40 COMPAEISONS OF STRUCTURE IN ANIMALS. 



and the clavicles are doiibly iinited to the 

 blade-bones. The hand is a hook, (trebled in 

 some species, doubled in another,) by means of 

 ■which the animal suspends itself. The bones of 

 the wrist are consohdated into a single piece, and 

 the three (or two) fingers are short and arched 

 inwards, the joints of the bones being adjusted 

 upon a principle of unyielding strength. These 

 fingers are furnished with enormous curved 

 claws, or hooks, alone projecting from the un- 

 divided skin, which enshrouds together all the 

 rest, both fingers and wrist. Hence, on looking 

 at the dingers of the sloth, it would seem as if 

 these claws alone constituted the digital por- 

 tion. They can only move altogether ; and, in 

 their ordinary state, they are drawn forcibly 

 towards the palm by the action of elastic liga- 

 ments, and require the voluntary exertion of 

 the extensor muscles to unclose them ; and this 

 being discontinued, the elastic springs again 

 draAv them to the palm. In chnging, therefore, 

 whether during repose or while travelUng 

 along, the sloth has not to trust alone to the 

 exertion of voluntary muscles for its safety. 

 The ligaments, ever in operation, are suffi- 

 ciently tense to counteract the tendency of the 

 body's weight to relax them. The long and 



