This plate rambles a lot, and I have cut it down a bit. It reads like it was put in as an oversight, and that he was utterly excited about the parry.
I just gotta show you this utterly cool parry! It defends your head, which is really such a useful part of the body to have.
So he is in prima or whatever. You are in quinta(1). Raise your arm and turn to quarta and stepping forward stringere him on the inside.
If he seeks to disengage under your sword and to cut, turn your hand to seconda and join it with the dagger towards the rear of the forte of your sword, like the figure shows.
From there, you can strike safely in two ways: thrust to the face, or cut to the leg.
(1) If I recall correctly, this is the only place apart from the definition pictures where numbers higher than four are actually used. Quinta is shown on plate 4 as a position holding the sword and dagger together and back.