The extensor mechanism is the name for the tendon complex (green) that extends the finger.
It is much more complex than the flexor mechanism (brown). The two systems interact in a complex manner.

The extensor mechanism, seen above removed from a cadaver and illuminated from the bottom
shows that the line drawing above is an oversimplification of the complexity of the extensor mechanism.
The fibers are not simple and distinct, but blend together and interweave.