292 



PHYSIOLOGY FOR DENTAL STfDENTS. 



shorter "hair"' cells leaning up against them, particularly on tin- 

 side away from the central column. The sound waves which act on 

 the basilar membrane are transmitted to the fluid which fills the 

 uppermost of the three divisions of the cochlear tube (see Fig. 

 56) through a membrane covering an oval-shaped opening (the 

 oval window) in the bony partition separating the internal from 

 the middle ear. After reaching the apex of the cochlea they pass 

 through a small aperture in the basilar membrane into the lowest 



Fig. 56. Semidiagrammatic section through the right ear (Czermak) : G. 

 external auditory meatus ; T, membrana tympani ; P, tympanic cavity or 

 middle ear with the auditory ossicles stretching across it and the Eustachian 

 tube (E) entering it; o, oval window; r, round window; B, semicircular 

 canals; S, cochlea; Vt, upper canal of cochlea; Pt, lower canal of cochlea. 

 (From Howell's Physiology.) 



canal, down which they travel to lose themselves against the mem- 

 brane covering another opening (the round window) situated 

 near the oval window in the same partition of bone. As they pass 

 along these canals the waves cause the basilar membrane to move 

 or vibrate. The vibration affects the cells of the Organ of Corti. 

 and so sets up nerve impulses which are transmitted to the coch- 

 lear nerve by means of nerve fibers which connect with each 

 of the main cells of the Organ. A fine membrane (called Tec- 



