DEGLUTITION. 57 



A solid bolus, that more or less fills the oesophagus, excites a 

 typical peristaltic wave which is characterized by a dilatation 

 of the oesophagus immediately in front of, and a constriction 

 over and behind the bolus. This wave travels down the cesopha- 

 gus at such a rate that it reaches the cardiac sphincter in about 

 five or six seconds. On arriving here the cardiac sphincter, 

 ordinarily contracted, relaxes for a moment so that the bolus 

 passes into the stomach. The peristaltic wave travels much more 

 rapidly in the upper portion of the oesophagus than lower down 

 because of differences in the nature of the muscular coat, this 

 being of the striated variety above, and of the non-striated, be- 

 low. The purpose of more rapid movement in the upper portion 

 is no doubt that the bolus may be hurried past the regions, 

 where, by distending the oesophagus, il might interfere with the 

 function of neighboring structures, such as the heart. The peris- 

 taltic wave of the oesophagus, unlike that of the intestines (see 

 p. 79), is transmitted by nerves, namely, by the oesophageal 

 branches of the vagus. If these be severed, but the muscular it- 

 self left intact, the oesophagus becomes dilated above the level 

 of the section and contracted below, and no peristaltic wave can 

 pass along it ; on the other hand, the muscular coat may be sev- 

 ered (by crushing, etc.) but the peristaltic wave will jump the 

 breach provided no damage has been done to the nerves. 



The propagation of the wave by nerves indicates that the sec- 

 ond and third stages of deglutition must be rehearsed, as it were, 

 in the medullary nerve centers from which arise the fibers to the 

 pharynx and the different levels of the oesophagus. The afferent 

 stimuli which initiate this process proceed from the pharynx by 

 the fifth, superior laryngeal and vagus nerves and not at all 

 from the oesophagus itself; thus, a foreign body placed directly 

 in the oesophagus remains stationary, but immediately begins to 

 move if the pharynx be stimulated, as by touching it. The. af- 

 ferent fibers in the glossopharyngeal nerve exercise a powerful 

 inhibitory influence on the deglutition center as well as on that 

 of respiration. Thus, if swallowing movements be excited by 

 stimulating the central end of the superior laryngeal nerve, they 

 can be instantly inhibited by simultaneously stimulating the 



