A knowlege of anatomy is a must if you are interested in learning to paint, draw, or sculpt the human form. I first saw a copy of Gray's Anatomy in my sisters hand. She was in medical college and every student world over has had a copy to study.
Much later, when I saw a reference to it on Bartleby.com off I went to investigate. There I found an incredible figure drawing resource - 1247 engravings from Henry Gray's "Anatomy of the Human Body" for you to access online. Use it to study, draw or sculpt the skeleton, the muscles that cover them and how our joints move. At least those are my plans :D Here's a link to an index of these engravings.
Happy Figure Drawing!