In this part of the pretectal area, nine nuclear structures were described, eight of them--nuclear; these are ventral periventricular pretectal nucleus and its dorsal component, dorsal periventricular pretectal nucleus, nucleus of medial longitudinal bundle, subcomissural organ, medial and lateral intercalate nuclei, and central and posterior pretectal nuclei. 
It occurs as a consequence of a mesencephalodiencephalic lesion, either unilaterally or bilaterally, due to effects on structures such as the interstitial nucleus of Cajal, posterior commissure and rostral interstitial nucleus of the medial longitudinal bundle.
The majority of saccadic velocity abnormalities could be explained by disease in the medial longitudinal bundle.
Interruption of the medial longitudinal bundle approximately 1 mm rostral to the obex did not abolish the bilaterally symmetrical compensated reflex response in either muscle, indicating that the descending axons in the medial vestibulospinal tract are not essential in mediating the normal v.c.r.
One pathway travels in the medialmost aspect to the medial longitudinal bundle and terminates in the dorsal accessory olive.
On anaesthetized animals, macropotentials evoked by electrical stimulation of the ampullar nerve from the horizontal semi-circular canal were recorded at three levels: on the cortex, the vestibular zone is restricted to the lower lip of the suprasylvian gyrus; in the thalamus, our results demonstrate the vestibular character of the magnocellular part of the medial geniculate body; at the mesencephalic level, our recordings indicate the existence of an ascending vestibular pathway situated laterally and ventrally with respect to the medial longitudinal bundle.
These rays extend in the areas of the medulla occupied by the medial lemniscus, tectospinal portion, and medial longitudinal bundle.
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