FIFTH PAIR OF NERVES. 



303 



division of the fifth are voluntary nerves to the 

 pterygoid, the masseter, the temporal, and 

 buccinator muscles." Here again he has not 

 reached the conclusion, though he has fallen 

 but little short of it, and though, as in the 

 former instance with regard to sensation, he 

 has been the first to announce a restriction of 

 the motor properties of the nerve to particular 

 branches. The opinion expressed by Bell, in 

 June 1823, has been already quoted, and 

 from it we are bound to admit, that then at least 

 he recognised the distinction at present acknow- 

 ledged with reference to the appropriate function 

 of the ganglion ic and non-ganglionic portions. 

 But in Mayo's Commentaries for July 1823, the 

 conclusion is for the first time expressly stated 

 thus : " In the last paper of the preceding 

 number, I mentioned that the division of the 

 supra-orbital, infra-orbital, and inferior max- 

 illary nerves, at the points where they emerge 

 from their canals upon the face, produces loss 

 of sensation, and of that alone, in the corres- 

 ponding parts or the face. I have since, after 

 the division of the fourth branch which emerges 

 on the face, namely, that which joins the 

 portio dura, ascertained that this branch like- 

 wise is a nerve of sensation, inasmuch as the 

 cheek loses sensation upon its division. I 

 mentioned in addition that I concluded that 

 other branches of the fifth nerve, from their 

 distribution, are voluntary nerves. Now it is 

 well known that the fifth nerve at its origin 

 consists of two portions ; a larger part, which 

 alone enters the Gasserian ganglion, and ano- 

 ther smaller, which does not enter, but passes 

 below the ganglion to join itself with the third 

 division of the fifth. Towards the close of 

 last summer I endeavoured to trace the final 

 distribution of this small portion in the ass, 

 and succeeded in making out that it furnishes 

 those branches, which are distributed exclu- 

 sively to muscles : I have since ascertained 

 that in the human body precisely the same 

 distribution exists. But the lemaining branches 

 of the fifth are proved to be nerves of sensation ; 

 thus it appears that the fifth nerve consists of 

 two portions, one of which has no ganglion, 

 and is a nerve of voluntary motion (and pro- 

 bably of muscular sensation); and another, 

 which passes through a ganglion, and furnishes 

 branches, which are exclusively nerves of the 

 special senses." 



We return now to the question of the pro- 

 perties of the non-ganglionic portion of the 

 fifth nerve. It has been stated that Mayo was 

 the first to announce the restriction of the 

 voluntary influence of the fifth to certain 

 branches, and that he was led to this conclu- 

 sion from the observation of the fact that certain 

 branches of the nerve are distributed exclusively 

 to muscles. These muscles he has stated, in 

 the first part of his Commentaries, to be the 

 pterygoid, the masseter, the temporal, and 

 buccinator; to which he has added, in his 

 second part, the circumflexus palati ; by dis- 

 section he ascertained that as well in man as 

 in the ass, the lesser portion of the nerve " fur- 

 nishes those branches which are distributed ex- 

 clusively to muscles;" and having already 



determined that the ganglionic portions of the 

 nerve are destined exclusively to sensation, he 

 came to the conclusion that the non-ganglionic 

 portion is a nerve of voluntary motion. His 

 first conclusion upon this point he himself 

 states to have " involved a trifling error : the 

 pterygoid, masseter, and temporal muscles are 

 indeed exclusively supplied by the fifth, and 

 therefore, without doubt, the branches so dis- 

 tributed are voluntary nerves, but the bucci- 

 nator receives branches from the portio dura as 

 well, and I have found subsequently, that 

 pinching the branch of the fifth that perforates 

 the muscle, produces no action in it : and in 

 accordance with this view he writes in his 

 Physiology,* " I was led to observe that there 

 were muscles which received no branches from 

 any nerve but the fifth ; these muscles are the 

 masseter, the temporal, the two pterygoids, 

 and the circumflexus palati. After some care- 

 ful dissection, I made out that the smaller 

 fasciculus of the fifth is entirely consumed 

 upon the supply of the muscles 1 have named." 

 The determination of the constitution and 

 function of the bucral branch of the inferior 

 maxillary nerve has become a matter of greater 

 importance since the publication of Bell's 

 work on the Nervous System in 1830. In it 

 he says, " I am particular in re-stating this, 

 because from time to time it has been reported 

 that I had abandoned my original opinions, 

 whereas every thing has tended to confirm 

 them." Now, it will be remembered that 

 Bell's original opinion is, that the muscles of 

 the face are endowed with two powers, a volun- 

 tary one, dependent on the fifth nerve, and an 

 involuntary respiratory one, dependent on the 

 portio dura ; also, that in the first instance he 

 attributed the voluntary power of these muscles 

 to the facial branches of the fifth, but that he 

 had abandoned that idea, and acknowledged 

 that what he had attributed to loss of motion 

 was in fact due to loss of sensation. In the 

 work adverted to he has taken new ground, 

 and at the same time reiterates his first opinion 

 with regard to the existence of the two distinct 

 contractile powers in the muscles of the face, 

 and attributes to the buccal nerve that influence 

 over their voluntary motion which he had 

 before referred to the infra-orbital, &c. Thus, 

 " but finding that the connexion between the 

 motor root and the superior maxillary nerve 

 proved to be only by cellular texture, and con- 

 sidering the affirmation of M. Magendie and 

 those who followed him, that the infra-orbitary 

 branch had no influence upon the lips, I pro- 

 secuted with more interest the ramus buccinalis 

 labialis," the buccal nerve, " and nobody, 

 I presume, will doubt that the distribution of 

 this division confirms the notions drawn from 

 the anatomy of the trunk, not only that the fifth 

 nerve is the manducatory nerve as it belongs 

 to the muscles of the jaws, but also that it is 

 distributed to the muscles of the cheek and 

 lips to bring them into correspondence with 

 the motions of the jaws." To the point at 

 issue the writer has directed particular atten- 



* 1833, p. 261. 



