Why do some bones in my armature disappear when I go into Edit mode? I made a rig for a model of a dragon and for some reason,
when I go into Edit Mode, some of the bones disappear:



I don't know if this is relevant or not, but I created the rig using the standard release of 2.69, but now I'm using the standard version of 2.70.

Here is my blend file.
Unhide Bones

Your bones were hidden. To unhide them, once in Edit mode press ALTH and your bones will be back! 



Hidden Bones are only Hidden in Specific Modes

It is worth noting that bones hidden in one mode may be visible in another mode, and vice-versa. Here is an explanation from the Blender Manual:


  Note that hidden bones are specific to a mode – i.e. you can hide some
  bones in Edit mode, they will still be visible in Pose mode, and
  vice-versa. Hidden bone in Pose mode are also invisible in Object
  mode. And in Edit mode, the bone to hide must be fully selected, not
  just his root or tip…