418 Quadrupeds. 



upper jaw, which is slightly curved : each has a central body of vas- 

 cular dentine, enclosed in a cylinder of hard unvascular dentine, 

 which forms a prominent ridge, and which is again cased in a cover- 

 ing of cement. 



The inference the author derives from the structure of the teeth, is 

 that the Mylodon fed on the leaves or slender terminal twigs of trees, 

 in this respect resembling the giraffe, the elephant and the sloth. The 

 extraordinary stature of the giraffe raises its mouth to the immediate 

 vicinity of its food; the trunk of the elephant conveys the food to its 

 mouth ; and the light figure of the sloth enables him to run along the 

 under side of the boughs, till he finds he has reached a commodious 

 feeding-place : but the Mylodon and his congeners possessed short 

 and massive necks, no trunk, and the bulk of a Hippopotamus or Rhi- 

 noceros ; so that to obtain their food in the same manner as either 

 the giraffe, the elephant or the sloth, appears decidedly impossible, 

 unless, with Dr. Lund, we imagine a vegetation gigantic in propor- 

 tion ; but even granting this, it is difficult to believe that creatures ri- 

 valling the Hippopotamus in bulk, would approach the leaves, which 

 are usually placed on the most slender twigs. Professor Owen, after 

 alluding to the very perfect clavicles of the Mylodon, which have been 

 received alternately as evidence of the burrowing and climbing hypo- 

 theses, does not necessarily imply the faculty of climbing or burrow- 

 ing, since the bear, a climbing, and the badger, a burrowing animal, 

 are perfectly destitute of them : but from a comparison of the hand of 

 the Mylodon with that of certain ant-eaters, he thinks it may be in- 

 ferred that it was an instrument employed in digging or displacing the 

 earth. The author considers the unequalled bulk of the posterior ex- 

 tremities, and the corresponding excess of muscular power, as shown 

 by the spinal crest of the sacrum, and the broad, rugged, and anteri- 

 orly produced margin of the ilium, as further evidence against the 

 climbing theory ; and he regards the hind legs as uniting with the 

 enormous tail in forming a tripod, which supported the weight of the 

 animal, leaving the hands at liberty. 



" If the foregoing physiological interpretation of the osseous frame- work of the gi- 

 gantic extinct sloths be the true one, they may be supposed to have commenced the 

 process of prostrating the chosen tree by scratching away the soil from the roots ; for 

 which office we find in the Mylodon the modern scansorial fore-foot of the sloth mo- 

 dified after the type of that of the partially fossorial ant-eater. The compressed or 

 subcornpressed form of the claws, which detracts from their power as burrowing instru- 

 ments, adds to their fitness for penetrating the interspaces of roots, and 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 



