The private pilot was practicing takeoffs and landings and reported that while maneuvering through the traffic pattern, the canopy became partially opened. The canopy was equipped with two side latches and one main latch at the rear of the canopy. The right-side latch held the canopy partially secured until the final approach segment when it also released, and the canopy opened completely. The airplane subsequently nosed down and contacted the ground nose first just short of the runway whereupon the nose landing gear separated from the airplane and the main landing gear collapsed, which resulted in substantial damage to the fuselage. The pilot was seriously injured. The pilot reported forgetting to lock the main rear latch to the canopy after opening it during taxi. The pilot reported that there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.