Posterior view of right dorsal cerebellum and posterior cerebrum. The quadrigeminal cistern is a subarachnoid cistern located between the collicular plate, splenium of corpus callosum, and dorsal surface of the cerebellum. It contains the posterior cerebral arteries, the superior cerebellar arteries, the great cerebral vein (of Galen), and the trochlear nerve (CN IV). The great cerebral vein merges with the inferior sagittal sinus (removed) to form the straight sinus located at the intersection of the falx cerebri and tentorium cerebelli. The trochlear nerve is the cranial nerve that arises from the dorsum of the midbrain. (Image courtesy of AL Rhoton, Jr.)