A, The cerebellomedullary fissure extends upward between the tonsils and medulla. Both tonsils have been removed by dividing the peduncle of the tonsil. Removing the tonsil exposes the inferior medullary velum and tela choroidea forming the lower part of the ventricular roof. The inferior cerebellar peduncle ascends along the posterolateral medulla. The choroid plexus arises on the inner surface of the tela choroidea. The taeniae are the site of attachment of the tela choroidea along the inferolateral margins of the ventricle floor. The telovelar junction is the site of attachment of the inferior medullary velum to the tela choroidea. The nodule, on which the inferior medullary velum arises, is hidden deep to the uvula. B, The tela, in which the choroid plexus arises, has been removed to expose both lateral recesses. The superior cerebellar peduncle forms the lateral wall of the upper half of the ventricle. The inferior cerebellar peduncle forms the anterior and upper margin of the lateral recess. The middle cerebellar peduncle, which forms a large prominence on the lateral surface of the pons, is separated from the ventricular surface by the superior and inferior cerebellar peduncles. C, Lateral surface of the left tonsil. All of the tonsillar surfaces, except at the superolateral margin, are free surfaces. The peduncle of the tonsil, located along the superolateral margin of the tonsil, attaches the tonsil to the remainder of the cerebellum. The posterior surface of the tonsil faces the cisterna magna. The medial surface faces the other tonsil. The anterior surface faces the posterior medulla. The rostral pole faces the inferior medullary velum and tela choroidea. The lateral surface below the peduncle of the tonsil faces the biventral lobule. D, Posterior view of the left tonsil. The peduncle of the tonsil is located along the superolateral margin. Dividing the narrow peduncle allows the tonsil to be separated from the remaining cerebellum. (Images courtesy of AL Rhoton, Jr.)