On the Innervation of the Double Eye

Abstract

I define the fixation space of the double eye as the space within which the intersection of both lines of sight, that is, the binocular visual point, can be moved with unchanged head position. This fixation space is to be thought of as tightly tied to the head, and changes its position only when the head changes its position. Every point in the fixation space has, therefore, an unchangeable position relative to the head or to the points of rotation of the eyes. If each eye possessed only the four rectus muscles, it would immediately be specified which muscles and degrees of contraction would be necessary for any given position of the lines of sight in fixation space in order to hold the lines of sight, and with them the point of vision, steady in this position. Because each eye has six muscles, however, one can think of the fixation of the lines of sight in a given position as brought about in varying ways by the muscles. Fixation on one and the same point of visual space could then be maintained now with this and now with another muscle, and the various muscle actions would of course correspond to varying innervations.