The brain and spinal cord are covered by three thin membranes, collectively called meninges (pronounced men-in-jeez or min-in-jeez). The names of the individual membranes are:

• the dura mater - a thick,tough outer layer
• the arachnoid mater - the middle layer
• the pia mater - the inner layer, that is attached to the brain and spinal cord, and which carries most of the blood vessels that supply the central nervous system.

The space between the dura mater and the arachnoid mater is called the subdural space (subdural = 'below the dura').

The space between the arachnoid mater and the pia mater is the subarachnoid space (subarachnoid = 'below the arachnoid').