The Nature of the Tectorial Membrane 129 



figures seem rather low when compared with the 74 microns obtained 

 here for the first half-turn of the membrane of the pig. 



The Structure of the Tectorial Membrane. 



Surface marJcings. Since the beginning of its study, the natural 

 tendency has been to divide the membrane into zones. These zones vary 

 in the different descriptions both as to their number and their bound- 

 aries, as is to be expected from the fact that some investigators have 

 dealt wholly with appearances seen in vertical sections of the cochlea, 

 others with the surfaces of isolated pieces of the membrane, and the 

 majority with preparations more or less distorted by the action of 

 reagents. Gottstein, "72; Coyne and Cannieu, '85; Barth, '89; Dupuis, 

 '94, and others made three zones: (1) The inner zone, comprising the 

 thin, attached strip spreading from the inner edge, at the insertion of 

 the vestibular membrane, and terminating with Huschke's teeth or the 

 edge of the labium vestibulare; (2) the middle or second zone, com- 

 prising the body of the membrane which spreads from Huschke's teeth 

 to the outer, bruskly rounded border; and (3), believing Lowenberg's 

 border plexus to be a part of the membrane, they called this the outer 

 or third zone. 



In 1863, Hensen, examining the surface of the membrane, observed 

 a line running along the middle of the main body, approximately parallel 

 with the edge of the labium vestibulare and apparently constant in 

 occurrence. Later, this line was farther observed by Eetzius and Schwalbe 

 who described it as a transparent, glittering strand on the under surface 

 of the membrane, having the appearance of a hyaline thickening along 

 the middle zone. By both of these investigators it was given the name 

 "Hensen's stripe." This stripe or streak, while it has been reported 

 absent in some animals (the rabbit, for example), has been used as a 

 boundary line by those who have chosen to divide the membrane into 

 three zones, exclusive of Lowenberg's border plexus whether admitted 

 or denied. Divided in this wa}^, the first zone comprises the strip 

 attached upon the labium vestibulare; the second or the middle is the 

 strip between the labium vestibulare and Hensen's stripe, while the third 

 or outer zone comprises the balance of the width from Hensen's stripe 

 and including the outer edge of the membrane. Most of the more 

 recent papers divide the membrane into zones in this way, though some, 

 for example, Eickenbacher, '01, divide it into two zones: an inner, as 



