A, The retrotonsillar veins pass upward in the fissure between the tonsil and biventral lobule and empty into the inferior vermian veins. B, The tonsils have been removed to expose the veins of the cerebellomedullary fissure, which pass laterally on the inferior medullary velum and across the lateral recesses to join the veins in the cerebellopontine angles. The medial end of the veins of the cerebellomedullary fissure anastomose with the veins around the tonsil. C, Another specimen. The tonsils and part of the biventral lobules have been removed to expose the paired veins of the cerebellomedullary fissure, which cross the inferior medullary velum to empty into the veins in the cerebellopontine angles. D, The cerebellar hemispheres, except for the right tonsil, have been removed. The right retrotonsillar vein courses along the posterior surface of the tonsil and empties into an inferior vermian vein. The left vein of the cerebellomedullary fissure passes through the lateral recess to join the vein of the middle cerebellar peduncle, which ascends to empty into a superior petrosal vein. The paired veins of the superior cerebellar peduncle ascend on the peduncle and join to form the vein of the cerebellomesencephalic fissure. An interpeduncular vein courses between the superior and middle cerebellar peduncles. (Images courtesy of AL Rhoton, Jr.)