Bird and Pterosaur Wing - Continued (1)

Modern bird fused fingers:
http://en.wikipedia.org/wiki/Bird_anatomy
"The carpus and metacarpus form the "wrist" and "hand" of the bird, and the digits (fingers) are fused together."

In the transition from the pterosaur to the modern bird, the finger configuration was modified including some of the digits being fused. This is because the modified bone structure is more effective in conjunction with feathers.