NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 23 



Dorsal view. — In dorsal view (see pis. 1 and 2) the rostrum does 

 not taper forward nearly so abruptly as shown by Cope (1884b, 

 pi. 25 f, fig. 13a). The nasals are broad and elongate, extending 

 from about even or slightly forward of the greatest anterior extremity 

 of the premaxillae to a posterior limit well into the frontal segment, 

 nearly halfway in some specimens. They are wide anteriorly, at the 

 anterior extremity of the naso-premaxillary suture, and somewhat 

 constricted about midway in their length, near the premaxillo-maxil- 

 lary suture, but reach the greatest width where the frontals join the 

 maxillae. Posterior to this they taper gradually, and about a third 

 of the way across the frontals they are abruptly rounded off with a 

 strong reentrant of the frontals along the midline of the skull. The 

 nasals are very much like those in Phenacodus except that in the 

 latter there is greater penetration into the frontal area and the greatest 

 width is carried posterior to the f ronto-maxillary suture well into the 

 frontal area. In marked contrast the nasals in Hyopsodus terminate 

 rather abruptly posterior to the f ronto-maxillary suture. 



The frontals are broad and flat between the orbits and reach 

 forward to contact with the maxillae, although a short distance later- 

 ally the frontals and maxillae are widely separated by the lachry- 

 mals. Posteriorly the frontals generally show a shallow depression 

 between the postorbital processes which is posteriorly defined by the 

 strong temporal ridges. The latter converge abruptly medial and 

 posterior to the postorbital processes. 



The frontals in Phenacodus are much more convex transversely, 

 and a longitudinal convexity is better emphasized somewhat farther 

 forward over the posterior region of the nasals. The postorbital 

 processes are not nearly so well defined in Phenacodus, and the 

 temporal crests converge posteriorly much more gradually than in 

 Meniscotherium. The frontals in Hyopsodus are gently convex 

 transversely, and there are no postorbital processes. The compara- 

 tively weak temporal crests diverge forward with little or no flexure 

 to become the orbital rims. 



From the union of the temporal crests at about the postorbital 

 constriction in Meniscotherium the well-developed sagittal crest 

 extends nearly straight over the elongate-appearing cranial portion to 

 divide again into the two posteriorward flaring halves of the lamb- 

 doidal crest. The most conspicuous feature of the elongate temporal 

 fossae is the nearly a dozen or more prominent vascular foramina 

 in the posterior portion of the areas, for the most part near the 

 parieto-squamosal suture but lacking any symmetry with respect to 



