The outermost, toughest, and most fibrous of the three membranes (meninges) that cover the brain and spinal cord.
The brain is made up of the dura mater, arachnoid mater, and pia mater. The dura mater is made up of two layers of whitish, nonelastic film or membrane. The outer layer is called the periosteum. The dura, or inner layer, lines the inside of the skull and creates small creases or sections in which parts of the brain are protected and secured. The two main folds of the dura in the brain are the falx and the tentorium. The falx separates the left and right half of the brain and the tentorium separates the upper and lower parts of the brain.