Many thanks to Gael Langevin, the creator of the InMoov 3D-printed robot (http://www.inmoov.fr), to Bob Houston, the creator of the Articulated Neck (http://www.thingiverse.com/thing:845793) and monnerby for his Modified InMoov Head (http://www.thingiverse.com/thing:992918).
This thing is an alternative modification of the neck and the lower back skull. The idea was to move the rear servo to a position that allows a channel through the neck.
In the picture there are 2 pieces without modification. The ring is taken from the original head design by Gael Langevin. The Neck is the one from monnerby.
3 parts were changed. The 2 sides of the lower back skull were merged together. Additionally, the holes were removed and a hold for the rear servo was added. To leave as much "connected" space as possible, the servo was turned by 90 degrees and moved as far back as possible. The asymmetric position (3 mm) is necessary to leave enough space for the gear.
The gear itself is designed to be screwed to the servo horn before the horn is connected to the servo.
There were 2 goals for the modification of the upper neck joint. On the one hand, a lot of space is needed inside the neck joint, especially at the junction to the lower neck joint. On the other hand it should be able to be printed with as little support as absolutely necessary. Currently the support is necessary just for the lateral connectors and the internal "guiding knobs".