298 FUNCTIONS OF THE NERVOUS SYSTEM. 



ing food within reach of this orifice. In the Sea-Anemone, the Hydra, and 

 other Polypes, for example, we find that aperture surrounded by tentacula; 

 which have an evident tendency to lay hold of anything that touches them, so 

 as to bring it, by their contraction, within reach of the muscles immediately 

 surrounding the aperture. This is just the purpose of the pharyngeal muscles 

 of Man. The lower part of the oesophagus, near its termination in the sto- 

 mach, has the same simple tendency to contraction from above downwards 

 (so as to convey into the stomach anything which is brought within its reach), 

 as have the muscles surrounding the mouth of the Polype; but there is need 

 of some more complex apparatus, for the purpose of laying hold of the food, 

 and of conducting it into its grasp. This is provided for, in the higher animals, 

 in the muscles of that funnel-like entrance to the oesophagus, which is called 

 the Pharynx. The actions of these are most distinctly reflex; and it is inte- 

 resting to remark, that the movements can neither be caused nor controlled by 

 the direct influence of the will. In the case of the movements of respiration, 

 we found sufficient provision made for their constant maintenance; and yet, 

 for secondary purposes, they were placed in a considerable degree under the 

 control of the brain. But here there are no secondary purposes to be an- 

 swered ; the introduction into the stomach of food, brought by the will within 

 reach of the pharyngeal muscles, is the only object contemplated by them; 

 and they are accordingly placed under the sole government of the Spinal Cord. 



383. No attempts, on our own part, will succeed in producing a really 

 voluntary act of Deglutition. In order to excite it, we must supply some 

 stimulus to the fauces. A very small particle of solid matter, or a little fluid 

 (saliva, for instance), or the contact of the back of the tongue itself, will be 

 sufficient ; but without either of these we, cannot stvallow 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 suspended, 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 ex- 

 citable, 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 de- 

 stroyed, either by division of the trunks, or by injury of any kind to the por- 

 tion 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 Deglutition is lost, and then respiration also speedily 

 ceases. 



384. 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 



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



