Anterior inferior endoscopic view of the upper pons looking into the interpeduncular fossa. The basilar artery overlies the pons, which receives several pontine branches. Distally, the basilar artery gives rise to the superior cerebellar arteries before terminating into right and left posterior cerebral arteries. The upper border of the pons represents the posterior border of the rhomboid-shaped interpeduncular fossa. Here, a very thin arachnoid membrane, Liliequist's membrane, forms a barrier within the basilar cisternal complex. It is described as having three components or sheets: sellar, diencephalic, mesencephalic that separate the chiasmatic cistern, interpeduncular cistern, and prepontine cistern. (Image courtesy of AL Rhoton, Jr.)