OUR ANCIENT RELATIVES 



Permian of Texas) lived another, decidedly higher 

 reptile, which had already acquired a significant 

 resemblance to some of the lower mammal-like 



Fig. 19. Two Critical Stages in the Early 

 Evolution of the Skull. 



A. Generalized reptile, retaining the full complement of amphibian 



skull elements. (After data of Broili, Watson, Williston.) 



B. Primitive theromorph reptile, with reduced number of skull 

 elements (after Williston). For details, see p. xvi. 



33 



