Dura cranialis

Cranial dura mater has two layers called lamellae, a superficial layer (also called the periosteal layer), which serves as the skull's inner periosteum, called the endocranium and a deep layer called the meningeal layer.

When it covers the spinal cord it is known as the dural sac or thecal sac.

Unlike cranial dura mater, spinal dura mater only has one layer, known as the meningeal layer.

The potential space between these two layers is known as the epidural space.