A simple shoulder can be created with one bone running from the top of the spine to the top of the arms. For many types of characters, this sort of setup works perfectly fine. Those who want to create a truly realistic character, however, will need to construct a more accurate skeleton.
In real life, the shoulder is a complex series of joints that centers on the actions of the scapula (shoulder blade) and the clavicle (collarbone), as shown in Figure 20. The interaction of these two bones affects the way the skin deforms within a character.
Figure 20 The shoulder is a complex series of joints.
Creating this same effect in a skeleton can be a bit tricky. One way is to create a scapula that follows the action of the clavicle. This way, the scapula can affect the underlying deformation of the skin more accurately. The scapula can simply be a bone that is linked hierarchically to the clavicle. As the clavicle animates, the scapula simply follows, as shown in Figure 21. A more complex setup would involve creating a set-driven key to mimic the precise action of the scapula.
Figure 21 As the arm lifts above the head, the clavicle and the scapula lift as well.