EFFECTS OF STIMULATION AND LESION OF THE MEDIAN LONGITUDINAL FASCICULUS IN THE MONKEY

Abstract

Anatomically, the median longitudinal fasciculus, or the posterior longitudinal bundle, is composed of fibers which arise largely from the vestibular nuclei. According to Papez, the mesial portion of the fasciculus contains fibers which originate in the opposite triangular, or medial, vestibular nucleus and cross the midline at the level of the genu of the facial nerve. The lateral horn of the median longitudinal fasciculus has fibers which originate in the ipsilateral superior vestibular nucleus. These crossed and direct vestibulomesencephalic tracts ascend in the bundle to make connections with the nuclei controlling the oculomotor muscles. The median longitudinal fasciculus also contains descending fibers (a) in the crossed tract, which originates in the contralateral descending vestibular nucleus, and (b) in the direct tract, the axons of which are contributed by the reticular nuclei in the pons and medulla.¹ The exact function of each tract is not clearly understood, but since the