This is a 3D print ready model. No non-manifolds. The inside of the head is hollowed and the foramen magnum left open for the resin to leak out if using a resin printer.
There is no sphenoid bone (the one on the base of the sull, behind the jaw) or smaller cavities in order to have a nicely printable model. If the scaling is too small in your slicer when you open the file, just go to the scaling and change the 100% to 1000%, so it scales it up 10 fold. For some reason some slicers don't understand the scale correctly that has been created with blender.
The skull model is sculpted with blender.
Included files are:
Skull.stl
Skull.obj and .mtl