These are two different types of structures of the Skull. The Occiptial Bun found on Homo Sapien Neanderthals is an actual extension of the occiptial bone, which contained additional brain structure. While the nuchal torus is a thickening of the bone generally ranging from the parietal bones around to the occiptial to which neck muscles are attached. It does not expand the carnial vault.

Unlike the occiptial bun, the nuchal torus is not consistently present.