THE (ESOPHAGUS AND STOMACH 99 



esophagus. The student should observe the motion of the larynx 

 in swallowing by pressing the fingers lightly on the front of the 

 throat during the act. 



As soon as the food enters the upper portion of the oesophagus, 

 the circular muscles in the walls of that tube contract just above 

 it, thus forcing it a little downward. This action is repeated by 

 all the circular muscular fibres throughout the tube, each set con- 

 tracting just above the food only till it passes into the stomach. It 

 must not be understood, however, that the food is forced down 

 the oesophagus by a series of distinct movements or jerks ; but 

 that the successive muscular contractions produce a regular wave- 

 like motion throughout the tube. The longitudinal muscular 

 fibres also contract at the sides, thus helping the oesophagus to 

 grasp the food more effectually. 



It will have been observed that the act of swallowing is purely 

 a muscular action that the food does not fall into the stomach 

 by its own weight, but is forced downward. This being the case, 

 the act of swallowing may be performed with the body in any 

 position. Thus jugglers sometimes eat, and even drink while 

 standing on their heads, drink being conveyed into the stomach 

 in exactly the same manner as solid food. 



After the food has passed to the back of the mouth, the 

 remainder of the act of swallowing or deglutition (Lat. de, down ; 

 and glutio, I swallow) is purely involuntary, and consequently we 

 cannot then stop the bolus in its passage to the stomach. The 

 mucus secreted by the internal mucous membrane of the oesophagus, 

 acts as a lubricant, and thus facilitates the passage of the food. 



When the oesophagus is not engaged in swallowing, it is flat- 

 tened, its front and back walls being in contact. In order that 

 the act of deglutition may take place with regularity and ease, the 

 bolus of food must be sufficiently large to be within the grasp of 

 the contracting muscles. It is on this account that some persons 

 experience a considerable difficulty in swallowing a pill, especially 

 if it be a small one, unless food or drink be taken at the same 

 time. 



The general form, size, and position of the stomach have 

 already been described in Lesson XIII. ; we have now to notice 

 the structure of its walls, and its action on the food. 



The walls of the stomach consist of four distinct coats. The 

 outer coat is a layer of the peritoneum which is reflected round 

 ' most of the organs of the abdomen. It is a serous membrane, 

 that is, one which secretes a watery fluid called serum. The use 

 of the serum is to moisten or lubricate the surfaces of organs which 

 glide more or less over each other. 



The other three coats of the stomach correspond exactly with 



H 2 



