THE TEETH OF MAMMALS 177 



which are found in the Eocene formations of 

 the West. One genus — Anaptomorphus — had the 

 generalized characteristics of the progenitors of 

 the Primates. It had the tritubercular upper 

 molar, and a monkey of the later Eocene had the 

 quadritubercular form such as is found in the 

 later Primates and man today. 



Fig. 75. — Teeth of New- world Monkey (species unknown). 



The true monkeys are divided into two great 

 classes, — first the Platyrrliine (wide-nosed), or 

 New World Monkeys (Fig. 75), and second the 

 Catyrrliine (narrow-nosed), or Old World Mon- 

 keys. The Platyrrliine, or American Monkeys, 

 have prehensile tails, wide nostrils, and the dental 

 formula, usually, of the Cebidse, — 



