252 DIVERSIONS OF A NATURALIST 



and blood supply between them and that all-important 

 organ contained in the neighbouring bony box, the 

 brain. As the great teeth and long jaw have dwindled, 

 the brain has increased in volume, and, what is more 

 important, in activity. 



Other neighbouring bony structures have dwindled 

 whilst the brain has increased. The great longitudinal 

 and transverse crests of bone seen on the skull of the 

 gorilla may never have existed in that form of ape from 

 which man is derived, but a tendency to such ridge-like 

 outgrowth and to a greater thickness of the bony wall 

 of the brain-case characterizes apes as distinguished from 

 men, and its disappearance is one of the changes which 

 have accompanied the expansion of the brain-case and the 

 increased size of brain in man. Lower races of existing 

 men have frequently thicker skulls than the higher races. 

 The bony development of the skull in the higher apes 

 is especially remarkable in the region just above the eye. 

 The upper border of the orbit is greatly thickened, and 

 projects as a bony arch overhanging the eye. But the 

 extent of this growth, as also of crests on the skull, varies 

 in individuals, and is much smaller in females than in 

 males. In the young these ridges and prominences are 

 absent. It is accordingly no very great change that 

 they should disappear altogether in man, even were they 

 as large in the ape-like ancestor of man, which probably 

 they were not. But the existence of a considerable 

 thickening and forward growth of the eyebrow region of 

 the skull is noticed in many human skulls. It is 

 particularly large in some skulls of Australian " black- 

 fellows," and is still larger in and characteristic of the 

 ancient species of men of the Moustierian period in 

 Europe, Homo Neanderthalensis. 



