VOL. LXVni.] PHILOSOPHICAL TRANSACTIOXS. 425 



pulling in opposite directions, though both upwardly, at the same time that the 

 lower pinions are kept down by the muscles on the anterior, by those on the 

 posterior and inferior part of the scapula ; I say, the effect of the action of these 

 two muscles is, to pull the pinions upward, and at a greater distance from one 

 another, or in other words to expand the wing ; for the joint does not allow of 

 any motion upward, and if it did, it would not in the least influence the size of 

 it. The other muscles that lie on the external, internal, and inferior parts of the 

 scapula ; together with several small ones that run backward, also serve to move the 

 wing backward and forward. This scapula and wing, witli all its apparatus of mus- 

 cles, can be easily divided, except at the superior part, from the muscles that form 

 the fore part of the body of the fish, being only connected by a cellular medium. 



The globe of the eye is large in proportion to the animal ; the pupil large too, 

 and nearly, if not altogether, circular. The cornea is less transparent than in 

 the generality of fishes ; tlie fore part of the globe is a good deal flatted, as if a 

 segment or portion had been cut off, for so small a part of the aqueous humour 

 is contained between the cornea and iris, which is of a silver colour, that they 

 are nearly in contact. The optic nerve, though at its egress from the skull it is 

 united by a common external membrane with that of the other eye, does not 

 seem blended with it ; this nerve, which is very large, pierces the external coat 

 on the bottom of the ball, but not in the centre ; it enters on the side of the 

 axis next the fish's body. The external tunic into which the muscles are imme- 

 diately inserted, and which gives strength and figure to the whole, is very firm, 

 tough, and almost horny: when the eye is boiled, it seems to have a continua- 

 tion of fibres, and indeed is of the same colour with the septum of the eye or 

 iris, the cornea separating readily from it, and having then the appearance of the 

 small segment of a great circle or globe, applied to the great segment or side of 

 a much smaller one. All the bottom of the ball is covered with this strong 

 membrane, except in the posterior part, where it becomes abruptly much thinner, 

 more pliant, and of a shape nearly resembling the space left by the union of 4 

 circles, or a kind of square with its sides bent inward ; in the centre of this the 

 optic nerve enters, close to the side of which an opening, like a pin-hole, ap- 

 pears, through which I imagine a small artery passes. The crystalline humour, 

 both in the recent and boiled subject, is entirely spherical ; in one it had the ap- 

 pearance of bottle glass; in the other it was bright as crystal. When boiled it 

 seemed to be attached to the vitreous humour, which was not then coagulated ; 

 it had an oblong blackish substance fixed to it, like the fragment of a blood 

 vessel, which I could with difficulty separate. 



In the fresh fish, the bottom of the eye, except where the optic nerve 

 entered like a small elevated white speck, was laid over with a downy pearl- 



VOL. XIV. 3 I 



