A PART TENTH. URO-GENITAL APPARATUS. — EMBRYOLOGY. ORIGIN AND DEVELOPMENT OF THE URO-GENITAL 2 V I APPARATUS. THE uro-genital mucous surface and its appendages, on their first appearance, are only a portion of the alimentary canal, of the mucous layer of the blastoderma. At the period when the intestinal canal exists only in the form of a tube, its middle portion communicates with the germinal vesicle, and each end terminates in a cul-de-sac; on its lower 1 part may be seen a protuberance (B), (Fig. 124), and a partition (E) which separates the primitive tube from the later protuberance; in this protuberance, which becomes more and more prominent, may be found two cavities: 1. The older cavity of the digestive tract or Diagram of the forma- tube, which will later become the tion of the uro-genital organs." * rectum; and, 2. In front a uro-genital cavity or sinus uro-genitalis, from which are formed every part of the urinary and genital organs. Fig. 124. SU E B I E *1. I, I, Intestinal tube, with the protuberance B, which will soon be separated by the partition E. 2. The partition has extended; the protuberance B is very much developed, and has given place to the allantoïs A (the commencement of which, the pedicle, can only be seen), and successively, proceeding from the allantois towards the intestinal tube the urachus O, the bladder V, the genito-urinary sinus SU, which has also given off three protuberances: for the Wolffian body 1, for the duct of Müller 2, and for the kidney 3. In fact this uro-genital sinus (beside the allantois, Fig. 124, A, that we shall examine further on) gives origin to three protuberances or cæca on each side; these elongate in the direction of the superior portion of the germinal vesicle. 1. The first of these protuberances, or, more properly speaking, germs (Fig. 124, 1), itself gives rise to lateral vegetations, from which a penniform organ is formed; this is the Wolffian body, which in fatal life is developed to a great size and occupies the largest portion of the abdominal cavity. At this same period it comprises elements analogous to the glomeruli or corpuscles of Malpighi in the kidney, and seems to possess the same functions that afterwards belong to this latter organ; in consequence of which function the Wolffian body has been called the primordial kidney (Jacobson, Rathke). But, towards the close of the first half of foetal life in the female foetus, these organs become atrophied and disappear, whilst, on the other hand, a portion of the male genital organs is developed from them. 2. The second protuberance or cæcum elongates without presenting secondary vegetations; this forms a single tube known by the name of Müllerian duct or organ of Müller (Fig. 124, 2). This is essentially arranged for the formation of the most important portions of the female genital organs, Fallopian tubes and uterus; in man they form comparatively useless rudimentary vestiges of the embryonic state, such as the utriculus prostaticus (prostatic vesicle), and a small appendage of the epididymis, the corpora Morgagnii, hydatids of Morgagni. 3. The third protuberance or cæcum (Fig. 124, 3) presents quite a number of secondary vegetations, originating and radiating from the end of the tube. These secondary protuberances assume the form of canaliculi placed side by side, interlace and finally converge in a little vascular tuft, against which, as it were, their extremity abruptly terminates in a cæcum; beyond this point they are not developed. Each of these embraces, by its cæcal extremity, a vascular tuft; this latter fills up the interior of the hollow of the cul-de-sac in such a way as to be lodged in a terminal capsule. Thus are formed the uriniferous tubes and the malpighian corpuscles (glomeruli Malpighii), in one word, the kidney. Finally, beyond these three protuberances on each side, the anterior extremity of the uro-genital sinus is developed, and constitutes the allantoid canal (urachus) and the allantoid bladder (vesicula allantoidiana, Fig. 124, 0, A), whe tions we shall presently study when we consider the placenta. We will in this place only mention that the allantoïs and its canal, the urachus, both disappear in the adult. The inferior portion of the canal alone remains, and being developed to an enormous size, constitutes the reservoir, called the bladder. This rapid review of the origin of the genital and urinary organs exhibits a close relationship between these two systems, and consequently teaches the close analogy between their epitheliums; since these mucous surfaces always originate from the epithelium of the sinus uro-genitalis, which latter is an offshoot from the intestinal epithelium, that is, the internal layer of the blastoderm. We shall study in succession the urinary system and the genital system of the male and the female. We shall else- · where recur to the embryological conditions of the two latter, which alone furnish facts that establish the homology of the organs of the two sexes. I. URINARY APPARATUS. A. Secretion of urine. In their structure the canals or tubes which compose the renal parenchyma resemble the sudoriferous glands. These are straight tubules in the medullary portion of the kidney (ducts of Bellini, Fig. 125), then becoming convoluted or twisted together (ducts of Ferrein) in the cortical substance.1 1 The connections of the straight tubules, of the convoluted tubules (tubuli contorti), and of the glomeruli (Malpighian corpuscles) of the kidney, especially demonstrated by Schumlansky, Bowman, and Isaacs, have met with formidable antagonism from Müller and Henle. Henle especially has undertaken to describe some looped tubules among the uriniferous tubes, which he considered as terminating in culs-de-sac, or dividing into smaller tubuli. There are, indeed, very remarkable looped tubules in the kidney, but a study of these tubules, called tubules of Henle, undertaken by Kölliker, Zawarickin, and especially SchweiggerSeidel, has demonstrated that these formed no separate system, as was formerly supposed by Henle (see "Traité d'Anatomie," by Cruveillier and M. Sée. 4th edition, 1839). By the action of acids on the substance of the kidney, Schweigger-Seidel was the first to show that Henle's tubules have the most intimate connection with the classical straight and convoluted tubules of the kidney, and that they are not in the least degree blood-vessels, as Chrzon At this point each of these terminates in a sac-like dilatation into which projects, hernia-like, a vascular tuft (glomerulus Malpighii), formed by the capillarization of an arteriole (afferent vessel), Fig. 125, a. These capillary tufts converge to form a small efferent vessel which leaves the glomerulus at sczewsky and Sucquet tried to prove. These looped tubules (going from the glomeruli towards the medullary substance of the kidney, and, in fact, following the same course as the urine) are continuations of the tubes of Ferrein, whose walls at a certain place become much smaller, rectilinear, and descend in the medullary substance * Origin and dichotomy of the uriniferous canaliculi in the medullary substance of the human kidney (tubes of Bellini). (Schumlansky.) the same or near the point where the afferent vessel enters (Fig. 126, p V). But it must be noted that the efferent vessel RC Tb Tf G A Fig. 126. - Diagram of the kidney and its circulation.* does not immediately reunite with its fellows to form the renal vein; almost immediately after it has left the glomerulus it divides again and forms a capillary system in the renal parenchyma (RC), the vascular network of which interlaces with the uriniferous tubes. This efferent vessel does not merit the name of a vein; it belongs to a separate system which we might perhaps consider as a renal portal vein, since it is intermediate between two capillary systems, viz., the glomeruli and the renal parenchyma; the true origin of the renal vein is subsequent to these last-named capillaries. This arrangement of the vascular system in the kidney forms the basis of all the modern theories upon the urinary secretion; a filtration is the fundamental process on which these theories depend. If we recall the fact that differences of pressure between the various parts of the circulatory system do not bear any relation to the especial form of these parts (trunks, small vessels, or capillaries), but to their distance from two extreme points (left ventricle and right auricle) of the origin and ter of the pyramids of Ferrein (alongside of the tubules of Bellini), then reascend again, becoming larger, and go into the cortical substance; there these tubes take a new direction, and finally continue with the true tubes of Bellini. In brief, the tubes of Henle become loops in form of inverted siphons between the tube of Ferrein and that of Bellini. The only physiological knowledge that we at present possess of these looped tubes is dependent on their constriction in the descending branches, and the dilatation in their ascending branches. Yet their epithelium is clear and transparent in the straight and descending branch, turbid and granular in the large and descending portion (towards the bases of the pyramids). (See Ch. Fr. Gross, Essai sur la Structure Microscopique du Rein." Thèse de Strasbourg, 1868, No. 95.) *Tb, Straight tube of Bellini. Tf, Convoluted tube of Ferrein. G, Glomerulus, with its vascular tuft. a, Afferent arteriole, going to the capillaries of the corpuscle. pV, Efferent vessel forming smaller capillaries among the renal tubuli in RC, before forming the true venous vessel V. |