A surgical tool assembly, comprising: a surgical end effector comprising: a first jaw; and a second jaw comprising a second jaw body portion and a second jaw mounting portion, said second jaw mounting portion pivotally coupled to said first jaw for selective movement relative thereto between an open position and closed positions and wherein said surgical tool assembly further comprises: a tubular closure member axially movable in response to closing and opening motions applied thereto, said closure member comprising at least one opening cam formed thereon, said at least one opening cam being configured to movably engage a corresponding cam surface formed on said second jaw body portion such that upon application of said opening motion to said closure member, said at least one opening cam movably engages said corresponding cam surface to move said second jaw to said open position and upon application of said closure motion to said closure member, said closure member engages said second jaw to move said second jaw to one of said closed positions; wherein said at least one opening cam comprises: a first hook portion extending distally from a distal end of said closure member and being configured to cammingly engage a first one of said cam surfaces formed on said second jaw body portion; and a second hook portion extending distally from said distal end of said closure member and being configured to cammingly engage a second one of said cam surfaces formed on said second jaw body portion; wherein said surgical tool assembly further comprises secondary jaw opening means for applying additional opening motion to said second jaw, characterised in that said secondary jaw opening means comprises a spring corresponding to each of said first and second hook portions and attached thereto, said secondary jaw opening means arranged to apply additional opening forces to the corresponding secondary jaw opening cam. a surgical end effector comprising: a first jaw; and a second jaw comprising a second jaw body portion and a second jaw mounting portion, said second jaw mounting portion pivotally coupled to said first jaw for selective movement relative thereto between an open position and closed positions and wherein said surgical tool assembly further comprises: a tubular closure member axially movable in response to closing and opening motions applied thereto, said closure member comprising at least one opening cam formed thereon, said at least one opening cam being configured to movably engage a corresponding cam surface formed on said second jaw body portion such that upon application of said opening motion to said closure member, said at least one opening cam movably engages said corresponding cam surface to move said second jaw to said open position and upon application of said closure motion to said closure member, said closure member engages said second jaw to move said second jaw to one of said closed positions; a first jaw; and a second jaw comprising a second jaw body portion and a second jaw mounting portion, said second jaw mounting portion pivotally coupled to said first jaw for selective movement relative thereto between an open position and closed positions and wherein said surgical tool assembly further comprises: a tubular closure member axially movable in response to closing and opening motions applied thereto, said closure member comprising at least one opening cam formed thereon, said at least one opening cam being configured to movably engage a corresponding cam surface formed on said second jaw body portion such that upon application of said opening motion to said closure member, said at least one opening cam movably engages said corresponding cam surface to move said second jaw to said open position and upon application of said closure motion to said closure member, said closure member engages said second jaw to move said second jaw to one of said closed positions; wherein said at least one opening cam comprises: a first hook portion extending distally from a distal end of said closure member and being configured to cammingly engage a first one of said cam surfaces formed on said second jaw body portion; and a second hook portion extending distally from said distal end of said closure member and being configured to cammingly engage a second one of said cam surfaces formed on said second jaw body portion; a first hook portion extending distally from a distal end of said closure member and being configured to cammingly engage a first one of said cam surfaces formed on said second jaw body portion; and a second hook portion extending distally from said distal end of said closure member and being configured to cammingly engage a second one of said cam surfaces formed on said second jaw body portion; wherein said surgical tool assembly further comprises secondary jaw opening means for applying additional opening motion to said second jaw, characterised in that said secondary jaw opening means comprises a spring corresponding to each of said first and second hook portions and attached thereto, said secondary jaw opening means arranged to apply additional opening forces to the corresponding secondary jaw opening cam.