636 PHYSIOLOGY OF DIGESTION AND SECRETION. 



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 by 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 like the lid 

 of a box and thus effectually protects the respiratory passage. It 

 has been shown, however, that removal of the epiglottis does not 

 prevent normal swallowing, and Stuart and McCormick* have 

 reported the case of a man in whom part of the pharynx had been 

 permanently removed by surgical operation and in whom the 

 epiglottis could be seen during the act of swallowing. In this 

 individual, according to their observations, the epiglottis was not 

 folded back during swallowing, but remained erect. Kanthack and 

 Anderson f state that in normal individuals the movement of the 

 epiglottis backward during swallowing may be felt by simply passing 

 the finger back into the pharynx until it comes into contact with the 

 epiglottis. According to most observers, it is not necessary for 

 the protection 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 



* "Journal of Anatomy and Physiology," 1892. 

 t" Journal of Physiology," 14, 154, 1893. 



