FORAMEN Ovale, an oval aperture or passage thro' the heart of a fetus, which closes up after birth. It arises above 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 fetus, till such time as the infant breathes, and the lungs are open; it being generally reckoned one of the temporary parts of the fetus, wherein it differs from an adult; although almost all anatomists, Mr Chefelden excepted, assure us, that the foramen ovale has sometimes been found open in adults. See Fœtus.