Figures in addition to the L form and the inverted T were analyzed systematically. Four conditions were arranged, according to the 4 directions of the dividing line. In each condition 9 different positions of the dividing line in relation to the divided line were used. Principal findings (1) In the vertical-horizontal figures 2 different illusions appear: (a) the classical overestimation of the vertical line as compared with a horizontal line of equal length, and (b) the overestimation of the dividing line. Together they produce the phenomenon that has, until now, been erroneously called the vertical-horizontal illusion. (2) The main differences of these illusions are: (a) The overestimation of the vertical line is always connected with the vertical position, whereas the illusion due to the dichosection is independent of this direction. Here we overestimate the dividing line as compared with the divided line. (b) Unlike the classical illusion, the latter is variable, it has a maximum at the midpoint position and two minima at the 2 end positions. (c) The amount of the overestimation of the dividing line can be considerably stronger than the overestimation of the vertical line, depending on the distance from the midpoint position. (3) Where the dividing line was vertical and the divided line horizontal, the 2 illusions operated in the same direction, and the amount of the total illusion was equal to their sum; where the dividing line was in a horizontal position and the divided line was vertical, the 2 illusions were acting in opposite directions, and the amount of the total effect was equal to the difference between their individual effects. (4) At the 2 end positions, where one part of the divided line is equal to the whole length of the line (the L figure), the illusion due to the dichosection equals zero, and only the overestimation of the vertical line produces the illusory effect. An attempt is made to express quantitatively the magnitude of the overestimation of the dividing line as well as the magnitude of the total illusion.