224 



THE UROGENITAL SYSTEM 



Whether due to the active shortening of the gubernaculum testis or to its retarded 

 growth, the descent of the testis into the vaginal sac begins during the seventh 

 month of fetal life, and by the eighth month, or at least before birth, the testis 

 is usually located in the scrotum (Fig. 234). It must be remembered that the 

 testis and gubernaculum are covered by the peritoneum before the descent be- 

 gins, consequently the testis follows the gubernaculum along the inguinal canal 

 dorsal to the peritoneum, and, when it reaches the scrotum, is invaginated mto 

 the saccus vaginalis, but does not he in the ccelomic extension. The guber- 

 naculum is said to degenerate during the descent of the testis or immediately 

 after. Abnormally, the testis may remain in the abdomen, a condition known 

 as cryptorchism (concealed testis) and associated with sterihty in man. In 

 some mammals (bat, whale, and elephant) it is the normal condition. 



Shortly after birth the inguinal 

 canal, connecting the saccus vaginahs 

 with the abdominal cavity, becomes 

 solid and its epithelium is resorbed. 

 The now isolated vaginal sac becomes 

 the tunica vaginalis of the testis. Its 

 visceral layer is closely appHed to the 

 testis and its parietal layer forms the 

 Hning of the scrotal sac. The ductus 

 deferens and the spermatic vessels and 

 nerves are of course carried down into the scrotum with the testis and epididy- 

 mis. They are surrounded by connective tissue, and, with the spermatic vessels, 

 constitute the spermatic cord. Owing to the descent of the testis, the ductus 

 deferens is looped over the ureter in the abdomen (Fig. 238 C). In some cases 

 the inguinal canals remain open so that the testis may slip back into the ab- 

 dominal cavity. Such conditions may lead to inguinal hernia of the intestine. 

 Open inguinal canals occur normally in rodents. 



In the female, shallow peritoneal pockets, the diverticula of Nuck, corre- 

 spond to the vaginal sacs of the male. Rarely a more or less complete descent of 

 the ovary into the labium majus occurs. 



Fig. 234. — Descent of the testis (Cunning- 

 ham), a.c, Abdominal cavity; ^.i'., vaginal sac; 

 t., testis; j., scrotum; t.v., tunica vaginalis; x., 

 rudiment of vaginal sac. 



THE EXTERNAL GENITALIA 



Indifferent Stage. — The external genitalia of both sexes are identical until 

 the beginning of the third month of development, when the indifferent anlages 

 become moulded into sexually distinct organs. There develops early in the 



