DEGLUTITION. 



225 



food passes downwards to its base. As the food reaches the 

 front pillars of the velum of the palate being pushed into 

 the pharynx by the tongue laid against the roof of the mouth 

 it is seized by the pharynx, which rises before it, on account 

 of the contraction of its longitudinal fibres. The circular 

 fibres of this muscular tube immediately contract successively, 

 and drive the food before them into the oesophagus, where it 

 continues its progress by means of a similar peristaltism 

 that is, successive contraction of the circular muscular fibres, 

 driving the food before them, while the contraction of the 

 longitudinal fibres draws towards it those parts of the tube 

 in which it is to become involved. 



While the food crosses the pharynx, the two communica- 

 tions between this tube and the windpipe are obliterated. 



The upper communication (pharynx and nasal chambers) 

 is not obliterated by a movement of the velum of the palate 

 resembling that of a drawbridge, as was for a long time sup- 

 posed (Bichat) ; it takes place by means of the posterior 

 pillars of the velum of the palate. In order to effect this 

 obliteration, the pillars approach each other : while the mus- 

 cular fibres of these pillars (pharyngeal muscles) are directed 



Fig. 63. Diagram, showing the occlusion of the naso-pharyngeal passage, by the 

 action of the muscles of the posterior columns (Staphylo-pharyngeals.)* 



obliquely, downwards and backwards, across the lateral walls 

 of the pharynx, and are again joined together, along a con- 

 siderable part of the posterior median line, so as to form an 



* A, This part is seen in profile. N, Nasal cavity. B, Mouth. L, Tongue. 

 E$ Epiglottis. Y, Uvula. P, P, Course of the staphylo-pharyngeal muscle. 



B, Diagram of the orifice, enclosed by the two staphylo-pharyngeals as by a 

 Bphincter. 1 (P'), In the state of repose. 2 (P"), Semi-occlusion. 3 (P "), 

 Perfect occlusion. /. Uvula. 



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