142 



sider the construction of the fore-foot, and especially the number and form of the 

 claws. 



In the habitual burrowers, whose feet are best organized for displacing the 

 dense earth, as the Mole, the Mole-rat, the Condylure and Echidna, the claws 

 are long and broad, of nearly equal size on each digit, and can be extended in 

 the same plane as the hand, which is of considerable breadth. In those Arma- 

 dillos which are most remarkable for their rapid perforation of the soil, as the 

 Dasypi gigas and unicinctus, the three outer claws, which are principally deve- 

 loped for that office, are scarcely less remarkable for their great breadth, than for 

 their length, but they are of unequal size. The breadth of the long fossorial 

 claws of the Orycterope also surpasses their depth. 



In the Sloths, on the contrary, the depth or vertical diameter of the claws, 

 which are unusually long, much exceeds their transverse diameter or breadth ; 

 they are also more curved than in the burrowers, and are much restricted in 

 their movements, especially in that of extension. The fore-foot of the Sloths is 

 likewise long and narrow, and only three fingers in one species and only two in 

 another species, are furnished with claws, which are nearly of equal length. 

 The chmbing Ant-eater {Myrmecophaga didactyla), which destroys the tree- 

 termite, has its two toes shaped nearly as in the Sloths. The Great Ant-eater, 

 which breaches the strong fortresses of the terresti'ial termites, has its long fore- 

 claws of nearly equal breadth and depth, and the chief power of the fossorial ex- 

 tremity is concentrated on one digit, which is much superior in size to the rest. 

 In the work to which this modified digging instrument is put the soil has not to 

 be displaced in great quantities as in the excavation of a hiding-place or burrow, 

 but it needs only to be partially disturbed in order that something which is hid- 

 den may be exposed. 



The Megatherioid quadrupeds are not characterized by the true fossorial 

 hand in which all the five digits are provided with sub-equal, long and broad 

 claws ; but at most only two or three of the digits were provided with claws. 

 The depth of these claws exceeds their breadth in the Megatherium, especially 

 in the longest and largest claw : the more curved and more compressed claws 

 of the Megalonyx very nearly resembled those of the Sloth. In the Mylodon, 

 the claws, though equally remarkable for their length, and nearly as much 

 curved as in the Megalonyx, were neither depressed as in the burrowers, nor 



compressed as in the climbers, but had their vertical and transverse dimensions 



* 



