VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. 667 



The eyes of birds are larger in proportion than those of any other animal, 

 the eye of a thrush being equal to that of a rabbit. They are also broader in 

 proportion to their depth than in the quadruped; and the cornea is more promi- 

 nent. The cornea is very thin when examined immediately after death, and is 

 at that time more elastic than afterwards. In the goose, it was stretched so as 

 to be elongated -^ of an inch, but in an hour afterwards it had become thicker, 

 and less elastic. The cornea is not united to the sclerotic coat by the terminating 

 of one abruptly in the other; but the two edges are bevilled off, and laid over 

 each other for nearly -jV of an inch in the eye of the goose, and more where the 

 eye is larger. In the recent state, the thin edge of the cornea is readily torn off 

 from the inner surface of the sclerotic coat to which it adheres, so as to show 

 this mode of union. This circumstance was known to Haller, and is particularly 

 described in his works. 



There is a bony rim surrounding the basis of the cornea in the eyes of birds, 

 which is peculiar to this class of animals. It is made up of a number of different 

 parts, very commonly 13 in number; some of these are lapped over each other, 

 but some have an irregular union, one part passing before, and the other behind 

 the bony scale next to it. This bony circle, thus made up, is not equally broad 

 in its different parts; it is broadest where it covers the upper and outer part of 

 the eye, and narrowest where it covers the cornea towards the inner canthus. 

 This bony rim does not give an origin to the cornea, as might appear to a super- 

 ficial observer, but is a bony hoop laid over the junction between the sclerotic 

 coat and cornea; and as the thin edge of the cornea passes within the sclerotic 

 coat, the principal attachment of the bony rim must be to that coat. The bony 

 rim is adapted to the surface on which it lies ; the greatest part of its breadth is 

 firmly connected to the sclerotic coat; and where the cornea projects, the ante- 

 rior edge of the rim is turned forwards to correspond with that projection; here 

 the scales are extremely thin, they terminate in a fine edge, and admit of being 

 forced a little asunder, to adapt them to the stretched state of the cornea; but 

 no such effect can be produced on the posterior part of the rim, the different 

 parts being too firmly connected to admit of any separation. 



The structure of this bony rim differs in different birds. In the goose and 

 turkey the scales are thin and weak; in the cassuary they are thicker; and in the 

 eagle they are very strong. In the owl, they put on a very different appearance; 

 they are 15 in number, f of an inch long, and instead of being lapped over each 

 other, as in other birds, they are united by indented sutures; each portion is 

 broadest next the sclerotic coat, and narrowest towards the cornea, giving the 

 bony rim a conical form. This structure in the owl's eye differs from that in 

 other birds, the anterior edge not admitting of being dilated to correspond with 

 the change of figure in the cornea; tliis purpose in the owl is answered by a cir- 



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