THE FACE AND THE CRANIUM 97 



and supplies the whole facial area with blood ; the internal 

 jugular vein returns the blood from the brain, and the 

 external jugular vein drains the area supplied by the 

 external carotid artery. These two sets of vessels are 

 of varying importance in different animals. Primitively, 

 the external carotids and the external jugulars are by 

 far the largest and most important vessels in the head 

 region, and the internal carotids and internal jugulars 

 are, relatively, inconsiderable channels. But in arboreal 

 life, with hand-feeding and increasing brain growth, their 



FIG. 33. OUTLINE OF THE SKULL OF A DOG, TO SHOW TUB 

 RELATIVE PORTIONS DEVOTED TO THE SKELETON OF THE 

 FACE AND TO THE SKELETON OF THE BRAIN CAVITY. 



relative importance becomes altered, and finally in Man 

 and in the higher Primates the internal carotids and in- 

 ternal jugulars far outweigh in size and importance the 

 arteries and veins of the facial area. The gross changes 

 which take place in the contour of the head have already 

 been touched on, and they need no further emphasis, 

 since they are conspicuous. A primitive arboreal Insec- 

 tivore, such as Tupaia, has a relatively small head and a 

 long snouty face (see Fig. 37); many Lemurs have snout 

 regions almost as long, but others, such as Tarsius spec- 

 trum, have faces which are already distinctly flat (see 

 Fig. 70). In Monkeys and Anthropoids, although the 

 jaws protrude considerably in the adults of some species, 

 the rounded skull case and flattened forehead dominate 



7 



