MOVEMENTS OE THE ALIMENTARY CANAL, ETC. 373 



of the will. The classical description of the act given by Magendie divides it 

 into three stages, corresponding to the three anatomical regions, the mouth, 

 pharynx and oesophagus, through which the swallowed morsel passes on its 

 way to the stomach. The first stage consists in the passage of the bolus of 

 food through the isthmus of the fauces — that is, the opening lying between the 

 ridges formed by the palato-glossi muscles, the so-called anterior pillars of the 

 fauces. This part of the act is usually ascribed to the movements of the tongue 

 itself. The bolus of food lying upon its upper surface is forced backward by 

 the elevation of the tongue against the soft palate from the tip toward the base. 

 This portion of the movement may be regarded as voluntary, to the extent at 

 least of manipulating the food into its proper position on the dorsum of the 

 tongue, although it is open to doubt whether the entire movement is usually 

 effected by a voluntary act. Under normal conditions the presence of moist 

 food upon the tongue seems essential to the complete execution of the act ; 

 and an attempt to make the movement with very dry material upon the tongue 

 is either not successful or is performed with difficulty. The second act com- 

 prises the passage of the bolus from the isthmus of the fauces to the (esophagus 

 — that is, its transit through the pharynx. The pharynx being a common 

 passage for the air and the food, it is important that this part of the act should 

 be consummated quickly. According to the usual description the motor power 

 driving the bolus downward through the pharynx is derived from the contrac- 

 tion of the pharyngeal muscles, particularly the constrictors, which contract from 

 above downward and drive the food into the oesophagus. Simultaneously, 

 however, a number of other muscles are brought into action, the general effect 

 of which is to shut off the nasal and laryngeal openings and thus prevent the 

 entrance of food into the corresponding cavities. The whole reflex is therefore 

 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 contraction of the 

 muscles of the anterior pillars of the fauces. The opening into the nasd 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 

 (palato-pharyngei muscles) and the elevation of the uvula (azygos uvulae mus- 

 cle). The soft palate, uvula, and posterior pillars thus form a sloping surface 

 shutting oil' the nasal chamber and facilitating the passage of the food backward 

 into the pharynx where the constrictor muscles may act upon it. The respira- 

 tory opening into the larynx is closed by the adduction of the vocal cords (lat- 

 eral crico-arytenoids and constrictors of the glottis) and by the elevation of the 

 entire larynx and a depression, in pari mechanical, of the epiglottis over the 

 larynx (action of the thyro-hyoids, digastrics, genio-hyoids, and mylo-hyoids 

 and the muscles in the aryteno-epiglottidean folds). 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. Ii has been shown, 

 however, that removal of the epiglottis does not prevent normal swallowing, 



