MR. BELL ON THE NERVES OF THE FACE. 
325 
the cheeks. Conceiving that there must be such an accordance, and contem- 
plating the roots of the fifth pair and their distinct functions, I had imagined 
that this office was performed by the branches of the second division of the 
fifth. But finding that the connection between the motor root and the superior 
maxillary nerve proved to be only by cellular texture, and considering the 
affirmation of M. Magendie and those who followed him, that the infra-orbi- 
tary branch had no influence upon the lips, I prosecuted with more interest 
the Ramus Buccinalis Labialis. 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 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. Let us take in illustration the articulation of the bones. In the joints 
the muscles are attached to the capsular membrane in such a manner as to 
draw it from between the bones and adapt it to the degree of flexion of the 
joint. If the cheek were a passive membrane like the capsule of a joint, it 
would have required some such mechanical connection with the jaw or its 
muscles, as might have drawn it from between the teeth in the motions of 
mastication. But being a muscular part, to bring it into just relation with 
the motions of the teeth, it must have an accordance through nerves, and act 
in sympathy ; — relax when the jaws are apart, and contract when they are 
closed. I think therefore we may perceive why a branch of the motor nerve 
of the muscles of the jaws sends a division to the muscles of the cheek and to 
the angle of the mouth. 
By such a process of reasoning we see also why a branch of the same nerve 
should prolong its course under the chin to the muscles which are opponents 
to those which close the jaw. 
In short, the motor portion of the fifth nerve sends no twigs with the 
ophthalmic division, nor the superior maxillary nerve, but only with the lower 
maxillary nerve. To the muscles of the lower jaw alone which are in action 
during mastication, and to the muscles necessarily associated in that action, 
the manducatory nerve is distributed. 
It remains only that we observe what takes place in man, and compare the 
circumstances with experiments on brutes. 
