Nice! Anatomy is looking pretty good! - I've made this up myself, but when I study the 3D model it looks like the 12 ribs' attachment at the back is halfway between the sternum and bottom of ribcage. Maybe a useful hint. - The primary volume feels a bit wobbly. Before drawing the detailed contour, draw the egg shape and wrap an equator line around it (you could add two more if you want, one vertical dividing left and right, and another vertical dividing front to back.) This came to mind when I imagined a ring being wrapped around the ribcages it it felt like it would be wobbly. Hope this helps :)

Looks good! - I would recommend drawing through the forms just like Stan does. I've found it really helpful to be able to identify the sternum in a back view - In the first image, I think the 12th rib is attaching to high up on the spine. The twelvth rib attaches to the 12th thoracic vertebrae right before we reach the lumbar section. It has helped me to think of the ribcage and the thoracic portion of the spine as a single unit; the thoracic portion of the spine is tucked into the ribcage and they both share the same c-curve arc. Hope this helps :)