THE FIFTH NERVE, OR TRIGEMINAL 553 



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 move- 

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

 pupil becomes, according to Valentin, 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 move- 

 ments of the iris may be ascribed to the affection of vision in consequence 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. 

 Commonly, 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 

 lingual 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 have recently been traced back to the pars intermedia and chorda 

 tympani of the seventh, figures 387 and 388. It forms also one chief sensory 

 link in the nervous circle .or reflex action in the secretion of saliva. But, de- 

 ferring this question until the glosso-pharyngeal nerve is to be considered, 

 it may be observed that in some brief time after complete paralysis or division 

 of the fifth nerve, the power of all the organs of the special senses may be im- 

 paired. They may lose not merely their sensibility to common impressions, 

 for which they all depend directly on the fifth nerve, but also their sensibility 

 to the special stimuli to which they are adapted. 



