NERVOUS MECHANISM OF DEGLUTITION. 121 



The afferent impulses which excite the nerve centres in the 

 medulla, and give rise to reflex acts which cause the swallowing 

 movements, pass from the mucoas membrane of the fauces along 

 (1) the descending palatine branches of the spheno-palatine gan- 

 glion and the second division of the trigeminus, also along (2) the 

 pharyngeal branches of the superior laryngeal branch of the 

 vagus to the medulla, where the coordination of the pharyngeal 

 spasm and ossophageal peristalsis is accomplished. Thence the 

 efferent impulses pass along (1) the hypoglossal to the hyoid and 

 glossal muscles, (2) the glosso-pharyngeal and vagus to the 

 pharyngeal plexus to supply the constrictors, and (3) along the 

 facial and fifth to supply the fauces and palate, as indicated by 

 their anatomical distribution. 



The act of deglutition can be readily excited in an animal 

 which is deprived of all the nerve centres down to the medulla 

 oblongata, and may also be seen in those human monstrosities 

 (anencephalous foetus) which are born without the upper part of 

 the brain being developed, but can both suck and swallow. 



The movements of the oesophagus are reflections from the cen- 

 tral nervous system (medulla), both sets of impulses (possibly the 

 afferent and certainly the efferent) passing along the branches of 

 the vagus. 



It would appear that the normal peristaltic movements of the 

 oesophagus are always initiated by a pharyngeal spasm, and that 

 they form an inseparable sequel to it. Thus the wave of con- 

 traction passes along the entire length of the oesophagus, even 

 when the bolus is stopped mechanically, and on the other hand a 

 body introduced into the oesophagus without passing through the 

 pharynx excites no peristaltic wave, and remains motionless. 



But it has been observed, in apparent contradiction to the fore- 

 going statement, that the oesophagus when removed from the 

 body, and, therefore, quite independent of the pharynx and its 

 nervous connections, can be excited to move peristaltically. In 

 this case the medulla or vagus can have no part in bringing 

 about this wave of movement. To explain this discrepancy it 

 may be urged that the local nerve and muscle mechanism in the 

 tissues of the oesophagus are capable by themselves of carrying 

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