226 DIGESTIVE SYSTEM. 



elliptic sphincter, in an oblique line from front to back and 

 from top to bottom. (Fig. OB.) The anterior and posterior 

 extremities of this elliptic sphincter being nearly fixed, its 

 orifice can only be obliterated by reducing it to an antero- 

 posterior slit. By means of this movement the two sides of 

 the velum of the palate resemble two curtains drawn to- 

 gether, the pharyngeal muscles, which are concave when in 

 the state of repose, having their curve reduced to a straight 

 line ; and representing in this state of contraction the string 

 of the bow which they represented when in the state of 

 repose (Fig. 63 ; B, 2) ; an opening still remains, however, 

 more or less wide, but this is obliterated by the contractions 

 of the middle and inferior sphincters of the pharynx. The 

 uvula, finally, is intended to close any crack which may still 

 remain open, but it is not indispensable (Fig. 63, B, 3, I). 

 By means of these movements, some idea of which was 

 formed by Albinus and Sandifort, though they have been 

 most clearly demonstrated by Gerdy and. Dzondi, the occlu- 

 sion of the isthmus of the fauces is made even hermetical. 

 Indeed, if the nostrils be stopped up during deglutition, we 

 find that hearing is slightly obstructed. This is because, 

 during the succession of peristaltic movements of the 

 pharynx, its upper part is inclined ; and, as the pharyngeal 

 sphincter still remains shut, rarefaction of the air in the 

 nasal chambers ensues. 1 But as, during deglutition, the base 

 of the velum of the palate is stretched out and fixed by the 

 contraction of its superior muscles, and thus opens the Eus- 

 tachian tube, it follows that the rarefaction of the air of the 

 nasal chambers is communicated to the tympanic drum, 

 and kept up until a fresh movement of deglutition places 

 this drum in communication with the freely opened nasal 



1 This fact of the rarefaction of the air suggested to Maissiat 

 (1838) a singular theory of deglutition, which has been refuted by 

 the explanation given here. Maissiat maintained that when deglu- 

 tition takes place a vacuum is formed in the cavity of the pharynx 

 by means of its rising and subsequent enlargement: the, food is 

 precipitated into this cavity by the pressure of the atmosphere, 

 forming what Maissiat calls the involuntary jerk (saccade) of deglu- 

 tition. 



This phenomenon does occur; but, in the first place, it is not in 

 the pharynx, properly so called, but in the naso-pharyngeal cavity; 

 and, in the second, the formation of this vacuum does not correspond 

 with the rising of the pharynx, but with its descent; not at the be- 

 ginning, but at the end, of deglutition. 



