The breast does not have muscles. Breast tissue is located on top of the muscles of your chest wall. Blood vessels and lymphatic vessels (a system of vessels that drains fluid) are located through the entire breast. Breast tissue starts to sort from the fourth 7 days of fetal existence. https://grok.com/share/c2hhcmQtMw%3D%3D_21b4ddf4-c274-418a-a078-c9d2af4898ff