116 



ARBOREAL MAN 



In the normal method of progression a dog carries its 

 head nearly in line with its vertebral column, but when 

 it sits up to beg it bends its head and neck so that its 

 eyes and face are still directed forwards, and the head 

 becomes almost at right angles to the axis of its vertebral 

 column. This position becomes habitual in the arboreal 



Fig. 39. — Base of the Skull of a Baboon {Cynocephalus). 



Primates, for in them the trunk has so frequently to be 

 more or less upright, and in proportion to the permanency 

 of this position there comes about a shifting of the site 

 of the condyles. 



Posture alone determines this change, for the more 

 quadrupedal Baboons (Cynocephalus) do not share so 

 fully in this feature, which is so characteristic of their 

 truly arboreal allies (see Fig. 39). In most monkeys the 

 occipital condyles are situated well forward upon the 



