NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 55 



cylindrical with the long axis parallel to the plane of flattening and 

 distinctly oblique to the long axis of the shaft, extending distally 

 toward the styloid or posterolateral margin. 



In attempting to articulate the bones of the fore limb I note that 

 a comparatively prone position for the manus requires that the 

 posterior margin of the ulna be turned decidedly outward and although 

 articulation with the humerus permits appreciable rotation, a rela- 

 tively normal relationship requires appreciable abduction of the arm. 



In Phenacodus, as noted above, the ulna is relatively larger and the 

 shaft appears less flattened than in Meniscotherium. The proximal 

 portion of the sigmoid notch is very much like that in Meniscotherium 

 with a similar transverse convexity and lateral flare, but the distal 

 portion of the surface is much more expanded lateral to the coronoid 

 process so that the head of the radius has a more nearly transverse 

 articulation with the ulna, and a slightly more anterior or ungulate- 

 like position with respect to its humeral articulation. Moreover, 

 this expansion of the sigmoid notch lateral to the coronoid process is 

 accompanied by a proximally more nearly triangular shaft. The 

 robust olecranon in Phenacodus, though similar, has a straighter 

 posterior margin or it curves somewhat backward rather than forward 

 as in Meniscotherium. 



The distal portion of the Phenacodus ulna is rather enlarged from 

 the moderately flattened shaft, and the long axis of the distal artic- 

 ular surface for the cuneiform appears more transverse with respect 

 to the flattening of the shaft, seemingly less oblique to the axis of 

 articulation at the sigmoid notch than in Meniscotherium. 



MANUS 



As noted with regard to the forearm, the forefoot of Menisco- 

 therium (see pi. 7) is relatively much smaller than that of Phenac- 

 odus; also, the carpals are proximodistally more compressed than 

 in the latter. The carpals, however, show somewhat the same serial 

 arrangement observed in Phenacodus but with slightly more over- 

 lapping. I was unable to verify the presence of a central in the 

 carpus of Meniscotherium, although Marsh (1892, fig. 1) shows 

 this element in the "Hyracops socialis" foot that he figured. Slightly 

 more preparation on the specimen (Y.P.M. 10276) that evidently 

 guided Marsh reveals that the prominence in the position of a central 

 is firmly joined to the distolateral angle of the scaphoid and may well 

 be an integral part of that bone. Although this process is variable, 

 it is more prominently developed in the Marsh specimen than in 



