The faculties of birds / [Anon].

James Rennie

Date:: 1847

Catalogue details

Licence: Public Domain Mark

Credit: The faculties of birds / [Anon]. Source: Wellcome Collection.

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M. Vaillant mentions a similar circumstance which he more than once observed in different species of owls, if they chanced to be roused from their lurking places by day, when instead of pursuing small birds, which are their natural prey, they fled from them in fear *. Wilson says of the snowy owl (Stry.r nyctea) that “ the conformation of the eye forms a curious and interesting subject to the young anatomist. The globe of the eye is immoveably 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, overlapping a little at the base or narrow end, and seem as if capable of being enlarged or contracted, perhaps by the muscular membrane in which they are encased.” “ In five other different species of owls,” adds Wilson, “ which I have since examined, 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 circlet-’’ In nocturnal birds, M. de Blainville remarks that the eye, besides being comparatively very large, is flat (comprime) both before and behind, while the transparent cornea is placed at the end of a sort of tube formed by the bony portion of the sclerotic. The retina is consequently comparatively very large and extended, and the iris also; while the mem- * Oiseaux d’Afrique, tom. i. t Amer. Ornith. iv. 56, 1st edit.

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