I did another quick test to see how these new bones work — everything in the head was fine, however now the new bones are slightly pulling on the chest area. The easiest way to quickly fix this is to simply add a chest stabilising bone.

To do this, I selected the chest bone and added a child bone. The child bone was rotated to point outwards from the chest and then Rested. Another test quickly showed me that this area of the character was fixed nicely.

Another common area where deformations can be funky or messy is the armpit and body region. By quickly rotating the shoulder joint (that tiny bone I created in Modeler) I quickly saw that the chest area is being deformed badly by the arm bone. This means that some stabilisation bones will be needed in the chest areas.

To add these in, I selected the shoulder bone (the big bone connecting the chest and arm) and added a child bone to it. However, I did not tweak this bone's rotation at all...

Instead, this bone I want to utilise as a pseudo-deltoid muscle — The easiest way to do this was to simply target this bone to the chest bone, so that it always pointed inwards, much like the muscle would. This can be done through the Windows > Motion Options Panel

Once I had activated Targetting, I then rested the bone. Resting the bone before targetting would have caused the shoulder region to be dragged inside the chest cavity. (But this can be fixed with another Rest after the targetting if I'd forgotten the first time)

The other shoulder was quickly updated with child bone to stabilise the other side of the chest. Rotating the arm downwards revealed that the chest now maintained its form nicely without the unsightly deformations seen previously.

By rotating the shoulder bone upward, the bone targetted the chest, retaining a fairly good shape to the chest area.