COCHLEA. 1 1 5 



membrane rests Corti's organ. External and internal to it lie several rows of cells. Beginning 

 at the outer end of the basilar membrane observe the supporting cells of Hensen, and then a 

 row of cells with fine bristles projecting from their upper surface the outer hair-cells. These 

 cells occur in three or four rows. Passing onwards we come to the arch of Corti, composed of 

 an outer and an inner rod or pillar, each in a single row. Each rod has the shape of an f, and 

 they are so arranged as to touch with their upper part or head, whilst the base rests on the 

 membrana basilaris, thus leaving a triangular space between them. Each rod consists of a 

 head, a narrow middle part or body, and a broad, wing-shaped base or foot. The head of 

 the inner rod has a concavity on its outer surface which receives the convex surface of the 

 outer rod. A flat process or head-plate proceeds outwards which helps to cover in the head 

 of the outer rod. It terminates in the membrana or lamina reticularis. The outer rod also 

 sends outwards a short process which forms the first phalanx of the membrana reticularis. 

 The outer rods are longer, thicker, and more numerous than the inner rods. At the foot of 

 each rod, on the surface directed towards the triangular tunnel under the rods, is a small 

 nucleated mass of protoplasm. 



The inner hair-cells of Deiters lie immediately inside the inner rods. They occur in a 

 single row, and possess fine hairs, projecting from their free surface just like the outer hair-cells. 

 Internal to these there is a row of nucleated columnar epithelial cells, which support these 

 cells. They are continued inwards over the membranous portion of the membrana basilaris 

 as far as the sulcus spiralis. The lamina or membrana reticularis will be seen in section. It 

 is a cuticular, hyaline, very resistant membrane which stretches outwards from the heads of 

 Corti's rods to the outer hair-cells. In it exist a number of round or oval apertures, through 

 which the outer hair-cells project. The parts of this membrane which exist between these 

 holes, being shaped like a finger, were called phalanges by Deiters. (Indicate the membrane of 

 Reissner, Corti's rods and cells, and the membrana tectoria in PI. XXVII., Fig. 4.) 



The organs of taste (p. 62) and touch (p. 95) have already been alluded to. 



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