Dura mater

The cranial dura is made of dense collagen in two layers. The periosteal layer is firmly attached to the inner table of the skull, especially at the sutures and the skull base. The meningeal layer is continuous with the spinal dura through the foramen magnum and gives off four dural reflections:
• the falx cerebri in the longitudinal fissure;
• the tentorium cerebelli, a tent over the cerebellum whose free edge bounds the tentorial notch around the midbrain;
• the falx cerebelli;
• the diaphragma sellae roofing the pituitary fossa.
These partitions limit movement of the brain but also create the compartments across which brain tissue herniates. Along the attached edges of the falx and tentorium the layers enclose the superior and inferior sagittal, straight, transverse and sigmoid sinuses. The meningeal layer also forms sleeves around the cranial nerves as they leave, for example the optic nerve sheath.

The spinal dura is a single meningeal layer forming the dural sac. It is anchored above to the foramen magnum, ends at S2, and continues as the coccygeal ligament around the filum terminale. Lateral sleeves accompany each spinal nerve root to the intervertebral foramen. The epidural space between dura and vertebral canal contains fat and the valveless internal vertebral (Batson) venous plexus, which offers a route for metastasis.

The dura is richly innervated, which is why traction on it or on its vessels causes headache:
• supratentorial dura: CN V, including the tentorial branch of V1;
• posterior-fossa dura: C1–C3 and the vagus.
Its blood supply comes from the middle meningeal artery (from the maxillary artery through foramen spinosum), with smaller anterior and posterior meningeal branches.