HEARING. 431 



cone, where it suddenly terminates in a curved 

 point, or hook (h), leaving an aperture by which 

 the two portions of the tube communicate to- 

 gether. In Fig. 395, a bristle (b, b) is passed 

 through this aperture. The central pillar, round 

 which these tubes take two and a half circular 

 turns, is termed the modiolus. Its apex is seen 

 at (m). One of these passages is distinguished 

 by the name of the vestibular tube*, in conse- 

 quence of its arising from the cavity of the ves- 

 tibule ; and the other by that of the tympanic 

 tube'\, because it begins from the inner side of 

 the membrane which closes the fenestra rotunda, 

 and forms the only separation between the 

 interior of that tube, and the cavity of the tym- 

 panum. The trunk of the auditory nerve occu- 

 pies a hollow space immediately behind the 

 ventricle, and its branches pass through minute 

 holes in the bony plate which forms the wall of 

 that cavity, being finally expanded on the dif- 

 ferent parts of the membranous labyrinth.]; 



* Scala vestibuli. t Scala tymprmi. 



X In Fig. 396, the anterior trunk of the auditory nerve is seen 

 (at g) distributing brandies to the ampullsc (a, a), the utricle 

 (u), and the calcareous body it contains; while the posterior 

 trunk (n) divides into a branch, which supplies the sacculus (s) 

 and its calcareous body (o), and a second branch (k) which is 

 distributed over the cochlea, (d) is the nerve called the portio 

 dura, which meiely accompanies the auditory nerve, but has no 

 relation to the sense of hearing. In Fig. 390, the auditory 

 nerve (n) is seen entering at the back of the vestibule. 



