THE SCALA MEDIA. 



237 



communicates with the middle ear by the fenestra rotunda, 

 closed by the secondary tympanic membrane. 



The scala media (canalis or ductus cochlearis) is the middle 

 passage of the cochlea ; it ends blindly above, and communi- 

 cates below with the saccule by the small canalis reuniens. 



FIG. 93. 



Radial section of portion of cochlea of guinea-pig (Klein), a, scala vestibuli ; 6, 

 scala tympani : c, scala media ; d, rnembrana tectoria ; h, membrane of Reiss- 

 ner ; j, organ of Corti, resting on basilar membrane ; k, stria vascularis ; I, liga- 

 mentum spirale; m, limbus ; n, nerve-fibres in lamina spiralis ; o, spiral gan- 

 glion ; p, nerve-fibres in modiolus ; s, bony wall. 



The upper wall of the scala media, separating it from the 

 scala vestibuli, is formed by the membrane of Reissner, a very 

 thin fibrous membrane lined on the vestibular surface with 

 endothelium, and on the surface within the scala media with 

 simple squamous epithelium. 



