140 



THE MERYCOIDODONTID/E 



The brain case is comparatively small, and the lateral convexities are present but not large. 

 The occipital pillar is well developed and bounded by deep lateral concavities. The small external 

 auditory meatus is directed somewhat upward and backward and is closely compressed between the 

 postglenoid and paroccipital processes. It has a flattened wing which is suturally united with the 

 posterior surface of the postglenoid process near its base. The basicranial axis is steep. The bulla; 

 are comparatively small, are laterally compressed, and extend in advance of the postglenoid 

 processes. The palate is narrow, possibly in part because of lateral crushing, and the U-shaped 

 palatonarial border lies well aft of the posterior of M 3 . The glenoid articular surface is trans- 

 versely long and anteroposteriorly narrow, with a gentle convexity and with the long axis slightly 

 oblique to the sagittal plane. The postglenoid processes are moderately deep and anteroposteriorly 



Fig. 96. — Promerycoc/iaerus montanus grandis Douglass. Skull and jaw. HT. 



size. (After Douglass, 1907.) 



Cat. No. 990 CM. About 1/3 nat. 



compressed, with nearly vertical borders. The paroccipital processes are long, with the greater axis 

 obliquely anteroexternal to the sagittal plane, are closely appressed to the bulls, and approach 

 closely to the postglenoid processes. Index: 0.46. 



Mandible: The ramus is moderately long and slender. The chin profile is concave, and the 

 symphysiodental angle is 40°. The mental tubercle is large. The inferior border of the horizontal 

 ramus is slightly convex. The angle is small. The low condyle is inset but very slightly from the 

 posterior border of the ascending ramus. The sigmoid notch is small, and the coronoid process is 

 small and low. A character in this jaw that is unique and very peculiar is, as Douglass interprets it, 

 an apparently enormous enlargement of the normally small fossa, located on the anterior part of the 

 ascending ramus, above and posterior to ML. This fossa is very deep and large and is posteriorly 

 bounded by a plate of bone separating it from the masseteric fossa, which is comparatively small and 

 shallower than the anterior fossa. The coronoid process has been moved somewhat aft from the 

 position normal in this genus. This peculiar structure is found on both sides of the jaw, and I have 

 never seen it in any other merycoidodont. I believe Douglass' interpretation is correct, and that the 

 masseteric fossa is not divided, although both fossas may have contributed to the insertion of the 

 masseteric muscle. This character does not seem to be the result of disease or injury, as there is no 

 evidence of an abnormal condition on the other bones of the skull or mandible. 



