Nerve fibers at the pontomedullary junction. Corticospinal tract fibers descend from the cerebral cortex through the crus cerebri within the midbrain and into the pons and medulla. The fibers form the medullary pyramids before decussating and descending into the spinal cord. Corticopontine fibers synapse with deep pontine nuclei, which give rise to second order transverse pontine (pontocerebellar) fibers that cross the pons to enter the middle cerebellar peduncle to reach the contralateral cerebellum.  The facial and vestibulocochlear nerves (facial-vestibulocochlear nerve complex) emerge from the lateral pontomedullary junction near the cerebellopontine angle. The anterior median fissure separates the pyramids, which are flanked laterally by the olives. The anterolateral or preolivary sulci intervene between the pyramids and the olives. From these sulci emerge the roots of the hypoglossal nerve. The roots of the glossopharyngeal, vagus, and accessory nerves emerge in a rostro-caudal sequence from the postolivary sulci. Choroid plexus material can be seen protruding from the lateral foramina (of Luschka) of the fourth ventricle.  (Image courtesy of PA Rubino)