Which connective tissue membrane covers the brain's innermost layer?

The connective tissue membrane that covers the brain's innermost layer is the pia mater. This membrane is a delicate and thin layer that closely adheres to the surface of the brain and spinal cord, following its contours and grooves. The pia mater plays a critical role in providing nutrients and support to the nervous tissue, as it is rich in blood vessels.

Understanding the anatomy of the meninges—the protective layers surrounding the brain and spinal cord—helps clarify why the pia mater is the correct answer. The outermost layer is the dura mater, which is sturdy and protective, while the middle layer is the arachnoid mater, which has a web-like appearance and is situated between the dura and pia matter. The falx cerebri, another structure mentioned in the options, is a fold of dura mater that separates the cerebral hemispheres but is not a connective tissue membrane in its own right.