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PEOFESSOE OWEN ON THE MEGrATHEEIUM. 
Sloths, the hind foot is pentadactyle, and four of the toes have a long claw, even in the 
httle arboreal Uyrmecy)haga diiactyla-. the departure by degradation from the penta- 
dactyle type is a peculiar characteristic of the Sloth-tribe in the order. It is carried 
further m the same dnection m the Megatherium and other great extinct terrestrial 
Sloths. 
Guided by the general rule that animals having the same kind of dentition have the 
same kind of food, I conclude that the Megatherium must have subsisted, like the Sloths, 
on the foliage of trees; but that the greater size and strength of the jaws and teeth, 
and the double-ridged grinding surface of the molars in the Megatherium, adapted it to 
brmse the smaller branches as well as the leaves, and thus to approximate its food to 
that^ of the Elephants and Mastodons. The Elephant and the Giraffe are specially 
modified to obtain their leafy food ; the one being provided with a proboscis, and the 
entire frame of the lofty ruminant adapting it to browse on branches above the reach of 
its largest congeners. If the Megatherium possessed, as Cuvies conjectured, a proboscis, 
it cannot, judging from the suborbital foramina, have exceeded in size that of the Tapir, 
and could only have operated upon branches brought near the mouth. Of the use of 
such a proboscis in obtaining nutritious roots, on the Cuvierian hypothesis that such 
formed the sustenance of the Megatherium, it is not easy to speculate: the Hog’s 
snout might be supposed to be more serviceable in obtaining those buried parts of 
vegetables; but no trace of the prenasal bone exists in the skull of the Megatherium. 
A short proboscis might he useful in rending off the branches of a tree when prostrated 
and withm reach of the low and broad-bodied Megatherium, but this ofilce has been 
provided for by the organization of the tongue, of which, both the hyoid skeleton by its 
strength and articulation, and the foramina for the muscular nerves by their unusual 
area, attest the great size and power. 
As regards the hmbs, the Megatherium difiers from the Giraffe and Elephant in the 
unguiculate character of certain of its toes, in the power of rotating the bones of the 
fore arm, in the corresponding development of supinator and entocondyloid ridges on 
the humerus, and in the possession of complete clavicles. These bones are requisite to 
ghe due strength and stability to the shoulder-joint for varied actions of the fore arm, 
as in gi’asping, climbing, and burrowing. But they are not essential to scansorial or 
fossorial quadrupeds : the Bear and the Badger have not a trace of clavicles, and merely 
rudiments of these bones exist in the Babbit and the Fox. We must seek, therefore, 
in the other parts of the organization of the Megatherium, for a clue to the nature of 
the actions by which it obtained its food. In habitual burrowers the claws can be 
extended in the same plane as the palm, and they are broader than they are deep. In 
the Megatherium the depth of the claw-phalanx exceeds its breadth, especially in the 
large one of the middle finger ; and not any of the claws can be extended into a line 
with the metacarpus, but they are all more or less bent inward and downward. Thus, 
although they might be used for occasional acts of scratching up the soil, they are 
better adapted for grasping; and the whole structure of the fore foot militates against 
MDCCCLIX. 5 Q 
