NERVES OF THE ORGAN OF HEARING. 451 



the organ of hearing by sending a few filaments to the muscles 

 of the bones of the tympanum. The canal of the petrous bone, 

 through which it passes, is very crooked; beginning at the 

 larger orifice of the meatus internus in its upper fossa, it passes 

 outwards until it nearly reaches the Vidian foramen, on the front 

 of the petrous bone; it then turns very abruptly backwards, form- 

 ing an angle, and is continued in a circuit around the superior 

 and the posterior parietes of the tympanum, till it terminates in 

 the stylo-mastoid foramen. Its course is marked by a ridge 

 projecting into the tympanum, above the foramen ovale, and 

 passing between the semicircular canals and the cochlea. This 

 canal has been very much misnamed by the calling of it the 

 aqueduct of Fallopius, as its only use is to conduct nerves and 

 blood vessels. It is lined by a delicate fibrous membrane, be- 

 tween which, and its contained parts, there is so little adhesion, 

 that the latter may be drawn out entire. 



The facial nerve is joined at the Vidian foramen by the Vi- 

 dian nerve, shortly after which it sends a filament to the tensor 

 tympani muscle.* As it passes the base of the pyramid it de- 

 taches another filament, which supplies the stapedius muscle. 



Shortly after this, it is abandoned by the Vidian nerve, and 

 does not give off any more branches till it escapes from the sty- 

 lo-mastoid foramen, when it sends off a branch, the posterior 

 auricular (Auricularis Posterior,) which is distributed by fila- 

 ments, some of which run into the mastoid process; other 

 branches mount on the side of this process, to the skin which 

 covers it, and to the occipital muscle: others go to the concha 

 of the ear, being spent upon its skin, upon the posterior auricu- 

 lar muscle, and some of them, penetrating the pinna, are lost 

 upon the integuments of the meatus externus. The trunk of 

 the facial then goes to its destination on the face. 



4. The Chorda Tympani or Superficial Petrous Nerve, is a 

 branch of the Pterygoid branch of the Trigeminus, and leaves 

 it near the anterior part of the carotid canal of the petrous bone. 

 It, as just mentioned, under the name of Vidian nerve, joins the 

 facial nerve at the angle of the canal of Fallopius, and conti- 



* The tensor tympani is also supplied by a nerve from the Third Branch of 

 the Trigeminus. 



