NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN yj 



this on the medial surface there are two well-separated, oval facets 

 adjacent to the distal surface, for articulation with the second meta- 

 tarsal. The lateral surface of the external cuneiform on its more 

 proximal portion shows the dorsoventrally elongate, but variable and 

 often bilobed, surface for the cuboid. On the proximal portion of 

 the transversely narrow ventral surface there is an elongate process 

 that extends somewhat medially as well as ventrally and exhibits a 

 distally deflected, hooklike extremity. The concave portion bounded 

 proximally by this hooklike process, and in part distally by the ventral 

 extension of the distal surface, is the continuation medially of the 

 peroneal groove, so well defined on the cuboid. The ventral process 

 of the external cuneiform extends beyond that on the middle cunei- 

 form, and while it may have included an insertion of the tibialis 

 posterior, it no doubt supported part of the ligamentous cover of the 

 peroneus groove and probably tendon for certain of the interosseous 

 muscles. 



The Phenacodus external cuneiform differs only in minor respects 

 from that of Meniscotherium. The distal articular facet for the third 

 metatarsal is less concave dorsoventrally. That laterally for the 

 cuboid is generally large and oval shaped, not extending onto the 

 ventral process. The ventral process appears to be relatively a little 

 shorter but deeper and more massive. 



The external cuneiform of Tetraclaenodon is proximodistally elon- 

 gate and relatively more slender, dorsoventrally as well as trans- 

 versely, than in Meniscotherium. The facet for the cuboid is rather 

 like that in Phenacodus. The ventral process is missing on the 

 specimen examined. 



Metatarsal I. — The first metatarsal, the smallest of the five in 

 Meniscotherium is about half the length of the second, and its slender 

 dorsally bowed shaft is more compressed transversely than dorso- 

 ventrally. The extremities are somewhat enlarged, the proximal 

 extremity being the larger, with a simple, dorsoventrally convex prox- 

 imal surface for the internal cuneiform. This surface, moreover, is 

 broad and slightly convex transversely as well, permitting abduction 

 as well as flexure and extension. Ventrolaterally the base is roughened 

 and may be enlarged, evidently for the terminal or most medial 

 insertion of the peroneus longus. The distal articular surface is 

 dorsoventrally convex and shows a weak median keel. It is, more- 

 over, relatively narrower and more oblique than in the second 

 metatarsal. 



The Phenacodus first metatarsal has about the same relative length 



