The milk line, also known as the mammary ridge, is a linear elevation that appears during embryonic development and gives rise to the mammary glands.
During the early stages of development, around the sixth week in humans, the milk line extends from the axilla (armpit) to the groin region on both sides of the developing embryo. This line represents the initial site where mammary glands can potentially form. In most mammals, mammary glands develop along this entire line. However, in humans, only the mammary glands in the pectoral region (chest area) typically persist and develop into functional breasts.
Here's a breakdown of the milk line's significance:
- Developmental Origin: It's the embryonic precursor to mammary glands.
- Location: Extends from the armpit to the groin.
- Persistence: Usually only persists in the chest region in humans, leading to the formation of breasts.
- Abnormalities: In rare cases, remnants of the milk line may persist elsewhere along the line, resulting in accessory nipples (polythelia) or accessory mammary glands (polymastia) in areas like the armpit or abdomen.
In summary, the milk line is a crucial structure in early development, marking the potential sites for mammary gland formation.
