THE UPPER TRIASSIC OF WESTERN TEXAS. 



67 



may he somewhat exaggerated by pressure in the specimen, but even in the normal 

 skull it was a prominent feature. 



The miners do not appear upon the lower surface of the skull. This is very different 

 from the condition of the palate as figured by the various authors in the described forms. 

 If seems probable that the interpretation of the vomer as appearing on the lower surface 

 of the skull is due to the condition of the specimens. In the deep V formed by the approxi- 

 mation of the pterygoids in their anterior portions there is evidence of a pair of very 

 slender bones which have the same relations, i. e., they meet below to form a V; these 

 are apparently the much-reduced vomers. The position and reduced condition of the 

 veil ers. the articulation of the palatine with the anterior bones of the roof of the mouth, 

 in this case the promaxillaries, and the elevation of the pterygoids are very suggestive 

 of the condition in the Crocodilin. 





Fro 26. 

 bde with outer baaet removed to ihow the structure of internal nares. 



Lettering as usual. 



X0.8. 



The choaruB. — The openings of the internal nares are separated by a bar composed 

 of the palatines, pterygoids, and probably the vomers. There was a distinct space 

 between the internasal septum of the external nares and the septum between the choanse 

 below. Huene's description of this region is fairly accurate, but he has not recognized 

 the exact relations of the pterygoids, palatine, and vomers, and has not recognized 

 that the palatines extend forward to meet the premaxillaries. The bar between the 

 choana is formed by three bones, all paired. The lower pair is the palatine portion. 

 These bones gradually approximate; the posterior portion of the bar is V-shaped, the 

 anterior portion a complete oval bar with a complete upper edge. Between the arms of 

 the V formed by the palatines there is a second V formed by the anterior portion of the 

 pterygoids, which retain this form to the anterior end The lower edge of the pterygoid 

 V rests upon the upper edge of the palatine bar at the extreme anterior end. Between 

 the arms of the V formed by the pterygoids there is evidence of a third V, formed by 

 the vomers. 



The maxiUaries. The alveolar edge of the mamillaries is supported on the inner 

 side by a strong, horizontal palatine plate. There are 21 sockets in the maxillary, the 

 anterior of which are rounded in section, but the posterior 10, or more, are oval. The 

 strong median prominences on the premaxillaries gradually die out upon the palatine 

 processes of the maxillary. 



The premaxillariea. The anterior end of the premaxillary is but slightly expanded; 

 it accommodates two enlarged sockets for the tusk-like anterior teeth. Posterior to 



