538 HANDBOOK OF PHYSIOLOGY. 



cations with the sympathetic, and the subsequent distribution of its 

 filaments after joining the sixth nerve,, are quite unknown. 



The Seventh or Facial Nerve. 



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

 arises from the floor of the central part of the fourth ventricle to the 

 outside of and deeper down than the sixth nucleus. It may be con- 

 nected with the hypoglossal nucleus. There are two roots, the lower 

 and smaller is called the portio intermedia, 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; 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 gan- 

 glion, 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 an- 

 terior two-thirds; and by branches given off before it comes upon the 

 face, it supplies the muscles of the external ear, the posterior part of the 

 digastricus, 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. 



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 palpebrae; 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. 



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 towards the upper part of the nasal cavities in which part alone 

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



