f)54 PRIMATES. 



The Primates include the Monkeys, Apes and Man. With 

 the exception of the last named they are all well covered with 

 hair, inhabit for the most part the warmer regions of the Old 

 and New World, and are on the whole arboreal inhabit. The 

 baboons (Papio), however, inhabit rocky mountain regions. 

 The most important characters are stated in the definition. 

 In addition to those the following may be mentioned. The 

 incisors are never more than - ; the canines are -^ and gener- 

 ally project ; the upper molars have generally 4 cusps, but the 

 posterior inner cusp may be weak or, in the American monkeys, 

 absent ; the lower molars are tetracuspidate, but the last usually 

 has a talon (rarely present in the New- World forms). In the 

 Old- World monkeys the molars usually increase in size from 

 before backwards * ; in the New- World forms they dimmish, 

 the last being usually the smallest. The premolars have two 

 cusps. There is generally a small gap between the incisors and 

 canines particularly in the upper jaw. 



The cranial cavity is spacious, and with the increase of the 

 brain the cranial capsule becomes rounder and the foramen 

 magnum gradually moves from the posterior part on to the 

 lower surface. The orbits look forward and are always com- 

 pletely shut off from the temporal fossa, by the backward and 

 inward extension of the postorbital processes of the frontal 

 and jugal to meet the alisphenoid ; the lacrymal foramen is 

 intraorbital. In most of them the two frontals meet ventrally 

 over the presphenoid between the ethmoid and orbit osphenoid, 

 but this does not happen in Homo, Simia, Anthropopithecus and 

 some Cebidae. The mastoid portion of the periotic appears on 

 the surface between the squamosal and exoccipital, but does not 

 form a process except in Homo. The stylohyal is never ossified 

 except in Homo and occasionally in Simia, and the tympano- 

 hyal is very small or absent. 



The vertebrae are C7, Dll-14, L4-7, S2-6, and caudal vari- 

 able. 



A clavicle is always present. The humerus never has an 



by the restriction of the villi to a discoidal area. In the discoidal type 

 of placenta the placentation is discoidal from the beginning, and the 

 chorion does not surround the embryo, but is confined to a discoidal 

 patch. 



* In Homo and some other genera of the Anthropomorphidse, the 

 last molar is smaller than the others. 



