ORGAN OF CORTI. 



761 



basilar memorane. The number of the elements of the organ of Corti is es- 

 timated at about 4,500, for the outer, and 6,500, for the inner rods. The 

 relations of these structures to the membranous labyrinth are seen in Fig. 

 271. The external pillars are longer, more delicate and more rounded than 



FIG. 273. The two pillars of the organ of Corti (Sappey). 



A, external pillar of the organ of Corti : 1, body, or middle portion ; 2, posterior extremity, or base ; S, 

 cell on its internal side ; 4, anterior extremity ; 5, convex surface, by which it is joined to the inter- 



nal pillar ; 6, prolongation of this extremity. 



B, internal pillar of the organ of Corti : 1, body, or middle portion ; 2, posterior extremity ; 3, cell on its 



external side ; 4, anterior extremity ; 5, concave surface, by which it is joined to the external pillar ; 

 6, prolongation, lying above the corresponding prolongation of the external pillar. 



C, tie two pillars of the organ of Corti, united by their anterior extremity, and forming an arcade, the 



concavity of which presents outward : 1,1, body, or middle portion of the pillars ; 2, 2, posterior 

 extremities ; 3, 3, cells attached to the posterior extremities ; 4, 4, anterior extremities joined 

 together ; 5, terminal prolongation of this extremity. 



the internal pillars. The form of the pillars is more exactly shown in Figs. 

 273 and 274, the latter figure, however, exhibiting other structures which 

 enter into the constitution of the organ of Corti. It will be remarked that 



FIG. 274. Vertical section of the organ of Corti of the dog ; magnified 800 diameters (Waldeyer). 

 i-ft, homogeneous layer of the basilar membrane ; v, tympanic layer, with nuclei, granular cell-proto- 

 plasm and connective tissue ; a 3 , tympanic lip of the crista spiralis ; c, thickened portion of the 

 basilar membrane ; d. spiral vessel ; e, blood-vessel ; /, h. bundle of nerves ; g, epithelium ; i. inner 

 hair-cell, with its basilar process, k ; I, head-plate of the inner pillar ; m, union of the two pillars ; 

 n, base of the inner pillar ; o, base of the outer pillar ; p, <j, r, outer hair-cells, with traces of the 

 cilia : f, bases of two other hair-cells ; z, Hensen's prop-cell ; M,, lamina reticularis ; w, nerve-fibre 

 passing to the first hair-cell, p. 



a small, nucleated body is attached to the base of each pillar. At the summit, 

 where the internal and the external pillars are joined together, is a delicate 

 prolongation, directed outward, which is attached to the covering of the 

 quadrilateral canal. 



The above description comprises about all that is definitely known of the 



