THE UROGENITAL SYSTEM 



;2i 



Descensus of Gonads. A comparison of earlier and later stages 

 leveals 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. 



. .AN 0UCT\ 



TESTIS C. SEX CORU B OVARY C&WTNElOs DUCT) 



Fig. 285. — Diagrams of the testis (A) and ovary (B) showing the homologies of their 

 components. (Redrawn after Mall, modified.) 



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

 position in the scrotum is 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 



Tes*M 



Gcbe 



Pig. 286. — 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 



