554 



SEVENTH PAIR OF NERVES. 



periment affords is somewhat uncertain and 

 conflicting. Mechanical irritation of the root 

 of the facial nerve in various animals has 

 failed to excite contractions of the muscles 

 of the palate, both with Valentin* and Hein.f 

 The stimulus of galvanism has also acted 

 irregularly and variably, being sometimes fol- 

 lowed by contractions, sometimes not. It is, 

 on the whole, difficult to avoid coming to the 

 conclusion that the facial nerve is intimately 

 associated with the movements of the palate 

 by its greater petrosal branch : but the actual 

 transmission of its uninterrupted filaments 

 through the spheno-palatine ganglion is, on 

 anatomical grounds, exceedingly doubtful. 

 And the experiments above mentioned, to- 

 gether with others in which Hein found that 

 its division did not affect pre-existing move- 

 ments from other nervous sources, render the 

 term " motor nerve " clearly an inapplicable 

 name. 



Concerning the influence of the facial 

 nerve on hearing, little is known at present. 

 Longet, in quoting the above case of M. 

 Roux, in which comparatively faint sounds 

 were painfully distinct, has given a very pro- 

 bable and ingenious explanation of the fact, 

 by pointing the derivation of the nerve to the 

 tensor tympani from the otic ganglion, which 

 is itself associated with the geniculate gan- 

 glion and facial nerve. Regarding this muscle 

 as the regulator of the acoustic drum, and 

 the tension of this as the means of moderating 

 excessive stimulus, just as the iris does in 

 the eye, he shows the probability that the 

 paralysis of the tensor in this manner de- 

 prives the ear of an important protection, and 

 increases the loudness of the sound received. 



It has thus been deduced that the facial is 

 chiefly a nerve of motion ; or, in other words, 

 that by its central and peripheral organization 

 it is adapted to determine the contraction of 

 the facial muscles. It has next to be con- 

 sidered whether it is exclusively motor, or 

 whether, on the contrary, it contains a certain 

 proportion of nervous filaments, the office of 

 which is the production of sensations. 



The highly sensitive integument which 

 forms the surface of the face, evidently re- 

 ceives its nervous supply solely from the 

 different divisions of the fifth; and the 

 anatomy of the distribution of these branches 

 is confirmed by comparing the results which 

 are obtained by artificial section of the facial 

 and fifth nerves. In the case of the divided 

 portio dura, it was previously mentioned, that 

 while motion is lost, sensibility is unaffected ; 

 while in the common instance of th^ divided 

 fifth, mobility remains, but the sensibility of 

 this surface completely vanishes, and no ex- 

 pression of pain can be obtained even by 

 cauterising large portions of the integuments. 



The facial is thus excluded from all share 

 in the tactile sensibility of this surface ; yet it 

 by no means follows that the nerve itself is 

 wholly insensible. On the contrary, the ex- 



* Lehrbuch der Physiologie, B. ii. S. 673. 

 f Muller's Archiv. 1844. Heft. 3, 4. 



periments of most physiologists from the time 

 of Bell agree in verifying the fact of its sensi- 

 bility ; as shown by the expressions of pain 

 which are called forth on mechanically irri- 

 tating the nerve in the living animal. Thus, 

 pinching the trunk of the facial, or any of its 

 larger branches, or the act of section itself, 

 have been constantly found to be accompanied 

 by the most unequivocal indications of suffer- 

 ing. 



From the evidence above stated, it is mani- 

 fest that the sensory filaments which we 

 must suppose the trunk of the facial to con- 

 tain, are not distributed to the cutaneous 

 surface of the face. But although the skin is 

 the chief organ of common sensation, it is by 

 no means the only seat of the function : a 

 variable but necessary share is possessed by 

 the whole body, and accomplishes the general 

 purpose of protection, perhaps also confers 

 the muscular sense. Thus, by means of sensa- 

 tion, the injury of any particular part deter- 

 mines the occurrence of pain which is referred 

 to that situation ; and in this manner atten- 

 tion is directed to the seat of injury, and 

 its duration or increase is prevented by a 

 voluntary act. And it is probable that the 

 sensitive branches which accompany the 

 portio dura are of this kind ; branches which, 

 although very different in function, travel 

 with the motor nerve, because they experience 

 a distribution in its immediate neighbourhood. 

 Indeed it is perhaps not unlikely that some of 

 the sensory filaments which are included in 

 the facial may bear a protective relation to 

 this important nerve itself, possibly by a 

 virtual distribution among its fibres : a 

 notion which would thus far approximate to 

 the supposed " nervi nervorum " of the old 

 authors. 



But although the sensibility of the facial 

 nerve is well ascertained, the origin or imme- 

 diate cause of this endowment is still a matter 

 of considerable dispute. The numerous views 

 adopted by different authors offer many 

 slighter modifications, but they are all re- 

 ducible to two chief theories. One of these 

 considers that the facial nerve is insensible at 

 its origin from the brain ; and that whatever 

 amount of sensibility it subsequently exhibits 

 is due to foreign filaments, which come from 

 the acknowledged sensitive nerves of the 

 fifth and pneumogastric ; and which, joining 

 the portio dura in different parts of its course, 

 accompany it beyond these points included in 

 its substance. The other regards the facial 

 nerve as arising by two roots, whereof the 

 larger is motor, the smaller sensitive ; and 

 that the sensibility of the nerve as a whole is 

 the result of its double constitution, and is 

 effected by its own sensory filaments. 



Each of these theories has received the 

 sanction of distinguished anatomists. Thus, 

 amongst many others, the first has obtained the 

 support of Magendie, Cruveilhier, Eschricht, 

 Lund, &c. ; while the latter numbers amongst 

 its advocates, Arnold, Bischoff, Goedechens, 

 Barthold, and, more lately, Morganti. 



The dispute scarcely involves the function 



