A. Selective right carotid arteriography in lateral projection showing anomalously originating right occipital artery from the posterior aspect of the internal carotid artery (arrow). B. Selective left carotid arteriography in lateral projection showing anomalously originating left occipital artery from the postero-medial aspect of the internal carotid artery (arrow). C, D. Its route (arrowheads) and anastomosis with left vertebral artery (arrow).