shoulder anatomy

• bones: scapula and humerus. that's it.
• the joint is a ball-and-socket joint. but the surface of the joint on the scapula is 1/4 the size of the head of the humerus: this is commonly called golf-ball-and-tee to give you an intuition.
• thie joint is synovial, meaning it joins bones together with a joint capsule . There is only connective tissue keeping this thing together. (that's probably true of many less fraught joints. here it's like, how much do you expect this ridiculous contraption to do?)