80 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



extremity of the fourth metatarsal is narrower laterally and its axis 

 is slightly oblique, more distal on the medial side. 



Differences from the Phenacodus and Tetraclaenodon fourth meta- 

 tarsal are essentially those noted with regard to the second and third 

 metatarsals, but it may be noted that the ventral portion of the 

 cuboid facet is not nearly so recurved, so that in these forms the 

 base of the fourth metatarsal does not extend so noticeably into the 

 peroneal groove. 



Metatarsal V. — The fifth metatarsal of Meniscotherium is a little 

 longer than the first and about two-thirds the length of the fourth. 

 The shaft is compressed in a dorsolateral-ventromedial direction, and 

 the broadly expanded proximal extremity is gently deflected ventro- 

 medially. The base is essentially trilobed with a dorsomedial lobe 

 or prominence that articulates with the lateral concavity in the base 

 of the fourth metatarsal. The margin from this lobe to the more 

 proximoventral lobe lies adjacent to the lateral margin of the cuboid 

 surface of the fourth metatarsal. With the posterior margin of this 

 latter surface, the proximoventral lobe of the fifth metatarsal extends 

 into the peroneal groove and, I suspect, receives a portion of the 

 insertion of the peroneus longus. The third or ventrolateral lobe 

 probably includes insertion of the peroneus brevis, an extensor from 

 a more dorsal direction. 



The Phenacodus fifth metatarsal is also about two-thirds the 

 length of the fourth, but is straighter and much more robust. Its 

 proximal extremity lacks the trilobed appearance, and the artic- 

 ulation with the cuboid is not so oblique to the shaft. The base of 

 the fifth metatarsal in Tetraclaenodon is transversely flattened, 

 somewhat as in Meniscotherium, and exhibits a prominent ventral 

 knob, evidently for the peroneus longus, which is less proximally 

 directed than in Meniscotherium, but the ventrolateral process, noted 

 in the latter, is missing. 



Phalanges. — The proximal phalanges in the second to the fourth 

 digits are a little less than half the length of the metatarsals. They 

 are broad but taper somewhat distally and are flattened, particularly 

 the shaft, and the distal extremity is much more compressed dorso- 

 ventrally than the proximal. The second phalanges are nearly two- 

 thirds the length of the first in each digit and are also distally tapering 

 and flattened. The phalanges of the third digit are broader than 

 those of the second and fourth. The distal phalanges are elongate 

 but a little shorter than the first, with a somewhat spatulate anterior 

 half and a narrow posterior neck. The spatulate portion is dorsally 



