Location and external morphology of the mammary glands 1. Location The female breast is located on the surface of the pectoralis major muscle and the pectoral fascia, which usually extends from the second rib to the sixth rib, medially to the paraspinal line, and laterally up to the midaxillary line. The nipple is located in the 4th intercostal space or 5th rib. 2, the external form of the surface of the breast is the nipple, the tip of which has the opening of the milk ducts, the milk can flow down the ducts, through the nipple of the small holes outflow. The nipple consists of dense connective tissue and smooth muscle, the smooth muscle is arranged in a circular or radial pattern, playing the role of sphincter, when there is a mechanical stimulation or nerve signal, the smooth muscle will contract and accumulate pressure on the ducts, the nipple erect and straight. The skin area around the nipple with more pigmentation is called areola, and the surface of areola has many small point-like elevations which are the opening parts of deep areola glands, and the deep surface of areola glands, which can secrete fatty substances to moisten the nipple, and play the role of lubrication and protection. The skin of the nipple and areola is weak and easily damaged. During pregnancy and breastfeeding, the mammary glands are enlarged and the breasts increase in size. After breastfeeding stops, the mammary glands shrink and the breasts become smaller. Breast atrophy is more pronounced in older women.