Supernumerary mammary glands derived from rudiments of the embryonic milk lines or mammary ridges in the vulva are considered a source of a series of unusual tumors resembling lesions of the breasts. This phenomenon was reevaluated in light of recent observations of mammary-like anogenital glands (MLG), which are a normal constituent of the vulva and appear to be closely related to eccrine glands. An analysis of the literature reveals that the concept of "milk lines" originated in a mixture of phylogenetic and ontogenetic theories at the beginning of this century and was not supported by observations in human embryos, which show that primordia of the mammary glands do not extend beyond the axillary-pectoral area. The breasts and the vulva are so widely separated by time and space that the vulvar MLG can not be derived from the mammary ridges or milk lines. The profile of the MLG, which can also reveal some eccrine or apocrine features, makes these glands the most likely source of a series of lesions occurring in the anogenital region and comprising lactating glands, lactating adenoma, fibroadenoma, hidrocystoma, hidradenoma papilliferum, and most cases of extramammary Paget's disease and invasive adenocarcinoma.