The Collaborative International Dictionary of English v.0.48:

Mastax \Mas"tax\, n. [NL., fr. Gr. ? mouth, jaws.] (Zool.)
      (a) The pharynx of a rotifer. It usually contains four
          horny pieces. The two central ones form the incus,
          against which the mallei, or lateral ones, work so as
          to crush the food.
      (b) The lore of a bird.
          [1913 Webster]