172 PHYSIOLOGY. 



muscular coat has two layers, an inner with circularly 

 arranged fibers, and an outer layer with longitudinally 

 arranged fibers. When the food enters the gullet the 

 muscle fibers, especially the circular fibers, shorten, and 

 by a wave-like action push the mass rapidly along into the 

 stomach. The first part of swallowing is voluntary ; but 

 after the bolus has entered the gullet the action is involun- 

 tary, The mucous lining of the gullet has many mucous 

 glands which lubricate the passageway by the mucus which 

 they secrete. 



Illustration of Passage through the Gullet. The passage of the 

 food through the gullet may be illustrated as follows : Let several per- 

 sons hold a large rubber tube with their hands in contact. Put an egg- 

 shaped piece of wet soap in the tube. The first hand is shut and 

 pushes the soap along into the part of the tube held by the next hand ; 

 this hand now compresses the tube, while the first hand remains clinched ; 

 and so, in turn, the object is pushed the whole length of the tube. 



The Stomach. Just beyond the diaphragm the diges- 

 tive tube widens suddenly, forming the stomach; the 

 stomach is an oval sac lying just beneath the diaphragm, 

 with the large end to the left and the small end to the 

 right. The smaller end, by narrowing, becomes the small 

 intestine. When the stomach is empty it collapses, as its 

 walls are soft and flexible. When distended it may hold 

 three pints, or when abnormally distended even more. 



The Coats of the Stomach. The stomach and intestines have four 

 coats, in the following order, beginning at the outside : the peritoneum, 

 the muscular, the submucous, and the mucous coats. The muscular 

 coat of the stomach consists of three layers, distinguished by the 

 arrangement of the fibers, a circular layer, a longitudinal layer, and an 

 oblique layer. The mucous lining is somewhat loosely attached to 

 the muscular coat by the intervening submucous coat, and when the 

 stomach collapses the mucous coat is thrown into folds, usually running 

 lengthwise. 



