How does the bucket on a dump truck work?

The dump truck contains a hydraulically power controlled cylinder that expands as fluid is injected, resulting in the "dump" trailer lifting from the frame of the vehicle. This system is referred to as a PTO, or Power Take-Off.

Info:
http://en.wikipedia.org/wiki/Power_take-off

Photo:
http://img.alibaba.com/photo/209566984/dump_truck.jpg