Dural sheath or dura matter
Which part of the heart encases the heart in a tough outer membrane?
Periosteum is a membrane that lines the outer surface of all bones,[1] except at the joints of long bones.
Cell Wall
The tough outer covering that lies just outside the cell membrane in a plant cell is called the cell wall. In plant cells, it is usually made up of cellulose, hemicellulose and pectin.
The stratum corneum is the tough outer layer of the skin.
The outer layer of the dura mater, which is the layer that protects the spinal cord, is a tough fiberous sheath. This sheath also lines the cranial cavity and serves as the periostium to the inner surface.
I think it is the cell wall or the cell membrane
The dura mater which is Latin for "tough mother" and would also make a kickin' name for a sports team.
Collagenous fibers are the tough fibers of connective tissue.
The tough, fibrous membrane, which lines the cavity of the skull and spinal column, and surrounds the brain and spinal cord; -- frequently abbreviated to dura.
The dura is the tough, fibrous outermost membrane covering the brain and the spinal cord.
Endoskeleton