In repeated dissections, both upon the hu man subject and the dog, I have found, in tracing the branches of this nerve to their ulti mate distribution upon the pharynx and fauces, that those branches of the glosso-pharyogeal which do not anastomose with the pharyngeal branch of the par vagum are principally distri buted upon the mucous membrane, and that comparatively a small number of these fila ments seem to terminate in the muscular fibre. The uncombined twigs of the pharyngeal branches of the par vagum are, on the other hand, distributed entirely to the muscular fibre. In a dissection of this kind care must be taken to select those twigs only which proceed to their distribution without exchanging filaments with any other nerve. It can be made more favourably in the dog than in the human spe cies. The glosso-pharyngeus is still distri buted upon the tongue in birds, in the frog, and certain of the amphibia, while this organ receives no branch from the fifth pair, and from this circumstance it has been considered the nervus gustatorius of these animals. In fishes there is a branch of the par vagum called glosso-pharyngeal, which escapes from the base of the cranium by a separate opening, and is distributed upon the gills, and also upon the tongue as far as the skin of the mouth.
Physiology.—It is only to the labours of anatomists and physiologists within the last few years that we are to look for any thing like accurate data in enabling us to judge of the functions of this nerve. Its deep situa tion, its proximity to important parts, and the consequent difficulty of exposing it in the living animal, have until very lately deterred physio logists from making it an object of experimental investigation. Some have supposed that it supplies the nervous filaments upon which the sense of taste at the root of the tongue de pends, while the third branch of the fifth pair furnishes those of the anterior part of this organ. Mr. Mayo* states that " when this nerve is pinched in an ass recently killed, a distinct convulsive action ensues, apparently including and limited to the stylo-pliaryngeus muscle and upper part of the pharynx." Ile concluded from this that the glosso-pharyngeal is in part, probably, a nerve of voluntary mo tion; and from its distribution upon the sur face at the root of the tongue, that it is also partly a nerve of common sensation. Sir C. Bell believes that this is the respiratory nerve of the tongue and pharynx, associating the movements of those organs with the muscles of respiration in speech and in deglutition. And we find it stated by Mr. Shaw t that its power of combining the movements of the tongue and pharynx in deglutition " has been shown by several experiments, the results of which were very curious, and corroborative of the views deduced from comparative anatomy." Panizza$ has undertaken an experimental in vestigation into the functions of the nerve, and obtained very unexpected results.
From these we are led to believe that when this nerve is pricked in a living animal, this is attended by no indications of suffering and no convulsive movements ; that section of both nerves is followed by loss of taste, while the tactile sensibility of the tongue and the mus cular movements of deglutition and mastication remain unimpaired ; that section of the fifth pair is on the contrary followed by loss of common sensation' without any apparent effect upon the taste. From these and other experi ments upon the nerves supplying the tongue, lie concludes that the glosso-pharyngeal is the nerve upon which the sense of taste depends, and is therefore the true gustatory nerve. Dr. M. Hall and the late Mr. Broughton§ had, from experiments performed previous to the publication of those of Panizza, arrived at the conclusion that this nerve is not a nerve of com mon sensation. These gentlemen likewise reported at the meeting of the British As.. sociation for 1836 an experiment, the results of which were in exact accordance with those obtained by Panizza upon this nerve, but no details of these experiments have yet been pub fished. Mr. Mayo* has stated several objec tions to these conclusions of Panizza. Ile rests his grounds of dissent principally upon the fact that the distribution of this nerve is con lined to the posterior part of the tongue; while the sense of taste, he maintains, is also present in the anterior part of that organ, and consequently it cannot, in that part at least, depend upon the glosso-pharyngeal. The persistence of the sense of taste after section of the fifth pair may, Mr. Mayo supposes, depend upon the palatine twigs of the second branch of the fifth pair distri buted upon the palate and isthmus of the fauces.
Mr. Mayo attempted to decide the matter by experiment, but he did not carry this suffi ciently far to obtain any satisfactory results. Dr. Alcockf has also lately examined into the functions of this nerve experimentally, and has arrived at conclusions at direct variance with those of Panizza; for according to Dr. Alcock, when this nerve is exposed and irritated in the living animal, it excites pain and spasmodic contractions of the pharynx and muscles of the throat. When divided on both sides, the ani mal's taste, " to say the least of it, did not ap pear to be much affected." Ile believes that the sense of taste enjoys " two media of percep tion, and that these are the glosso-pharyngeal nerve and the lingual and palatine branches of the fifth." He also states that the muscular movements of deglutition are very much im paired after section of the nerve on both sides. He concludes, then, that the glosso-pharyngeal are sentient nerves, and also influence muscular motion. He, however, is doubtful in what manner these muscular movements are excited by irritation of this nerve, for though " dis posed to regard the result in question as the effect of a sentient impression excited through the nerve, and referred to the interior of the pharynx," from the fact that this movement ex tends to muscles not supplied by this nerve, and forms an associated movement, he admits " that the circumstance may be as well ex plained by an exalted degree of muscular excitement, or by a higher one than that ne cessary to produce the simple starting." I'ro fessor 14liiller believes that an examination of the position of the ganglion jugulare will de cide that the glosso-pharyngeal is a mixed nerve, and he maintains that the distribution of this nerve, partly for sensation (mucous mem brane of the root of tongue), partly for the movements of muscles (stylo-pharyngeus and pharynx), exactly resembles that of the two roots of the nerves trigeminus. Unable amidst these discordant statements to come to any sa tisfactory conclusions upon the proper func tions of this nerve, I entered into a lengthened experimental and anatomical investigation for this purpose. The experiments were twenty seven in number, and were performed upon as many different dogs. Seventeen of these were uixm the living animal, with the view of as certaining if this nerve were to be considered both a nerve of sensation and motion, and what are the effects of its section upon the associated movements of deglutition, and on the sense of taste. The other ten were performed on ani mals immediately after they had been deprived of sensation, for the purpose of satisfying my self to what extent it was to be considered a motor nerve. The most remarkable effect wit nessed in these experiments was an extensive convulsive movement of the muscles of the throat and lower part of the face on irritating this nerve in the living animal, provided the irritation was applied to the trunk of the nerve before it had given off its pharyngeal branches, or to one of these pharyngeal branches sepa rately. These movements were equally well marked upon pinching the cranial end of the cut nerve after it bad been divided at its exit from the foramen lacerum, as when the trunk of the nerve and all its branches were entire. In some of these experiments we observed a remarkable difference between the effects of irri tating this nerve before and after it had given off its pharyngeal branches, which is valuable on this account, that it may explain the discrepan cies between the results obtained by Dr. Al. Ilall, and the late Mr. Broughton on the one hand, and Dr. Alcock on the other. For though 1 do not mean to affirm that pinch ing the lingual portion of the nerve is never followed by indications of suffering, (for from the irregularity in the origin of the pharyngeal twigs, and the difficulty of judging at the bottom of a deep wound in the living animal at what particular part these are all given off, it is generally impossible to decide where the lingual portion may be said to begin,) yet I have no hesitation in saying that if in several of these experiments we had operated only on that portion of the nerve which first presented itself, and not proceeded to dissect it hack wards towards its place of exit from the cra nium, we should have gone away with the impression that the irritation of this nerve was followed by no convulsive movements, and little if any indications of suftering.