xx hi 



CRANIAL CAPACITY 



O05 



The special developments of the receptors and brain have marked 

 effects on the skull, whose facial portion becomes shorter and the 

 brain-case relatively larger and rounder; the foramen magnum comes 

 to face downwards, rather than backwards. As the eyes are directed 

 forwards the orbits become closed off from the temporal fossae behind. 



14 



o 12 



-c: 



10 



£> 



.^ 



6 



.3 



2-\r= 



10 20 



30 40 

 Body 1 



50 60 

 ighb Kg. 



70 80 90 



Fig. 382. The relative cranial capacity as a function of body-weight in various primates. 

 The brain grows relatively faster in man than in either monkeys or apes. The curves are 

 constructed by measuring cranial capacity and body-weight of individuals of differing 

 ages. The monkeys included various Cercopithecidae, the apes only gorillas, chimpanzees, 

 and orangs. (Modified after Schultz, Am. J. phys. Anthropol. 28.) 



The head is more clearly marked off from the body than is usual in 

 mammals and the neck is very mobile, allowing the eyes to be turned 

 in all directions. 



The skeletal and muscular systems become arranged to allow jump- 

 ing, swinging, and grasping. The pentadactyl plan is retained, without 

 the loss of digits or fusion of bones that are found in most mammals, 

 but the hand and foot are made suitable for grasping by development 

 of adduction movements of pollex and hallux. The digits mostly have 

 sensitive pads and the original claw is replaced by a flat nail. The 

 clavicle remains large and indeed is specially developed in primates to 

 allow mobility of the fore-limb, the muscles being arranged to allow 

 rotation of the scapula, increasing the range of movement. Still further 



