Unilateral electrolytic les i ons were placed manually or sterotaxically in the superior colliculus, and the ensuing degeneration in the diencephalon was studied using the Nauta-Gygax ('54) silver method.
1. The superior colliculus sends ascending fibers directly or by way of the brachium of the superior colliculus to the pretectal region, the medial and lateral geniculate bodies, the dorsal thalamic nuclei and the ventral thalamus on the ipsilateral side. It contributes some fibers to the commissure of Gudden.
2. Within the pretectum tectofugal fib e rs terminate in the pretectal nucleus, the nucleus of the optic tract and the nuclei of the posterior commissure.
3. Th e superior colliculus projects fibers to the pars magnocellularis and the most dorsal and dorsomedial portion of the pars principalis of the medial geniculate body. In the lateral geniculate body tectofugal fibers terminate largely in the ventral nucleus, but a few fibers are found to end in lamina B of the dorsal nucleus in cases with lesions in the lateral and middle part of the superior colliculus.
4. A number of ascending tectofugal fibers are distributed in the medial, lateral and inferior pulvinar nuclei and the suprageniculate nucleus as well as the intralaminar nuclei in a wide sense, which include the centre median, parafascicular and lateral central nuclei. A few tectal fibers are scattered in the most posterior part of the posterior lateral nucleus, but no fibers are found in the ventral nuclei.
5. A few tectofugal fibers reach the region just lateral to the lateral habenular nucleus, but no fibers are seen entering this nucleus. Very few if any tectal fibers are found in the dorsomedial nucleus.6. In the ventral thalamus tectofugal fibers terminate in the zona incerta and the field of F ore 1. The reticular thalamic nucleus receives no fibers from the superior colliculus.
7. A fair number of tectofug al f i bers cross the posterior cornmissure and andth e commissure of the superior colliculus and end in the pars magnocellularis and the dorsomedial portion of the pars principalis of the medial geniculate body, the medial and inferior pulvinar nuclei, the suprageniculate nucleus, the zona incerta, the pretectal nucleus and the nuclei of the posterior commissure on the opposite side.