FORAMEN Ovale, an oval aperture or passage through the heart of a foetus, which closes up after birth. It arises from the coronal vein, near the right auricle, and passes directly into the left auricle of the heart, serving for the circulation of the blood in the foetus, till such time as the infant breathes, and the lungs are open: in this the foetus differs from the adult; although almost all anatomists, Mr Cheselden excepted, assure us, that the foramen ovale has sometimes been found in adults. See FOETUS.