I. The shape of the breast The shape of the breast can vary greatly due to race, genetics, age, breastfeeding and other factors. The breasts of adult women in China are generally hemispherical or conical in shape. Both sides are basically symmetrical, with a certain degree of sagging or slightly flattened after breastfeeding. In older women, the breasts are often atrophied and saggy. The central part of the breast is the nipple. Normal nipples are cylindrical or cone-shaped. They are symmetrical on both sides and have a pink or brown surface. The nipple is usually located at the 4th or 5th intercostal level and 1 cm outside the midclavicular line in young women; in middle-aged women, it is located at the 6th intercostal level and 1 cm outside the midclavicular line. the diameter of the nipple is about 0.8-1.5 cm, and there are many small fossae on it, which are the openings of the milk ducts. The annular area with deeper skin pigmentation around the nipple is the areola. The areola has a diameter of about 3-4 cm and varies in color from rose-red during puberty to dark brown during pregnancy and lactation. The skin of the breast is thicker around the glands and thinner at the nipple and areola. Sometimes superficial subcutaneous veins can be seen through the skin. The breast is located in front of the pectoralis major muscle on both sides of the chest, and its position is also related to age, body shape and the degree of breast development. The breasts of adult women are generally located between the 2nd and 6th ribs in front of the chest, with the inner edge near the sternum and the outer edge reaching the anterior axillary line, and up to the mid-axillary line when the breasts are enlarged. The outer upper pole of the breast is long and narrow, forming the axillary tail of the breast reaching into the axilla. Because of the large individual differences in the shape and position of the breast, the development of the female breast is also affected by age and various factors such as different physiological periods, therefore, the normal range of breast shape and position should be avoided as pathological, thus creating an unnecessary burden of thought. The structure of the breast The breast is mainly composed of glands, ducts, fatty tissue and fibrous tissue, and its internal structure is like a small tree growing upside down. The breast gland is composed of 15 to 20 glandular lobes, each glandular lobe is divided into several glandular lobules, and each glandular lobe is composed of 10 to 100 glandular vesicles. These vesicles are arranged closely around the ducts, and the openings of the vesicles are connected to the ducts. The ducts converge to form interlobular ducts, which further converge to form a duct for the entire lobe of the breast, also known as the “milk duct”. There are 15 to 20 milk ducts, which are arranged in a radial pattern with the nipple as the center, and the ones that converge at the areola and open at the nipple are called “milk ducts”. The milk ducts are narrower at the nipple and then expand into a pot belly, called the sinus of the milk duct, which has the role of storing milk. The surface of the nipple is covered with a double layer of squamous keratinous epithelium, and the epithelium is very thin. The papillae are composed of dense connective tissue and smooth muscle. The smoothness is arranged in a circular or radial pattern, and when there is mechanical stimulation, the smooth muscle contracts. The nipples can be erected and the ducts and sinuses can be squeezed to drain their 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 secrete to protect the skin, lubricate the nipple and the baby’s lips. The fatty tissue in the breast is encapsulated around the mammary gland in the form of a hemispherical whole, and this encapsulated fatty tissue is called the “fat capsule”. The thickness of the fat capsule can vary greatly depending on age, childbirth and other reasons. The mammary glands are located between the superficial and deep subcutaneous layers of the superficial fascia. The superficial fascia extends into the breast tissue to form a gap of lobules, attached to the pectoralis fascia at one end and to the skin at the other, which anchors the breast glands in the subcutaneous tissue of the breast. These fibrous connective tissues that support and hold the breast in place are called the “suspensory ligament of the breast” or “Cooper’s ligament. The deep layer of the superficial fascia is located on the deep side of the breast and is connected to the superficial layer of the pectoralis major fascia with loose tissue, called the “posterior breast space”, which allows the breast to be relatively fixed and to have some mobility in the chest wall. Sometimes, some of the breast glands can pass through the lax tissue and penetrate into the superficial layer of the pectoralis major muscle, therefore, the pectoralis major muscle fascia and muscle should be removed together with radical breast cancer surgery. Most of the breast is located on the surface of the pectoralis major muscle, the deep surface of which is laterally located on the surface of the serratus anterior muscle and medially and inferiorly located on the surface of the fascia of the external oblique and rectus abdominis muscles. In addition to the above structures, the breast is also rich in blood vessels, lymphatic vessels and nerves, which play a nutritional role and maintain the metabolism of the breast, and have important external scientific significance.