THE EAR, HEARING, TASTE AND SMELL 233 



edge of this bony plate is the membranous cochlea (scala media), 

 a tube triangular in cross-section and attached by its base to the 

 outer side of the bony cochlear spiral. The spiral lamina and the 

 membranous cochlea thus subdivide the cavity of the bony tube 

 (Fig. 73) into an upper portion, the scala vestibuli, SV, and a lower, 

 the scala tympani, ST. Between these lie the lamina spiralis (Iso) 

 and the membranous cochlea (CC), the latter being bounded 

 above by the membrane of Reissner (R) and below by the basilar 

 membrane (6). The free edge of the lamina spiralis is thickened 

 and covered with connective tissue which is hollowed out so as to 

 form a spiral groove (the sulcus spiralis, ss) along the whole length 

 of the membranous cochlea. The latter does not extend to the 



FIG. 73. Section of one coil of the cochlea, magnified. SV, scala vestibuli; 

 R, membrane of Reissner; CC, membranous cochlea (scala media); Us, limbus 

 lamince spiralis; t, tectorial membrane; ST, scala tympani; Iso, spiral lamina; 

 Co, rods of Corti; b, basilar membrane. 



tip of the bony cochlea; above its apex the scala vestibuli and 

 scala tympani join; both are filled with perilymph, and the former 

 communicates below with the perilymph cavity of the vestibule, 

 while the scala tympani abuts below on the round foramen, which, 

 as has already been pointed out, is closed by a membrane. The 

 membranous cochlea contains certain solid structures seated on 

 the basilar membrane and forming the organ of Corti; the rest of 

 its cavity is filled with endolymph, which has free passage to that 

 in the sacculus. 



The Organ of Corti. This contains the end organs of the coch- 

 lear nerves. Lining the sulcus spiralis are cuboidal cells; on the 

 inner margin of the basilar membrane the cells become columnar, 

 and then are succeeded by a row which bear on their upper ends a 



