FLIGHT. 275 
*'The vertebre of the back being fixed in birds, 
and the pelvis reaching high, there is no motion in 
the body ; indeed, if there were, it would be inter- 
rupted by the sternum. We cannot but admire, 
therefore, the composition of the neck and head, 
and how the extension of the vertebra, and the 
length and pliability of the neck, while they give to 
the bill the office of a hand, become a substitution 
for the loss of motion in the body, by balancing the 
whole, as in standing, running, or flying. Is it. not 
curious to observe how the whole skeleton is adapt- 
ed to this one object, the power of the wings ? 
‘“ While the ostrich has no keel in its breastbone, 
birds of passage are, on dissection, recognisable by 
the depth of this ridge of the sternum. The reason 
is, that the angle formed by this process, and the 
body of the bone, affords lodgment for the pectoral 
muscle, the powerful muscle of the wing. In this 
sketch of the dissection of the swallow, there is a 
curious resemblance to the human arm; and we 
cannot fail to observe, that the pectoral muscle con- 
stitutes the greater part of the bulk of the body. 
Borelli makes the pectoral muscles of a bird exceed 
in weight all the other muscles taken together, 
while the pectoral muscles of man are but a seven- 
tieth part of the whole mass of the muscles. And 
here we see the correspondence between the 
strength of this muscle and the rate of flying of the 
swallow, which is a mile in a minute, for ten hours 
every day, or six hundred miles a day. Mr. White 
says truly, that the swift‘lives on the wing; it eats, 
drinks, and collects materials for its nest in flying, 
and never rests but during darkness. If it be true 
that birds, when migrating, require a wind that blows 
against them, it implies an extraordinary power as 
well as continuance of muscular exertion. 
** We see how Nature completes her work, when 
the intention is that the animal shall rise buoyant 
and powerful in the air: the whole texture of the 
