Vasculature at interpeduncular fossa. The interpeduncular fossa of the anterior midbrain is directed toward the bottom of the image. From its lateral surface emerge the oculomotor nerves. These pass forward between the posterior cerebral and superior cerebellar arteries. Posterior to the cerebral peduncles are the pigmented substantia nigra, the largest nuclei of the midbrain. Anterior to the fossa are the posterior cerebral arteries, terminal branches of the basilar artery. From the proximal portions (P1 segments) of these arteries  arise several small perforating arteries that enter the interpeduncular fossa and penetrate its posterior perforating substance to supply part of the midbrain and thalami. These are augmented by circumflex branches of the posterior cerebral arteries that wrap around the sides of the cerebral peduncles. (Image courtesy of PA Rubino)