744 



HEARING 



[CH. LIT. 



Fio. 546. View of the osseous cochlea 

 divided through the middle. 1, Central 

 canal of the modiolus ; 2, lamina spiralis 

 ossea ; 3, scala tympani ; 4, scala vesti- 

 buli ; 5, porous substance of the modiolus 

 near one of the sections of the canalis 

 spiralis modioli. f (Arnold.) 



these two meeting at the outer edge of the bony lamina spiralis. 

 Following the turns of the cochlea to its apex, the scala media there 

 terminates blindly ; while towards the base of the cochlea it is also 



closed, with the exception of a very 

 narrow passage (canalis reuniens) 

 uniting it with the saccule. The scala 

 media (like the rest of the membranous 

 labyrinth) contains endolymph. 



Organ of Corti. Upon the basilar 

 membrane are arranged cells of 

 various shapes. About midway be- 

 tween the outer edge of the lamina 

 spiralis and the outer wall of the 

 cochlea are situated the rods of Corti. 

 Viewed sideways, they are seen to 

 consist of an external and internal 

 pillar, each rising from an expanded foot or lose attached to the basilar 

 membrane (o, n, fig. 548). They slant inwards towards each other, 

 and each ends in a swelling termed the head ; the head of the inner 

 pillar overlies that of the outer (fig. 548). Each pair of pillars 

 forms a pointed roof arching over a space, and by a succession of 

 them a tunnel is formed. 



There are about 3000 of these pairs of pillars, in proceeding from 

 the base of the cochlea to- 

 wards its apex. They are 

 found progressively to in- 

 crease in length, and become 

 more oblique ; in other words 

 the tunnel becomes wider, 

 but diminishes in height as 

 we approach the apex of the 

 cochlea. Leaning against the 

 rods of Corti are certain 

 other cells called hair-cells, 

 which terminate in small 

 hair-like processes. There 



FIG. 547. Section through one of the coils of the cochlea 



Sliagrammatic). ST, Scala tympani ; SV, scala vesti- 

 uli ; CC, canalis cochlea or canalis membranaceus ; 

 R, membrane of Reissner ; Zso, lamina spiralis ossea ; 

 Us, limbus laminae spiralis; ss, sulcus spiralis; nc, 

 gs, ganglion spirale; t, membrana 



are several rows of these on 



the outer and one row on 



the inner side. Between 



them are certain supporting 



cells called cells of Deiters 



(fig. 548, x). This structure 



rests upon the basilar membrane ; it is roofed in by a fenestrated 



membrane or lamina reticularis into the fenestrae of which the tops 



of the various rods and cells are received. When viewed from 



cochlear nerve : 



tectoria (below the membrana tectoria is the lamina 

 reticularis) ; 5, membrana basilaris ; Co, rods of Corti ; 

 Isp, ligamentum spirale. (Quain.) 



