Cooper's ligaments

Cooper's ligaments are the connective tissue in the breast that holds them up. As any ligament, over time, they may lose strength and tension in the elderly - especially so in females (as you may have observed, e.g. the wrists of your girlfriend are much more flexible than yours). That makes the breast hang down with the years. Samuel Shem (author of the "House of God") called them Cooper's Droopers in this state of tension.