ACTIONS PRELIMINARY TO DEGLUTITION. 299 



in some way connected with it ; and this, when carefully examined, discloses 

 the important fact, that the nerve scarcely sends any of its branches to the 

 muscles which they enter ; but that these mostly pass 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 

 scarcely ever produces muscular movements. Hence it is not in any great 

 degree an efferent or motor nerve ; and its distribution would lead us to sup- 

 pose its function to be, 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 Medulla Oblongata, 

 and the other parts are uninjured, pinching, or other severe irritation of the 

 Glosso-Pharyngeal, will often excite distinct acts of deglutition. Such irrita- 

 tion, 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 power- 

 ful 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 irrita- 

 tion of the lingual division being effectual to the purpose. 



385. If, then, the muscles of deglutition are 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 Oblon- 

 gata ; and Dr. Reid has been equally successful in proving, that this function 

 is chiefly performed by the pharyngeal branches of the Par Vagum. Ana- 

 tomical 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 the pharyngeal branches of the Par Vagum the sole motor 

 nerves, concerned in deglutition ; for after the former has been perfectly di- 

 vided 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 degluti- 

 tion, and of the influence of various nerves upon them, Dr. Reid draws the 

 following conclusions : The excitor impressions are conveyed to the Me- 

 dulla Oblongata chiefly through the Glosso-Pharyngeal, but also along the 

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

 branches of the Superior Laryngeal distributed upon the pharynx. The 

 motor influence passes chiefly along the pharyngeal branches of the Vagus ; 

 along the branches of the Hypo-glossal, distributed to the muscles of the 

 tongue, and to the. sterno-hyoid, sterno-thyroid, and thyro-hyoid muscles ; 

 along the motor filaments of the Recurrents, ramifying upon the larynx ; 

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

 lower jaw; along the branches of the Portio Dura, ramifying upon the digas- 

 tric and stylo-hyoid muscles, and upon the muscles 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. 



386. When the food has been propelled downwards by the Pharyngeal 

 muscles as far as their action extends, its further progress through the (Eso- 

 phagus is effected by the peristaltic movement of the muscular coat of the 

 tube itself. This movement is not, however, due only to the direct stimulus 

 of the muscular fibre by the pressure of the food, as it seems to be in the 

 lower part of the alimentary canal ; for Dr. J. Reid has found, by repeated 



