Scapula of birds

The scapula is a long blade in birds.

I want to know what the significance is of the shape of the scapula in terms of how that is involved in flight.  I think it has to do with regulation of fine motor control of the wing because the wing itself is quite mobile.  

Please do some research and write a couple paragraphs on what you come up with.  I haven't been able to find a definitive answer to this question, even after asking several professors.  Please read the question carefully.  I know the wording is not the best, but I think you will understand what I am looking for.  Please list your sources that you use from the web.  Thanks so much!