DEGLUTITION. 227 



chambers. This shows how complete is the obliteration 

 of the isthmus of the fauces ; and it may also be shown by 

 means of a tube communicating at one end with the nasal 

 chambers (the nostrils being closely pressed against the 

 tube), while the other end is immersed in water (experiment 

 by Maissiat) : at each movement of deglutition the water 

 rises in the tube, on account of the rarefaction of the air of 

 the nasal chambers (by the descent of the constricted isthmus 

 of the fauces) ; this rarefaction is communicated to the air 

 in the tube, as it is to that in the hollow of the tympanum. 



The isthmus of the fauces thus undergoes a triple change 

 during deglutition : it closes by the contraction of its con- 

 strictors ; it rises slightly as deglutition begins; and descends 

 slightly as this is finished. This rising and falling is produced 

 by the simultaneous movement of the pharynx. The descent 

 explains the vacuum produced in the closed nasal chambers: 

 the ascent shows us why a probe introduced horizontally 

 into the nasal chambers, as far back as possible, will be 

 slightly pushed forward as each movement of deglutition 

 begins (experiment by Debrou) ; this led Bichat to believe 

 that there was some disarrangement at the top of the velum 

 of the palate, and others that the velum is simply raised ; but 

 we have seen that not only the velum, but the whole isthmus 

 of the fauces when constricted, rises and sinks again imme- 

 diately. 



The occlusion of the antero-inferior orifice of communica- 

 tion, or orifice of the larynx, is effected by means of the 

 epiglottis, which, when free, leaves the respiratory orifice 

 uncovered, but, as it is formed of elastic tissue, bends under 

 the weight of the food as it passes. The epiglottis is not, 

 however, indispensable to this obliteration. As the pharynx 

 rises, the larynx, sharing the movement, strikes against the 

 base of the tongue (which is there protuberant), and this 

 mechanism is sufficient to protect the respiratory orifice, or 

 at least to secure the retroversion of the epiglottis over it. 

 The small cartilages placed above the arytenoid cartilages 

 join with the epiglottis in effecting the occlusion of the 

 opening of the larynx. 



The absence of the epiglottis is scarcely any hinderance to 

 the deglutition of solids : the movements of the whole larynx 

 under the cushion, at the base of the tongue, suffice to pro- 

 tect the respiratory orifice. The case is not the same, how- 

 ever, with the deglutition of fluids, and this shows us the 

 purpose of the epiglottis. When the deglutition of a mass 



