DEGLUTITION. 209 



tected during the deglutition of solids and liquids, one has only to carefully 

 follow the articles as they pass over the inclined plane formed by the back 

 of the tongue and the anterior and inferior part of the pharynx. As the 

 food is making this passage in obedience to the contraction of the muscles 

 which carry the tongue backward, draw up the larynx and constrict the 

 pharynx, the soft base of the tongue and the upper part, of the larynx are 

 applied to each other, with the epiglottis, which is now inclined backward, 

 between them ; at the same time the glottis is closed, in part by the action 

 of the constrictor muscles attached to the sides of the thyroid cartilages, and 

 in part by the action of the intrinsic muscles. If the food be tolerably con- 

 sistent and in the form of a single bolus, it slips easily from the back of the 

 tongue along the membrane covering the anterior and inferior part of the 

 pharynx ; but if it be liquid or of soft consistence, a portion takes this 

 course, while another portion passes over the epiglottis, being directed by it 

 into the two grooves by the side of the larynx. It is by these means, 

 together with those by whicft the posterior nares are protected, that all solids 

 and liquids are passed into the oesophagus, and the second period of degluti- 

 tion is safely accomplished. 



The third period of deglutition is the most simple of all. It merely 

 involves contractions of the muscular walls of the oesophagus, by which the 

 food is passed into the stomach. The longitudinal fibres shorten the tube 

 and slip the mucous membrane, lubricated by its glairy secretion, above the 

 bolus ; while the circular fibres, by a progressive peristaltic contraction from 

 above downward, propel the food into the stomach. In experiments on the 

 lower animals, it has been observed that while the peristaltic contractions of 

 the upper two-thirds of the tube is immediately followed by a relaxation, 

 which continues till the next act of deglutition, the lower third remains con- 

 tracted generally for about thirty seconds after the passage of the food into 

 the stomach. During its contraction, this part of the oesophagus is hard, 

 like a cord firmly stretched. This is followed by relaxation; and alter- 

 nate contraction and relaxation continue, even when the stomach is empty, 

 although, during digestion, the contractions are frequent in proportion to the 

 quantity of food in the stomach. The contraction is always increased by 

 pressing the stomach and attempting to pass some of its contents into the 

 oesophagus (Magendie). This provision is important in preventing regurgi- 

 tation of the contents of the stomach, especially when the organ is exposed 

 to pressure, as in urination or defecation. 



An approximate estimate of the duration of the acts of deglutition is 

 given in the following quotation from Landois : 



" According to Meltzer and Kronecker, the duration of deglutition in the 

 mouth is 0*3 sec. ; then the constrictors of the pharynx contract O9 sec. ; 

 afterward, the upper part of the oesophagus ; then after 1/8 sec. the middle ; 

 and after another 3 sec. the lower constrictor. The closure of the cardia, 

 after the entrance of the bolus into the stomach, is the final act in the total 

 series of movements." 



