A, The left half of the tentorium has been removed while preserving the tentorial sinuses. The anterior group of superior vermian and superior hemispheric veins arise on the upper part of the tentorial surface and ascend to reach the veins exiting the cerebellomesencephalic fissure, which empty into the vein of Galen. The posterior group of superior vermian and superior hemispheric veins arise on the posterior part of the tentorial surface and descend to empty into tentorial sinuses. The inferior hemispheric veins, which arise on the suboccipital surface, also empty into the tentorial sinuses. B, Both halves of the tentorium have been removed while preserving the large tentorial sinuses. The superior hemispheric veins from the posterior part of the tentorial surface and the inferior hemispheric veins from the suboccipital surface drain into the paired large tentorial sinus that join the torcula. The veins draining the anterior part of the tentorial surface empty into the tributaries of the vein of Galen. C, Lateral view of the cerebellomesencephalic fissure. The largest vein in the fissure is the vein of the cerebellomesencephalic fissure. The internal cerebral veins pass above the pineal to join the vein of Galen. D, The veins draining the walls of the cerebellomesencephalic fissure join the vein of Galen, as do the internal cerebral and basal veins. A pineal vein also joins the Galenic group. (Images courtesy of AL Rhoton, Jr.)