DR KNOX on the Comparative Anatomy of the Eye. 47 



Of the Figure of the Globe of the Eye; of the Form and Propor- 

 tions of its Chambers, and of the Density of its Transparent 

 Parts. 



I have but little to add from personal observation, to the la- 

 bours of preceding writers on this subject. Indeed I suspect 

 that little remains to be done relative to the matter announced 

 in the section. So important an organ is that of sight, that it has 

 at all times attracted the attention of the profoundest philoso- 

 phers, and the examination of its various parts has been deemed 

 not unworthy the labours of the greatest mathematicians of the 

 present age. To the splendid works of these gentlemen I beg 

 to refer the Society. 



The anterior part of the eye in fishes, and in the cetacea, is 

 flat. In the cuttle-fish, the cornea and aqueous humour are 

 wanting. In man, and in quadrupeds, it is almost spherical. 

 The cornea makes a slight projection anteriorly, because its con- 

 vexity is a portion of a sphere smaller than that of the rest of 

 the eye. In the porcupine and the opossum, this is said not to 

 be apparent, and it seems to me that the same remark is nearly 

 applicable to the ornithorinchus paradoxus. In birds, the cornea 

 is exceedingly convex, and is sometimes completely hemispheri- 

 cal. Thus we see, that the difference in the eyes of these ani- 

 mals is connected with the proportional density of the media in 

 which they live. It is true that the ostrich and cassowary ne- 

 ver rise from the ground, and yet have their eyes formed like 

 those of other birds; but as Nature has formed the various 

 classes of animals agreeably to certain determinate laws, and as 

 in none of these classes has she adhered so strictly to these laws 

 as in birds, so we can see no good reason why the eye of the os- 

 trich should differ much from that of other birds ; or perhaps it 



