Bird, Pterosaur, and Bat forelimbs are homologous as limb structures, with respect to the sequential relationship of humerus, radius, ulna, and digits as inherited independently from flightless ancestors.

    Forelimbs are analogous as flight structures, and have evolved independently in each group. The digits are arrayed in radically different patterns in the flight surfaces. The bird wing is supported by the entire forearm. The Pterosaur has a single Brachiopatagium extending from the 4th digit to the hindlimbs, whereas the Bat has a Dactylopatagium supported by the 2nd-5th digits, and a Plagiopatagium between the 5th digit and the hindlimbs. Pterosaurs and Bats both have a Propatagium extending from the wrist to the neck, but in the former it is supported by a novel bone.