THE FIFTH NERVE. 429 



its motor power from the facial, for it is paralyzed together 

 with the other muscles that are supplied by the facial, but 

 retaius its power when the other muscles of mastication are 

 paralyzed. Whether, however, the branch of the fifth nerve 

 which is supplied to the buccinator muscle is entirely sensi- 

 tive, or in part motor also, must remain for the present doubt- 

 ful. From the fact that this muscle, besides its other func- 

 tions, acts in concert or harmony with the muscles of mastica- 

 tion, in keeping the food between the teeth, it might be sup- 

 posed from analogy, that it would have a motor branch from 

 the same nerve that supplies them. There can be no doubt, 

 however, that the so-called buccal branch of the fifth, is, in 

 the main, sensitive ; although it is not quite certain that it 

 may not give a few motor filaments to the buccinator muscle. 



The sensitive function of the branches of the greater divi- 

 sion of the fifth nerve is proved by all the usual evidences, 

 such as their distribution in parts that are sensitive and not 

 capable of muscular contraction, the exceeding sensibility of 

 some of these parts, their loss of sensation when the nerve is 

 paralyzed or divided, the pain without convulsions produced 

 by morbid or experimental irritation of the trunk or branches 

 of the nerve, and the analogy of this portion of the fifth to the 

 posterior root of the spinal nerve. 



But although formed of sensitive filaments exclusively, the 

 branches of the greater or ganglionic portion of the fifth nerve 

 exercise a manifold influence on the movements of the mus- 

 cles of the head and face, and other parts in which they are 

 distributed. They do so, in the first place, by providing the 

 muscles themselves with that sensibility without which the 

 mind, being unconscious of their position and state, cannot 

 voluntarily exercise them. It is, probably, for conferring 

 this sensibility on the muscles, that the branches of the fifth 

 nerve communicate so frequently with those of the facial and 

 hypoglossal, and the nerves of the muscles of the eye ; and it 

 is because of the loss of this sensibility that when the fifth 

 nerve is divided, animals are always slow and awkward in the 

 movement of the muscles of the face and head, or hold them 

 still, or guide their movements by the sight of the objects 

 towards which they wish to move. 



Again, the fifth nerve has an indirect influence on the mus- 

 cular movements, by conveying sensations of the state and 

 position of the skin and other parts : which the mind perceiv- 

 ing, is enabled to determine appropriate acts. Thus, when 

 the fifth nerve or its infra-orbital branch is divided, the move- 

 ments of the lips in feeding may cease, or be imperfect ; a fact 

 which led Sir Charles Bell into one of the verv few errors of his 



