vI FORM AND FUNCTION 139 
and that of an unmusical bird is that the muscles 
of the former are, in most cases, more numerous and 
stronger. The syrinx of the Skylark is almost a ball 
of muscle, whereas the Pigeon’s has but very little 
to show. But it is very remarkable how muscular a 
syrinx some few non-singers have. Among these are 
the Crow and the Raven. Perhaps a more striking 
instance is that of the Bullfinch who sings very feebly 
in the wild state. The hen-bird also, who, I believe, 
is almost voiceless, has highly developed voice muscles. 
In the cock-bird they have clearly not lost their power, 
for in captivity he becomes a splendid vocalist. 
However first-rate the syrinx and its muscles may be, 
itis wonderful that so small a creature as, for instance, 
a Nightingale, can produce such an amount of voice. 
Even the Wren sends out a flood of powerful notes. 
The Thrush’s song is wonderful as a tour de force. 
If the bird were nothing but a musical instrument, the 
volume of sound sent forth would be astonishing ; and 
when we consider the variety of functions which its 
small body has to perform its musical powers supply 
far greater reason for wonder. The air-sacks, no doubt, 
are a great assistance. Those great reservoirs of air 
must make it easier for the bird to avoid the awkward 
crises that come to the untrained human vocalist 
when he finds, at the moment his grandest notes are 
expected of him, that his voice is becoming thin and 
feeble for want of breath. The trachea sometimes 
takes strange forms which might be thought to influ- 
ence the voice. In the Drake, just in front of the syrinx, 
it has a big box-like appendage, which looks as if it 
might be intended to give the voice greater resonance. 
