OKGAN OF CORTI. 



119 



the cochlea externally, is much thickened by a development of re ti form, connective 

 tissue, and is covered by the epithelium of that tube, which here forms .a single layer 

 of columnar cells, which contain pigment, and are prolonged by forked or arborescent 

 processes into the subjacent connective tissue. There is usually a slight inward 

 projection a little above the spiral ligament, containing a prominent blood-vessel 

 (figs. 131, 135). In the tract between this prominence and the membrane of 

 lleissner, the substance of the periosteum is also frequently pigmented, and from 

 containing large and numerous blood-vessels, the capillary loops of which may even 

 project between the bases of the epithelium-cells, is termed stria vascularis. Imme- 

 diately beneath the epithelium of the outer wall is a basement membrane, through 

 which, in section, the cell-processes above mentioned may be seen passing from the 

 epithelium into the subjacent connective tissue. 



The spiral ligament (fig. 131 l.sp., fig. 135) appears in section as a triangular 

 prominence attached to the outer wall of the cochlea, with the basilar membrane 

 prolonged from its apex. It is composed of a retiform connective tissue, many of 

 the cells of which have an elongated shape and radiate from the point of attachment 

 of the basilar membrane. They have been considered by some to be muscular, but 

 there is no distinct proof of their contractile nature. 



Organ of Corti. The epithelium which covers the basilar membrane includes 



limbus 



membrana tectoria 



outer hair-cells 



.- : 

 



:<&> 



nerve fibres 



inner rod vas 

 spimh 



basilar 

 membrane 



outer cells of Deilers 

 rod 



Fig. 136. SECTION THROUGH THE ORGAN OP CORTI OF THE MIDDLE TURN OP THE HUMAN COCHLEA. 



(G. Retzius.) Highly magnified. 



the highly-specialised structures which are known by the name of the organ of 

 Corti (fig. 136). The central part of this apparatus is formed by two sets of stiff, 

 rod-like bodies the inner and outer rods of Corti (fig. 132) which stand upon the 

 basilar membrane, the outer series (e.r.), at some little distance from the inner (i.r.), 

 and are inclined towards each other, coming in contact above. In this way each 

 pair of rods forms a pointed arch with slanting sides (fig. 137), and since the rods 

 of each series are in lateral juxtaposition, the double row of inclined columns forms 

 a tunnel (fig. 132) along the whole extent of the cochlear canal. 



On the inner side of the inner series of rods is a row of epithelial cells (fig. 136), 

 which are surmounted by a brush of fine, short, stiff hairlets, and external to the 

 outer rods are three or four successive rows of similar but more elongated cells. 

 These cells are termed respectively the inner and outer hair-celts. The hairlets of 

 the outer hair-cells project through apertures in a curiously formed cuticular mem- 

 brane, termed the reticular lamina (fig. 132, /.r., 140), which covers this part of 



