3IO 



E. C. CASE 



exactly the same position, but are relatively much larger than figured 

 by Broom. 



Posteriorly the parasphenoid is much reduced, and is attached as a 

 slender vertical plate of bone to the anterior end of the basisphenoid 

 between the basiptergoid processes. Above, the parasphenoid articu- 

 lates directly with a thin vertical plate of bone which expands antero- 







."V**- s 



Fig. 6. — Lower jaws of Dimetrodon incisiviis ( ?), showing the inner and outer 

 surfaces. Full length of jaws, 33 c™. 



posteriorly as it rises in the skull, and finally articulates in the median 

 line with the under side of the frontals. This bone can only be 

 the ossified ethmoid portion of the median cartilaginous septum. 

 The anterior edge of the ethmoid is somewhat irregular and thin, 

 and represents the true vomer; the posterior inferior angle is rounded 

 and thickened, and there is an excavation which evidently marks the 

 exit of the 1 1 nerve from the skull. The presence of a median septum 

 of this character is very peculiar in view of the fact that there are well- 

 developed epipterygoid bones indicated by the preserved lower ends 

 in contact with the posterior portion of the pterygoids. 



