220 



THE MERYCOIDODONTID/E 



diameter anteroposterior, and are bounded by the usual bones. The nasal bones are widest just 

 posterior to the narial opening; they are short and diminish very rapidly in width in advance of the 

 narial opening, terminating in sharply rounded ends about on a line above the posterior of the canine 

 alveolus. Posterior to the maximum they diminish gradually in width, ending about on a line across 

 the anterior borders of the orbits. The posterior ends are semicircular. These bones are gently 

 convex anteriorly, gradually flattening posteriorly. The lacrimal bone is of rather small extent on 

 the face, owing to its invasion by the large facial vacuity. The lacrimal fossa is small and shallow. 

 The frontals are very shallowly convex transversely and nearly flat anteroposteriorly, rising gently 

 to the highest point near the top of the frontoparietal suture. These bones are wider than in 



Fig. 161. — Merychyus arenarum minimus Peterson. Skull and jaw. HT. 



(After Peterson, 1906.) 



Cat. No. 1466 CM. 1/2 nat. size. 



M. curtus and M. a. leptorhynchus and extend forward of the lacrimals. The orbits are relatively 

 large and are placed a little higher than the average in Merychyus. They are nearly circular in 

 outline. The temporal ridges unite at a point in a plane above the postglenoid tubercles to form a 

 very short, low sagittal crest. The supraoccipital crest is low, extending beyond the condyles but of 

 very moderate overhang, and the wings are wide apart. The brain case is relatively rather small 

 and not much inflated laterally. The palate is rather narrow, but the type skull has suffered trans- 

 verse deformation, so that the cross dimensions may not be entirely accurate in all instances. The 

 palatonarial border seems to have been V-shaped, with its anterior part on a line across the middle of 

 the posterior lobes of M 3 . The basicranial axis is shallow. The glenoid surfaces are nearly flat, and 

 the postglenoid processes are small and narrow anteroposteriorly. The paroccipital processes are 

 wide transversely at the upper part and extend downward, the long diameter becoming antero- 

 posterior, with the process terminating in a point. The bulla is large, extending from the paroc- 

 cipital process to the mid-line of the glenoid surfaces. Index: 0.55. 



Mandible: The chin forms an angle of 42° with the tooth row and is almost straight vertically 

 and strongly convex horizontally. There is a marked tubercle at the inferior termination of the 

 strong symphysis. The posterior depth, including the coronoid process, is nearly two-thirds of the 

 length of the ramus. The angle is well rounded and not well demarcated. From the angle the 

 inferior border of the ramus slopes upward to the symphysis, and the width decreases anteriorly 

 rather rapidly under the molars and P 4 . The coronoid process is moderately short and quite 

 slender. The sigmoid notch is wide open and extends but very slightly below the condyle. The 

 condyle is nearly flat on its articular surface. The masseteric fossa is shallow and does extend below 

 the line of the alveolar parapet. 



