THE PRIMATES — EXCEPT MAN 117 



(Monkeys and Apes) we find successive reductions in the pre- 

 molar series. In the American Monkeys the premolar for- 

 mula is: 



3 



3 



but in all Old- World Monkeys, in Anthropoids and in Man it 

 has become: 



2 



2 



THE AMERICAN MONKEYS 



Little is known concerning the ancestry of the New-World 

 Monkeys (Platyrrhinae) and as they are an off-shoot of the 

 main Primate stock they will be only briefly considered. The 

 two families are the Hapalidae or Marmosets and the Cebidae 

 which comprise all other varieties. The Hapalidae differ from 

 the other family in having only two molars in each jaw instead 

 of three. The members of this family are very specialized and 

 retrogressive. Of the Cebidae two examples are presented, the 

 first showing an omnivorous dentition and the second a purely 

 herbivorous adaptation. 



Ateleus belzebuth, the white bellied or "Mexican" Spider- 

 monkey from the region of the Orinoco (Fig. 39), feeds upon a 

 mixed diet of insects, eggs, birds and fruit and presents a 

 fairly typical omnivorous dentition. The formula is: 



2 13 3 

 1^, C^Pf.Mf. total 36. 



Z Y o o 



Its specialized position is indicated by the termination of the 

 palate at the level of the second molar and by the almost 

 parallel limbs of the dental arch. The incisors of both jaws 

 are gently sloping; this is not a primitive character but pseudo- 

 primitive having been adopted comparatively recently. The 

 canines are of moderate length and the premolars, especially 

 those of the maxilla, are bicuspid. All these features, as pre- 



