Many thanks to Gael Langevin, the creator of the InMoov 3D-printed robot (http://www.inmoov.fr).
This post is a remake of my transversal cut forehead design. It corrects an error of the topskull parts which may led to a gap between the front and the back of the skull. Additionally a new back skull is designed, including a "service flap".
Since the front and back parts are divided equally to the original design, it is also possible to use just the front or just the back.