Breast: The breasts, or mammary glands, are modified sweat glands. The breasts lie on top of the chest wall immediately over the pectoral muscles, pectoralis major and pectoralis minir, and are attached to the pectoralis major by a layer of connective tissue, the pectoral fasia. On the lower lateral aspect of the chest wall, the breasts are in contact with the serratus anterior muscles. Each breast consists of many separate glands that are connected by individual ducts (lactiferous ducts) to the nipple. These glands constitute the lobes of the breast, 15-20 lobes (glands) for each breast. Each lobe is composed of many lobules which are formed from minute ducts and contain secreting cells (alveoli). Located in the center of each breast is a nipple bordered by a circular pigmented area of skin called the areola. The lactiferous ducts from the lobes of the breast converge in the nipple. The blood supply to the breast is from both the internal thoracic (subclavian) and the lateral thoracic (axillary) arteries. The veins form both superficial and deep plexuses and correspond in general to the arterial pattern. The regional lymph nodes of the breast are axillary lymph nodes, which are subdivided into low axillary (Level I): area adjacent to the tail of the breast; mid axillary (Level II): central, interpectoral [Rotter's node]; high axillary (Level III): apex of the axillary including those designated as subclavicular, infraclavicular, and apical nodes; internal mammary (parasternal) lymph nodes (ipsilateral): in the intercostal spaces along the edge of the sternum in the endothoracic fascia.