ps. Just to be clear there is a camera at the front of the jet that projects its image onto the rear seat HUD. Not only do you see normal HUD symbology but also a video image of the forward view.
Great stuff. So the back-seat HUD is also useful for landing the aircraft in case the student is incapacitated in some way. The Lord Stirrup got his Air Force Cross for landing a Jaguar from the back-seat after a rather nasty bird strike which started an engine fire and a loss of communication with his student. I bet he would have been really grateful for a second HUD back then!