792 



HEARING 



[CH. LVI. 



into two spiral staircases or scaled, the scala tympani and scala 

 vestibuli (fig. 493). The scala vestibuli is separated from the 



tympanum by the membrane of the 

 fenestra ovalis, and the scali tympani is 

 similarly separated from the tympanum 

 by the membrane of the fenestra rotunda. 



.E. 



C.R. 



FIG. 492. Diagram of the right mem- 

 branous labyrinth. U, utricle, into 

 which the three semicircular canals 

 open ; S, saccule, communicating 

 with the cochlea (C) by C.R., the 

 canalis reunions, and with the utricle 

 by a canal having on it an enlarge- 

 ment, the saccus endolymphaticua 

 (S.B.). The black shading repre- 

 sents the places of termination of 

 the auditory nerve, namely, in the 

 maculae of the utricle and saccule ; 

 the cristae in the ampullary ends of 

 the three semicircular canals ; and 

 in the whole length of the canal of 

 the cochlea. (After Schiifer.) 



FIG. 493. View of the osseous cochlea 

 divided through the middle. 1, Central 

 canal of the modiolus ; 2, lamina spiralis 

 ossea ; 3, scala tympani ; 4, scala vesti- 

 buli ; 5, porous substance of the modiolus 

 near one of the sections of the canalis 

 spiralis modioli. f . (Arnold.) 



Both scalse are filled with perilymph. 

 The basilar membrane increases in breadth 

 from the base towards the apex of the 

 cochlea. It contains fibres (about 24,000 

 in all) imbedded in a homogeneous matrix, 

 and running radially, from the spiral lamina to the spiral ligament, 

 where its other end is again attached to the bone. At the 



apex of the cochlea, the 

 lamina ends in a small hamu- 

 lus, the inner and concave 

 part of which being detached 

 from the summit of the 

 modiolus, leaves a small aper- 

 ture named the helicotrema, 

 by which the two scalae, sepa- 

 rated in all the rest of their 

 length, communicate. 



Besides the scala vestibuli 

 and scala tympani, there is 

 a third space between them, 

 called scala media or canal of 



,-i M n -t-i f nn fi <tr\i\ T 

 t/ie COCflUa (GO, tig. 494). In 



qppf-irm if ia fr inn mi lav if a 

 Sectia *S triangular, itS 



external Wall beinef 1 formed 

 ,, ,, , & . . 



by the wall of the cochlea, 

 its upper wall (separating it from the scala vestibuli) by the 



FIG. 494. Section through one of the coils of the cochlea 

 (diagrammatic). ST, scala tympani ; SV, scala vesti- 

 buli ; CC, canalis cochlea or canalis membranaceus ; 

 R, membrane of Reissner ; Iso, lamina spiralis ossea ; 

 Us, limbus laminae spiralis; ss, sulcus spiralis; nc, 

 cochlear nerve; gs, ganglion spirale; t, membrana 

 tectoria (below the membrana tectoria is the lamina 

 reticularis) ; &, membrana basilaris ; Co, rods of Corti ; 

 Isp, ligamentum spirale. (Quain.) 



