18 NEW REPTILES AND STEGOCEPHALIANS FROM 



of these peculiar structures is not certain; a careful study of both the upper and lower 

 surfaces and the broken edges revealed no indication of separate basioccipital or basi- 

 sphenoid ossification. It is probable that the basisphenoid cartilage became much reduced 

 and the internal carotid arteries were forced down upon the parasphenoid and passed 

 for a short distance through the arches. This suggestion is supported by the position 

 of the arches and the fact that the internal carotid arteries entered the brain-case through 

 the posterior part of the palatine vacuities and then turned backward. Watson ^ 

 identified markings in the specimen of Laccocephalus in this position as the grooves of 

 the internal carotids, though he interpreted the method of the arterial entrance into the 

 skull in a different manner. On the surface of each arch, nearer to the inner than the 

 outer end, there is a small foramen penetrating through the wall to the canal below. 

 Just anterior to the inner ends of the arches there are shghtly elongated rugosities; 

 these are in the direct line of the continuation of the ridges on the upper side of the 

 parasphenoid and of the ridges on the inner edges of the pterygoids. Anterior to these 

 rugosities there are small foramina entering the skull from before backward; they are 

 probably no more than openings for nutrient vessels. The sutures between the para- 

 sphenoid and the pterygoids can be easily traced; they run irregularly backward from a 

 point at the center of the posterior edges of the palatine vacuities and pass beneath the 

 outer edges of the arches just described, i. e., the arches are entirely upon the parasphe- 

 noid. Posterior to the arches the sutures appear again and continue backward, convex 

 outwardly, and then converge to end very close together at the base of the deep notch 

 between the exoccipitals. 



The pterygoids. — The upper face of the anterior ramus of the pterygoid is marked 

 by a wide, shallow groove which becomes more distinct posteriorly to a point about 

 opposite the posterior edge of the palatine vacuity; the outer edge of the groove is distinct 

 for its whole length, but the inner becomes definite only in its posterior portion. The 

 outer edge of the ramus is raised into a slight prominence just at the origin of the anterior 

 rising process of the quadrate ramus of the pterygoid. The pterygoid joins the para- 

 sphenoid, as is indicated in figure 1 b, and connects with the exoccipital just posterior to 

 the origin of the quadrate ramus. Just anterior to the junction of the pterygoid and the 

 exoccipital there is a foramen near the inner edge of the pterygoid; on the left side the 

 bone is broken around the foramen and shows that it enters into a considerable cavity 

 in the body of the bone. 



The upper surface of the quadrate ramus is most interesting. The perfection of 

 the structures preserved has rendered it a little difficult to reconcile the conditions found 

 with ij^e descriptions of less perfect specimens, but, in the light cast by the study of this 

 specimen, the previous descriptions can be brought into more or less harmony. There 

 are two distinct rising processes, an anterior and a posterior (see figs. 2 a and 2 b). These 

 are directly continuous with the body of the bone and extend for nearly the full length 

 of the ramus; there is no trace of a suture in the specimen, where every suture is revealed 

 with almost diagrammatic clarity. The processes are inclined backward as they rise 

 and are separated by a considerable space at their inner ends, but are very closely approxi- 

 mated, if not actually united, at their outer euds. The anterior process rises to the roof 

 of the skull; its upper edge was thin, with the inner half attached to the lower surface 

 of the parietal and squamosal by cartilage; this is demonstrated by the thinning and 

 irregularity of the upper edge, by the line of low rugosities on the roof-bones mentioned, 

 and by the fact that the bones were found in this position with a thin fine of matrix 

 between them (fig. 2 b). 



1 Watson, D. M. S., Transactions Philosophical Society of London, vol. 209, Series B, pi. 2, 1919. 



