The Nature of the Tectorial Membrane 147 



in the width of the tectorial membrane proper occurs chiefly in the 

 decrease in the width of the zone or strip on the outer side of Hensen's 

 stripe. The decrease in the width of the accessory membrane is rela- 

 tively much more gradual than that of this zone under which it lies. 

 At its greatest width, in the apical turn (Figs. 1 and 2), its outer 

 edge is considerably within the outer edge of the tectorial membrane 

 jjroper, but its decrease is so much more gradual that by the time the 

 seventh half-turn is reached, the outer edges of the two membranes 

 coincide (Figs. 1 to 5). Also, at the apical end, its inner edge extends 

 not quite to Hensen's stripe, but below, this edge comes to coincide with 

 Hensen's stripe, and, at the basal end, the tips of its fibers may occa- 

 sionally overlap the stripe. If Hensen's stripe coincides throughout 

 with the line of the enclasped phalanges of the rods of Corti, then the 

 accessory membrane can only come in contact with the hairs of the 

 outer series of the hair cells. 



Of the illustrations given of transverse sections. Fig. 7 alone shows 

 a structure whose position warrants its being interpreted as a section 

 of the accessory membrane. The structure is naturally attacked severely 

 by the reagents, being very thin and fragile, and distortion renders it 

 unrecognizable and often invisible in sections. One unaware of its 

 existence would never discover it in even the best of sections. 



Some of the observations recorded in the literature of the tectorial 

 membrane may refer to this accessory membrane. It is somewhat prob- 

 able that the irregular, transparent, reticular fringe described by Lowen- 

 berg, '64, as existing along the outer edge, and since referred to by 

 some as "Lowenberg's border plexus" and by others as the third or 

 outer zone of the tectorial membrane, may have been nothing more 

 than the displaced outer edge of the accessory membrane projecting 

 irregularly beyond the outer edge of the tectorial membrane proper. 

 Coyne and Cannieu, '85, may have used this in their claim that the 

 tectorial membrane is attached as far over as the cells of Claudius; 

 Dupuis, '94, notes that Lowenberg's border plexus is very irregular and 

 not alwa5rs present; Von Ebner, '02, in Kolliker's Gewebelehre, notes 

 and illustrates it as filamentous; Kishi, '07, considers it an artifact. 

 Hensen, '63; Bottcher, '72; Ferre, '85, and several others since them 

 deny the existence of the border plexus. The latter may have been 

 dealing with more nearly normal conditions. Further, several observers, 

 to be mentioned below, claim filamentous attachments between the under 

 surface of the tectorial membrane and the hairs of the hair cells and 



