OF THE NERVUS OCTAVUS. 15 



cochlea, may be either ruptured or pressed downward - - then the 

 broad, flat edge of a small hook, having been bent vertically for 

 this purpose, is introduced through the foramen rotundum. 



This edge is pushed under the thin lamina of bone , which is 

 then lifted up. 



In most cases the lamina breaks off frontalward enough to offer 

 sufficient space, and the aperture may be widened with excavators. 

 Nevertheless a point de repere has been lost, because the foramen 

 rotundum forms now part of the breach in the bone. 



The lamina of bone having been removed, the convolutions of 

 the cochlea are lying bare, and it offers no difficulty to extract 

 these by means of an excavator or of a small, sharp spoon. The three 

 convolutions being removed, we touch the petrous bone, forming the 

 posterior wall of the cavity containing the cochlea. 



The operation is now terminated. The cochlea and therewith the 

 ganglion spirale N. cochlearis has been removed. The N. cochlearis 

 degenerates within a week. 



Endolymph is flowing forth. Perhaps the peripherical organs in 

 the vestibulum may degenerate. Certainly the ganglia along the 

 N. vestibularis do not so immediately. They are certainly without 

 any lesion consequently of the cochlea-removal. It is therefore not 

 only possible, but it follows necessarily, that the degeneration is 

 confined to the N. cochlearis, if indeed this nerve does not exchange 

 fibres with the N. vestibularis. 



b. The removal of the entire labyrinth and the section of the 

 N. octavus. 



Generally however it is thought desirable to remove the entire 

 labyrinth. 



To this purpose the operation is commenced in the same way 

 as described above. The bony lamella covering the cochlea is remo- 

 ved and the fenestrum rotundum is sought. After removing by 



o o / 



means of an excavator the anterior wall, that had remained stan- 

 ding, a breach is made between fenestrum rotundum and foramen 

 ovale in the bony wall covering the vestibulum. The stapes is 

 extracted from the foramen ovale, without injuring the tympanum. 

 The breach in the bone is enlarged as much as possible. Thus far the 

 operation may be made easily without the aid of a lens. At this 

 moment however it is preferable to examine the contents of the 

 vestibulum with a lens. The anterior ampulla is caught in an iris- 

 crotchet. The membranaceous anterior canal is cut through near 

 the ampulla and with slight tractions the membranous contents of 



