SEVENTH PAIR OF NERVES. 



553 



the eye is still more important. There is 

 complete inability to close the eyelids of the 

 affected side. This permanently open state 

 is due to the action of the levator palpebrae, 

 unopposed by the paralysed orbicularis pal- 

 pebrarum ; and the eye itself, no longer pre- 

 served from the contact of foreign bodies, or 

 swept over by the conjunctiva which lines the 

 eyelids, is often irritated into inflammation. 

 The hazy vision which accompanies this con- 

 dition is partly attributable to this cause ; 

 but more frequently depends on the im- 

 perfect removal of the lachrymal secretion, 

 which becomes irregularly diffused in a more 

 or less solid or dried state over the globe. 

 The general relaxation of the orbicularis 

 perhaps aids this, and it has also the effect of 

 altering the position of the puncta lachrymalia, 

 and thus preventing the natural exit of the 

 secretion, which is sometimes poured down 

 the face. But these effects are on the whole 

 rarely so complete as is above stated ; the 

 aperture between the eyelids is usually small, 

 and movements of the globe of the eye are to 

 some extent substituted for those of the lids ; 

 so that the general results offer the most 

 marked contrast to the rapid disorganization 

 which follows the section of the fifth nerve 

 which forms the sensitive supply of these 

 parts. 



Besides the influence of the facial nerve 

 on mastication, as shown by the result of its 

 paralysis or artificial division ; the sense of 

 taste appears to be considerably impaired on 

 the corresponding side. This fact has been 

 well illustrated by M. Claude Bernard *, who 

 has collected nine or ten cases of this kind. 

 The manner in which the sense is affected 

 seems to vary. Thus, he describes it as an 

 impairment, in which the most sapid sub- 

 stances failed to excite their ordinary im- 

 pressions, and are only perceived after a 

 considerable interval of time. Professor 

 Koux has left a recital of his sensations 

 during a rheumatic facial hemiplegia ; and in 

 his description, which Longet quotes -]-, he 

 mentions that everything on the affected side 

 tasted strongly metallic; whence it would 

 appear that this diminution of taste is some- 

 times substituted by a perversion or deprava- 

 tion of the function. 



And M. Bernard has conclusively shown 

 that the chorda tympani is the immediate in- 

 strument of the change. He has adduced 

 instances of paralysis from experiments, in 

 which the facial nerve being divided above 

 the point where this nerve diverges, the taste 

 was constantly impaired ; while in the facial 

 paralysis due to disease of the nerve below 

 its origin, the sense was unaffected. 



In connexion with these facts may be 

 mentioned the motor function of the chorda 

 tympani. It has been previously stated that, 

 among other courses ascribed to this nerve 

 after its union with the gustatory, Guariui 

 has succeeded in tracing its filaments to the 



* Archives Generales de la Medicine, 1843, 1844. 

 t Op. cit. torn. ii. p. 465. 



lingualis muscle. But in addition to this, 

 he has adduced experimental evidence of a 

 much more conclusive character. He found 

 that galvanising the fifth, ninth, and facial 

 nerves affected the muscles of the tongue in a 

 very different manner. When the sensitive 

 nerve was stimulated, the tongue remained 

 without movement ; but in the case of the 

 ninth and facial, an upward and downward 

 movement was perceptible. When the hypo- 

 glossal was galvanised, a backward and for- 

 ward motion was added to this common 

 movement; while on stimulating the facial 

 nerve, the middle tract of the tongue, which 

 had remained tranquil in the previous experi- 

 ments, was agitated in a vermiform manner. 

 This latter movement was instantly anni- 

 hilated by section of the chorda tympani. 

 The region which it occupied was that of the 

 lingualis muscle, and to it he traced some 

 branches of the nerve : while the upward and 

 downward movement belonged to the stylo- 

 glossus. The cause of the affection of the taste 

 is very imperfectly understood ; since, in the 

 case of the tongue, it seems difficult to con- 

 nect such an impairment of the special sense 

 with any mere loss of motion. Bernard has, 

 however, offered such an explanation ; in 

 which, as a preliminary, he supposes a vermi- 

 form movement like that observed to be ne- 

 cessary to taste, and that it acts by increasing 

 the contact of the papillae of the tongue with 

 the sapid particles. And although this is 

 sufficiently unlikely, yet it is advisable to 

 recollect that, unless guided by experience, 

 we might have asserted the same improba- 

 bility in the instance of smell ; while this 

 sense has been seen to experience an equal 

 impairment, and in a method very similar to 

 this which Bernard has supposed : viz. by a 

 diminution of effective contact between the 

 object of the special sense and the distribution 

 of its nerve, which contact is itself in part the 

 result of the contractions of certain muscles, 

 supplied by branches of the facial. 



The mixed nature of the chorda tympani, 

 as laid down by Morganti, may perhaps ex- 

 plain these effects in a different manner; by 

 suggesting that the paralysis of this nerve 

 involves the loss of some of the sentient as 

 well as motor filaments distributed to the 

 tongue. And the varieties in the nature of 

 the affection which were indicated above, per- 

 haps render this explanation a more probable 

 one. 



A connection has also been traced between 

 the paralysis of the portio dura and an ab- 

 normal state of the soft palate: the curtain 

 of the palate itself being somewhat relaxed, 

 while the uvula is drawn towards the unaf- 

 fected side. In a great number of facial 

 palsies, however, this deviation is absent. 

 But although materials on this point are yet 

 somewhat few, it may be safely stated that 

 its presence or absence varies according 

 to the seat of the disease causing the para- 

 lysis : if above the geniculate ganglion, the 

 deviation appears pretty constantly present ; 

 if below, it is absent. The light which ex- 



