304 



FIFTH PAIR OF NERVES. 



tion : he has made repeated dissections of the 

 distribution of the lesser packet of the nerve 

 both in the horse and in man, and after a care- 

 ful examination, it appears to him that Mayo 

 is essentially right, though the view given by 

 him does not exactly agree with the^arrange- 

 ment of the nerve as found by the author 

 either in the horse or in man. In the former the 

 masseteric branch arises from the lesser packet 

 by two fasciculi, one of which runs round the 

 ganglionic portion of the third division of the 

 nerve, and joins the other and larger fasciculus 

 before it : the facial portion of the buccal 

 nerve appears to the author to be purely gan- 

 glionic, but the root of the nerve in part 

 appears to be derived from the non-ganglionic 

 portion and is not ; and in part may or may 

 not be considered to proceed from it. It is 

 entangled at its origin with fasciculi of that por- 

 tion, more or fewer of the filaments which it 

 derives from the ganglionic packet passing be- 

 tween and even interlacing with fasciculi of the 

 non-ganglionic ; but by a patient proceeding 

 these may be traced to their proper source, and 

 the nerve be extricated from this connexion. It 

 is, however, difficult to accomplish it at times, 

 at others it is sufficiently easy. Again, one or 

 more branches of the non-ganglionic portion 

 accompany the buccal nerve for some distance, 

 connected to it more or less intimately, but 

 apparently not enclosed within the same sheath, 

 though communicating with the nerve by fila- 

 ments from a ganglionic fasciculus and separa- 

 ble without injury to either. These branches, 

 however, separate from the nerve again for dis- 

 tribution before it leaves the zygomatic fossa ; 

 they may be considered, or not, to belong to 

 the nerve, but they do not affect the question 

 with regard to its facial portion ; and the author 

 believes that the arrangement described is not 

 uniform, the branches adverted to not always 

 accompanying the buccal nerve. 



Again, on the one hand it has been already 

 shewn that division of the portio dura on both 

 sides deprives the facial muscles of all inde- 

 pendent* contractile power, whether voluntary 

 or involuntary ; and on the other, Mayo has 

 found that irritation of the buccal nerve does 

 not excite contraction in those muscles : the 

 author has taken occasion several times to 

 repeat the experiment of Mayo upon the latter 

 nerve after it had emerged upon the face, and 

 he has not succeeded in obtaining contraction 

 of the facial muscles thereby, while the strug- 

 gles of the animal, excited by the irritation of 

 the nerve, proved it to be one of exquisite sen- 

 sibility. It appears then to the author impos- 

 sible to admit that the facial muscles either 

 possess two contractile powers dependent on 

 distinct nerves, or that they derive any volun- 

 tary power from the fifth. 



It is extraordinary that Magendie, who was 

 the first to detect the error into which Bell had 

 fallen with regard to the influence of the infra- 

 orbital nerve over the motions of the muscles 



* This expression has been used because the 

 muscles may be still excited to contraction by irri- 

 tation of the portion of the nerve connected with 

 them. 



of the face, and has, according to his own 

 report, divided the portio dura on animals, 

 should, notwithstanding all that has been 

 written upon the subject, have adopted the 

 opinion that the muscles of the face are en- 

 dowed with the two distinct faculties of motion, 

 one of which is derived from the fifth. His view 

 will be found at page 703-4, Anatomic des 

 Systemes Nerveux, &c., and the opinion there 

 expressed is implied in a note at page 191, 

 Journal de Physiologic, t. x. In the former 

 he says, " Now Mr. Charles Bell in England 

 and M. Magendie in France by cutting the 

 facial nerve have paralyzed the respiratory 

 motions of all the side of the face correspond- 

 ing to the nerve cut. But the muscles which 

 receive at once filaments from the facial nerve 

 and from the fifth pair were paralyzed only in 

 their action relative to respiration and to the 

 expression of the physiognomy." 



The influence of the fifth nerve upon the tac- 

 tile sensibility of the parts with which it is con- 

 nected has been discussed : its influence upon 

 their ordinary sensibility also requires notice. 

 From the preceding details it appears esta- 

 blished that it is to the same nerve that this 

 property also of the parts in general is due; 

 but there is reason to believe that the nerve 

 exerts a more extended control over this faculty 

 than was at first supposed. At the commence- 

 ment of the inquiries into the functions of the 

 nerves of the face, the opinion generally held 

 was that the facial nerve portio dura of the 

 seventh pair was devoid of sensibility. Fur- 

 ther observations, however, showed that this 

 conclusion was erroneous, and that the insen- 

 sibility to any injury done to the nerve in 

 question manifested by the subjects of experi- 

 ment, and from which the inference had been 

 drawn, was only apparent, and to be referred 

 to the constitution of the individual animal or 

 of its species. The sensibility of the facial 

 nerve having been established, a question arose, 

 whether that property was independent and 

 proper to it, or whether it was conferred by 

 another ? Those who first observed the sensi- 

 bility of the nerve adopted the former opinion ; 

 but considerations entitled certainly to much 

 weight led Eschricht to suspect that the facial 

 nerve is not endowed with independent sensi- 

 bility, and that the sensibility which is manifested 

 when it is injured is conferred on it by the fifth 

 nerve. In order to determine the question he 

 performed a series of experiments in which he 

 divided the fifth nerve within the cranium upon 

 one side after having opened the cavity and 

 removed so much of the corresponding hemi- 

 sphere of the brain as was necessary for the 

 accomplishment of his purpose : the facial 

 nerve of the same side was then exposed, and 

 its properties tested. The faculties of the 

 animal are so little affected by the removal of 

 the brain, that the result of the experiment 

 seems free from objection, while all influence 

 of the fifth nerve upon the sensibility of the 

 facial or other parts must be destroyed. In his 

 first successful experiment irritation of the 

 facial excited spasms of the lips, and also in- 

 dications of suffering so decided that a doubt 



