188 MOUTH DIGESTION. 



which acts to raise the larynx when the hyoid bone ascends, and 

 its opening closed by the contraction of the arytenoideus and the 

 lateral crico-arytenoidei, supplied by the inferior or recurrent 

 laryngeal nerve, a branch of the pneumogastric. 



Whether the epiglottis is folded back or remains in its usual 

 erect position during deglutition is a matter of dispute. Those 

 who claim that it closes the glottis give various arguments to 

 sustain the opinion and explain how it takes place. The action 

 of the thyrohyoid, just referred to, is regarded by one authority as 

 causing or permitting " the folding back of the epiglottis over the 

 upper orifice of the larynx." It is further claimed that this 

 movement can be felt by simply passing the finger into the throat 

 until it comes in contact with the epiglottis and then performing 

 the act of swallowing. On the other hand, there is a case on 

 record in which enough of the pharynx was removed in a 

 surgical operation to permit the actual inspection of the epiglottis 

 during the act of swallowing, and it was observed to undergo no 

 change of position. Whatever may be the fact in this regard, 

 there is no question that the larynx is perfectly protected against 

 the entrance of food, even though the epiglottis does not fold 

 back during the act of deglutition. 



At the close of the first stage the pharynx is raised so as to 

 receive the bolus, and at the same time it is enlarged. This is 

 due to the forward movement of the larynx and the tongue, both 

 of which as they are elevated are also carried forward ; and also 

 to the contraction of the stylopharyngei, whose action is to draw 

 upward and outward the sides of the pharynx, thus separating 

 them and enlarging the cavity laterally. The bolus being well 

 within the pharynx, the muscles which raised the latter relax, and 

 it descends, carrying with it the bolus, which is now passed along 

 by the constrictors of the pharynx to the opening of the esoph- 

 agus. The stylopharyngeus receives its nerve-supply from the 

 glossopharyngeal, while the constrictors are supplied by the 

 pharyngeal plexus, the inferior constrictor being supplied by the 

 external laryngeal branch of the superior laryngeal and the recur- 

 rent laryngeal. 



Third Stage. In this stage the bolus passes through the esoph- 

 agus into the stomach. This canal is about 23 cm. in length, and 

 from 1.8 to 2.4 cm. in breadth. When empty its walls are in 

 apposition, and in section it presents the appearance of a trans- 

 verse slit. It has three coats : 1. An internal, composed of mucous 

 membrane, covered with stratified epithelium, as is that of the 

 mouth and that of the pharynx from the soft palate down. 2. A 

 submucous coat, in which are the esophageal glands, compound 

 racemose glands which open by ducts upon the surface of the 

 membrane, and which secrete mucus. These glands are most 

 abundant near the cardiac orifice, where they encircle the esoph- 



