Wet Fingers Always Wrinkle the Same Way, but Why?

Everyone knows from childhood that every time you dip your fingers in water, they get wrinkled. But did you know that the wrinkles always have the exact same pattern? It's like having a second, wet fingerprint. According to new research, the explanation is that wrinkles follow the path of blood vessels under the skin's surface, which normally stay in place. But why do wrinkles form?