An end effector of a surgical instrument, the end effector comprising: (a) a first jaw, wherein the first jaw is configured to receive a staple cartridge; and (b) a second jaw, wherein the second jaw is movable relative to the first jaw, wherein the second jaw is configured to provide an anvil for forming staples driven from a staple cartridge received in the first jaw, wherein the anvil comprises: (i) a tissue contacting surface, and (ii) a staple forming pocket (510, 610, 710) adjacent to the tissue contacting surface, wherein the staple forming pocket defines a length along a longitudinal axis, wherein the staple forming pocket comprises: a first staple forming surface region configured to receive a first staple leg, wherein the first region has a length greater than half of the length of the staple forming pocket, and a second staple forming surface region configured to receive a second staple leg, wherein the second staple forming surface region has a length greater than half of the length of the staple forming pocket, wherein the staple forming pocket defines a single continuous channel (512, 612, 712) extending from one end of the staple forming pocket to an opposite end of the staple forming pocket and the first staple forming surface region and the second staple forming surface region are both formed in the single continuous channel; characterised in that the staple forming pocket comprises a first deflection protrusion (520, 620, 720) projecting laterally into the single continuous channel and a second deflection protrusion (540, 640, 740) projecting laterally into the single continuous channel. (a) a first jaw, wherein the first jaw is configured to receive a staple cartridge; and (b) a second jaw, wherein the second jaw is movable relative to the first jaw, wherein the second jaw is configured to provide an anvil for forming staples driven from a staple cartridge received in the first jaw, wherein the anvil comprises: (i) a tissue contacting surface, and (ii) a staple forming pocket (510, 610, 710) adjacent to the tissue contacting surface, wherein the staple forming pocket defines a length along a longitudinal axis, wherein the staple forming pocket comprises: a first staple forming surface region configured to receive a first staple leg, wherein the first region has a length greater than half of the length of the staple forming pocket, and a second staple forming surface region configured to receive a second staple leg, wherein the second staple forming surface region has a length greater than half of the length of the staple forming pocket, (i) a tissue contacting surface, and (ii) a staple forming pocket (510, 610, 710) adjacent to the tissue contacting surface, wherein the staple forming pocket defines a length along a longitudinal axis, wherein the staple forming pocket comprises: a first staple forming surface region configured to receive a first staple leg, wherein the first region has a length greater than half of the length of the staple forming pocket, and a second staple forming surface region configured to receive a second staple leg, wherein the second staple forming surface region has a length greater than half of the length of the staple forming pocket, a first staple forming surface region configured to receive a first staple leg, wherein the first region has a length greater than half of the length of the staple forming pocket, and a second staple forming surface region configured to receive a second staple leg, wherein the second staple forming surface region has a length greater than half of the length of the staple forming pocket,