55 



339. The left astragalus. The chief characteristic of this hone is the convex 



protuberance formed by the inner half of the upper articular surface and 

 the broad, convex outer portion of the same surface. The upper half of 

 the surface for the os naviculare is concave ; the posterior part of the 

 surface for the calcaneum is separated from the remaining part by a deep 

 and rough canal : the anterior part is continuous with the convex portion 

 of the cuboido-navicular surface. 



340. The left os calcis. This is very remarkable for its great size and the 



unusual prolongation of its posterior part. 



341. The left os naviculare. The articular surface for the astragalus is nearly 



equally divided into an upper convexity and a lower concavity. The 

 anterior part of the bone presents but two surfaces, for two cuneiform 

 bones, which surfaces are continuous to a small part of their extent. 



342. The left os cuboides. The articular surface which joins the astragalus is 



concave : the surface presented to the fifth metatarsal bone is set at right 

 angles with that for the fourth metatarsal. 



343. The internal and larger cuneiform bone, its anterior convex articular 



surface shows that the base of the metatarsal bone which it supported 

 was at least four inches in vertical and three inches in transverse extent, 

 which agrees with the proportions of that bone in the figure by Bru and 

 Pander of the Madrid skeleton. This metatarsal bone does not exist in 

 the present collection of Megatherian remains. 



344. The ungual phalanx of the third or middle toe of the left hind-foot. This 



toe, called the third from the analogy of the ordinary pentadactyle feet, 

 is the innermost or first in the Megatherium, and the only one provided 

 with a claw in the hind-foot. 



345. The analogue of the second or middle cuneiform bone in Man, but the 



innermost of the two cuneiform bones in the Megatherium. Its proximal 

 end or base is occupied by the long, narrow, undulating surface adapted 

 to that on the os naviculare. On the outer or fibular side, near the upper 

 end of the base of the bone, there is a flat, sub-circular articular surface, 



