no AYERS. [Vol. VI. 



interressant fiir das Verstehen der Boettcher'schen Angaben 

 iiber den Zusammenhang der Membran mit den Haaren der 

 Haarzellen ; 7nit diesen Haaven hat die Membran tind ihre Fas- 

 em nichts zu thimy — II, p. 305, PI. XXII, D, i. 



Barth (1889, 17) describes a homogeneous layer of substance 

 separating the two fibrous layers of the membrana tectoria of 

 the mammalian cochlea. He thinks that this membrane is 

 much more important than usually supposed, and considers that 

 it serves to fix the organ of Corti in its place. 



The membrana tectoria of the mammalian ear has been de- 

 scribed as a more or less gelatinous plate which, owing to its 

 position overhanging the organ, is supposed to act as a damper 

 upon the vibratory action of the sensory hairs. 



The plate is continuous, and of course follows the windings 

 of the cochlear organ. It is said to be firmly fixed (by adhe- 

 sion, Retzius) to the limbus spiralis of the cochlea, and although 

 easily removed from its position, not unfrequently brings away 

 with it some of the pavement epithelium forming the covering 

 of this portion of the limbus. The membrana tectoria has been 

 described by Boettcher alone as possessing attachments to the 

 organ of Corti itself, though more often so figured, and it is 

 usually considered as a subsidiary structure, a mere cuticular 

 secretion of the epithelial ridge known as the organ of Corti. 



In the views which have been restated above, most of the 

 investigators have described the minute structure of the mem- 

 brane as distinctly fibrous, divided by certain inadequately 

 known structural characters into inner and outer zones. There 

 has been more general agreement upon these two points than 

 upon any others. The striations of the body produced by its 

 component fibres are continued, as I find, without hindrance 

 through these zones. The fibrous striation of the organ is 

 drawn outwards, toward the apex of the cochlea, and appears 

 to pass from the inner edge (the so-called fixed edge) outward 

 toward the outer side of the cochlear tube (free edge of the 

 plate). We have been entirely in the dark as to the signifi- 

 cance of this structure, its physiological function not having the 

 least foundation in the actual structure of the organ. What is 

 the phylogenetic origin of the tectorial membrane } This is a 

 question which has proved up to date, under the prevailing 

 views of its physiological importance, an insoluble puzzle. 



