Thanks Make-n-break, Simson, H Rhodes, Mullet.
Mullet, I stained the rawhide with some mahogany leather stain. I've done this once before and I don't know if I'll do it again. It always seems to leave a little bit of a red edge between the skins and the wood. Maybe it's just inexperience? Anyway, that's the reason for the black lines. In retrospect, I'm pretty happy with the outcome.