35 



structure of the teeth yields the crowning proof that it is to the diminutive arboreal 

 Sloths that the Mylodon and its more or less bulky congeners have the closest 

 natural affinity. 



The chief differences observable in the cranial anatomy of the Sloths, as com- 

 pared with that of the Mylodon, are the greater relative depth and breadth, and 

 the more convex outline of the coronal aspect of the skull. The zygomatic 

 process of the temporal bone is relatively shorter, and does not attain the malar 

 bone ; this, therefore, has not the middle process for supporting the zygoma, 

 and is bifurcate, instead of being, as in the Mylodon, trifurcate. In the greater 

 breadth and exterior sculpturing of the descending process of the malar, and in 

 the greater relative length and minor convexity of the upper part of the skull, 

 the resemblance of the Unau to the Mylodon is greater, but in the large size of 

 the anterior tooth in both jaws it is less than that of the Ai. 



The Mylodon, in the more elongated form and straighter contour of its skull, 

 and in the complete zygomatic arch, is more like the Orycterope and Arma- 

 dillos than the Sloths ; but the unimportant character of these approximations 

 is apparent on a closer comparison. The length of the head in the fossorial 

 Edentata is chiefly due to the prolongation of the jaws, the orbits being situated 

 in the posterior half of the skull. The zygoma is a simple arch without 

 ascending or descending processes ; at best a rudiment only of the latter ap- 

 pears in the Chlamyphore — the smallest of the existing Armadillo tribe*. The 

 angular process of the lower jaw is short or obsolete. The exaggerated length 

 of the slender edentulous jaws of the Ant-eaters and Pangolins, and their defective 

 zygomatic arches, remove them to a greater distance from the Mylodon. With 

 other existing Mammals, not of the Edentate order, it would be lost time to pur- 

 sue the present comparison, with a view to the elucidation of the natural affini- 

 ties of the Mylodon. It needs only to place the skull of the species under con- 

 sideration by the side of that of the Horse, Ox, Elk, Tapir, Rhinoceros, Dugong, 

 or other vegetable feeder of corresponding size, to be struck with the pecuUari- 

 ties of the fossil, and to infer that the habits and mode of feeding of the Mylo- 

 don must have been such as are no longer manifested by the large Herbivora 

 of the present day. 



* It would seem that the large extinct Glyptodon had the origin of the masseter extended by an 

 inferior prolongation of the malar, similar to that in the Megatherium and Sloth tribes. 



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