THE NERVOUS SYSTEM. 139 



FIFTH OR TRIGEMINAL NERVE. 



Functions. The fifth or trigeminal nerve resembles, as already 

 stated, the spinal nerves, in that its branches are derived through two 

 roots; namely, the larger or sensory, in connection with which is the Gas- 

 serian ganglion, and the smaller or motor root which has no ganglion, and 

 which passes under the ganglion of the sensory root to join the third 

 branch or division which issues from it. The first and second divisions 

 of the nerve, which arise wholly from the larger root, are purely sensory. 

 The third division being joined, as before said, by the motor root of the 

 nerve, is of course both motor and sensory. 



(a.) Motor Functions. Through branches of the lesser or non- 

 ganglionic portion of the fifth, the muscles of mastication, namely, the 

 temporal, masseter, two pterygoid, anterior part of the digastric, and 

 mylo-hyoid, derive their motor nerves. Filaments are also supplied to 

 the tensor tympani and tensor palati. The motor function of these 

 branches is proved by the violent contraction of all the muscles of masti- 

 cation in experimental irritation of the third or inferior maxillary division 

 of the nerve; by paralysis of the same muscles, when it is divided or 

 disorganized, or from any reason deprived of power; and by the retention 

 of the power of these muscles, when all those supplied by the facial nerve 

 lose their power through paralysis of that nerve. The last instance proves 

 best, that though the buccinator muscle gives passage to, and receives 

 some filaments from, a buccal branch of the inferior division of the fifth 

 nerve, yet it derives its motor power from the facial, for it is paralyzed 

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

 retains 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 sensory, or in part motor also, must remain 

 for the present doubtful. From the fact that this muscle, besides its 

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

 tion, in keeping the food between the teeth, it might be supposed from 

 analogy, that it would have a motor branch from the same nerve that sup- 

 plies them. There can be no doubt, however, that the so-called buccal 

 branch of the fifth is, in the main, sensory; although it is not quite cer- 

 tain that it does not give a few motor filaments to the buccinator muscle. 



(b.) Sensory Functions. Through the branches of the greater or 

 gangiionic portion of the fifth nerve, all the anterior and an tero- lateral 

 parts of the face and head, with the exception of the skin of the parotid 

 region (which derives branches from the cervical spinal nerves), acquire 

 common sensibility; and among these parts may be included the organs 

 of special sense, from which common sensations are conveyed through the 

 fifth nerve, and their special sensations through their several nerves of 



