410 SPECIAL PHYSIOLOGY. 



vibrations are terminated. Those of greater force enter simultaneously 

 the two opposite openings of the semicircular canals. The orifices and 

 commencement of each canal differ as to size and form, and conse- 

 quently each entering wave of undulatory vibration is modified, thus 

 losing their consonance of expansion, and when they meet interference 

 and suppression result. Reflection of sonorous vibrations is com- 

 pletely provided against. 



"Parallel conditions exist in the cochlea. Its two canals the 

 superior scala vestibuli, and the inferior scala vestibuli are filled 

 with lymph fluid, continuous and identical with that of the vestibule. 

 The first, the scala vestibuli, according to the latest investigations of 

 Kolliker, is the principal seat of hearing. On its lamina spiralis is 

 expanded a sentient, nervous structure, the recipient of the sonorous 

 vibrations excitative of the sense of hearing. It is the homotype of 

 the retina of the eye. The scala tympani furnishes space for spread- 

 ing out the filaments of the nerve, but the terminal extremities pass 

 through the membranous spiral lamina, to be incorporated with the 

 sentient organ of hearing in the superior canal or scala vestibuli. The 

 filaments of the inferior canal or scala tympani are mere conductors 

 of the nervous excitement of the auditive sentient membrane. The 

 scala tympani, similar to the semicircular canals, has no direct con- 

 nection with the production of hearing. It is the homotype of the 

 semicircular canals, and performs the same office. 



" The sonorous vibrations, starting from the stapes and fenestra 

 ovalis, rushing into the adjacent opening of the scala vestibuli, excite, 

 by their impulse, the auditory membrane or retina, spread over its 

 lamina spiralis, and reach its termination, where it opens into the scala 

 tympani. Feeble vibrations may subside spontaneously by exhaustion 

 from their extension. The stronger pass on into the scala tympani, 

 where they fade away, or are suppressed by the interference of vibra- 

 tions entering the inferior canal by the fenestra rotunda, from the 

 tympanum. The condition for perfect hearing, for the distinct per- 

 ception and appreciation of the finest tones and notes, so that each 

 vibration shall make but one, single, distinct impression, and then be 

 suppressed, is thus amply fulfilled. 



" Analogous provisions are perceived to exist in the tympanum, to 

 preserve in that cavity the perfect wave systems of undulations, indis- 

 pensable to the perfection of the sense of hearing. Vibrations exist- 

 ing in air, contained in a cavity with plane walls, would continue to 

 be reflected from side to side, producing confused sounds or noise. 

 The air in the tympanum is thrown into vibrations by impulses of the 

 membrani tympani. They are communicated, pure, and in perfect ac- 

 cord, to the membrane of the fenestra rotunda. This curious and 

 beautiful result is effected in the following mariner: on one side the 

 tympanum communicates, by numerous openings, with the mastoid 

 cells communicating with one another. All the vibrations impinging 

 on this side are suppressed in the mastoid cells. Those that reach 

 the opposite side are swallowed up and lost in the Eustachian tube. 

 All resonance and reflection of vibrations are suppressed, and the 

 wave systems of sonorous vibrations traverse the tympanum undis- 



