when drawing dragons wings I've found that photos of bat wings are good sources. It's important to actually look at the photo and examine it though, because it's not until then that a lot of people suddenly realize what one actually looks like rather than just what they thought one looked like. I hadn't realized until I did that they're basically an arm with four long fingers plus a small thumb (that's what the hook part really is) and skin between, complete with an elbow and everything. Try that and see how it works for you.