MAN'S RELATIVES: THE PRIMATES 



475 



face is turned more nearly at right angles to the spine. The placenta is 



disk-shaped and shed at birth. 



The anthropoids are divided into two groups, geographically separated 



today and in the past. The more 

 primitive of the two includes the 

 flatnosed monkeys (platyrrhines) 

 of the New World; all the Old 

 World primates (advanced types 

 of monkeys, apes, man) belong 

 to the narrow-nosed group, the 

 catarrhines. x 



In the New World monkeys the 

 nostrils are directed forward and 

 separated by a low, wide septum; 

 each jaw has three premolar teeth on 



Fig. 29.4. Lion-maned marmosets, or 

 tamarins, Leontocebus. {Courtesy Zoological 

 Society of Philadelphia.) 



Fig. 29.5. A South American spider 

 monkey, Ateles, family Cebidae. {Courtesy 

 Zoological Society of Philadelphia.) 



each side; and there are no callous areas on the buttocks as in the Old World 

 monkeys. The marmosets (Hapalidae) are primitive platyrrhines quite 



1 " Platyrrhine " simply means 

 wardly directed nose." 



'flat-nosed"; "catarrhine" means "with down- 



