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CHAPTER III. 
Plate III. — the eye or birds and of the eel. 
Fig. 1, 2. The flexible rim , or hoop, of the eye of birds, consist¬ 
ing of bony plates, which occupy the front of the sclerotic; lying 
close together and overlapping each other. These bony plates in 
general form a slightly convex ring, Fig. 1, but in the accipitres 
they form a concave ring, as in Fig. 2, the bony rim of a hawk. 
Fig. 3, 4, 6. Exhibit the marsupium; it arises from the back of 
the eye, proceeding apparently through a slit in the retina; it pas¬ 
ses obliquely into the vitreous humour, and terminates in that part, 
as in the eagle. Fig. 3, a section of the eye of the falco chrysaetos. 
In some species it reaches the lens, and is attached to it as in Fig. 
4, 6. In the plate the marsupium is marked with a # . 
Fig. 5. The hdad of an eel; the skin is represented turned back; 
and as the transparent , homy covering of the eye, a, a, is a cuticular 
covering, it is separated with it. Other fish have a similar, insensi¬ 
ble, dense, and thick adnata, which is designed to protect the eye; 
and it seems especially necessary, as fish have no eyelids. 
