322 ON THE CLASSIFICATION OF BIRDS. 
noiseless flight : the quills themselves are unusually 
broad, while the barbs, no less than the general plu- 
mage, is remarkably soft and lax, in order to permit a 
free escape of the air in all directions. That these cir- 
cumstances, however, should not diminish the powers 
of flight too much, the wings are generally rather long, 
and the four outer quills have that abrupt sinuosity on 
their inner webs which is so universal among the swift- 
flying falcons. 
(258.) An exquisite sense of hearing is another 
peculiarity of these birds — a faculty which is essential 
to the discovery of their prey in the .dusky hours of 
twilight. The great sixe of the head is well known, 
and its apparent disproportion to that of the body is 
rendered necessary, on account of its containing several 
large cavities, which communicate internally with the 
ears, and thus tend to the unusual development of those 
organs. The external orifice is, in general, enormously 
large, and, even in the aberrant species, generally exceeds 
that of ordinary birds. In the typical examples, the 
external opening is protected by a fleshy operculum, or 
lid, thickly covered on the outside with feathers, and 
as freely moveable as is a door on its hinges. But if the 
faculty of hearing is so essential to an owl, how much 
more so is that of sight, when it has to pursue its prey 
in the dark. Yet here again we trace, in a beautiful 
and wonderful instance, “ the wisdom of God in the 
creation.” The eyes, in the first place, are of an enor- 
mous size : but as if this were not sufficient, they are 
surrounded with two large concave disks — generally 
composed of white and shining feathers, — for the pur- 
pose of concentrating a greater extent of light to he 
reflected upon the eye, which is placed in the centre. 
There can be little doubt on this being the true use of 
the facial disk in owls, although the circumstance ap- 
pears never yet to have been touched upon. We all 
know the effect upon our own sight, when, by looking 
through the hand, as we would a telescope, we contract 
the light, and are enabled to see further and much 
