THE DIGESTION OF FOOD 



101 



The food tube then narrows again into the small intestine, 

 which is coiled upon itself in the abdomen. It now expands 

 again into the large intestine, 

 from which are discharged 

 the waste materials. 



Layers of muscles which 

 help to push along the food 

 surround this long food 

 tube. In and around this 

 tube are many organs called 

 glands. 1 They pour out 

 certain fluids, which moisten 

 the food, change it chemi- 

 cally, and otherwise make 

 it ready to be taken into 

 the blood. 



146. The Mouth. The 

 first change which food 

 undergoes when taken into 

 the alimentary canal is in 

 the mouth. 



In the mouth the food is 

 rolled over by the tongue, 

 mixed with saliva, and 



FIG. 63. A View of the Back Part 

 of the Adult Mouth. 



The head is represented as having been 

 thrown back, and the tongue drawn 

 forward. A, , incisors; C, canine; 

 D, E, bicuspids; F, H, K, molars; 

 M, anterior pillar of the fauces-; N, 

 tonsil ; L, uvula ; O, upper part of the 

 pharynx; />, tongue drawn forward; 

 R, linear ridge, or raphe. 



1 Glands are curious organs of 

 various shapes and sizes, whose 

 special work it is to take out of the 

 blood something to be used again, 

 or to rid it of something to be cast 

 out of the body. Thus, the salivary 

 glands make saliva, or spittle, and 

 the sweat glands make sweat. The liver, which weighs from three to four 

 pounds, is a single gland, and secretes bile ; while the glands in the intestines 

 are so very small that they cannot be seen by the naked eye (Fig. 68). 



