Bats are collectively called Chiroptera, which is Latin for hand-wing. Here's a dorsal view of a Southern Yellow Bat, Lasiurus ega. As with most mammals, bat bodies are covered with fur but since their wings and tail membranes are largely naked, a bat’s skin is far more evident than that of most other mammals. The wing (and tail) membrane is an extension of the skin of the body, and is made up of external epidermal and internal dermal layers interlaced with blood vessels and nerves. The wing membrane is both flexible and durable and will heal remarkably fast if torn with little or no long term damage. Bats carefully groom their wings to keep the skin in good condition, using oils secreted from glands to ensure they are kept moist and supple. The wing itself consists of the upper arm, a longer forearm, the wrist and hand. The bones of the hand and the four finger bones (which I am holding at right) are greatly elongated, but light and slender, providing support and flexibility to the wing membrane in flight. The short and slender thumbs of this species are sticking up from the wrist where the wing bends. (Trinibats)