Which layer of the meninges is involved in the absorption of cerebrospinal fluid?

The arachnoid membrane is the correct choice as it plays a crucial role in the absorption of cerebrospinal fluid (CSF). This middle layer of the meninges is situated between the dura mater (the outer layer) and the pia mater (the inner layer). On its surface, the arachnoid membrane has structures called arachnoid villi (or granulations), which project into the dural sinuses of the brain. These villi are responsible for the absorption of CSF into the bloodstream, helping to regulate the fluid balance in the brain's environment.

The dura mater, while it is the toughest of the three meninges and serves as a protective layer, does not facilitate CSF absorption. Similarly, the pia mater, which closely envelopes the brain and spinal cord, is primarily involved in providing support and nourishment but does not play a significant role in CSF absorption. Lastly, the cerebral cortex is the outer layer of the brain itself, and while it is essential for various brain functions, it does not have a direct role in the absorption of cerebrospinal fluid. Thus, the arachnoid membrane is specifically tailored to manage cerebrospinal fluid dynamics, making it the correct answer.