THE SWIPT. 
41 
tration we may take the Swift^ a typical example of this sec- 
tion^ and quote the excellent observations of the late Pro- 
fessor Macgillivray^ on this bird : — 
If we suppose that the swift is destined to feed exclu- 
sively on insects as they flutter in the air^ we can be at no 
loss to trace the reason of its peculiar form. Its body is 
lights but moderately stout^ and its pectoral muscles are 
large^ otherwise it could not move its wings with the neces- 
sary strength and rapidity. The wings are extremely elon- 
gated and narrow^ because great rapidity of flight is required 
in the pursuit of animals which themselves fly with speedy 
and because sudden turns require to be executed in seizing 
them. A shorty broad^ concave wing^ as that of a partridge, 
on being rapidly moved produces considerable rapidity, but 
is not fitted for either buoyant gliding or quick evolution. 
For the latter the surface of the wing must be extended in 
length and narrowed^ and instead of presenting a concavity, 
must be straight in the horizontal direction. Accordingly 
in the swift the wing has its humeral articulation peculiarly 
free, insomuch that holding one alive in your hand you at 
first imagine that its wings have been broken. At the same 
time their muscular apparatus is remarkably strong. Then 
* History of British Birds, vol. iii. p. 619. 
