A torso sculpture released by user watakach with a CC0 license on BlendSwap.com. The model has been repaired to be a complete solid through Netfabb, but besides that, I've done nothing to modify it.

Credit to Cosmo Wenman for his open access work. He's released a similar model scanned and released from the Louvre, with a CC-BY license. If you want a small fraction more of the missing anatomy, use his model.