DEG L UTITION. 189 



agus. 3. A muscular coat, which is arranged in two layers, an 

 inner (circular) and an outer (longitudinal). The fibers of the 

 circular layer form at the cardiac orifice, where the esophagus 

 enters the stomach, a sphincter which keeps the opening closed, 

 especially when the stomach contains food. The muscular tissue 

 of the upper third is principally striated, while the remainder is 

 of the involuntary variety. The nerves of the esophagus come 

 from the pneumogastric and the sympathetic. 



The circular layer of the muscular coat is continuous with the 

 inferior constrictor, and the contraction of the fibers of this layer 

 follows immediately upon that of the constrictor, carrying the 

 bolus onward in its passage to the stomach. This is a continuation 

 of the reflex act which begins certainly in the pharynx, possi- 

 bly in the mouth. The bolus stimulates the mucous membrane 

 as it passes along, and a wave of peristalsis follows. Thus each 

 successive portion of the muscular coat contracts behind the bolus, 

 gradually pushing it onward. When it reaches the cardiac orifice, 

 the sphincter relaxes and the bolus is forced into the stomach. 

 This can sometimes be heard by applying a stethoscope over the 

 epigastric region. The time occupied by the passage of the bolus 

 from the beginning of swallowing to the moment it enters the 

 stomach is about six seconds. The action of the longitudinal fibers 

 is not understood, although some authorities think that their con- 

 traction precedes that of the circular fibers, and thus tends to 

 dilate the esophagus and bring it forward over the bolus. 



The process of deglutition has been very thoroughly studied 

 by Falk and Kronecker, by Kronecker and Meltzer, and still 

 more recently by Cannon and Moser. The first-named experi- 

 menters have shown that there is pressure enough produced by 

 the rapid contraction of the muscles of the mouth to force liquid 

 food through the esophagus independently of peristalsis, and 

 indeed before the peristaltic wave passes along. Thus, when cold 

 water is swallowed its presence is recognized in the epigastrium 

 almost immediately ; and it has been also noted by them that 

 when strong acids pass through the esophagus only parts of it are 

 corroded, and not the entire surface of the mucous membrane, as 

 would be the case were they swallowed by peristaltic action. 



The second named experimenters conclude from their experi- 

 ments that liquids and semisolids are forced down the esophagus, 

 or " squirted " down, by the rapid contraction of the mylohyoid 

 muscles, nearly as far as the cardia (cardiac orifice), and that they 

 remain here until the peristaltic wave reaches this point, when 

 they are carried into the stomach, which is about six or seven 

 seconds from the beginning of swallowing. 



In these experiments only liquids and semisolids were employed, 

 and it is manifest that what might be true of these might not be 

 true of solids. It was to determine the actual movements of 



