220 DIGESTION. 



usually depress the lower jaw, but which are now acting from this bone as the fixed 

 point. The muscles which produce this movement act chiefly upon the hyoid bone. 

 They are the digastric (particularly the anterior belly), the mylo-hyoid, the genio-hyoid, 

 the stylo-hyoid, and some of the fibres of the genio-glossus. It is probable, also, that the 

 thyro-hyoid acts at this time to draw the larynx toward the hyoid bone. With this ele- 

 vation of the larynx, there is necessarily an elevation of the anterior and inferior portions 

 of the pharynx, which are, as it were, slipped under the alimentary bolus as it is held by 

 the constrictors of the isthmus of the fauces. 



Contraction of the constrictor muscles of the pharynx takes place almost simulta- 

 neously with the movement of elevation ; and the superior constrictor is so situated as to 

 grasp the morsel of food, and with it the soft palate. The muscles, the constrictors act- 

 ing 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 accomplished 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 performed with regularity, no portion of the liquids and solids 

 swallowed ever finds its way into the air-passages. The entrance of foreign substances 

 into the posterior nares is prevented in part by the action of the superior constrictors of 

 the pharynx, which, as we have seen, embrace, during their contraction, not only the ali- 

 mentary 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, and its mechanism has also 

 been observed in the human subject, by Bidder and Kobelt. In one case that of a young 

 man who had lost the superior maxillary bone, as well as the zygoma the soft palate 

 could be observed from its superior surface ; and, at each movement of deglutition, the 

 palate, which is naturally inclined downward, became more horizontal, and the posterior 

 wall of the pharynx came forward to meet it. The same movement of the pharynx was 

 observed by Kobelt in the case of a soldier who received a severe sabre-cut in the neck. 



While the food is passing through the pharynx, the palato-pharyngeal muscles, which 

 form the posterior pillars of the soft palate, are in a state of contraction by which the 

 edges of the pillars are nearly approximated, forming, with the uvula between them, 

 almost a complete diaphragm between the postero-superior and the antero-inferior parts 

 of the pharynx. This, with the application of the posterior wall of the pharynx to the 

 superior face of the soft palate, completes the protection of the posterior openings of 

 the nasal fossae. The fact that the posterior pillars are thus contracted and approximated 

 during deglutition may be easily verified by simply watching these parts with a mirror 

 during an effort at swallowing. In a case, observed by Berard, it was shown that the 

 muscular action of the soft palate was absolutely necessary to the protection of the nares, 

 particularly in swallowing liquids. In this instance, a young lady was affected with 

 complete paralysis of the velum, which allowed liquids to return so freely by the nose in 

 swallowing that she was obliged to retire from observation whenever she drank. 



Protection of the Opening of the Larynx, and Uses of the Epiglottis in Deglutition. 

 The entrance of the smallest quantity of solid or liquid foreign matter into the larynx 

 produces violent and distressing cough. This accident is of not infrequent occurrence, 

 especially when an act of inspiration is inadvertently performed while solids or liquids 

 are in the pharynx. During inspiration, the glottis is opened, and at that time only can 

 a substance of any considerable size find its way into the respiratory passages. Respira- 

 tion is interrupted, however, during each and every act of deglutition ; and there can, 



