NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 53 



head, but shows a rounded, well-defined fossa for the teres minor. 

 The lesser tuberosity is scarcely more than a scar for the subscapu- 

 laris on the medial side of the head. The distal portion of the 

 humerus is known for Hyopsodus paulus, as well as Hyopsodus 

 walcottianus (see Matthew, 1915, fig. 10). In both of these the 

 trochlea shows the high anterior crest on the medial margin and the 

 high outer crest extending posteriorly from the median convexity on 

 the anterior surface, quite as in Meniscotherium, and possibly more 

 emphasized in H. walcottianus. The entepicondylar foramen is 

 present and a broadly open supratrochlear foramen. The greater 

 part of the shaft of the humerus is not preserved in Hyopsodus 

 material at hand. 



RADIUS 



The elements of the forearm in Meniscotherium are distinctly 

 smaller, relative to the humerus and hind limbs than in Phenacodus. 

 This would appear in part to be in keeping with the disparity in size 

 of vertebrae relative to these quarters. The radius (see pi. 7) is 

 decidedly slender proximally but shows a noticeable transverse expan- 

 sion of the proximal extremity or head for articulation with the 

 humerus. The articular surface is nearly rectangular in appearance 

 with a broad median depression for the anterior convexity of the 

 trochlea, and the internal portion or margin of the surface turns 

 distally in conformity with the forward-extending medial margin of 

 the trochlea. The head of the radius articulates with the ulna at 

 the distal margin of the sigmoid notch, anterolateral to the coronoid 

 process. 



The proximal portion of the shaft of the radius may show a rather 

 pronounced groove on its posteromedial surface curving somewhat 

 more medially distally, most noticeable in M. robustum. This may 

 well define a portion (fifth) of the origin of the flexor profundus 

 digitorum. Distally the shaft of the radius increases in diameter and 

 curves inward, passing from an anterolateral position proximally to 

 a more medial position distally with respect to the ulna. The postero- 

 lateral margin of the distal half of the radius is generally somewhat 

 rugose for attachment of the interosseous membrane. The anterior 

 surface shows a prominent crest arising on the distal half of the shaft 

 and extending distomedially to terminate near the styloid process, 

 and a somewhat more subdued crest terminating anterior to the 

 lateral portion of the distal extremity. 



