Device bone anchor with a shank (2, 102, 202) intended to be anchored in a bone or a vertebra, a head (3, 103, 203), and a receiving part (4) in which is housed the head (3, 103, 203) for connecting the shaft (2, 102, 202) to a rod, consisting of the shaft (2, 102, 2092) and the head (3, 103, 203) in separate parts, the head having (3, 103, 203) having a bore (31, 131, 231) with an inner surface, and at least one slit (35, 235, 235) extending from the inner surface to the outer surface (30, 130, 230 ) of the head (3, 103, 203), and wherein the shaft (2, 102, 202) a first portion (21, 121, 221) for anchoring in the bone or vertebra and a second portion (23, 123, 223 ) with an outer surface adjacent a free end (27, 127, 227), a projection (7, 107) being provided on the outer surface of the second part (23, 123, 223) or on the inner surface of the head (3, 102, 203) and being previst an annular groove (34, 134, 234 24, 224) in the other corresponding surface, i.e., on the inner surface of the head (3, 103, 203) or on the outer surface of the second part (23, 123, 223) hooking together the projection (7, 107) and slot (34, 134, 234 24, 224) when the second part (23, 123, 223) of the shaft (2, 102, 202) is inserted into the bore ( 31, 131, 231) of the head (3, 103, 203), wherein the inner surface of the bore (31, 131, 231) of the head (3, 103, 203) is cylindrical and the outer surface of the second part (23, 123, 223) of the shaft (2, 102, 202) is cylindrical.Dispositivo de anclaje de hueso con un vástago (2, 102, 202) destinado a ser anclado en un hueso o una vértebra, una cabeza (3, 103, 203), y una pieza de alojamiento (4) en la que se aloja la cabeza (3, 103, 203) para conectar el vástago (2, 102, 202) a una varilla, consistiendo el vástago (2, 102, 2092) y la cabeza (3, 103, 203) en piezas independientes, presentando la cabeza (3, 103, 203) un taladro (31, 131, 231) con una superficie interior, y al menos una hendidura (35, 235, 235) que se extiende desde la superfi
