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), 

 and nearer the jaw 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 corre- 

 sponding 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 tips of the tongue is an oval elevation, 

 having on its surface a longitudinal slit, called the 

 glottis (gl), 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 membrane, 

 which will be pierced if sufficient force is used. The 

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



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

 made in the skin of the belly, and a probe pushed in 



PRACT. ZOOL. r 



