A bone anchoring device comprising a receiving part (1) for connecting a shank of a bone anchoring element to a rod, a rod (7) and a securing element (10) the receiving part (1) comprising a first end (2) and a second end (3), a recess (4) having a substantially U-shaped cross section, said recess (4) extending from the first end (2) in direction of the second end (3) forming two legs (5, 6) open at the first end (2), said recess (4) defining a channel to receive said rod (7), said channel having a longitudinal axis (L), said legs (5, 6) having an inner thread (9) to receive the securing element (10) having an outer thread cooperating with said inner thread to secure the rod, and wherein the receiving part (1) is polyaxially connectable to the bone anchoring element and has a bone (20) extending from the first end (2) to the second end (3) for passing through the shank of the bone anchoring element, the bone having a central axis (M). a pressure element (25) is provided which is slidable in the bone (20) exerting pressure on a head of the bone anchoring element to fix the bone anchoring element in angular position with respect to the receiving part, characterized in that said legs (5, 6) are provided with stiffening structures (11, 12, 15 11’, 12’, 15’ 115) which are formed by an enhanced wall thickness (D) of the outer edges of said legs (5, 6) which is larger than the wall thickness (d) of said legs (5, 6) at a location closest to the central axis (M) of the bone, the wall thickness measured radially with respect to the central axis (M), and wherein the enhanced wall thickness (D) is located at the height of the longitudinal axis of the rod when the rod is inserted in the receiving part, the stiffening structures going over in slanted portions with diminishing wall thickness towards the first end (2) of the receiving part.(Fig. 1)一種骨骼固定裝置,包括供一骨骼固定元件的一柄部連接於一桿所用之一承座件(1),一桿(7)和一安全元件(10);該承座件(1)包括:一第一端(2)和一第二端(3);具有實質上U形截面之一凹部(4),該凹部(4)從該第一端(2)按該第二端(3)方向延伸,形成二股部(5,6),
