E. L. Troxell — Entelodonts in Marsh Collection. 255 



to press the food between the teeth, or again to give the 

 mandible the strong backward motion, referred to on a 

 previous page, in the process of mastication. 



There is the additional possibility that these lateral 

 extensions from the face and jaws supported cheek 

 pouches or " muscular walls" comparable to those 

 ascribed to the Ceratopsia by Professor Lull, 4 for retain- 

 ing large quantities of food within the mouth before it was 

 ready to be swallowed. 



The dependent process from the jugal arch, in all pro- 

 bability, gave origin to the masseter muscle which gener- 

 ally arises from the jugal and is inserted broadly on the 

 wide angle of the ramus. From the tip of the process the 

 fibres of the muscle might have given the forward, the 

 backward, and even a sideward movement to the mandi- 

 ble, for, judging from the wear on the teeth and the form 

 of the molars, there was a definite transverse motion. 



The condyles of the ramus permitted an unusual free- 

 dom of movement to the jaws in nearly every direction, 

 including the opening to a wide angle, but the various 

 hypothetical muscles would have fortified against pulling 

 the condyles out of the shallow glenoid cavity. In the 

 enormously developed jugal of M. zygomaticus (fig. 15), 

 it is important to notice that the process extends back- 

 ward so that its outer, posterior edge almost parallels the 

 border of the angle of the ramus. "Whatever may have 

 been the original purpose of this dependent process, it is 

 evident that these animals profited by its use until it 

 reached the enormous size shown in this species, probably 

 the last of its race. 



4 Lull, E. S., IT. S. Geol. Survey, Mon. 49, p. 194, 1907. 



TO BE CONTINUED. 



