52 COMPARISONS OF STRUCTURE IX ANDIALS. 



sharp claws. In others, as in the Cap3 

 leaping-hare, the fore-paws, amied with stou^. 

 claws, are expressly adapted for burrowing. 

 In the aquatic copybara of South America, 

 the toes are furnished with small claws, cloaely 

 resembhng little hoofs. Generally speaking, 

 in the rodent order, the fore-arm enjoys, to a 

 considerable extent, the power of pronation 

 and supination,* that is, of being turned par- 

 tially round at the elbow-joint, though in the 

 porcupine and the agouti this power is very 

 much restricted. Most possess cla\'icles, more 

 or less perfectly developed, and many hold 

 their food between their two fore-paws, while 

 they sit on their haunches and nibble it ; they 

 also use the paws in cleaning and dressing 

 their fur. 



We must now pass on to the considera- 

 tion of limbs modelled upon a plan differing 

 materially from any that we have hitherto 

 explained— Kmbs the structure of which is 

 utterly incompatible with the presence of a 

 collar-bone, with any degree of rotation at the 

 shoulder-joint, the slightest power of pronation 



* If the fore-arm be placed on a table, flat, and v,-ith the ]i:lm 

 uppermost, the fore-arm is in a state of supination; but if it b^ 

 turned round, so as to make the back of theTUand uppermost, it 

 is in a state of pronation. 



