A surgical instrument apparatus comprising: a handle portion; a shaft housing a firing bar; an end effector comprising an anvil (101, 115, 123, 145), a lower jaw, and a stapling and severing assembly responsive to a longitudinal closing motion produced by the handle portion and the shaft, wherein the anvil (101, 115, 123, 145) comprises a plurality of staple-forming pockets; a removable staple cartridge, wherein the lower jaw is configured to receive the staple cartridge, the staple cartridge comprising: a housing, a plurality of staples disposed in the housing, and a deck disposed over the plurality of staples, the deck defining apertures, each aperture substantially disposed over each staple and each aperture corresponding to a respective staple-forming pocket; and a removable anvil cartridge (100A, 100B, 112, 120, 142) configured for receipt in the anvil (101, 115, 123, 145); wherein the anvil (101, 115, 123, 145) comprises an anvil slot (103, 143) and an opening (106, 114, 136, 144) disposed above and in communication with the anvil slot (103, 143), and the anvil cartridge (100A, 100B, 112, 120, 142) is configured for receipt in at least the opening (106, 114, 136, 144); and wherein the firing bar is configured to advance through the anvil slot (103, 143) in response to the longitudinal closing motion produced by the handle portion and the shaft along a length sufficient to sever the anvil cartridge (100A, 100B, 112, 120, 142) when the anvil cartridge (100A, 100B, 112, 120, 142) is received in at least the opening (106, 114, 136, 144) of the anvil (101, 115, 123, 145) and simultaneously drive the staples from the staple cartridge toward the staple-forming pockets on the anvil (101, 115, 123, 145); characterized in that the staple cartridge, anvil (101, 115, 123, 145) and anvil cartridge are so configured that the staples are driven from the staple cartridge toward the staple-forming pockets without passing through the anvil cartridge (100A, 100B, 112, 120, 142). a handle portion; a shaft housing a firing bar; an end effector comprising an anvil (101, 115, 123, 145), a lower jaw, and a stapling and severing assembly responsive to a longitudinal closing motion produced by the handle portion and the shaft, wherein the anvil (101, 115, 123, 145) comprises a plurality of staple-forming pockets; a removable staple cartridge, wherein the lower jaw is configured to receive the staple cartridge, the staple cartridge comprising: a housing, a plurality of staples disposed in the housing, and a deck disposed over the plurality of staples, the deck defining apertures, each aperture substantially disposed over each staple and each aperture corresponding to a respective staple-forming pocket; and a housing, a plurality of staples disposed in the housing, and a deck disposed over the plurality of staples, the deck defining apertures, each aperture substantially disposed over each staple and each aperture corresponding to a respective staple-forming pocket; and a removable anvil cartridge (100A, 100B, 112, 120, 142) configured for receipt in the anvil (101, 115, 123, 145); wherein the anvil (101, 115, 123, 145) comprises an anvil slot (103, 143) and an opening (106, 114, 136, 144) disposed above and in communication with the anvil slot (103, 143), and the anvil cartridge (100A, 100B, 112, 120, 142) is configured for receipt in at least the opening (106, 114, 136, 144); and wherein the firing bar is configured to advance through the anvil slot (103, 143) in response to the longitudinal closing motion produced by the handle portion and the shaft along a length sufficient to sever the anvil cartridge (100A, 100B, 112, 120, 142) when the anvil cartridge (100A, 100B, 112, 120, 142) is received in at least the opening (106, 114, 136, 144) of the anvil (101, 115, 123, 145) and simultaneously drive the staples from the staple cartridge toward the staple-forming pockets on the anvil (101, 115, 123, 145); characterized in that the staple cartridge, anvil (101, 115, 123, 145) and anvil cartridge are so configured that the staples are driven from the staple cartridge toward the staple-forming pockets without passing through the anvil cartridge (100A, 100B, 112, 120, 142).