294 
BIRDS. 
LEFT SIDE OF SHOULDER AND BREAST-BONES OF A 
FLIGHTLESS BIRD. 
directed backward parallel with the element termed the ischium; the three 
elements being united together as in Mammals, but differing from them, 
with two exceptions, in that neither the ischium nor the pubis unites with its 
fellow of the opposite side in the middle line. Moreover, the cup in the pelvis for 
the head of the thigh-bone is always open at the base. The firm union of the 
haunch-bones with such a large portion of the backbone is necessary to afford 
a solid basis of support for the rest of the skeleton in flight. 
Equally essential is a solid union 
between the bones of the shoulder 
and the breast-bone. Accordingly, 
we find that, as in the Egg-laying 
Mammals, the blade-bone or scapula 
(.s) is connected with the breast¬ 
bone ( st ), by a metacoracoid (c); 
the scapula and metacoracoid thus 
jointly forming the cup for the 
articulation of the head of the arm- 
bone or humerus (h). Although in 
fligditless Birds the metacoracoid is 
short and broad, in other species it 
is more or less elongated; and in 
either case its lower expanded end 
s, blade-bone or scapula; c, metacoracoid; h, arm-bone received in a glOOVe On the 
or humerus ; /, furcula; st, breast-bone or sternum.—After summit of the breast-bone. Usually 
the collar-bones, or clavicles, are 
well-developed, and united together to form a V or U-shaped bone, now known as 
the “ merry-thought,” or furcula (/); this furcula generally articulating with a 
process on the metacoracoid (a), and also with the anterior 
end of the breast-bone. The breast-bone in flying Birds is 
provided with a strong keel up the middle of its inferior 
surface, as shown in the figure of the skeleton of a parrot 
on p. 292, in order to afford support for the powerful muscles 
moving the wing; but in flightless Birds, as in the figure on 
this page, it is smooth and rounded. To the sides of the 
upper part of the breast-bone are attached the lower segments 
of the ribs; the ribs themselves being few in number, and 
distinguished from those of Mammals by the presence of 
oblique (uncinate) processes projecting from their hinder 
borders. 
With regard to the limbs, the bones of a bird’s wing 
correspond generally to those of the arm or fore-leg: of a 
"l .... FRONT SURFACE OF THE 
mammal; the arm-bone or humerus having distinct condyles left metacoracoid of 
(a, b) for the articulation of the bones of the fore-arm (radius 
and ulna); and being sometimes furnished with a projecting 
process above the outermost of these two condyles. The 
two bones of the fore-arm always remain separate from bone' 
A flying bird. 
a, process for articulation 
of furcula; b, c, d, surface 
for junction .with breast- 
