Vertebral anchoring device and its blocking device on a polyaxial screw

A vertebral anchoring device including a polyaxial anchoring screw having a spherical head; a connecting rod; a connection element for receiving portions of the connecting rod; a clip having a pressure screw positionable to engage the connecting rod; and a connector installable on the spherical head for receiving the connecting rod. The connector includes a socket and a ring which co-act with one other about the spherical head of the screw in an installed orientation. The socket includes two portions bridged together at an upper level of the socket so that the two portions are positionable in a spaced apart orientation to enable the socket to be installed on the spherical head. Pressure of the pressure screw against the connecting rod bears the connecting rod against the ring which bears the ring against the spherical head of the screw.