Other than the canon demands, the Space Marines I describe lack the ribcage, fused into a solid block. Their ribs are stronger and broader, overlapping each other but they are still able to move in the natural pattern known from humans. I chose to commit this breach because I am utterly convinced that the Emperor would have a deep understanding of anatomy and design His warriors with full lung capacity.

Lord Emperor, I failed you. I could not bring myself to implement the Imperial system. I’m too German I guess… Forgive the humble sinner and let her live on in a well measured world.