Top: Left, Phlegmatic or subject altruist Right, Choleric or subject egoist.
Bottom: Left, Sanguine or object altruist Right, Melancholic or object egoist
I don't think the actual head shapes mean that much even though I can think of more than a few people who might be pure types who have this.
Instead I think that the egoists on the right side have an expression of hate that is seen in the furrowed brows and the altruists on the left have an open expression. Specifically the object altruist looks like he has a scared or easily excitable expression while the subject altruist looks like he has a dissociated look.