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Like the leg, the bones of the wing are recognisably evolved from a basic plan that can be found in all vertebrates, including mankind. The wing consists of a humerus which at one end is attached to the main thorax via the scapula, and at the other end to both ulna and the radius. Note that like us, birds have two bones in the lower part of the limb. The rest of the wing is composed of modified hand bones. The carpometacarpus, like the tarsometatarsus in the leg, is elongate forming the basis for the third major section of the bird's wing. The first digit is small, comprising 2 phalanges and arises from the carpometacarpus just out from the joint with the ulna. It supports the Alula. The second digit is again comprised of 2 phalanges, in this case larger and flatter as they extend the wing and support the primary flight feathers, as does the carpometacarpus and the Ulna. Flight feathers originating along the humerus are called secondaries. The third digit is very small, it arises, like the second at the distal end of the carpometacarpus and also helps support the primaries . It consists of only one phalanx. (Distal = furthest away from the body, proximal = the closest end of a limb to the main trunk of the body). The fourth and fifth digits of the hand have, like the fifth of the foot, been lost completely in birds, another weight saving feature.


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Last updated: 24 November 2002