
As you can see in the first image, that is caused by some shading issues and geometry of your skull in combination with the Subdivision Surface.
To solve this:
1.- Delete the Normal Tag that the Head and Jaw has (the one that looks like chessboard).
2.- Select the Head and the Jaw, then go to polygon Mode and select all the Polygons (Ctrl + A).
3.- Right Click and move the mouse to Untriangle and click over THE GEAR NEXT TO THIS COMMAND.
4.- inside the Untriangle Command Menu increase the Angle to 50.
5.- activate the Phong tag and increase to 60.

Good Luck
Imagination is the best tool…