An expandable interbody fusion device includes superior and inferior endplates that are configured to receive a sequentially inserted stack of expansion members or wafers in interlocking engagement. The expansion members are formed to each have a generally U-shaped rearward facing opening. The superior and inferior endplates have openings through their outer surfaces in at least partial alignment and communication with the rearward facing openings of the expansion members. The inferior endplate has a fully bounded cavity for telescoping receipt of the superior endplate. The inferior endplate also has a fully bounded channel extending through the rear endwall thereof in direct communication with the rearward facing opening of at least one expansion member for the receipt of bone graft material into the device to promote fusion between opposing vertebral bodies of the spine.