Final answer:
The projections of the arachnoid membrane into the dural sinuses are called arachnoid granulations. They allow for the reabsorption of cerebrospinal fluid back into the blood.
Step-by-step explanation:
The projections of the arachnoid membrane into the dural sinuses are called arachnoid granulations. These granulations allow for the reabsorption of cerebrospinal fluid (CSF) back into the blood. The arachnoid mater, which is the middle layer of the meninges, forms a loose sac around the central nervous system (CNS) and extends into the dural sinuses as the arachnoid granulations.