MOVEMENTS OF THE ALIMENTARY CANAL. 635 



corresponding to the three anatomical regions mouth, pharynx, 

 and esophagus 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 palatoglossi 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 ele- 

 vation of the tongue against the soft palate from the tip toward 

 the base. This portion of the movement may be regarded as vol- 

 untary, 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 comprises 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 older 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 esopha- 

 gus. Kronecker and Meltzer,* however, have shown that the con- 

 traction of the mylohyoid muscle in the floor of the mouth is the 

 most important factor in this act of shooting the food suddenly 

 through the pharynx into the esophagus. The contraction of this 

 muscle marks the beginning of the purely involuntary part of the 

 act of swallowing. The bolus of food lies upon the dorsum of the 

 tongue and by the pressure of the front of the tongue against the 

 hard palate it is shut off from the front part of the mouth cavity. 

 When the mylohyoids contract sharply the bolus is put under pres- 

 sure and is shot into and through the pharynx. This effect is aided 

 by the contraction of the hyoglossi muscles, which by moving the 

 tongue backward and downward tend to increase the pressure put 

 upon the food. Simultaneously, 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 



* Kronecker and Meltzer, " Archiv f . Physiologic, " 1883, suppl. volume, 

 p. 328; also ''Journal of Experimental Medicine," 2, 453, 1897. For later 

 \rork, consult Cannon and Moser, "American Journal of Physiology," 1, 

 435, 1898; Schreiber, "Archiv f. exper. Pathol. u. Pharmakologie, " 46, 

 414, 1901; and Eykman, "Archiv f. die gesammte Physiologic," 99, 513, 

 1903. 



