Depicting the lower arm in a figure drawing can get tricky because of the two bones it has, the radius and ulna. There is a significant amount of information that needs to be considered in order to render the lower arm successfully in a figure sketch. Especially considering the supination / pronation motion and the muscles involved in the limb.
This video is from figure drawing instructor Robert Stollar, a self-taught sculptor with a passion for figure drawing. A passion and, of course, a necessity. He lives in Sydney, Australia with his beautiful wife and three dogs, working as a sculptor and teaching figure drawing.
For those who cannot attend his classes in person Robert has an online version of the lectures at Figure Drawing Online.