A, The veins in the posterior are divided into three groups: a galenic group (green) that drains into the vein of Galen; a petrosal group (blue) that drains into the petrosal sinuses; and a tentorial group (brown) that drains into the sinuses near the torcula. Tentorial surface, superior view. The tentorium has been removed except in the area of the tentorial sinuses. B, Veins of the posterior fossa. The veins in the posterior are divided into three groups: a galenic group (green) that drains into the vein of Galen; a petrosal group (blue) that drains into the petrosal sinuses; and a tentorial group (brown) that drains into the sinuses near the torcula. suboccipital surface, posterior view. The right tonsil and the medial part of the biventral lobule have been removed to expose the structures on the ventral wall of the cerebellomedullary fissure. (Images courtesy of AL Rhoton, Jr.)