CH. LYL] 



THE ORGAN OF CORTI 



793 



membrane of Keissner, 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; 

 at the base of the cochlea a narrow passage (canalis reuniens) unites 

 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 between 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 

 base attached to the basilar membrane (o, n, fig. 495). They slant 



u 



FIG. 495. Vertical section of the organ of Corti from the dog. 1 to 2, Homogeneous layer of the 

 membraria basilaris ; u, vestibular layer ; v, tympanal layer, with nuclei and protoplasm ; a, pro- 

 longation of tympanal periosteum of lamina spiralis ossea ; c, thickened commencement of the 

 membrana basilaris near the point of perforation of the nerves h ; d, blood-vessel (vas spirale) ; e, 

 blood-vessel; /, nerves ; g, the epithelium of the sulcus spiralis internus; i, internal hair-cell, with 

 basal process k, surrounded with nuclei and protoplasm (of the granular layer), into which the 

 nerve-nbres radiate ; I, hairs of the internal hair-cell ; n, base or foot of inner pillar of organ of Corti ; 

 TO, head of the same uniting with the corresponding part of an external pillar, whose under half is 

 missing, while the next pillar beyond, o, presents both middle portion and base ; r, s, d, three 

 external hair-cells ; t, bases of two neighbouring hair or tufted cells ; x, supporting cell of Belters; 

 w, nerve-fibre arborising round- the nrst of the external hair-cells ; I I to I, lamina reticularis. 

 x 800. (Waldeyer.) 



inwards towards each other, and each ends in a swelling termed the 

 head ; the head of the inner pillar overlies that of the outer. 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 towards its apex. They are found pro- 

 gressively 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 against the rods of Corti 

 are certain other cells called hair-cells, which terminate in small 



