At the base of the skull, the internal carotid artery enters the carotid canal in the petrous portion of the temporal bone. Directly posterior to the internal carotid, the internal jugular vein exits the skull via the jugular foramen. A branch of the internal maxillary division of the external carotid artery, the middle meningeal artery, enters the skull through the small foramen spinosum of the sphenoid bone.
Within the base of the skull, the vertebral arteries unite to form the basilar artery. The basilar artery lies in the central sulcus of the pons and terminates by bifurcating into the posterior cerebral arteries. The carotid (anterior circulation) and vertebral (posterior circulation) vessels communicate at the arterial circle of Willis.
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