A stapler cartridge comprising: a cartridge body elongated between a distal end and a proximal end, the cartridge body comprising a plurality of openings at an upper surface for ejecting staples, the cartridge body comprising an upward sloping distal cam surface , a longitudinal slot , and a central cavity ceiling ; a drive member slidingly coupled to the cartridge body, the drive member comprising a receptacle and one or more distally-facing ramps (176-4) configured to deploy staples as the drive member is advanced distally; and a knife member comprising a body portion disposed within the longitudinal slot , a cutting blade , a first protrusion extending from the body portion transverse to the longitudinal slot , and a second protrusion extending from the body portion transverse to the longitudinal slot wherein the first protrusion is configured to be contacted by the drive member during a distal advancement of the drive member so that the knife member is advanced distally with the drive member during a first portion of the distal advancement of the drive member , the knife member being configured to be constrained by both the drive member and the central cavity ceiling during the first portion of the distal advancement of the drive member , and wherein, the second protrusion is configured to be disposed within the receptacle during the distal advancement of the drive member , a distal end portion of the knife member being configured to be driven along the upward sloping distal cam surface during a second portion of the distal advancement of the drive member so as to rotate the knife member relative to the drive member around the second protrusion , thereby lowering the cutting blade into the cartridge body . a cartridge body elongated between a distal end and a proximal end, the cartridge body comprising a plurality of openings at an upper surface for ejecting staples, the cartridge body comprising an upward sloping distal cam surface , a longitudinal slot , and a central cavity ceiling ; a drive member slidingly coupled to the cartridge body, the drive member comprising a receptacle and one or more distally-facing ramps (176-4) configured to deploy staples as the drive member is advanced distally; and a knife member comprising a body portion disposed within the longitudinal slot , a cutting blade , a first protrusion extending from the body portion transverse to the longitudinal slot , and a second protrusion extending from the body portion transverse to the longitudinal slot wherein the first protrusion is configured to be contacted by the drive member during a distal advancement of the drive member so that the knife member is advanced distally with the drive member during a first portion of the distal advancement of the drive member , the knife member being configured to be constrained by both the drive member and the central cavity ceiling during the first portion of the distal advancement of the drive member , and wherein, the second protrusion is configured to be disposed within the receptacle during the distal advancement of the drive member , a distal end portion of the knife member being configured to be driven along the upward sloping distal cam surface during a second portion of the distal advancement of the drive member so as to rotate the knife member relative to the drive member around the second protrusion , thereby lowering the cutting blade into the cartridge body . <EOS>