The Collaborative International Dictionary of English v.0.48:

Mammillary \Mam"mil*la*ry\, a. [Cf. F. mammilaire. See
   Mammilla.]
   1. Of or pertaining to the mammilla, or nipple, or to the
      breast; resembling a mammilla; mammilloid.
      [1913 Webster]

   2. (Min.) Composed of convex convex concretions, somewhat
      resembling the breasts in form; studded with small
      mammiform protuberances.
      [1913 Webster] Mammillate