How Our Bodies Digest Food 



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The walls of the esophagus, like those of the entire canal, con- 

 sist partly of muscular fibers so constructed as to force the food 

 downward. The outer wall is composed of longitudinal muscles, 

 the inner, of circular muscles. 

 These sets of muscles contract, 

 or grow shorter, and expand, 

 or stretch, alternately, squeez- 

 ing the food always towards 

 the lower end of the canal. 

 This action, known as peri- 

 stalsis, takes place throughout 

 the alimentary canal, from the 

 time the food leaves the mouth. 

 The act of swallowing sets the 

 muscles in motion and the 

 peristalsis is continued all the 

 way down the canal. Peri- 

 stalsis in the esophagus forces 

 the food into the stomach. 



The Stomach. The stom- 

 ach is a very important organ 

 of digestion. It is a pear- 

 shaped pouch, having a normal 

 capacity in an adulty>f about 

 three to five pints. It has two 

 openings. The one by which 

 the food enters from the 

 esophagus is called the cardiac 

 opening. The other, through 

 which the food passes into the 

 small intestine, is called the 

 pylorus. In an adult the 

 stomach is from ten to twelve 

 inches in length and about five 

 inches in diameter, and its walls are not over one-eighth of an 

 inch in thickness. The walls are made up of several coats, or 

 layers. The outer surface is covered with a thin, shiny membrane 



Went 

 THE ALIMENTARY CANAL 



