Understanding the movement of the upper limb is a notorious hurdle for artists, often described as an "artist's mortal enemy" due to its high range of motion and complex deformations. Arm and Hand in Motion
You're looking for a free PDF download of "Arm and Hand in Motion: Anatomy for Sculptors"! Understanding the movement of the upper limb is
Try to do "draw-overs" of the PDF pages to find the rhythm lines. Understanding the movement of the upper limb is