LYNN – A passenger on a northbound commuter rail train reportedly leapt from the door of the still-moving car Thursday evening at Central Square Station just before 9 p.m., severely injuring himself.The Newburyport-Rockport MBTA line train was scheduled to stop at Lynn Station at 8:49 p.m., but one passenger reportedly got impatient and jumped, tumbling out onto the Broad Street end of the platform before the car came to a complete stop.The victim was described in police transmissions as a “59-year-old white male, 5-foot, 9 inches tall” and as having a “life-threatening head injury.”Lynn fire, police and emergency medical personnel were immediately called to the scene and hoisted the victim onto a stretcher. The gurney was brought down to street level and loaded into an ambulance, according to transmissions, bound for Mass. General Hospital in Boston.Lynn police detectives then held the train on the northbound platform at Lynn Station for purposes of an investigation.The MBTA held trains in both directions on the line, then brought another train down the southbound tracks. That train stopped at Lynn Station and picked up the estimated 100 passengers left traveling north. That train departed Lynn northbound on the southbound tracks at 10:05 p.m.The incident remains under police investigation.