The Xature of the Tectorial Membrane 135 



Tflider surface; (3) most of those on the inner side of Hensen's stripe 

 curve from tlie inner zone, first slightly outwards, then sharply down- 

 wards, and finally inwards to contribute to the striation of the under 

 surface, thus following an S-shaped course. Apparently, these two gen- 

 eral directions would result in a midregion either free from fibers, or, 

 in which the general direction would be neither the one nor the other; 

 but, in the sections, the transitions of curvature seem to be so gradual 

 that this region is never definitely marked. Further, the two directions 

 should result in a zone of the under surface in which the ends of the 

 fibers from the two directions intercross. The sections show this inter- 

 crossing, and that, while it occurs to some extent in the body of the 

 membrane, the greater part of it, as to be expected, occurs in the imme- 

 diate under surface, and by no means all in one line (see Fig. 7). 



The cut ends of the segments of the membrane represented in Figs. 

 2, 3, i and 5 were, of course, not possessed by those segments, but were 

 outlined upon them and the arrangement of the fillers drawn in accord- 

 ance M-ith the arrangement apparent from the study of the sections, in 

 order to illustrate the relation between tlie fibers of the upper and under 

 surfaces. The intercrossing of the ends of the fibers in the under surface 

 is seldom apparent in the ordinary sections because such sections are 

 usually more shrunlvcn than those represented in Figs. 6, 7 and 8, and the 

 intercrossing, and indeed the whole parallel arrangement, is involved 

 in the more deeply staining peripheral condensation of the substance 

 produced by the reagents. In Fig. 7, Pc, for some reason or other 

 during the manipulation, probably in the sectioning, this peripheral 

 condensation seems to have partially peeled off from the under surface 

 of the inner side of the membrane and the strip to have become stuck to 

 the inner supporting cells of the organ of Corti. 



Looking down upon and into the under surface of the freed mem- 

 brane, with the compound microscope and with transmitted light, this 

 surface, and all focal planes near it, appear studded with numerous fine 

 dots which manipulation of the focus shows to be the ends of fibers. 

 These ends are most numerous in and along either side of Hensen's 

 stripe. 



Hensen's stripe, or streak, in my preparations has a structure, and, 

 I think, a significance. Hensen, who discovered it, and Eetzius and 

 Schwalbe, who named it and described it as a hyaline, transparent 

 strand on the under surface of the "middle zone," probably had to do 

 with preparations shrunken at the periphery at least. Transparent 



