HEARING. 



203 



outwards from the edge of this is a fibrous partition, the 

 basilar membrcme, dividing the tube longitudinally into two 

 parts, and attached at its outer edge to the wall of the tube 

 by muscular fibres, which can keep it tense. Another and 

 much more delicate partition, the membrane of Reissner, 

 extends upwards and outwards from the lamina spiralis to 

 the outer wall of the tube; and thus there are three parallel 

 passages separated from one another. Of these, the upper 

 or that turned towards the apex of the cochlea, is called the 

 scala vestibuli , and commences in the cavity of the vestibule ; 

 the middle passage, placed between the basilar membrane 

 and membrane of Reissner, is called the canalis membranacea, 

 and is continuous with the membranous vestibule, being con- 

 nected with the saccule by a little duct, the canalis reuniens; 

 while the lower passage, the scala tympani, starts from the 

 closed fenestra rotunda, and is separated from the vestibule 

 by the basilar membrane, so that its only continuity with 

 that cavity, in the fresh state, is by a small opening at the 

 apex of the cochlea, the helicotrerna, where it communicates 

 with the scala vestibuli beyond the blind extremity of the 



Fig. 131. COCHLEA OF NEW-BORN PIG, section, a, Canalis mem- 

 braiiacea; 6, scala tympani; c, scala vestibuli; d, basilar mem- 

 brane and organ of Corti; e, membrane of Keissner; /, spiral 

 ganglion. Reichert. 



