290 



AMPHIBIA 



anterior to the rather wide medulla oblongata. Ventrally one sees 

 the paired optic nerves, which cross (optic chiasma), the infundibulum 

 to which is attached the pituitary gland or hypophysis. There are 

 ten pairs of cerebral nerves. (See table, below.) 



Sense Organs. — Olfactory sense is served by small nasal cavities 

 with folded walls of nasal membrane. The anterior nares lead to the 

 cavities from the outside and t\\t posterior nares open into the mouth. 

 In the fish, as already noted, the olfactory openings were used only 

 for smell, but in the amphibia and higher vertebrates, the nares are 

 important in respiration. The eyes are well developed, but the 



Origin, Components, Function and Distribution of the Ten Cerebral Nerves 



OF Fishes and Amphibia 



