Cool, I think there’s a fine sense of solidity for such loose sketches. The rib cage might be a bit too large in numbers 4 and 6. See if you can better define the connection between the spine and the pelvis’s bucket. What mainly calls my attention though is that maybe you can try being a bit more assertive with the linework, clarifying the spatial hierarchy (what’s in front, what’s towards the back) through line weight. Here’s an example of how I imagine it could be done (see image). Hope this helps!