The clavicle meets the scapula at the top of the shoulder where it connects to the acromion process, forming the acromioclavicular joint. The Humerus (upper arm bone) The humerus is the upper arm bone. The head of the humerus is the ball of the ball and socket joint at the shoulder. The head fits into the glenoid fossa of the scapula. The most important aspect of the shoulder is the large range of movement that it permits, which is central to many activities of daily living.