88fl 



DEVELOPMENT OF THE URINARY APPARATUS. 



extends so far downwards as to pass over the transverse colon and the loops of the small intestine 

 (III, X). As the mesogastrium originally consists of two plates, of course the omentum must 

 consist of four plates. At the 4th month, the posterior surface of the omental sac unites with 

 the surface of the transverse colon (Joh. MiiUcr). 



450. URINARY AND GENERATIVE ORGANS. Urinary apparatus. The first indica- 

 tion of this apparatus occurs in the chick at the 2nd day and in the rabbit at the 9th, as the 

 ducts of the primitive kidneys or Wolffian ducts (fig. 682, 1, W), which are formed from some 

 cells mapj>ed off from the lateral plate above and to the side of the protovertebrse, and extending 

 from the fifth to the last vertebra. The ducts are solid at first, but soon become hollow, and 

 from their cavities there extend laterally a series of small tubes, which in the chick communi- 

 cate freely with the peritoneal cavity {Kolliker). Into one end of each of these tubes grows a 

 tuft of blood-vessels forming a structure resembling the glomeruli of the kidney. The tubes 

 elongate, form convolutions, and increase in number. The upper end of the Wolffian duct is 

 elosed at first, its lower end, which lies in a projecting fold the plica urogenitalis of Waldeyer 

 in the peritoneal cavity, opens into the uro-genital sinus. Close above the orifice of the 

 Wolffian duct appears the ureter as the duct of the kidney. The duct elongates, and branches 

 at its upper end. Each canal at its end is like a stalked caoutchouc sac ( Toldt), and into it 

 there grow the already formed glomeruli. The duct of the kidney opens independently into 

 the uro-genital sinus, and forms the ureter. The part where the branching of the duct stops 

 forms the pelvis of the kidney, and the branches themselves the renal tubules. Toldt found 



Malpighian corpuscles in the human kidney at the 

 2nd month, and Henle's loops at the 4th. The first 

 appearance of the urinary bladder is at the 4th week 

 (His), and is more distinct at the 2nd month, as 

 the dilated first part of the allantois (fig. 682). The 

 upper part of the allantois remains as the obliterated 

 urachus, in the middle vesicle ligament. 



Internal Reproductive Organs. In front of and 

 internal to the Wolffian bodies, there arises in the 

 mesoblast the elongated reproductive gland, germ- 

 ridge, or mass of germ- epithelium (fig. 682, I, D), 

 which in both sexes is originally alike (fig. 683, K, E). 

 In addition, there is formed a canal or duct parallel to 

 the Wolffian duct (W), which also opens into the 

 uro-genital sinus ; this is Muller's duct (M). The 

 elevation of the future reproductive gland is covered 

 originally by germ -epithelium ( Waldeyer). The 

 upper end of the Mullerian duct opens free into the 

 abdominal cavity, while the lower ends of both ducts 

 unite for a distance. Some of the germinal cells 

 covering the surface of the future ovary enlarge to 

 form ova, and sink into the stroma to form ova em- 

 bedded in their Graafian follicles ( 433) (fig. 683). 

 In the female, the Mullerian ducts form the Fal- 

 lopian tube (II, T), and the lower united ends the 

 uterus. 



In the male, the germ-epithelium is not so tall. 

 According to Waldeyer, there are two kinds of tubes 



Fig. 683. 

 Section of mammalian ovary showing de 

 velopment of ova and their follicles. 



Ei, Ripe ovum ; Q, follicular cells of 1? the Wolffian bodies, and some of these penetrate 

 germinal epithelium ; g, blood-vessels th . e .P osltlon of the reproductive gland. These tubes, 



which are connected with the Wolffian ducts, be- 



germinal epithelium; Lf, li'quor folTi'- c m e the seminiferous tubules (v. Wittich), and the 



r.iL . r~ Wolffian duct itself becomes the vas deferens, with 



AT, germinal vesicle and spot ; KE, 

 liquo 

 membrana granulosa 



zona pellucida; PS, ingrowths' from H 16 vesicul{e seminales. According to some other 

 germinal epithelium, ovarian tubes bv observer8 however, tubes which become the semi- 

 means of which some of the nests retain n . lferous tubules, are developed within the reproduc- 

 their connection with the epithelium tlve gland itself ' and these tubes lined with their 

 S, cavity which appears within the ^rm -epithelium ultimately form a connection with 

 Graafian follicle; So, stroma of ovary; th ^i2*? ducts ' ._ ,, . 



Tf, Theca folliculi or ovi-capsule U , Th L e MuUenan ducte > which are reall y the ducts 

 primative ova. ' ' of the reproductive glands, disappear in man, all 



. ,' . . except the lowest part, which becomes the male 



w e Vi S r E" cn,a .P* ta tca A", w)-the homologue of the uterus. The upper tubules of the 

 \\ olfhan body unite at the 3rd month with the reproductive gland (which has now become the 

 iKHly of the testis) and become the coni vasculosi of the epididymis, which are lined by ciliated 

 epithelium (E) ; the remainder of the Wolffian body disappears. Some detached tubules form 



