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DEGLUTITION. 229 



of the larynx thus has an important share in the protection 

 of the respiratory organs (Longet) ; it is intended to prevent 

 the entrance of foreign bodies into these organs, an occur- 

 rence which the animal would have no power to prevent, if 

 the opening of the glottis were once passed (see larynx and 

 obtuse sensibility of the trachea). 



A final obstacle to the entrance of these bodies into the 

 trachea is found in the fact that the opening of the glottis 

 closes whenever deglutition takes place; this occlusion is, 

 however, only a precautionary measure ; and it must not be 

 supposed that, in the normal state, the substances which are 

 being swallowed come in contact with the edges of the glot- 

 tis. Magendie, who first discovered this closure of the glottis 

 during deglutition, attached too much importance to it, and 

 was mistaken as to the mechanism by which it is produced, 

 attributing it to the muscles of the larynx, in this special 

 case (arytenoid, aryteno-epiglottidean) innervated by the 

 upper laryngeal nerve. Longet, who understood the subject, 

 has shown both the accessory importance of this occlusion 

 and its mechanism, which consists in the movement of the 

 thyroid cartilage by means of the contraction of the sphincter 

 muscles of the pharynx. The movements of the glottis 

 accompanying deglutition are thus subjected to other muscu- 

 lar agents than those which act upon this same orifice, dur- 

 ing the production of the vocal and respiratory phenomena. 

 (Longet). Finally, Claude Bernard has completed the study 

 of this interesting question, which here we can only sum up 

 rapidly, by showing that the spinal accessory nerve inner- 

 vates the inferior constrictor muscle of the pharynx in 

 order to produce this occlusion of the glottis ; and we can 

 thus add to Longet's conclusion, that the nerves which pre- 

 side over this occlusion of the glottis Curing deglutition are 

 not the same as those which govern its respiratory move- 

 ments ; they are the filaments from the spinal accessory nerve, 

 whose influence here, as in all its other functions, is opposed 

 to that of the pneumogastric nerve (Cl. Bernard). 



A very important part of the physiology of deglutition is 

 the way in which it is directed by the nervous system : de- 

 glutition is one of the most striking examples of reflex influ- 

 ence. We cannot simply swallow, without giving rise to a 

 local excitation, which serves as a point of departure of the 

 reflex action : there must be some substance in the mouth, a 

 small portion of food or of saliva ; and, when we fancy 

 that we are swallowing nothing, the movement is really for 



