BONES OF WING OF BIRD.
(After Sundevall.)
(a) Humerus; (B) Cubitus; (c) Ulna; (d) Radius; (E) Manus, or hand; (f) Carpus; (g, h, i) Metacarpus; (k) Pollex, or thumb; (l) Second digit; (m) Third digit.
The chief muscle thus employed is the “great pectoral,” attached to the large keel (or ridge) on the breast-bone, and inserted into the “humerus,” or “arm-bone.” This “great pectoral” is generally the largest muscle in the bird’s body, and in fact often equals in bulk all the other muscles put together.
The wing is opened out by straightening the elbow and the wrist-joints. The former process is effected by the contraction of the triceps; the latter chiefly by the action of the so-called “radial extensors,” and by the elasticity of the long “tensor,” or ligament, which comes from the shoulder muscles along the front border of the anterior wing-membrane, and is attached to the base of the thumb, at the front side of the wrist.
The wing is folded by the bending of the elbow and the adduction of the wrist-joints. The elbow is bent principally by the contraction of the “biceps” and the “internal brachial,” the wrist-joint chiefly by the contraction of the “hand-adductor,” and of the “ulnar wrist-flexor.”
As already stated, the possession of feathers is one of the most characteristic features in a bird. These beautiful structures are modifications of the skin, just as are the scales of the feet and the claws of the toes. Feathers and hairs, scales and claws, are all produced out of, and are modifications of, the cells of the upper skin, or epidermis, and of the under, or true skin, or cutis. The feathers differ much in their minute construction in some birds; and all those of a bird are of course not of the same size and shape, but they have the following parts in common.
FEATHERS OF WING OF BIRD.
(After Sundevall.)
(A) Feathers of the manus, or primary quills; (B) Feathers of the cubitus, or secondary quills; (C) Coverts of the manus, or primary-coverts; (D) Lesser primary-coverts; (E) Coverts of the cubitus, or secondary-coverts; (F) Median coverts; (G) Lesser coverts; (H) Feathers of the thumb, or bastard wing.