Identifier: birditsformfunct07beeb (find matches)
Title: The bird, its form and function
Year: 1906 (1900s)
Authors: Beebe, William, 1877-1962
Subjects: Birds Birds
Publisher: New York : Henry Holt
Contributing Library: Internet Archive
Digitizing Sponsor: Internet Archive

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he white-blood animals in being able to stretch out and contractin only one direction. When we will our arm to closetogether, bringing our hand close to our shoulder, a thickcolony or bunch of these muscle-animals shortens, be-comes stouter, and bulges up under the skin on our upperarm. In our own body the bones of the spinal column aremovable, and we can bend in almost every direction,and so we are provided with many important back-muscles.But if we have ever carved a chicken, we shall remem-ber that the ribs and shoulder-bones are close to the sur-face, and but poor pickings are to be had from them.The breast and chest, on the contrary, are hidden in athick mass of muscles, most of which are concerned withmoving the wings in flight. The immense pectoral or I 90 The Bird breast muscle, which makes possible the all-importantdownward sweep of the wings, weighs one-fifth as muchas the entire bird, bones and all. This arrangement ofa great weight of muscle hung below the point of attach-
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Fig. 139.—Wing and breast of Pigeon, showing immense pectoral muscles, andtendons of wing used in flight. ment of the wings is, for mechanical reasons, the onlyone possible in a bird of flight; since any excess of weightabove the wings would instantly overbalance the bird.If we remove the skin from the upper arm of a bird, Muscles and Nerves 191 we shall see a tangle of bundles of red flesh—the muscleswhich unite to make the arm of a bird such an exquisiteflying-machine. Where a muscle narrows and is fastenedto a bone, its fibres merge into a thin, tough white cord— Fig. 140.—Model of birds foot, showing perching tendons; toes extended. a tendon. This is not elastic like the main portion ofthe muscle, but is much more tough. In the slender legs and feet of birds there is little morethan bone, tendon, and skin. The tendons which claspand unclasp the toes are very interesting, and if we will 192 The Bird bend the tarsus back and forth in the leg of a dead chicken,the workings of

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