I2 THE FROG 
(3) Using a dry prepared skull, examine a maxillary tooth 
carefully with a hand lens. Distinguish crown and root. How 
are the teeth inserted on the jaw bone (1. e., in sockets or other- 
wise)? Do they offer more resistance to an object entering or 
leaving the mouth (test with the finger)? Are they adapted: for 
biting, for chewing, or merely for holding the prey? 
(b) The posterior nares (internal openings of the nasal or 
olfactory sacs), lying lateral to the vomerine teeth. Pass a bristle 
through the anterior nares and notice where it emerges into the 
mouth. 
(c) The Eustachian tubes, a pair of cavities at the sides of the 
posterior part of the roof; where do they lead? 
(d) A pair of rounded prominences in front of the Eustachian 
tubes; how are they caused? Press one of the eyes with your 
finger, and observe that the eye may be made to protrude into 
the mouth cavity. 
2. On the floor: 
(a) The lower jaws forming the margin. Do they bear 
teethir 
(b) The floor proper is soft and fleshy, and slightly stiffened 
by the cartilaginous body of the hyoid apparatus (examine a 
preparation of the hyoid apparatus). 
(c) The tongue. Observe its shape and manner of attach- 
ment. In a fresh specimen observe that the tongue is sticky; of 
what advantage is this to the animal? Examine a preparation of 
a frog with the tongue protruded. If possible observe the action 
of the tongue in a hungry frog which may be induced to snap at 
a small piece of red cloth dangled before it with a cord. The 
tongue is of use in capturing small animals (e. g., insects). 
(d) The glottis, a longitudinal slit on the summit of a promi- 
nence far back in the throat region. Force it open with a seeker ; 
the cavity into which it leads communicates with the lungs. 
(e) The opening of the esophagus, a distensible tube leading 
from the posterior part of the mouth cavity to the stomach. 
(f) In the male: the openings of the vocal sacs just within 
the angle of the mouth. 
The posterior part of the mouth cavity, into which the glottis 
and the Eustachian tubes open, is called the pharynx. 
