DIGESTION 285 



the contraction of the palato-pharyngeal muscles which lie 

 in their posterior pillars. The larynx is pulled upwards 

 and forwards by the contraction of the thyro-hyoid muscle, 

 and the elevation of the hyoid bone by the muscles which 

 connect it to the lower jaw. The glottis is closed by the 

 approximation of the vocal cords and the arytenoid car- 

 tilages, assisted it may be by the folding down of the 

 epiglottis like a lid. But this organ can hardly play the great 

 part which has been assigned to it in closing the larynx, since 

 swallowing proceeds in the ordinary way when it is absent. 

 The morsel of food, grasped by the middle and lower con- 

 strictors as it leaves the back of the tongue, passes rapidly 

 and safely over the closed larynx, the process being accele- 

 rated by the pulling up of the lower portion of the pharynx 

 over the bolus by the action of the palato- and stylo-pharyngei. 

 The second cr oesophageal portion of the involuntary 

 stage is a more leisurely performance. The bolus is carried 

 along by a peculiar contraction of the muscular wall of the 

 oesophagus, which travels down as a wave, pushing the food 

 before it. When the food reaches the lower end of the 

 gullet the tonic contraction of that part of the tube is for 

 a moment relaxed, apparently by reflex inhibition, and the 

 morsel passes into the stomach. 



Such is the view of the mechanism of deglutition that has hitherto 

 commanded the largest amount of support ; and when the bolus is 

 of such consistence and of such size that it actually distends the 

 oesophagus, there is little doubt that this view is substantially correct. 

 But it has been shown that liquid or semi-solid food is swallowed in 

 a different way. The food lying on the dorsum of the tongue is 

 suddenly put under pressure by the sharp contraction of the mylo- 

 hyoid muscles in the floor of the mouth. Prevented from passing 

 forwards by the contact of the tip of the tongue with the palate, it is 

 shot rapidly in the direction of least resistance down to the lower 

 part of the lax oesophagus, its movement in this direction being ac- 

 celerated by the simultaneous contraction of the two hyoglossi which 

 pull the tongue backward and downward. So far the whole process 

 has only occupied one-tenth of a second. But it is only after about 

 six seconds that the food is forced through the cardiac sphincter into 

 the stomach by the arrival of the tardy peristaltic contraction of the 

 cesophageal wall (Kronecker and Meltzer). (See also p. 349.) 



There are certain remarkable peculiarities which distinguish 

 this peristaltic movement of the oesophagus from that of 



