How Our Bodies Digest Food 



399 



The Mouth. The mouth takes in the food. It is provided 

 with teeth, for use in chewing and preparing the food for diges- 

 tion ; with cheeks, which are muscular walls that allow the jaws 

 room to move in chewing; with a wall or roof, formed by the 

 hard, bony palate in front and the soft palate behind; with a 

 tongue, a muscular organ that aids in moving the food in the 

 mouth when chewing, and also causes the sensation of taste by 

 means of minute projections, called papilla, on its upper surface. 

 The mouth also contains salivary glands that secrete saliva to 

 moisten and help digest the food. The surface of all these parts, 

 the teeth excepted, is composed of mucous membrane. 



Teeth. Nature provides each person who lives to adult age 

 with two sets of teeth. The first is a set called milk teeth, twenty 

 in number, ten in each jaw, which belongs to the earlier years of 

 childhood. The second is a permanent set, which develops as soon 



TYPES OF HUMAN TEETH 



1. An incisor, or cutting tooth. 



2. A canine, or tearing tooth. 



3 and 4. Molars, or crushing teeth. 



as the milk teeth are lost. There are thirty-two teeth in the perma- 

 nent set, sixteen in each jaw. Each half-jaw has eight teeth of 

 similar shape and arranged in the same order, as follows: two 

 incisors, well adapted for cutting by their sharp, chisel-like edges ; 

 one cuspid, sometimes called canine, adapted for tearing by its 

 sharp-pointed structure ; two bicuspids, adapted for crushing and 

 grinding food by their blunt crowns ; and three molars, especially 

 adapted for crushing and grinding food by their broad, rough, 

 uneven surfaces. The third molar in each half-jaw is called the 

 wisdom tooth. It develops late and is often not as strong and 

 useful as the other teeth. 



