The breast is not developed in children and men, but in adolescent women, the breast is hemispherical, located at the height of the second to sixth ribs, between the shallow and deep layers of the superficial fascia, the surface of the pectoralis fascia, from the parasternal line outward up to the mid-axillary line. 1, the internal structure of the breast The breast is mainly composed of glands, ducts, fatty tissue and fibrous tissue. The breast gland is composed of 15-20 lobes, each of which is divided into several lobules, and each lobule is composed of 10-100 vesicles. Each glandular lobe is divided into several lobules, and each lobule is composed of 10 to 100 vesicles. The vesicles are arranged closely around the small milk ducts, and their openings are connected to them. Many small milk ducts come together to form interlobular milk ducts, and several interlobular milk ducts come together to form a whole lobe of milk ducts, also known as milk ducts. There are 15 to 20 ducts, which are arranged in a radial pattern centered on the nipple and converge on the areola, with the opening at the nipple, called the foramen ovale. The milk ducts are narrower at the nipple and expand into a pot belly, called the sinus of the milk duct, which can store milk. The opening of the ducts is lined with squamous epithelial cells and the narrowing is lined with migrating epithelium, while the ducts below the pot belly are double-layered columnar epithelium or single-layered columnar epithelium, and the terminal ducts are lined with cuboidal epithelium near the alveoli. The amount of adipose tissue in the breast is one of the most important factors in determining the size of the breast. The fatty tissue is encapsulated in a capsule around the breast, forming a hemispherical whole, which is called the fat capsule. The thickness of the fat capsule can vary greatly between individuals due to age, childbirth, etc. The mammary glands are located between the superficial and deep layers of the superficial subcutaneous fascia. The superficial fascia extends into the breast tissue to form lobular septa that are attached to the pectoralis fascia at one end. The other end is attached to the skin and holds the mammary glands in the subcutaneous tissue of the breast. These fibrous connective tissues that support and hold the breast in place are called the suspensory ligaments of the breast. The deep layer of superficial fascia is located on the deep side of the breast and is connected to the superficial layer of the pectoralis major fascia by loose tissue, which allows the breast to be both relatively fixed and somewhat mobile in the chest wall. The fibrous tissue surrounding the mammary gland sends small bundles of fibers to the deep surface and is attached to the pectoral fascia. From the surface of the mammary glands, small bundles of fibers are also attached to the skin and nipples, and these bundles are more developed in the upper part of the breast. These fibrous bundles are called the suspensory ligaments of the breast, and they play a role in fixing the breast. 2, the external structure of the breast The nipple is composed of dense connective tissue and smooth muscle. Smooth muscle is arranged in a circular or radial pattern, when there is mechanical stimulation, smooth muscle contraction, can make the nipple erect, and squeeze the ducts and sinuses to discharge its contents. The skin of the areola has hairs and glands. The glands are sweat glands, sebaceous glands and mammary glands. The sebaceous glands, also known as areolar glands, are large and superficial, and secretions have the role of protecting the skin, lubricating the nipples and the baby’s lips.