284 MOVEMENTS OF THE (ESOPHAGUS. [BOOK u. 



also by branches of the fifth, and by the pharyngeal branches 

 of the superior laryngeal division of the vagus. 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 facial, to the muscles of the fauces and 

 pharynx: their exact paths being as yet not fully known, and 

 probably varying in different animals. The laryngeal muscles are 

 governed by the laryngeal branches of the vagus. 



The centre of the reflex act lies in the medulla oblongata. 

 Deglutition can be excited, by tickling the fauces, in an animal 

 rendered unconscious by removal of the brain, provided the 

 medulla be left. If the medulla be destroyed, deglutition is 

 impossible. The centre for deglutition lies higher up than that 

 of respiration, so that the former act is frequently impaired or 

 rendered impossible while the latter remains untouched. It is 

 probable that, as is the case in so many other reflex acts, the 

 whole movement can be called forth by stimuli affecting the 

 centre directly, and not acting on the usual afferent nerves. 



Movements of the (Esophagus. As we have already said, in 

 certain cases at all events, the food is carried down from the 

 pharynx to the stomach in a comparatively slow manner, by the 

 action of the muscular coat of the oesophagus itself. Contractions of 

 the circular fibres occur in succession from above downwards, driving 

 the food before them, very much as a fluid may be driven along a 

 tube by squeezing it. The movement is probably assisted by 

 a similarly progressive contraction of the longitudinal muscular 

 coat ; but the exact manner in which this acts is uncertain. Such 

 a progressive movement, of which we have already spoken on 

 p. 101, and which is much more pronounced in the small intestine 

 than in other parts of the alimentary canal, is spoken of as "peristaltic 

 action." These peristaltic movements of the oesophagus may, like 

 those of the intestine, be seen after removal of the organ from the 

 body ; and indeed may continue to appear upon stimulation, for an 

 unusual length of time. Nevertheless, in the intact body, the 

 movements of the oesophagus seem to be much more closely 

 dependent on the central nervous system than do those of the 

 intestines ; the contractions are not, as in the latter case, trans- 

 mitted from section to section of the tube, but afferent impulses 

 started in the pharynx and passing to the medulla oblongata, give 

 rise to reflex efferent impulses which descend along nervous tracts 

 to successive portions of the organ. If the oesophagus be cut 

 across some way down, or if a portion of the middle region be 

 excised, stimulation of the pharynx will produce a peristaltic 

 contraction, which travelling downwards will not stop at the 

 section but will be continued on into the lower disconnected 

 portion by means of the central nervous system. And it is stated 

 that ordinary peristaltic contractions of the lower part of the 



