166 ON THE SENSES. 



buli, by a real winding staircase, the stairs 'of which consist of many thousand 

 small and closely contiguous steps, each step being represented by the trans- 

 versely directed terminal part of one of these nerve filaments. It is still in 

 dispute whether this terminal apparatus floats freely in the fluid of the scala 

 vestibuli, or adheres by its outer end to the membranous lamina ; whether it is 

 covered over by a second delicate membrane and thus is enclosed between two 

 membranes, &c. 



We proceed now to a consideration of the transmission of sound in the lab- 

 yrinth. We have seen that the waves of sound are communicated to the fluid 

 of the labyrinth by the piston-like movements of the stapes in the fenestra ovalis, 

 and have been led to recognize the corresponding out and inward curvatures of 

 the membrane of the fenestra rotunda as the indispensable condition through 

 which the undulatory movement of the fluid is rendered possible. But how 

 these waves are constituted, how propagated, what their special destinations in 

 the different divisions of the labyrinth, in what manner they operate on the ex- 

 tremities of the nerves in the vestibule and the cochlea, for what reason these ex- 

 tremities present to them so peculiar an apparatus and arrangement, these are 

 questions which press for an answer, and until answered debar us from a solution of 

 the mystery in which the excitation of the nerves by the waves of sound is envel- 

 oped ; the answers given to them have thus far, however, proved poor and un- 

 satisfactory. The nature of the fluid-waves of the labyrinth is essentially the 

 same with that of the air- waves ; according as the stapes presses inwards or is 

 withdrawn, there is a succession of waves of condensation and rarefaction, in 

 which the single particles of the fluid, as they follow one another, act precisely 

 as was above explained in reference to the particles of air. The course of the 

 waves is, at least in its principal features, clearly and definitely prescribed ; the 

 waves must first be propagated into the vestibule, whereby the membranous 

 sacs suspended therein, together with the extremities of their nerves, will be 

 agitated. Were the vestibule entirely shut ip, while only the fenestra rotunda, 

 closed with its membrane, found a place at a point of the osseous wall, the 

 waves would be restricted in their play, and would everywhere bound against 

 the solid structure and be beaten back from it like the sea from a rocky coast. 

 The repulsed waves would encounter those which were following, and disturb 

 their action by giving to their advancing particles a contrary impulse. As, in 

 this way, the whole effect of the waves in producing a regular excitation of the 

 nerves would be frustrated, it is evidently of the utmost importance that the 

 A-estibule should be provided with the numerous openings which lead to the canals 

 filled with fluid ; these canals serve as conduits for the waves of the vestibule, 

 which must necessarily traverse them as well as the long passages of the coch- 

 lea before reaching the fenestra rotunda, which lies at their further extremity, 

 and which, by the yielding of its elastic membrane, alone renders the existence 

 of the waves possible. The action and course of the wave in the semicircular 

 canals are diificult to ascertain with physical accuracy ; but, as regards the 

 cochlea, it is at least clear that, since only the upper scala opens into the vesti- 

 bule from which it takes its name, the wave must traverse the whole canal by 

 this passage to the apex, then pass over into the scala tympani and descend by 

 the latter, which lies underneath the dividing lamina, until it finally takes effect 

 on the membrane of the -fenestra rotunda at the base. During its course through 

 the scala vestibuli it must strike in regular succession upon all the nerve ex- 

 tremities which cross that passage, and exert upon each of them, one after the 

 other, its peculiar excitation. This is but a rough sketch, it ia true, of the 

 movement of the waves of the labyrinth, but it is nearly all that we know with 

 certainty. Efforts have not been wanting to penetrate further, and especially 

 to ascertain whether, where, and in what direction the waves are reflected or 

 thrown back, whether this reflection produces an increased degree of undulating 

 intensity through resonance (somewhat in the manner of the reflection of the 



