153 



might attack the larger branches ; in attaining which, they would derive advan- 

 tage by the addition to its prehensile power which the hind-foot gains by its 

 natural inversion ; and to this extent the climbing hypothesis may be admissible. 



But the preponderating development of the hind-quarters, and predominant 

 modifications adapting the hind-foot to progression on the ground, forbid the 

 supposition that its apphcation to climbing could have been habitual or frequent. 

 The probability however that it was an occasional action in the less gigantic 

 species, is increased by the fact of the inversion of the sole being least con- 

 spicuous in the Megatherium, whose bulk and strength would be adequate to 

 the prostration of trees too large for the eiforts of the Mylodon, the Megalonyx 

 or the Scehdotherium. I may here also remark, that the modifications of the 

 claws and of the bones of the extremities, especially the calcaneum of the Me- 

 galonyx, by which it differs from other Megatherioids, would add to its power 

 of climbing in the same degree as they detract from its strength. 



With regard to the Mylodon, it is obvious, from the great disparity of size in 

 the two claws of the hind-foot, that the larger one would be chiefly, if not ex- 

 clusively used in the act of digging, of grasping, or of fixing the hind-foot to the 

 ground. The total absence in the Megatherium of the toe corresponding with 

 the small internal unguiculate one in the Mylodon, suggests the application of 

 the claw of that toe to some purpose for which it was not required in the Me- 

 gatherium. The position of this inner toe, divaricated from the large adjoining 

 one, together with its small size, makes it so closely analogous to the two slender, 

 coadunate, fur-cleansing inner toes of the hind-foot in the Kangaroo and other 

 Marsupials, as to suggest a similar application of the inner claw of the Mylodon 

 to scratching and dressing a hairy covering. And such an office explains its 

 absence in the Megatherium, which we may well suppose to have diff'ered from 

 its less bulky congeners in having its thick and callous integument as scantily 

 clothed with hair as in the Elephant. 



The foregoing physiological review of the skeleton of the Mylodon has thus 

 led to the conclusion, that as the teeth and jaws were expressly adapted for the 

 comminution of fohage, so the trunk and extremities derived from their appa- 

 rently ill-assorted proportions the requisite power of obtaining such food by the 

 uprooting of trees. The Megatherium or Mylodon having completed this task, 

 would have abundant food before it for some days at least ; and I now proceed 



V 



