After refining the basic "flattened egg" shape of the ribcage, I was finally able to etch the ribs and carve them out a bit. The hardest part was getting the distribution and spacing correct: 10 attached ribs, 2 floating ribs, each spaced equally apart! A hint: The 8th rib at the back lines up with the 5th rib at the front.
The skull has been refined a bit - I look forward to "nerding out" on the details!
More info about my ecorche/anatomy class with Andrew Ameral: