116 THE MAMMALIA. 



After a detailed account of the various parts of the 

 limbs, he says : ' The principle of viewing structures 

 and instruments, in reference to the work that they 

 do, is shown to be good in gaining insight into the 

 mode of life of extinct animals, in a striking degree 

 through its application to the skeletons of the 

 M'egatheriods (Giant Sloths). The teeth of these 

 conform so closely in all characters with those of 

 the Sloths as to suggest leaves rather than roots to 

 have been their food. In the light, slender Sloths 

 the modifications of structure for climbing, cling- 

 ing, and living altogether in trees are carried out 

 to an extreme. In the colossal extinct kinds, the 

 foliage was obtained in a different way. The huge, 

 single claw on the hind foot l would be applicable 

 as a pickaxe to clear away the soil from between 

 the ramifications of the roots : a second claw 2 would 

 have interfered with such work. The foot is 

 organised to give great strength to that claw; 

 dislocation of its toe is specially guarded against ; 

 the rest of the tarso-metatarsal structure relates 

 to the power of the foot to sustain superincumbent 

 pressure, with a position of the claw bringing its 



1 This is the claw of the middle toe. The other toes appear 

 to have been furnished with a kind of hoof. 



2 The reader who finds this explanation somewhat too odd 

 not forget that Owen is a decided teleologist. 



