A mammary alveolus (pl.: alveoli, from Latin alveolus, "little cavity") is a small cavity or sac found in the mammary gland.[1][2] Mammary alveoli are the site of milk production and storage in the mammary gland.[1][2] Mammary alveoli cluster into groups called mammary lobules, and each breast may contain 15 to 20 of these lobules.[1][2] The lobules drain milk through the lactiferous ducts out of the nipples.[1][2]
