====== Proximal dural ring ======

The most proximal aspect of this membrane
defines the proximal [[dural ring]]. The proximal ring is incompetent and
admits a variable number of veins from the cavernous plexus that
accompany the ICA throughout its clinoid segment.

C4 (cavernous): covered by vascular membrane lining sinus, still surrounded by PGSNs. Passes anteriorly then supero-medially, bends posteriorly (medial loop of ICA), travels horizontally, and bends anteriorly (part of anterior loop of ICA) to anterior [[clinoid process]]. Ends at the [[proximal dural ring]] (incompletely encircles ICA), which is formed by the medial and inferior periosteum of the [[anterior clinoid process]]. The cavernous segment is surrounded by the [[cavernous sinus]].