Subdivide
Reference
Mode:
Edit Mode
Menu:
Armature ‣ Subdivide
You can subdivide bones, to get two or more bones where there was just one bone. The tool will subdivide all selected bones, preserving the existing relationships: the bones created from a subdivision always form a connected chain of bones.
To create an arbitrary number of bones from each selected bone in the Subdivide Multi Adjust Last Operation panel.
Number of Cuts
Specifies the number of cuts. As in mesh editing, if you set n cuts, you will get n + 1 bones for each selected bone.