PLATE XXII. 



Under surface of the bones of the left hind-foot. 



a. Astragalus. 



h. Calcaneum*. 



c. Naviculare. 



d. Cuboides. 



e. External cuneiforme. 



/. Second, here the internal, cuneiforme. 

 m2. Second, here the internal, metatarsalf. 

 m3. Third or middle metatarsal. 

 m4. Fourth metatarsal. 

 m 5. Fifth or external metatarsal. 

 / Proximal phalanx. 

 j2. Middle or second phalanx. 

 S Distal or ungual phalanx. 



* In the comparison of the os calcis of the Mylodon, p. 132, the following characters of that of the 

 Megalonyx have been omitted : it differs from the scaolcis of the Mylodon and agrees with that of 

 the Megatherium in haWng the surface for the astragalus separated into two by an intervening rough 

 tract ; it differs from both in having the cuboidal surface separated from the astragalar surface by a 

 deep groove ; but the calcaneum of the Megalonyx is most remarkable for the form of the great 

 posterior projection, which is much compressed, and expands into a broad vertical plate of bone ; 

 thus resembling the os calcis of the Sloths more than that of the Megatherium or Mylodon, but 

 differing from that of the Sloths in its greater depth and less length. 



\ The first metatarsal, or that of the hallux, is not developed. 



