164 



PHYSIOLOGY 



CHAP. 



surface of the root of the tongue, which in the state of rest is 

 turned backwards, retracts, and carries the epiglottis with it, so 

 that the glottis closes mechanically. At the same time, the palate 

 is raised and stretched, not passively, but by the contraction of 

 the elevator and tensor muscles of the palate, so as to occlude and 

 separate the nasal from the pharyngo-buccal cavity, with the 

 assistance of the palato-pharyngeal and the superior constrictor 

 muscles of the pharynx, which contract and bring forward the 



FIG. 55. Diagram showing position of soft palate, tongue, glottis, pharynx, etc. A, at rest ; 

 B, during deglutition. (Zaufal.) t, Salpingo-pharyngeal fold ; I, fold of levator palati ; 

 c, musculo-superior constrictor ; a, azygos uvulae which completes the closure of the nasal 

 cavity. 



pharyngeal walls forming Passavant's swelling, as shown in Fig. 

 55. This, according to Kronecker, comprises the fundamental 

 mechanism of deglutition : the rest, as minutely described by 

 certain authors, is accessory, and serves principally to prevent the 

 food or drink from taking the wrong path to the glottis or nasal 

 fossae, and to clear the canal of the food residues, or to drive the 

 bolus (when it is blocked at the lower end of the oesophagus) into 

 the stomach, by overcoming the resistance of the cardia. 



Another important fact discovered by Kronecker and Meltzer 

 is that every active movement of swallowing carried out in the 

 primary segment of the alimentary canal, particularly from the 

 contraction of the mylohyoid or hypoglossal muscles, produces an 

 inhibition of the movements of the deeper segments. When, on 



