Hypodermic syringe with retractable needle mount

A hypodermic syringe comprising a barrel for containing medicament or other liquid, piston means movable within said barrel between a first end and a second end thereof, needle mounting means disposable within said barrel, means for imparting movement to said need mounting means, restraining means located towards said first end, said needle mounting means when in a first position having a portion thereof extending from said first end, said extending portion being provided with a taper on which an interchangeable needle can be seated, said needle mounting means being restrained from movement by engagement with said restraining means, said restraining means being integral with said barrel and taking a form of an annular structure extending inwardly of the inner wall of the barrel, said annular structure containing a plurality of radially-extending weakened portions, which may be fractured by forces exerted by means provided on said piston means, and being operable to release said needle mounting means when said piston means approaches said first end and then to engage and restrain from reverse movement said piston means, said piston means having a shaft provided with a chamber capable of receiving and retaining said needle mounting means and frangible sealing means to seal said chamber, wherein said needle mounting means, when released, is propelled from said first position to a second position wherein it is received and retained within said chamber after passing through said frangible sealing means;

• wherein said restraining means engages said piston means after release of said needle mounting means so that said piston means cannot be withdrawn from said first end of the hypodermic syringe without causing damage to said restraining means.