236 



Organ of Hearing. 



Internal 

 fibres of Co 



External Tnterst.oft. Connecting 



fibres.of Corti Membr. retic. -oedicles 



'foramina o.t 

 liabtnt. perfor 



pedicles 



alanyes 



323. The Organ of Corti seen from above. (Diagrammatic.) 



Cells 



External . Cells 



fi bres of Corti ofDeit ers 



Lam.spiral.oss. ganglionar. 



324. The Organ of Corti in Section. (Diagrammatic.) 



The spiral canal is divided by the bony spiral lamina, 

 Lamina spiralis ossea, which projects into it from the modiolus, into two 

 passages ; of these, the lower, Scala tympani, communicates with the 

 tympanum by means of the Fenestra rotunda, while the upper, Scala 

 vestibuli, opens into the Recessus hemispTiaericus vestibuli (Fig. 320). In the 

 Scala tympani, behind the Fenestra rotunda, is the orifice of a small canal, 

 the Aquaeductus ad cocldeam. The osseous spiral lamina ends at the last 

 half turn in a h o o k - 1 i k e process, Hamulus, turned towards the Scyphus 

 (Fig. 320); it reaches only about half way towards the outer wall of 

 the spiral canal ; the two Scalae are closed by means of a membrane, 

 the Lamina spiralis mcmbranacea. Between the two layers of this membrane 

 is a canal, the Scala media s. canalis cochleae; upon that layer which lies 

 in the plane of the osseous spiral lamina, usually called the Membrana 

 basilaris, the Organ of Corti lies. The Lamina spiralis membranacea 

 reaches in the cupola of the cochlea beyond the Hamulus and surrounds an 

 opening, Helicotrema Bresclieti, by means of which Scala vestibuli and Scala 

 tympani communicate with each other. 



