MaDi, a reader of this blog, sent in these two pictures. The second one was done according to the directions of the exercise. Notice the thumb. Unlike the first drawing, you can see here the steep angles where the phalanges meet, and the one where the first phalange of the thumb meets the metacarpal (trapezium) bone. MaDi did not suddenly take anatomy lessons: she just started looking. She did not name body parts, but she drew them, and she felt them “through the skin”, and became aware of their effect on contour. Also, note how the rendering is so much more forceful when instead of messing around with small timid lines as in the first picture she just boldly advanced with a single motion for better or worse. The other fingers did not go as well, however. Why? MaDi told me she got confused with the more complex position of the fingers in 3D space. The solution to this is simply to follow the exercise scrupulously. You should not even realize there is such a thing as a finger lying in 3D space. Just move over each line. Do not see the fingers. Do not see even a single finger. Do not see a nail. Just focus on each line. Focus so much that you don’t see anything else. Use tunnel-vision (and Tunnel-thinking. Better yet, do not think at all during this exercise!). Then what you see is very simple. A line, on paper can only have a tangent whose angle with the horizon goes between 0 and 360 degrees. Any such line is as easy to draw as any other. Therefore any position of the finger is as easy to draw as any other - as long as you see each line in turn, never the finger.
This, of course, requires great concentration.