Cfl. Llll] 



THE ORGAN OF* COKTI. 



721 



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 3,000 of these pairs of pillars, in proceeding 

 from the base of the cochlea towards 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 against these 

 external and internal pillars are certain other cells-, called hair- 

 cells, which terminate in small hair-like processes. There 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. 546. Vertical section of the organ of Corti from the dog. i to 2, homogeneous 

 layer of the membrana basilarix ; , vestibular layer; v, tympanal layer, with 

 nuclei and protoplasm ; , prolongation of tympanal periosteum of lamina spiralis 

 OMea ; c, thickened commencement of the membrana basilaris near the point of per- 

 foration of the nerves h ; d, blood-vessel (vas spirale) ; , blood-vessel; /.nerves: 

 /, the epithelium of the sulcus spiralis interim* ; t, internal hair-cell, with basal 

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

 the nerve-fibres radiate; /, hairs of the internal hair-cell ; , base or foot of inner 

 pillar of organ of Corti ; m. head of the same uniting with the corresponding part of 

 an external pillar, whose under half is missing, while the next pillar beyond, , 

 presents both middle portion and base ; r d, three external hair-cells ; t, bases of two 

 neighbouring hnir or tufted cells; x, supporting cell of Deiters ; w, nerve-fibre 

 arborising round the first of the external hair-cells ; 1 1 to I, lamina reticularis. 

 x 800. (Waldeyer.) 



Most of the above details are shown in the accompanying figure 

 (fi<:. 546). This structure rests upon the basilar membrane; it 

 is roofed in by a fenestrated membrane or lamina reticularis into 

 the fenestrse of which the tops of the various rods and cells arc 

 received. When viewed from above, the organ of Corti shows a 

 remarkable resemblance to the key-board of a piano. The top of 

 the organ is roofed by the meml/rana tectoria (fig. 545, t) that 

 extends from the end of the limbus (Us, fig. 545), a connective- 

 tissue structure on the spiral lamina. In close relatioti with the 

 hair-cells which form the auditory nerve epithelium, arc filaments 



K.P. :i A 



