214 STRUCTURE OF THE COCHLEA. [BOOK in. 



the tympanic lip, beneath what we shall speak of as the " tunnel " 

 of the organ of Corti, a blood vessel, lyinx apparently in the midst 

 of the epithelioid cells, may be traced for some distance up tin- 

 spiral; this ras spirale as it is called, serves to secure the due 

 nourishment of the important structures lying over it. 



832. On the side of the basilar membrane which looks 

 towards the canalis cochlearis, the epithelium of the canal lies 

 immediately on the membrane or is separated from it by a thin 

 layer of homogeneous ground substance in which here and there 

 a corpuscle may be seen ; and the part of this epithelium which is 

 modified into auditory epithelium is called, as we have said, the 

 organ of Corti. 



At about the middle of the organ of Corti and forming as 

 it were the key-stone of its structure, are the bodies known as 

 the rods of Corti (Figs. 179 i.r.,o.r., 180 B, B'), peculiarly modified 

 epithelial cells, arranged along the length of the spiral in two 

 rows, an inner row and an outer row. Each cell in each row has 

 become, in large part, converted into a curved rod of peculiar 

 shape, inclined at an angle to the basilar membrane in such a 

 way that the inner rods and the outer rods lean against each 

 other, their upper parts or " heads " being in contact, but their 

 lower parts, or " feet," which rest on the basilar membrane, being 

 wide apart; hence they with a strip of the basilar membrane 

 lying between their feet, enclose a space, triangular in vertical 

 section, forming along the length of the spiral the " tunnel " 

 spoken of above (Fig. 179). 



On the inner or median side of the row of inner rods, lies a 

 single row of epithelial cells bearing hairs, the inner hair-cells, 

 seen in vertical section as a single cell (Fig. 179 i.h.c.). At the 

 base of the inner hair-cells lies a group of nuclei (%.c.) not 

 unlike those forming the nuclear layer of a crista or macula; 

 and just below these, the fibres of the auditory nerve pierce, 

 as we shall see in detail presently, the tympanic lip in order 

 to make connections with the epithelial organ of Corti. Next 

 to the inner hair-cells, to the inner side, comes a row of tall 

 columnar epithelium cells (seen in vertical section of course as 

 a single cell) ; and this row is succeeded in the direction of the 

 spiral groove, by other rows of cells diminishing in altitude until 

 in the groove itself they thin away altogether leaving bare of 

 epithelium the auditory teeth which, as we have said, overhang 

 the groove. 



To the outside of the row of outer rods come four (or in certain 

 parts of the spiral three or five) rows of complicated cells, which 

 we may for the present speak of as outer hair-cells (Fig. 1 79 o.h.c.). 

 These are succeeded outwards by a group of tall columnar or 

 conical cells, of simple character, massed together in a group 

 forming a hump to the outside of the outer hair-cells. These, 

 which are called " Hensen's cells " (H.c.), are in turn succeeded 



