For what it’s worth- to me number 2 looks like there isn’t enough leaning back of the rib cage, it looks too straight up and down. Number 3 is a bit difficult to read but I think the beveled edges coming in to the spine are too wide and sore,thing is off re the alignment of the rib cage-mnotmsure how.

Wow! Great structure! In the second image, the ribcage should be a little larger and the 10th rib is farther down. Otherwise these look pretty accurate to me! One thing that helped me get the first rib (the top plane) right is to imagine laying my hand on it (really imagining!). In a front view for example, you can start by finding the top of the manubrium (which the first rib attaches to), then from there imagine the first rib. I elaborated a little more on the artist's X-ray vision in a critique to another student. I attached a screenshot, feel free to read it. Hope this helps :)

I think this was a good attempt. I don't see the gesture line. That should ALWAYS come first. All of your RoboBoxes should be governed by the line of action. I'll give them a try and post my results.

That's a good job finding the landmarks. That's gonna be very important when you're drawing muscles. But in this exercise you're supposed do take a step further and draw the 3d forms of the shoulder bones. Drawing the structure helps you understand the form in space and in the future it can aid you drawing from imagination. So don't skip on this exercise. Best Regards