Do other motor systems obey Listing's law or Donders' law?
The head obeys Donders' law. This is because head
position is constrained to a surface. 
The head does not
obey Listing's law. This is because this surface is twisted (i.e. not a plane).
The direction of this twist is consistent with the head acting like a Fick gimbal.
A Fick gimbal has a horizontal axis (full angle rule) mounted on a vertical axis (zero angle rule).
Why? The possibilities are:
1) The neck is built this way.
2) Lifting the head up and down takes more effort than moving it from side to side (note
that a Fick gimbal optimizes rotations about the horizontal axis).
The outstretched arm acts in the same way as the head when pointing.
