If you need some more ideas for such drawings, do a Google search on "celtic skull" and when the results load, click on the "Images" link to get to this:

https://www.google.com/search?q=celtic+skull&hl=en&client=firefox-a&hs=Yys&tbo=u&rls=org.mozilla:en-US:official&channel=np&tbm=isch&source=univ&sa=X&ei=QcbCUPqFOIKo8QTWuYC4CA&ved=0CC4QsAQ&biw=1024&bih=586

Might be something in there that could give you an idea or two.

Yep, looks good. I like the "torn paper" look, too...nice touch.