CHAPTER XXXVIII 



DIGESTIVE SYSTEM 



Introduction. We have just discussed the composi- 

 tion of foods and the uses of foods to the body. It is 

 evident to everyone, however, that many changes must 

 take place before the food which we eat can become 

 a part of the body. These changes take place in a set 

 of organs which we call the digestive system. This 

 system consists of two parts, the alimentary canal and 

 the digestive glands. 



Alimentary canal. The alimentary canal is a long 

 tube extending through the body and having two 

 openings, the mouth at one end and the anus at the 

 other. In some animals this tube is almost straight 

 and of about the same diameter throughout the body. 

 In man, however, it is over thirty feet long and with 

 a diameter which varies greatly. 



It begins at the mouth opening, enlarges and forms 

 the mouth cavity, which in turn communicates with the 

 smaller throat cavity. Posterior to the throat is a tube 

 which is called the gullet, or esophagus, opening into an 

 enlarged pouch, the stomach. From the stomach the 

 food is conducted into the long coiled intestine, which 

 fills most of the lower part of the trunk of the body. 



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