graft substitute or a combination thereof so that when the system is implanted in the spine the contained bone graft material can contact at least one vertebral bony surface through the aforementioned aperture of the walls or through the upper lower boundaries of the cavity 109 that surround cavity 1109 the bone graft material may then form a fusion mass with that bony surface with reference to fig5 and fig6 b the side wall 1102 of each body member 110 includes a channel 11022 that is sized and shaped to accept a corresponding locking member 122 the other side wall 1102 also includes a complementary channel 11042 the locking member 122 is sized and shaped so that it can be inserted onto a respective body member 110 over the channels 11022 and 11042 as shown in fig2 with reference still to fig5 6 a and 6 b the wall 1102 includes one or more cut outs or seats 11024 sized and shaped to accept an instrument that can compress each of the two body members 110 toward and into the side bony aspect of a vertebral spinous process once the system 105 is coupled to a vertebral body the seat 11024 does not necessarily extend through the full thickness of wall 1102 the wall 1104 of each body member 110 includes one or more protrusions 11044 that are adapted to forcibly penetrate and fixate.