720 



MAMMALIA. 



which septa pass internally, whereby the seminiferous tubes are 



divided into several fasciculi : after piercing the proper fibrous 



tunic of the testes, the sperm-secreting tubes are collected into an 



extremely tortuous 



duct, that by its F'g- 332. 



convolutions forms 



the epididymis, as 



in Man, and is then 



continued, under the 



name of vas defe- 



rens, to the com- 



mencement of the 

 urethra, into which 

 the two ducts open 

 (B, 6, b). In the 

 Horse, and many 

 Ruminants, the vas 

 deferens presents a 

 remarkable struc- 

 ture : before its ter- 

 mination it suddenly 

 swells to a consider- 

 able diameter, de- 

 pending upon the 

 increased thickness of the walls of the canal, which at the same 

 time become cellular, and secrete a gelatinous fluid that escapes 

 into the cavity of the duct. 



(849.) In their situation the testes of placental Mammals are 

 found to offer very striking differences. In the Cetacea, the 

 Elephant, and the Seal tribes, they remain permanently in the 

 abdomen, bound down by a process of the peritoneum. In Man, 

 and most quadrupeds, on the contrary, they pass out of the abdo- 

 minal cavity through the inguinal rings, and are suspended in a 

 scrotal pouch formed by the skin, and a cremaster muscle, and 

 lined by a serous prolongation of the peritoneal sac. The sper- 

 matic cords, therefore, formed by the vessels and excretory canal 

 of the testes will take a different course, in conformity with the 

 variable position of these organs, and, where a scrotum exists, must 

 enter the abdomen through an inguinal canal. Still, from their 

 horizontal posture, quadrupeds are but little liable to hernise, 



