The mammary gland, the second female sex characteristic, is composed of skin, subcutaneous fibrofatty tissue and mammary gland tissue. Each glandular lobe is divided into several glandular lobules, which in turn are composed of many glandular vesicles. The vesicles are connected by ducts, which eventually converge into a large duct. The glandular lobules and ducts are surrounded by fibrofatty tissue. Blood vessels, lymphatic vessels, and nerves all travel through them. The lobules are the main site of common breast diseases.