occiput
The back part of the head or skull.
And then came Turbor, who sat quietly and unemotionally through the fifteen minute process, and Munn, who jerked at the first touch of the electrodes, and then spent the session rolling his eyes as though he wished he could turn them backwards and watch through a hole in his occiput.
Where it comes from
Borrowed from Latin occiput (“the back part of the head”). Compare sinciput.
Adapted from the Wiktionary entry occiput (CC BY-SA 4.0).