No. I.] THE VERTEBRATE EAR. 115 



actual condition of the surface. On this account many ob- 

 servers have described the so-called inner zone of the mem- 

 brana tectoria as homogeneous, glassy in transparency, and 

 consequently of entirely different structure from the outer 

 zone. However, as previously stated, even this inner edge 

 when thus modified by reagents may be seen to be composed 

 of fibres under proper manipulations of light and a sufficient 

 magnifying power, unless it is completely melted down by the 

 reagents. 



The outer edge is thickest, and appears much thicker from 

 the outside than it is in reality. The apparent edge when the 

 band is in place is of course that part of its dorsal surface pre- 

 sented at right angles to the major part of this surface. The 

 actual outer edge is that part of the structure composed of the 

 basal ends of the long hairs, and its thickness equals the dis- 

 tance between the outer edge of the row of outer hair cells and 

 the inner edge of the inner row of hair cells. When broken off 

 from their respective rows the hairs are drawn closer together 

 by capillary attraction, and the other forces at work altering 

 the relations of the structures of the cochlea. 



The two ends of the cochlear hair band are somewhat rounded, 

 since the hairs at the extreme ends of the band are shorter than 

 in any other part of the organ. The reason for this is the re- 

 duction in size and number of the hair cells at the ends of the 

 organ of Corti, and, as we shall have occasion to notice further 

 on, the membrana basilaris itself ends in rounded borders. The 

 hair band is consequently thinner at its ends, and fades out 

 quite suddenly at the limits of the hair-cell rows. 



The individual hairs run entirely free and unsupported for 

 their whole length, and are consequently completely bathed by 

 the endolymph. Their extremely fine tips are specially free 

 and well situated for the reception of the wave motions prop- 

 agated through the endolymph. The space between the hairs 

 is necessarily very small, and although difficult of measurement, 

 I judge them to be less than the diameter of a hair in the mid- 

 dle, more massive part of the band. The hairs as they leave 

 the top of the sensory cells are placed close together on the cell 

 cap, but not always do they enter the cell cap with perfect 

 regularity, which often appears concave from without inwards, 

 though in many preparations the cap seems to be a simple plate 



