CHAPTER XVII 



THE DIGESTIVE APPARATUS AND NUTRITION 



306. The apparatus for digestion consists of the alimen- 

 tary canal with its appendages. This is a long, irregular 

 tube having a continuous lining of raucous membrane. 

 It comprises the mouth, pharynx, esophagus, stomach, and 

 large and small intestines. Numerous glands along its 

 length furnish the digestive juices. 



307. The Mouth (Fig. 108) is the chamber which re- 

 ceives the food through the opening and closing lips. 

 The soft palate at the back forms a curtain over the 

 opening at the back, while the hard palate of the roof, 

 the soft muscular walls of the cheeks, and the large muscle 

 of the tongue, together with the teeth, all assist in the 

 process of mastication to which the food is first subjected. 

 As in the skin, many minute papillce are found in the 

 mucous membrane, containing networks of nerves and 

 blood vessels. Some of these contain taste corpuscles. 

 Some have organs for touch. 



308. The Teeth are the special organs for cutting and 

 grinding the food. Two sets" of teeth are provided. 

 The first, which appear in infancy and are only twenty 

 in number, are called temporary or milk teeth. They fall 

 out after a few years, to be replaced by the permanent 

 teeth, thirty -two in number. 



The four front teeth on each jaw are called incisors. 



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