An injection device comprising: a housing adapted to receive a fluid container and hold the fluid container stationary relative to the housing during use of the device; a hollow catheter connected to a distal end of the housing wherein the hollow catheter comprises an exit aperture at its distal end; a plunger adapted to discharge fluid from the fluid container, a discharge nozzle movable between a first retracted position in which the discharge nozzle is contained within the catheter and does not project from the exit aperture of the catheter, and a first extended position in which the discharge nozzle has moved relative to the fluid container and extends from the housing through the exit aperture of the catheter, wherein the discharge nozzle is a needle, wherein the fluid container and discharge nozzle are in fluid communication with each other in the first extended position; and a drive adapted to advance the discharge nozzle from its first retracted position to its first extended position and further adapted to act upon the plunger to expel fluid from the fluid container through the discharge nozzle, such that only when the discharge nozzle has reached its first extended position, the drive acts upon the plunger to expel fluid from the fluid container through the discharge nozzle, characterized in that the plunger comprises a serrated ratchet and in that the drive comprises: a first member which is connected to the discharge nozzle; a second member which comprises a resiliently biased member adapted to engage the ratchet at a predetermined position of the drive relative to the housing; and a retainer which prevents the second drive member from engaging with the serrated ratchet for a predetermined distance. a housing adapted to receive a fluid container and hold the fluid container stationary relative to the housing during use of the device; a hollow catheter connected to a distal end of the housing wherein the hollow catheter comprises an exit aperture at its distal end; a plunger adapted to discharge fluid from the fluid container, a discharge nozzle movable between a first retracted position in which the discharge nozzle is contained within the catheter and does not project from the exit aperture of the catheter, and a first extended position in which the discharge nozzle has moved relative to the fluid container and extends from the housing through the exit aperture of the catheter, wherein the discharge nozzle is a needle, wherein the fluid container and discharge nozzle are in fluid communication with each other in the first extended position; and a drive adapted to advance the discharge nozzle from its first retracted position to its first extended position and further adapted to act upon the plunger to expel fluid from the fluid container through the discharge nozzle, such that only when the discharge nozzle has reached its first extended position, the drive acts upon the plunger to expel fluid from the fluid container through the discharge nozzle, characterized in that the plunger comprises a serrated ratchet and in that the drive comprises: a first member which is connected to the discharge nozzle; a second member which comprises a resiliently biased member adapted to engage the ratchet at a predetermined position of the drive relative to the housing; and a retainer which prevents the second drive member from engaging with the serrated ratchet for a predetermined distance. a first member which is connected to the discharge nozzle; a second member which comprises a resiliently biased member adapted to engage the ratchet at a predetermined position of the drive relative to the housing; and a retainer which prevents the second drive member from engaging with the serrated ratchet for a predetermined distance.