MAMMALIA. 511 
the skeleton. Let us first glance at the skulls of the two 
types. Notice in both the large development of the facial 
region in comparison with the cranial. This is due not 
only to the large maxilla, but also to the part taken by the 
jugal and the lacrymal in the formation of this region. 
Fig. 351.—VENTRAL VIEW OF SKULL or Horse 
(Zgeus Caballusx%). (Ad nat.) 
-- Incisors. 
Canine, 
Hard Palate —... 3 Molars (three 
Premolars_ in 
front of them). 
Internal Nares.,.~ 
Pterygoid..... 
T: ic. 
SRE ne 'Glenoid Cavity. 
c 
Occipital Condyle. Foramen Magnum. 
Hence the small size of the orbit, which is also completely 
bounded by bone,* a postorbital process of the frontal 
descending to meet the zygomatic arch below, 
In both types the mandibles are large and heavy, ex- 
panded behind into broad strong plates, evidently built 
* This complete closure of the orbit is not effected in the lower Perissodactyla 
(¢.g., Rhinoceros and Tapir), nor in the more primitive Artodactyla (e.g., Pig). 
