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Mammary fold --> mammary ridge

Bandlike thickening of ectoderm in the embryo extending on either side from just below the axilla to the inguinal region; in human embryos, the mammary glands arise from primordia in the thoracic part of the ridge, the balance of the ridge disappearing; in some lower mammals which give birth to a litter of young, several milk glands develop along these lines.

Synonym: mammary fold, milk line, milk ridge.