1; The fact that your arm has two bones splits the energy in two, and each bone that snaps reduces the total energy of the force by a lot. The less energy is travelling through your body, the less damage your internal organs will receive. That's part of why they occur closer to the extremities.
Explanation:
2; The ribs are separate because if they were one solid plate and they'd get smashed and shoot shrapnels into your lung. ... If the bony thorax were solid instead of having gaps, you wouldn't be able to breathe because your lungs couldn't expand when they fill with air as the diaphragm descends.
