Dura Mater: Latin terms meaning [tough mother]. The dura mater is the outermost of the three meninges. It is quite tough, forming a sac containing the spinal cord and brain, known as the dural sac or thecal sac. The image, from a book by Andreas Vesalius, shows a head with the dura mater in situ (label "A").
For more information on the meninges, click here.
Original images from Andreas Vesalius' "De Humani Corporis Fabrica; Libri Septem" (1543)