A substance delivery device includes an elongated tubular body having opposing proximal and distal ends, a plunger assembly slidably received within the tubular body at the proximal end thereof, and a hollow needle secured within the tubular body at the distal end thereof. The tubular body includes a longitudinal opening located between the proximal and distal ends that is adapted to allow a substance cartridge to be inserted within the tubular body. The plunger assembly includes a plunger that is in slideable sealing engagement with an inside wall of the tubular body, an engagement head positioned proximate an opposite end of the longitudinal opening, and a rod extending between and connecting the plunger and engagement head.