Quadrupeds. 



117 



Notice of Fossil Sloths. 

 (Concluded from p. 287) 



Skull of Mylodon robustus, Owen. 



Professor Owen, proceeding to a detailed description of the skull, 

 gives a minute and elaborate analysis of the malar bone : this remark- 

 able bone projects from the skull somewhat in the manner of a small 

 elk-antler; it commences with a short thick stem, somewhat flattened 

 above, where it forms the floor of the orbit, and there expands into a 

 broad vertical trilobed plate, as represented in the above figure. In no 

 family of existing or extinct animals, besides the sloths, do we find any 

 approach to this extraordinary formation : though the more lengthened 

 and straightened skull of the Mylodon, and its more complete zygoma- 

 tic arch, are characters possessed more fully by the armadilloes than by 

 the sloths. With all other mammals it were useless to compare the skull 

 now before us : once place it beside that of the horse, ox, elk, tapir, 

 rhinoceros, dugong, or any other herbivorous animal of equal bulk, and 

 we shall not only be struck with the manifold discrepancies, but at once 

 conclude that the Mylodon obtained its food in a manner no longer 

 practised by living animals. The extinct Megatherium, however, pre- 

 sents us with a conformation similar in many respects to that of the 

 Mylodon, and more especially in the possession of that singular de- 

 scending process of the malar bone, which so peculiarly characterizes 

 the sloth, and which alone is sufficient to show the close affinity of 

 these gigantic antediluvians with our existing sloths. 



The teeth of the Mylodon are eighteen in number, five on each side 

 above and four below : they are simple, long, fangless, of uniform sub- 

 stance and nearly straight, with the exception of the first tooth in the 

 ii D 



