Final answer:
The structure labeled 'c' is the dura mater, the outermost protective layer of the meninges, providing a thick sheath over the brain and spinal cord.
Step-by-step explanation:
The connective tissue structure labeled 'c' is an extension of the meninx (meningeal layer) better known as the dura mater. The dura mater is the outermost layer of the meninges that provides a thick, fibrous, and strong protective sheath over the entire brain and spinal cord. It is this layer that is anchored to the inner surface of the cranium and vertebral cavity and contains vein-like structures that carry blood from the brain back to the heart. In contrast, the arachnoid mater is the middle layer of the meninges, resembling a spider web with its trabeculae extending between it and the pia mater. The arachnoid mater contains a space known as the subarachnoid space which is filled with cerebrospinal fluid (CSF). The arachnoid granulations allow for the reabsorption of CSF back into the blood for drainage from the nervous system. The last and innermost layer of the meninges is the pia mater, which adheres closely to the brain and spinal cord, following their contours closely.