A collapsible anvil assembly and applicator instrument for use with a surgical stapler. The collapsible anvil assembly includes an anvil shaft and a plurality of anvil segments, having staple clinching buckets thereon, flexibly affixed to the anvil shaft which are movable between a collapsed or radially inwardly deflected condition and an expanded or radially outwardly deflected condition. Immobilizing means in the form of an axially slidable locking ring is provided to fix and maintain the anvil segments in the expanded condition. Mounting element are also provided for subsequent detachable mounting of the anvil assembly on a surgical stapler. The collapsible anvil assembly may also include a suction purse stringing device which attracts and holds a surrounding tissue section within the anvil segments. Additionally, an axially slidable tissue holding ring or snap cap is provided to lock the held tissue section within the anvil segments.