SECT, 



234-] 



THE COCHLEA. 



5 8 9 



.§ 234. Cochlea. — The canal of the cochlea, filled with the fluid 

 of the labyrinth, contains not only the two well-known spiral 

 cavities, but also a third narrower space, which I propose to call 

 the scala media, situated in great measure within the lamina 

 spiralis. This is placed between the lamina spiralis membranacea 

 or basilar membrana of Claudius, on the one hand, and a peculiar 

 second lamina, which should be named the membrana Cortii, on 

 the other hand. (This structure was first indicated by Corfi, 



though it was not 

 thoroughly under- 

 stood by him). At 

 the beginning of 

 the scala media in 

 the vestibule, and 

 at its termination 

 in the cupola of the 

 cochlea, its relations 

 are not yet well 

 understood. The 

 scalos vestibuli and 

 tympani, apart from 

 the portions of them 

 which adjoin the 

 walls of the scala 

 media, are lined by 

 a periosteum dotted 

 with pigment, which 

 is in all respects con- 

 structed like that of 



Fig. 241. 



Transverse section through the spiral lamella of the first turn of 

 the cochlea. From the ox; magnified 100 diameters. Set. Scala 

 tympani; Sc.v. Scala veslibuli ; Sc.m. Scala media; a. sidcus 

 spiralis ; b. teeth of the first series ; c. membrana Cortii, its 

 thicker part ; d. membrana basilaris ; e. Corti's membrane, its 

 thinner part ; /. tig. spirale ; g. stria vascularis ; k. nervous 

 expansion in the zona ossea ; i. vas spirale internum ; Jc. layer of 

 corpuscles of connective tissue, with varicose processes from them ; 

 I. organ of Corti, only just indicated. — The epithelium is nowhere 

 shown in this figure. 



the vestibule, and is also extended over a part of the lamina 

 spiralis ossea. This periosteum is covered by an epithelium o - oo5'" 

 in thickness, with delicate flat polygonal cells of O'ooy'" to o - ooo/" 

 in diameter, often presenting a little pigment in the lower animals ; 

 and this epithelium extends over those portions of the scalse 

 which adjoin the basilar membrane and the membrana Cortii. — 

 The most important part of the cochlea is the lamina spiralis, 

 taken in its widest sense, as including the membrane of Corti and 

 the scala media. In its osseous zone, it contains anastomosing 

 cam's, with narrow intervals between them; these are for the 

 reception of the cochlear nerves, and unite towards the free border 

 of the lamina to form a fissure-like space, so that here the bony 

 spiral lamina really consists of two plates. The membranous zone 



