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XII. Observations on the Structure of the Eyes of Birds. By Mr. 
Pierce Smith, Student of Physic. Communicated by George 
Pearson, M. D. F. R. S. 
Read March 2 6 , 1795. 
While examining the eyes of birds, I observed in them a 
singular structure, which I believe has not been hitherto no- 
ticed ; and though not the object I had in view in the examina- 
tion, it will perhaps elucidate several remarkable circumstances 
in the natural history of these animals, and may ultimately be 
applied to the eyes of other animals, and add one additional 
discovery to those already made on this beautifully constructed 
organ. 
In March, 1792, I observed, while dissecting the eyes of 
birds, an irregular appearance of the sclerotica, in that part of 
it which immediately surrounds the cornea, and which in 
them is generally fiat. On a more minute examination, it ap- 
peared to be scales lying over each other, and which appeared 
capable of motion on each other. These appearances I shewed 
to Dr. Fowler, of London, and likewise to Mr. Thomson, 
surgeon, Edinburgh. In June, this paper was copied out at 
my request, by Mr. Irving, who resided in the same house 
with me. On investigating this singular structure, the scales 
were found to be of bony hardness, at least much more so 
than any other part of the sclerotica. On the inside of the 
sclerotic coat of the eye there was no appearance of these 
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