I just got a snakeskin backed osage bow that lookes like it has crackes running with the length of the belly of the lower limb but I can't feal any thing thur the finish is this a problem

Not usually as long as they are running with the grain, which is what it sounds like.

I have a few bows like that, as long as the checks don't run off the side of the limb the bow will be fine.

The cracks have probably been filled with super glue. This teatment is a good fix and they shouldn't be a problem.

That is usually caused by adding moisture to an already dry stave and sealing the back(snake skin)but usually with sinew backed bows. I have a halibut skin covered sinew backed bow, supposedly made by Jay Massey, that has deep belly cracks. I remember an article by Jay about this reaction. It shouldn't effect the performance as long as the cracks stay in the limb. If it doesn't already have super glue in the cracks like Eric mentioned , I would add some for insurance.     Pat

I could'nt have said it better PAT.