THE ANTERIOR LIMBS OF QUADRUPEDS. 35 



indeed, as a general rule, the hinder graspers 

 of these animals approach nearer to the human 

 ha;ad, as far as the development of the thumb 

 is concerned, than do the fore-hands, or 

 graspers. In some of the American monkeys, 

 the thumb is wanting, or reduced to a mere 

 rudiment beneath the skin, and in those which 

 possess it, it is on the same plane with the 

 fingers, or utterly uncpposable to them, and 

 bends like the fingers in the same direction. 

 A true thumb, however, exists in the hinder 

 graspers ; and it is remarkable that among 

 certain groups of the American monkeys, we 

 meet with an accessory organ for grasping, 

 namely, a strongly prehensile tail, by whicli 

 they can suspend themselves head downwards 

 from the branches. The prehensile tail of the 

 spider-monkeys, of the opossums, and some 

 other quadrupeds, may indeed be regarded as 

 an accessory hand, or grasper, not only from 

 the power of clinging tenaciously with which it 

 is endowed, but also from the sense of touch 

 which it possesses, apparently in as high a 

 degree, or even perhaps higher, than tlie paws 

 themselves. Indeed, the extremity of the tail, 

 in the spider-monkey, is finger-like, and is 

 capable of seizing small objects with great 



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