MOVEMENTS OF THE ALIMENTARY CANAL. 711 



food into the corresponding cavities. The whole reflex is there- 

 fore an excellent example of a finely co-ordinated movement. 



The following events are described: The mouth cavity is shut 

 off bv the position of the tongue against the palate and by the con- 

 traction of the muscles of the anterior pillars of the fauces. The 

 opening into the nasal cavity is closed by the elevation of the soft 

 palate (action of the levator palati and tensor palati muscles) and 

 the contraction of the posterior pillars of the fauces (palatopharyn- 

 geal muscles) and the elevation of the uvula (azygos uvulae muscle). 

 The soft palate, uvula, and posterior pillars thus form a sloping 

 surface shutting off the nasal chamber and facilitating the passage of 

 the food backward through the pharynx. The respiratory opening 

 into the larynx is closed by the adduction of the vocal cords (lateral 

 crico-arytenoids and constrictors of the glottis) and by the strong 

 elevation of the entire larynx and a depression of the epiglottis over 

 the larynx (action of the thyrohyoids, digastrics, geniohyoids, and 

 mylohyoids and the muscles in the aryteno-epiglottidean folds). 

 If the elevation of the larynx be prevented by fixation of the thy- 

 roid the act of swallowing becomes impossible. There is also at 

 this time, apparently as a regular part of the swallowing reflex, 

 a slight inspiratory movement of the diaphragm, the so-called 

 swallowing respiration. The movements of the epiglottis during 

 this stage of swallowing have been much discussed. The usual 

 view is that it is pressed down upon the laryngeal orifice Hke the lid 

 of a box and thus effectually protects the respiratory passage. 

 According to most observers, it is not necessary for the pro- 

 tection of the larynx that the epiglottis shall be actually folded 

 down over it by the contraction of its own muscles. The forcible 

 lifting of the larynx, together with the descent of the base of 

 the tongue, effects the same result by mechanically crowding the 

 parts together, and the larynx is still further guarded by the ap- 

 proximation of the false and true vocal cords, thus closing the glottis. 

 The whole act is very rapid as well as complex, so that not more 

 than a second elapses between the beginning of the contraction ot 

 the mylohyoids and the entrance of the food into the upper end of 

 the esophagus. 



The passage of the food through the esophagus differs apparently 

 with its consistency. When the food is liquid or very soft Kronecker 

 and Meltzer have shown that it is shot through the whole length of 

 the esophagus by the force of the initial act of swallowing. It 

 arrives at the lower end of the esophagus in about 0.1 sec, and may 

 pass immediately into the stomach or may lie some moments in the 

 esophagus according to the conditions of the sphincter guarding 

 the cardiac orifice. When, however, the food is solid or semi- 

 solid, as was shown by Cannon and Moser, it is forced down the 



