OF THE SWORDFISH. 
117 
from the whole surface of the cornea, with which it appears 
to be connected by cellular substance. But, by the same 
treatment, the cornea can as easily be separated into many 
layers, as into the two formed by tearing off the conjunc- 
tiva. The cornea is very thin, compact, and of equal thick- 
ness throughout ; it is lodged in a small groove of the os- 
seous plate ; but, at the nasal side of the eye, it passes a 
little over the inclined margin of that plate. The outer 
layer of the sclerotic coat consists of strong white shining 
tendinous fibres, forming a compact membrane, which ad- 
heres firmly to the whole outer surface of the osseous plate. 
The fibres of the outer covering of the optic nerve, which 
is considered to be a continuation of the dura mater, are 
very distinctly seen to mix and disappear among the 
fibres of the sclerotic, so as to form with it a continuous 
membrane. This layer of the sclerotic is connected, 
like the conjunctiva, to the outer margin of the cornea. 
The osseous plate of the sclerotic covers the whole of the 
eyeball, excepting the aperture on the fore part covered by 
the cornea, and a space nearly of the same size on the back 
part of the eye. The irregular round opening on the fore 
part of the plate is 1| inch in diameter, with an inflected 
margin S lines in thickness. The plate is hard, translucent, 
somewhat brittle, of a yellowish-white colour, and strongly 
marked fibrous texture. It is thinnest and most pellucid 
where its diameter is greatest, and it terminates posteriorly 
by a thin and very uneven margin. It does not effervesce 
in nitric acid, like substances containing carbonate of lime, 
and appears to be of a condensed horny texture, containing 
a quantity of oily matter between its fibres. It is divided 
into two equal parts, an upper and a lower, by an uneven 
suture, passing from before backward, or in the direction 
of the axis. The tendinous extremities of the straight and 
oblique muscles of the eye pass through the outer layer of 
