330 ELEMENTS OF HISTOLOGY. [Chap. X-LI. 



outer rod is larger and longer than the inner, the 

 latter being slightly bent in. the middle. Owing to 

 the position of the rods, the two files form an arch 

 the arch of Corti. Between it and the corresponding 

 part of the basilar membrane is a space the tunnel of 

 the arch, triangular in cross section. 



479. The substance of the rods, or pillars, of Corti 

 is bright, highly refractive, and slightly and longitu- 

 dinally striated. 



The head of the inner rod is triangular, a short 

 process extending inwards towards the inner hair-cell, 

 a long process extending outwards over the head of 

 the outer pillar. Outwards, the triangular head pos- 

 sesses a concave surface grasping the convex surface of 

 the head of the outer rod. This latter possesses a 

 process directed outwards, and firmly applied to the 

 outer process of the head of the inner rod, the two 

 together forming part of the membrana reticularis (see 

 below). 



The relation between the outer and inner rods is 

 such that the head of one outer rod fits into those of 

 about two inner rods. 



480. At the foot, each rod has, on the side directed 

 towards the tunnel, a granular, nucleated, lump of 

 protoplasm, probably the remnant of the epithelial 

 cell from which the lower half of the rod is derived ; 

 the upper part sometimes possesses a similar remnant, 

 proving that this also has been formed by an epithelial 

 cell, so that each rod is in reality derived from two 

 epithelial cells (Waldeyer). 



481. Next follow three or four rows of outer hair- 

 cells, similar in. size and structure to the inner hair- 

 cells. Each of the outer hair-cells represents a iilo 

 of hair-cells, extending on the membrana basilaris 

 along the whole extent i.e., two and a-half turns 

 of the scala media. Each hair-cell possesses an oval 

 nucleus and a number of stiff rods, or hairs, disposed 



