129 THE ORGANS OF SENSE. , | 
than the inner, especially in the upper part of the cochlea. They are more inclined | 
towards the membrana basilaris, and form with it an angle of about 40°. The head of each 
is convex internally, to fit the concavity on the head of) the inner rod, and is prolonged 
Outer rod of Corti 
Inner rod of Corti 
(Inner hair cel 
Outer hair cells 
Hensen’s stripe Cells of Hensen 
Membrana tectoria 
Sulcus spiralis 
Limbus lamin J2ternus 
spiralis | 
| 
Membrana basilaris 
Cells of Claudius 
| 
| 
z a 
Sj nh 
FA = 
= ~ 
"3 = 
) oO 
iS ra 
S. z 
a) | =) 
n = 
g | ; 
3 Inner spiral | Cells of Deiters 
= fasciculus 
‘a Vas spirale | Space of Nuel 
Tunnel of Corti 
Fic. 528.—TRANSVERSE SECTION OF Cortr’s ORGAN FROM THE CENTRAL COIL OF COCHLEA (Retzius). 
outwards as a plate, the phalangeal process, which becomes connected with the lamina 
reticularis. In the head is an oval body which has an athnity for certain reagents. The 
main part of each rod consists of a nearly homogeneous material, which is finely striated. 
At the base of each, on its tunnel side, is anucleated mass of protoplasm which reaches as 
far as the heads of the rods, and covers also the greater part of the tunnel floor. This 
may be regarded as the undifferentiated part of the cell from which the rod was developed. 
Slit-like intervals, for the transmission of nerves, exist between the intermediate portions 
of adjacent rods. 
Hair Cells.—These, like Corti’s rods, form two sets, inner and outer. The former 
consists of a single row lying immediately ineeraal to the inner rods—the latter of three, or, 
it may be, four rows placed to the outer side of the external rods. The inner hair cells 
are about 3500 in number, and have a greater diameter than the inner rods, and so each is 
supported by more than one rod. Somewhat oval in shape, their free extremities are sur- 
mounted by about twenty fine hair-like processes, arranged in the form of a crescent, with 
its concavity directed inwards. ‘The deep end of the cell is rounded, and contains a large 
nucleus. It reaches only about half-way down the rod, and in contact with it are the 
arborisations of the nerve terminations. To the inner side of this row of hair cells are two 
or three rows of elongated columnar cells, which act as supporting cells and are continuous 
with the low columnar cells lining the sulcus spiralis internus. The outer hair cells num- 
ber about 12,000, and form three rows in the basal coil and four rows in the upper two 
coils, although in the higher coils the rows are not so regularly arranged. Their rounded 
free extremities support some twenty hairlets arranged in the ‘form of a crescent, opening 
inwards. Their deep extremities reach about half-way to the membrana basilaris, and are 
in contact with the nerve arborisations. 
Alternating with the rows of the outer hair cells are the rows of Deiters’ supporting 
cells, the lower extremities of which are expanded on the membrana basilaris, whilst their 
upper ends are tapered ; the nucleus is placed near the middle of each cell, and, in addi- 
tion, each cell contains a bright, thread-like structure, called the supporting fibre. This 
fibre is attached, by a club-shaped base, to the membrana basilaris, and expands, at the 
free end of the cell, to form a phalangeal process of the membrana reticularis. 
The cells of Hensen, or outer supporting cells, consist of about half a dozen rows, 
immediately outside Deiters’ cells, and form a well-marked elevation on the floor of the 
ductus cochlearis. Their deep extremities are narrow and attached to the membrana 
basilaris, while their free ends are expanded ; each cell contains a distinct nucleus and 
some pigment granules. The columnar cells, situated externally to the cells of Hensen, 
cover the outer part of the zona pectinata, and are named the cells of Claudius. <A space, 
the space of Nuel, exists between the outer rods of Corti and the neighbouring row of hair 
cells. It communicates internally with Corti’s tunnel, and extends outwards between the 
outer hair cells as far as Hensen’s cells. 
