vI FORM AND FUNCTION 135 
(1) No species of bird has what can properly be 
called an external ear. The Owl has a flap of skin, 
forming a kind of valve, by which it is said that it can 
close the ear at pleasure. Certainly it possesses 
muscles for this purpose. Often the ear valve is larger 
on one side than the other, the whole skull being at the 
same time lopsided. During the breeding season, the 
cock Capercailzie has moments of complete deafness, 
owing to a fold of skin which becomes swollen with 
blood and closes the opening of the ear. In other 
species the flap of skin is very little developed. 
(2) The three small bones which in the human ear 
convey the vibrations of sound from the membrane 
which forms the outer wall of the drum of the ear to 
the inner membrane that forms a window in the bony 
labyrinth are represented in birds by one bone, the 
columella (C). But it is almost certain that this is 
formed by a fusion of three, corresponding to those 
which we find in mammals. It was usual, till recently, 
to see in the quadrate bone, to which the lower jaw of 
birds and reptiles is hinged, one of the three bones of the 
mammalian ear. If these three are combined in the 
columella, where are we to look for the quadrate in 
man and other mammals? The best authorities are 
of opinion that it is represented only by an insig- 
nificant ring of bone, called the annulus, which forms 
a frame for the membrane of the drum of the ear. 
(3) In place of the spiral cochlea birds have a 
slightly curved bone to which the name of the lagena 
has been given (Lg). It is similar in reptiles. 
(4) The absence of the organ of Corti in the bird’s 
ear is aremarkable fact. It is true there isa very 
