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MANUAL OF PHYSIOLOGY. 



out peristaltic contraction independently of the central nerve 

 organs, but that this power is, under ordinary circumstances, 

 held in check by the vagus. The inhibition is temporarily sus- 

 pended as a sequence of pharyngeal spasm, and consequently a 

 wave of peristaltic contraction is excited in the oesophagus mus- 

 cles, either in response to the direct stimulus of a passing bolus, 

 or as a result of impulses reflected along the vagus channels from 

 the medulla. 



Motion of the Stomach. The stomach and greater part 

 of the intestinal tract move freely within the abdomen, being 

 covered by the smooth serous lining of that cavity, which also 



FIG. 54. 



Diagram of Wall of the Stomach, showing the relative thickness of the mucous mem- 

 brane (a, 6, c), and the transverse (e), oblique (/), and longitudinal muscle fibres. 



keeps in position, so as to restrict their movements, those parts, 

 such as the duodenum, into which the ducts of large glands open. 

 When the stomach is empty it hangs with the great curvature 

 downward, and the muscular coats are quiescent. On being 

 filled it is passively rotated on its long axis, so that the greater 

 curvature is turned forward, here meeting with less resistance, 

 and the lesser curvature is turned backward to its line of attach- 

 ment. In the main, the motions of the stomach are peristaltic. 

 They become very active about fifteen minutes after the intro- 

 duction of food, and gradually become more and more energetic 

 until the end of stomach digestion, which lasts about five hours. 



