conjoined twins
monozygotic twins whose bodies join or fail to separate completely during embryonic life; the exact mechanism and cause are not understood. Many conjoined twins are stillborn or die shortly after birth. Conjoined twins may have two bodies that are attached at the rib cage, head, or other location; alternatively, they may share one torso, limbs, or some internal organs. In some cases, surgical separation is possible. The popular name, Siamese twins, derives from the brothers Eng and Chang (1811–1874), who were born in Thailand (Siam) and exhibited in sideshows.