A syringe assembly (101, 300, 400, 500) comprising: a body (110, 210, 230, 310, 410)) for fluid that includes a side wall (112, 312)) having an inner surface (114 , 314) defining a chamber (115, 315) for fluid to retain fluid and having a first width in cross section, an open proximal end (119, 319) and a distal end (111, 311) that includes a distal wall (117, 317)； a rod (160, 360, 460) of the piston disposed inside the fluid chamber comprising a distal end, a proximal end (199, 399, 499), a body of the piston rod extending from the distal end to the proximal end, and a stop (160, 170, 370) disposed at the distal end of the piston rod to form a fluid tight seal with the inner surface of the body； a retraction body (120, 220, 320, 420) disposed adjacent to the side wall of the fluid body, the retraction body including a wall (122, 223, 322, 422) having an inner surface (124, 134) defining a needle chamber (125, 135), an open proximal end, an open distal end (121, 221, 321) that includes a barrier wall, an opening (123, 323) between the wall of the retraction body and the side wall of the fluid body allowing fluid communication between the fluid chamber and the needle chamber and a needle cone assembly (140, 200, 340, 540) comprising a cone (142, 342, 542) of the needle, a needle cannula (150, 205, 350, 550) attached to the needle cone, the needle cannula being in fluid communication with the opening and being pushed to move in a proximal direction； and a trigger element (190, 390, 490, 492, 590) disposed inside the needle chamber and removable inside the retraction body independently of the piston rod, characterized in that the trigger element includes a proximal end, an open and free distal end (191) that provides the firing force, and a firing element body (192, 392, 492, 592) extending from the proximal end to the distal end and including an inner surface defining a hollow interior (193, 393), the firing element providing a firing force that causes the needle can
