10 C. WINKLER. THE CENTRAL COURSE 



the vestibulum are drawn out and removed. By this proceeding 

 the membranous wall of the semicircular canals, lying enclosed in 

 very hard bone, are stretched and ruptured above their ampullae , 

 and it is advisable to help with a sharp excavator, and to section 

 them , as they present themselves , in order to obtain their easily 

 following the tractions. And yet it is very difficult to remove the 

 vestibulum whith maculae and cristae as a whole. Ordinarily the 



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anterior ampulla is breaking of. In that case the wall of the vesti- 

 bulum again is caught in the iris-pincet , and the tractions are 

 recommenced , until all ampullae are removed. 



After the removal of the cochlea, of the vestibulum with its 

 appendixes and of the ampullae, the trunk of the N. octavus is 

 lying bare. The trunk may be sectioned at the interior auditory 

 meatus, an operation that is often combined with the removal of 

 the vestibulum and the ampullae. 



For the removal of the cochlea is, in its relation to the central 

 nerve-system , an operation very different from the removal of vesti- 

 bulum and ampullae. With the cochlea the ganglion spiral e is remo- 

 ved, but if the vestibulum with the ampullae is extracted , it does 

 not follow necessarily that the ganglion vestibulare is totally extir- 

 pated. Therefore it is often thought desirable to destroy the trunk 

 of the N. octavus, that becomes visible directly after the removal 

 of the cochlea. For along this trunk in the meatus auditorius 

 interims are situated continuously the nerve-cells forming the ganglion 

 plexiforme Scarpae. 



Only when the nerve has been sectioned between these cells 

 and the central nerve-system, the N. vestibularis is in the same 

 condition as that of the N. cochlearis after the removal of the 

 cochlea. Only then there are no longer an}* cells between the lesion 

 of the nerve and the central nerve-system. It is even questionable 

 whether it be possible, in experimenting on rabbits, to section 

 the N. vestibularis centralward from the ganglion vestibulare wit- 

 hout injuring the medulla oblongata and the N. facialis is mostly 

 injured in that case. 



It is therefore rather easy to obtain isolated atrophy of the 

 N. cochlearis. On the contrary it is impossible to obtain atrophy 

 of the N. vestibularis, without injuring likewise the N. cochlearis. 

 As soon as the vestibulum is removed, necessarily the N. cochle- 

 aris is damaged too. 



In the course of the operation neither the nerves, running in 

 the interior of the petrous bone, nor the N. facialis, nor the chorda 

 tympani, become visible. 



