THE UROGENITAL SYSTEM 



443 



Descensus of Gonads. A comparison of earlier and later stages 

 reveals the fact that the gonads shift their position posteriorly in the body 

 cavity. The prime factor in this backward migration is the continued 

 growth of the posterior portion of the gonads and the associated atrophy 

 of the anterior portion. These processes result in the change of the 

 gonads from an abdominal to a pelvic position. The ovaries retain this 

 position throughout life but the testes migrate into the scrotal sac. 



The testis is originally an abdominal organ like the ovary, and its 

 position in the scrotum the result of a migration or descensus in which it 

 drags with it blood vessels, lymphatics, nerves, and the cremaster externus 

 and internus muscles, which, together with the ductus, constitute the 

 spermatic cord. 



During the third to the sixth month of development, paired out- 

 pocketings of the body cavity, vaginal sacs, extend ventral to the pubic 



Fig. 370. — Schematic diagrams illustrating the descent of the testis as seen from the 

 side. d. def., ductus deferens; Proc. Vag., processus vaginalis (the diverticulum 

 of the peritoneum pushed into the scrotal sac). (From Patten's "Embryology of the 

 Pig.") 



bones into the scrotal sacs. During the seventh to the ninth month, 

 the testes descend into the scrotal sacs. This "descensus" occurs not 

 into the vaginal sacs but beneath the peritoneum dorsal to the vaginal 

 sacs. Normally, the passage between the body cavity and the vaginal 

 sac is obliterated soon after the migration of the testis (7th to 9th month). 

 Failure to close results in liability to inguinal hernia. The condition of 

 undescended testes is known as cryptorchism and is accompanied by 

 sterility since spermatozoa are unable to survive the normal temperature 

 of the body. The scrotal sac appears to act as a thermoregulator. 



The factors involved in the descensus of the testes are complex. 

 Chief among them appears to be the contraction of the connective tissue 

 gubemaculum testis which extends from the testis to the posterior wall 

 of the scrotum. The gubernaculum contracts to one quarter of its 

 original length and after the descensus almost completely atrophies. 

 During the course of its descent, each testis rotates through an arc of 

 180° so that its anterior and posterior ends are reversed. 



Rarely, the ovaries undergo a similar descent into the labia majora. 

 Normally, however, the enlargement and relations of the uterus prevent 

 this migration. 



