STRUCTURE OF THE VERTEBRATES 



59 



:^Iammal-like Reptiles. These animals are all extinct and 

 known only as fossils. Two orders are recognized, which are 

 classified together as the sub-class Synapsida; and from the 

 standpoint of human evolution are the most interesting of the 



Order 

 Theromorpha 



Reconstructions of two 

 Extinct mammal-like 

 reptiles 



Fig 21 At the top are extinct mammal-like reptiles (Sub-class Synap- 

 sida) which gave rise to the Class Mammalia. The other three are recent 



Diapsid reptiles. 



