THE FACIAL NERVE. 551 



tive nerves, whose filaments being mingled with its own 

 are the true source of the pain. 



Besides its motor influence, the facial is also, by means 

 of the fibres which are supplied to the subm axillary 

 and parotid glands, a so-called secretory nerve (p. 475). 

 For through the last-named branches impressions may 

 be conveyed which excite increased secretion of saliva. 

 For example, if, in a dog, the submaxillary gland be 

 exposed, and the chorda tympani be divided, it will 

 be seen that on stimulating the distal end of the 

 nerve by a weak electric current, the gland becomes ex- 

 ceedingly vascular, and saliva is secreted in largely in- 

 creased amount. Under ordinary circumstances of in- 

 creased secretion of saliva by the submaxillary gland, as 

 from the presence of food in the mouth, the stimulus 

 is conveyed by the same channel, the chorda tympani 

 being the efferent nerve in a reflex action, in which the 

 afferent fibres are branches of the fifth and glosso-pharyn- 

 geal nerves. 



When the facial nerve is divided, or in any other way 

 paralyzed, the loss of power in the muscles which it sup- 

 plies, while proving the nature and extent of its functions, 

 displays also the necessity of its perfection for the perfect 

 exercise of all the organs of the special senses. Thus, in 

 paralysis'of the facial nerve, the orbicularis palpebrarum 

 being powerless, the eye remains open through the un- 

 balanced action of the levator palpebrse ; and the conjunc- 

 tiva, thus continually exposed to the air and the contact of 

 dust, is liable to repeated inflammation, which may end in 

 thickening and opacity of both its own tissue and that of 

 the cornea. These changes, however, ensue much more 

 slowly than those which follow paralysis of the fifth nerve, 

 and never bear the same destructive character. In paraly- 

 sis of the facial nerve, also, tears are apt to flow constantly 

 over the face, apparently because of the paralysis of the 

 tensor tarsi muscle, and the loss of the proper direction 



