Royal Society. 243 



further from its characteristics in other Edentata. In all the existing 

 Edentata, save the Sloths, the hind-foot is pentadactyle, and four of 

 the toes have a long claw, even in the little arboreal Myrmecophaga 

 didactyla: the departure by degradation from the pentadactyle type 

 is a peculiar characteristic of the Sloth-tribe in the order. It is 

 carried further in the same direction in the great extinct terrestrial 

 Sloths. In these the mutilation of the foot has commenced on the 

 outer side by the removal of the ungual phalanx from the fifth and 

 fourth toes ; but this accompanied by modifications which adapt these 

 toes to the important office of support and progression of the body on 

 level ground. Jn the scansorial Sloths, the three middle digits being 

 equally developed for prehension, one toe on the outer and one on 

 the inner side of the foot, are reduced to their metatarsal basis. In 

 the Megatherium the mutilation of the foot on the inner side is 

 carried to a greater extent; the innermost toe or hallux, with its 

 entocuneiform bone, is wholly removed : the second toe is repre- 

 sented, like the first in the Sloths, by its cuneiform bone and a 

 coalesced rudiment of the metatarse : and it is only the third toe or 

 medius that repeats the condition of the claw-bearing toes in the 

 climbing Sloths. 



Finally, the author enters upon the question of the habits and food 

 of the Megatherium. Guided by the general rule that animals 

 having the same kind of dentition have the same kind of food, he 

 concludes that the Megatherium must have subsisted, like the 

 Sloths, on the foliage of trees ; but that the greater size and strength 

 of the jaws and teeth, and the double-ridged grinding surface of the 

 molars in the Megatherium, adapted it to bruise the smaller branches 

 as well as the leaves, and thus to approximate its food to that of the 

 Elephants and Mastodons. The existing Elephants and the Giraffe 

 are specially modified to obtain their leafy food ; the one being 

 provided with a proboscis, and the entire frame of the lofty Giraffe 

 adapting it to browse on branches above the reach of its largest 

 ruminant congeners. If the Megatherium possessed, as Cuvier 

 conjectured, a proboscis, it cannot, judging from the suborbital 

 foramina, have exceeded in size that of the Tapir, and could only 

 have operated upon branches brought near its mouth. Of the use of 

 such a proboscis in obtaining nutritious roots, on the prevalent hypo- 

 thesis that such formed the sustenance of the Megatherium, it is 

 not easy to speculate : the hog's snout might be supposed to be more 

 serviceable in obtaining those parts of vegetables; but no trace of 

 the preenasal bone exists in the skull. A short proboscis would be very- 

 useful in rending off the branches of a tree prostrated and within 

 reach of the low and broad-bodied Megatherium, and it would be 

 aided in this act by the tongue, of which^ both the hyoid skeleton, by 

 its strength and articulation, and the foramina for the muscular 

 nerves by their unusual area, attest the great size and power. 



As regards the limbs, the Megatherium differs from the Giraffe and 

 Elephant in the unguiculate character of certain of its toes, in the 

 power of rotating the bones of the fore-arm, in the corresponding 

 development of supinator and entocondyloid ridges in the humerus, 

 and in the possession of complete clavicles. These bones are requi- 



