A, Superior surface of the tentorium. Some of the tentorial sinuses can be seen through the tentorial surface. Veins from both the cerebrum and cerebellum empty into the tentorial sinuses. The veins in the quadrigeminal cistern and the cerebellomesencephalic fissure empty into the vein of Galen and its tributaries. B, The left half of the tentorium has been removed while preserving the tentorial edge. The inferior hemispheric veins from the suboccipital surface cross the posterior part of the tentorial surface to empty into one of the tentorial sinuses with some of the superior hemispheric veins. Two veins from the right posterior temporal lobe empty into the transverse sinus. C, Superolateral view of the tentorium. A complex and variable group of venous sinuses course within the tentorium and empty into the straight, transverse, and superior petrosal sinuses. The veins draining the suboccipital surface and posterior part of the tentorial surface empty into the tentorial sinuses. The majority of veins from the upper part of the tentorial surface drain toward the cerebellomesencephalic fissure and empty into tributaries of the vein of Galen. Some veins from the lateral part of the tentorial surface may empty into the superior petrosal sinus. D, Lateral cerebral and cerebellar surfaces. The sinuses in the tentorium receive drainage from both the cerebrum and cerebellum. Veins from the lateral and inferior surfaces of the cerebral hemisphere pass toward, but often turn medially above the transverse sinus to join the tentorium sinuses that empty into the transverse sinus. The inferior hemispheric veins from the suboccipital surface ascend toward, but often pass below the transverse sinus to empty into the tentorial sinuses. A mastoidectomy has been completed to expose the sigmoid sinus and jugular bulb. (Images courtesy of AL Rhoton, Jr.)