[TA] a longitudinal bundle of fibers extending from the upper border of the mesencephalon primarily into the cervical segments of the spinal cord, located close to the midline and anterior to the central gray matter; it is composed largely of fibers from the vestibular nuclei ascending to the motor neurons innervating the external eye muscles (abducens, trochlear, and oculomotor nuclei), and descending to spinal cord segments innervating the musculature of the neck. SYN: fasciculus longitudinalis medialis [TA], Collier tract, medial longitudinal bundle, posterior longitudinal bundle.