The Digestion of Food 99 



Other digestive organs which are tributary to this canal, 

 and discharge their secretions into it, are the salivary glands, 1 

 the liver, and the pancreas. 



The digestive process may be subdivided into three steps, 

 which take place respectively in the mouth, in the stomach, 

 and in the intestines. 



X149. The Mouth. The mouth is the cavity formed by 

 the lips, the cheeks, the palate, and the tongue. Its bony 

 roof is made up of the upper jawbone on each side in front, 

 and of the palate bones behind. This is the hard palate. 



The mouth continues behind into the throat, the separa- 

 tion between the two being marked by fleshy pillars which 

 arch up from the sides to form the soft palate. In the 

 middle of this arch there hangs from its free -edge a little 

 lobe called the uvula (Figs. 45 and 51). 



On each side where the pillars begin to arch is an 

 almond-shaped body known as the tonsil. When we take 

 cold one or both of the tonsils may become inflamed, and 

 so swollen as to obstruct the passage into the throat. 

 xl50. Mastication, or Chewing. The first step in the 

 process of digestion is chewing, or mastication, the cutting 

 and grinding of the food by the teeth. While the food is 



1 Glands. Glands are organs of various shapes and sizes, whose special 

 work it is to separate materials from the blood for further use in the body, 

 the processes being known as secretion and excretion. The means by which 

 secretion and excretion are effected are, however, identical. 



The essential parts of a gland" are a basement membrane, on one side of 

 which are found the secreting cells, on the other the blood current, flowing 

 in exceedingly thin-walled vessels known as the capillaries. The cells are 

 able to select from the blood whatever material they require, which they 

 elaborate into their particular secretion. 



In Fig. 47 is illustrated, diagrammatically, the structure of a few typical 

 secreting glands. The continuous line represents the basement membrane. 

 The dotted line represents the position of the cells on one side of the base- 

 ment membrane. The irregular lines show the position of the blood vessels. 



