THE FACIAL NERVE. 551 



appears to be the consequence of defective nutrition of the 

 retina ; for although, in some cases, it has ensued imme- 

 diately, as if from concussion of the retina, yet in some it 

 has come on gradually like slowly progressive amaurosis, 

 and in some with inflammatory disorganisation, followed 

 by atrophy of the whole eye.* 



Physiology of the Facial Nerve. 



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 mas- 

 tication already enumerated (p. 545) ; it supplies, also, 

 through the connection of its trunk with the Vidian nerve, 

 by the petrosal nerves, some of the muscles of the soft 

 palate, most probably the levator palati and azygos uvulse ; 

 by its tympanic branches it supplies the stapedius and 

 laxator tympani, and, through the otic ganglion, the tensor 

 tympani ; through the chorda tympani it sends branches 

 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 external ear, the 

 posterior part of the digastricus, and the stylo-hyoideus. 



To the greater number of these muscles it is the sole 

 motor nerve, and it is probably exclusively motor in its 

 power ; no pain is produced by irritating it near its origin 

 (Valentin), and the indications of pain which are elicited 

 when any of its branches are irritated, may be explained 

 by the abundant communications which, in all parts of its 

 course, it forms with sensitive nerves, whose filaments 

 being mingled with its own are the true source of the 

 pain. Such communications are effected with the fifth 

 nerve through the petrosal nerves, and probably also 

 through the chorda tympani, and with the pneumogastric 

 nerve through its auricular branch, even before the facial 

 leaves the cranium. 



* Such a case is recorded by Snabilie in the Nederlandsch Lancet, 

 August, 1846. 



