OSTEOLOGY OF AMERICAN PERMIAN VERTEBRATES 405 



of the interpterygoidal space. That all of these should be fractures, 

 so exactly alike on the two sides, seems strange, but there can hardly 

 be any other interpretation of the inner divisions, at least. They 

 all bear teeth forming a continuous dentigerous surface between the 

 mandibles, back of the nares. The two inner pieces are crowded 

 nearly in contact over what is probably a slender parasphenoid in 

 this specimen; in the other specimen, 

 however, the base of a narrow para- 

 sphenoid is seen between the two sides. 



In one or the other of the two skulls 

 the structure of the posterior palatine 

 region is definitely shown. The basi- 

 sphenoid is a broad, flat, or gently con- 

 cave bone, lying contiguous with the 

 posterior processes of the pterygoids 

 in front, and terminating in front, as I 

 have figured it, apparently in a slender 

 parasphenoid. Posteriorly the very 

 stout stapes fits closely into an inter- 

 val between the posterior angle of the 

 basisphenoid and the exoccipitals. It 

 is directed outward and backward, as 

 a heavy, somewhat curved, cyhndrical 

 rod, to near the lower end of the quad- 

 rate, lying in close relation to the 

 posterior process of the pterygoid. 



The basioccipital forms the whole 

 of the gently curved, cordate-shaped 

 condyle, with a short, broad surface 

 below in front. On either side the 

 exoccipital is distinctly separated from the basioccipital, extend- 

 ing up on either side of the foramen magnum to near the top, 

 as in Dimetrodon. These sutures are clearly shown; that between 

 the exoccipital and paroccipital is less certain, though, from the 

 agreement of lines on both sides in both specimens, I believe 

 that the suture is situated as I have figured it in dotted lines. 

 A small foramen for the posterior cranial nerves is visible as I 



Fig. 10. — Casea broilii: A , skull 

 from below; B, the same, from 

 behind, three-fifths natural size; 

 po, paroccipital; pa, palatine; bs, 

 basisphenoid; Jo, basioccipital; pt, 

 pterygoid; 9, quadrate; ^^, stapes; 

 eo, exocciptal; so, supraoccipital 

 ds, dermosupraoccipital. 



