PROMERYCOCHCERUS 



131 



posterior part of the orbit, from which point it descends aft and then, in a sweeping curve, rises 

 vertically at the posterior part about to an anteroposterior plane through the middle of the orbit. 

 The outer border is rounded. The nasal sutures are fused, but the bones are apparently narrow and 

 posteriorly truncated. The lacrimal fossas are very deep and large. The unreduced frontals are 



Fig. 86. — Promerycochaerus lulli Thorpe. Right half, superior view of skull. HT. Cat. No. 10234 Y.P.M. 1/4 nat. size. 



(After Thorpe, 1921.) 



narrow and strongly decurved above the orbits. The latter are medium in size and look chiefly 

 outward, slightly forward, and not at all upward. The temporal ridges unite well aft, above the 

 anterior of the postglenoid surfaces, to form a very high and thin sagittal crest. The supraoccipital 

 crest is posteriorly well produced, and the thin wings are close together. The brain case is very 

 narrow and small, with a very prominent lateral convexity. The external auditory meatus is moder- 



Fic. 87. — Promerycochcerus lulli Thorpe. Left half, inferior view of skull. HT. Cat. No. 10234 Y.P.M. 3/8 nat. size. 



Fig. 88. — Promerycochcerus lulli Thorpe. Superior view of right ramus. HT. Cat. No. 10234 Y.P.M. 1/2 nat. size. 



ately large and is directed upward and backward. The basicranial axis is shallow. The palate is 

 narrow and vaulted, with the palatonarial border well aft of the tooth row. The glenoid articular 

 surface is moderately narrow fore and aft and is not greatly elongate transversely. The post- 

 glenoid process is medium in size and of nearly the same dimensions in both diameters. The bulls 

 are moderately large, are oval in basal outline, and extend downward slightly below the level of the 

 inferior edge of the postglenoid processes. The paroccipital processes are long, rather slender, and 



