THE SENSES. r;s:-j 



the cochlea, its upper wall (separating it from the scala vestibuli) by 

 the membrane of Reissner, and its lower wall (separating it from the 

 scala tympani) by the basilar membrane, 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 toward the base 

 of the cochlea it is also closed with the exception of a very narrow pas- 

 sage (canalis reuniens) uniting it with the sacculus. The scala media 

 (like the rest of the membranous labyrinth) contains endolympJi. 



Organ of Corti. Upon the basilar membrane are arranged cells of 

 various shapes. About midway between the outer edge of the lamina 



Fig. 403. Section through one of the coils of the cochlea (diagrammatic). ST, scala tym- 

 pani; SV, scala vestibuli; C<7, canalis cochleae or canalis membranaceus : jR, membrane of 

 Reissner; Iso, lamina spiralis ossea; Us, limbus laminae spiralis ; ss, sulcus spiralis ; nc, cochlear 

 nerve ; gs, ganglion spirale ; , membrana tectoria (below the membrana tectoria is the lamina 

 recticularis) ; ft, membrana basilaris ; Co, rods of Corti ; Isp, ligamentum spirale. (Quain.) 



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 base on the basilar mem- 

 brane (0, n, fig. 404). They slant inward toward each other, and each 

 ends in a swelling termed the head ; the head of the inner pillar overly- 

 ing that of the outer (fig. 404). Each pair of pillars forms, as it were, 

 a pointed roof arching over a space, and by a succession of them a little 

 tunnel is formed. 



It has been estimated that there are about 3000 of these pairs of pil- 

 lars, in proceeding from the base of the cochlea toward its apex. They 

 are found progressively to increase 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, as it were, against these 

 external and internal pillars are certain other cells, of which the external 

 ones, hair cells, terminate in small hair-like processes. Most of the 

 above details are shown in the accompanying figure (fig. 404). This 

 complicated structure rests, as we have seen, upon the basilar membrane ; 

 it is roofed in by a remarkable fenestrated membrane or lamina reticu- 



