The =leg= has three divisions: the uppermost is the _thigh_ (called
the “second joint” in a fowl); the middle division is the _shank_
(or “drumstick”); and the lowest, which is the slender bone covered
with scales, is formed by the union of the _ankle_ and _instep_. (The
bones of the three divisions are named the femur, tibiotarsus, and
tarsometatarsus). The _foot_ consists entirely of toes, the bones of
which are called phalanges. Is there a bone in each claw? (See Fig.
285.) Supply the numerals in this sentence: The pigeon has ____ toes,
the hind toe having ____ joints; of the three front toes, the inner has
____ joints (count the claw as one joint), the middle has ____ joints,
and the outer toe has ____ joints (Fig. 285). Is the thigh of a bird
bare or feathered? The shin? The ankle? Where is the ankle joint of
a bird? Do you see the remains of another bone (the splint bone, or
fibula) on the shin bone of the shank? (Fig. 285 or 286.) Why would
several joints in the ankle be a disadvantage to a bird?
[Illustration: FIG. 285.--LEG BONES OF BIRD.]
[Illustration: FIG. 286.--SKELETON OF BIRD.
_Rh_, vertebræ; _Cl_, clavicle; _Co_, coracoid; _Sc_, scapula; _St_,
sternum; _H_, humerus; _R_, radius; _U_, ulna; _P_, thumb; _Fe_, femur;
_T_, tibia. See Fig. 394.
=Questions:= Which is the stiffest portion of the vertebral column? How
are the ribs braced against each other? Which is longer, thigh bone or
shin? Compare shoulder blade with man’s (Fig. 399). Which is the extra
shoulder bone? Compare tail vertebræ with those of extinct bird, Fig.
290.]
The _thigh_ hardly projects beyond the skin of the trunk, as may be
noticed in a plucked fowl. The thigh extends forward from the hip joint
(Figs. 286, 299) in order to bring the point of support forward under
the center of weight. Why are long front toes more necessary than long
hind toes? As the bird must often bring its head to the ground, the hip
joints are near the dorsal surface and the body swings between the two
points of support somewhat like a silver ice pitcher on its two pivots.
Hence stooping, which makes a man so unsteady, does not cause a bird to
lose steadiness.
The =wing= has three divisions which correspond to the upper arm,
forearm, and hand of man (Fig. 286). When the wing is folded, the three
divisions lie close alongside each other. Fold your arm in the same
manner. The similarity of the bones of the first and second divisions
to the bones of our upper _arm_ and _forearm_ is very obvious (Fig.
286). Explain. The _hand_ of a bird is furnished with only three digits
(Fig. 287). The three palm bones (metacarpals) are firmly united (Fig.
287). This gives firmness to the stroke in flying.
[Illustration: FIG. 287.--HAND AND WRIST OF FOWL (after Parker).
_DG. 1-3_, digits; _MC. 1-3_, metacarpals; _CC. 3_, wrist.]
[Illustration: FIG. 288.--HAND, WRIST (_c_), FOREARM, AND ELBOW OF
YOUNG CHICK (after Parker).]
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