752 
MR. A. SANDERS ON THE ANATOMY OF THE 
The third layer consists of granular matter, with closely packed fibres, arranged 
radially so as to give it a smoothly striated appearance. 
The fourth layer has the radial fibres not very closely placed, and the remainder 
of the layer consists of obliquely directed fibres, as in the second layer. 
The fifth layer consists of transverse fibres derived from the crura lobi optici. This 
layer is clearer in colour than the remainder of the tectum, owing to the absence of 
granular matter, and also to the fibres not becoming so readily coloured as the other 
parts of the tectum ; some radial fibres run across this stratum also. 
The sixth layer consists of small cells arranged on branched stems which are pro- 
longed into the radial fibres occurring in the other layers. 
The seventh is a layer of connective tissue of varying thickness in different parts of 
the tectum ; it forms on its external edge a support for the cells of the sixth layer, 
and internally terminates by a single layer of epithelial cells which form a smooth 
surface towards the ventricle of the optic lobe ; this “ ependyma ” forms a support for 
the radiating fibres of the crura lobi optici in their passage from the torus semi- 
circularis to the tectum ; this connective tissue is composed of an inextricable network 
of fibri Use derived from its epithelial layer of cells. 
Stieda (58) makes eight strata in the tectum by the expedient of dividing the 
ependyma into two, making the epithelial layer of cells distinct from the connective 
tissue beneath them ; but as the fibrillse of this layer are derived from the cells, it 
seems scarcely correct to separate them. In other respects his division corresponds 
very closely to mine. 
The cells of the sixth layer are of two different forms : those situated on the inner 
edge which make the terminal enlargement of the radial fibres, and those of the deeper 
part of the stratum which are attached to the sides of the fibres of the first, like 
grapes to their stalk. 
The cells (fig. 18, b.) which make up the inner row of this layer may be described 
as fusiform, oval, or rhomboidal in shape ; they generally show a distinct oval nucleus 
in which also a distinct spot-like nucleolus is visible : they vary in length from O'OIO 
millim. to 0'015 millim., and in width from 0*002 millim. to 0*005 millim. ; the 
nucleus measures in length from 0*004 millim. to 0'005 millim., and from 0*003 
millim. to 0'004 millim. in width; the connective tissue of the seventh layer is 
attached to the inner end of some of the cells, while their outer end j>asses off into a 
fibre which runs radially towards the external surface of the tectum, and probably 
extends as far as the second layer. 
The fibres of these cells have a tendency to run in bundles formed of several united 
together; the bulk of this stratum is made up of cells (fig. 18, c.) of a smaller size 
than those described, and generally more rounded ; these are attached to the fibres of 
the former cells sometimes by a short stalk, and in other cases they are sessile ; they 
usually measure 0‘004 millim. by 0'003 millim., with but slight variation in size. 
There is present in most cases a distinct nucleus, which is generally rounded, but 
