Anatomy of Human Breast

The breasts are modified sudoriferous (sweat) glands, producing milk.
The breasts are covered by skin. Each breast has one nipple surrounded by the areola. The areola is colored from pink to dark brown and has several sebaceous glands. The larger mammary glands within the breast produce the milk. They are distributed throughout the breast, with two-thirds of the tissue found within 30 mm of the base of the nipple.[2] These are drained to the nipple by between 4 and 18 lactiferous ducts, where each duct has its own opening. The network formed by these ducts is complex, like the tangled roots of a tree. It is not always arranged radially, and branches close to the nipple. The ducts near the nipple do not act as milk reservoirs. Ramsay et al. have shown that conventionally described lactiferous sinuses do not, in fact, exist.
The remainder of the breast is composed of connective tissue (collagen and elastin), adipose tissue (fat), and Cooper’s ligaments. The ratio of glands to adipose tissues rises from 1:1 in nonlactating women to 2:1 in lactating women.
The breasts sit over the pectoralis major muscle and usually extend from the level of the 2nd rib to the level of the 6th rib anteriorly. The superior lateral quadrant of the breast extends diagonally upwards towards the axillae and is known as the tail of Spense. A thin layer of mammary tissue extends from the clavicle above to the seventh or eighth ribs below and from the midline to the edge of the latissimus dorsi posteriorly.
The arterial blood supply to the breasts is derived from the internal thoracic artery (formerly called the internal mammary artery), lateral thoracic artery, thoracoacromial artery, and posterior intercostal arteries. The venous drainage of the breast is mainly to the axillary vein, but there is some drainage to the internal thoracic vein and the intercostal veins. Both sexes have a large concentration of blood vessels and nerves in their nipples. The nipples of both females and males can become erect in response to sexual stimuli.
The breast is innervated by the anterior and lateral cutaneous branches of the fourth through sixth intercostal nerves. The nipple is supplied by the T4 dermatome.
The primary anatomical support for the breasts is thought to be provided by the Cooper’s ligaments, with additional support from the skin covering the breasts themselves, and it is this support which determines the shape of the breasts. The external shape or size of the breast is not predictive of its internal anatomy nor of its lactation potential. In a small fraction of women, the frontal milk sinuses (ampulla) in the breasts are not flush with the surrounding breast tissue, which causes the sinus area to visibly bulge outward

(source from wikipedia.org)