The Hind-Brain

The hind-brain comprises the medulla oblongata or bulb, the pons Varolii, and the cerebellum. Within it, is a shallow diamond-shaped cavity - the fourth ventricle. The medulla and pons form the floor of this cavity; the cerebellum lies in the upper part of the roof, while the lower part of the roof is devoid of nervous material, and is composed merely of the lining membrane of the ventricle covered by the pia mater.