Trying to understand the ellipse when the head turns, using the 3d model

Those are all from imagination without corrections from the 3D model, and I had trouble cutting the ball (shape of the ellipses), back to the 3d model I suppose... :/

I have tried to draw from imagination but got some trouble with the jaw, so I have done a few more using the 3D model. Any feedback is appreciated.

The assigment for this lesson, not sure I got the characteristic of the subjects. Any feedback is appreciated.

I am trying to do all the assignments, using the 3D model as reference. Any feedback is appreciated.

Assignment done using the 3d model, any feedback is appreciated.