144 HAND-BOOK OF PHYSIOLOGY. 



the sixth nerve is irritated; and the muscle is paralyzed when the nerve is 

 divided. In all such cases of paralysis, the eye squints inward, and cannot 

 be moved outward. 



In its course through the cavernous sinus, the sixth nerve forms larger 

 communications with the sympathetic nerve than any other nerve 

 within the cavity of the skull does. But the import of these communi- 

 cations with the sympathetic, and the subsequent distribution of its fila- 

 ments after joining the sixth nerve, are quite unknown. 



SEVENTH OR FACIAL NERVE. 



Functions. The facial or portio dura of the seventh pair of nerves, 

 is the motor nerve of all the muscles of the face, including the platysma, 

 but not including any of the muscles of mastication already enumerated 

 (p. 225, Vol. I.); it supplies, also, the parotid gland, and through the 

 connection of its trunk with the Vidian nerve, by the petrosal nerves, 

 some of the muscles of the soft palate, probably the levator palati and 

 azygos uvulae; by its tympanic branches it supplies the stapedius and laxator 

 tympani, and, through the otic ganglion, the tensor tyinpani; through 

 the chorda tympani it sends branches to the submaxillary gland and to 

 the lingualis and some other muscular fibres of the tongue; and by branches 

 given off before it comes upon the face, it supplies the muscles of the ex- 

 ternal ear, the posterior part of the digastricns, and the stylo- hyoideus. 



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

 which are supplied to the submaxillary and parotid glands, a secretory 

 nerve. For, through the last-named branches, impressions may be con- 

 veyed which excite increased secretion of saliva (p. 232, Vol. I.). 



Symptoms of Paralysis of Facial Nerve. When the facial nerve 

 is divided, or in any other way paralyzed, 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 palpebrge; and the conjunctiva, 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. 



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 toward 



