THE UPPER TRIASSIC OF WESTERN TEXAS. 53 



marked by a slight ridge, and below this is a groove which is continuous with a foramen 

 which excavates the pterygoid and connects with the small palatine vacuity which is 

 not visible from below. The bone is narrowed in the median portion and then expands 

 to articulate with the maxillary, the palatine, and the jugal. The outer face is bent 

 sharply down and forms a nearly vertical face; its distal end is reflected upon the inner 

 sides of the maxillary and jugal. 



The jxtltilines are elongate bones lying between the maxillaries and the pterygoid. 

 On the right side the palatine is separated by a fracture from the maxillary, but on the 

 left side the bones are in contact. The surface of the palatine is convex downwardly 

 in the middle of its length, but the anterior and posterior ends are natter. The greatest 

 height of the convexity is near the inner edge of the bone and the whole surface of the 

 middle portion is slightly rugose. 



The anterior termination of the pterygoids and the palatines is uncertain. They 

 apparently join the vomers near the median line, but as the premaxillaries of the two 

 sides meet in the median line as far back as a point just below the posterior edge of 

 the external narial opening, the palatines, pterygoids, and vomers must have risen 

 somewhat in the skull at this point. Just posterior to the point where the premaxillaries 

 terminate, the inner edges of the median bones of the palate are slightly excavated and 

 rounded, indicating the position of the very narrow internal nares, but whether the 

 boundaries of these openings are formed by the vomers alone or by the vomers and 

 pterygoids can not be made out. There is no suggestion of a median septum, but the 

 opening was probably paired. In the light cast by the study of the skull of Leptosuchus, 

 this interpretation may be erroneous. 



The maxillaries appear on the lower side of the skull only as the alveolar edges; 

 anterior to the external narial opening they join the premaxillaries by oblique sutures 

 running backward and inward, so that the posterior ends of the premaxillaries extend 

 backward as long processes between the maxillaries. 



The premaxillaries extend forward with nearly straight outer sides; the lower 

 surface is divided between the alveolar edges and smooth convex surfaces; the two bones 

 meet in a broad median symphysis. This symphysis is divided into an upper and a lower 

 part; between the two articulating surfaces there is a smooth, somewhat concave area, 

 indicating the presence of a narrow median cavity running nearly the full length of the 

 rostrum. On either side of this groove the palatal surface of the premaxillaries is raised 

 into convex (longitudinally) ridges, forming, with similar process on the dentaries, a 

 buttress which prevented injury to the teeth when the jaws were snapped together. 



The teeth are typically phytosaurian in shape and arrangement. The posterior 

 teeth are broader and lower, with sharp anterior and posterior serrate cutting edges. 

 The inner side of each tooth is nearly flat, except at the tip, where the convexity becomes 

 greater; the outer side is decidedly convex. The cutting edges are sharply crenulate 

 from the apex nearly to the base. The greater part of the teeth are lost, but certainly 

 at the middle of the premaxillaries the teeth were elongate and slender. The inner side 

 of the few anterior ones preserved is less convex than the outer and the cutting edges 

 are lower; the crenulations do not appear on the single tooth, which is well preserved, 

 but they were probably present to some extent. The extremity of the snout was occupied 

 by four large teeth, which on the right side are represented only by the base of the inner 

 one and the apex of the just erupting outer one. The apex of the outer tooth shows 

 the same disparity between the convexity of the inner and outer sides that appears in 

 the other teeth of the series. There are 47 teeth and alveoli on each side in the upper 

 jaws. The separation of the two sides of the skull at and anterior to the external narial 

 opening permits of some observations upon this region. As shown in figure 21, there 

 is a pair of bones, at the level of the surface of the skull posterior to the narial opening, 



