A, The right half of the cerebellum has been removed. The right PICA passes between the rootlets of the vagus and accessory nerves to reach the surface of the inferior cerebellar peduncle. The left PICA, as it courses around the rostral pole of the tonsil, is hidden by the remaining left half of the uvula. The SCA passes around the brainstem below the oculomotor nerve and above the trigeminal nerve. B, The part of the uvula and nodule medial to the tonsil has been removed to expose the PICAs passage through the cerebellomedullary fissure and around the tonsil. The artery frequently forms a caudal loop at the lower margin of the tonsil and a cranial or supratonsillar loop that wraps around the rostral pole of the tonsil. C, The tonsil has been removed to expose the PICA’s looping course through the cerebellomedullary fissure. D, The inferior medullary velum, which stretches across the rostral pole of the tonsil, has been folded downward to expose the dentate tubercle, a prominence near the fastigium that underlies the dentate nucleus. The lateral recess is also exposed. The telovelotonsillar segment of the PICA courses in the cerebellomedullary fissure between the tela and velum on one side and the tonsil on the other side. (Images courtesy of AL Rhoton, Jr.)