DIGESTION OF FOOD: THE (ESOPHAGUS 



Abdomen 



passage open up, while those behind the mass contract and 

 thus push it along. The result is much the same as when one 

 forces a slippery ball 

 through a rubber 

 tube by squeezing 

 the tube between the 

 thumb and finger be- 

 hind the ball. This 

 action on the part of 

 the muscles would, 

 of course, carry food 

 along the tube, no 

 matter what the po- 

 sition of the body. 

 Even water does not 

 run down the gullet; it 

 is pushed down, grav- 

 ity having little or 

 nothing to do with the 

 process. This pecu- 

 liar method of move- 

 ment, called peristal- 

 sis, occurs through- 

 out the entire alimen- 

 tary canal. In man, a wave passes from the pharynx to the 

 stomach in about six seconds. 



BODY CAVITY AND ITS SUB-DIVISIONS 



All the space inside the ribs and the body wall, from the 

 hips to the shoulders, is called the body cavity. This is not 

 all in one large space, but is divided into an upper and a 

 lower part by a horizontal partition, called the diaphragm; 

 Fig. 46. At its center this is a thin sheet of tendinous material 

 from the edges of which muscles radiate to the body wall; 

 it extends across the body cavity between the ribs ; backbone 



FIG. 46. SHOWING THE BODY CAVITY DIVIDED 

 BY THE DIAPHRAGM INTO THORAX AND AB- 

 DOMEN 



