36 



THE HISTORY OF THE PELYCOSAURTA, WITH 



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

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



Fig. I. 



P*<V 



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

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

 Fig. 3. Skull of Dimetrodon, 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 1 e becomes 



