204 



COMPARATIVE ANATOMY. 



is 



opposite wall (Figs. 168, Lso, Lso 1 , and 169, Lo, Lei 1 }. This 

 continued outwards by two laterally-diverging lamellae (Fig. 169, B, 

 .R), mentioned above as the membrana basilaris and mem- 

 brana Reissneri; these lie at an angle to one another and 

 correspond to the inner walls of the membranous cochlea. The outer 

 wall of the latter is completed by a portion of the peripheral part 

 of the bony cochlea (the region between Ls and the peripheral end 

 of R in Fig. 169). The membranous cochlea, which thus appears 



FIG. 168. BONY COCHLEA OF MAN. (After A. Ecker.) 



A, axis ; Lso, Lso 1 , lamina spiralis ossea, the free edge of which, perforated by the 

 fibres of the auditory nerve, is visible at t ; H, hamulus. 



FIG. 169. DIAGRAMMATIC TRANSVERSE SECTION OF THE COCHLEA OF A 



MAMMAL. 



KS, bony cochlea ; Lo, Lo 1 , the two layers of the lamina spiralis ossea, between which 

 at JV" the auditory nerve (together with the ganglion, left of L) is seen ; L, 

 limbus laminae spiralis ; B, membrana basilaris, on which the neuro-epithelium 

 lies ; B, Reissner's membrane ; tiv, scala vestibula ; St, scala tympani ; Sin, 

 scala media (membranous cochlea) ; 0, membrane of Corti ; Ls, ligamentum 

 spirale. 



approximately triangular in transverse section, is called the ductus 

 cochlearis or scala media. It is apparent that the scala media 

 does not by any means fill up the lumen of the bony cochlea, but 

 that a cavity is left on either side of it, corresponding to those we 

 have already met with in the auditory organ of Birds, and known 

 as the scala vestibuli and scala tympani (Fig. 169, Sv, St}. 



Both of these are continuous with the cavum perilymphaticum, 

 and, following the direction of the scala media, open into one another 



