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Just today, I've learned something. When I was on Deviant Art, someone told me that it's almost true that the rib cage and the pelvis are oval shaped. Here's the thing, the rib cage is more of a squashed oval with distinct sides. For the pelvis, the front and back are flat and the sides are distinct. since I don't know the word distinct, I'm glad to have this information of the rib cage and pelvis. Enjoy the advice!
Those are good tips! And perhaps this will help you with distinct? <a title="definition of distinct" href="http://www.merriam-webster.com/dictionary/distinct" target="_blank" rel="nofollow">http://www.merriam-webster.com/dictionary/distinct</a>