thin flat rectangular envelope with parallel upper and lower surfaces 36 as best shown in the configuration of fig1 thus it can be seen in fig7 that surfaces 44 are offset from the longitudinal axis of the half cage so that when flipped the opposed flanges providing surfaces 44 will mesh or nest with other in this manner the two half cages 12 and 14 can easily be surgical slid between two adjacent vertebrae greater detail of the shape of half cages 12 and 14 are shown in the bottom and top perspective views of fig7 and 8 more of the detail of the shape and surfaces of half cages 12 and 14 is described below in the context of assembly of fusion cage 10 the plunger 16 is initially coupled to the proximal end of the two half cages 12 and 14 by means of engagement as shown in fig1 of a distal cam 38 best shown in fig6 on the plunger 16 which fits into notches 40 defined in the two half cages 12 and 14 as best seen in fig8 this coupling allows plunger 16 which is grasped by springs 20 of tool 18 to handled as an integral unit and to be inserted and withdrawn from the surgical site initially the plunger 16 longitudinally extends from the two half cages 12 and 14 in the proximal.