A surgical instrument, comprising: a first jaw comprising a pair of laterally aligned vertical slots formed in a proximal end portion, each said vertical slot having an open upper end; a second jaw movably supported for selective pivotal travel relative to said first jaw between a fully open and a fully closed position, said second jaw comprising: a second jaw body; and a pair of pivot members protruding laterally from a proximal end of said second jaw body wherein each said pivot member is pivotally received in a corresponding one of said vertical slots in said first jaw such that said pivot members may pivot therein to facilitate said pivotal travel of said second jaw relative to said first jaw, and wherein said surgical instrument further comprises: a retainer member configured to operably engage said proximal end portion of said first jaw and retain said pivot members in said corresponding vertical slots as said second jaw moves between said fully open and said fully closed positions; and an axially movable closure member configured to apply closing and opening motions to said second jaw and retain said retainer member in retaining engagement with said proximal end portion of said first jaw, wherein each said vertical slot is formed in a corresponding upstanding vertical wall portion of said first jaw and wherein said retainer member comprises: a retainer body sized to span between said vertical wall portions; a slot cap corresponding to each said vertical slot and sized to extend therein through said open end; and a mounting formation on said retainer body and corresponding to each said upstanding vertical wall portion and being configured to be seated in a correspondingly shaped mounting opening therein. a first jaw comprising a pair of laterally aligned vertical slots formed in a proximal end portion, each said vertical slot having an open upper end; a second jaw movably supported for selective pivotal travel relative to said first jaw between a fully open and a fully closed position, said second jaw comprising: a second jaw body; and a pair of pivot members protruding laterally from a proximal end of said second jaw body wherein each said pivot member is pivotally received in a corresponding one of said vertical slots in said first jaw such that said pivot members may pivot therein to facilitate said pivotal travel of said second jaw relative to said first jaw, a second jaw body; and a pair of pivot members protruding laterally from a proximal end of said second jaw body wherein each said pivot member is pivotally received in a corresponding one of said vertical slots in said first jaw such that said pivot members may pivot therein to facilitate said pivotal travel of said second jaw relative to said first jaw, and wherein said surgical instrument further comprises: a retainer member configured to operably engage said proximal end portion of said first jaw and retain said pivot members in said corresponding vertical slots as said second jaw moves between said fully open and said fully closed positions; and an axially movable closure member configured to apply closing and opening motions to said second jaw and retain said retainer member in retaining engagement with said proximal end portion of said first jaw, a retainer member configured to operably engage said proximal end portion of said first jaw and retain said pivot members in said corresponding vertical slots as said second jaw moves between said fully open and said fully closed positions; and an axially movable closure member configured to apply closing and opening motions to said second jaw and retain said retainer member in retaining engagement with said proximal end portion of said first jaw, wherein each said vertical slot is formed in a corresponding upstanding vertical wall portion of said first jaw and wherein said retainer member comprises: a retainer body sized to span between said vertical wall portions; a slot cap corresponding to each said vertical slot and sized to extend therein through said open end; and a mounting formation on said retainer body and corresponding to each said upstanding vertical wall portion and being configured to be seated in a correspondingly shaped mounting opening therein. a retainer body sized to span between said vertical wall portions; a slot cap corresponding to each said vertical slot and sized to extend therein through said open end; and a mounting formation on said retainer body and corresponding to each said upstanding vertical wall portion and being configured to be seated in a correspondingly shaped mounting opening therein.