A surgical end effector, comprising: a lower jaw comprising an elongated channel configured to operably support a surgical staple cartridge therein; an anvil assembly comprising: a proximal anvil mounting tube, wherein the proximal anvil mounting tube is pivotally coupled to said lower jaw for selective pivotal travel relative thereto about a pivot axis (A-A) between open and closed positions upon application of closing and opening motions to said proximal anvil mounting tube; and a distal anvil portion movably coupled to said proximal anvil mounting tube and supported for parallel movement toward and away from the lower jaw when the proximal anvil mounting tube is in said closed position and wherein said surgical end effector further comprises: a firing member operably supported for operable travel within said surgical end effector relative to said upper and lower jaws (15, 13) when said proximal anvil mounting tube is in said closed position and firing motions are applied to said firing member, wherein said firing member is configured to move said distal anvil portion toward said lower jaw as said firing member travels in a distal direction through said surgical end effector. a lower jaw comprising an elongated channel configured to operably support a surgical staple cartridge therein; an anvil assembly comprising: a proximal anvil mounting tube, wherein the proximal anvil mounting tube is pivotally coupled to said lower jaw for selective pivotal travel relative thereto about a pivot axis (A-A) between open and closed positions upon application of closing and opening motions to said proximal anvil mounting tube; and a distal anvil portion movably coupled to said proximal anvil mounting tube and supported for parallel movement toward and away from the lower jaw when the proximal anvil mounting tube is in said closed position and wherein said surgical end effector further comprises: a firing member operably supported for operable travel within said surgical end effector relative to said upper and lower jaws (15, 13) when said proximal anvil mounting tube is in said closed position and firing motions are applied to said firing member, wherein said firing member is configured to move said distal anvil portion toward said lower jaw as said firing member travels in a distal direction through said surgical end effector. a proximal anvil mounting tube, wherein the proximal anvil mounting tube is pivotally coupled to said lower jaw for selective pivotal travel relative thereto about a pivot axis (A-A) between open and closed positions upon application of closing and opening motions to said proximal anvil mounting tube; and a distal anvil portion movably coupled to said proximal anvil mounting tube and supported for parallel movement toward and away from the lower jaw when the proximal anvil mounting tube is in said closed position and wherein said surgical end effector further comprises: a firing member operably supported for operable travel within said surgical end effector relative to said upper and lower jaws (15, 13) when said proximal anvil mounting tube is in said closed position and firing motions are applied to said firing member, wherein said firing member is configured to move said distal anvil portion toward said lower jaw as said firing member travels in a distal direction through said surgical end effector.