Lateral view of a left-sided deep white matter dissection of the mesiotemporal lobe, diencephalon and brainstem.  The anterior commisure (AC) is a bundle of white matter that is shaped like a bicycle handlebar and interconnects the bilateral temporal lobes and olfactory structures. The AC travels laterally, ventral to the anterior limb of the internal capsule and globus pallidus in "Gratiolet's canal" and posterior to the uncinate fasciculus and terminates in the temporal pole. The stria medullaris thalamus runs along the dorsomedial surface of the thalamus and connects the septal and preopticohypothalamic regions with the habenula in the epithalamus. The epithalamus also contains the habenular commissure, pineal recess of III ventricle, and pineal gland. The pineal gland lays in the midline dorsal to the superior colliculi, which along with the inferior colliculi form the quadrigeminal plate or midbrain tectum. The trochlear nerves decussate at midline as they exit the dorsal surface of the braintem behind the inferior colliculi. The oculomotor nerve travels forward through the red nucleus and medial region of the substantia nigra and crus cerebri to exit the midbrain anteriorly in the interpeduncular fossa between the cerebral peduncles. The trigeminal nerve enters the mid-pons at the junction of the middle cerebellar peduncle and the basis pons.  The middle cerebellar peduncle is a major cerebellar afferent fiber system (cortico-ponto-cerebellar pathway). The superior cerebellar peduncle is a major cerebellar efferent fiber system that crosses the midline in the caudal midbrain at the level of the inferior colliculus and is mostly composed of crossed dentato-thalamic fibers (connecting the dentate nucleus with the thalamus) and cerebello-rubral fibers (connecting the cerebellar interposed nucleus, made up of the globose and emboliform nuclei, with the red nucleus). (Image courtesy of AL Rhoton, Jr.)