No. I.] THE VERTEBRATE EAR. 113 



hairs, appears very often in microscopic preparations under a 

 low power to be homogeneous and glassy, but I have not yet 

 seen a hair band whose inner edge was not resolvable into 

 striation (the hairs) under adequate magnifying power. The 

 densest part of the membrane is near the middle of its trans- 

 verse section, and this coincides with the line of inner hair 

 cells. The thickest part of the membrane is at the same time 

 the most open, owing to the fact that it includes the origin of 

 the hairs from all the sensory cells of Corti's organ, and of 

 course the relatively large interspaces between the cell tops 

 project up into the hair band, though continually narrowing 

 until they fade out near the middle of the band. The band 

 rises from the cochlear hair cells and with a gentle and graceful 

 curve sweeps upwards and inwards, when, after reaching the 

 height of its course, it slopes down to near the junction of the 

 membrane of Reissner with the floor of the cochlear tube, where 

 it ends. It declines on its inner face more gradually than it 

 rises on its outer face. During life it is not attached to the 

 limbus spiralis, as has been commonly believed, and, although I 

 cannot say positively that it does not come in contact with this 

 surface ever during life, I am sure that for the most part the 

 hairs end free in the endolymph. The hair ends are to be seen 

 on the surface of the band all along its course beyond the outer 

 two-thirds of its breadth, projecting slightly above the surface 

 of the band. 



The band is composed of five (more or less) rows of bundles 

 of hairs. Each bundle is the product of a single cell. The 

 bundles remain distinct for a short part of their course, then 

 apparently soon merging into a common structure. The spaces 

 between the rows are greater than the spaces between the cells 

 of the same row in the inner row of hair cells and the first row 

 and, for the most part, the second row of outer hair cells, but 

 often in the third and fourth rows of outer hair cells the inter- 

 spaces between the neighboring cells of the same row are quite 

 as great as the space between the rows. This circumstance 

 renders the structure of this zone of the hair band looser and 

 more irregular than the first-mentioned zones (PI. XII). 



The weakest part of the hair band is along the line of inser- 

 tion of the hairs into the hair-cell caps, more strictly their 

 origin therefrom. This condition is due mainly to the isolation 



