NUTRITION 365 



diameter, to permit the carrying out of special functions in various 

 parts. 



The Mouth. So far as digestion is concerned, the mouth per- 

 forms two functions: in it the food is crushed or cut into smaller 

 portions and at the same time it is mixed with saliva, one of the 

 digestive fluids, whose function will be dealt with later. The 

 mouth cavity is bounded above by the palate, below by the tongue, 

 and at front and sides by the teeth, lips, and cheeks. There are 

 six openings into this cavity, from within, namely 



1. Two nasal openings, behind the palate and connecting with 



the nostrils, above. 



2. Two eustachian tubes, also far back, high up at the sides 



and connecting with the ears. 



3. The trachea and gullet below, the former in front and con- 



necting with the lungs, and the latter behind it and com- 

 municating with the stomach. 



Other organs are immediately connected with the mouth cavity, 

 most of which can be seen by studying your own mouth with a 

 mirror or by looking into a friend's mouth with a small electric 

 light. The " roof of the mouth " or hard palate can be easily 

 recognized. Back of it is a downward projecting sheet of muscle, 

 the soft palate; at either side rounded projections may be seen, 

 which are tonsils. 



Behind the soft palate and near the opening into the nasal cavity 

 is the location of adenoid growths which may obstruct the breath- 

 ing and have to be removed if they reach abnormal size. The 

 tonsils also sometimes become enlarged and act as nests for bac- 

 terial growth, necessitating their removal. Their function is not 

 thoroughly understood, and when diseased their removal is bene- 

 ficial. 



The openings of the eustachian tubes are protected by their 

 high location and by folds of membrane beside them. The trachea 

 is protected by the base of the tongue and the epiglottis, which is 

 a door-like organ that covers the trachea during swallowing. 



The Tongue. The tongue is easily studied, but few of us really 

 know its shape, size or structure. The best way to find out is to 



