188 Mr. Yarroll on the Analomt/ of Birds of Prey. 



plumage in owls, as well as their deficiency in muscle and bone, 

 rapid flight is denied them as useless, if not dangerous, from the 

 state of the atmosphere at the time they are destined to seek their 

 food ; but they are recompensed for this loss, partly by their 

 acute sense of hearing, from an extension of the posterior edge 

 of the cranium forming a conch, coupled with a very large 

 external orifice; and partly by the beautifully serrated exterior 

 edge of the iving primaries, which, allowing them to range without 

 noise through the air, enables them to approach unheard ; and the 

 unsuspecting victim falls an easy prey to the silent flight and 

 piercing eye of an inveterate enemy. Some increase and varia- 

 tion will be found in the strength and form of such of the owls as 

 depart from the type of the true nocturnal bird. In the snowy 

 and short-eared owls, which are described as occasionally seeking 

 their food by day, the furcula is stronger and less angular in 

 proportion than in the wood and barn owls. 



The external convex form of the bony ring in the Golden Eagle, 

 ■will be found to extend through all the species of every genus of 

 British Birds, except the owls, in all of which it is concave. The 

 bony ring of the Snowy Owl (.S'. Nydea) is represented of the na- 

 tural size, and the fifteen plates forming the circle, are considerably 

 lengthened. The transparent cornea being placed as it were at 

 the end of a tube, is thus carried forward beyond the intervention 

 of the loose and downy feathers of the head. It is this position 

 of the eyes, giving a particular fullness and breadth to the head, 

 •which has gained for the owl the intellectual character universally 

 awarded to it. In other birds the position of the eyes is much 

 more lateral. 



The crystalline lens of the Snowy Ow 1 is also contrasted with the 

 same part in the Golden Eagle. The extent of vision enjoyed by 

 the Falcons is probably denied to the owls, but their more sphe- 

 rical lens and corresponding cornea give them an intensity better 

 suited to the opacity of the medium in which they are required to 

 exercise this power. They may be compared io a person near- 

 sighted, who sees objects with superior magnitude and brilliancy 

 ■when within the prescribed limits of his natural powers of vision, 

 from the increased angle these objects subtend. 



