This is some further refinement from http://www.thingiverse.com/thing:4126 both with and without the mandible from http://www.thingiverse.com/thing:3580, both whole and sliced in half.

In my previous attempt, I deleted all of the inside to create a solid object with all the porous and hollow parts filled in, and all external holes closed.

This time, I did the reverse, deleting all of the outside and the smaller internal features, to create simple internal volume (mostly the brain cavity). Then I subtracted the cavity from the solid object, did a small amount of further refinement, and then split it. I reduced the resolution of the mandible from http://www.thingiverse.com/thing:3580 to match the resolution of the skull then smoothed, scaled and rotated it to fit as closely as possible. I then cut off and cleaned the remains of the skull's original mandible and subtracted this mandible from the results.

This should give a partially hollow model that still has all the small internal details that can't be seen removed. I have uploaded (and included in the blender file) both the original cleaned skull and the one with the replacement mandible fit in. I also sliced both skulls, but only included the bottom for the second one, since the top didn't change.

I hope that the results will take less time to print than the previous two models.

Work on this model was done with Meshlab and blender.