Left retrosigmoid exposure of the lower cranial nerves. The sigmoid sinus is retracted laterally and the cerebellum retracted medially. Visible here are cranial nerves V through XII. Cranial nerve XII exits the medulla and courses laterally and anteriorly into the hypoglossal canal, just superior to the occipital condyle. Cranial nerves IX, X, and XI exit the medulla and enter the jugular foramen along with the jugular bulb. The V3 segment of the vertebral artery is visible entering the dura to become V4. The lateral medullary segment and tonsillar medullary segments of the posterior inferior cerebellar artery (PICA) course lateral and posterior around the medulla. Cranial nerves VII and VIII enter the internal acoustic meatus and course toward the inner ear. The labyrinthine artery, a branch of the anterior inferior cerebellar artery (AICA), courses with the facial and vestibulocochlear nerves. Cranial nerve VI is in the background (medially). (Image courtesy of AL Rhoton, Jr.)