No. I.] THE VERTEBRATE EAR. 105 



the reticular membrane, it will allow of our making an hypothe- 

 sis as to its physiological role. It there comes into contact with 

 the rods of Corti's cells ; quite probably the latter are plunged 

 into its mass in a manner similar to the acoustic hairs which 

 in the ampulla are thrust into the otoliths. The membrane of 

 Corti will thus, very properly, annihilate the vibrations com- 

 municated to the acoustic cells (by the fibres of the basilar 

 membrane probably), and thus play with respect to them the 

 role of damper. The membrane itself is not capable of being 

 put into vibration. It is a very poor resonator. 



Embryological researches prove that the membrane of Corti 

 is derived, not from the cells which constitute the embryonic 

 acoustic papilla, but from the epithelium which covers the habe- 

 nula perforata. 



Retzius (1884, 237). In his extended monograph on the verte- 

 brate ear, Retzius describes the membrana tectoria as extend- 

 ing from the insertion of Reissner's membrane to the outer 

 hair cells. It is fixed to the tissue of the spiral blade, from its 

 origin at the root of Reissner's membrane to inner edge of 

 limbus lamina spiralis, but not structurally. This zone (the 

 outer) is very thin, especially its inner border, growing thicker 

 inwards. When the membrane is released from its position, 

 which is readily done, the upper layer of the flat epithel of the 

 limbus often pulls off with it, and gives rise to the polygonal 

 areas or markings so often observed on its under surface. 



Where the membrane leaves the free edge of the limbus it is 

 marked by a fine line. From here it extends freely across the 

 cochlear space, covering over the sulcus spiralis internus and 

 the papilla acustica basilaris quite to its outer border — i.e. to 

 the third row of hair cells — without, however, coming in con- 

 tact with these cells. 



The membrane closes in the relatively narrow space of the 

 sulcus spiralis, which communicates with the other larger endo- 

 lymphatic space only at the outer border of the membrane. 



In this submembranous space the hairs of the auditory cells 

 freely project. Whether they are in any way in contact with 

 the membrane is extremely difficult to determine. In most 

 preparations it appears as if they were not, since the lower sur- 

 face of the membrane stands somewhat above them. In a few 

 cases I saw it resting on the upper surface of the hairs. The 



