14 
NOTICE OP TIIE MEGATHERIUM. 
and in one species of Sloth this bone is incomplete. The structure of the fore-foot, moreover, 
militates against. the theory | for the outer digit is modified, after the hoof type, for the exclu- 
sive office of supporting -the body in ordinary terrestrial progression. In the best climbing 
animals the hind-legs are much shorter thau the fore-legs, and the pelvis is not extraordinary 
in size, as we find it in the Megatherium. The preponderating weight of this part is a riddle, 
on the scansorial hypothesis ; for the hind extremities, needing only the requisite prehensile 
power, ought to have had their bulk reduced in order to facilitate their being drawn upwards 
towards the fore-legs. As to the tail, it was too short for prehensile purposes ; besides, the 
articular surfaces of the vertebrse show that the ordinary inflection was pot forwards but 
backwards and downwards, as in the Kangaroo. Another question relates to the fossorial 
powers of the Megatherium ; did it habitually burrow, like the Rabbit or Mole ? In this latter 
animal; — so typical as an excavator, — the pelvis is remarkably slender and feeble ; in the 
Megatherium it is remarkably large. Clavicles, though commonly present in burrowing Mam- 
mals are not indispensable ; for they are wanting in the Badger, and are merely rudimentary 
in the Rabbit and the Fox. In animals whose feet are best organized for digging, the claws 
form a continuous plane with the palm of the foot, and they are broader than they are deep. 
In the Megatherium, on the contrary, the depth of the claw -phalanx much exceeds the breadth; 
and not one of the claws can be brought into a line with the metacarpus, but all are more or 
less bent inwards and downward. Such au insertion of the claws would singularly interfere 
with their efficiency as instruments for excavation. Though they might be used for occasional 
acts of scratching up the soil, they are evidently best adapted for grasping. The theory of 
Prof. Owen is, then, in all probability, the true one ; that the Megatherium was neither a 
climber nor a burrower, but that his great strength was given him for the purpose of uproot- 
ing the trees that bore his sustenance, or for breaking off the largest of their lower branches. 
The hand of the monster beast cannot be contemplated without the conviction that it was 
designed to overcome unusual resistance ; evidence of which is furnished by the deep groves 
and sharp ridges in the radius and ulna, — the starting points of stout tendons and muscles. 
All the bones, from the shoulder down, are eminently suggestive of prodigious force. The 
moment we estimate this force, the colossal proportions of the hind extremities lose their 
anomaly, and harmonize with the front. The application of the fore-arms to the work of 
tearing down a tree would demand a corresponding fulcrum, such as we find in the heavy 
pelvis and the massive hind legs. The earth was probably first removed from the roots by 
the claw of the hind-foot, which, like a pickaxe, was well adapted for that purpose. 
“ The tree being thus partly undermined and firmly grappled with, the muscles of the 
trunk, the pelvis and hind limbs, animated by the nervous influence of the unusually large 
spinal cord, would combine their forces with those of the anterior members in the efforts at 
prostration. And now let us picture to ourselves the massive frame of the Megatherium, 
convulsed with the mighty wrestling, every vibrating fibre reacting upon its bony attachment 
with a force which the sharp and strong crests and apophyses loudly bespeak : — extraordinary 
must have been the strength and proportions of that tree, which, rocked to and fro, to right 
and left, in such an embrace, could long withstand the efforts of its ponderous assailant,”* 
Owen on the Mylodon, p. 148. 
