1. In an X-ray table assembly: a. a cubical table base; b. an elongated first table top mounted on said base and extending therebeyond in both lengthwise directions; c. said first table top being movable in both the lengthwise and transverse directions relative to said base; d. said first table top including a frame having thereon a flatsurfaced panel having inclined lengthwise side edge portions; e. a side rail supported along each lengthwise edge of said first-table-top frame; f. a patient-receiving second table top supported on said panel of said first table top for manually actuated sliding movement thereon; g. said second table top having a narrow head board portion at its forward end; h. said second table top having along its lengthwise edge portions metal guide rails having downwardly inclined portions having therein strips of lowfrictional material facing said inclined edge portions of said first-table-top panel for guiding said second table top in its sliding movement on said first table top; i. anti-tilt retaining means supported in depending position from a rearward side portion of said second table top for engaging the under-surface of said side rails of said firsttable-top frame for preventing tilting of said second table top relative to said first table top when said second table top is moved slidingly forward to position said head board beyond said first table top; and j. attachment means at spaced intervals along said metal guide rails of said second table top for attachment of a plurality of accessory devices, whereby said accessory devices move with said patient.