Anatomy of the breast

The breast develops from the milk streak (mammary ridge), which regresses in the human fetus to the site of the adult nipple. This buds into 15–20 epithelial columns, which canalize before birth in to the lactiferous ducts. At puberty, masses of cells proliferate at their endings. Secreting alveoli develop during pregnancy to secrete milk after delivery. The glandular tissue atrophies after the menopause. The bulk of breast tissue localizes to its upper outer quadrant. It lies mainly on pectoralis major, overlapping onto serratus anterior and rectus abdominis. A tongue, the axillary tail, projects into the axilla. Being an epithelial derivative, the breast is enclosed in its own pocket of superficial fascia, enabling its clean dissection at mastectomy.

Its rich blood supply is derived from the internal thoracic (internal mammary) artery and from branches of the axilllary artery, accompanied by the corresponding veins. Lymphatic drainage accompanies these blood vessels, and passes principally to the axillary lymph nodes (divided into levels one, two and three by pectoralis major), and to the internal thoracic nodes, with some drainage passing to the intercostals nodes near the heads of the ribs.