PUPILLOCONSTRICTOR FIBERS OF POSTERIOR COMMISSURE AND PUPILLOCONSTRICTOR NUCLEUS IN RABBIT

With application of Glees' silver method, modification of Bielschow-sky's method, on 11 rabbit's brain with intersected posterior commissure, we examined the degenerated axis cylinder of the posterior commissural fibers paticipating in the pupillary light reflex pathway and the terminal degeneration of axis in the constrictor nucleus in order to elucidate the light reflex pathway histologically. 1. The fibers directly connecting the bilateral pretectal nuclei pass through the posterior commissure, and join with the pretectal nuclei by the way of dorsolateral archiform fiber system, ventromedial archi-form fibers system and tractus sublentiformis (Kuhlenbeck). 2. There is a connection between the descending fibers of posterior commissure and interstitial nuclei (Kuhlenbeck). 3. Constituting the afferent fibers of pupillary light reflex running in the descending peduncles of posterior commissure, there are two routes; namely, the way reaching to the constrictor nucleus by the way of the lateral surface of the central gray matter, and another one reaching to the same by joining with the fasciculus longitudinalis medialis and ascending dorsalad from it. 4. The constrictor nucleus is located between the fasciculus longitudinalis dorsalis and fasciculus longitudinalis medialis, covers about 1200 μ from about 200 μ in front of the main oculomotor nucleus down roughly to the middle of the nucleus anterodorsal way toward the dorsal parts of the same, and is composed of a pair of medium-sized cell groups on both sides. 5. The efferent pupillary light reflex pathway is assumed to be projected from the constrictor nucleus to the pupillary constrictor muscle by the way of the oculomotor fibers.