Art Anatomy Study - Forearm/Hand Flexors

Hi, welcome to my continuing series on anatomy for artists. Join me as I investigate different anatomical articles to produce an artistic study of how the human body can be accurately rendered in drawing. My sources include wikipedia, youtube, and textbooks (e.g. OpenStax textbook on Anatomy & Physiology). My approach is to build a rudimentary understanding as relevant to figure drawing.

The human hand has a bewildering number of parts; in this post, I study two deep muscles that are fundamental to the fingers and the wrist.

How do your fingers close in a fist?

The fingers and thumb are bent inward when tendons inside it are pulled. These tendons are attached to two sides of the same bone in the forearm.

The thumb is pulled by the Flexor Pollicis Longus

The muscle is attached to the forearm bone called the ulna, the larger and longer of the two bones in the forearm. Sometimes it is attached also to the humerus. You can see in my drawing that I have tried to render its location on the ulna... "upper middle", you might call it.

Activate this muscle, and you will move the tip of the thumb inwards. When investigating my own hand, I think there might be an interior muscle in the base of my thumb that moves it too, but I haven't done any research on that yet. Stay tuned.

The fingers are closed by the Flexor Digitorum Profundus

There are 4 skinny tendons that go from the fingers (maybe the finger tips, some of my reading has been unclear) all the way to a deep muscle attached to the ulna again. This time, it attaches higher than the Flexor Pollicis Longus. Also, see in my back view rendering, the muscle wraps around the bone a little from the middle up.

Make a fist!

My current understanding is that, like a puppet string, if you pull on the Digitorum Profundis, because the tendons are attached to the inside of the fingers, then bend forward 1,2,3,4 and make a fist. However, this is not the only thing you can do...

Hold the fingers straight, then bend the wrist.

Try making a fist and then bending your wrist. You will not be able to achieve the same angle!

What is happening here is that you are keeping your fingers neutral or straight so that when you engage the same muscle, what bends is the at the wrist. I am unsure of the role of the Flexor Pollicis Longus in the wrist motion. My readings have not been clear about this point and if I tuck in my thumb, this also inhibits wrist movement.

Figure drawing studies

Based on the work above, I sketched some different positions of the hand. This knowledge lets me decide what the limits are for making a hand look natural. For example, I can emphasize a little bit of muscle engagement in the forearm for the corresponding position of the finger. Also, if I draw a wrist that is bent, the fingers should be a little more relaxed, because the tendons will not allow your to flex the fingers and the wrist together very easily.

Thank you for reading and following my investigations.

Past work
Latimus Dorsi - (First posts, just art) 1, 2