The limbus of fossa ovalis (annulus ovalis) is the prominent oval margin of the fossa ovalis

Fossa ovalis

Fossa ovalis can refer to:* Fossa ovalis , also called the saphenous opening* Fossa ovalis , an embryonic remnant of the foramen ovale...

. It is in the right atrium.

It is most distinct above and at the sides of the fossa

Fossa (anatomy)

In anatomical terminology, fossa has come to mean a depression or hollow, in general, in a bone. Other parts of the body may be involved, for example, the antecubital fossa...

; below, it is deficient.

A small slit-like valvular opening is occasionally found, at the upper margin of the fossa, leading upward beneath the limbus, into the left atrium

Left atrium

The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...

; it is the remains of the fetal aperture between the two atria

Atria

Atria may refer to:*Atrium , an anatomical structure of the heart*Atrium , a large open space within a building*Atria or Alpha Trianguli Australis, a star in the constellation Triangulum Australe...

.