142 
SYSTEM OF NATURE. 
No. 5. 
Page 16, line 3 .—“ The Megatherium was endowed with strength 
sufficient to uproot the giants of the forest with his tremendous 
clawsT * 
“If the foregoing physiological interpretation of the osseous frame¬ 
work of the gigantic extinct sloths be the true one, they may be supposed 
to have commenced the process of prostrating the chosen tree, by scratch¬ 
ing away the soil from the roots; for which office we find in the Mylo- 
don the modern scansorial fore foot of the sloth modified after the type of 
that of the partially fossorial ant-eater. The compressed or subcompressed 
form of the claws, which detracts from their power as burrowing instru¬ 
ments, adds to their fitness for penetrating the interspaces of the roots, 
for exposing and liberating them from the attached soil. This operation 
having been duly effected by the alternate action of the fore feet, aided 
probably by the unguiculate digits of the hind feet, the long and curved 
fore claws, which are habitually flexed and fettered in the movements of 
extension, would next be applied to the opposite sides of the loosened 
trunk of the tree : and now the Mylodon would derive the full advantage 
of those modifications of its fore feet by which it resembles the Brady- 
pus; the correspondence in the structure of the prehensile instruments of 
the existing and extinct sloths extending as far as was compatible with 
the different degrees of resistence to be overcome. In the small climbing 
sloth the claws are long and slender, having only to bear the weight of 
the animal’s light body, which is approximated by the action of the mus¬ 
cles towards the grasped branch as to a fixed point. The stouter propor¬ 
tions of the prehensile hooks in the Mylodon accord with the harder task 
of overcoming the resistance of the part seized, and bringing it down to 
the body. For the long and slender brachial and antebrachial bones 
of the climbing sloth, we find substituted in its gigantic predecessor a 
humerus, radius, and ulna of more robust proportions — of such propor¬ 
tions, indeed, in the Mylodon robustus, as are unequalled in any other 
* The first part of this essay, consisting of 64 pages, was published in November, 1842, 
and anterior to Professor Owen’s work. 
