118 



THE ANATOMY OF VERTEBRATED ANIMALS. 



The kidneys of the Elasmohranclui do not extend so far 

 forward as those of most other fishes. The ureters generally 

 become dilated near their terminations, and open by a common 

 urinary canal into the cloaca behind the rectum. 



The brain is well developed. It usually presents a large 

 cerebellum, overlying the fourth ventricle, the side-walls of 

 which {corpora resti/ormia) are singularly folded (Fig. 37, A., 

 a) ; and moderate-sized optic lobes, which are quite distinct 

 from the conspicuous thalamencephalon, or vesicle of the third 



ri«. 87.— The brain of the Skate (iSo^o iaiis). A. From above ; B. A portion of the tbd- 

 tral aspect enlarged ; s, the olfactory bulbs ; a, the cerebral hemispheres which are milted 

 In the middle line ; b, the thalamencephalon ; c, the mesenccptialon ; <?, the cerebellum • 

 a a, the plaited bands formed by the corpora restiformia ; L, II., IV., V., the cerebral 

 nerves or the corresponding pah's; f, the medulla oblongata : w, a blood-vessel. In R ; 

 ch, the chiasma of the optic nerves; h, the pituitary body; mand v. vessels connected 

 with It; *, the saceua vaeouloaua; p, the pyramids of the medulla oblongata. 



