An experimental anatomical study on the optic nerve fibers in the rat: courses of the accessory optic tract.

By means of silver impregnation and an HRP method, courses of the accessory optic tract were examined in albino and pigmented rats. The accessory optic tract is composed of 3 fasciculi: anterior, lateral and dorsal. The anterior fasciculus gives off fibers to the subthalamic nucleus and terminates in the medial terminal nucleus. The lateral fasciculus branches from the main optic tract at the level of the ventral nucleus of the lateral geniculate body and descends the lateral surface of the crus cerebri to enter the medial terminal nucleus after contributing a few fibers to the lateral terminal nucleus. The dorsal fasciculus originates from the brachium colliculi superioris and descends the posterior surface of the medial geniculate body and the posterolateral surface of the crus cerebri as an independent fasciculus to enter the medial terminal nucleus. This fasciculus supplies many fibers to the dorsal terminal nucleus.