958 



A MANUAL OF PHYSIOLOGY 



contains the organ of Corti, which (Fig. 424) consists of a series of 

 modified epithelial cells planted upon the basilar membrane. The 

 epithelial cells are of three kinds : (i) supporting epithelial cells ; 

 (2) the pillars or rods of Corti, in two series (inner and outer), sloped 

 against each other like the rafters of a roof, and covering in a vault 

 or tunnel which runs along the whole of the scala media from the base 

 to the apex of the cochlea ; (3) . the hair-cells, around which the 

 fibres of the auditory nerve arborize. These last are columnar 

 epithelial cells, surmounted by haiis. They are arranged in several 

 rows, one row lying just internal to the inner line of pillars, and 

 several rows external to the outer line of pillars. Between the outer 



spl 



FIG. 423. VERTICAL SECTION OF THE FIRST TURN OF THE COCHLEA (AFTER 



RETZIUS). 



D.C, canal of cochlea ; tC, tunnel of Corti ; b.m, basilar membrane ; h.i, h.e, 

 internal and external hair-cells ; Mt, membrana tectoria ; s.sp, spiral groove ; 

 str.v, stria vascularis ; sp.l, spiral lamina ; n, fibres of the cochlear nerve ; I, 

 limbus laminae spiralis ; R, Reissner's membrane ; s.v, scala vestibuli ; s.t, scala 

 tympani ; l.sp, spiral ligament. 



hair-cells are supporting cells (cells of Deiters}. A thin membrane, 

 the reticular lamina or membrana reticularis, composed of fiddle- 

 shaped rings or phalanges, covers the hair-cells, and through openings 

 in it the hairs project. A thicker membrane, the membrana tectoria, 

 springing from the edge of the osseous spiral lamina near the attach- 

 ment of Reissner's membrane, forms a kind of canopy over both 

 pillars and hair-cells. The outer wall of the canal of the cochlea is 

 clad by cubical epithelium covering a membrane r^hly supplied 

 with bloodvessels (stria vascularis}. The fact that the hair-cells of 

 Corti's organ are connected with the fibres of the cochlear division 

 of the auditory nerve, and its elaborate structure, suggest that it 

 must play a peculiar part in auditory sensation. Comparative 



