CHAP, II THE FROG: MOUTH AND PHARYNX 17 



be observed in the . interior of the mouth. All round the 

 edge of the upper jaw is a row of small conical teeth (Fig. 

 7;. There are no teeth in the lower jaw; but on the 

 roof of the mouth, a short distance behind the snout, are 

 two little patches of teeth, called the vomerine teeth (vo. t). 

 Just behind these are two apertures, called the internal 

 nostrils {p. no) : a guarded bristle passed into one of the 

 external nostrils and pushed gently backwards and down- 

 wards, will be found to enter the mouth by the correspond- 

 ing internal nostril. 



Behind the internal nostrils are two large hemispherical 

 projections, due to the roof of the mouth being bulged out 

 by the huge eyes, as can be readily made out by pushing 

 the eyes from outside. 



On the floor of the mouth is the large, flat tongue 

 {tng), remarkable for the fact that it is attached at its front 

 end, its hinder end being free and double-pointed. When 

 the frog uses it to catch insects it is suddenly thrown for- 

 wards, almost like a released spring. Just behind the back- 

 wardly-turned tip of the tongue is an oval elevation, 

 having on its surface a longitudinal slit, called the glottis 

 (gi), which leads, as we shall see afterwards, into the lungs. 

 The back of the mouth narrows considerably, and the 

 soft skin or mucous membrane lining it is here thrown into 

 folds. A probe gently pushed backwards passes, as we 

 shall see, into the stomach. The narrowed region of the 

 mouth is the throat, or pharynx. On its upper wall, near 

 the angles of the mouth, are two pits : a guarded bristle 

 passed into one of these will be found to come into 

 contact with the corresponding tympanic mernbrane, 

 which will be pierced if sufficient force is used. The 

 pits are known as the Eustachian recesses or tubes (eus. t). 

 Dissection of the Frog : Skin and Muscles. — If a slit is 



Pbact. Zool. C 



