Lateral (left) and anterior views (right) of the left internal carotid artery (ICA) and A and B, segments of the supraclinoid (C4) portion. A, lateral view of the C4 portion. B, anterior view of the C4 portion. The ICA is divided into four parts. These parts, from proximal to distal, are the C1 through the C4 portions. The cervical portion (C1, red) extends from the origin of the ICA to the external orifice of the carotid canal in the petrous temporal bone. The petrous portion (C2, orange) extends from the external orifice of the carotid canal to where the artery exits the carotid canal to enter the cavernous sinus. The cavernous portion (C3, yellow) begins where the artery enters the cavernous sinus and terminates where it emerges from the dura mater on the medial side of the anterior clinoid process to enter the intracranial cavity. The intracranial (supraclinoid) portion (C4, beige) begins where the artery enters the cranial cavity medial to the anterior clinoid process and terminates below the anterior perforated substance where the artery bifurcates into the anterior and middle cerebral arteries. The ICA gives rise to the ophthalmic, posterior communicating, anterior choroidal, anterior cerebral, and the middle cerebral arteries. The supraclinoid portion of the ICA is divided into three segments based on the origin of these branches. The ophthalmic segment (C4-Op., dark blue) extends from the origin of the ophthalmic artery to the origin of the PComA. The communicating segment (C4-Co., light green) extends from the origin of the PComA to the origin of the anterior choroidal artery. The choroidal segment (C4-Ch., dark green) extends from the origin of the anterior choroidal artery to the bifurcation of the internal carotid artery into the anterior and middle cerebral arteries. (Images courtesy of AL Rhoton, Jr.)