NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 75 



of the broad medial surface of the cuboid has a dorsoventrally elon- 

 gate facet for the navicular. On the distal portion of this surface the 

 facet for the external cuneiform is variable and may be dorsoventrally 

 long and possibly bilobate or separated into two parts. Occasionally 

 the surfaces for the navicular and external cuneiform are in contact 

 or partially merged. 



The Phenacodus cuboid is much more elongate, and the proximal 

 surface though convex and oblique is much less so than in Menisco- 

 therium. The broad distal articular surface also provides a relatively 

 larger area for the fifth metatarsal. The ventral surface is broadly 

 expanded and ventrodistally flaring, extending well down over the 

 peroneal groove but does not appear so triangular in outline as in 

 Meniscotherium. On the medial surface the large facet for the navic- 

 ular is proximoventrally located and about as deep as it is long. 



In Tetraclaenodon the cuboid is decidedly slender and elongate 

 in dorsal view, and the proximal extremity is more like that of 

 Phenacodus. The ventral surface although expanded over the per- 

 oneal groove is relatively much narrower transversely, and the 

 medial surface is narrower dorsoventrally. Also, the facet for the 

 navicular is noticeably convex dorsoventrally. It is straight or slightly 

 concave in Meniscotherium. 



Internal cuneiform. — The internal cuneiform is flattened with its 

 medial facing surface relatively broad and long. Proximally this sur- 

 face in Meniscotherium narrows and its proximodorsal margin is 

 deeply concave for articulation with the navicular. Marginal to this 

 concavity the lateral surface exhibits an arcuate facet, convex in its 

 more dorsal portion but concave proximally, that articulates with the 

 medial side of the middle cuneiform. The distal extremity, which 

 extends well beyond the middle cuneiform, has a dorsoventrally elon- 

 gate concavity for articulation with the first metatarsal. There does 

 not appear to be any definable facet for the second metatarsal in the 

 material at hand. 



The Phenacodus internal cuneiform is similar appearing, but the 

 ventral margin is thicker, and the dorsoventrally elongate facet for 

 the navicular is less concave and faces more nearly proximal. In 

 consequence the relatively flattened facet for the middle cuneiform 

 has a more dorsoventral orientation. Except for its thicker ventral 

 margin the Tetraclaenodon internal cuneiform more nearly resembles 

 that of Meniscotherium, notably in the deeply concave, proximo- 

 dorsally placed navicular facet. The distal extremity is similar in all 

 three forms. 



