Hi Sofa! I apologize I got a little carried away but I really like figure drawing. I think you did a great job with construction, it’s solid and it’s clear you understand things. The arm connects in a complex combination of muscles which are usually represented by overlapping lines (3 lines in this case because of the angle). I divided the muscles by colors. I hope it helps! I understand you wanted to study construction, so gesture wasn’t on your mind but since your construction is already solid I suggest you try incorporating gesture into your figures to make them more fluid. I hope I could help you a bit and thank you for sharing

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!