Segments of the SCA. A, Superior view. The SCA arises at the level of the midbrain and dips caudally along the pontomesencephalic junction to enter the cerebellomedullary fissure and supply the tentorial surface of the cerebellum. The s1 courses anterior to the midbrain, the s2 lateral to the upper brainstem, the s3 in the cerebellomesencephalic fissure (Cer. Mes. Fiss.), and the s4 is formed by the cortical branches. B, Lateral view of the right pontomesencephalic junction showing s1 to s3. The s2 loops downward toward the trigeminal nerve. C, Anterior view. The s1 arises anterior to the midbrain, and the s2 loops downward to the level of the junction of the trigeminal nerve with the midpons. D, The SCA bifurcates early and both the rostral and caudal trunks dip in to the cerebellomesencephalic fissure to form the s3. E, The superior lip of the cerebellomesencephalic fissure has been removed to expose the s3 within the fissure where it gives branches that continue down the superior cerebellar peduncle (Sup. Cer. Ped.) to the dentate nucleus. F, Superior view of the s4 formed by the cortical branches supplying the tentorial surface of the cerebellum. (Images courtesy of AL Rhoton, Jr.)