EE WAS COUPLING A ROCK DUSTER TO A 12 TON LOCOMOTIVE. AS HE WAS INSERTING PIN INTO PLACE, HIS CO-WORKER BACKED THE LOCOMOTIVE, MOVING PIN, FOWLING EE'S FINGER AGAINST THE LOCOMOTIVE FRAME (LEFT INDEX FINGER) LACERATING THE FINGER TO THE POINT OF THE AMPUTATION OF THE TIP FLESHY END OF THE FINGER.