THE HEAD AND NECK. Ill 



that it did not exist in any of the primitive Ungulates 

 of the Eocene period, in which, consequently, these 

 two cavities, or fossae, were freely continuous (see- 

 skull of Phenacodus in Fig. 2, p. 21). Moreover, it 

 does not exist in any other of the Perissodactyles of 

 the present time (tapir or rhinoceros), but is a spe- 

 cial and recently acquired character, developed only 

 in the later stages of the horse group, not being met 

 with in any of the ancestral forms until after the 

 close of the Miocene period. 



The horse, however, is by no means alone among 

 mammals in possessing it ; but whenever it occurs, it 

 appears to be an evidence of advance in structure, 

 being found in the higher and more recent forms of 

 several groups, the lower and more ancient members 

 of which do not possess it. In man it has attained 

 its most complete development, for not only is there 

 a bridge, but also a wall extending inwards from it, 

 cutting off almost completely the two cavities from 

 one another. 



In front of the orbit a great, flat expanse, the 

 " cheek," extends quite to the fore-part of the face, 

 giving room for the long row of upper molar teeth, 

 and within, for the lodgment of the highly-devel- 

 oped organ of smell. This is roofed over above by 

 " nasal bones n (n) of great size, terminating in front 

 by freely-projecting, pointed, and somewhat decurved 



