When you bind a character to a skeleton (described in the next lesson), the skeleton provides a structure for the character’s skin and prevents the skin from collapsing as you pose the skeleton.

It’s useful to add extra joints in areas of the character where you want the surface to keep its volume upon deformation. In the next steps, you’ll add ribs to Jackie’s skeleton. Although you will not bind the character in this lesson, the technique of adding ribs is important to learn so that when you do bind a character, the skin in the torso area will not collapse as you pose shoulder and spinal rotations. The rib joints are for structure only, not for posing the skeleton.

To add ribs to the skeleton

1. In the Hypergraph, click the mid_back joint to highlight the joint in the front view. Remember the location of the joint in the front view so you can select it later.
2. Select Skeleton > Joint Tool.
3. In the front view, click on the mid_back joint to select it again.
4. Click to the side of the joint to add a rib bone, then press Enter (Windows and Linux) or Return (Mac OS X).
   
5. With the same technique as in the prior steps, create two more ribs for the left side. The ribs extend from the mid_back, lower_back, and pelvis joints.
   
6. For easy identification in the Hypergraph, you can optionally name the ribs as desired. For instance, name them left_top_rib, left_mid_rib, left_bottom_rib, and so on.
7. Mirror each of the left rib joints to create ribs for the right side of the skeleton.