384 CHORDATA. 
another cavity (the thoracic cavity) containing, as will be 
seen, the heart and lungs. 
The buccal cavity can be exposed by cutting one man- 
dible. The ¢ongue is large and mobile, and behind its base 
is the glottis covered by a flap, the ¢figdotiis. 
Almentary: ‘The internal nares open very far back, almost 
over the glottis. This is due to the formation of a 
palate or secondary roof to the buccal cavity which shuts 
off a complete nasal chamber, at the hind-end of which 
open the two Lustachian apertures. 
Fig. 277.—PERMANENT DENTITION OF THE HARE 
(Lepus timidus). 
Note the long incisors, four above and two below, and the cheek-teeth -_ 
Into the mouth there open the ducts of four pairs of 
salivary glands—the parotid, below the ear; the infra-orbital, 
below the eye; the susmaxillary, between the mandibles ; 
and the sublingual gland, under the.tongue. ‘These secrete 
saliva which is mixed with the food by mastication and has 
a digestive action on certain foods. 
At the anterior end of the jaws is a pair (upper and 
lower) of large sharp-edged incisor teeth. These have hard 
enamel mainly on the outer surface and are kept sharp by 
wearing upon each other. They grow throughout life as 
