Mammalia: Visceral Systems 



-OVARIAN LIGAMENT. 

 -OVARY. 



655 



Fig. 495. The human female urinogenital system. (After Sobotta. Courtesy, Neal 

 and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) 



and body-wall. In the case of the testis, a specialized agent plays an 

 important part in the later phase of the "descent." At an early period 

 in the development of the testis a peritoneal fold becomes transformed 

 into a ligament stretching from the hind end of the testis to that 

 particular spot in the posterior abdominal wall where the scrotum is 

 destined to develop. After the scrotum has been formed, this ligament, 

 the gubernaculum, is found to be attached to the posterior wall of 

 the scrotum (Fig. 493) and external to the tunica vaginalis. By some 

 obscure process this gubernacular Ligament (not muscular) shortens 

 and in so doing pulls the testis into the scrotum, thus completing the 

 "descensus." 



The advantage which accrues to a mammal in possessing a scrotum 

 is far from obvious. A testis which normally resides in a scrotum ceases 

 to produce spermatozoa if it remains in the abdominal cavity. Crypt- 



Fic 194.— (Continued.) 

 surface of the expanding bladder. The mesonephric ducts in the male, serving as 

 the spermatic ducts, retain their openings into the urinogenital sinus which 

 becomes extremely contracted and elongated to form the urethral canal of the 

 penis (see Fig. 492), while the Mullerian ducts degenerate. In a female, shown 

 in (D) and (E), the mesonephric ducts degenerate and, as the ureters are carried 

 forward onto the bladder, the oviducts retain their connection with the urino- 

 genital sinus which appears as the vestibule of the adult. (E) shows a common 

 adult condition — the posterior regions of the two oviducts joined to form a median 

 vagina into which open right and left uteri (see also Fig. 495). 



