THE FROG 19 



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 Eu- 

 stachian 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 

 teeth? 



(b) The floor proper is soft and fleshy, and slightly stif- 

 fened by the cartilaginous body of the hyoid apparatus (ex- 

 amine a preparation of the hyoid apparatus). 



(c) The tongue. Observe its shape and manner of at- 

 tachment. 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. The 

 tongue is of use in capturing small animals (e. g. } insects). 



(d) The glottis, a longitudinal slit on the summit of a 

 prominence 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 oesophagus, a distensible tube 

 leading from the posterior part of the mouth cavity to the 

 stomach. 



