143 



equal. A portion of the hand in all the Megatherioids, including the two outer 

 digits in the Mylodon, was modified after the ungulate type for the exclusive 

 ofiice of supporting the body in ordinary terrestrial progression. 



In the investigation of the nature of the collateral uses of the anterior ex- 

 tremity of the Megatherioids, to which uses all that is superadded to the ordinary 

 structure of an ungulate limb relates, we must consider these superadditions in- 

 dependently, or exclusively of the parts which were merely concerned in progress- 

 ive motion. The unguiculate portion of the fore-foot, thus viewed apart from the 

 ungulate portion, agrees with the scansorial type, being long and narrow, with 

 long and curved claws, which appear to have been habitually in a state of flexion, 

 and could hardly be extended in the same plane as the hand. These characters, 

 though not manifested in so extreme a degree as in the Sloths, evidently indi- 

 cate a fore-foot better fitted for grasping than for digging. Such a foot is not, 

 however, an instrument unfitted for cleaving or displacing the earth ; but 

 rather, in so far as it differs from that of the Sloths and is less fitted for climb- 

 ing, it gains in fossorial power. 



It may be justly inferred from the diminished curvature and length, from the 

 increased strength and from the inequality of the claws, especially from the dis- 

 proportionate size of that of the middle finger, that the hand of the Mylodon 

 was occasionally applied by the short and strong fore-limb in the act of digging ; 

 but its close analogy with that of the Ant-eaters, teaches that the fossorial 

 actions were limited to the removal of the surface-soil in order to expose some- 

 thing there concealed, and not for the purpose of burrowing. Such an instru- 

 ment would be equally effective in the disturbance of roots or ants ; it is, how- 

 ever, better adapted for grasping than for delving. But to whatever task the 

 unguiculate part of the hand of the Mylodon might have been applied, the bones 

 of the wrist, of the fore-arm, of the arm and of the shoulder, alike attest the 

 prodigious force which would be brought to bear upon its execution. 



The general organization of the anterior extremity of the Mylodon appears to 

 me to be incompatible with the idea of its having been a strictly scansorial or 

 burrowing animal, and at the same time both teeth and jaws decidedly negative 

 the supposition that it was an eater of ants ; for the two extremes in the length 

 of the jaws are presented by the phyllophagous and myrraecophagous species of 

 the Edentate order, and the anomalous brevity of the face which characterises 

 the leaf-eating Sloths, is repeated, even to exaggeration, in the Mylodon. 



