How does the structure of an arm or wing affect its motion?

The orientation of the muscles and joints determine the movement, but the limb itself is defined by it's purpose.
To put it simply arms lift things up and so the muscles and joints are designed to make that easier.
Wings are designed to push air downwards and similarly the muscles and joints are designed with this in mind.
Humans can't fly and birds cant do weightlifting, nature had something else in mind for us both.