Sagittal Perspective of Cerebellar Lobules, Fourth Ventricle, and Brainstem. The cerebellum is divided into 10 lobules. Lobules I and II are small and contained exclusively within the vermis anterior to the precentral fissure. Lobule X is synonymous with the flocculonodular lobe. The remainder of the lobules include portions of both the cerebellar vermis and cerebellar hemisphere. The regional association between the middle cerebellar peduncle and the fourth ventricle is apparent on the left side of this image and highlights the challenge in achieving fourth ventricular floor exposure from a Telovelar approach given the cerebellar hemispheres are pedicled closely to this region.  (Image courtesy of AL Rhoton, Jr.)