Cerebral Integration of Ocular Movements*

It is customary among us to commemorate great men from time to time by a lecture or discourse relating to their work or to some subject in which they were interested. To-day we meet to pay a tribute to the memory of Victor Horsley, almost on the twenty-second anniversary of his death in the service of his country, while striving for those ideals which characterized his life-the relief of suffering and the defence of liberty. Horsley's name is indelibly inscribed on the records of human achievement. His workas a physiologist is incorporated in the heritageof our knowledge, and he will ever be remembered as a pioneer in the surgery of the net-vops system, which since his day has grown as only his faith could ha, -foreseen. But great though his achievements were in the realm of science, it is his personality which keeps his memory most vividly alive to those of us who had the privilege and good fortune to work with him. We recall his amazing energy, his enthLusiasm for knowledge, the help he gave so liberally to younger colleagues, his kindness and generosity, and his unswerving devotion to the welfare of his fellows. I accept gratefully this opportunity to add my contribution to his memory. The subiect of this lecture' is one to which Horsley's investigations contributed materially ; some of his earliest work defined accurately an area of the cortex by stimulation of which ocular movements could be obtained; later he described the anatomical paths connecting the visual cortex with the oculomotor apparatus in the midbrain; and his latest experiments on the cerebellum, which unfortLinately have never been published in full, dealt with the movements and postures of the eyes which can be elicited on electrical stimulation of this organ or result from lesions of it. There are several categories of ocular movements. In the first place we can move our eyes by an act of volition, bit few of their ordinary movements are in this sense voluntary or the result of a consciotus effort. Any peripheral stimulus, as movement, a flash of light, or a sound, may deviate our eyes involuntarily towards its source, while accurate vision demands accommodation and fusion, ,which is effected by so arranging the visual axes that the images of the object at which we look fall on corresponding parts of the two retinae. Finally, there are the compensatory or adjusting movements by which the eyes are kept directed on an object when either it or our heads move. The upper part of the brain stem contains