The internal anatomy of the breast, which includes the lobules, blood vessels, and nerves. 1. Lobules: The mammary gland is divided into 15-20 lobules by connective tissue. Each lobule has a duct that opens at the nipple. Between the lobules there is an abundance of adipose tissue and, in between, there are bundles of fibrous connective tissue fibers, also known as the suspensory ligaments of the breast. 2. Blood vessels: The mammary glands also have an abundant blood supply. The main arterial vessels, such as the internal thoracic artery (internal mammary artery), the lateral thoracic artery, and the anterior branches of the 3rd-5th intercostal arteries, penetrate the mammary glands to increase the blood supply. 3. Nerves: The cutaneous lateral branches of the 2nd-6th intercostal nerves and 3-4 nerve branches of the cervical plexus, which are distributed within the mammary gland. Knowledge of the anatomy of the mammary gland can help to understand breast lesions. At the same time, during surgery, knowledge of these blood vessels and nerve routes can reduce surgical damage to the mammary gland, ensure blood supply to the mammary gland as well as nerve sensation, and improve the quality of life after surgery.