the cells of the theca interna. In this account we shall follow Sobotta, whose careful observations on the development of the corpora lutea of the mouse and rabbit support strongly the former view. According to this observer, the walls of the Graafian follicle collapse after its rupture. The cells of the follicular epithelium, which remains within the collapsed follicle, hypertrophy, the cells attaining many times their original size. As the epithelial cells enlarge, a yellowish pigment known as Lutein makes its appearance. The cells are now designated as lutein cells. At the same time the vascular connective tissue of the inner thecal layer penetrates between the hypertrophied epithelial cells in the shape of processes accompanied by leucocytes.
The structure' which thus develops is known as the corpus luteum. On the rupture of the follicle hemorrhages often take place on account of the laceration of the blood-vessels. The remains of such hemorrhages are found in the form of hematoidin crystals.
After a variable time the corpora lutea degenerate ; in this regressive metamorphosis the epithelial cells (lutein cells) undergo fatty degeneration, and the connective tissue trabeculae become atrophied. Each corpus luteum is thus changed into a corpus albicans, which in turn is absorbed, and in its place there remains only a connective tissue containing very few fibers.
Not all of the eggs and follicles reach maturity ; very many are destroyed by a regressive process known as atresia of the follicles. This process may begin at any stage, even affecting the primitive ova while still imbedded in the germinal epithelium first attacking the egg itself and later the surrounding follicular epithelium, although in both the degenerative process is identical. The germinal vesicle and the nuclei of the follicular cells usually undergo a chromatolytic degeneration, although they sometimes disappear without apparent chromatolysis (direct atrophy), while the cell-bodies are generally subjected to a fatty degeneration or may even undergo what is known among pathologists as an albuminous degeneration i. e., one characterized by granulation and showing no fat reaction but numerous reactions such as are observed where albumin is present. These two forms of metamorphosis result in a liquefaction of the cell-body, and finally lead to a hyaline swelling, which renders the substance of the cell homogeneous. The zona pellucida softens, increases in volume, becomes wrinkled, and after some time is absorbed. A further stage in the regressive process consists in the formation of scar tissue, as in the case of the corpus luteum. Here leucocytes accompany the proliferation from the tunica interna of the theca folliculi, and assist in absorbing the products of degeneration, the result being a connective-tissue scar (vid. G. Ruge, and Schottlander, 91, 93).
The blood-vessels of the ovary enter at the hilum and branch in the medullary substance of the ovary. From these medullary vessels branches are given off which penetrate the follicular zone, giving off branches to the follicles and terminating in a capillary network in the tunica albuginea (Clark, 1900). The relations of the branches to the follicles are such that in the outer layer of the theca folliculi the vessels form a network with wide meshes while the inner layer contains a fine capillary network. The veins are of large caliber and form a plexus at the hilum of the ovary.
The lymphatics of the ovary are numerous. They begin in clefts in the follicular zone, which unite to form vessels lined by endothelial cells in the medulla. They leave the ovary at the hilum.
The nerves accompany and surround the blo*od-vessels, while very few nerve-fibers penetrate into the theca folliculi ; those doing so form a network around the follicle and end often in small nodules without penetrating beyond the theca itself. Ganglion cells of the sympathetic type also occur in the medulla of the ovary near the hilum (Retzius, 93 ; Riese, Gawronsky).
3. The Fallopian Tubes, Uterus, and Vagina
The Fallopian tubes or ova ducts consist of a mucous membrane, muscular coat, and peritoneal covering.
The mucous membrane presents a large number of longitudinal folds which present numerous secondary folds which frequently communicate with one another. Very early in the development four of these folds are particularly noticeable in the isthmus ; these may also be recognized at times in the adult. These are the chief folds, in contradistinction to the rest, which are known as the accessory folds (Frommel). The accessory folds are well developed in the isthmus, and are here so closely arranged that no lumen can be seen with the naked eye. The epithelium lining the tubes is composed of a single layer of ciliated columnar cells which entirely cover the folds as well as the tissue between them. Glands do not occur in the oviducts, unless the crypts between the folds may be considered as such. The mucosa beneath the epithelium contains relatively few connective-tissue fibers, but numerous cellular elements. In the isthmus it is compact, but in the ampulla and infundibulum its structure is looser. The mucosa contains a few nonstriated muscle-fibers, which have a longitudinal direction and extend into the chief folds, but not into the accessory folds.
External to the mucosa is found the muscular coat, consisting of an inner circular and an outer and thinner longitudinal layer consisting of bundles of nonstriated muscular tissue separated by connective tissue and blood-vessels. The longitudinal layer is imperfectly developed in the ampulla and may be entirely absent in the infundibulum. The peritoneal layer consists of a loose connective tissue covered by mesothelium.
Fig. 284. Section of oviduct of young woman. To the left and above are two enlarged ciliated epithelial cells from the same tube ; X I 7
The ova ducts have a rich blood-supply. The terminal branches of the arteries pass into the primary and secondary folds of the mucosa, where they form capillary plexuses under the epithelium. The blood is returned by means of a well-developed venous plexus. The lymphatic vessels have their origins in the folds of the mucosa. Nerve-fibers have been traced to the musculature and to the lining epithelial cells.
The uterus is composed of a mucous, a muscular, and a peritoneal coat.
The mucosa of the body of the uterus and cervix is lined by a single layer of columnar ciliated epithelial cells ; these are some what higher in the cervix than in the corpus. Barfurth (96) has found intercellular bridges between the cells of the uterine epithelium in the guinea-pig and rabbit. In the cervix of the virgin the ciliated columnar epithelium extends as far as the external os, at which point this usually changes to a stratified squamous epithelium. In multiparae the squamous epithelium extends into the cervical canal and may be found, with occasional exceptions (islands of ciliated epithelium), throughout its entire lower third. This arrangement is subject to considerable variation, so that even in children the lower portion of the cervical canal may sometimes be lined by stratified epithelium. Recent investigations have established the fact that in both the uterus and oviducts the general direction of the wave-like ciliary motion is toward the vagina (Hofmeier). In the body of the uterus the mucosa is composed of a reticular connective tissue consisting of relatively few connective-tissue fibers and branched connective-tissue cells arranged in the form of a network, in the meshes of which are found lymphocytes and leucocytes. Under low magnification the mucosa presents more the appearance of adenoid tissue than of areolar connective tissue. The mucosa of the cervix is somewhat denser, containing more fibrous tissue. In the cervical canal the mucosa of the anterior and posterior walls is elevated to form numerous folds, extending laterally from larger median folds. These folds are known as the plica palmatce.
The mucosa of the body of the uterus and of the cervix contains numerous glands, the uterine and cervical glands. The uterine glands are branched tubular in type, and extend through the mucosa and certain ones may even extend for a short distance into the muscular layer. They are lined by ciliated columnar epithelium, resting on a basement membrane. The cervical glands are larger and more branched than those of the body of the uterus, and belong to the type of tubulo-alveolar glands ; they have a mucous secretion. The glands and crypts extend as far as the external os. In the mucous membrane of the cervical region we find peculiar closed sacs of varying size lined by simple cylindric epithelium, the socalled ovula Nabothi, which probably represent cystic formations (yid. A. Martin).
Three layers of muscular tissue are to be seen both in the corpus and cervix uteri an inner longitudinal, a middle nearly circular, in which the principal blood-vessels are found, and an outer longitudinal. The inner and outer layers are known respectively from their position as the stratum mucosum and stratum serosum, the middle and more vascular as the stratum vasculosum. As compared with the middle, the inner and outer muscle layers are poorly developed. The complicated conditions found in the uterine musculature can be better understood if some attention be paid to its origin. The circular layer should be regarded as the original musculature of the Miillerian ducts. The outer longitudinal layer develops later, and is derived from the musculature of the broad ligament. Between these two are the large vessels accompanied by a certain amount of muscular tissue a condition which persists throughout life in the carnivora. In man the blood-vessels penetrate into the circular musculature and only appear later in the inner muscular layer. A true muscularis mucosse is not present in the human uterus (Sobotta, 91).
The serous or peritoneal layer consists of a layer of mesothelial cells and submesothelial connective tissue.
The uterus derives its blood supply from the uterine and ovarian arteries, which enter from the broad ligament through its lateral portion. These vessels pass to the stratum vasculosum of the muscular layer, where they branch repeatedly, some of the branches entering the mucosa, where they form capillary networks surrounding the glands and a dense capillary network situated under the uterine epithelium. The veins form a venous plexus in the deeper portion of the mucosa, especially well developed in the cervix and os uteri. From this plexus the blood passes to a second welldeveloped venous plexus situated in the stratum vasculosum of the muscular layer, whence the blood passes to the plexus of uterine and ovarian veins.
Fig. 285. From uterus of young woman ; X 34- (From a preparation by Dr. J. Amann.)
The lymphatics begin in numerous clefts in the uterine mucosa ; from here the lymph passes by way of lymph-vessels to the muscular coat, between the bundles of which are found numerous lymph-vessels especially in the middle or vascular layer. These lymph-vessels terminate in larger vessels found in the subserous connective tissue.
The uterus receives numerous medullated and nonmedullated nerves. The latter terminate in the muscular layers. Medullated fibers have been traced into the mucosa, where they form plexuses under the epithelium, from which branches have been traced between the epithelial cells and between the gland cells. In the course of the nerves ganglion cells of the sympathetic type have been observed.
Fig. 286. From section of human vagina.
In the vagina we distinguish also three coats the mucous membrane, the muscular layer, and the outer fibrous covering.
The epithelium of the mucous membrane is of the stratified squamous type, and possesses, as usual, a basal layer of cylindric cells. The mucosa of the vagina consists of numerous connectivetissue fibers mingled with a number of exceptionally coarse elastic fibers. Papillae containing blood-vessels are present everywhere except in the depressions between the columnar rugarum. It is generally stated that the vagina has no glands, but according to the observations of von Preuschen and C. Ruge, a few isolated glands occur in the vagina. They are relatively simple in structure, form irregular tubes, and are lined by ciliated columnar epithelium. The excretory ducts are lined by stratified squamous epithelium. Diffuse adenoid tissue is met with in the mucosa, which sometimes assumes the form of lymphatic nodules.
The muscular coat, which in the lower region is quite prominent, may be separated indistinctly into an outer longitudinal and an inner circular layer ; the latter is, as a rule, poorly developed, and may be entirely absent. The muscular coat is especially well developed anteriorly in the neighborhood of the bladder.
Fig. 287. From section of human labia minora.
The outer fibrous layer consists of dense connective tissue loosely connected with the adjacent structures.
At its lower end the vagina is partially closed by the hymen which must be regarded as a rudiment of the membrane which in the embryo separates the lower segment of the united Miillerian ducts from the ectoderm of the sinus urogenitalis. Accordingly, the epithelium on the inner surface of the hymen partakes of the character of the vaginal epithelium ; that on the outer surface resembling the skin in structure (G. Klein).
The epithelium of the vestibulnm gradually assumes the characteristics of the epidermis ; its outer cells lose their nuclei and sebaceous glands occur here and there in the neighborhood of the urethral orifice and on the labia minora. Hair begins to appear on the outer surface of the labia majora.
The clitoris is covered by a thin epithelial layer, resembling the epidermis. This rests on a fibrous-tissue mucosa having numerous papillae, some of which contain capillaries, others special nerveendings. In the clitoris of the adult no glands are found. The greater portion of the clitoris consists of cavernous tissue, homologous to the corpora cavernosa of the penis ; the corpus spongiosum is not present in the clitoris.
The glands of Bartholin, the homologues of the glands of Cowper in the male, are mucous glands situated in the lateral walls of the vestibule of the vagina. The terminal portions of their ducts are lined by stratified squamous epithelium.
Free sensory nerve-endings, with or without terminal enlargements, have been demonstrated in the epithelium of the vagina (Gawronski). The sensory nerve-fibers form plexuses in the mucosa, and lose their medullary sheaths as they approach the epithelium. Sympathetic ganglia are met with along the course of these nerves, and nonmedullated nerves terminate in the involuntary muscular tissue of the vaginal wall.
In*the connective-tissue papillae and in the deeper portions of the mucosa of the glans clitoridis are found, besides the ordinary type of tactile corpuscles and the spherical end-bulbs of Krause, the socalled genital corpuscles (see p. 171). Numerous Pacinian corpuscles have been observed in close proximity to the nerve-fibers of the clitoris and the labia minora.
In varying regions of the medullary substance of the ovary, but more usually in the neighborhood of the hilum, there occur irregular epithelial cords or tubules provided with columnar epithelium, ciliated or nonciliated, which constitute the paroophoron. These are the remains of the mesonephros, and are continuations of that rudimentary organ the epoophoron of similar structure which lies within the broad ligament. The separate tubules of the epoophoron communicate with the duct of Gartner (Wolfifian duct), which in the human being is short, ends blindly, and never, as in certain animals, opens into the lower portion of the vagina. These derivatives of the primitive kidney consist of blindly ending tubules of varying length lined by a ciliated epithelium, the cells of which are often found in process of degeneration.
The hydatids of Morgagni are duplications of the peritoneum.
D. The Male Genital Organs
1. The Spermatozoon
The semen, or sperma, is a fluid that, as a whole, consists of the secretion of several sets of glands in which the sexual cells, the spermatosomes, or spermatozoa, which are formed in the testes, are suspended.
We shall first consider the structure of the typical adult spermatosome, taking up consecutively its component parts. Three principal parts may be distinguished the head, the middle piece, and the tail or flagellnm. The round or oval body of the head terminates in a lanceolate extremity. The former consists of chromatin, and is most intimately associated with the phenomenon of fertilization. The middle piece, which is attached to the posterior end of the head, is composed of a protoplasmic envelop which surrounds a portion of the so-called axial thread. The latter is enlarged anteriorly just behind the head to form the terminal nodule, which fits into a depression in the head. From the middle piece on, the axial thread
Fig. 288. Diagram showing the general characteristics of the spermatozoa of various vertebrates : a, Lance ; b, segments of the accessory thread ; c, accessory thread ; d, body of the head ; e, terminal nodule ; f, middle piece ; g, marginal thread ; h, axial thread ; i, undulating membrane ; k, fibrils of the axial thread ; /, fibrils of the marginal thread ; m, end piece of Retzius ; ;/, rudder-membrane.
is continued into the tail of the spermatozoon, and is here surrounded by a transparent substance the sheatJi of the axial thread. The envelop is lacking at the posterior extremity of the tail, where the axial thread extends for a short distance as a naked filament called the end-piece of Retzius. From the middle piece a still finer thread is given off", the marginal thread, which extends at a certain distance from the axial thread as far as the end-piece of Retzius. In its course it crosses and recrosses the axial thread at various points, and may even wind around it in a spiral manner. In all instances it is connected with the sheath of the axial thread by a delicate membrane the undulating membrane. Another and still more delicate filament the accessory thread runs parallel with the axial thread along the surface of its sheath and terminates at a certain distance from the end-piece of Retzius. Near the extremity of the flagellum and immediately in front of the end-piece is another and shorter membrane, the rudder membrane, which is continuous with the undulating membrane. Maceration reveals a fibrillar structure of both the axial and marginal threads (Ballowitz), while the accessory thread is separated into a number of short segments. In mammalia, and especially in man, the spermatozoa seem to be" more simply constructed. Here the head is pyriform, and somewhat flattened, with a slight ridge along the depression at either side of its anterior thinner portion (Fig. 289). In some mammalia (mouse), the head is provided with a socalled cap, which corresponds to the lance previously mentioned. The middle piece is relatively long and shows a distinct crossstriation, which may be attributed to its spiral structure. Here also the middle piece is traversed by the axial thread, which ends at the head in a terminal nodule, and may be separated as in other mammalia into a number of fibrils. Some years ago Gibbes described an undulating membrane in the human spermatozoon, an observation which was confirmed by W. Krause (81). The head of the .human spermatosome is from 3 /j. to 5 [i long, and from 2 u to 3 u in breadth ; the middle piece
Fig. 289. Human ' J ' spermatozoa.
The two is 6 // long and I fj. in breadth ; the tail is from at the left after Retzius 40 // to 60 /J. long, and the end-piece 6 fj. long.
extreme left ^ seen* in ^he spermatozoa are actively motile, a phe profile; the other in nomenon due to the flagella, which give them
surface view; the one a S pi ra 1 boring motion. They are character at the right is drawn as described by Jensen -. a, lz ed by great longevity and are very resistant Head ; l>, terminal nod- to the action of low temperatures (vid. Pier ule; c, middle piece; gol g \ j n SQme spedes o f bat the Spera, tail ; e, end-piece of . L r
matozoa penetrate into the oviduct of the female in the fall, but do not contribute to impregnation until the spring, when the ova mature. (For the structure of the spermatosomes see Jensen, Ballowitz.)
2. THE TESTES.
The testis is inclosed within a dense fibrous capsule, the tunica albuginea, about one-sixteenth of an inch in thickness, and surrounded by a closed serous sac, derived from the peritoneum during the descent of the testes, and therefore lined by mesothelial cells. This serous sac the tunica vaginalis consists of a visceral layer attached to the tunica albuginea, and a parietal layer which blends with the scrotum. The cavity contains normally a small amount of serous fluid. On the inner surface of the tunica albuginea is found a thin layer of loose fibrous tissue containing blood-vessels the tunica vasculosa. The tunica albuginea is thickened in its posterior portion to form the mediastinum testis, or the corpus Highmori, which projects as a fibrous-tissue ridge for a variable distance into the substance of the testis. The gross structure of the testis is best seen in a sagittal longitudinal section. Even a low magnification will show that the testis is composed of lobules. These are produced by septa which extend into the substance of the organ and are derived from the investing tunics of the testis and diverge in a radiate manner from the mediastinum testis. The lobules are of pyramidal shape, with their bases directed toward the capsule and their apices toward the mediastinum. They consist principally of the seminiferous tubules, whose transverse, oblique, and longitudinal as closed canals, which are closely coiled upon each other (convoluted tubules) and describe a tortuous course, until they finally reach the corpus Highmori. Immediately before they reach the latter, the convoluted tubules change into short, straight and narrow segments' the straight tubules, or tubuli recti. Within the corpus Highmori, all the straight tubules of the testis unite to form a tubular network the rete testis (Haller).
Fig. 290. Longitudinal section through human testis and epididymis. The light areas between the lobules are the fibrous-tissue septa of the testis ; X 2
sections may be observed in sections of the testis. When isolated, these tubules are seen to begin in the testis From this network about fifteen tubules the vasa efferentia arise. The latter, at first straight, soon begin to wind in such a manner that the various convolutions of each canal form an independent system, invested by a fibrous sheath of its own coni vasculosi Halleri. These lobules constitute the elements of the globus major of the epididymis. In cross-section the vasa efferentia are seen to be stellate in shape. The vasa efferentia gradually unite to form one canal the vas epididyntidis. This is markedly convoluted and is situated in the body and tail of the epididymis itself.
The epithelium of the convoluted seminiferous tubules consists of sustentacular cells (cells or columns of Sertoli) and of spermatogenic elements. The former are high, cylindric structures (see below), the basilar surfaces of which are in contact. They do not form a continuous layer, but their basal processes are interwoven to form a superficial network surrounding the epithelium of the
Fig. 291. Fig. 292.
Sustentacular cells (cells of Sertoli) of the guinea-pig (chrome-silver method). Figure 291, surface view of the seminiferous tubules ; figure 292, profile view ; X 22 : a, Basilar surface of a cylindric sustentacular cell ; i>, flattened sustentacular cell ; <-, <r, depressions in the sustentacular cells due to pressure from the spermatogenic cells ; d, basilar portion of sustentacular cells.
seminiferous tubules. (Fig. 292.) In the meshes of the reticulum are deposited numbers of plate-like cells, which lie in contact with the basement membrane and also represent sustentacular elements (vid. Merkel, 7 1 ).
Between the sustentacular cells are found from four to six rows of cells, possessing relatively large nuclei, rich in chromatin, and derived from cells of the deeper strata by mitotic cell division. The epithelium of the convoluted portion of the seminiferous tubules is, therefore, a stratified epithelium. The cells of this epithelium present various peculiarities according to their stage of development, and will be considered more fully in discussing spermatogenesis. Externally, the walls of the convoluted tubules are limited by a single layer or several layers of spindle-shaped, epithelioid cells. A basement membrane is present, but very thin, and in some cases hardly capable of demonstration. The convoluted tubules are separated from each other by a small amount of connective tissue, in which, in addition to the vessels, nerves, etc., are found peculiar groups of large cells containing large nuclei, and known as interstitial cells. Nothing definite is known regarding the significance of these cells ; but they are probably remains of the Wolffian body. Reinke (96) found repeatedly crystalloids of problematic significance in the interstitial cells of the normal testis.
The stratified epithelium of the convoluted tubules changes in the tubuli recti to an epithelium consisting of a single layer of short columnar or cubical cells resting on a thin basement membrane.
Fig. 293. From section of human testis, showing convoluted seminiferous tubules.
The canals of the rete testis (Haller) are lined by nonciliated epithelium, which varies in type from flat to cubical. Communicating with the rete testis is a blind canal, the vas aberrans of the rete testis, lined with ciliated epithelium.
The vasa efferentia are lined partly by ciliated columnar and partly by nonciliated cubical epithelium. The two varieties form groups which alternate, giving rise to nonciliated depressions, which represent gland-like structures (Schaffer, 92), but do not cause corresponding evaginations of the mucosa. The mucosa, which consists of fibrous connective tissue, contains flattened endothelioid cells, which resemble nonstriated muscle-cells. The latter are found only at the end of the vasa efferentia, just before reaching the vas epididymidis.
Fig. 294. Section through human vasa efferentia : a, Glands ; b, ciliated epithelium ; f, glandular structure ; d, connective tissue.
Fig. 295. Cross-section of vas epididymidis of human testis.
The vas epididymidis is lined by stratified ciliated columnar epithelium, resting on a thin mucosa, outside of which there is found an inner circular and an outer, though thin and not continuous, longitudinal layer of nonstriated muscular tissue.
An aberrant canaliculus also communicates with the vas epididymidis, and is here known as the vas aberrans Halleri. Numbers of convoluted and blindly ending canaliculi are frequently found imbedded in the connective tissue around the epididymis. These constitute the paradidymis, or organ of Giraldes.
The blood-vessels of the testis spread out in the corpus Highmori and in the tunica vasculosa of the connective-tissue septa and of the tunica albuginea, their capillaries encircling the seminal tubules in well-marked networks.
The lymphatic vessels begin in clefts in the tunica albuginea and in the connective tissue between the convoluted tubules. They converge toward the corpus Highmori and pass thence to the spermatic cord.
Retzius (93) and Timofeew (94) have described plexuses of nonmedullated, varicose nerve-fibers surrounding the bloodvessels of the testis. From such plexuses single fibers, or small bundles of such, could be traced to the seminiferous tubules, about which they also form plexuses. Such fibers have not been traced into the epithelium lining the tubules. In the epididymis Timofeew found numerous sympathetic ganglia, the cellbodies of the sympathetic neurones of which were surrounded by pericellular plexuses. In the wall of the vas epididymidis and the vasa efferentia were observed numerous varicose nerve-fibers, arranged in the form of a plexus, many of which seemed to terminate on the nonstriated muscle cells found in these tubes. Some of the nerve-fibers were traced into the mucosa, but not into its epithelial lining.
Fig. 296. Section of dog's testis with injected blood-vessels (low power) : a, Seminiferous tubule ; b, connective-tissue septum ; c, blood vessel.
3. The Excretory Ducts
The vas deferens possesses a relatively thick muscular wall, consisting of three layers, of which the middle is circular and the other two longitudinal. The subepithelial mucosa is abundantly supplied with elastic fibers and presents longitudinal folds. The lining epithelium is in part simple ciliated columnar and in part stratified ciliated columnar, with two rows of nuclei. The cilia are, however, often absent, beginning with the lower portion of the vas epididymidis. According to Steiner, the epithelium of the vas deferens varies. It may be provided with cilia in the lower segments, or it may even be similar to that found in the bladder and ureters.
The inner muscular layer is wanting in the ampulla of the vas deferens ; here the epithelium is mostly simple columnar and pigmented. Besides the folds, there are also evaginations and tubules which sometimes form anastomoses structures which may be regarded as glands.
The seminal vesicles are also lined, at least when in a distended condition, by simple, nonciliated columnar epithelium containing yellow pigment. In a collapsed condition the epithelium is pseudostratified, with two or even three layers of nuclei. The arrangement of the epithelial cells in a single layer would therefore seem to be the result of distention. The mucous membrane shows numerous folds, which, in the guinea-pig for instance, present a delicate axial connective -tissue stroma. Besides scanty subepithelial connective tissue, the seminal vesicles are provided with an inner circular and an outer longitudinal layer of muscle-fibers. Spermatozoa are, as a rule, not met with in the seminal vesicles.
Fig. 297. Cross-section of vas deferens near the epididymis (human).
The epithelium of the ejaculatory ducts is composed of a single layer of cells ; the inner circular muscle-layer is very poorly developed. In the prostatic portion of the ejaculatory ducts the longitudinal muscle-layer mingles with the musculature of the prostate and loses its individuality. The ejaculatory ducts empty either directly into the urethra at the colliculus seminalis, or indirectly into the prostatic portion of the urethra through the vesicula prostatica.
The prostate is a compound branched tubulo-alveolar gland. Its capsule consists of dense layers of nonstriated muscle-fibers, connective tissue, and yellow elastic fibers. Processes and lamellae composed of all these elements extend into the interior of the gland, converging toward the base of the colliculus seminalis. Between the larger trabeculae are situated numerous glands, consisting of large, irregular alveoli, separated by fibromuscular septa and trabeculas. The alveoli are lined by simple columnar epithelium, the inner portion of the cells often showing acidophile granules. Now and then the alveoli present a pseudostratified epithelium, with two rows of nuclei (Rudinger, 83). A basement membrane, although present, is difficult to demonstrate and consists of a network of delicate connective-tissue threads, as was shown by Walker. The numerous excretory ducts, lined by simple columnar epithelium, become confluent and form from 1 5 to 30 collecting ducts which empty, as a rule, either at the colliculus seminalis or into the sulcus prostaticus. Near their terminations the larger ducts are lined by transitional epithelium similar to that lining the prostatic portion of the urethra.
Fig. 298. Cross-section of wall of seminal vesicle, showing the folds of the mucosa (human).
Fig. 299. From section of prostate gland of man.
In the alveoli of the glands, peculiar concentrically laminated concrements are found, known as prostatic bodies or concretions (corpora amylacea). They are more numerous in old men, but are found in the prostates of young men and also of young boys. The secretion of the prostate (succus prostaticus) is not mucous in character, but resembles a serous secretion and has an acid reaction. The vesicula prostatica (sinus pocularis) is lined by stratified epithelium, consisting of two layers of cells and provided with a distinct cuticular margin upon which rest cilia. In its urethral region occur short alveolar glands.
The glands of Cowper are branched tubular alveolar glands, the alveoli being lined by mucous cells. The smaller excretory ducts, lined by cubical epithelium, unite to form two ducts, one on each side of the urethra ; these are I ^ inches long, and are lined by stratified epithelium consisting of two or three layers of cells.
The blood-vessels of the prostate ramify in the fibromuscular trabeculae and form capillary networks surrounding the alveoli. The veins collecting the blood pass to the periphery of the gland, where they form a plexus in the capsule. The lymphatics begin in clefts in the trabeculae and follow the veins. The terminal branches of the vessels supplying Cowper's glands are, in their arrangement, like those of other mucous glands.
Numerous sympathetic ganglia are found in the prostate under the capsule and in the larger trabeculse near the capsule. The neuraxes of the sympathetic cells of these ganglia may be traced to the vessels and into the trabeculae ; their mode of ending has, however, not been determined. Small medullated nerve-fibers terminate in these ganglia in pericellular baskets. Timofeew has described peculiar encapsulated sensory nerve-endings, found in the prostatic and membranous portions of the urethra of certain mammalia. They consist of the terminal branches of two kinds of nerves, inclosed within nucleated laminated capsules : one large medullated nerve -fiber, after losing its medullary sheath, breaks up into a small number of ribbon-shaped branches with serrated edges, which may pass more or less directly to the end of the nerve-ending or may be bent upon themselves ; and very much smaller medullated nerve-fibers which, after losing their medullary sheaths, divide into a large number of varicose fibers which form a dense network encircling the ribbon-shaped fibers previously mentioned.
The penis consists of three cylindric masses of erectile tissue the two corpora cavernosa, forming the greater part of the penis and lying side by side, and the corpus spongiosum, surrounding the urethra and lying below and between the corpora cavernosa. The two latter are surrounded by a dense connective-tissue sheath, the tunica albuginea. These erectile bodies are surrounded by a thin layer of skin, containing no adipose tissue and no hair-follicles. The corpus spongiosum is enlarged anteriorly to form the glans penis.
The principal substance of the erectile bodies is the so-called erectile tissue : septa and trabeculae, consisting of connective tissue, elastic fibers, and smooth muscle-cells inclosing a system of communicating spaces. These latter may be regarded as venous sinuses, the walls of which, lined by endothelial cells, are in apposition to the erectile tissue. Under certain conditions the venous sinuses are distended with blood, but normally they are in a collapsed state and form fissures which simulate the clefts found in ordinary connective tissue. In other words, there is here such an arrangement of the blood-vessels within the erectile tissue that the circulation may be carried on with or without the aid of the cavernous spaces. The arteries of the corpora cavernosa possess an especially well-developed musculature. They ramify throughout the trabeculas and septa of the erectile tissue and break up within the septa into a coarsely meshed plexus of capillaries. A few of these arteries empty directly into the cavernous spaces. On the other hand, the arteries give off a rich and narrow-meshed capillary network immediately beneath the tunica albuginea. This is in communication with a deeper and denser venous network, which, in turn, gradually empties into the venous sinuses. Aside from these there are anastomoses between the arterial and venous capillaries, which later communicate with the venous network just mentioned. The blood current, regulated as it thus is, may pass either through the capillaries alone, or may divide and flow through both these and the venous sinuses. These conditions explain both the erectile and quiescent state of the penis. The relations are somewhat different in the corpus spongiosum urethrae and in the glans penis. In the corpus spongiosum the arteries do not open directly into the venous spaces, but break up first into capillaries. In the submucosa of the urethra there is found a rich venous plexus. In the glands the arteries end in capillaries which pass over into veins with well-developed muscular walls. The blood is collected by means of the venae emissariae which empty into the vena dorsalis penis and into the venae profundae.
The epithelium of the urethra varies in the several regions. The prostatic portion possesses an epithelium similar to that of the bladder. In the membranous portion, the epithelium may be similar to that found in the prostatic portion, but more often presents the appearance of a pseudostratified epithelium with two or three layers of nuclei. The cavernous region is lined by pseudostratified epithelium, except in the fossa navicularis, where a stratified squamous epithelium is found. Between the fibre-elastic mucosa and the epithelium there is a basement membrane. There occur in the urethra, beginning with the membranous portion, irregularly scattered epithelial sacculations of different shapes. Some of these show alveolar branching, and are then known as the glands of Littre.
The submucosa of the cavernous portion of the urethra, which contains nonstriated muscle-tissue arranged circularly, is richly supplied with veins, and contains pronounced plexuses communicating with cavernous sinuses, which correspond in general to those of the corpora cavernosa penis.
The glans is covered by a layer of stratified squamous epithelium, often possessing a thin stratum corneum (see Skin). Near the corona of the glans penis there are now and then found small sebaceous glands (see Hair), known as glands of Tyson. The prepuce is a duplication of the skin, the inner surface presenting the appearance of a mucous membrane.
The nerves terminating in the glans penis have recently been studied by Dogiel, who made use of the methylene-blue method in his investigation. He finds Meissner's corpuscles in the connectivetissue papillae under the epithelium, Krause's spheric end-bulbs somewhat deeper in the connective tissue, and the genital corpuscles situated still deeper (see Sensory Nerve-endings). In the epithelium are found free sensory nerve-endings. Pacinian corpuscles have also been found in this region.
In order that the student may obtain an understanding of the complicated process of spermatogenesis we shall give a description of it as it occurs in salamandra maculosa, which of all vertebrate animals presents the phenomena in their simplest and best known form. The student should understand, however, that many of the details here described have not been observed in the testes of mammalia ; and, since the spermatozoa of many of the mammalia are of simpler structure than those of the salamander, the development of the spermatozoa of the former is consequently simpler. It should also be noticed that the general structure of the testes of the salamander differs in some respects from that of the testes of mammalia, as given in the preceding pages.
At first the seminiferous tubules consist of solid cellular cords, and it is only during active production of spermatozoa that a central lumen is formed, in which the spermatosomes then lie. The cells which compose these solid cords may be early differentiated into two classes those of the one class being directly concerned in the production of the spermatosomes ; those of the other appearing to have a more passive role. The cells of the first class the spcrmatogonia, or primitive seminal cells undergo a process of division accompanied by an increase in size. In this way they soon commence to press upon the cells of the second class \\\& follicular o\~ sustentacular cells. The result is that the nuclei of the latter are forced more or less toward the wall of the seminal tubule, while their protoplasm is so indented by the adjacent spermatogonia that the cells assume a flattened cylindric shape presenting indentations and processes on all sides. In this stage the spermatogonia have a radiate arrangement and entirely surround the elongated sustentacular cells. At present three periods are distinguished in the development of the male sexual cells (spermatosomes) from the spermatogonia. The first period embraces a repeated mitotic division of the spermatogonia the period of proliferation. In the second, the spermatogonia, which have naturally become smaller from repeated division, begin to increase in size the period of growth. The third is characterized by a modified double mitotic division without intervening period of rest, and results in the matured spermatozoa the period of maturation, figure 300. During the third period, a very important and significant process takes place the reduction in the number of chromosomes, so that in the spermatids, the chromosomes are reduced to half the number present in a somatic cell of the same animal. The manner in which this reduction in the number of chromosomes takes place will be described as it occurs in salamandra maculosa.
Fig. 300. Schematic diagram of spermatogenesis as it occurs in ascaris (after Boveri). ("Ergebn. d. Anat. u. Entw.," Bd. I.)
After the cells composing the last generation of spermatogonia have attained a certain size (period of growth), they undergo karyokinetic division. First, the usual skein or spirem is formed, but instead of dividing into twenty-four chromosomes, as in the somatic cell, the filament of the skein segments into only twelve loops. The cell thus provided with twelve chromosomes now enters upon the period of maturation, and is known as a spermatocyte of the first order, or a "mother cell" (O. Hertwig, 90). The division of these cells is heterotypic (vid. p. 70); the chromosomes split longitudinally and in such a way that the division begins at the crown of the loops, extending gradually toward their free ends. In this case the daughter chromosomes remain for some time in contact, so that the metakinetic figure resembles a barrel in shape. Finally, the daughter chromosomes separate and wander toward the poles. As soon as the daughter stars (diaster) are developed, the number of chromosomes is again doubled by a process of longitudinal division. The spermatocyte of the first order thus divides into two spermatocytes of the second order, or daughter cells (O. Hertwig, 90). The nuclei of the daughter cells now contain twenty-four chromosomes, as is the case in the somatic cell, and, without undergoing longitudinal splitting, the daughter chromosomes are distributed to the two nuclei of the spermatids. In other words, the latter contain only twelve chromosomes. The spermatozoa are formed from the spermatids by a rearrangement of the constituent elements of these cells. It may thus be said that even in the stage of the segmenting skein in the mother cells, the spermatocytes of the first degree contain twice as many chromosomes as a somatic cell, a condition which is first clearly seen in the stage of the diaster (here only an apparent duplication in the diaster stage). As a result, there is, first, a decrease in the double number of chromosomes found in the spermatocytes of the second degree to the normal number ; second, a decrease in the number of chromosomes in the spermatocytes of the third degree (spermatids) to one-half the number present in a somatic cell, a condition probably due to the fact that here there is no stage of rest nor longitudinal splitting of the chromosomes. This is the general process in heterotypic division. Besides the heterotypic form, there occurs in the division of the spermatocytes another (homeotypic) form of karyokinetic cell-division. This differs from the heterotypic in the shortness of the chromosomes, the absence of the barrel phase, the late disappearance of the aster, and the absence of duplication in the chromosomes of the diaster. According to Meves (96), the spermatocytes of the first degree undergo heterotypic, those of the second degree, homeotypic division.
The spermatids develop into the spermatozoa, beginning immediately after the close of the second division of maturation. This process has been fully described for salamandra maculosa by Hermann, Flemming, Benda, and others, but need not engage our attention at this point beyond the statement that the chromatin of the nuclei of the spermatids develops into the heads of the spermatozoa, while the remaining structures are developed from the protoplasm. " The mature spermatozoon of the salamander represents a completely metamorphosed rell ; in the course of its development no portion of the original cell is cast off" (Meves, 97).
Spermatogenesis in mammalia may be compared to the foregoing process, with the exception that here the different stages are seen side by side in the seminiferous tubule and without any apparent sequence, making the successive stages more difficult to demonstrate. The various generations of cells form columns, and are arranged in such a manner that the younger are found near the lumen and the older close to the wall of the tubule. (Figs. 301 and 302.) These columns are separated from each other by high sustentacular cells, or Sertoli's cells or columns. The metamorphosis of the cells into spermatids and spermatosomes is accomplished by the changing of the cells bordering upon the lumen and then of those in the deeper layers, etc., into spermatids and then into spermatosomes. During this process the spermatids arrange themselves around the ends of Sertoli's columns, a phenomenon which was formerly regarded as representing a copulation of the two elements, although it was clearly understood that no real fusion or interchange of chromatin occurred, but that the close relations of the two were for the purpose of furnishing nourishment to the developing spermatosomes. The whole forms a spermatoblast of von Ebner. Since the spermatids lining the lumen are changed into spermatozoa, and the process is repeated in the cells of the deeper layers as they come to the surface, the result is that the entire column is finally used up. The compensatory elements are supplied by the proliferation of the adjacent spermatogonia. The resulting products again divide, and thus build up an entirely new generation of spermatogenic cells. Hand in hand with these progressive phenomena occurs an extensive destruction of the cells taking part in spermatogenesis. This is shown by the presence of so-called karyolytic figures in the cells, which later suffer complete demolition.
Fig. 301. Schematic diagram of section through convoluted seminiferous tubule of mammal, showing the development of the spermatosomes. The number of chromosomes is not shown in the various generations of the spermatogenic cells. The progressive development of the spermatogenic elements is illustrated in the eight sectors of the circle : a, Young sustentacular cell ; b, spermatogonium ; c, spermatocyte ; d, spermatid. In I, 2, 3, and 4 the spermatids rest on the enlarged sustentacular cell in the center of the sector ; on both sides of the sustentacular cells are the spermatogenic or mother cells in mitosis. In the sectors 5, 6, 7, and 8 spermatozoa are seen in advanced stages resting on the sustentacular cells, with new generations of spermatids on each side. [From Rauber (after Brown) with changes (after Hermann).
Fig. 302. Section of convoluted tubule from rat's testicle (after von Ebner, 88). The pyramidal structures are the sustentacular cells, together with spermatids and spermatosomes. Between these are spermatogenic cells, some of which are in process of mitotic division. Below, on the basement membrane and concealing the spermatogonia, are black points representing fat-globules, a characteristic of the rat's testicle. Fixation with Flemming' s fluid.
These developmental changes are represented in the preceding schematic figure (Fig. 301), and may in part be observed in figure 302.
In mammalia it has been possible to trace the development of the spermatids into the spermatosomes. These phenomena have been studied and described by numerous writers, and although many conflicting views have been expressed, the essential steps of this process seem quite clearly established. The account here given is based in part on the recent observations of v. Lenhossek and the observations of Benda. Before considering the method o/ development of the spermatosomes from the spermatids, a few words concerning the structure of the latter may be useful. The sharply outlined spermatid possesses a slightly granular protoplasm and a round or slightly oval nucleus with a delicate chromatic network. In the protoplasm there is found a sharply defined globule, known as the sphere or sphere substance, which lies near the nucleus and presents throughout a nearly homogeneous structure. This substance is first noticed in the spermatocytes, disappears during the cell-divisions resulting in the spermatids, and reappears in the latter. In the protoplasm of the spermatid, lying near the nucleus, there is further found a small globular body, the chromatoid accessory nucleus of Benda, smaller than the sphere and staining very deeply in Heidenhain's hematoxylin. A true centrosome may also be found in the spermatid.
The nucleus of the spermatid develops into the head of the spermatosome, during which change the originally spheric nucleus becomes somewhat flattened and at the same time assumes a denser structure and moves toward that portion of the spermatid pointing away from the lumen of the seminiferous tubule. Accompanying these changes in the nucleus, marked changes are observed in the shape and structure of the sphere, which marks the position of the future anterior end of the head of the spermatosome, and applies itself to the nucleus on the side pointing away from the lumen of the tubule. In this position it differentiates into an outer clear homogeneous zone and a central portion which stains more deeply and to which v. Lenhossek has given the name akrosome. From these structures are developed the head-cap and the lance of the spermatosomes, which differ in shape and relative size in the spermatosomes of the different vertebrates. Recent investigation seems to establish quite clearly that the axial thread of the tail is developed from the centrosome (from the larger, if two are present), which is situated at some distance from the nucleus. Soon after the beginning of the development of the axial thread the centrosome wanders to the posterior part of the future head of the spermatosome (the pole of the nucleus opposite the head-cap) and becomes firmly attached to the nuclear membrane in this position (observations made on the rat by v. Lenhossek, and on the salamander by Meves). The middle piece and the undulating membrane, it would appear, are differentiated from the protoplasm, although the question of the mode of their development is still open to discussion. The chromatoid body assumes a position near the axial thread at its junction with the cell membrane ; its fate has not, however, been fully determined.
According to Hermann (97), the end-piece in the selachia is derived from the centrosome, the ring-shaped body from the invaginated half of the intermediate body of the spermatid formed during the last spermatocytic division, and the axial thread from filaments of the proximal half of the central spindle. The lance, according to him, represents a modified portion of the nuclear membrane of the spermatid.
For further particulars regarding spermatogenesis see the investigations of v. la Valette St. George, 67-87 ; v. Brunn, 84 ; Biondi, Benda, Meves, and v. Lenhossek.
The ovaries of the smaller animals are better adapted to study than those of the human being, since the former are more easily fixed.
The germinal epithelium and its relations to the egg-tubes of Pfliiger are best studied in the ovaries of young or newly born animals cats, for instance, being especially well adapted to this purpose.
Normal human ovaries are usually not easily obtainable. Human ovaries very often show pathologic changes, and in middle life frequently contain but few follicles.
Fresh ova may be easily procured from the ovaries of sheep, pig, or cow in the slaughter-houses. On their surfaces are prominent transparent areas the larger follicles. If a needle be inserted into one of these follicles and the liquor folliculi be caught upon a slide, the ovum may as a rule be found, together with its corona radiata. That part of the preparation containing the ovum should be covered with a cover-glass under the edges of which strips of cardboard are laid. If no such strips are employed, the zona pellucida of the ovum is likely to burst in the field of vision, giving rise to a funnel-shaped tear. These tears have often been pictured and described as preformed canals (micropyles).
The best fixing fluid for ovarian tissue is Flemming's or Hermann's, either of which may be used for small ovaries or pieces of large ovaries ; safranin is then used for staining. Good results are also obtained with corrosive sublimate (staining with hematoxylin according to M. Heidenhain), and also with picric acid (staining with borax carmin).
The treatment of the Fallopian tubes is the same as that of the intestine ; in order to obtain cross -sections of a tube it is advisable to dissect away the peritoneum near its line of attachment and then distend the tube before fixing. It is instructive to dilate the tube by filling it with the fixing agent, thus causing many of the folds to disappear.
No special technic is necessary in fixing the uterus and vagina. The epithelium is, however, best isolated with one-third alcohol.
Seminal fluid to which normal salt solution has been added may be examined in a fresh condition. The effect upon the spermatozoa of a very dilute solution of potassium hydrate ( i % or weaker) or of a very dilute acid (acetic acid) is worth noticing. The spermatozoa of salamandra maculosa show the different structural parts very clearly (lance, undulating membrane, marginal thread, etc.). In macerated preparations (very dilute chromic acid), or in those left for some time in a moist chamber, the fibrillar structure of the marginal and axial threads may be seen quite distinctly. The spermatozoa may also be examined in the form of dry preparations (treatment as for blood), stained, for instance, with safranin. Osmic acid, its mixtures, and osmic vapors are useful as fixing agents, certain structures being better brought out so than by employing the dry methods.
In examining the testicle (spermatogenesis) it is advisable to begin with the testis of the salamander, which does not show such complicated structures as do the testes of mammalia. Here also either Flemming's or Hermann's fluid may be used as a fixing agent, the latter being followed by treatment with crude pyroligneous acid. For the salamander Hermann recommends a mixture composed of i % platinum chlorid 15 c.c. , 2% osmic acid 2 c.c., and glacial acetic acid i c.c., and for mammalia the same solution with double the amount of osmic acid. The fluid is allowed to act for some days, the specimen then being washed for twenty-four hours in running water and carried over into alcohols of ascending strengths. Paraffin sections are treated as follows : Place for from twenty-four to forty-eight hours in safranin (safranin i gm. is dissolved in 10 c.c. of absolute alcohol and diluted with 90 c.c. of anilin water). After decolorizing with pure or acidulated absolute alcohol the sections are placed for three or four hours in gentian-violet (saturated alcoholic solution of gentian -violet 5 c.c. and anilin water 100 c.c.), and are then placed for a few hours in iodo-iodid of potassium solution until they have become entirely black (iodin i, iodid of potassium 2, water 300); finally, they are washed in absolute alcohol, until they become violet with a dash of brown. The various structures appear differently stained : for instance, the chromatin of the resting nucleus and of the dispirem, bluish-violet ; the true nucleoli, red ; while, on the other hand, in the aster and diaster stages the chromatin stains red.
It is of especial importance that small testicles should not be cut into pieces before fixing, as this causes the seminal tubules to swell up and show marked changes, even in regions at some distance from the cut (Hermann, 93, I).
The treatment of the remaining parts of the male reproductive organs requires no special technic.
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Reference: Böhm AA. and M. Von Davidoff. (translated Huber GC.) A textbook of histology, including microscopic technic. (1910) Second Edn. W. B. Saunders Company, Philadelphia and London.
Cite this page: Hill, M.A. (2020, September 27) Embryology Book - A textbook of histology, including microscopic technic (1910) Special Histology 5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_A_textbook_of_histology,_including_microscopic_technic_(1910)_Special_Histology_5
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