Head Shoulders Knees and Toes

Head: One of my dreams is to draw heads really well, heads that look like they belong to the models I am actually drawing instead of their wrinkly sad cousin. My professor keeps making us draw the skull of our faulty classroom skeleton, then superimpose the live model's face on the skull. This exercise blows my mind, because I'm thinking "But no, the model's head has to be totally different inside." My prof insists that all skulls are basically the same. How can this be?

Shoulders: The shoulders that I draw are ass-kicking.

Knees: I ignore them when I draw. Ironic?

Toes: Slowly improving, in real life as well as in art class.