Before merging and forming the basilar artery, each vertebral artery gives rise to a posterior inferior cerebellar artery (PICA) and posterior spinal artery and contributes to the formation of the anterior spinal artery (eFig. 9.42). The PICA perfuses the lateral aspect of the medulla and the inferior portion of the cerebellum. The medial and anterior portions of the medulla receive vascular supply from the paramedian branches off of the vertebral and anterior spinal arteries.