Meninges:Dura mater (in general)

The **dura mater**, also known as **pachymeninx**, a fibrocallogenous surrounds the central nervous system and is pierced by the cranial nerves, the internal carotid arteries and the vertebral arteries.

Intracranially it is formed by two layers:

* outer endosteal layer: continuous via sutures and foramina with the periosteum. Blood vessels pierces these to supply the bone.
* inner meningeal layer: continuous inferiorly with the theca of the spinal cord at the foramen magnum. it consists of a dense and strong fibrous membrane (the dura mater proper).

These two layers are adherent except were separated by the dural venous sinuses which are analogous to the epidural venous plexus of the spinal canal.

In the young the extension across unfused sutures makes the dura inseparable from these, thus limiting extradural haemorrhages to the sutures. As the calvarial bones fuse the suture layer involutes. The dura however becomes thicker and more adherent to the overlying bone with age, also accounting for the decrease of EDHs in the elderly.

Folds of the dura mater: the inner meningeal layer project into the cranial cavity forming double layers septations within the fissures of the brain. They minimize rotary displacement of the brain.

**Tentorium cerebelli**: flange of the inner layer that projects from the margins of the transverse sinuses and superior petrosal sinuses.

* A*ttachment:* to the posterior clinoid processes, along the upper borders of the petrous temporal bones, horizontally along the inner surface of each side of the skull to the internal occipital protuberance.
* The free margin of the tentorium, is U shaped forming a tentorial notch (incisure), which passes posteriorly the upper part of the brainstem. Anteriorly it passes forward to the anterior clinoid processes and forms a ridge of dura mater on the roof of the cavernous sinus, which is pierced by the 3rd and 4th nerve.

**Falx cerebri:** sickle shaped flange of the inner layer in the sagittal fissure.

* a*ttachment:* anteriorly to the crista galli of the ethmoid bone, and posteriorly to the upper surface of the tentorium cerebelli in the midline at the internal occipital protuberance.
* Its convex upper border is attached to the inner surface of the skull and separate to form the sagittal sinus, while its concave lower border is free and contains the inferior sagittal sinus (just above the corpus callosum). Where the tentorium meets the falx cerebri, the straight sinus, is contained.

**Falx cerebelli:** low elevation of the inner layer of the midline of the posterior cranial fossa.

* *attachment:* internal occipital protuberance along the internal occipital crest to the posterior margin of the foramen magnum.
* it lodges the small occpital sinus between its layers.

**Diaphragma sellae:** horizontal sheet of inner layer that forms a roof for the pituitary fossa. The dura of the floor of the fossa is prolonged up to the sides and attached to the middle and posterior clinoid processes. It then extends medially to form the diaphragma which is perforated by the pituitary stalk.

Arterial supply:

The outer layer is richly supplied mostly by the middle meningeal artery. This artery is a branch of the maxillary and arise in the infratemporal fossa and pass up into the foramen spinosum.

* anterior cranial fossa - meningeal branches of the opthalmic and anterior/posterior ethmoidal artery and branch of the middle meningeal artery.
* middle cranial fossa - middle and accessory meningeal arteries and meningeal branches o the ICA and ascending pharyngeal artery
* posterior cranial fossa - meningeal branches of the vertebral artery.

Venous drainage:

The middle meningeal veins are sinuses in the dura mater and accompany the branches of the artery. They lie between artery and the bone.

Nerve supply:

* Tentorial nerve from the opthalmic division of CNV course up and back from the anterior end of the cavernous sinus to supply the falx, the dura of the vault, the upper surface of the tentorium cerebelli,
* Anterior fossa: anterior and posterior ethmoidal nerves
* Middle fossa: anterior portion of the maxillary nerve and meningeal branch of the mandibular nerve
* Posterior fossa: meningeal branches of the vagus and hypoglossal nerve (carrying C1 and C2 fibres)