THE CENTKAL COURSE OF THE NERVUS OCTAVUS. 157 



In their psychological aspect however a striking difference does 

 appear between these two functions. 



Consciousness directly teaches us, that we hear. Everyone knows 

 what is meant, when hearing is spoken of. The ,,perception of sound" 

 is an expression with a definite meaning for everyone. 



On the contrary consciousness teaches us nothing about a tonic 

 octavus-function . 



Nobody knows what is meant, when a perception of equilibra- 

 tion is spoken of. 



This idea is a result from the penetrating researches of the phy- 

 siologists. 



Nobody knows the precise limits of the meaning of expressions, 

 such as ,,perception of equilibrium" and ,,dizziness" are and as 

 consciousness does not give us an immediate perception of the tonic 

 function, it cannot be otherwise. 



It is necessary to retain in mind, this simple though important 

 and even fundamental psychological difference, which is too often 

 forgotten. 



For instance, often a question was laid before me, that demon- 

 strates better than anything else the confusion around this matter. 



If it is beyond doubt so was asked that the alterations 

 produced in CORTI'S cells by sound-waves, find their way to the 

 temporal lobe of the cortex cerebri and consequently perception of 

 hearing is localisated in this defined area of the cortex in which 

 part of the brain may then be localised the perception of equilibration. 



Such a question should not be asked. 



Wether a sharp difference between the functions of the cochlear 

 and the vestibular nerve may be admitted or not, never a sensory 

 function as the perception of sound our hearing is, ought 

 to be compared, with the influence upon the rnotility exerted by 

 the eighth nerve, even if there existed a conscious sensation of this 

 sensu-motor or tonic octavus-function. 



A similar opinion was held by one of the first investigators in 

 this matter, by FLOURENS. This author, after describing the two 

 nerves by which the nervus octavus is composed, and having postu- 

 lated that the cochlear-nerve acts as a sensory nerve, preparing the 

 function of hearing, speaks of the vestibular-nerve. He says: ,,1'autre 

 nerf, le nerf des canaux-semicirculaires , nest pas un nerf de sens; 

 il est doue de la faculte singuliere d'agir sur la direction des 

 mouvements." 



GOLTZ also refers , in his sagacious deductions and experiments 

 on the functions of the labyrinth, to the fundamental fact, that 



