Anterior Perspective of the Prepontine, Perimesencephalic, and Suprachiasmatic Region. The cerebrovasculature of the posterior circulation and circle of Willis are well demonstrated within this image. The basilar artery gives rise to multiple transverse pontine arteries (not labeled) and paired superior cerebellar arteries before bifurcating into its terminal posterior cerebral arteries (PCA).  The oculomotor nerve exits the interpeduncular fossa on each side between the posterior cerebral artery and superior cerebellar artery. The internal carotid arteries course posteriorly within the image before bifurcating into their terminal middle cerebral artery (M1) and anterior cerebral artery (A1). (Image courtesy of AL Rhoton, Jr.)