The medial longitudinal fasciculus is one of a pair of crossed fiber tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are composed of both ascending and descending fibers that arise from a number of sources and terminate in different areas. Medial longitudinal fasciculus is the main central connection for the oculomotor nerve, trochlear nerve, and abducens nerve. The vertical gaze center is at the rostral interstitial nucleus.
The medial longitudinal fasciculus ascends to the interstitial nucleus of Cajal, which lies in the lateral wall of the third ventricle, just above the cerebral aqueduct.