"The pterosaur wing membrane is divided into three basic units. The first, called the propatagium ("first membrane"), was the forward-most part of the wing and attached between the wrist and shoulder, creating the "leading edge" during flight."
"Here is an image of a White Ibis in flight showing full breeding plumage, in this instance the bird is pushing it's wings down and the arm is stretched out. As you can see, we get a good view of where the bones are positioned in the wing, notice that they don't run along the front of the wing. The elbow is set back from the leading edge and the bend in the arm is hidden by the Propatagium, a fold of skin inside the front part of the wing which connects to the shoulder and the wrist."
"The [bird] propatagium is variably deployed, relative to elbow extension, in flight; support for its cambered shape is maintained by multilayered collagenous and elastic tissue networks suspended between leading edge and dorsal antebrachium."