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.