56 fig1 that terminates in a generally conical surface 58 additionally the plunger 26 includes a second end 60 and a mid portion 61 located between the first end 56 and the second end 60 plunger 26 also includes an external surface 62 that may be cylindrical or of any other suitable cross section the concave rib 44 extends about the axis 54 and expands towards the first end 56 of the plunger 26 in the illustrated example the concave rib 44 extends over the conical surface 58 of the plunger and towards the first end 56 of the plunger 26 still further in the illustrated example the concave rib 44 extends over a portion of the conical surface 58 the conical surface 58 cooperates with the nozzle 38 to push any remaining medicaments from ampule 30 referring to fig1 12 it will be understood that plunger 26 may also include a second rib 64 the second rib 64 is positioned between the concave rib 44 and the second end 60 of the plunger 26 the second rib 64 cooperates with the concave rib 44 to stabilize the plunger 26 as it is driven through the ampule 30 the design of the.