. Key to North American birds; containing a concise account of every species of living and fossil bird at present known from the continent north of the Mexican and United States boundary. Illustrated by 6 steel plates and upwards of 250 woodcuts. Birds. STRUCTURE OF THE WING. 31 § 56. The Mechanism of these bones is admirable. The shoulder- joint is loose, much like ours, and allows the humerus to swing all about, though chiefly up and down. The elbow-joiut is tight, permitting only bending and unbending in a horizontal line. The finger bones have scarcely any motion. But it is in the wrist th
. Key to North American birds; containing a concise account of every species of living and fossil bird at present known from the continent north of the Mexican and United States boundary. Illustrated by 6 steel plates and upwards of 250 woodcuts. Birds. STRUCTURE OF THE WING. 31 § 56. The Mechanism of these bones is admirable. The shoulder- joint is loose, much like ours, and allows the humerus to swing all about, though chiefly up and down. The elbow-joiut is tight, permitting only bending and unbending in a horizontal line. The finger bones have scarcely any motion. But it is in the wrist that the singular mechanism exists. In the first place, the two forearm bones are fixed with relation to each other so that they cannot roll over each other, like ours. Stretch your arm out on the table; without moving the elbow, you can turn the hand over so that either its palm or its back lies flat on the table. It is a motion {rotation) of the bones of the forearm, resulting in what is called pronation and su- pination. This is absent from the bird's arm, necessarily; for if the hand could thus roll over, the air striking the pinion-feathers, when the bird is flying, Avould throw them up, and render flight diflicult or impossible-. Next, the hinging of the hand upon the wrist is such, that the hand does not move up and down, like ours, in a plane perpendicular to the plaue of the elbow-bend, but back and forwards, iu a plaue horizontal to the elbow; it is as if we could bring our little finger and its side of the baud around to touch the corresponding border of the forearm. Thus, evidently, extension of the hand upon the wrist-joint increases and completes the unfolding of the wing that commenced by straightening out the forearm at the elbow. There is another essential feature in a bird's wing. In the figure, 6, abo represents a deep angle formed by the bones, but none such is seen upon the outside of the wing. This is because this triangular space is filled up by a fold of
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbirds, bookyear1872
