hello! You picked a fair difficult one! (it took me forever to understand shoulder blade & arm ) but i tried to do a recap for you. Basically the arm is connected at the scapular bone and clavicular bone, and then you have the muscles to keep em in place. I tried to give u a stylized version, a bone one and a muscle one, sorry if it results confusing but i'd need like 3 sheets like this to explain how it works better XD Hope it helps! | Artwod Feedback