The vermis (pl: vermes) of the cerebellum is an unpaired medial structure which separates the cerebellar hemispheres. The neocerebellar posterior lobes join in the midline behind the primary fissure to separate the vermis into superior and inferior portions. The vermis can be further subdivided into nine lobules which are formed by groups of folia (sing: folium). Each lobule of the vermis is associated with two paired cerebellar hemisphere lobules and is subject to variability in terms of their size, shape and number of folia . A helpful mnemonic to remember the lobules of the vermis can be found here.