192 DIGESTION. 



powerful of the muscles of the pharynx and the stylo- 

 pharyngeus contract in connection with the superior con- 

 strictors. These muscles, the constrictors acting from the 

 median raphe, assist to elevate the anterior and inferior walls 

 of the pharynx and pass the food rapidly into the upper part 

 of the oesophagus. All these complex movements are accom- 

 plished with great rapidity, and the larynx and pharynx are 

 then immediately returned to their original position. 



Protection of the Posterior Nares during the Second 

 Period of Deglutition. When the act of deglutition is per- 

 formed with regularity, no portion of the liquids and solids 

 swallowed ever find their way into the air-passages. The 

 entrance of foreign substances into the posterior nares is pre- 

 vented in part by the action of the superior constrictors of 

 the pharynx, which, as we have seen, embrace, during their 

 contraction, not only the alimentary mass, but the velum 

 pendulum palati itself ; and in part, also, by contraction of 

 the muscles which form the posterior pillars of the soft 

 palate. 



During the first part of the second period of deglutition, 

 the soft palate is slightly raised, being pressed upward by 

 the morsel of food. This fact has been observed in cases in 

 which the parts have been exposed by surgical operations, 1 and 

 was demonstrated by M. Debrou, who passed a tube along 

 the floor of the nares to the pharynx, and noted a sudden de- 

 pression of the end projecting from the nose with each act 

 of swallowing, as though the soft palate struck suddenly 

 against the other extremity. 2 This mechanism has also 

 been observed in the human subject by Bidder and Kobelt. 

 In this case a young man who had lost the superior maxil- 

 lary bone, as well as the zygoma the soft palate could be 

 observed from its superior surface ; and at each movement of 



1 BEUARD (op. cit., tome ii., p. 25) cites a case of this kind observed by Rid- 

 der. 



tt DEBROU, Theses de VEcole de Medecine de Paris, 1841, No. 266, p. 8. 



