A delivery assembly (20, 140) for delivering material such as bone cement into living tissue. The assembly includes an access cannula (22) that defines a portal to the tissue to which the material is delivered. The material is delivered from a delivery cannula (82) that is seated in the access cannula. The access cannula includes a valve (48, 146). The valve prevents the flow of material out of the access cannula. The valve also prevents the pressure head at the site at which the access cannula is inserted from forcing the delivery cannula out of the access cannula.