Cerebellar and Associated Cerebrovascular Anatomy. A, The right half of the cerebellum was removed by dividing the vermis sagittally and the cerebellar peduncles transversely. The PICA courses around the rostral pole of the tonsil in the cleft between the tonsil on one side and the tela choroidea and inferior medullary velum on the other side. B, The tonsil has been removed and the inferior medullary velum has been displaced downward to expose the opening into the lateral recess. The dentate nucleus forms a prominence, the dentate tubercle, in the superolateral recess of the roof of the fourth ventricle near the site of attachment of the inferior medullary velum. (Images courtesy of AL Rhoton, Jr.)