552 THE NERVOUS SYSTEM. 



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 

 and form of the orifices of the puncta lacrymalia. From 

 these circumstances, the sense of sight is impaired. 



The sense of hearing, also, is impaired in many cases 

 of paralysis of the facial nerve; not only in such as are 

 instances of simultaneous disease in the auditory nerves, 

 but in such as may be explained by the loss of power in 

 the muscles of the internal ear. The sense of smell is 

 commonly at the same time impaired through the inability 

 to draw air briskly towards the upper part of the nasal 

 cavities, in which part alone the olfactory nerve is distri- 

 buted ; because, to draw the air perfectly in this direction, 

 the action of the dilators and compressors of the nostrils 

 should be perfect. 



Lastly, the sense of taste is impaired, or may be wholly 

 lost, in paralysis of the facial nerve, provided the source 

 of the paralysis be in some part of the nerve between its 

 origin and the giving off of the chorda tympani. This 

 result, which has been observed in many instances of 

 disease of the facial nerve in man, appears explicable only 

 by the influence which, through the chorda tympani, it 



