'makehuman' is free (&open source) software to create models of humans by pulling sliders, but it does not contain generation of internal organs.

You could always use that to generate some humans, then cut them into parts in the modelling program of your choice, then use free software 'mechmixer' to put the parts together in new and interesting ways.

But, for all the body scanning and medical imaging hype going on lately, generation and simulation/animation of skeletal structure and internal body parts seems to be a sparsely researched complex of topics atm, e.g. there's not much research papers available on it.