In the male the medullary cords, infiltrated with germ 

 cells, form the seminiferous tubules, while in the female the 

 medullary cords are repressed. Clumps and strands of cor- 

 tical cells, with germ cells among them, become partly en- 

 closed by thin strands of medullary cells. The medullary 

 strands supply thecal (encapsulating) cells to the cortical 

 cords in which the nests of female germ cells develop. Late 

 in development the ovary moves posteriorly below its peri- 

 toneal cover. Its suspensory ligament marks this movement. 

 It still remains in contact with the body wall, but the ovi- 

 duct now loops below and in front of it (Figure 10-37). 



The MuUerian ducts form the tubular portion of the fe- 

 male system, conducting the egg from the ovary, supplying 

 it with the proper environment for its development (uterus), 

 and aiding in fertilization by means of a copulatory pouch, 

 the vagina. The Mullerian ducts appear relatively late (20 

 mm) in man and develop by a process of infolding, begin- 

 ning at the anterior end of the mesonephros and extending 

 posteriorly. It should be noted that the ostium of this tube 

 lies well anterior to the genital part of the mesonephric 

 kidney. 



The first evidence of this duct is a thickening of the 

 epithelium of the kidney ne.\t to the nephric duct. This 

 thickening forms a groove (Figure 35 A) which closes 

 over, except at its anterior end, the ostium. This process of 

 invagination and tubulation extends back along the kidney 

 through the genitoinguinal fold to the midline anterior to 

 the urogenital sinus. Here the two ducts unite and extend 

 back to enter the urogenital sinus just in front of the neph- 

 ric duct (see Figure 355, Patten, 1946). The genitoinguinal 

 fold has been modified by the medial movement of the pos- 

 terior end of the Mullerian ducts. From the anterior end of 

 their fused area a fold now extends to the inguinal region, 

 passes out through the inguinal canal, and ends in the labia 

 majora. This is the round ligament of the uterus, corre- 

 sponding in part to the gubernaculum of the male. 



The vagina represents the terminal part of the fused 

 Mullerian ducts. This region is separated from the thick- 

 walled, glandular uterus by the cervix. The uterus opens 

 laterally into the two tubes (oviducts or Fallopian tubes). 

 These tubes open into the body cavity through a flaring 

 ostium with fimbriated (frilled) margins. Remnants of the 



urogenital sinus 



mesentery. 



penis pouch 

 penis 



owper's gland 



kidney 



epididymidis 

 ostium, 

 mesepididymium (mesentery) 

 testis 



cloaca 



vas deferens 

 genitoinguinal fold 



opening of urogenital sinus into gut 

 vestigial nephric duct 

 uterus 



urogenital canal 



Figure 10-34 Urogenital systems in both sexes of the Echidna (Tochyglossus). A, female in ventral 

 view; B, details of tubes opening into urogenital canal; C, mole in ventral view; D, male in lateral 

 view; E, bifurcate, spinous penis. (A, after van den Broek, 1933; E, after Grosse, 1955) 



cloacal aperture 



THE REPRODUCTIVE SYSTEM • 321 



