From a review of all the experiments which I have performed upon the glosso-pharyngeal nerves, I am inclined to draw the following conclusions:— I. That this is a nerve of common sensation, as indicated by the unequivocal expression of pain by the animal, when the nerve is pricked, pinched, or cut.
2. That mechanical or chemical irritation of this nerve before it has given off its pha ryngeal branches, or of any of these branches individually, is followed by extensive muscular movements of the throat and lower part of the face.
3. That the muscular movements thus ex cited depend, not upon any influence extending downwards along the branches of the nerve to the muscles moved, but upon a reflex action transmitted through the central organs of the nervous system.
4. That these pharyngeal branches of the glosso-pharyngeal nerve possess endowments connected with the peculiar sensations of the mucous membrane upon which they are distri buted, though we cannot pretend to say posi tively in what these consist.
5. That this cannot be the sole nerve upon which all these sensations depend, since the perfect division of the trunk of the nerve on both sides does not interfere with the perfect performance of the function of deglutition.
6. That mechanical or chemical irritation of the nerve, immediately after the animal has been killed, is not followed by any muscular movements when sufficient care is taken to in sulate it from the pharyngeal branch of the par vagum. And we here observe an important difference between the movements excited by irritation of the glosso-pharyngeal and those of a motor nerve, for while the movements pro duced by the irritation of the glosso-pharyngeal are arrested as soon as the functions of the central organs of the nervous system have ceased, those from irritation of a motor nerve such as the pharyngeal branch of the par vagum, continue for some time after this, and when all connexion between it and the medulla oblongata has been cut off by the section of the nerve.
7. That the sense of taste is sufficiently acute, after perfect section of the nerve on both sides, to enable the animal readily to recog nize bitter substances.
8. That it probably may participate with other nerves in the performance of the function of taste, but it certainly is not the special nerve of that sense.
The sense of thirst which is referred to the fauces and pharynx does not appear to de pend entirely upon the presence of this nerve. the animals in which it was divided lapped water of their own accord. I observed one of those in which the nerves were found satisfac torily divided, rise, though feeble, walk up to a dish containing water, lap some of it, and return again to the straw upon which he was previously lying.
In all experiments upon the glosso-pharyn geal nerve in the dog, too great care cannot be taken to avoid the pharyngeal branch of the par vagum, which is sometimes situated in im mediate contact with it, at other times one or two lines below it, and is frequently united to it by a considerable communicating branch, so that it may readily be mistaken for a large pha ryngeal branch of the glosso-pharyngeal. this precaution is the more necessary, as I am con fident that these two nerves differ from each other in function, and this must consequently seriously affect the results. I attribute the dif ficulty of deglutition after section of this nerve in the living animal, and the muscular move ments on irritating it in the animal recently killed, observed by two of the preceding ex perimenters, to a want of sufficient precaution in separating these nerves from each other. These results were only observed by me when the pharyngeal branch of the par vagum was im plicated in the experiment.
With regard to the argument in favour of the motal properties of this nerve, drawn by from its anatomy, it appears to me that this analogical mode of investigation, valuable though it is, must be permitted to yield to the more positive observations obtained from expe riment. And though it may be granted that the apparent limitation of the ganglion jugu lare to the posterior filaments of this nerve causes it here to resemble closely the double roots of the spinal nerves, yet we must be wary in drawing analogies between the glosso pharyngeal and spinal nerves, since we have another ganglion situated immediately below this, viz. the ganglion petrosum, which involves the whole of the nerve, and to this assuredly we have no analogical structure in the spinal nerves. No doubt Midler supposes that this inferior ganglion differs from those placed upon the posterior roots of the spinal nerves, and that rt. belongs to the sympathetic system. But as nothing like conclusive proof is advanced in support of this opinion, we may in the mean time reasonably suspend our belief as to the probable influence which this lower ganglion may exert upon the functions of the nerve.
Of course the fact that some of the filaments of the glosso-pharyngeal terminate in the mus cular fibre, is no proof that these filaments are motal, for the muscular bundles have their sen sitive as well as their motal filaments.
(John Reid.)