A History 
Birds. 
( J 23) 
THE BIRD WORLD. 
CHAPTER III. 
Flight and its Mechanism. 
While, in the possession of feathers, birds 
occupy an absolutely unique position in the 
animal kingdom, they are not to be so distin¬ 
guished in the matter of their flight, for many 
creatures far below them in the scale of life are 
no mean performers in this most enviable form 
of locomotion; while the Bats, which belong to 
the man’s own class—the Mammalia—on the 
other side of the scale are also adepts in the art. 
In the manner of their flight, at any rate, the 
birds are peculiar, though, for the matter of that, 
so also, it may be urged, are the Butterflies and 
the Bats. But, as we shall show, this is not 
altogether true. 
In the study of “the way of the bird in the 
air ” so many factors have to be taken into con¬ 
sideration that it is difficult to know where to 
begin, and even then, having made a beginning, 
it is by no means easy to make a plain, straight¬ 
forward tale of it. Technicalities will seem to 
thrust themselves in upon our argument, with 
many officious promises of making things 
clearer; but they shall be severely repressed ! 
Though birds are essentially flying animals, 
and though to attain this power they have be¬ 
come profoundly, modified as to their bodily 
shape, they have yet, in some respects, not gone 
so far as, say, the Bats, for the latter have almost 
completely sacrificed the power of terrestrial 
locomotion, while the birds have, with some few 
exceptions, preserved this, or, at any rate, they 
have preserved the hind-limbs as “ going con¬ 
cerns ” of some kind. With this preamble, let 
us come to closer terms with our subject. And 
this we can do better, surely, by a study of the 
bony framework of the body, in its relation to 
flight, than by any other way. 
Adaptation of the Body for Flight. 
Indirectly, of course, the whole body is 
moulded to bring it into harmony with the re¬ 
quirements of aerial locomotion. The long neck, 
passing insensibly into the body, which tapers 
again into the tail; the beautifully smooth, 
rounded surface formed by the close-fitting over¬ 
lapping feathers, are very important adaptations 
to this end, offering the least possible resistance 
to the air; while the large mass of the breast 
muscles attached to the under surface of the 
body—which during flight is, as it were, slung 
between the wings—contribute towards the right 
ordering of that all-important matter—gravity. 
In many birds special means have been adopted 
to secure extreme rigidity, as may be seen by the 
fact that the separate vertebrae of the back have 
become welded together to form a stiff, unyield¬ 
ing beam, though in many fliers, as the Parrots, 
the “ Perching-birds,” and Gulls, for example, 
these vertebrae retain their primitive independ¬ 
ence. But it is not till we come to examine the 
bones of the shoulder-girdle and sternum and the 
wings that we find the really obvious adapta¬ 
tions, or modifications, of the skeleton which 
flight has brought about. 
The Breast-bone and Adjacent Parts. 
I will not weary my readers by a long and 
probably wearisome comparison between the 
shoulder-girdle and sternum and fore-limbs of 
the Reptile and those of the bird, by way of 
showing how the one became changed into the 
other, because such a comparison could not pos¬ 
sibly carry conviction except to those who have 
made a life study of the subject. Let us rather 
examine the facts as they appear in the bird. 
By the shoulder-girdle, we may remark, is meant 
those bones which make up the shoulder-blade, or 
Fig. 1.—The Shoulder-girdle and Breast-bone of a bird. 
scapula, the long, straight pillars known as the 
“coracoids,” and the furcula or “merry¬ 
thought.” These form a sort of cage fixed on to 
the front of the sternum, or breast-bone. This 
bears, as everybody knows, a rough resemblance 
to the hull of a ship, but with an extremely deep 
keel. A reference to the figure here should 
make this clear. The deep keel and the broad, 
flat plate of the breast-bone serve for the attach¬ 
ment of the breast muscles, which in the bird are 
of enormous size, equalling or exceeding in 
weight all the other muscles of the body. 
The Pectoral Muscles. 
These muscles, which constitute the large 
mass of flesh familiar to everyone as the “ breast- 
meat ” of a bird as served up at table, are 
arranged in two layers. The outermost runs 
forward, to be inserted into a shelf of bone 
which projects from the upper surface of 
the humerus, or upper arm, whi’e the lower 
runs beneath it, along the coracoid, and finally 
passing into a round tendon, runs through 
a pulley formed by the meeting of the coracoid, 
blade-bone, and merry-thought and into the head 
of the humerus. These two muscles play the 
most important part in raising the body and 
keeping it in motion, for these by their contrac- 
