210 



THE EAR 



media is that the auditory nerve, which runs down the modiolus, 

 enters only this scala, passing along the basilar membrane and 

 ending in dendrites among the hair-cells of the organ of Corti. 

 This structure is a development of the epithelium lining the tube. 

 It is set on the basilar membrane at its junction with the limbus 

 laminae spiralis, and consists of four essential elements. (1) 

 Certain columnar cells with short stiff hair-like processes pro- 

 jecting from their free border, the hair cells, to which pass, as we 



FIG. 45. Vertical section of the first turn of the human cochlea ((?, Retzius). 



s.v, scala vestibuli ; s.t, scala tympani ; D.C, scala media ; sp.l, spiral lamina ; 

 n, nerve fibres ; l.sp, spiral ligament ; str.v, stria vascularis ; m.t, membrana tectoria ; 

 b.m., busilar membrane ; h.i, and h.e, internal and external hair cells ; R, section of 

 Reissner's membrane ; t.C, tunnel of Cortl ; I, limbus laminae spiralis. 



have just said, branches of the cochlear nerve ; (2) elongated 

 strengthening cells between the hair cells, cells of Deiters, the 

 peripheral processes of which join together to form a network 

 through which the hair-cells project (membrana reticularis) ; (3) 

 stiff short fibres set one against another in the form of an arch ; 

 and (4) an exceedingly delicate membrane attached to the upper 

 surface of the spiral lamina, and lying over or fixed to both the 

 outer and the inner walls of Corti's organ. 



The arch of Corti, which lies just outside the single row of inner 

 hair cells, is composed of a row of inner " rods," shaped like ulnar 

 bones, attached by their terminal end to the basilar membrane, and 



