Volume 4, Plate 4

Snow Owl
Male Sparrow Hawk

Snow Owl

The conformation of the eye of this bird forms a curious and interesting subject to the young anatomist. The globe of the eye is immovably fixed in its socket, by a strong elastic hard cartilaginous case, in form of a truncated cone; this case being closely covered with a skin, appears at first to be of one continued piece; but on removing the exterior membrane, it is found to be formed of fifteen pieces, placed like the staves of a cask, over lapping a little at the base, or narrow end, and seem as if capable of being enlarged or contracted, perhaps by the muscular membrane with which they are encased. In five other different species of owls, which I have since examine, I found nearly the same conformation of this organ, and exactly the same number of staves. The eye being thus fixed, these birds, as they view different objects, are always obliged to turn the head; and Nature has so excellently adapted their neck to this purpose, that they can, with ease, turn it round, without moving the body, in almost a complete circle.