CHAPTER XI. 



THE SKULL IN THE UNGULATA, HYRACOIDEA, AND 

 PROBOSCIDEA. 



Order UNGULATA ; Sub-order Perissodactyla. In the 

 Horse the whole skull is greatly elongated, chiefly in con- 

 sequence of the immense size of the face as compared with 

 the hinder or true cranial portion. The basal line of the 

 skull from the lower border of the foramen magnum to the 

 incisor border of the palate is very nearly straight. The 

 occipital and ethmoid planes are nearly perpendicular to this 

 line, the latter inclining slightly forwards. The tentorial 

 plane, strongly marked by inward projecting ridges of bone, 

 slopes obliquely backwards at an angle of 45. The cerebral 

 fossa is a smooth and regular oval, broad and rounded in 

 front, and with no distinct division into anterior and pos- 

 terior portions. The olfactory fossa is short, but deep from 

 above downwards. The pituitary fossa is very shallow, and 

 there are no distinct clinoid processes. The alisphenoid is 

 very obliquely perforated by the foramen rotundum, but the 

 foramen ovale is confluent with the large foramen lacerum 

 medium behind. There are considerable frontal and sphen- 

 oidal air sinuses, but the former do not extend any great 

 distance over the brain-cavity. 



