the flying Fijh. 795 
The optic nerve, though at its egrefs from the fkull 
it is united by a common external membrane with that 
of the other eye, does not feem blended with it; this 
nerve, which is very large, pierces the external coat on 
the bottom of the ball, but not in the center; it enters 
on the fide of the axis next the fifh’s body. The exter- 
nal tunic into which the mufcles are immediately in- 
ferted, and which gives fixength and figure to the whole, 
is very firm, tough, and almoft horny: when the eye is 
boiled, it feems to have a continuation of fibres, and in- 
deed is of the fame colour with the feptum of the eye 
or iris, the cornea feparating readily from it, and having 
then the appearance of the fmall fegment of a great cir- 
cle or globe, applied to the great fegment or fide of a 
much fmaller one. All the bottom of the ball is covered 
with this ftrong membrane, except in the pofterior part, 
where it becomes abruptly much thinner, more pliant, 
and of a fhape nearly refembling the fpace left by the 
union of four circles, or a kind of fquare with its fides 
bent inward ; in the center of this the optic nerve enters, 
clofe to the fide of which an opening, like a pin-hole, 
appears, through which I imagine a fmall artery pafies. 
The cryftalline humour, both in the recent and boiled 
fubjedt, is entirely fpherical; in one it had the appearance 
of bottle glafs ; in the other it was bright as cryftal. 
5 F a When 
