The folium vermis is a short, narrow, concealed band at the posterior extremity of the vermis

Cerebellar vermis

The cerebellar vermis is located in the medial, cortico-nuclear zone of the cerebellum, residing in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior surface of the cerebellum, dividing it into anterior and posterior lobes....

, consisting apparently of a single folium

Folium (brain)

A folium is a wrinkle on the surface of the cerebellum. The cortex of a folium consists of three layers of cells - the top molecular layer, the Purkinje layer, and the bottom granular layer - and this cortex covers deeper white matter ....

, but in reality marked on its upper and under surfaces by secondary fissures.

Laterally, it expands in either hemisphere into a considerable lobule, the superior semilunar lobule (lobulus semilunaris superior; postero-superior lobules), which occupies the posterior third of the upper surface of the hemisphere, and is bounded below by the horizontal sulcus

Horizontal sulcus

The largest and deepest fissure in the cerebellum is named the horizontal sulcus .It commences in front of the pons, and passes horizontally around the free margin of the hemisphere to the middle line behind, and divides the cerebellum into an upper and a lower portion.-External links:* via the...

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The superior semilunar lobules and the folium vermis form the lobus semilunaris.