758 SPECIAL SENSES. 



1. The portion below the bony and membranous septum, called the scala 

 tympani. This is formed by the periosteum lining the corresponding por- 

 tion of the cochlea and the under surface of the bony lamina, and the mem- 

 brana basilaris. 



2. The scali vestibuli. This is formed by the periosteum lining the cor- 



Fio. 271. Section of the first turn of the spiral canal of a cat newly-born. Section of the cochlea of a 

 human foetus at the fourth month. From a photograph, and somewhat reduced (Rudinger). 



Upper figure : 1, 2, 6, lamina spiralis ; 2, lower plate ; 3, 4, 5. 5, nervus cochlearis : 7. membrane of 

 Reissner ; 8, membrana 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; 17, 18, 19, liga- 

 mentum spirale ; 20, spiral canal, below the membrana basilaris. 



Lower figure : S T, S T, 5, 5, 7, 7, 8, 8, scala tympani ; S V, S V, 9. 9, scala vestibuli ; 1, base of the coch- 

 lea ; 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 laminae spiralis ; 15, membrane of Reissner ; 

 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. 



responding 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, 



