The day after being sent to University of Wisconsin Hospital with head injuries, Brandon J. Andreasen, 13, was in critical condition Monday after he fell off the back of an ATV driven by another juvenile. As the boys were riding on the all-terrain vehicle Brandon suddenly fell of the back and hit his head on the pavement. Andreasen, who was not wearing a helmet, was flown by helicopter ambulance to UW Hospital. The accident remains under investigation.