CHAPTER XVI 

 THE FACE AND THE CRANIUM 



WE have followed some of the phases by which hand- 

 feeding and alteration of life-habit have led to the re- 

 cession of the snout region, and we have seen the influence 

 which this recession exerts upon the dental series; but 

 its influences are felt in many other ways, and some other 

 of the accompanying phenomena must receive passing 

 attention. The snout recedes as a part of a general 

 evolution proceeding! in arboreal life, and one other 

 feature (to be dealt with later) which accompanies it is the 

 steadily increasing growth of the brain. The skull as 

 a whole may be said to consist of two parts a part which 

 is a containing bony case for the brain and the sense 

 organs, and a part which is the skeleton of the mechanism 

 for obtaining and masticating food (see Fig. 33). 



In the lowest arboreal animals, the second or facial 

 part is preponderately large in proportion to the first or 

 cranial part, but the relations of the two parts are soon 

 altered in arboreal evolution. The growing brain de- 

 mands a large brain case; the diminishing jaws require 

 less bony basis. In this way the configuration of the 

 skull is profoundly altered, for not only do the jaws 

 shrink back, but the brain case protrudes. Apart 

 altogether from the mere evidence of the relative sizes 

 of the bony parts in a skeleton, there is seen in this 

 evolution a gradual change in the arteries and veins 

 associated with these two constituents of the head region. 

 The internal carotid artery enters the cranium to supply 

 the brain, the external carotid artery runs to the face 



