THE VESTIBULAR NERVE 321 



the condition which existed immediately after the opera- 

 tion. In the re-education of the sense of equiUbrium the 

 central region concerned is the cerebral cortex, for when 

 this is removed from the animal which has to some extent 

 recovered its equihbrium a permanent relapse ensues. No 

 disturbance of equihbrium follows excision of the cerebrum 

 when the labyrinth is intact. 



How the canals act is shown by the classical experiment 

 of Ewald. Ewald bored two holes into one of the canals 

 and induced movements of the fluid by blowing into one 

 or other of the holes. The head was always moved in 

 the plane of the canal and in the direction of the current. 

 The terminations of the eighth nerve in the hairs of the 

 ampullae are therefore stimulated by movement of the 

 endolymph relative to the canal, such relative movement 

 being due to the inertia of the fluid. This is why giddi- 

 ness occurs, particularly wheiV"otation is suddenly stopped. 

 Some deaf mutes in whom the semicircular canals are 

 imperfectly formed do not feel giddiness when rotated. 



CENTRAL CONNECTIONS OF THE VESTIBULAR 



NERVE 



The cell-bodies of the vestibular nerve are situated 

 peripherally and form the ganglion of Scarpa. The axons 

 entering the brain-stem deep to the restiform body 

 (Fig. 58) divide into ascending and descending branches. 

 The descending branches pass downwards into the medulla. 

 The ascending, which are the more important, arborise 

 around (1) the principal vestibular nucleus, (2) the nucleus 

 of Deiters and nucleus of Bechterew, large cells situated 

 in the outer part of the floor of the fourth ventricle, 

 and (3) the nucleus fastigii of the cerebellum. By the 

 nuclei of Deiters and of Bechterew they come into 

 contact (a) with the cranial nerves by the posterior longi- 

 tudinal bundle, and (6) with the spinal nerves by the 

 vestibulo-spinal tract. 

 21 



