Falx cerebelli

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.
The name comes from two Latin words: "falx", meaning "curved blade or scythe", and "cerebellum", meaning "little brain". 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. The falx cerebelli generally lies somewhere between 2.8 and 4.5 cm in length and is approximately 1–2 mm thick.
Variations in morphology.
In its lower portion the falx cerebelli diminishes very rapidly in height and as it descends, it can divide into two smaller "folds" or "diverging limbs", which are lost on the sides of the foramen magnum. Other variations such as duplication, triplication, absence, and fenestration are much less common. As dural venous sinuses are concurrent with the development of dural folds, duplication of the falx cerebelli is usually associated with duplicated occipital sinus. Knowledge of these variations is important in preventing iatrogenic injuries in this region.