A 19-year-old man who was pinned between two  trucks when a mud-bogging truck fell  off a trailer was flown by helicopter to an area hospital Saturday.  According to St. Clair County Sheriff Department officials, firefighters responded to the incident about shortly after 11 a.m. Saturday.  Officials say the man and his father stopped by a residence in the 1500 block of Hough Road in Berlin Township to purchase a four-wheel-drive truck for mud bogging. The mud truck was being loaded on a trailer hitched to a towing truck when the mud truck went forward and pinned the 19-year-old man between the two trucks. Firefighters worked for some time to extract the man from between the vehicles. The man was conscious following the accident, but the extent of his injuries is now known.   Mussey and Berlin Township fire departments responded to the scene.