An end effector comprising a staple cartridge and an anvil is disclosed. The staple cartridge comprises a cartridge body including a deck, a cartridge longitudinal slot configured to receive a cutting member, a first set of staple cavities, and a second set of staple cavities. The staple cartridge further comprises staples, longitudinal rows of staple drivers, and an implantable layer assembly releasably attached to the cartridge body. The implantable layer assembly comprises a first layer positioned over the first set of staple cavities and a second layer positioned over the second set of staple cavities. The anvil comprises a plurality of staple-forming pockets comprising a first set of staple-forming pockets and a second set of staple-forming pockets. The anvil further comprises an anvil longitudinal slot comprising a T-shaped opening configured to receive the cutting member. The T-shaped opening extends behind the first set of staple-forming pockets.
