THE SENSE OF HEARING. 



819 



small crystals, otoliths or otoconia, composed chiefly of carbonate of lime. Oto- 

 conia are also found less constantly in the ampullae and even in the peri- 

 lymph space of the cochlea. In fishes there are large masses of calcareous 

 matter, otoliths, attached to the wall of the auditory sac. 



General Anatomy of the Cochlea. By far the most complex structure of 

 the ear is found in the cochlea (PL 2, Figs. 1, 3, 4 ; Figs. 275-278). The bony 

 cochlea continues from the anterior wall of the vestibule, and in the upright posi- 

 tion of the head the axis of the modiolus is nearly horizontal, pointing, from base 





FIG. 280. Diagram of a transverse section of a whorl of the cochlea (after Foster) : Sc, V, scala vestib- 

 uli; Sc.T, scala tympani; C.Chi, canalis cochlearis; Lam.sp, lamina spiralis; Gg.sp, ganglion spirale; 

 n.aud, auditory nerve ; m.R, membrane of Reissner ; Str.v, stria vascularis ; Lg.sp, ligamentum spirale ; 

 t.l, lymphatic epithelioid lining of basilar membrane on the tympanic side ; m.b, basilar membrane ; 

 Org.C, organ of Corti; L.t, labium tympanicum; Ib, limbus ; L.v, labium vestibulare; m.t, tectorial 

 membrane. 



to apex, outward and slightly down and forward, the base of the cochlea being 

 formed by the inner surface of the petrous bone. The membranous cochlea, 

 canalis or ductus cochlearis, is a tube of nearly triangular cross-section which 

 'winds round the modiolus from base to apex (Fig. 280). The base or outer side 



