Bat wings are homologous structures because they bear structural similarity to the limbs of other organisms and analogous structures because of their functional similarity to other organisms' wings. Bat wings are also an example of convergent evolution.
Bats belong to the taxonomic order Chiroptera, which is a combination of the Greek words for hand and wing. Bat wings are homologous with other mammalian forelimbs, including the human arm and hand. This means that bat wings share structural similarities with the limbs of much more distantly related species. A bat's wing exhibits a humerus, radius, ulna, metacarpals and phalanges. In comparison to many other mammals, a bat has a smaller ulna, more rigid wrist and longer phalanges, and a membrane of skin covers the entire limb. The bat's wing membrane is an extension of the skin of the body and consists of both epidermal and dermal layers.
Bat wings are analogous to bird wings. Analogous structures exhibit similarities in function even though, structurally, they are quite different. While a bat's fingers provide support for the wing membrane, a bird's digits are fused together and support the feathers. Analogous structures arise due to convergent evolution. In convergent evolution, unrelated species evolve similar structures because they utilize like behaviors or fill similar niches.