Mammary ridge

Mammary Ridge

The mammary ridge, also known as the milk line, is a critical embryological structure in mammals. It is a bilateral line of thickened ectoderm that extends from the axilla (armpit) to the groin on the ventral surface of the developing embryo. This ridge is the precursor to the mammary glands, which are essential for lactation in mammals.

Diagram showing the location of the mammary ridges in a human embryo.

Development

The development of the mammary ridge begins during the sixth week of embryogenesis. Initially, the ridge appears as a continuous line of thickened ectoderm. As development progresses, the ridge regresses in most areas, except at specific locations where the mammary glands will form. These locations correspond to the future positions of the nipples and areolae.

The mammary ridge is an example of a vestigial structure in humans, as it is more prominent in other mammals that have multiple pairs of mammary glands. In humans, typically only one pair of mammary glands develops, located in the pectoral region.

Clinical Significance

The mammary ridge is of clinical importance because it can give rise to supernumerary nipples or polymastia, conditions where extra nipples or breast tissue develop along the line of the ridge. These conditions are usually benign but can sometimes be mistaken for other pathologies.

Related Pages

• Mammary gland
• Embryogenesis
• Supernumerary nipple
• Polymastia