Mild bifid sternum EMBRYOLOGICALLY the sternum develops from two lateral cartilaginous bars. These unite at about the ninth month of intrauterine life. An arrest of development causes the appearance of a bifid sternum.1 All degrees of bifid sternum may occur, varying from an enlarged suprasternal notch to complete separation of the two halves of the sternum. Ectopia cordis may or may not accompany this defect in its more severe form.1-7 If the heart is not completely extrathoracic, repair can generally be carried out.