354 



DIGESTION AND ABSORPTION 



into the small intestine just below the stomach, and certain glands 

 {intestinal glands) in the wall of the intestine. 



It vnW be the purpose of this chapter to follow the various food 

 substances in the passage through the food tube in order to find 

 how and ivhere the changes take place in the various nutrients which 

 prepare them to become part of the blood. 



Mouth Cavity in Man. — In our study of a frog we foimd that 

 the mouth cavity had two unpaired and four paired tubes leading 

 from it. These are (a) the gullet or food tube, (6) the windpipe (in 

 the frog opening through the glottis), (c) the paired nostril holes 

 (posterior nares), (d) the paired Eustachian tubes, leading to the 

 ear. All of these openings are found in man. 



Opening of Eiista- 

 chia/n tube 



Soft palate 



— I/ard palate 



Tongue 



The mouth cavity of man. 



In man the mouth cavity, and all internal surfaces of the food 

 tube, are lined with a mucous membrane. The mucus secreted 

 from gland cells in this lining makes a slippery surface so that 

 the food may slip down easily. The roof of the mouth is formed 

 in front by a plate of bone called the hard palate, and a softer 

 continuation to the back of the mouth, the soft palate. These 

 separate the nose cavity from that of the mouth proper. The part 



