162 



THE MERYCOIDODONTID/E 



The basicranial axis is very steep. The large glenoid articular surfaces are markedly convex 

 from front to back and somewhat concave transversely. The postglenoid processes are broad trans- 

 versely, narrow anteroposteriorly, and rather deep. The paroccipital processes are posteriorly convex 

 and anteriorly are nearly flat or slightly concave, and the main axis is transversely directed. Above 

 these processes the exoccipitals are broad. The occipital condyles are anteroposteriorly narrow but 

 transversely broad. Index: 0.72. 



Fig. 114. — Pronomotherium altiramus (Douglass). Skull and jaw. HT. Cat. No. 759 CM. (jaw). PLT. Formerly 

 Cat. No. 9746 A.M.N.H. (skull). 2/5 nat. size. (After Douglass, 1907.) 



Mandible: The great depth of the posterior half of the jaw differentiates this genus from all 

 of the merycoidodonts. The symphysis is steep and very slightly concave, forming a marked 

 angle with the inferior border of the ramus. The horizontal ramus begins to deepen beneath M 2 

 and descends still more abruptly beneath M 3 . The masseteric fossa is deep but apparently not 

 extensive. 



Foramina: The infraorbitals are above the posterior half of M 2 . 



Dentition: The teeth are markedly hypsodont, increasingly so from Pf posteriorly, and the 

 lengths at the alveolar border increase in the same order. Douglass (1907A, pp. 819-820) 

 described the upper teeth as follows: 



The canine is not heavy. Its outer angle is sharp having an almost knife-like edge, and on the inner sur- 

 face there is a sharp and prominent slightly crescent-shaped ridge extending up and down on the tooth. The 

 posterior surface of the tooth is flat, the antero-external one nearly so and the antero-inner one strongly convex. 

 P 1 is much smaller than the other premolars and is not set obliquely in the jaw. The antero-inner ridge, which 

 usually separates the anterior and the anterio-inner facets in Merycoidodonts, in p 1 and p 2 of this specimen projects 

 far forward so that part of the anterior fossa is seen in a side view of the skull. On p 3 this fossa is broad and faces 



