fig8 fig6 illustrates the reverse situation where the stapler 10 is oriented in a position such that the anvil 54 will be gravity biased in a clockwise direction about its pivot pin 64 so as to engage the stop surfaces 78 and dispose the crown engaging surfaces 74 as well as the leg engaging surfaces 72 80 and 82 within the drive track 42 it will be understood that the driving movement of the staple driving element 40 in a pneumatically operated device such as the stapler 10 described above is a very rapid movement and there is a distance of travel that the staple must move before engaging any of the surfaces of the anvil 54 which are disposed in the drive track 42 thus the engagement will be an impact engagement since the free ends of the legs of the staple are leading in the drive track 42 during the driving motion they will engage the leg engaging surfaces 72 initially these surfaces 72 while having only a slight incline are sufficient when impacted with the anvil 54 under gravity bias to quickly move the entire anvil 54 including the surfaces 74 and 80 out of the drive track 42 as soon as the impact force moves all of the surfaces of the anvil 54 out of the drive track 42 the gravity acting on the anvil 54 tends to bias it so that the surfaces 74 and 80 thereof move back toward the drive track 42 by this time however the legs of the staple have moved into a.