It seems a well-established fact that all the movements of the eyeball which are innervated from the cerebral cortex are associate or conjugate. It also seems well established that lateral conjugate movements of the eyeball can be effected through stimulation of the center for the sixth nerve, or on the floor of the fourth ventricle. Of the associate or conjugate movements of the eyeballs, the lateral ones are the most extensive; and this is consistent with the fact that the human being can move about on a plane surface to an extent which is limited only by physical obstruction or the deficiency of his motor apparatus.
Dangers which threaten the human being come, as a rule, in the nature of things, from some direction in the plane on which he stands. They rarely come from above, and more rarely still from below. The associated movements of the eyeball downward are