Even though it's a WIP, I upload it because I haven't worked on it for a while and won't have time to finish it for another while, but I think some people can benefit from it already.
I started this project to study artistic anatomy for character design, but as often went over board. I had several scanned real skulls as reference to help me get an accurate model but still sculpted from scratch, as the scanned models were not so clean and all joined in one mesh (but mostly just for learning purposes).
Since the original file is too big for free3d.com, this is a
decimated version (still detailed enough for some use cases) but you can download the original here :https://www.dropbox.com/s/2dzmtveztcal4kk/Skull-fbx.zip?dl=0
You can also follow the progress and critiques here :https://blenderartists.org/forum/showthread.php?421289