The pit, located at the front of the midbrain
(mesencephalon), is bounded to the sides by the right and left cerebral hemispheres
(crus cerebri) which on their insides release cranial nerve 3
(n. occulomotorius). At the bottom of the pit, 10 - 20 round holes open straight into the midbrain. The holes are entrances for a bundle of narrow arteries/arteries that supply the central parts of the midbrain. The bottom of the pit is called the posterior blood vessel entry
(substantia perforata posterior).