My friend and student Jon Marshall brought in a great set of hand studies after various masters. We talked about various difficult spots including the knuckles and the "snuff box". Jon's drawings are in blue, my notes are in red and black.
Drawing of a mouth - side view - draw a straight line to see the angle/slant nose to chin; also look for negative space to get the form of the mouth. So helpful because I want to learn how to draw faces from the side as well as I do from the front!