When an animal which has had the portio dura divided upon one side only takes food, the lips remain motionless upon that side; and when it masticates, the lips continue in the same state, while on the other side they ac tively co-operate, the food and saliva escaping on the side at which the nerve has been cut, and on the other being confined within the mouth. Now, if any action of the lips be voluntary, it is assuredly that by which they co-operate in the prehension and mastication of food ; and since no action of their muscles can be excited by irritation of the branches of the fifth nerve, while such action can be ex cited by that of the portio dura, and all volun tary action is destroyed by the division of that nerve, but one inference remains, that of Mayo already adverted to, viz.—that those branches of the fifth in question possess no influence upon the voluntary faculty of the muscles ; that they are exclusively sentient ; and that the contractile power of the muscles of the Rice, whether voluntary or involuntary, is to be attri buted to another source.
After what has been stated, we must admit that Mayo has been the first expressly to an nounce that the function of these nerves is restricted to sensation. Beyond that, however, he has not gone, in reference to the question of sensation, in the publication alluded to, though it must be admitted that little remained to be added in order to complete the conclu sion, that the ganglionic portion of the nerve is exclusively sentient. At the same time he inferred, " from the preceding anatomical details,"—viz. their exclusive distribution to muscles,—" that other branches of the third 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 ganglionic 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,—aseertaioed 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 ganglioo, 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 1 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 remaining branches of the fifth arc 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-ganglionie 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 circumflexes 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 porno 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 circumflexes 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 I have named." The determination of the constitution and function of the buccal 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, &e. 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 buceinalis 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 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 fascieulus 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 he 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 ganglibnic 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.