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FIG 5. A, At the 4–5-mm embryonic stage bilateral longitudinal neural arteries (arrows)—one set of longitudinal neural arteries, dorsal aorta, and cervical intersegmental arteries is shown—are supplied by trigeminal artery (TA), otic artery (OA), hypoglossal artery (HA), proatlantal intersegmental artery (PA), and cervical intersegmental arteries (CIA1–6)
B, At the 7–12-mm embryo vertebral artery (VA) develops through the transverse anastomoses between adjacent cervical intersegmental arteries and distal part of the proatlantal artery becomes the horizontal portion of the vertebral artery (arrowheads) while proximal part regresses completely. Failure of this regression results as persistent proatlantal artery (dashed lines). Also note that at this stage of embryo TA, OA, and HA has disappeared after development of posterior communicating artery (PCA). AA, fourth aortic arch; DAo, dorsal aorta; ECA, external carotid artery; ICA, internal carotid artery; VAo, ventral aorta.
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