]()0 SPECIAL MUSCULAR MECHANISMS 



the opening of the stomach, in five or six seconds after the 

 contraction of the mylohyoid muscle. Of this total time 

 only one-tenth second is spent by the food in the pharynx. 

 The arrival of the food at the cardiac sphincter causes an 

 inhibition of the tone of the sphincter so that the swallowed 

 food may be passed into the stomach. In the case of liquid 

 food the passage of the esophagus is accomplished more quickly. 

 Such food is thrown or shot down into the lax esophagus to 

 a varying distance. The slight contraction of the diaphragm 

 just before deglutition sets in has the effect of placing the 

 esophagus under diminished pressure and perhaps of straighten- 

 ing it somewhat, both events facilitating the passage of the 

 food. The normal peristaltic wave follows later, gathering 

 together, as may be imagined, remnants clinging to the esopha- 

 geal wall and ultimately moves the whole mass into the stomach, 

 an event which may be appreciated by auscultation at the lower 

 end of the sternum. 



The peristalsis of the esophagus is of interest on account 

 of its close connection with the central nervous system. The 

 ligation, crushing or even section of the esophagus does not 

 interfere with the passage of the wave. Even when removed 

 from the body under proper conditions the esophagus con- 

 tinues to manifest its peristalsis. Ordinarily, stimulation of 

 the mucous membrane of the pharynx causes movements 

 of the esophagus while stimulation of its own mucous mem- 

 brane is ineffective. These facts are interpreted as follows: 

 That the esophagus possesses the power of peristalsis per se, 

 but that this is ordinarily carried out by reflexes having their 

 source in the pharynx at or near the area that also reflexly 

 determines the contraction of the mylohyoid. The term reflex 

 implies a centre, which has been located in the upper portion 

 of the medulla. The deglutition centre is connected with 

 sensory areas of the posterior portion of the tongue, the soft 

 palate, fauces, and tonsils by fibers of the superior laryngeal, 

 pharyngeal branches of the vagus, palatal branches of the 

 fifth and the glossopharyngeal. Stimulation of the central 

 end of the superior laryngeal will cause swallowing move- 

 ments, but if the central end of the glossopharyngeal is stimu- 

 lated at the same time the swallowing is inhibited. It is through 

 the mediation of fibers of the ninth nerve that in a series of 



