The greatest difficulty that they had to surmount was how to “foreshorten” their figures, or represent them in “foreshortening.” A simple way of understanding what this means is to stand in front of a mirror and stretch out your arms to left and right, like the arms of a cross. Each extends a long way. But now bring them in front of you and stretch them toward the mirror. At once they look shorter, or at any rate you cannot see their length. They appear foreshortened. Or you may practice a still more “violent” example of foreshortening, if you are able to place the mirror where you can see your body, when lying down with the feet toward it, for now the whole length of the body appears foreshortened in the mirror. The surface of the latter, you observe, corresponds exactly with the surface of a picture. It is a flat plane upon which is produced the appearance of successive or receding planes, and though you cannot see the length of your body because it is foreshortened, you are made to feel its length.