PATHWAYS FOR PUPILLARY CONSTRICTION: LOCATION OF SYNAPSES IN THE PATH FOR THE PUPILLARY LIGHT REFLEX AND OF CONSTRICTOR FIBERS OF CORTICAL ORIGIN

Among the fibers which pass from the retina are the afferent fibers of the pupilloconstrictor light reflex arc, for cutting the optic nerves abolishes the reactions of the pupils to light. The central course of the fibers concerned with this reflex was investigated in normal cats by Ranson and Magoun. 1 They reported that constrictor responses are obtained from stimulation of the optic chiasm, the optic tract on the lateral surface of the brain stem and ventral to the lateral geniculate body, the brachium of the superior colliculus, the pretectal region, the posterior commissure and the fibers emerging from it and arching ventrally around the central gray matter at the level of the transition between the third ventricle and the cerebral aqueduct and from the oculomotor nerve. Stimulation of the superior colliculus never produces constriction of the pupil. In stimulation experiments on cats and monkeys Karplus and Kreidl 2 were