The South Station building itself used to extend along Summer St and Atlantic Ave much further, and accommodated many more tracks. It was the busiest station in the world during the 1940's. When the Station was renovated, the building was chopped off at both sides (Stone and Webster took over the land on the Summer St. side), and the interior was gutted and almost completely reworked. There used to be a much more ornate ceiling in the waiting area, though I do not believe there ever was a glass canopy over the train tracks.