The<unk>  (annulus<unk>  is the prominent oval margin of the<unk><unk> .
It is most distinct above and at the sides of the<unk> ; below, it is deficient.
A small slit-like valvular opening is occasionally found, at the upper margin of the<unk> , leading upward beneath the<unk> , into the left atrium; it is the remains of the fetal aperture between the two atria.
Limbus of fossa ovalis
Cerebral crus
Foramen ovale 
Lateral sulcus
Posterior interventricular sulcus
Horizontal fissure of cerebellum
Intervertebral foramina
Periaqueductal gray