STRUCTURE OF THE VERTEBRATES 



49 



Their nervous system shows definite advances over the fish type, 

 except for the cerebellum which is poorly developed in recent 

 amphibia. The vascular system has several important structures 

 added which in later evolution became of supreme importance. 

 However, the system is poorly adapted for land life, and the 

 steady disappearance of species as soon as more efficient land 



Primitive Extinct Amphibian 

 (Stegocephalia) 



Fig. 17. Types of Amphibia. The extinct Stegocephaha gave rise to the 



recent orders. 



