60 



363. The proximal phalanx of the middle diyit of the left fore-foot of the Me- 



galonyx : it differs from that of the Mylodon by its greater relative 

 vertical diameter, and by the greater depth of the proximal and distal ar- 

 ticular canals. This bone is described and figured by Cuvier, loc. cit., 

 p. 365, pi. xxiii. fig. 3. 



364. The second phalanx of the same digit. It is twice as long in proportion 

 to its breadth as the corresponding bone in the Mylodon, and is more 

 symmetrical : the distal trochlea is narrower, but with a much deeper 

 median canal. The median ridge of the proximal articulation is more 

 developed, and the lower boundary of that articulation is more produced 

 than in the Mylodon. This bone is described and figured by Cuvier, 

 loc. cit., p. 364, pi. xxiii. fig. 2. 



365. The ungual phalanx of the same digit. It is much more compressed than 



the corresponding phalanx of the Mylodon ; the median ridge of the arti- 

 cular trochlea is sharper : the position of the joint equally favours the 

 downward inflection of the claw and prevents its retraction. Cuvier, in 

 his description of this phalanx, proves, by a comparison of it with the 

 ungual phalanges of the Sloth and Lion, that it could not have belonged 

 to a gigantic carnivorous species, as was conjectured by Jefferson and 

 Faujas : loc. cit , p. 362, pi. xxiii. fig. 1. 



366. The metacarpal bone of the fifth digit of the left fore-foot of the Mega- 



lonyx Jeffersonii. The proximal expansion presents two articular sur- 

 faces ; a terminal one for the os unciforme, and a lateral one on the radial 

 side for the adjoining surface of the fourth metacarpal. The distal end 

 presents the same modifications as the fifth metacarpal in the Mylodon : 

 a . simple vertically-oblong surface supports an arthrodial instead of a 

 ginglymoid joint for the proximal phalanx, below which there is a surface 

 for a sesamoid bone ; indicating that the digit which it supported was as 

 mutilated and short as in the Mylodon and Megatherium. 



367. This small ungual phalanx probably belongs to the first digit or pollex of 



the same fore-foot of the Megalonyx as the foregoing bones : it is de- 

 scribed and figured by Cuvier, loc. cit., p. 363, pi. xxiii. fig. 9. 



