114 AVERS. [Vol. VI. 



of the bundles, which throws greater strain upon a few hairs at 

 a time, whereas in other parts of the band the cohesion of the 

 elementary hairs and their practically even distribution in the 

 band lends a strength to the whole structure such that a strain 

 brought to bear upon any part of it, equal in area to a bundle 

 of hairs rising from a cell, though sufficient to rupture the hair 

 bundle, does not interrupt the continuity of the plate. 



A further arrangement lending strength to the hair band is 

 the crossing of the fibres ; for the hairs from different rows of 

 hair cells do not run parallel, but cross each other at varying 

 angles. There are two main courses of hairs, an upper and a 

 lower. The lower, from the inner hair cells, is more oblique to 

 the radius than the upper, thicker layer, from the outer hair 

 cells. 



The readiness with which the hair band is torn away from its 

 natural attachments and its frequent fixation to the spiral plate 

 by its other edge, explain why this structure has so long been 

 misunderstood, both in its make-up and in its purpose. 



In transverse section the hair band is "clef-shaped, the 

 figure being much thicker at one end than at the other. There 

 are two surfaces, two edges, and two ends. The morphologi- 

 cally dorsal surface has a convexity (that occurring in the thick- 

 ened region) over the hair cells of the ridge of Corti, and this 

 convexity may be said to be, in general, but a repetition in the 

 hair band of the convexity of the ridge of Corti. In sloping 

 downwards and inwards toward the root of Reissner's mem- 

 brane, the surface of the band may form a shallow depression, in 

 which case the usual "cleff "-form of the cross-section is attained; 

 sometimes the hairs seem to run nearly straight to their ends, 

 and then the section is ( •^ ) comma-shaped. The lower surface 

 follows these outlines in the main. The inner edge is exces- 

 sively thin, and in bands which have been treated with reagents 

 they usually present a glassy appearance, the longer the treat- 

 ment with reagents or the more active the reaction, the greater 

 the amount of changed tissue in the band, effected in all cases 

 by the penetration of the reagent, which of course has made 

 equal penetration over all the surface of the band, and caused 

 equal chemical change in the fibres, but, owing to the thickness 

 of the outer edge, the fibres in its central portion are unchanged 

 and show through the more transparent parts, obscuring the 



