The middle layer of the meninges, the arachnoid mater projects into the sinuses formed by the dura mater. These projections are known as the arachnoid granulation/villi. They transport cerebrospinal fluid from the ventricles to the bloodstream. Filled with cerebrospinal fluid, the subarachnoid space lies between the arachnoid mater and pia mater. The space contains blood vessels that appear web-like and cranial nerves.