Photo A shows a bird in flight, with a corresponding drawing of bird wing bones. Photo B shows a bat in flight with a corresponding drawing of bat wing bones. Photo C shows a horse, with a corresponding drawing of front leg bones. Photo D shows a beluga whale, with a corresponding drawing of flipper bones. Photo E shows a human arm, with a corresponding drawing of arm bones. All the limbs share common bones, analogous to the bones in the arms and fingers of humans. However, in the bat wing, finger bones are long and separate and form a scaffolding on which the wing's membrane is stretched. In the bird wing, the finger bones are fused together. In the horse leg, the ulna is shortened and is fused to the radius. The hand bones are reduced to one long thick bone and the finger bones are reduced to one long thick finger with a modified nail or hoof. In the whale flipper, the humerus, ulna, and radius are very short and thick.
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