The Bone Museum on Instagram: "Thoracopagus twins are the most common form of conjoined twinning, joined at the chest and often sharing vital organs such as the heart and liver. Because their anatomy is so closely intertwined, each case offers rare insight into human development. Conjoined twinning happens very early in pregnancy, around 13–15 days after fertilization, when the developing embryo begins to form the body plan. The leading theory is that the embryo partially splits but does not ful