THE FIFTH NERVE, OR TRIGEMINAL 655 



supply the tensor tympani and tensor palati (Kolliker). The motor func- 

 tion of these branches is proved by the violent contraction of all the muscles 

 of mastication in experimental irritation of the third or inferior maxillary 

 division of the fifth nerve; by paralysis of the same muscles when the nerve 

 is divided or disorganized; and by the retention of the power of these muscles 

 when the facial nerve is paralyzed. Whether 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 mastication 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 supplies them. However, the so-called buccal branch of the fifth 

 is, in the main, sensory. 



Sensory Functions. All the anterior and antero-lateral parts of the face 

 and head, with the exception of the skin of the parotid region, acquire com- 

 mon sensibility through branches of the ganglionic division of the fifth nerve. 

 The muscles of the face and lower jaw acquire muscular sensibility through 

 the filaments of the ganglionic portion of the fifth nerve distributed to them 

 with their proper motor nerves. 



Through its ciliary branches and the branch which forms the long root 

 of the ciliary or ophthalmic ganglion, it exercises some influence on the 

 movements of the iris. When the trunk of the ophthalmic portion is divided, 

 the pupil becomes, according to Valentine, contracted in men and rabbits, and 

 dilated in cats and dogs, but in all cases becomes immovable even under all 

 the varieties of the stimulus of light. How the fifth nerve affects the iris is 

 unexplained; it has been suggested the influence of the fifth nerve on the 

 movements of the iris may be ascribed to the affection of vision in conse- 

 quence of the disturbed circulation or nutrition in the retina. 



Trophic Influence. The morbid effects which division of the fifth nerve 

 produces in the organs of special sense make it probable that the fifth nerve 

 exercises some special or trophic influence on the nutrition of all these organs, 

 although the effects may in part be due to the loss of sensibility which is the 

 natural protective safeguard. Thus, after such division and within a period 

 varying from twenty-four hours to a week, the cornea begins to be opaque 

 and later it grows completely white. A low destructive inflammatory process 

 ensues in the conjunctiva, sclerotic coat, and in the interior parts of the eye. 

 The sense of smell may be at the same time lost or gravely impaired. Com- 

 monly, whenever the fifth nerve is paralyzed, the tongue loses the sense 

 of taste in its anterior and lateral parts, and according to Gowers in the 

 posterior part as well. 



In Relation to Taste. The tactile sensibility of the tongue is due to the lin- 

 gual branch of the fifth nerve, which supplies the anterior and lateral parts of 

 the tongue. The sense of taste in the lateral and anterior portions of the tongue 



