TEE AUDITORY APPARATUS. 



SO that its centre nearly corresponds to the inner wall of the tympanum. A 

 partition — the lamina spiralis, spiral like the cavity — divides it into two distinct 

 sections, or scales — a superior and inferior. This partition is attached by its inner 

 border to the central axis of the cochlea, but is free at its external margin, whick 

 does not quite reach the periphery of the cavity. The two scalse, therefore^ 



Fig. 512. 



SECTION THROUGH ONE OF THE COILS OF THE 

 COCHLEA. 



ST, Scala tympani ; SV, scala vestibuli ; CC, canalis 

 cochleae ; membrana of Reissner ; lis to Isp, lamina 

 spiralis membi-anacea; Us, limbus laminae spiralis; 

 ss, sulcus spiralis ; gs, ganglion spirale situated 

 on nc, the nervous cochlearis indicated by the 

 black line ; Iso, lamina spiralis ossea ; t, mem- 

 brana tectoria; 6, membrana basilaris ; Co, organ 

 of Corti; Isp, ligamentum spirale; Cc, cells of 

 Claudius. 1, Rod of Coiti of the first order ; 2, 

 rod of Corti of the second order. 



communicate, in the skeleton, by means of an 

 opening (the helico-trema) that follows the free 

 border of the lamina spiralis throughout its 

 extent. 



The inferior scala (or scala vestibuli) enters 

 the vestibule ; the commencement of the 

 superior scale, or scala tympani, is formed by 

 the fenestra rotunda {fenestra cochleae), which 

 brings it into communication with the middle 

 ear, without the presence of a membrane ex- 

 actly closing that aperture. 



Fig. 513. 



SECTION OF THE COCHLEA PARALLEL T0» 

 ITS AXIS, THROUGH THE CENTRE OP- 

 THE MODIOLUS. 



1, Modiolus ; 2, infundibulum in which 

 the modiolus terminates ; 3, 3, coch- 

 lear nerve, sending its filaments 

 through the centre of the modiolus ; 

 4, 4, scala tympani of the first turoi 

 of the cochlea ; 5, 5, scala vestibuli 

 of the first turn; the septum between 

 4 and 5 is the lamina spiralis; a. 

 filament of the cochlear nerve is 

 seen passing between the layers of 

 the lamina to be distributed in thfr 

 membrane investing the lamina ; 8, 

 loops formed by the filaments of the 

 cochlear nerve on the lamina spiralis;. 

 9, 9, scala tympani of the second 

 turn of the cochlea ; 10, 10, scala 

 vestibuli of the second turn ; the- 

 septum is the lamina spiralis; 11, 

 the remaining half turn of the scala. 

 vestibuli ; tlie dome above is the- 

 cupola, the line passing thi-ough it 

 leads to the remaining half turn of 

 the scala tympani. The osseous 

 lamina forming the floor of the scala 

 vestibuli curves spirally round to- 

 constitute the infundibulum, 2; 14, 

 the helicotrema through which a 

 bristle is passed ; its lower extremity 

 issues from the scala tympani of the- 

 middle turn of the cochlea. 



The Membranous Labyrinth. 



The membranous labyrinth comprises three parts, corresponding to the threfr 

 cavities of the osseous labyrinth. 1. The vestibule. 2. The semicircular canals. 

 3. The cochlea. 



1. The Membranous Vestibule (Fig. 513). 



This is composed of two sacs with thin, soft walls, lodged in the osseous; 

 labyrinth. The supei'ior is the largest, is oval-shaped, and is named the utriculus ; 

 it communicates with the semicircular canals, of which it is a confluent. The 



