THE INTERNAL EAR 



745 



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

 scala tympani. This is bounded by the periosteum lining the corre- 

 sponding portion of the bony cochlea and the under surface of the bony 

 lamina and by the 



membrana basilaris. 



2. The scala vesti- 

 buli. This is bounded 

 by the periosteum lin- 

 ing the corresponding 

 portion of the bony 

 cochlea and the upper 

 surface of the bony 

 septum and by the 

 membrane of Reissner. 



3. The true mem- 

 branous cochlea. This 

 is the spiral, trian- 

 gular canal, bounded 

 externally by the peri- 

 osteum of the corre- 

 sponding portion of 

 the wall of the coch- 

 lea, internally, by the 

 membrane of Reissner, 

 and on the other side, 

 by the membrana ba- 

 silaris. What is thus 

 called the membra- 

 nous cochlea is divided 

 by the limbus laminae 

 spiralis and the mem- 

 brana tectoria into 

 two portions; a tri- 

 angular canal above 

 (scala media), which 

 is the larger, and the 

 quadrilateral canal be- 

 low, between >the lim- 

 bus and membrana tectoria and the membrana basilaris. The quadri- 

 lateral canal contains the organ of Corti and various complex anatomical 

 structures. The relations of these parts are shown in Fig. 193, but the 

 numbers in the figure are made out with some difficulty. 



Fig. 193. 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 slightly reduced (Riidinger). 



Upper figure: i, 2, 6, lamina spiralis; 2, lower plate; 3, 4, 5, 5, 

 nervus cochlearis; 7, membrane of Reissner; 8, membrana tecto- 

 ria; 9, epithelium; 10, n, pillars of Corti; 12, inner hair-cells; 

 13, outer hair-cells; 14, 16, membrana basilaris; 15, epithelium in 

 the sulcus spiralis ; 17, 18, 19, ligamentum spirale ; 20, spiral canal, 

 below the membrana basilaris. 



Lower figure, 5 T, S T, 5, 5, 7, 7, 8, 8, scala tympani ; S V, S V, 

 9, 9, scala vestibuli ; i, base of the cochlea; 2, apex; 3, 4, central 

 column ; 10, 10, 10, 10, ductus cochlearis ; n, 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 fila- 

 ments; 20, union of the membrana basilaris with the ligamentum 

 spirale ; 21, epithelium of the peripheral wall of the ductus cochlea- 

 ris ; 22, 23, membrana tectoria; 24, spiral canal, below the mem- 

 brana basilaris. 



