a support for a surgical instrument , having a base that defines a seat with a concave surface and a flat surface facing in a first direction for placement against tissue and a connector having a convex surface to abut to and move universally relative to the concave base surface . a sleeve with a passage through which a surgical instrument can be directed is attached to the connector such that the sleeve follows universal movement of the connector relative to the base . cooperating structure on the connector and base maintains the connector and base in an operative position in which the convex surface on the connector resides adjacent to the plane of the flat base surface and does not project significantly in the first direction beyond the flat base surface .