THE UROGENITAL SYSTEM 85 



Remove both kidneys from the body. With a sharp 

 razor or scalpel divide one kidney into its dorsal and ven- 

 tral halves, and bisect the other by a transverse cut passing 

 through the hilum. The cut surfaces reveal the outer 

 cortical and inner medullary regions of the kidney. Within 

 the latter note the dorsoventrally flattened papilla which 

 projects into the internal cavity, or sinus, of the kidney. 

 The urine collects in the sinus and drains into the ureter 

 through its funnel-shaped anterior end, the pelvis, which 

 is located at the hilum of the kidney. Insert a fine bristle 

 into the pelvis where it surrounds the tip of the papilla and 

 by careful probing locate the lumen of the ureter. 



Exercise XXII. Draw the cut surfaces of the bisected kidneys. 



THE MALE UROGENITAL ORGANS 



The spermatozoa, or male sex cells, are produced in the 

 two testes, which develop in the embryo near the attach- 

 ment of the mesentery to the dorsal side of the abdominal 

 cavity. In the lower vertebrates the testes remain through- 

 out life near their embryonic position, but in most mam- 

 mals they come to lie in an integumentary sac, the scrotum, 

 ventral to the anus. This scrotal sac incloses two exten- 

 sions of the coelom, each of which communicates in the 

 embryo wdth the abdominal cavity through the inguinal 

 canal. This canal marks the position of the scrotal evagi- 

 nation. The testes usually descend from the abdominal 

 cavity, through the inguinal canals, into the scrotal sac, 

 though in the whale and elephant they remain in the 

 abdominal cavity. Such a condition (cryptorchism) oc- 

 casionally occurs in man. The inguinal canal remains open 

 in marsupials, bats, rodents (including the rat), insec- 

 tivores, etc. The descent of the testes in these animals is 

 temporary, and at the close of the breeding season the 

 testes are withdrawn into the abdomen by the cremaster 



