Fig. (1) Terminology of Main Cerebral Arterial Branches: Schematic diagram modified after Allis [9] showing main stems and branches of the internal carotid arterial pathways typical for vertebrates. Vessels supplying the internal carotid (ICA) vary widely among vertebrates but primitively include the paired dorsal aorta (DA) and efferent vessels of the hyoid (efferent hyoid artery, EHA) and mandibular arches (efferent pseudobranchial arteries, EPAs). Distribution branches supplying structures outside of the braincase typically include an orbital artery (Orb) branching from the extracranial internal carotid and an ophthalmic artery (Oph) branching from the EPAs (or equivalent). The cerebral carotids (CCAs) arise either as continuations of the paired dorsal aorta (dashed lines) or by bifurcation of a midline, unpaired carotid (= encephalic) trunk (green *). The cerebral carotids divide into anterior (ACCs) and posterior (PCCs) divisions, with an optic artery (OA) arising either immediately before or after the branching. The PCCs either meet in the midline beneath the rostral hindbrain to form an unpaired basilar artery (BA), or they continue caudally as paired basilar (rhombencephalic) vessels.