DIGESTION AND ABSORPTION 



335 



cavity, it gets beyond our direct control ; the muscles of the gullet, stimu- 

 lated to activity by the presence of food in the tube, push the food down 

 to the stomach by a series of contractions. 



Opening of 

 Eustachian tube — 



Soft palate 



Hard palate 



Pharynx — 



Tongue 



Vertical section of the head and neck. 



Demonstration. — Cut away the throat muscles of a frog so as to expose 

 the windpipe, or trachea; under this is a soft tube much wider in extent, 

 the gullet. 



Stomach of Frog. — Make a median cut through the muscles on the ven- 

 tral side of the abdomen of a frog; then make incisions at right angles to 

 this, just below the fore legs and immediately in front of the hind legs. 

 Fold back the outer skin and the muscles and pin them into place at the dor- 

 sal side of the body. Notice the thin glistening membrane lining the cavity 

 inside the body. This is called the peritoneum. The peritoneum forms a 

 fold on the dorsal side of the body cavity (called the mesentery), and in 

 this incloses all the organs of digestion, etc., so that they hang from the 

 dorsal side when the animal is in natural position. The peritoneum and 

 mesentery are present in man. 



The stomach may easily be found after lifting up the dark red, three- 

 lobed liver. Note the position and size of the stomach. This will vary 

 considerably according to the amount of food inside. 



Stomach of Man. — In man, the stomach has, in general, the 

 same position as in the frog. This difference, however, exists: 

 The gullet passes directly through a muscular partition, the dia- 

 phragm, which is lacking in the frog. The diaphragm separates 



