A, The SCAs pass around the midbrain to enter the cerebellomesencephalic fissure and, after a series of hairpin turns in the fissure, loop over the posterior lip of the fissure to reach the tentorial surface. The lower part of the quadrigeminal cistern extends in the cerebellomesencephalic fissure. The tentorial surface slopes downward from the apex just behind the fissure. B, Anterosuperior view. The left SCA arises on a duplicate artery. In their initial course, the SCAs loop laterally below the tentorial edge, but further posteriorly, they pass medially under the tentorial edge to enter the cerebellomesencephalic fissure. C, Another cerebellum. The SCAs loop into the cerebellomesencephalic fissure, where they undergo a series of hairpin turns before exiting the fissure to supply the tentorial surface. D, The posterior lip of the fissure has been retracted to expose the branches of the SCA within the fissure. (Images courtesy of AL Rhoton, Jr.)