6. A bone anchor receiver in combination with a tool for inserting a rod comprising: a) the receiver having a pair of laterally spaced upwardly extending arms forming a rod-receiving channel therebetween; b) each arm having a vertically slideably engageable tool attachment structure thereon, the vertically slideably engageable tool attachment structure including: 1) a horizontally extending groove which forms a downwardly facing surface, the groove located near a top of its respective arm of the receiver; and 2) each of the grooves extending along an outer surface of the receiver from a front surface to a back surface of its respective arm of the receiver; c) the tool having two discrete parts being spaced apart from each other from an upper end thereof to a lower end thereof to form a through channel therebetween, the through channel extending an entire length of the tool, the lower end of each part having a mating tool attachment structure having inwardly facing projections to detachably mate with, and completely cover, the receiver tool attachment structure; and d) wherein each tool part is independently manipulatable with respect to one another and separately attached to each receiver arm so as to form a side opening tool channel along a length thereof, said tool channel being alignable with the receiver rod-receiving channel, so as to receive a rod therebetween and guide the rod into the rod receiving channel; e) wherein each tool part is individually attachable to one receiver arm, one after the other.
7. The combination of claim 6 , wherein each tool has a outward facing planar surface.