482 DEGLUTITION. [BOOK n. 



oesophagus, being forced into the stomach by the sequent peristaltic 

 contraction of the oesophagus. 



It will be seen, from what has been said, that deglutition, 

 though a continuous act, may be regarded as divided into three 

 stages. The first stage is the thrusting of the food through the 

 isthmus faucium; this may be either of long or short duration. 

 The second stage is the passage through the upper part of the 

 pharynx. Here the food traverses a region common both to the 

 food and to respiration, and in consequence the movement is as 

 rapid as possible. The third stage is the descent through the grasp 

 of the constrictors. Here the food has passed the respiratory orifice, 

 and in consequence its passage again becomes comparatively slow, 

 except in case of fluids and small morsels, when, as we have seen, 

 it may continue to be rapid. The passage along the oesophagus 

 may perhaps be regarded as constituting a fourth stage ; but it 

 will be more convenient to consider the cesophageal movements by 

 themselves. 



The first stage in this complicated process is undoubtedly a 

 voluntary act. The raising of the soft palate and the approxi- 

 mation of the posterior pillars may also be, at times, voluntary, 

 since they have been seen, in a case where the pharynx was laid 

 bare by an operation, to take place before the food had touched 

 these parts; but the movement may take place without any 

 exercise of the will and in the absence of consciousness. Indeed 

 the second stage taken as a whole, though some of the earlier 

 component movements are, as it were, on the borderland between 

 the voluntary and involuntary kingdoms, must be regarded as a 

 reflex act. The third and last stage, whatever be the exact form 

 which it takes, is undoubtedly reflex ; the will has no power what- 

 ever over it, and can neither originate, stop, nor modify it. 



Deglutition in fact as a whole is a reflex act ; it cannot take 

 place unless some stimulus be applied to the mucous membrane of 

 the fauces. When we voluntarily bring about swallowing move- 

 ments with the mouth empty, we supply the necessary stimulus 

 by forcing with the tongue a small quantity of saliva into the 

 fauces, or by touching the fauces with the tongue itself. 



In the reflex act of deglutition, caused in the ordinary way by 

 the food coming in contact with the fauces, the afferent impulses 

 originated in the fauces are carried up to the nervous centre by 

 the glosso-pharyngeal nerve, by branches of the fifth, and by the 

 pharyngeal branches of the superior laryngeal division of the 

 vagus. The latter seem of special importance, since the act of 

 swallowing, quite apart from the presence of food in the mouth, 

 may be brought out by centripetal stimulation of the superior 

 laryngeal nerve. The efferent impulses descend the hypoglossal 

 to the muscles of the tongue, and pass down the glosso-pharyngeal, 

 the vagus through the pharyngeal plexus, the fifth, and the spinal 

 accessory, to the muscles of the fauces and pharynx : their exact 



