noun

• 1Embryology
  A ridge of thickened ectoderm that appears on either side of the ventral surface of a mammalian embryo, extending from the fore to the rear limb buds, on which the mammary glands form; (also) a line representing this in post-embryonic life, the line occupied by the mammary glands.

• 2Farming
  The main pipe or tube which carries milk from a milking shed to a holding tank.