THE SPIDER-MONKEYS. 229 



which, usually, a single minute nodular phalanx [finger-bone] 

 is articulated, and is completely hidden beneath the integu- 

 ment. Although thus rudimentary and functionless, all its 

 characteristic muscles, except one (the long-flexor) are present. 

 {Huxky.) The upper incisors are unequal, the interior being 

 the larger. There is a space (diastema) between the incisor 

 and the canine teeth (as in all A7ithropoidea^ except Man) ; the 

 canines are large and conical; the upper molars large, and 

 their crowns four-cusped, with transverse ridges between the 

 outer and inner front cusps and the outer and inner hind cusps, 

 and also an oblique ridge crossing from the outer front cusp to 

 the inner hind one. In the larynx of Ateles there is a single 

 median air-sac opening from the back of the windpipe, but there 

 is no such extension of the resonating apparatus as is seen 

 in the Howlers {Alouatfa). In its brain Ateles exhibits in 

 some respects a higher type than in even the Old World 

 Apes. 



In regard to this group of Monkeys, the late Mr. H. W. 

 Bates made the following interesting observations : — " In the 

 Coaitas the tail reaches its highest perfection as a prehensile 

 organ ; and on this account it would perhaps be correct to 

 consider the Coaitas as the extreme development of the 

 American type of Apes. As far as we know from living and 

 fossil species, the New World has progressed no further than 

 the Coaita towards the production of a higher form of the 

 Quadrumanous order. The tendency of Nature here has been, 

 to all appearance, simply to perfect these organs, which adapt 

 the species more and more completely to a purely arboreal 

 life ; and no nearer approach has been made towards the more 

 advanced forms of Anthropoid Apes-, which are the products of 

 the Old World solely. The tail of the Coaita is endowed with 



