Posterior view of medulla, fourth ventricle, internal auditory meatus, and jugular foramen.  The cerebellum has been removed to reveal the cut surfaces of the cerebellar peduncles (superior, middle, inferior). These provide the lateral borders of the fourth ventricle, connect the cerebellum to the brainstem, and allow communication of afferent and efferent pathways to the ipsilateral cerebellar cortex. The obex marks the caudalmost point of the fourth ventricle (and the level of the foramen magnum). It narrows to communicate with the central canal of the spinal cord. A portion of choroid plexus can be seen emerging through the lateral aperture (of Luschka). This opening is just posterior to the root of the glossopharyngeal nerve. The facial (CNVII) and vestibulocochlear (CNVIII) nerves leave the lateral pontomedullary junction and course to the internal auditory meatus, A loop of the anterior inferior cerebellar artery traverses these nerves. Emerging from the anterolateral surface of the medulla and traveling to the jugular foramen are the (rostral-to-caudal sequence) glossopharyngeal (CNIX), vagus (CNX), and cranial portion of the spinal accessory (CNXI) nerves. The spinal root of the accessory nerve arises from fibers emanating from the C1-C5 levels of the spinal cord and ascends through the foramen magnum to unite with the cranial portion within the jugular foramen. Rootlets of the hypoglossal nerve emerge more anteriorly from the medulla and course posterior to the vertebral artery toward the hypoglossal canal. The posterior inferior cerebellar artery is the largest of the branches of the vertebral artery and supplies the posterior surface of the cerebellum, inferior cerebellar peduncle, and lateral medulla. (Image courtesy of M Nunez)