36 



THE HISTORY OF THE PELYCOSAURIA, WITH 



frontals, nasals, maxillaries and lachrymals. The whole bone is bent upon itself at 

 a right angle, producing an upper horizontal and lower vertical portion. The posterior 



Fig. i. 



• W 



Fig. 1. Skull of Dimetrodon, Cope. Side view. 

 Fig. 2. Skull of Dimetrodon, Cope. From above. 

 Fig. 3. Skull of Dimetrodou, Cope. From below. 



edge is rounded and thickened, forming the upper anterior border of the orbital rim. 

 Just anterior to this there is a deep excavation, the preorbital pit. The bone becomes 



