ABSTRACT
The brain weighs approximately 3 pounds. It is surrounded by a bony chamber or vault known as the skull. Between the skull and the cerebral hemispheres lie three coverings, or membranes, which are termed the meninges. The outermost membrane is known as the dura mater. It is composed of a thick elastic material, which adheres to the inner surface of the skull. Below the dura mater is the arachnoid membrane. The third membrane is known as the pia mater. The outermost covering of the brain, the dura mater, forms what is known as the falx cerebri, which divides the two cerebral hemispheres. The dura mater also provides a protective covering (tentorium cerebelli) that divides the most posterior part of the cerebral hemispheres from the cerebellum. Located between the dura mater and the underlying subarachnoid membrane is the cerebrospinal fluid (CSF), which surrounds the brain and serves as a sort of shock absorber whenever the skull makes contact with an immovable object or the movement of the brain is rapidly accelerated or decelerated.
