An udder is an organ formed of the mammary glands of female quadruped mammals, particularly ruminants such as cattle, goats, sheep and deer. The udder is a single mass hanging beneath the animal, consisting of pairs of mammary glands. In cattle there are normally two pairs, in sheep, goats and deer there is one pair, and in some animals such as pigs there are many pairs. In animals with udders, the mammary glands develop on the milk line near the groin, and mammary glands that develop on the chest (such as in humans and apes) are generally referred to as breasts.