CHA.PTER III. 



Tab. III. — THE EYE OF 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 gen- 

 eral 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 passes ob- 

 #liquely 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 head of an eel ; the skin is represented turned back; 

 and as the transparent, horny covering of the eye, a, a, is a cuticular 

 covering, it is separated with it. Other fish have a similar, insensible > 

 dense, and thick adnata, which is designed to protect the eye \ and it 

 seems especially necessary, as fish have no eye-lids. 



