456 THE CRANIAL NERVES. 



Division of the fifth pair destroys also the general sensibility of 

 the external auditory meatus, the lining membrane of which is 

 supplied by its filaments. Inflammation of this membrane and its 

 consequent alterations, it is well known, interfere seriously with 

 the sense of hearing. It is no uncommon occurrence for an accu- 

 mulation of cerumen to take place after inflammation of this part, 

 so as to block up the auditory canal and produce partial or com- 

 plete deafness. It has not been ascertained, however, whether 

 division of the fifth pair is usually followed by similar changes in 

 this part. 



The lingual branch of the fifth pair supplies the anterior ex- 

 tremity and middle portion of the tongue both with general sensi- 

 bility and with the power of taste. The sensibility of the tongue 

 is accordingly provided for by two different nerves ; in its anterior 

 two-thirds, by the lingual branch of the fifth pair ; in its posterior 

 third, by the fibres of the glosso-pharyngeal. 



The facial branches of the fifth pair are the ordinary seat of tic 

 douloureux. This affection is not unfrequently confined to either 

 the supra-orbital, the infra-orbital, or the mental branch ; and the 

 pain may be accurately traced in the direction of their diverging 

 fibres. It has already been mentioned that the painful sensations 

 sometimes also follow the course of the facial, owing to some sensi- 

 tive filaments which that nerve receives from the fifth pair. 



FACIAL. This nerve was known to the older anatomists as the 

 "portio dura of the seventh pair." It leaves the cavity of the 

 cranium by the internal auditory foramen, in company with the 

 auditory nerve ; and, as the latter is of a softer consistency than the 

 former, they have received the names respectively of the "portio 

 mollis" and " portio dura" of the seventh pair. There is, however, 

 no physiological connection between these two nerves ; for while 

 the auditory is spread out in the cavity of the internal ear, the facial 

 passes onward through the petrous portion of the temporal bone, 

 emerges at the stylo-mastoid foramen, bends round beneath the 

 external ear, and passes forward through the substance of the 

 parotid gland, forming a plexus called the " pes anserinus," by the 

 abundant inosculation of its different branches. It then sends its 

 filaments forward in a diverging course, and is finally distributed 

 to the muscles of the external ear, to the frontalis and superciliaris 

 muscles, to the orbicularis oculi, the compressors and dilators of 

 the nares, the orbicularis oris. and to the elevators and depressors 



