THE DIGESTION OF THE FOODSTUFFS 127 



ing and swallowing lie in the medulla oblongata. (See Chapter 

 XVIII.) 



2. GASTRIC DIGESTION 



i. The movements of the stomach. Both the cardiac 

 and pyloric openings of the stomach are generally closed 

 by the tonic contraction of the sphincters. During the act 

 of deglutition, the cardiac aperture opens by the relaxation 

 in the tonus of its muscles when the peristaltic contraction 

 has reached the lower end of the esophagus. The pylorus 

 opens and closes to admit part of the contents of the stomach 

 into the duodenum. 



The stomach consists of two parts : 



(1) The fundus with feeble muscles. 



(2) The antrum with strongly developed muscles. The 

 two parts can be separated from each other by a sphincter- 

 like muscle. 



Corresponding to the distribution of the muscles, the 

 movements of the pyloric part of the stomach are much 

 stronger than those of the fundus. In the antrum, the 

 pressure caused by the contraction of the muscles may be as 

 high as 130 mm Hg; the pressure in the fundus only 35 mm. 



The movements of the fundus serve to mix the food with 

 the gastric juice, the movements of the antrum serve to 

 empty the contents of the stomach into the duodenum. 



The length of time during which the different foods remain 

 in the stomach varies greatly. Fluid and soft foods are 

 forced into the intestine soon after being swallowed, but 

 solid food remains for a longer time in the stomach. The 

 last particles of food have left the stomach 7-8 hours after 

 a meal. 



Even the excised stomach can execute movements. The 

 normal stimulation for the muscles of the stomach appears 

 therefore to be due to the nerve plexuses in its walls; but 

 the central nervous system influences these movements. 

 There are motor and inhibitory nerve-fibres for the stomach. 

 These fibres run in the vagus and sympathetic and their 



