146 FUNCTIONS OF THE NERVOUS SYSTEM. 



sufficient ; but without either of these we, cannot swallow at will. Nor can 

 we restrain the tendency, when it is thus excited by a stimulus ; every one 

 knows how irresistible it' is, when the fauces are touched in any unusual man- 

 ner ; and it is equally beyond the direct control of the will, in the ordinary 

 process of eating, voluntary as we commonly regard this. The only mode 

 in which the will can influence it, is by regulating the approach of the stimu- 

 lus necessary to excite it ; thus, we voluntarily bring a morsel of food, or a 

 little fluid, into contact with the surface of the fauces, and an act of deglutition 

 is then involuntarily excited ; or we may voluntarily keep all stimulus at a 

 distance, and no effort of the will can then induce the action. Moreover, this 

 action is performed, like that of respiration, when the power of the will is sus- 

 pended, as in profound sleep, or in apoplexy affecting only the brain ; and it 

 does not seem to be at all affected by the entire removal of the brain, in an 

 animal that can sustain the shock of the operation ; being readily excitable, 

 on stimulating the fauces, so long as the nervous structure retains its functions. 

 This has been experimentally proved by Dr. M. Hall; and it harmonizes with 

 the natural experiment sometimes brought under our notice in the case of an 

 anencephalous infant, in which the power of swallowing seems as vigorous as 

 in the perfect one. But, if the nervous circle be destroyed, either by division 

 of the trunks, or by injury of any kind to the portion of the nervous centres 

 connected with them, the action can no longer be performed ; and thus we see 

 that, when the effects of apoplexy are extending themselves from the brain to 

 the spinal cord, whilst the respiration becomes stertorous, the power of Deglu- 

 tition is lost, and then respiration also speedily ceases. 



192. Our knowledge of the nerves specially concerned in this action is 

 principally due to the very careful and well-conducted experiments of Dr. J. 

 Reid.* The distribution of the Glosso-Pharyngeal evidently points it out as 

 in some way connected with it; and Sir C. Bell, misled by imperfect know- 

 ledge of its anatomy, pronounced it to be a muscular nerve, whose function 

 was to excite the combined movements of the tongue and pharynx, which are 

 required in deglutition, and also in some acts of respiration. He was not 

 aware that such a combination of movements may be due as much to the 

 excitor nerve, and its termination in the Spinal Cord, as to the motor, and its 

 particular distribution to muscles. The function of the Glosso-Pharyngeal 

 nerve hasf been for some time one of the qusestiones vexatx of physiology ; 

 and the results obtained by different experimenters are so strangely at variance, 

 as almost to lead to the belief that they have operated on different nerves. In 

 this dilemma, we may advantageously have recourse to anatomical examina- 

 tion of its distribution ; and this, when carefully conducted, discloses the im- 

 portant 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 pro- 

 duces muscular movements. Hence it is not in any great degree an efferent 

 or motor nerve ; and its distribution would lead us to suppose its function to 

 be, the conveyance of impressions from the surface of the fauces to the me- 

 dulla oblonganta. 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 

 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 exciters of reflex movement than those 



* Edinb. Med. and Surg. Journ., vol. xlix. 



