NO. 2 A STUDY OF MENISCOTHERIUM GAZIN 79 



form is gently convex dorsoventrally, slightly oblique transversely, 

 and markedly constricted ventral to the broad and dorsally convex 

 superior margin. The constriction is greatest on the lateral side, and 

 ventral to this the ventrolateral margin of the surface for the middle 

 cuneiform may be slightly deflected proximally. Adjacent to this 

 there is a small flattened facet on the lateral surface for the ventral 

 portion of the fourth metatarsal base. Dorsal to this facet on the 

 lateral side of the third metatarsal there is a deeply concave, ventro- 

 lateral^ facing surface for articulation with a medial knob or promi- 

 nence close to the proximal extremity of the fourth metatarsal. The 

 medial surface of the base of the third metatarsal shows a distinct 

 knob, proximodor sally, that fits into a depression distal to the dorsal 

 facet for the external cuneiform on the base of the second metatarsal. 

 The convexity of the relatively broad distal extremity has an axis 

 at right angles to that of the shaft and exhibits a prominent keel 

 ventrally. 



The similar appearing Phenacodus third metatarsal, as the second, 

 has a generally flatter proximal surface for the external cuneiform 

 and a relatively broader distal extremity. It should be noted, how- 

 ever, that the proportions of the metatarsals as outlined here apply 

 more particularly to comparison with Phenacodus primaevus material, 

 as the Phenacodus copei metatarsals are relatively elongate and 

 slender, somewhat more as described for Tetraclaenodon. 



Metatarsal IV. — The Meniscotherium fourth metatarsal is a trifle 

 shorter than the second, and somewhat more so than the third, as 

 noted above. The shaft is dorsoventrally compressed but more slen- 

 der than that of the third and has a slight lateral curvature so that 

 the distal extremities tend to diverge. The proximal surface for the 

 cuboid is dorsoventrally and transversely convex over its broader dor- 

 sal portion, but the narrower, ventromedially directed part is notice- 

 ably deflected proximally, so that the ventral margin of the base 

 extends into the deeply impressed peroneal groove of the cuboid. 

 Adjacent to the recurved ventral portion of the cuboid surface, on 

 the medial side of the fourth metatarsal, is a facet for the third 

 metatarsal. A prominent knob on the medial side of the base, just 

 distal to the dorsomedial margin of the cuboid facet, is convexly 

 faceted for the concavity on the lateral side of the third metatarsal 

 base. The lateral side of the fourth metatarsal base is also deeply 

 concave and exhibits a distolaterally and somewhat ventrally facing 

 concave facet for the fifth metatarsal. The convexity on the distal 



