THE NERVOUS SYSTEM. 005 



the sixth nerve, running forward for some little distance dorsal to the 

 nucleus, then descending vertically, passing to outside of its own nucleus 

 between it and the ascending root of fifth nerve. It emerges at the 

 hinder margin of the pons lateral to the sixth nerve, opposite the front 

 edge of the groove between the olivary and restiform bodies. It may be 

 connected with the hypoglossal nucleus. There are two roots; the lower 

 and smaller is called the portio intermedia. 



Functions. The seventh nerve is the motor nerve of all the muscles 

 of the face, including the platysma, bat not including any of the mus- 

 cles of mastication already enumerated; 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 sup- 

 plies the stapedius and laxator tympani ; and through the optic ganglion, 

 the tensor tympani ; through the chorda tympani it sends branches to 

 the submaxillary gland and to the lingualis and some other muscular 

 fibres of the tongue, and to the mucous membrane of its anterior two- 

 thirds; and by branches given off before it comes upon the face, it sup- 

 plies the muscles of the external ear, the posterior part of the digas- 

 tricus, and the stylo-hyoideus. 



Beside 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. 



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 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 orbicu- 

 laris palpebrarum being powerless, the eye remains' open through the 

 unbalanced action of the levator palpebrae; and the conjunctiva, thus 

 continually exposed to the air and the contact of dust, is liable to re- 

 peated inflammation, which may end in thickening and opacity of the 

 cornea. These changes, however, ensue much more slowly than those 

 which follow paralysis of the fifth nerve, and never bear the same de- 

 structive 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 dis- 

 ease 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 com- 

 monly at the same time impaired through the inability to draw air 

 briskly toward the upper part of the nasal cavities in which part alone 

 the olfactory nerve is distributed ; because, to draw the air perfectly in 



