Trochlea

n.
  1. (Mach.) A pulley.
  2. (Anat.) A pulley, or a structure resembling a pulley; as, the trochlea, or pulleylike end, of the humerus, which articulates with the ulna; or the trochlea, or fibrous ring, in the upper part of the orbit, through which the superior oblique, or trochlear, muscle of the eye passes.