A syringe assembly , comprising: a syringe barrel having an inside surface defining a chamber , an open proximal end , and a distal end ; a substantially conical tip disposed on the distal end of the barrel, the substantially conical tip having an inside surface defining a passage in fluid communication with the chamber and a locking mechanism disposed within the passage; and a plunger assembly disposed at least partially within the syringe barrel, the plunger assembly comprising an elongate plunger rod , an extension disposed on the plunger rod and having a tip on a distal end thereof, and a plunger head slidably disposed on the extension between the tip of the extension and the plunger rod, wherein after completion of the injection cycle, the tip of the extension extends into the passage in the substantially conical tip and engages the locking mechanism so as to prevent removal of the tip of the extension from the substantially conical tip, characterized in that during an injection cycle the plunger head slides with respect to the extension and the plunger rod such that the plunger head engages the tip of the extension during aspiration and during an injection, the plunger head slides with respect to the extension until a proximal wall of the plunger head engages the distal end surface of the plunger rod, and the locking mechanism comprises a plurality of flexible protrusions disposed about an inside surface of the substantially conical tip and extending into the passage, and wherein the flexible protrusions are adapted to flex toward the inside surface of the substantially conical tip so as to allow the tip of the extension to pass between them. a syringe barrel having an inside surface defining a chamber , an open proximal end , and a distal end ; a substantially conical tip disposed on the distal end of the barrel, the substantially conical tip having an inside surface defining a passage in fluid communication with the chamber and a locking mechanism disposed within the passage; and a plunger assembly disposed at least partially within the syringe barrel, the plunger assembly comprising an elongate plunger rod , an extension disposed on the plunger rod and having a tip on a distal end thereof, and a plunger head slidably disposed on the extension between the tip of the extension and the plunger rod, wherein after completion of the injection cycle, the tip of the extension extends into the passage in the substantially conical tip and engages the locking mechanism so as to prevent removal of the tip of the extension from the substantially conical tip, characterized in that during an injection cycle the plunger head slides with respect to the extension and the plunger rod such that the plunger head engages the tip of the extension during aspiration and during an injection, the plunger head slides with respect to the extension until a proximal wall of the plunger head engages the distal end surface of the plunger rod, and the locking mechanism comprises a plurality of flexible protrusions disposed about an inside surface of the substantially conical tip and extending into the passage, and wherein the flexible protrusions are adapted to flex toward the inside surface of the substantially conical tip so as to allow the tip of the extension to pass between them. <EOS>