The Middle Finger

Where did the gesture of showing someone you’re mad at “the finger” come from?

What is the gesture by which you show that you’re mad at “the finger” again?
(I think I missed this one in American gestures 101)

As for “the finger” itself, I do believe that Cecil has already covered this one… http://www.straightdope.com/columns/980904.html

(if thats what you were really asking)

how did the term ‘the birdie’ or ‘the bird’ originate?