VII FLIGHT 265 
vertical to its surface and at a certain pace, 
would be more than double what it would be 
in the case of a plane one foot square under similar 
circumstances. Hence small birds get less support 
from the air than large ones. It is true that, as 
explained above (see p. 190), the front part of the 
wing does most of the work during its lightning-like 
downward movement, and therefore we find that 
the wings of most of the best flyers have narrow 
extremities. But during flight the bird’s whole under 
surface forms a parachute, and a gain in area means a 
disproportionate gain in supporting power, even when 
we make allowance for the principle just mentioned. 
Moreover, a short wing necessitates a quick stroke, 
and much power is lost by the small bird in constantly 
raising the wing for a fresh effort. A few less 
important advantages must also be mentioned. The 
great flyers, even when we take into consideration 
their greater size, have larger and stronger bones than 
the best flyers among small birds, and the absence of 
marrow has prevented an increase in weight that 
might have been set against the increase in strength. 
In large birds the coracoids, if we take the average, 
are directed more outwards than in small birds, a 
gain in strength without any drawbacks. It is 
probable that in proportion to their total bulk they 
require less flight muscle than small birds that 
resemble them in other respects. Some interesting 
measurements which go to prove this have been made 
by Legal and Reichel. In the case of the Pigeon, as 
I have shown (see p. 212), their figures do not agree 
with the facts, but in most cases they are, probably, 
