Command entry:Select a rig bone. Modify panel Setup rollout Add Bone
Exta bones are bones you can add to any bone in CAT for any reason. You can use extra bones for armor, breathing and facial animation, weapons, walking sticks, and so on.
Procedure
To add an extra bone:
Select the hub or bone to which to add the bone.
Do either of the following:
On the Modify panel Bone Setup rollout, click Add Bone.
In the viewport, right-click the bone or hub and from the Tools 2 quadrant, choose Add Extra Bone.
Modify panel 
Select the hub or bone to which to add the bone.