/ic/ - Artwork/Critique

I'm trying out the exercises from Loomis's "Drawing the Head and Hands". I'm slightly confused about the planes of the face, namely the lines connected to cheekbones. As far as I've figured, one line from every cheekbone goes to the center of the upper lip, and the other to the respective side of the mouth, is this correct?
Also, can anyone recommend something a little bit more elaborate about drawing the face? I feel I don't get enough understanding from his commentary.