806 TEETH OF MONKEYS AND LEMURS. 



the upper jaw (as in Fig. 76), the crown of a premolar 

 will be found above the third molar in place, as well as 

 above the second and first. As regards number, there- 

 fore, the molar series, in the South American monkeys 

 {Mycetes^ Aieles, Cehns\ is intermediate between that of the 

 genus Mustela and of Felis (Fig. 69) ; the little premolar, 

 'p z, in Mustela^ shows plainly enough which of the four is 

 wanting to complete the typical number in the South 

 American monkey, and which is the additional premolar 

 distinguishing its dental formula from that of the Old 

 World monkeys and man. 



Zoologists have rightly stated, as a matter of fact, that 

 the little marmoset monkeys {Hapale^ Ouistiti) " have only 

 the same number of teeth as the monkeys of the Okl 



World — viz: 32, z-,c ^m " But the difference 



4 1 — 1 5 — 5 



is much greater than this numerical conformity would 

 intimate. In a young Jacchus penicillatus^ I find that 

 there are three deciduous molars displaced by three pre- 

 molars, as in the other South American quadrumana, and 

 that it is the last true molar, m 3, the development of 

 which is suppressed, not the premolar,^ 2, and thus these 

 diminutive squirrel-like monkeys actually differ from the 

 Old World forms more than the Cehidce do ; i. e. they differ 



not only in having four teeth (p 2 ), which the mon- 

 keys of the Old World do not possess, but also by want- 

 ing four tqeth {m 3 ), which those monkeys, as well 



as the OehidcBj actually have. It is thus that the investi- 

 gation of the exact homologies of parts leads to a recog- 

 nition of the true characters indicative of zoological 

 affinity. 



