DIGESTIVE FLUIDS, ENZYMES 131 



membrane through which the food passes. The glands which 

 secrete the digestive fluids open into this tract. 



The digestive fluid of the mouth is saliva. 



The digestive fluid of the stomach is gastric juice. 



The digestive fluids of the intestines are intestinal juice, and 

 pancreatic juice (assisted by bile). 



Each of these fluids contains one or more of the peculiar sub- 

 stances called enzymes. 



An enzyme is a ferment which by its presence causes certain 

 changes in other substances. 



The enzymes of the digestive fluids cause the chemical changes 

 in food which are necessary for its digestion. 



The glands are 



Salivary, opening into the mouth. 

 Peptic, " stomach. 



Intestinal, " " intestines. 



Pancreas, small intestine. 



Liver, " small intestine. 



The tongue, teeth and glands are appendages of the alimentary canal. 



THE MOUTH 



The mouth, or oral cavity, is enclosed partly by muscles and 

 partly by bones. The muscles are the lip muscles in front, the 

 buccinator at the sides, and the mylo-hyoid in the floor. The bones 

 are the maxilla and the palate-bones above, and the mandible below. 



The roof of the mouth is called the palate ; the bony portion is 

 the hard palate; the muscular portion attached to it is the soft 

 palate or the velum palati (veil of the palate) . In the middle of the 

 soft palate is the uvula, which is a small projection downward. 

 All of these bones and muscles are in pairs, right and left. 



Surgical note. If, owing to lack of development they are not joined in 

 the middle line, cleft palate results. The cleft may be partial or complete, 

 and the divided upper lip is called harelip. 



The oral cavity is lined with mucous membrane which is always 

 moist in health. The part of the cavity between the lips and the 

 teeth is the vestibule. 



The mouth contains the teeth and the tongue. 



The teeth are already described. 



The tongue lies in the floor of the mouth with its base curved 

 downward at the back and attached to the hyoid bone. It is 

 composed of muscles, and covered with mucous membrane which 



