A, The left SCA arises as a duplicate artery. The caudal duplicate trunk crosses the rostral surface of the trigeminal nerve before entering the cerebellomesencephalic fissure. B, The right SCA does not divide into rostral and caudal trunks until it reaches the anterior edge of the cerebellomesencephalic fissure. C, Near its origin, the SCA courses below the oculomotor nerve and distally, near its entrance into the cerebellomesencephalic fissure, passes under the trochlear nerve. D, Another SCA. A large trunk passes directly from the side of the brainstem to the hemispheric surface without entering the fissure, although it does give off some smaller branches to the fissure. E, The posterior lip of the cerebellomesencephalic fissure has been removed and the upper half of the roof of the fourth ventricle opened. The SCA gives rise to perforating branches that pass down the superior cerebellar peduncle to supply the dentate nucleus. F, Oblique posterior view of the SCA branches within the cerebellomesencephalic fissure and the quadrigeminal cistern. The SCA supplies the cisternal walls below the sulcus between the superior and inferior colliculi, and the PCA supplies the wall above this level. (Images courtesy of AL Rhoton, Jr.)