F MEMBRANOUS LABYRINTH. 721 
membrana basilaris. The upper surface of the labium vestibulare presents a num- 
ber of furrows crossing each other, nearly at right angles, and intersecting a series 
of elevations which, at the free margin of the labium, form a row of tooth-lke 
structures, some 7000 in number, the 
auditory teeth of Huschke. Covering the 
limbus is a layer of apparently squamous 
epithelium; the deeper vrotoplasmic a 
portions of the cells, however, with their 
contained nuclei, fill up the intervals 
between the elevations and auditory 
teeth, and are continuous with the cells 
lining the sulcus spiralis internus. 
Membrana Basilaris.—The inner 
part of this membrane is thin, and sup- 4 
ports the organ of Corti; it is named the 
zona arcuata, and reaches as far as the 
footplate of the outer rod of Corti. Its 
outer part, extending froin the footplate 
of the outer rod of Corti to the crista 
basilaris,is thicker and distinctly striated, : 
and is termed the zona pectinata. The a 
substantia propria of the membrane is 
almost homogeneous, but exhibits, in its 
deeper part, numerous fibres. These 
fibres are most distinct in the zona a 
pectinata, and number, according to 
Retzius, about 24,000. Covering the 
under surface of the membrana, basilaris 
is a layer of connective tissue, which 
contains, in its inner part, small blood- 
vessels, one of which, larger than the rest, 
lies below the tunnel of Corti and is 
named the vas spirale. The width of 
‘the membrana basilaris increases from 
210 in the basil coil to 560» in the 
apical coil. 
— ( Juter attachment of 
Reissner’s membrane 
——Stria vascularis 
Bony wall of cochlea 
—— Ligamentum spirale 
Vas prominens 
r= Sulcus spiralis 
externus 
Cells of Claudius 
— Crista 
basilaris 
Organ of Corti (Hig. 528).—Placed 
upon the inner portion of the membrana 
basilaris, the organ of Corti consists of an 
epithelial eminence which extends along the. sie bon meanevmtee SucrioN amnoueetUnmee 
entire length of the ductus cochlearis and Watt or Ductus CocHLEarts (Schwalbe). 
comprises the following structures, viz. : 
(1) Corti’s rods or pillars, (2) hair cells (inner and outer), (3) supporting cells of Deiters, 
(4) the cells of Hensen and Claudius, (5) the lamina reticularis, and (6) a cuticular 
membrane, the membrana tectoria. 
The rods of Corti form two rows, inner and outer, of stiff, pillar-like structures, and 
each rod presents a base or footplate, an intermediate elongated portion, and an upper end 
or head. The bases of the two rows are planted on the membrana basilaris, some little 
distance apart. The intermediate portions incline towards each other and the heads come 
into contact, so that, between the two rows above and the membrana basilaris below, there 
is enclosed a triangular tunnel, the tunnel of Corti; this tunnel increases both in height 
and width on passing towards the apex of the cochlea., The inner rods number nearly 
6000, and the head of each resembles somewhat the upper end of the ulna, presenting a 
deep concavity, externally, for the reception of a corresponding convexity on the head of 
the outer rod. The part of the head which overhangs this concavity is prolonged out- 
wards, under the name of the head plate, and overlaps the head of the outer rod. The 
expanded bases of the imer rods are situated on the innermost portion of the membrana 
basilaris, immediately to the outer side of the foramina nervosa of the labium tympanicum. 
The intermediate parts of the inner rods are sinuously curved, and form, with the mem- 
brana basilaris, an angele of about 60°. The outer rods number about 4000, and are longer 
46 
