118 ARBOREAL MAN 



all the essentials of the human poise, but the preponder- 

 ately large face and jaws, in the adult Gorilla especially, 

 demand for their proper balance a large muscular leverage 

 applied to the back of the head. It is this muscle mass 

 which gives these animals their apparently short bull- 



FIG. 41. BASE OF THE HUMAN SKULL. 



necks, and which, acting from the spinous processes of 

 the cervical vertebrae, elongates these processes and pulls 

 them towards the skull. 



The poise of the skull, and the forward migration of the 

 occipital condyles and foramen magnum, are arboreal 

 features. Finishing touches have been put upon the 



