he turned back into the driver seat and clutched the wheel and hit the brake pedal and something slammed into the back of the rover , the sickening clatter of metal striking metal , jack punching on the headlights just in time to see the cycle turning end over end as it somersaulted off the road into darkness , throwing sparks every time the metal met the pavement , the rider deposited on the double yellow thirty yards ahead , the man sitting dazed and staring at his left arm which dangled fingerless and unhinged from his elbow , his unhelmeted head scalped to the bone .