The falx cerebelli is a small sickle shaped fold of dura mater, projecting forwards into the posterior cerebellar notch as well as projecting into the vallecula of the cerebellum between the two cerebellar hemispheres.

Its base is attached, above, to the under and back part of the tentorium cerebelli; its posterior margin, to the lower division of the vertical crest on the inner surface of the occipital bone. In its lower portion it diminishes very rapidly in height and as it descends, it sometimes to frequently divides into two smaller folds or diverging limbs, which are lost on the sides of the foramen magnum.