GUSTATION. 761 



It is now established beyond question that, in cases of facial palsy in which the lesion 

 affects the root so deeply as to involve the chorda tympani, there is loss of taste in the 

 anterior two-thirds of the tongue, tactile sensibility being unaffected; and numerous 

 cases illustrating this fact have been cited by various authors. Aside from cases of 

 paralysis of the facial with impairment of taste, in which the general sensibility of the 

 tongue is intact, numerous instances are on record of affections of the fifth pair, in which 

 the tongue is absolutely insensible to ordinary impressions, the sense of taste being pre- 

 sarved. A number of such cases have been reported, which show conclusively that the 

 fifth pair presides over general sensibility only, and that it is not a gustatory nerve, except 

 by virtue of filaments derived from the chorda^ tympani. 



Passing from the consideration of pathological cases to experiments upon living ani- 

 mals, the results are equally satisfactory. Although it is somewhat difficult to observe 

 impairment of taste in animals, Bernard and others have succeeded in training dogs and 

 cats so as to observe the effects of colocynth and various sapid substances applied to the 

 tongue. In a great number of experiments of this kind, it has been observed that, after 

 section of the chorda tympani or of the facial so as to involve the chorda tympani, the 

 sense of taste is abolished in the anterior two-thirds of the tongue on the side of the sec- 

 tion. However this result may be explained, the fact remains, that section of the nerve 

 in the lower animals is followed by the same results as those observed in pathological 

 observations. In a remarkable case reported by Moos, the introduction of an artificial 

 membrana tympani was followed by loss of taste upon the corresponding side of the 

 tongue, and upon both sides, when a membrane was introduced into each ear. This dis- 

 appeared when the membranes were removed, and the phenomena were referred to 

 pressure upon the chorda tympani. Experimenters are somewhat at variance with 

 regard to the effects observed upon animals, some asserting that the sensations of taste 

 are simply delayed in their manifestation ; but we must remember the difficulty of such 

 observations, and we are to rely mainly upon the unmistakable phenomena noted in 

 cases of affection of the chorda tympani in the human subject. 



It seems tolerably certain, first, that the gustatory filaments of the lingual branch of 

 the fifth are derived exclusively from the chorda tympani ; second, that the chorda tym- 

 pani, viewed as a gustatory nerve, is really a branch of the facial ; third, that many cases 

 of paralysis of the entire large root of the fifth, in the human subject, present loss of 

 general sensibility in the tongue and no alteration of taste ; and fourth, that paralysis ot 

 the facial, behind the origin of the chorda tympani, is attended with loss of taste in the 

 anterior two-thirds of the tongue, without any affection of the general sensibility of this 

 organ. 



As a summary of our knowledge regarding the gustatory properties of the anterior 

 two-thirds of the tongue, certainly in the human subject, it may be stated without 

 reserve, that these properties depend upon the chorda tympani, its gustatory filaments 

 being derived from the facial and taking their course to the tongue with the lingual 

 branch of the inferior maxillary division of the fifth. In addition, the lingual branch of 

 the fifth contains filaments, derived from the large root of this nerve, which endow the 

 mucous membrane with general sensibility. 



Glosso-Pharyngeal Nerve (First Division of the Eighth}. The glosso-pharyngeal is 

 distributed to those portions of the gustatory mucous membrane not supplied by filaments 

 from the chorda tympani. It is undoubtedly a nerve of taste ; and the question of its 

 other functions will be fully considered in connection with its general properties, as well 

 as the differences between this nerve and the chorda tympani. We have mentioned this 

 nerve in another chapter as the first division of the eighth pair according to the classifi- 

 cation of Willis, but we have to treat of its physiological anatomy in this connection, as 

 its most important function is in connection with gustation. 



Physiological Anatomy of the Glosso-Pharyngeal. The apparent origin of the glosso- 

 pharyngeal is from the groove between the lateral tracts of the medulla oblongata and 



