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Right subclavian, vertebral, and carotid artery connections

The first branch of the subclavian artery is the vertebral artery, which has a pre-foraminal portion (V1), then ascends through foramina in the transverse processes of C6 through C2 (V2), proceeds to the dura (V3), and then extends to its confluence with the opposite vertebral artery (V4) to form the basilar artery. The basilar artery bifurcates in the posterior cerebral arteries, which connect to the anterior circulation in the posterior communicating artery. The anterior terminus of the posterior communicating artery is the internal carotid artery prior to the terminal bifurcation of the internal carotid artery into the anterior and middle cerebral arteries. Thus, under certain circumstances, “subclavian steal” may steal blood from both the posterior and anterior circulations. (Contributed by Dr. Douglas Lanska. Source: Gray H. Anatomy of the Human Body. Philadelphia and New York: Lea & Fibiger, 1918.)