434 THE NERVOUS SYSTEM. 



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-pharyngeal nerves. 



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

 alyzed, the loss of power in the muscles which it supplies, 

 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 unbalanced action of the levator 

 palpebrse; and the conjunctiva, thus continually exposed to 

 the air and the contact of dust, is liable to repeated inflamma- 

 tion, 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 

 paralysis of the facial nerve, also, tears are apt to flow con- 

 stantly 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 lachrymalia. 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 to- 

 wards the upper part of the nasal cavities, in which part alone 

 the olfactory nerve is distributed ; because, to draw the air per- 

 fectly in this direction, the action of the dilators and com- 

 pressors 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 exercises on the movements of the 

 lingualis and the adjacent muscular fibres of the tongue ; and, 

 according to some, or probably in some animals, on the move- 

 ments of the stylo-glossus. We may therefore suppose that 

 the accurate movement of these muscles in the tongue is in 

 some way connected with the proper exercise of taste. 



Together with these effects of paralysis of the facial nerve 

 the muscles of the face being all powerless, the countenance 



