PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 



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2. The scala vestibuli. This is formed by the periosteum lining the corresponding 

 portion of the bony cochlea and the upper surface of the bony septum and is bounded 

 externally by the membrane of Reissner. 



3. The true membranous cochlea. This is the spiral triangular canal, bounded ex- 

 ternally by the periosteum of the corresponding portion of the wall of the cochlea, 



FIG. 266. Section of the first turn of 'the spiral canal of a cat newly-born Section of the cochlea of a human 

 fcctus at the fourth month. From a photograph, and somewhat reduced. (Kiidinger.) 



Upper figure : 1, 2, 6, lamina spiralis ; 2, lower plate ; 8, 4, 5, 5, nervus cochlearis ; 7, membrane of Keissner ; 8, mem- 

 brana tectoria; 9, epithelium ; 10, 11, pillars of Corti; 12, inner hair-cells; 13, outer hair-cells ; 14, 16, membrana 

 basilaris; 15, epithelium in the sulcus spiralis; IT,' 18, 19, ligamentum spirale; 20, spiral canal below the membrana 

 basilaris. 



Lower figure: S T, 8 T, 5, 5, 7, 7, 8, 8, scala tympani ; S V, 8 V, 9, 9, scala vestibuli; 1, base of the cochlea ; 2, apex ; 

 3, 4, central column; 10, 10, 10, 10, ductus cochlearis; 11, branches of the nervus cochlearis; 12,12,12, spiral 

 ganglion; 13, 14, limbus laminse spiralis; 15, membrane of Eeissner; 16, epithelium ; 17, outer hair-cells; 18, 

 epithelium of the membrana basilaris ; 19, nervous filaments ; 20, union of the membrana basilaris with the 

 ligamentum spirale ; 21, epithelium of the peripheral wall of the ductus cochlearis; 22, 23, membrana tectoria ; 

 24, spiral canal below the membrana basilaris. 



internally, by the membrane of Reissner, and, on the other side, by the membrana basi- 

 laris. 1 What we thus call the membranous cochlea is divided by the limbus lamina spi- 

 ralis and the membrana tectoria into two portions ; a triangular canal above, which is the 



1 Some anatomists include this canal in the scala vestibuli. For the sake of clearness, we describe it by itself, as a 

 distinct canal. 



