Posterior perforated substance

The posterior perforated substance is a layer of gray matter which is pierced by small apertures for the transmission of blood vessels. Its inferior part lies on the ventral aspect of the medial portions of the tegmenta and contains the interpeduncular nucleus; its superior part forms part of the floor of the third ventricle.

The PPS is situated between the two mesencephalic cerebral peduncles,  and posterior/caudal to the two mammillary bodies.  It is perforated by branches of the posterior cerebral arteries en route to the thalamus and basal ganglia.  The PPS forms part of the floor of the third ventricle,  and part of the roof of the interpeduncular cistern.