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trees, and have been able to browse even on the slender terminal twigs, affords 

 a difficult and interesting problem to the comparative anatomist : it is one that 

 probably would never have suggested itself, and certainly could never have been 

 resolved without the discovery of the fossil bones of the Megatherioids. 



The light and diminutive Sloths, the nearest living congeners of these great 

 extinct quadrupeds, climb for their sustenance ; and it is very true that in all 

 the modifications of the osseous frame- work of the Mylodon, by which it differs 

 most from the large Herbivora, if gains for its extremities prehensile as well 

 as locomotive powers ; this acquisition is most strikingly manifested by the pos- 

 session of clavicles, by the free rotation of the fore-arm, bj' a slight inversion 

 of the hind-foot, and by the great size and curvature of the claws, which ter- 

 minate certain digits on each foot. 



And inasmuch as the Megatherioids hereby deviate from the Giraffe and Ele- 

 phant, they correspond with the Sloths : but whether from such correspondence 

 it may as surely be concluded that their mode of obtaining the food was the same, 

 as from identity of dental and maxillary structure the same kind of food has 

 been inferred, demands some further and deeper consideration. 



The mere existence of clavicles cannot be allowed much weight in the argu- 

 ment that the Mylodon or Megatherium climbed trees, since in one of the species 

 of Sloth these bones are incomplete, without affecting, so far as is known, its 

 scansorial powers. The Bears, which are the heaviest quadrupeds now gifted with 

 the faculty of climbing, and some of which, the Sun-bears of the Eastern tropics, 

 for example, habitually obtain their food by this means, are destitute of even 

 the rudiment of a clavicle, as I have ascertained by the dissection of different 

 species. Clavicles, therefore, in any degree of development not being essential 

 to a climbing quadruped, we must seek for other relations and uses of the re- 

 markably strong and perfect collar-bones of the Mylodon, and of its congeners 

 the Scelidothere, Megalonyx, and Megatherium. 



Clavicles are usually present in those mammals which carry their food to the 

 mouth, either by one hand, as the Quadrumanes, or by both fore-paws, as 

 many Rodents and Marsupials. The claviculate species of Sloth has been like- 

 wise observed to grasp its food by bending its long claws upon the wrist*. But 



* Daubenton, who had the opportunity of observing the actions of a living Unau in the menagerie 



