NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 27 



sists of two fanlike projections of the supraoccipital supported in 

 the more mature specimens by two low and broadly rounded ridges 

 diverging upward from the broadly convex posterior surface of the 

 occiput above the foramen magnum. Such development of the lamb- 

 doidal crest tends to expand posteriorward the area of origin for 

 the temporal muscle and presents a strong rim of attachment for the 

 trapezius, splenius capitis, etc., which function in raising the head. 

 The lateral margins of these two fanlike projections extend downward 

 and forward, becoming nearly parallel, to a point near the upper 

 extremities of the mastoid portions. Below this a lateral flare of the 

 lambdoidal crest on each side is developed on the squamosal. The 

 mastoid portion of the periotic is exposed in a depressed area on 

 either side in the lower half of the occiput, near the lateral margin. 

 It is most broadly exposed in the upper portion and nearly pinches 

 out below between the very elongate paroccipital process and the 

 weakly developed mastoid process of the squamosal. Possibly the 

 sterno-mastoid muscle was attached to the crest of the squamosal 

 which extends as a prominent protecting rim to the lateral margin of 

 the mastoid. 



The occipital view of the Phenacodus skull is rather similar, 

 although the two flaring projections of the supraoccipital are relatively 

 broader and less overhanging, and the widely diverging ridges on the 

 occipital surface, serving as buttresses to the lambdoidal flares, are 

 more strongly rounded and extend upward and outward from about 

 the foramen magnum. Between these buttresses the occipital surface 

 is triangular and gently concave, lateral to them the surface on each 

 side, including the exposed portion of the mastoid, faces more later- 

 ally than in Meniscotherium. Moreover, the mastoid portion does 

 not become so nearly pinched out ventrally. 



In Hyopsodus the flaring of the occipital crest is directed more 

 dorsally and the buttresslike ridges seem comparatively weak and 

 widely separated and may not be well defined. The mastoid por- 

 tions of the occipital surface, as in Phenacodus, face more laterally, 

 and in marked contrast to Meniscotherium increase in breadth of 

 exposure ventrally. 



Palatal view. — In a ventral view the palate of Meniscotherium 

 (see pis. 1 and 2) is seen to be moderately broad and elongate with 

 the lingual margins of the cheek teeth aligned nearly parallel on the 

 two sides, although the palate may be slightly constricted between 

 first premolars. Anteriorly it is about evenly rounded within the 

 margin of canines and incisors. The anterior palatine foramina seem 



