HEARING. 241. 
awakened, for a slight noise will often rouse a sleep- 
walker, who had borne an intense light om his un- 
shut eyes without seeming in the least to feel its 
influence. 
The structure of the ear in birds would lead us 
to conclude that they could not hear so quickly as 
otheranimals. Nevertheless, we find that the sense 
of hearing:is enjoyed in an exquisite degree in birds ; 
that the organ of the sense is not imperfect, but is 
adapted to a new construction, and a varied appara- 
tus suited to the condition of the bird; and that 
there is no accidental dislocation or substitution of 
something less perfect than what we find in other 
classes of animals.’”* 
The internal parts of the ear in birds are much 
less complicated than in man and quadrupeds; but, 
without going into the minute particulars of differ- 
ence, we shall only mention one peculiarity, which 
is, that while the chamber of the drum communi- 
cates with three large cavities in the adjacent bony 
plates, these again communicate by an‘equal num- 
ber of openings with the drum in the same side, one 
of them extending over the scull to its fellow on 
the other side. Sir Everard Home has observed a 
similar kind of communication by means of the 
cells of the scull in the elephant. We have little 
doubt that the provision made for rendering birds 
more buoyant, consisting of air-vessels extended 
from the lungs throughout the body, and even to the 
bones themselves, contributes to render the vibra- 
tions of the air more distinct, muffled as they must 
always partially be by the feathers of the bird. 
_ The faculty of imitating sounds possessed by cer- 
tain birds, proves that their hearing must be ex- 
ceedingly delicate ; and though we suspend our be- 
lief of the great musical talents which some birds 
are said to have derived from education, we find 
* Bridgewater pute on the Hand, p. 139. 
