A surgical stapling apparatus for stapling tissue, comprising: a staple cartridge, comprising: a cartridge body, comprising: a proximal end; a distal end; a deck comprising a tissue-supporting surface; a plurality of staple cavities; and a longitudinal slot comprising a first sidewall and a second sidewall; a plurality of staples removably stored in said staple cavities; and a firing member movable from a proximal position toward a distal position to eject said staples from said staple cavities, wherein said longitudinal slot is configured to receive a portion of said firing member; an anvil configured to deform said staples; a layer positioned against said anvil, wherein said staples are configured to implant said layer against the tissue when said staples are ejected from said staple cavities, wherein said layer comprises a layer retainer positioned intermediate said firing member and said cartridge body when said firing member is in said proximal position, and wherein said layer retainer is released when said firing member is moved toward said distal position, wherein said layer retainer comprises a tail which is wedged or captured between the firing member and the cartridge body when the firing member is in the proximal position, characterized in that: the tail is positioned intermediate the firing member and the first sidewall when the firing member is in the proximal position; wherein the tail has an enlarged tab defined at an end thereof; and the first sidewall comprises a recess defined therein and configured to receive the enlarged tab. a staple cartridge, comprising: a cartridge body, comprising: a proximal end; a distal end; a deck comprising a tissue-supporting surface; a plurality of staple cavities; and a longitudinal slot comprising a first sidewall and a second sidewall; a plurality of staples removably stored in said staple cavities; and a firing member movable from a proximal position toward a distal position to eject said staples from said staple cavities, wherein said longitudinal slot is configured to receive a portion of said firing member; a cartridge body, comprising: a proximal end; a distal end; a deck comprising a tissue-supporting surface; a plurality of staple cavities; and a longitudinal slot comprising a first sidewall and a second sidewall; a proximal end; a distal end; a deck comprising a tissue-supporting surface; a plurality of staple cavities; and a longitudinal slot comprising a first sidewall and a second sidewall; a plurality of staples removably stored in said staple cavities; and a firing member movable from a proximal position toward a distal position to eject said staples from said staple cavities, wherein said longitudinal slot is configured to receive a portion of said firing member; an anvil configured to deform said staples; a layer positioned against said anvil, wherein said staples are configured to implant said layer against the tissue when said staples are ejected from said staple cavities, wherein said layer comprises a layer retainer positioned intermediate said firing member and said cartridge body when said firing member is in said proximal position, and wherein said layer retainer is released when said firing member is moved toward said distal position, wherein said layer retainer comprises a tail which is wedged or captured between the firing member and the cartridge body when the firing member is in the proximal position, characterized in that: the tail is positioned intermediate the firing member and the first sidewall when the firing member is in the proximal position; wherein the tail has an enlarged tab defined at an end thereof; and the first sidewall comprises a recess defined therein and configured to receive the enlarged tab. the tail is positioned intermediate the firing member and the first sidewall when the firing member is in the proximal position; wherein the tail has an enlarged tab defined at an end thereof; and the first sidewall comprises a recess defined therein and configured to receive the enlarged tab.