76 HUMAN PHYSIOLOGY CHAP. 



hind. On the sides it is bounded by the cheeks, above 

 by the hard palate, and below by the muscles and con- 

 nective tissues that form the floor. It contains the 

 teeth and the tongue, two very important organs of 

 digestion, and receives the saliva through a number of 

 small ducts leading from the three pairs of salivary 

 glands. The tonsils are two olive-shaped organs, one 

 on either side, at the back part of the mouth. They 

 produce a fluid that probably helps in swallowing. 



In the mouth the food is cut and ground up by the 

 teeth, mixed with saliva, moved about by the tongue, 

 and finally pushed back into the pharynx. 



Study carefully your own mouth as to shape, size, and organs, as 

 teeth, tongue, tonsils, and palate. This may easily be done with 

 the aid of a small mirror. 



68. The Teeth. At birth a child has no teeth. The 

 first set begins to appear at the age of from six to ten 

 months and to disappear at about the sixth or eighth 

 year. These are called milk teeth. This set consists of 

 twenty teeth ten in each jaw. The four flat, cutting 

 teeth are called incisors ; the one sharp, tearing tooth on 

 either side of the incisors is the canine ; and the two 

 double grinding teeth back of each canine are the 

 molars. 



Is it not strange that this set should disappear in 

 youth and another take its place ? Yes, but we shall 

 understand why when we learn that a tooth does not 

 grow larger after it is once fully cut. Our hands, feet, 

 and heads grow, but our teeth do not. A bone grows 



