216 PHYSIOLOGY CHAP. 



brush of fine, short, stiff hairlets, and external to the outer rods 

 are three or four successive rows of similar but more elongated 

 cells ; these are termed respectively the inner and outer hair- 

 cells. The external hair -cells are at some distance from each 

 other. Between each two is a filiform process of the sustentacular 

 cells, or cells of Deiters, which rest upon the basilar membrane. 

 A special cuticular membrane, the lamina reticularis, connects 

 and fixes the upper ends of the hair-cells and the filiform appen- 

 dices of Deiters' cells. The hairlets project through the openings 

 in this membrane. Externally to the hair-cells and sustentacular 

 cells is a prominent accumulation of large conical epithelial cells 

 which have no hairs, known as the external supporting cells or 



FIG. 85. Organ of Corti. Human. (G. Retzius.) m.t., membrana tectoria ; s.s., sulcus spiralis 

 internus ; r.b., nerve-fibres of ramus basilaris ; e.s.s., epithelium of sulcus spiralis internus ; 

 c.t., connective tissue lining scala tympanica ; v.s., vas spirale ; nl, nl. internal branches of 

 nervus spiralis; 3, 4, external branches of nervus spiralis; c.p.i., cells of internal pillar; 

 c.p.e., cells of external pillar; t., tunnel; c.i.u, inner hair cells; ce./i.i, ce.h.%, ce.h.3, first, 

 second, third row of outer hair cells; c.d., Deiters' cells; c.s.h., Hensen's supporting cells; 

 e.s.s.e., epithelium of sulcus spiralis externus. 



cells of Hensen. From these there is a gradual transition to the 

 simple cubical epithelium that lines the most external part of the 

 basilar membrane. The human cochlea, according to Eetzius, 

 contains about 12,000 external auditory cells, each provided with 

 some 20 hairlets. 



The hair-cells of Corti and the Deiters' cells beneath them are 

 richly innervated from the free endings of the fibres of the cochlear 

 nerve. These fibres pass outwards near the root of the spiral 

 lamina, through a spirally wound ganglionic cord (ganglion 

 spirale), situated in the spiral canal of the modiolus. The cells of 

 this ganglion are bipolar, and each nerve-fibre has one of the cells 

 interpolated in its course (see Fig. 75). From the peripheral side 

 of the ganglion the fibres, which are medullated, penetrate in 

 small bundles into the separate canaliculi of the bony lamina; 

 losing their sheath, they pass through the small apertures near 



