Fig. 43-20. Vertebral angiograms in vivo. A, lateral view. B, Postero-anterior view. The right and left vertebral arteries (V) unite to form the basilar artery (B), which divides into the two posterior cerebral arteries (P). The posterior communicating arteries (asterisk in A) run forward to take part in the circulus arteriosus (see fig. 43-17). An important branch of the vertebral, the posterior inferior cerebellar artery (P.I.CA.), forms a characteristic loop. (Courtesy of Arthur B. Dublin, M.D., Sacramento, California.) Click for high resolution image.