From the 1755 edition of Samuel Johnson's Dictionary :

PA'STERN n. s. [pasturon, French.]

  1. The knee of a horse.
    I will not change my horse with any that treads on four pasterns.
    --- Shakespeare's Henry V.
    The colt that for a stallion is design'd,
    Upright he walks on pasterns firm and straight,
    His motions easy, prancing in his gait.
    --- Dryden.
    Being heavy, he should not tread stiff, but have a pastern made him, to break the force of his weight : by this his body hangs on the hoof, as a coach doth by the leathers.
    --- Grew.
  2. The legs of a human creature in contempt.
    So straight she walk'd, and on her pasterns high.
    If seeing her behind, he lik'd her pace,
    Now turning short, he better lik'd her face.
    --- Dryden