156 



The Sloths, though specially and admirably organized for clinging to the 

 boughs of trees, yet in the course of an existence exclusively spent therein 

 are liable, through unforeseen contingencies of rotten branches or sound ones 

 yielding to the force of winds, to be occasionally thrown to the ground ; with- 

 out attaching undeserved credit to the story of these excellent climbers choosing 

 that abrupt and hazardous mode of descent by preference*. The coarse 

 matted hair with which their light body is densely covered is well suited to break 

 the force of such falls, whilst any injury to the brain seems to have been pro- 

 vided against by the strong double bony wall of the cranial cavity which results 

 from the extension of the air-cells from the frontal along the upper part of the 

 head to the occipital region. But the same structure exists to an equal or 

 greater extent in the Mylodon, which according to my interpretation of its or- 

 ganization was not a climber ; not subject therefore to a fall. Yet the liability of 

 the Mylodon, in the habitual practice of uprending and prostrating large trees, 

 to be struck by the trunk or some of the large branches, must have been greater 

 than that of the Sloth to a fall from its tree ; and therefore the advantage to 

 the Mylodon of having a double brain-case would not be less. 



Certain it is, that the habits of life, or the conditions under which the Mylodon 

 existed, did render it obnoxious to violent blows on the headf, and that it was 

 owing to the extensive and deep cellular diploe of the skull, that they were not, 

 in the present instance, death-blows. 



It is at least not probable that any large mammiferous animal could have 

 survived so extensive and complicated a fracture and depression of the vitreous 

 table at the back part of the skull, as that which in the Mylodon is here confined 

 to the outer table. Either of the blows, however, to the force of which that 

 strong plate of bone has yielded, must have stunned, and, at least, have tem- 

 porarily disabled the animal ; and, if inflicted by the paw of some sufficiently 

 powerful Carnivore, would have left the Mylodon its easy and unresisting prey. 

 If the skull of an animal so destroyed had been preserved and afterwards dis- 

 covered in a fossil state, the broken bones would not have presented any of 

 those effects of the reparative processes which are so extensively manifested in 

 the very remarkable specimen under consideration. 



* Buffon, Histoire Naturelle, torn. xiii. p. 3. f See Plate III. 



