Plate 18 has the following text (in the Wilson/Swanger translation):
FIGURE THAT STRIKES THE THROAT IN QUARTA ON A PASSATA OF THE LEFT FOOT
The figure designated as C having the sword of the figure B stringered on the outside, and the same figure B disengaging to give a stoccata to the face of figure C, C strikes him in quarta in the t hroat or the face during the disengage on a pass as the picture shows.
But if B had been an experienced person he would have disengaged his sword by way of a feint, with his body held back somewhat to the rear, and C approaching confidently to pass with the quarta, B executing an inquartata with a void of his body, passing with his left leg behind his right, would strike him in the chest.
You can also find it in the The Rapier Footwork Form