All the following ribs aiculate directly with sternum except
The first 7 ribs which are connected through their cailages to the sternum are called true ribs, or veebrosternal ribs. The remaining five are false ribs. Out of these the cailages of the eighth, ninth and tenth ribs are joined to the next higher cailage and are known as veebrochondral ribs. The anterior ends of the eleventh and twelfth ribs are free and are called floating ribs or veebral ribs. Ref : B D Chaurasia's Human Anatomy, Seventh edition , volume 1 , pg. no. 204
2nd rib
4th rib
5th rib
8th rib
Thorax