MOVEMENTS OP THE ALIMENTARY CANAL. DEGLUTITION. 403 



portant fact that the nerve scarcely sends any of its branches to the muscles 

 which they enter, these mostly passing through them, to be distributed to the 

 superjacent mucous surface of the tongue and fauces. Further, when the trunk 

 is separated from the nervous centres, irritation produces scarcely any muscular 

 movements. Hence it is not in any great degree an "efferent" or motor nerve; 

 and its distribution would lead us to suppose its chief function to be "afferent;" 

 namely, the conveyance of impressions from the surface of the fauces to the 

 Medulla Oblongata. This inference is fully confirmed by the fact that, so long 

 as its trunk is in connection with the centre, and the other parts are uninjured, 

 pinching, or other severe irritation of the Glosso-pharyngeal, will often excite 

 distinct acts of deglutition. Such irritation, however, may excite only convulsive 

 twitches, instead of the regular movements of swallowing ; and it is evident that 

 here, as elsewhere, the impressions made upon the extremities of the nerves are 

 much more powerful excitors of reflex movement than those made upon the 

 trunk, though the latter are more productive of pain. It was further observed 

 by Dr. Reid, that this effect was produced by pinching the pharyngeal branches 

 only ; no irritation of the lingual division being effectual to the purpose. If, 

 then, the muscles of deglutition be not immediately stimulated to contraction 

 by the Glosso-pharyngeal nerve, it remains to be inquired, by what nerve the 

 motor influence is conveyed to them from the Medulla Oblongata ; and Dr. Reid 

 was equally successful in proving that this function is chiefly performed by the 

 Pharyngeal branches of the Pneumogastric. Anatomical examination of their 

 distribution shows, that they lose themselves in the muscles of the pharynx ; 

 and whilst no decided indications of suffering can be produced by irritating them, 

 evident contractions are occasioned, when the trunk, separated from the brain, 

 is pinched or otherwise stimulated. It appears, however, that neither is the 

 Glosso-pharyngeal the sole excitor nerve, nor are pharyngeal branches of the 

 Pneumogastric the sole motor nerves, concerned in deglutition ; for, after the 

 former has been perfectly divided on each side, the usual movements can still 

 be excited, though with less energy ; and, after the latter have been cut, the 

 animal retains the means of forcing small morsels through the pharynx, by the 

 action of the muscles of the tongue and neck. From a careful examination of 

 the actions of deglutition, and of the influence of various nerves upon them, 

 Dr. Reid drew the following conclusions : The excitor impressions are conveyed 

 to the Medulla Oblongata chiefly through the Glosso-pharyngeal, but also along 

 the branches of the Fifth pair distributed upon the fauces, and probably along 

 the superior Laryngeal branches of the Pneumogastric distributed upon the 

 pharynx. The motor influence passes chiefly along the Pharyngeal branches 

 of the Pneumogastric ; along the branches of the Hypoglossal, distributed to 

 the muscles of the tongue, and to the sterno-hyoid, sterno-thyroid, and thyro- 

 hyoid muscles ; along the motor filaments of the Recurrent laryngeals ; along 

 some of the branches of the Fifth, supplying the elevator muscles of the lower 

 jaw; along the branches of the Facial, ramifying upon the digastric and stylo- 

 hyoid muscles and upon those of the lower part of the face ; and probably along 

 some of the branches of the Cervical plexus, which unite themselves to the 

 Descendens noni. It was further observed by Dr. Reid (Op. cit., pp. 258 260), 

 that the stylo-pharyngeus muscle is usually thrown into contraction, when the 

 roots of the Glosso-pharyngeal nerve are irritated; and this has also been noticed 

 by Mayo, Volkmann, and others ;* so that we are to consider the Glosso-pharyn- 

 geal as a motor nerve, in so far as that muscle is concerned. 



1 It seems not improbable that the discrepant results obtained by different experimenters 

 on this point are partly to be explained by differences in the distribution of the nerves in 

 the several animals operated on. . .' 



