Injection devices

1. An injection device for a syringe, the device comprising:

a housing for the syringe;

a needle shroud captive to the leading end of the housing and movable before use between extended and retracted positions;

a drive member releasable from a rearward position within the housing to urge the syringe forwards to project a needle beyond the retracted needle shroud and then to express a dose through the needle; and

locating members on the housing for capturing the drive member at its forward position attained after expressing the dose,

wherein the captured drive member is arranged to block retraction of the needle shroud from its extended position, and

wherein the needle of the syringe has a collapsible rubber sheath which acts as a support for the forward end of the syringe.

2. An injection device according to claim 1 , wherein the tip of the sheath is located in a small cup-like formation of the housing provided with a central aperture through which the needle, but not the sheath, can penetrate.

3. An injection device for a syringe, the device comprising:

a housing for the syringe;

a needle shroud captive to the leading end of the housing and movable before use between extended and retracted positions;

a drive member releasable from a rearward position within the housing to urge the syringe forwards to project a needle beyond the retracted needle shroud and then to express a dose through the needle; and

locating members on the housing for capturing the drive member at its forward position attained after expressing the dose,

wherein the captured drive member is arranged to block retraction of the needle shroud from its extended position,

wherein the drive member has arms that extend forwardly to co-operate with the interior of the housing and the needle shroud, and

wherein locating formations on the housing are provided to cause the leading ends of the arms to be flexed inwards and to enter the retracted needle shroud.

4. An injection device according to claim 3 , wherein abutments on the outsides of the arms are provided to be in registry with said locating formations on the inside of the housing so that, after completion of the injection operation, the drive member cannot be pushed back.

5. An injection device according to claim 4 , wherein said abutments are hooked for positive interengagement.

6. An injection device for a syringe, the device comprising:

a housing for the syringe, said housing having an external facing wall;

a needle shroud captive to a leading end of the housing and movable between extended and retracted positions;

a Y-shaped drive member having a longitudinal member and two arms extending forwardly of said longitudinal member, said two arms each including a radially extending tooth between a respective distal end of said arms and the longitudinal member, said drive member being releasable from a rearward position within the housing to urge the syringe forward to project a needle of the syringe beyond the retracted needle shroud and then to expel a dose through the needle; and

locating members on an inner wall of the housing for capturing a corresponding tooth of the drive member at a forward position attained after expelling the dose, the captured drive member being structured and arranged to block retraction of the needle shroud from its extended position.

7. An injection device according to claim 6 , wherein the needle of the syringe has a compressible rubber sheath that compresses within the needle shroud when the dose is being expelled.

8. An injection device according to claim 6 , wherein each said tooth is hooked for positive interengagement.