A surgical apparatus (10) comprising: a handle assembly (100)； an elongated body portion (14) extending distally from the handle assembly (100) and defining a first longitudinal axis； a tool assembly (17) pivotally supported at the distal end (14b) of the elongated body portion (14) about an axis of rotation substantially orthogonal to the first longitudinal axis, the tool assembly (17) defining a second longitudinal axis and being able to move between a first position, in which the second longitudinal axis is aligned with the first longitudinal axis, and a second position, in which the second longitudinal axis is located at an angle with respect to the first longitudinal axis； and an axial drive assembly (212) that includes: a flexible blade drive arm (266) extending from a proximal position of the axis of rotation to a distal position of the axis of rotation, the flexible arm of actuation having the blade (266) a distal end (266b) that can be moved relative to the tool assembly (17) to drive the tool assembly (17)； and a gear drive assembly (355, 355 ', 356) at the interface with the flexible blade drive arm (266) to allow movement of the distal end (266b) of the flexible blade drive arm (266) ) in relation to the tool assembly (17), in which at least one advance and recoil of the blade drive arm at a distal end thereof in relation to the tool assembly (17) drives the tool assembly ( 17)； characterized in that the gear drive assembly (355 ', 355', 356) comprises: a primary drive gear (358) that meshes with the flexible blade drive arm (266) to effect the movement of the flexible arm of blade drive (266), and the primary drive gear (358) is a crown gear (360, 360 ', 361) having first and second opposing surfaces (360a, 360b), including the crown gear (360 , 360 ', 361) a support shaft (366) centrally disposed therein which defines a rotation axis of the crown gear (360, 360', 361), including the crown gear (360, 360 ', 361) on the first surface (360a) a spiral cam
