You can sit before the desk (or in front of the desk). The professor can sit on
the desk (when he's being informal) or behind the desk, and then his feet are
under the desk or beneath the desk. He can stand beside the desk (meaning next
to the desk), before the desk, between the desk and you, or even on the desk (if
he's really strange). If he's clumsy, he can bump into the desk or try to walk
through the desk (and stuff would fall off the desk). Passing his hands over the
desk or resting his elbows upon the desk, he often looks across the desk and
speaks of the desk or concerning the desk as if there were nothing else like the
desk. Because he thinks of nothing except the desk, sometimes you wonder about
the desk, what's in the desk, what he paid for the desk, and if he could live
without the desk. You can walk toward the desk, to the desk, around the desk, by
the desk, and even past the desk while he sits at the desk or leans against the
desk.