84 HUMAN BIOLOGY 



fish and frog, lie outside the alimentary canal itself, but are 

 connected with ito These are the digestive glands. They 

 produce digestive ferments (P. B., 53), which after being 

 dissolved in water are carried into the food canal through 

 small pipes or ducts. Thus the salivary glands pour their 

 secretions into the mouth cavity, and the liver and pancreas, 

 situated near the stomach, empty their juices into the in- 

 testine (Fig. 26). 



II. THE MOUTH CAVITY AND ITS FUNCTIONS 



113. Study of the mouth cavity. (Home work.) 



Take a position with your back toward a window or some 

 bright light, and study your mouth cavity by means of a hand 

 mirror. 



A. Walls of the mouth cavity. The walls that are rigid 



are composed largely of bone; those that are 

 yielding are largely made of muscle. 



1. Press your forefinger against the roof, the side walls, 



and the floor of the mouth cavity beneath the 

 tongue Which walls are composed of bone? 

 which of muscle ? 



2. What is the color of the inner walls of the mouth 



cavity? This color is due to the blood vessels 

 that lie close to the surface. 



3. Rub your finger over the mucous membrane which 



covers these walls. The substance on your finger 

 is largely mucus. Describe the mucus and tell 

 where it is found. 



B. Tongue. 



1. To what part of the mouth cavity is the tongue 



attached ? 



2. Chew a piece of apple or other solid food ; note and 



describe the action of the tongue during the process 

 of chewing food. 



3. Swallow some solid food, and describe the action of 



the tongue in the process of swallowing. 



