Sankaku Channel/glands of montgomery

Areolar glands or Glands of Montgomery are sebaceous glands in the areola (of the nipple). The glands make oily secretions (lipoid fluid) to keep the areola and the nipple lubricated and protected.

The portion of the gland on skin's surface is called Montgomery tubercles. The round bumps are found in the areola, but also on the nipple itself. They can become exposed and raised when the nipple is stimulated. The skin over the surface opening are lubricated and tend to be smoother than the rest of the areola. The tubercles become more pronounced during pregnancy.

Wikipedia.