How do I show only log messages for commits on a specific branch?

Hello list,

[ git v1.6.3.3 ]

imagine this:

	     --A--*--B (new)
	    /
	*--X--*--Y (master)

Now I'd like to list only log messages for A..B (X..B would be okay too).

I know of 

	git log master..new

however then I need to remember that I branched new of master, and to be honest, sometimes I forget.

So how do I:

	git please-tell-me-the-branch-I-started-this-branch-from new

Thanks in advance,

	Stefan