The author indicated in the former studies that many figures of tridimensional appearance contain the forms Y and ↑ in their structures. There are, however, some figures which look tridimensional, though they do not contain thee forms. This stutdy observes and discusses the characteristics of such figures and their relation to the forms Y and ↑.Parallelogram _??_, cross-shape + and L-shape _??_ are tridimensional figures without Y and ↑, when their lateral lines are aslant. Figures of parallelogram were prepared, which had two side lines standing vertically and two side lines aslant in various angles. The experimenter showed them to the subjects who expressed the degree of the apparent depth with a newly devised apparatus. The subjects saw the figures not on the front parallel plane, but with the tridimensional impression always. The conclusion is as follows : The relation between the angles of parallelogram and its apparent depth may be expressed adequately in a linear equation.L-shape looked tridimensional more easily than parallelogram and cross-shape. There-fore one could conclude that the most imprortant factor for tridimensional appearance is the slanting of the lines or the size of the angles. The author had believed that every angle must have its proper solidity, and, now, the result of the experiment proved the correctness of that idea. Parallelogram contains four angles of similar solidity and irregular quadrilateral has four angles of different solidity. The surface of the former looks plane and that of the latter looks distorted.Next it was ascertained that the apparent depths of the figures _??_ and ↓ are more exactly observed than those of the figures _??_ and _??_. The comparison of the figure of the open book with one of the closed book has also shown the same result. The cause of it may lie in the accumulation of the tridimensional impression in their two or three angles. The solidity of necker cube and other solid figures is emphasized in the same way by the accumulation of their partial solid impressions. The function of the accumulation is more effective in the figures containing the angles of different solidity then those containing the angles of similar solidity. Therefore its character may be of the nature of contrast.After all the tridimensional appearance of plane drawings can be explained on the ground of the two facts that every angle has its own solidity and that the solid impression is intensified by accumulation.Thus, it is not necessary to use the principle of good configuration, so far as the depth perception of two dimensional drawings concerns.