THE UPPER TRIASSIC OF WESTERN TEXAS. 65 



is no indication of a composite structure of the rostrum, i. e., a presphenoid and a 

 parasphenoid portion, as described by Huene in M. plieningeri. 



The side of the basioccipital-basisphenoid.— The structure of the sides of these 

 bones coincides very closely with those described in other specimens. Between the 

 ridge connecting the side of the condyle with the tubera and the suture between the 

 basioccipital and basisphenoid there is a deep groove passing upward and terminating, 

 apparently, in the otic opening. Just posterior to the upper end of this groove and in 

 the exoccipital bones, which are in place, there are two foramina — a posterior, larger for 

 the exit of the XII nerve, and an anterior, smaller, which probably transmitted the 

 IX, X, and XI. Between the tubera and the basipterygoid process, on each side, are 

 the openings of the foramina for the internal carotid arteries, which open into the base 

 of the small hypophysial cavity. 



The upper surface of the basioccipital-basisphenoid. — The exoccipitals come together 

 below, forming the floor of the foramen magnum; anterior to these can be seen the very 

 distinct suture between the basisoccipital and basisphenoid. On the right side this 

 suture terminates in a deep pit entirely upon the upper surface of the bones. The 

 left side is partly obscured by the prootic, but the pit is apparently present, showing 

 that its occurrence on the right side is normal. The presence of the pit can not be 

 confirmed from other specimens, but its presence is suggested in No. 7505. The sella 

 turcia is prominent just posterior to the hypophysial pit. On either side of the 

 pit the edges of the basisphenoid are thickened, forming a strong articulation with the 

 prootic. 



The proolics. — The prootic of the left side is in place; that of the right side was 

 found detached, but it fits well into its position. The posterior portion extends back- 

 ward in a point for some distance, and articulates with the opisthotic both above and 

 below; an epiotic is not distinguishable as a separate element. The upper edge is 

 thickened for attachment to the parietal, and the lower and anterior edges are thickened 

 for attachment to the basisphenoid. Near the anterior end is the foramen for the 

 V nerve; this is a vertical oval with the greatest diameter nearly twice as long as the 

 horizontal diameter. The portion of the bone anterior to the large foramen is bent 

 inward nearly at right angles, to form the anterior wall of the brain-case. The two 

 bonea do not meet in the median line. On the anterior face of this portion of the bone, 

 at about the level of the lower edge of the large foramen (in the undistorted bone of 

 the right side), there is a small foramen which probably transmitted a branch of the V. 

 On the inner side of the prootic, posterior to the large foramen, is a large and deep pit 

 which sheltered a portion of the inner ear. When the bone is in position this pit comes 

 into close association with two pits on the anterior inner end of the opisthotic and the 

 large pit on the suture between the basioccipital and basisphenoid. On the lower edge 

 there is a groove continuous with the groove on the lower edge of the opisthotic. 



The pterygoid* show the usual tripartite form, but are rather different in shape 

 from that common to most of the reptiles. The middle portion of the bone is thickened 

 and has a decided notch which fits, loosely, the basipterygoid process of the basisphenoid. 

 The quadrate process fa a thin plate standing nearly vertical in the skull, which extends 

 backward and slightly outward and articulates with the pterygoid process on the 

 inner side of the quadrate. The outer process is fairly heavy. Its anterior edge is 

 deeply concave, giving the whole process a distinctly crescentic form. The process 

 extends outward, downward, and backward. The distal end is broad and very thin 

 and lies upon the upper surface of the distal portion of the transverse, meeting it by 

 a very smooth, flat surface which undoubtedly permitted free movement. The 

 anterior process extends forward and quickly becomes a thin vertical plate. In the 



