404 PHYSIOLOGY CHAP. 



chorda, and not when it involves the trunk of the nerve proximal 

 to the ganglion. 



If the taste fibres for the anterior part of the tongue come 

 neither from the trigeniinal nor the facial, they may be derived 

 indirectly from the glosso-pharyngeal, through Jacobson's nerve, 

 or from the small superficial petrosal which unites the glosso- 

 pharyngeal with the facial. This opinion, which is well estab- 

 lished from the anatomical point of view, was confirmed by Carl 

 (1875) from accurate observations on himself. He noticed that 

 the left anterior part of his tongue was entirely deficient in sensi- 

 bility to taste. He had no affection of the facial or trigeniinal 

 nerves, but from early youth had suffered from left otorrhoea with 

 almost complete destruction of the tympanum. His left chorda 

 tympani seemed to be healthy, since its secretory and sensory 

 fibres reacted immediately to excitation. The loss of taste in the 

 anterior part of the tongue must be due therefore to injury to 

 other branches of the tympanic plexus. He concluded that the 

 taste fibres of this region came from the petrosal ganglion of the 

 glosso-pharyngeal, ran in the tympanic branch (Jacobson's nerve) 

 to the tympanic plexus, and thence by the small superficial petrosal 

 nerve, to the otic ganglion and the lingual nerve ; or partly to the 

 geniculate ganglion, and so by the chorda tympani to the lingual. 



Von Urbantschitsch (1876) took the same view as Carl, on the 

 strength of his clinical observations, and held that taste fibres 

 run through the tympanic plexus, which is connected by Jacob- 

 son's nerve with the glosso-pharyngeal. This theory, while not 

 confirmed directly by experiment, seems the most acceptable. It 

 readily explains the cases of trigeminal paralysis, and those in 

 which the facial is injured by a lesion of the trunk above the 

 geniculate ganglion without noticeable disturbance of the sense of 

 taste. If we accept this conclusion, it confirms Panizza's original 

 statement that the function of taste is served exclusively by the 

 glosso-pharyngeal nerve. 



Another question not yet fully cleared up is whether the fibres 

 of the glosso-pharyngeal subserve only taste, or tactile and pain 

 sensibility also, in the parts which they supply. Panizza held 

 that the intracranial mechanical stimulation of the glosso- 

 pharyngeal produces no sensations of pain, but others, including 

 Longet, deny this. On the other hand, no conclusion in favour 

 of the thesis that the 9th is exclusively a taste nerve can be 

 drawn from the fact that pain sensibility persists in the tongue, 

 fauces, and anterior surface of the epiglottis, after section of the 

 glosso-pharyngeal. Volkmann found that after this operation 

 irritation of the posterior part of the tongue, fauces, and pharynx 

 no longer cause reflex nausea and vomiting; but this might 



O O ' O 



obviously depend on loss of the taste sense in this region rather 

 than on paralysis of tactile or pain sensibility. In fact, after 



