OF THE ORNITHORHYNCHUS PLATYPUS. 
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consists of fibres running lengthways, in the direction of the scala ; these fibres have 
spindle-shaped nuclei, which present a rounded appearance like the nuclei of epithelium 
when seen in transverse sections of the cochlea. The next layer, the thickest, is 
more homogeneous in appearance, its component fibres run transversely from the lower 
lip of the marginal sulcus to the ligamentum cochleae with which they blend. The 
upper layer is simply composed of one layer of fine fibres covering the inner part of 
the second layer; these are continuous with the rods of Corti, to be described later. 
The ligamentum cochleae is a large cushion of connective tissue, somewhat triangular 
in section; its inner surface is closely adherent to the wall of the cochlea, and its 
outer one is raised up into two horizontal ridges one above the other. The lower is 
pointed and situated opposite the lower lip of the sulcus; to this ridge the membrana 
basilaris is attached : the upper is rounded off, corresponds and is opposite to the 
upper lip of the sulcus. The grove between may be called the secondary sulcus. 
The connective tissue of the ligament is made up chiefly of fine interlacing fibres, 
but those composing the lower ridge are much coarser and transparent, they radiate 
from the point of attachment of the membrana basilaris. The whole substance of the 
ligament is very vascular. 
The membrane of Reissner is composed of a very delicate basement membrane, 
which is exceedingly difficult to demonstrate, and a layer of cells on each side—those 
on the outer or upper side being the endothelial cells of the scala vestibuli, and those 
on the inner or under side the epithelial cells lining the scala media. These epithelial 
cells are hexagonal in form and arranged in a single layer; they are much thicker than 
the endothelial cells, and have larger nuclei. 
Here and there on the upper surface of the membrane of Reissner are found blood¬ 
vessels, which pass across from the lamina to the ligament, and in certain spots a 
blood-vessel becomes convoluted so as to form an elevated knot (see Plate 46, fig. 7). 
The epithelium lining the Scala Media .—That portion which lines the membrane of 
Reissner has just been described, and if the cells of this layer be traced downwards 
on to the limbus they will be seen to become more rounded in form. At first they 
cover the surface of the limbus, but presently they are seen dipping down into 
the grooves between the teeth of the limbus, getting deeper and deeper, and thus 
entering the marginal sulcus without covering the teeth at all. The cells lining the 
sulcus and outer part of its lower lip are still rounded, but before arriving at the 
point of the lower lip the cells become entirely altered so as to form the organ 
of Corti, which will be described later. On the other side of the organ of Corti the 
epithelium is cuboid, and in this form it lines the inner part of the membrana basilaris 
and the surface of the ligamentum cochleae to a little beyond the upper ridge. From 
this point to the attachment of the membrane of Reissner the epithelium is 
peculiarly modified, and is traversed by numerous blood-vessels which chiefly run 
longitudinally (to the cochlea) ; this is the stria vascularis. 
The shape of these epithelial cells is irregular, somewhat resembling transitional 
