206 



COMPARATIVE ANATOMY. 



HISTOLOGY OF THE MAMMALIAN COCHLEA. 



Tin.- filuvs df the auditory nerve running along the axis of the bony cochlea 



extend in their murse laterally outwards, and come to lie between the two 



plates of the lamina spiralis ossea (Fig. 168, Lso, Ls<> 1 , Figs. 169, 170, JV, 



between L and /."' . On the free border of the latter, these pass out, and 



k up into terminal iibrilhe on the inner surface of the basilar membrane 



I . ITo. .V, .V. .V-',. 





| 

 1 g . ; 



Lo 







Lo 1 



FIG. 170. THE ORGAN OF CORTI. 



(After Lavdowsky.) 



Lo, Lo 1 , the t\vo plates of the lamina spiralis ossea ; N, auditory nerve with ganglion ; 

 N 1 , N' 2 , the nerve branching up into fibrillne and passing to the auditory cells 

 (G,G) ; Ba, Ba, bacilli, or supporting cells ; Mz, niembrana reticularis ; C, mem- 

 braue of Corti ; Ls, ligaim-ntum spirals, passing into the basilar membrane ; 

 >'/, seala media ; K, membrane of Reissner ; B, B, basilar membrane. 



The fibrillfc extend to the sensory or auditory cells (G, G), and these are 

 * in a frame between the firm supporting and isolating cells or 

 bacilli (Ba, Bo}. From the surface of the bacilli a resistant net-like mem- 

 brane iii'-nibraiia reticiilaris; extend- laterally, and through the. meshes of the 

 latter the hairs of the auditory cells project (Fig. 170, ;!/;). The number of 

 lie- outer hair-cells may be estimated at about 12,000. The auditory cells 

 are covered by a thick and firm membrane the niembrana tectoria s. Corti 

 (Tig. 170, C) which probably arts as a damper, and which arises from the 

 labium ve-tibulare ,,f the lamina spiralis ossea. The whole extent of the basilar 

 membrane mn-ists of clear thread-like and very elastic fibres, of which about 

 in,oO< to 2<>,000 can be made out in Man. These are capable of vibrating 

 freely, and, as their length varies definitely in different regions of the cochlea, 

 they might lie looked upon (were it, not that they are absent from Kirds) as 

 forming a sorl of ke\!n.ard or harp, that is, as a definite apparatus of strings 

 rapable of analysing the dilferent waves of sound, the vibrations of which are 

 communicated to tip- auditory cells, and t hener by means of the nerves to 

 the brain. 



