The Nature of the Tectorial jMembrane 131 



and viewed under surface upward, are four only: (1) The fine fibers 

 of which the membrane consists, the prevailing course of which is 

 obliquely transverse and which are embedded in the transparent, colla- 

 genous matrix; (2) the line of impress, the boundar}^ of the zone of 

 attachment, left by the edge of the labium vestibulare; (3) Hensen's 

 stripe, always present, whose variations and significance will be men- 

 tioned below; (-1) a line on the outer zone which, in passing from the 

 apical to the basal end, gradually approaches and comes to coincide 

 with the outer edge of the membrane, and which constitutes the outer 

 edge or back of the accessory tectorial merribrane to be described below, 

 and from which may usually be detected short fibers extending obliquely 

 towards Hensen's stripe. Some of the descriptions for Lowenberg's 

 border plexus, some of the claims of attachment of the outer zone of the 

 tectorial membrane to the cells of the organ of Corti, and some of the 

 descriptions of extra lines on the surface were very probably dealing 

 with this accessory membrane, for it seems to be easily displaced, and, 

 in shrunken preparations, is diminished and distorted beyond recog- 

 nition. 



All the papers dealing with the appearance of detached pieces, seem to 

 agree that the upper surface of the membrane is smooth and more or 

 less evenly convex. Beyond the effect given by the component, obliquely 

 transverse fibers of the membrane, the upper surfaces of my preparations 

 showed no markings that could not 1)e interpreted as due either to 

 injuries from manipulation, adherent debris or coagulum filaments. The 

 highest point in the convexity of this surface remains throughout in 

 about the same relation to the organ of Corti. 



The -fibrous structure of the tectorial membrane is very evident in 

 teased preparations, though the .exact internal arrangement of the fibers 

 is somewhat difficult to determine. As mentioned above, the fibers are 

 imbedded, or distributed throughout, in a transparent matrix, seemingly 

 having the character of a glutinous or collagenous semi-solid. It is the 

 nature of this matrix that allows of that most remarkable flexibility 

 and sensitiveness possessed by the membrane and probably determines 

 its low specific gravity. The matrix is stiffened Init slightly by fixing 

 agents, shrinks severely in dehydration and stain tests indicate that it 

 is not of a mucous nature. It is due to its shrinkage that the membrane 

 so often appears in sections as an irregularly shaped, deeply staining, 

 amorphous mass lying in various positions above the organ of Corti, and 

 it is with this appearance the investigators have had frequently to deal. 



