FIELD OF THE INVENTION  
       [0001]     The present invention relates to automatic injection devices for hypodermic syringes generally.  
       BACKGROUND OF THE INVENTION  
       [0002]     The following U.S. Patents are believed to represent the current state of the art: U.S. Pat. Nos. 4,474,572; 4,475,906; 4,484,910; 4,487,602; 4,505,710; 4,512,767; 4,515,590; 4,518,387; 4,529,401; 4,529,403; 4,530,695; 4,534,759; 4,547,189; 4,553,962; 4,573,970; 4,573,976; 4,578,061; 4,578,064; 4,580,561; 4,592,744; 4,594,073; 4,596,558; 4,597,753; 4,600,403; 4,601,708; 4,613,328; 4,620,540; 4,620,847; 4,624,660; 4,650,468; 4,658,830; 4,659,326; 4,664,651; 4,664,654; 4,666,436; 4,672,967; 4,681,565; 4,687,465; 4,687,467; 4,689,042; 4,699,614; 4,710,170; 4,723,937; 4,735,618; 4,738,663; 4,743,234; 4,744,955; 4,745,907; 4,747,829; 4,747,831; 4,753,636; 4,755,169; 4,758,227; 4,758,230; 4,758,231; 4,766,908; 4,767,407; 4,767,413; 4,770,655; 4,781,683; 4,781,685; 4,781,688; 4,784,640; 4,787,384; 4,787,893; 4,790,823; 4,790,827; 4,795,432; 4,795,433; 4,798,587; 4,799,921; 4,804,370; 4,808,169; 4,813,937; 4,813,940; 4,820,275; 4,820,286; 4,826,484; 4,826,489; 4,826,490; 4,828,548; 4,832,682; 4,832,693; 4,834,704; 4,834,718; 4,842,598; 4,846,811; 4,850,961; 4,850,968; 4,850,971; 4,850,976; 4,850,977; 4,850,994; 4,861,338; 4,863,427; 4,863,435; 4,863,436; 4,865,592; 4,874,372; 4,874,382; 4,883,466; 4,883,472; 4,886,499; 4,887,998; 4,892,107; 4,892,523; 4,894,054; 4,894,055; 4,898,589; 4,900,303; 4,900,307; 4,900,311; 4,902,279; 4,904,242; 4,906,236; 4,908,022; 4,909,794; 4,909,795; 4,911,706; 4,913,702; 4,915,702; 4,917,672; 4,919,146; 4,919,657; 4,923,443; 4,923,445; 4,927,414; 4,929,237; 4,929,241; 4,931,040; 4,932,944; 4,932,946; 4,932,947; 4,935,013; 4,935,014; 4,936,830; 4,941,879; 4,944,723; 4,944,725; 4,946,441; 4,950,240; 4,950,241; 4,950,250; 4,950,252; 4,955,866; 4,955,868; 4,955,869; 4,955,870; 4,961,728; 4,966,589; 4,966,592; 4,966,593; 4,973,310; 4,973,317; 4,976,704; 4,988,335; 4,988,339; 4,994,045; 4,998,921; 4,998,922; 5,000,736; 5,000,737; 5,002,548; 5,007,903; 5,011,475; 5,015,240; 5,017,187; 5,019,043; 5,019,044; 5,019,047; 5,019,048; 5,021,059; 5,024,665; 5,026,349; 5,030,208; 5,034,003; 5,037,306; 5,037,382; 5,037,393; 5,037,400; 5,041,094; 5,042,977; 5,045,066; 5,047,016; 5,049,133; 5,049,136; 5,053,010; 5,053,018; 5,055,102; 5,057,086; 5,057,089; 5,059,180; 5,059,185; 5,061,249; 5,061,251; 5,064,419; 5,067,490; 5,067,948; 5,071,353; 5,080,104; 5,084,027; 5,084,029; 5,084,030; 5,085,640; 5,085,641; 5,085,642; 5,088,986; 5,088,988; 5,092,843; 5,092,851; 5,092,852; 5,092,853; 5,098,382; 5,098,400; 5,098,401; 5,102,393; 5,102,397; 5,104,378; 5,104,380; 5,104,384; 5,104,385; 5,106,370; 5,106,372; 5,106,379; 5,108,378; 5,108,379; 5,112,307; 5,112,316; 5,114,404; 5,120,310; 5,120,314; 5,120,321; 5,122,118; 5,122,124; 5,125,898; 5,125,899; 5,127,910; 5,135,507; 5,135,510; 5,137,515; 5,137,516; 5,141,496; 5,143,414; 5,147,311; 5,147,326; 5,147,327; 5,149,323; 5,152,751; 5,156,599; 5,160,326; 5,163,916; 5,163,917; 5,163,918; 5,167,632; 5,167,641; 5,169,389; 5,169,392; 5,176,641; 5,176,655; 5,176,656; 5,176,657; 5,183,468; 5,183,469; 5,188,614; 5,190,526; 5,193,552; 5,195,982; 5,195,983; 5,195,985; 5,199,952; 5,201,708; 5,201,710; 5,205,826; 5,205,827; 5,207,646; 5,207,699; 5,209,739; 5,211,628; 5,211,629; 5,215,524; 5,215,533; 5,215,534; 5,215,535; 5,215,536; 5,217,437; 5,219,338; 5,221,262; 5,222,943; 5,222,947; 5,222,974; 5,224,936; 5,226,882; 5,228,883; 5,232,457; 5,232,458; 5,238,654; 5,242,388; 5,242,401; 5,242,416; 5,242,420; 5,246,428; 5,250,031; 5,256,152; 5,257,976; 5,261,894; 5,263,933; 5,267,961; 5,267,963; 5,269,761; 5,269,762; 5,269,766; 5,273,532; 5,273,538; 5,273,539; 5,273,541; 5,273,544; 5,279,554; 5,279,566; 5,279,577; 5,279,579; 5,279,581; 5,279,582; 5,279,583; 5,279,590; 5,282,793; 5,282,822; 5,282,827; 5,284,479; 5,290,233; 5,290,239; 5,290,240; 5,290,254; 5,292,314; 5,295,963; 5,295,965; 5,295,972; 5,295,973; 5,295,974; 5,295,975; 5,300,029; 5,300,030; 5,300,040; 5,300,045; 5,304,137; 5,304,138; 5,306,251; 5,306,258; 5,308,332; 5,311,841; 5,312,353; 5,312,366; 5,312,368; 5,312,370; 5,312,371; 5,312,372; 5,314,503; 5,318,538; 5,320,609; 5,322,517; 5,324,265; 5,328,475; 5,328,482; 5,328,484; 5,330,430; 5,334,149; 5,334,158; 5,334,173; 5,336,180; 5,336,187; 5,336,199; 5,338,303; 5,338,311; 5,342,310; 5,342,320; 5,344,407; 5,344,408; 5,346,475; 5,346,480; 5,346,481; 5,348,544; 5,352,200; 5,352,202; 5,352,203; 5,354,287; 5,356,387; 5,358,489; 5,360,410; 5,364,362; 5,364,370; 5,366,447; 5,368,568; 5,368,570; 5,368,571; 5,370,619; 5,370,626; 5,374,250; 5,378,240; 5,383,857; 5,385,550; 5,385,551; 5,385,557; 5,389,076; 5,389,085; 5,391,151; 5,391,183; 5,395,317; 5,395,337; 5,399,163; 5,401,246; 5,401,249; 5,401,251; 5,403,286; 5,403,287; 5,405,326; 5,405,327; 5,407,436; 5,409,466; 5,411,487; 5,415,638; 5,415,645; 5,415,648; 5,419,766; 5,419,773; 5,423,746; 5,425,715; 5,425,722; 5,429,611; 5,429,612; 5,429,613; 5,431,631; 5,431,632; 5,433,712; 5,445,618; 5,445,620; 5,451,210; 5,458,576; 5,458,580; 5,460,611; 5,462,531; 5,466,223; 5,468,227; 5,474,687; 5,478,314; 5,478,316; 5,478,328; 5,480,385; 5,480,387; 5,480,390; 5,482,039; 5,484,414; 5,486,163; 5,486,164; 5,487,732; 5,487,733; 5,487,734; 5,489,272; 5,492,536; 5,496,278; 5,501,672; 5,512,048; 5,512,050; 5,514,097; 5,514,107; 5,520,639; 5,520,649; 5,522,797; 5,522,812; 5,527,283; 5,527,284; 5,527,307; 5,529,189; 5,531,691; 5,531,692; 5,531,694; 5,531,704; 5,531,706; 5,533,975; 5,533,984; 5,536,243; 5,536,253; 5,536,257; 5,538,506; 5,538,508; 5,540,664; 5,540,666; 5,542,920; 5,542,927; 5,549,558; 5,549,568; 5,549,570; 5,549,572; 5,549,708; 5,558,648; 5,562,623; 5,562,624; 5,562,626; 5,562,631; 5,569,202; 5,569,203; 5,573,513; 5,575,770; 5,578,011; 5,578,014; 5,578,015; 5,582,591; 5,586,976; 5,591,133; 5,591,134; 5,591,138; 5,593,387; 5,593,390; 5,599,309; 5,599,313; 5,599,316; 5,599,318; 5,601,532; 5,601,535; 5,605,544; 5,609,577; 5,611,781; 5,611,782; 5,613,500; 5,613,951; 5,613,952; 5,615,771; 5,616,123; 5,616,132; 5,616,134; 5,616,135; 5,620,422; 5,620,425; 5,624,401; 5,624,405; 5,628,765; 5,630,803; 5,632,730; 5,632,733; 5,634,906; 5,634,909; 5,634,937; 5,637,092; 5,637,094; 5,643,220; 5,643,222; 5,647,851; 5,649,622; 5,651,774; 5,653,687; 5,653,688; 5,653,693; 5,656,031; 5,658,256; 5,658,257; 5,658,258; 5,658,259; 5,662,610; 5,662,617; 5,665,071; 5,665,075; 5,669,889; 5,672,155; 5,672,161; 5,681,291; 5,681,295; 5,688,240; 5,688,251; 5,693,016; 5,693,022; 5,693,023; 5,695,472; 5,704,911; 5,704,921; 5,707,393; 5,709,662; 5,709,667; 5,709,668; 5,713,866; 5,713,871; 5,713,872; 5,720,727; 5,725,498; 5,738,655; 5,741,223; 5,743,879; 5,743,887; 5,743,888; 5,743,891; 5,746,718; 5,749,854; 5,749,860; 5,755,692; 5,769,822; 5,769,827; 5,779,675; 5,779,677; 5,779,684; 5,788,677; 5,788,713; 5,792,107; 5,792,121; 5,792,122; 5,795,336; 5,797,885; 5,800,403; 5,807,334; 5,807,345; 5,807,352; 5,810,775; 5,810,784; 5,817,054; 5,817,070; 5,820,602; 5,823,997; 5,823,998; 5,827,293; 5,830,130; 5,836,911; 5,836,920; 5,843,036; 5,843,047; 5,848,990; 5,851,197; 5,853,390; 5,853,393; 5,855,839; 5,858,000; 5,865,227; 5,865,804; 5,868,711; 5,879,337; 5,882,342; 5,885,257; 5,891,052; 5,891,092; 5,891,097; 5,891,105; 5,897,508; 5,899,885; 5,899,886; 5,908,404; 5,908,408; 5,910,131; 5,911,706; 5,919,166; 5,921,959; 5,921,960; 5,921,961; 5,921,963; 5,921,964; 5,925,019; 5,928,188; 5,928,194; 5,928,205; 5,931,813; 5,938,638; 5,938,639; 5,941,850; 5,944,692; 5,944,693; 5,951,522; 5,954,699; 5,957,892; 5,957,895; 5,957,897; 5,960,797; 5,961,491; 5,971,953; 5,976,111; 5,980,487; 5,980,488; 5,980,491; 5,980,494; 5,984,899; 5,984,900; 5,989,219; 5,989,221; 5,993,417; 5,993,418; 5,997,500; 5,997,511; 5,997,513; 6,001,080; 6,007,474; 6,010,486; 6,010,487; 6,015,396; 6,015,438; 6,017,325; 6,022,337; 6,033,386; 6,033,387; 6,036,674; 6,039,713; 6,050,974; 6,050,977; 6,056,716; 6,056,724; 6,056,734; 6,063,040; 6,063,053; 6,066,115; 6,068,616; 6,074,360; 6,074,369; 6,074,370; 6,077,245; 6,080,135; 6,083,199; 6,083,200; 6,086,562; 6,086,569; 6,090,077; 6,090,078; 6,090,080; 6,093,172; 6,099,500; 6,099,503; 6,099,504; 6,102,844; 6,113,574; 6,117,112; 6,117,113; 6,126,637; 6,129,710; 6,142,972; 6,149,626; 6,149,629; 6,156,008; 6,156,010; 6,156,013; 6,156,015; 6,159,161; 6,159,181; 6,159,185; 6,171,284; 6,179,812; 6,183,444; 6,183,446; 6,186,980; 6,192,891; 6,193,695; 6,206,856; 6,206,857; 6,210,369; 6,217,550; 6,217,559; 6,221,044; 6,221,051; 6,221,052; 6,224,576; 6,228,054; 6,228,055; 6,235,006; 6,241,707; 6,241,708; 6,254,575; 6,254,580; 6,258,056; 6,261,264; 6,261,265; 6,267,748; 6,270,472; 6,270,481; 6,273,870; 6,280,399; 6,280,420; 6,280,421; 6,283,941; 6,293,925; 6,299,601; 6,309,374; 6,309,375; 6,312,409; 6,315,113; 6,319,233; 6,319,234; 6,322,536; 6,325,781; 6,325,789; 6,331,173; 6,332,875; 6,344,031; 6,356,783; 6,361,525; 6,368,303; 6,371,938; 6,379,336; 6,387,078; 6,402,716; 6,409,701; 6,409,703; 6,409,706; 6,412,490; 6,413,236; 6,413,237; 6,416,323; 6,416,497; 6,419,658; 6,428,463; 6,428,517; 6,432,035; 6,432,082; 6,432,087; 6,436,068; 6,440,098; 6,443,929; 6,447,480; 6,454,743; 6,458,105; 6,461,331; 6,461,333; 6,468,247; 6,475,194; 6,478,780; 6,482,176; 6,485,469; 6,485,474; 6,494,863; 6,500,155; 6,508,755; 6,511,454; 6,514,230; 6,517,516; 6,517,517; 6,524,278; 6,527,734; 6,527,742; 6,530,896; 6,530,904; 6,537,249; 6,537,252; 6,544,234; 6,547,764; 6,551,275; 6,551,276; 6,551,278; 6,554,798; 6,558,351; 6,558,357; 6,565,533; 6,565,538; 6,569,115; 6,572,584; 6,572,585; 6,575,939; 6,579,256; 6,582,405; 6,584,910; 6,585,690; 6,585,693; 6,585,702; 6,589,158; 6,592,508; 6,592,555; 6,592,556; 6,595,962; 6,599,268; 6,599,269; 6,599,272; 6,605,058; 6,605,067; 6,605,073; 6,607,508; 6,607,509; 6,613,019; 6,613,022; 6,616,630; 6,616,638; 6,616,639; 6,620,136; 6,620,137; 6,620,138; 6,623,455; 6,623,458; 6,623,459; 6,626,864; 6,629,957; 6,629,959; 6,632,198; 6,637,587; 6,638,248; 6,638,255; 6,641,561; 6,645,181; 6,652,482; 6,656,164; 6,659,975; 6,659,982; 6,663,593; 6,669,666; 6,673,034; 6,673,044; 6,673,049; 6,678,550; 6,679,863; 6,679,864; 6,685,676; 6,685,677; 6,689,091; 6,689,106; 6,689,107; 6,689,108; 6,692,470; 6,692,471; 6,699,218; 6,702,784; 6,706,011; 6,706,015; 6,706,019; 6,709,416; 6,712,787; 6,712,788; 6,716,191; 6,716,197; 6,716,198; 6,719,721; 6,719,728; 6,719,730; 6,723,068; 6,723,072; 6,726,655; 6,726,658; 6,726,661; 6,726,662; 6,730,059; 6,736,800; 6,740,059; 6,743,203; 6,749,833; 6,752,782; 6,752,784; 6,752,798; 6,761,706; 6,767,336; RE 33,585; RE 34,335; RE 34,936; RE36,398; RE 36,447; RE 37,110; RE 37,252 and RE 37,487.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention seeks to provide an improved automatic injection device.  
         [0004]     There is thus provided in accordance with a preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a needle guard adapted for selectable positioning with respect to the housing element and a selectable driving element adapted, when actuated, to be driven by the at least one resilient element for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and thereafter displacing the at least one syringe piston in the syringe to effect drug delivery and displacing the needle guard into a needle guarding position.  
         [0005]     There is also provided in accordance with another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston and a selectable driving element adapted, prior to being actuated, to retain the syringe in a non-penetration position and, when actuated, to be driven by the at least one resilient element for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and thereafter displacing the at least one syringe piston in the syringe to effect drug delivery.  
         [0006]     Preferably, the automatic injection device also includes a needle guard adapted for selectable positioning with respect to the housing element and wherein the selectable driving element is also operative for displacing the needle guard into a needle guarding position.  
         [0007]     There is further provided in accordance with yet another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a needle guard adapted for selectable positioning with respect to the housing element and a selectable driving element adapted, when actuated, to be driven by the at least one resilient element for displacing the syringe relative to the housing element from a non-penetration position to a penetration position, the needle guard being operative to permit actuation of the selectable driving element for displacing the syringe relative to the housing element from the non-penetration position to the penetration position.  
         [0008]     Preferably, the selectable driving element is also operative when actuated, following suitable displacement of the needle guard relative to the housing element and resulting displacement of the syringe relative to the housing element from the non-penetration position to the penetration position, to be driven by the at least one resilient element for displacing the at least one syringe piston in the syringe to effect drug delivery.  
         [0009]     There is yet further provided in accordance with still another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a selectable driving element adapted, when actuated, to be driven by the at least one resilient element for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and a motion damper operative to limit impact on the syringe produced by motion of the selectable driving element.  
         [0010]     Preferably, the selectable driving element is also operative for displacing the at least one syringe piston in the syringe to effect drug delivery and displacing the needle guard into a needle guarding position.  
         [0011]     Preferably,. the motion damper is operative to limit impact on the at least one syringe piston produced by motion of the selectable driving element. Additionally or alternatively, the motion damper is operative to limit impact on a flange of the syringe produced by motion of the selectable driving element.  
         [0012]     Preferably, the motion damper includes at least one elastomeric element. Additionally, the at least one elastomeric element is operative to damp relative axial motion between the housing element and the selectable driving element. Additionally or alternatively, relative axial motion between the at least one elastomeric element and a surface of varying cross-sectional area produces an extent of damping which varies with the relative axial positions of the housing element and the selectable driving element.  
         [0013]     Preferably, the motion damper provides decreasing damping as the selectable driving element moves forwardly relative to the housing element. Additionally, the decreasing damping is produced by engagement of the at least one elastomeric element with a surface of decreasing cross-sectional area as a function of forward displacement of the selectable driving element relative to the housing element.  
         [0014]     There is still further provided in accordance with yet another preferred embodiment of the present invention an automatic injection device including a housing element at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a plunger operative for displacing the at least one syringe piston, the plunger extending in and rearwardly of the housing element and a selectable driving element adapted, when actuated, to be driven by the at least one resilient element for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position.  
         [0015]     Preferably, the selectable driving element is also operative for displacing the at least one syringe piston in the syringe to effect drug delivery. Additionally or alternatively, the plunger is manually operable for displacing the at least one syringe piston.  
         [0016]     In accordance with still another preferred embodiment of the present invention the automatic injection device also includes a vial adaptor adapted for operative association with the syringe and with a drug vial for effecting fluid transfer between the syringe and the vial.  
         [0017]     There is further provided in accordance with another preferred embodiment of the present invention an automatic injection device including a housing element, a syringe including at least one syringe piston, a plunger operative for displacing the at least one syringe piston, the plunger extending in and rearwardly of the housing element and a selectable driving element adapted, when actuated, for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and a vial adaptor adapted for operative association with the syringe and with a drug vial for effecting fluid transfer between the syringe and the vial.  
         [0018]     There is even further provided in accordance with yet another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe and a needle guard adapted for positioning with respect to the syringe in a mutually locked orientation, whereby displacement of the needle guard relative to the housing requires corresponding displacement of the syringe.  
         [0019]     There is still further provided in accordance with yet another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe and a needle guard adapted for positioning with respect to the syringe and with respect to the housing element in a mutually locked needle guarding orientation, whereby displacement of the needle guard in a first direction relative to the housing is prevented by engagement of the needle guard with the syringe and displacement of the needle guard in a second direction relative to the housing, opposite to the first direction, is prevented by engagement of the needle guard with the housing element.  
         [0020]     Preferably, the housing element includes at least one window permitting contents of the syringe to be viewed from outside the housing element. In accordance with another preferred embodiment of the present invention the needle guard includes at least one window permitting contents of the syringe to be viewed from outside the needle guard. Additionally or alternatively, the housing element includes at least one transparent portion permitting contents of the syringe to be viewed from outside the housing element. Alternatively or additionally, the needle guard includes at least one transparent portion permitting contents of the syringe to be viewed from outside the needle guard.  
         [0021]     There is yet further provided in accordance with another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a plunger operative to selectably drive the at least one syringe piston in axial motion relative to the housing element and a selectable driving element threadably engaging the plunger and adapted, when actuated, to be driven by the at least one resilient element for initially axially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and thereafter displacing the at least one syringe piston in the syringe to effect drug delivery, wherein manual rotation of the plunger relative to the selectable driving element also produces axial movement of the plunger.  
         [0022]     There is further provided in accordance with yet another preferred embodiment of the present invention an automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a plunger operative to selectably drive the at least one syringe piston in axial motion relative to the housing element and a selectable driving element adapted, when actuated, to be driven by the at least one resilient element for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and at least partially coincidentally therewith engaging the plunger.  
         [0023]     Preferably, the vial adaptor includes a rearward facing portion configured such that upon mounting of the vial adaptor, rearward movement of the needle guard is prevented.  
         [0024]     There is still further provided in accordance with still another preferred embodiment of the present invention an automatic injection device including a housing element, a syringe including at least one syringe piston, a needle guard adapted for selectable positioning with respect to the housing element and a resilient selectable driving element adapted, when actuated, for displacing the syringe relative to the housing element from a non-penetration position to a penetration position, the needle guard being operative to permit actuation of the selectable driving element for displacing the syringe relative to the housing element from the non-penetration position to the penetration position.  
         [0025]     There is even further provided in accordance with yet another preferred embodiment of the present invention an automatic injection device including a housing element, a syringe including at least one syringe piston, a needle guard adapted for selectable positioning with respect to the housing element and a selectable driving element adapted, when actuated, to be driven for displacing the syringe relative to the housing element from a non-penetration position to a penetration position, the needle guard being operative to permit displacing the syringe relative to the housing element from the non-penetration position to the penetration position.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0027]      FIG. 1  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0028]      FIG. 2  is a simplified pictorial illustration of a rear housing element which forms part of the automatic injection device of  FIG. 1 ;  
         [0029]      FIGS. 3A and 3B  are respective top and side view simplified planar illustrations of the rear housing element of  FIG. 2 ;  
         [0030]      FIGS. 4A, 4B  and  4 C are sectional illustrations taken along respective section lines and directions IVA-IVA, IVB-IVB and IVC-IVC in  FIGS. 3A and 3B ;  
         [0031]      FIG. 5  is a simplified pictorial illustration of a selectable driving assembly which forms part of the automatic injection device of  FIG. 1 ;  
         [0032]      FIGS. 6A and 6B  are respective top and side view simplified planar illustrations of the selectable driving assembly of  FIG. 5 ;  
         [0033]      FIGS. 7A, 7B  and  7 C are sectional illustrations taken along respective section lines and directions VIIA-VIIA, VIIB-VIIB and VIIC-VIIC in  FIGS. 6A and 6B ;  
         [0034]      FIG. 8  is a simplified pictorial illustration of a forward housing and actuator element which forms part of the automatic injection device of  FIG. 1 ;  
         [0035]      FIGS. 9A and 9B  are respective top and side view simplified planar illustrations of the forward housing and actuator element of  FIG. 8 ;  
         [0036]      FIGS. 10A, 10B  and  10 C are sectional illustrations taken along respective section lines and directions XA-XA, XB-XB and XC-XC in  FIGS. 9A and 9B ;  
         [0037]      FIG. 11  is a simplified pictorial illustration of a needle guard element which forms part of the automatic injection device of  FIG. 1 ;  
         [0038]      FIGS. 12A and 12B  are respective top and side view simplified planar illustrations of the needle guard element of  FIG. 11 ;  
         [0039]      FIGS. 13A, 13B  and  13 C are sectional illustrations taken along respective section lines and directions XIIIA-XIIIA, XIIIB-XIIIB and XIIIC-XIIIC in  FIGS. 12A and 12B ;  
         [0040]      FIGS. 14A, 14B ,  14 C,  14 D,  14 E,  14 F,  14 G,  14 H and  14 I are simplified pictorial illustration of various stages of typical use of the automatic injection device of  FIG. 1 ;  
         [0041]      FIG. 15  is a simplified assembled view illustration of the automatic injection device of  FIGS. 1 and 14 A in a pre-use operative orientation;  
         [0042]      FIGS. 16A and 16B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 15 ;  
         [0043]      FIGS. 17A and 17B  are sectional illustrations taken along respective section lines and directions XVIIA-XVIIA and XVIIB-XVIIB in  FIGS. 16A and 16B ;  
         [0044]      FIG. 18  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 B in an optional titration operative orientation;  
         [0045]      FIGS. 19A and 19B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 18 ;  
         [0046]      FIGS. 20A and 20B  are sectional illustrations taken along respective section lines and directions XXA-XXA and XXB-XXB in  FIGS. 19A and 19B ;  
         [0047]      FIG. 21  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 C in an actuated operative orientation;  
         [0048]      FIGS. 22A and 22B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 21 ;  
         [0049]      FIGS. 23A and 23B  are sectional illustrations taken along respective section lines and directions XXIIIA-XXIIIA and XXIIIB-XXIIIB in  FIGS. 22A and 22B ;  
         [0050]      FIG. 24  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 D in a needle penetration, pre-drug delivery operative orientation;  
         [0051]      FIGS. 25A and 25B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 24 ;  
         [0052]      FIGS. 26A and 26B  are sectional illustrations taken along respective section lines and directions XXVIA-XXVIA and XXVIB-XXVIB in  FIGS. 25A and 25B ;  
         [0053]      FIG. 27  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 E in drug delivery operational orientation;  
         [0054]      FIGS. 28A and 28B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 27 ;  
         [0055]      FIGS. 29A and 29B  are sectional illustrations taken along respective section lines and directions XXIXA-XXIXA and XXIXB-XXIXB in  FIGS. 28A and 28B ;  
         [0056]      FIG. 30  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 F in an immediate post-drug delivery operational orientation;  
         [0057]      FIGS. 31A and 31B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 30 ;  
         [0058]      FIGS. 32A and 32B  are sectional illustrations taken along respective section lines and directions XXXIIA-XXXIA and XXXIIB-XXXIIB in  FIGS. 31A and 31B ;  
         [0059]      FIG. 33  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 G in its operation orientation as it is being disengaged from an injection site;  
         [0060]      FIGS. 34A and 34B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 33 ;  
         [0061]      FIGS. 35A and 35B  are sectional illustrations taken along respective section lines and directions XXXVA-XXXVA and XXXVB-XXXVB in  FIGS. 34A and 34B ;  
         [0062]      FIG. 36  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 H in a needle protected operational orientation;  
         [0063]      FIGS. 37A and 37B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 36 ;  
         [0064]      FIGS. 38A and 38B  are sectional illustrations taken along respective section lines and directions XXXVIIIA-XXXVIIIA and XXXVIIIB-XXXVIIIB in  FIGS. 37A and 37B ;  
         [0065]      FIG. 39  is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 I in a needle-guard push back misuse operational orientation;  
         [0066]      FIGS. 40A and 40B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 39 ;  
         [0067]      FIGS. 41A and 41B  are sectional illustrations taken along respective section lines and directions XLIA-XLIA and XLIB-XLIB in  FIGS. 40A and 40B ;  
         [0068]      FIG. 42  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with another preferred embodiment of the present invention;  
         [0069]      FIGS. 43A and 43B  are simplified pictorial illustrations of a main housing element which forms part of the automatic injection device of  FIG. 42 ;  
         [0070]      FIGS. 44A and 44B  are simplified pictorial sectional illustrations of the main housing element of  FIGS. 43A and 43B , taken along lines XLIVA-XLIVA and XLIVB-XLIVB in  FIG. 43A ;  
         [0071]      FIGS. 45A and 45B  are respective top and side view simplified planar illustrations of the main housing element of  FIGS. 43A-44B ;  
         [0072]      FIGS. 46A, 46B  and  46 C are sectional illustrations taken along respective section lines and directions XLVIA-XLVIA, XLVIB-XLVIB and XLVIC-XLVIC in  FIGS. 45A and 45B ;  
         [0073]      FIGS. 47A and 47B  are a simplified pictorial illustrations of a selectable driving element which forms part of the automatic injection device of  FIG. 42 ;  
         [0074]      FIGS. 48A and 48B  are simplified pictorial sectional illustrations of the selectable driving element of  FIGS. 47A and 47B , taken along lines XLVIIIA-XLVIIIA and XLVIIIB-XLVIIIB in  FIG. 47A ;  
         [0075]      FIGS. 49A and 49B  are respective top and side view simplified planar illustrations of the selectable driving element of  FIGS. 47A-48B ;  
         [0076]      FIGS. 50A and 50B  are sectional illustrations taken along respective section lines and directions LA-LA and LB-LB in  FIGS. 49A and 49B ;  
         [0077]      FIGS. 51A and 51B  are simplified pictorial illustrations of a forward housing element which forms part of the automatic injection device of  FIG. 42 ;  
         [0078]      FIGS. 52A and 52B  are simplified pictorial sectional illustrations of the forward housing element of  FIG. 51A and 51B , taken along lines LIIA-LILA and LIIB-LIIB in  FIG. 51A ;  
         [0079]      FIGS. 53A and 53B  are respective top and side view simplified planar illustrations of the forward housing element of  FIGS. 51A-51B ;  
         [0080]      FIGS. 54A and 54B  are sectional illustrations taken along respective section lines and directions LIVA-LIVA and LIVB-LIVB in  FIGS. 53A and 53B ;  
         [0081]      FIGS. 55A and 55B  are simplified pictorial illustrations of a needle guard element which forms part of the automatic injection device of  FIG. 42 ;  
         [0082]      FIGS. 56A and 56B  are simplified pictorial sectional illustrations of the needle guard element of  FIG. 55A and 55B , taken along lines LVIA-LVIA and LVIB-LVIB in  FIG. 55A ;  
         [0083]      FIGS. 57A and 57B  are respective top and side view simplified planar illustrations of the needle guard element of  FIGS. 55A and 55B ;  
         [0084]      FIGS. 58A, 58B  and  58 C are sectional illustrations taken along respective section lines and directions LVIIIA-LVIIIA, LVIIIB-LVIIIB and LVIIIC-LVIIIC in  FIGS. 57A and 57B ;  
         [0085]      FIGS. 59A, 59B ,  59 C,  59 D and  59 E are simplified pictorial illustrations of various stages of typical use of the automatic injection device of  FIG. 42 ;  
         [0086]      FIG. 60  is a simplified assembled view illustration of the automatic injection device of  FIGS. 42 and 59 A in a pre-use operative orientation;  
         [0087]      FIGS. 61A and 61B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 60 ;  
         [0088]      FIGS. 62A and 62B  are sectional illustrations taken along respective section lines and directions LXIIA-LXIIA and LXIIB-LXIIB in  FIGS. 61A and 61B ;  
         [0089]      FIG. 63  is a simplified pictorial illustration of the automatic injection device of  FIGS. 42 and 59 B in an actuatable operative orientation;  
         [0090]      FIGS. 64A and 64B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 63 ;  
         [0091]      FIGS. 65A and 65B  are sectional illustrations taken along respective section lines and directions LXVA-LXVA and LXVB-LXVB in  FIGS. 64A and 64B ;  
         [0092]      FIG. 66  is a simplified pictorial illustration of :the automatic injection device of  FIGS. 42 and 59 C in an actuated needle penetration operative orientation;  
         [0093]      FIGS. 67A and 67B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 66 ;  
         [0094]      FIGS. 68A and 68B  are sectional illustrations taken along respective section lines and directions LXVIIIA-LXVIIIA and LXVIIIB-LXVIIIB in  FIGS. 67A and 67B ;  
         [0095]      FIG. 69  is a simplified pictorial illustration of the automatic injection device of  FIGS. 42 and 59 D in a post-drug delivery operative orientation;  
         [0096]      FIGS. 70A and 70B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 69 ;  
         [0097]      FIGS. 71A and 72B  are sectional illustrations taken along respective section lines and directions LXXIA-LXXIA and LXXIB-LXXIB in  FIGS. 70A and 70B ;  
         [0098]      FIG. 72  is a simplified pictorial illustration of the automatic injection device of  FIGS. 42 and 59 E in post injection site disengagement operational orientation;  
         [0099]      FIGS. 73A and 73B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 72 ;  
         [0100]      FIGS. 74A and 74B  are sectional illustrations taken along respective section lines and directions LXXIVA-LXXIVA and LXXIVB-LXXIVB in  FIGS. 73A and 73B ;  
         [0101]      FIG. 75  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with yet another preferred embodiment of the present invention;  
         [0102]      FIG. 76  is a simplified assembled view illustration of the automatic injection device of  FIG. 75  in a pre-use operative orientation;  
         [0103]      FIGS. 77A and 77B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 76 ;  
         [0104]      FIGS. 78A and 78B  are sectional illustrations taken along respective section lines and directions LXXVIIIA-LXXVIIIA and LXXVIIIB-LXXVIIIB in  FIGS. 77A and 77B ;  
         [0105]      FIG. 79  is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in an actuatable operative orientation;  
         [0106]      FIGS. 80A and 80B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 79 ;  
         [0107]      FIGS. 81A and 81B  are sectional illustrations taken along respective section lines and directions LXXXIA-LXXXIA and LXXXIB-LXXXIB in  FIGS. 80A and 80B ;  
         [0108]      FIG. 82  is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in an actuated needle penetration operative orientation;  
         [0109]      FIGS. 83A and 83B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 82 ;  
         [0110]      FIGS. 84A and 84B  are sectional illustrations taken along respective section lines and directions LXXXIVA-LXXXIVA and LXXXIVB-LXXXXIVB in  FIGS. 83A and 83B ;  
         [0111]      FIG. 85  is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in a post-drug delivery operative orientation;  
         [0112]      FIGS. 86A and 86B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 85 ;  
         [0113]      FIGS. 87A and 87B  are sectional illustrations taken along respective section lines and directions LXXXVIIA-LXXXVIIA and LXXXVIIB-LXXXVIIB in  FIGS. 86A and 86B ;  
         [0114]      FIG. 88  is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in post injection site disengagement operational orientation;  
         [0115]      FIGS. 89A and 89B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 88 ;  
         [0116]      FIGS. 90A and 90B  are sectional illustrations taken along respective section lines and directions XCA-XCA and XCB-XCB in  FIGS. 89A and 89B ;  
         [0117]      FIG. 91  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a further preferred embodiment of the present invention;  
         [0118]      FIG. 92  is a simplified pictorial illustration of a rear housing element which forms part of the automatic injection device of  FIG. 91 ;  
         [0119]      FIGS. 93A and 903B  are respective top and side view simplified planar illustrations of the rear housing element of  FIG. 92 ;  
         [0120]      FIGS. 94A, 94B  and  94 C are sectional illustrations taken along respective section lines and directions XCIVA-XCIVA, XCIVB-XCIVB and XCIVC-XCIVC in  FIGS. 93A and 93B ;  
         [0121]      FIG. 95  is a simplified pictorial illustration of a selectable driving assembly which forms part of the automatic injection device of  FIG. 91 ;  
         [0122]      FIGS. 96A and 96B  are respective top and side view simplified planar illustrations of the selectable driving assembly of  FIG. 95 ;  
         [0123]      FIGS. 97A, 97B  and  97 C are sectional illustrations taken along respective section lines and directions XCVIIA-XCVIIA, XCVIIB-XCVIIB and XCVIIC-XCVIIC in  FIGS. 96A and 96B ;  
         [0124]      FIG. 98  is a simplified pictorial illustration of a forward housing and actuator element which forms part of the automatic injection device of  FIG. 91 ;  
         [0125]      FIGS. 99A and 99B  are respective top and side view simplified planar illustrations of the forward housing and actuator element of  FIG. 98 ;  
         [0126]      FIGS. 100A, 100B  and  100 C are sectional illustrations taken along respective section lines and directions CA-CA, CB-CB and CC-CC in  FIGS. 99A and 99B ;  
         [0127]      FIG. 101  is a simplified pictorial illustration of a needle guard element which forms part of the automatic injection device of  FIG. 91 ;  
         [0128]      FIGS. 102A and 102B  are respective top and side view simplified planar illustrations of the needle guard element of  FIG. 101 ;  
         [0129]      FIGS. 103A, 103B  and  103 C are sectional illustrations taken along respective section lines and directions CIIIA-CIIIA, CIIIB-CIIIB and CIIIC-CIIIC in  FIGS. 102A and 102B ;  
         [0130]      FIG. 104  is a simplified assembled view illustration of the automatic injection device of  FIG. 91  in a pre-use operative orientation;  
         [0131]      FIGS. 105A and 105B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 104 ;  
         [0132]      FIGS. 106A and 106B  are sectional illustrations taken along respective section lines and directions CVIA-CVIA and CVIB-CVIB in  FIGS. 105A and 105B ;  
         [0133]      FIG. 107  is a simplified pictorial illustration of the automatic injection device of FIGS.  91  in an optional titration operative orientation;  
         [0134]      FIGS. 108A and 108B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 107 ;  
         [0135]      FIGS. 109A and 109B  are sectional illustrations taken along respective section lines and directions CIXA-CIXA and CIXB-CIXB in  FIGS. 108A and 108B ;  
         [0136]      FIG. 110  is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in an actuated operative orientation;  
         [0137]      FIGS. 111A and 111B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 110 ;  
         [0138]      FIGS. 112A and 112B  are sectional illustrations taken along respective section lines and directions CXIIA-CXIIA and CXIIB-CXIIB in  FIGS. 111A and 111B ;  
         [0139]      FIG. 113  is a simplified pictorial illustration of the automatic injection device of FIGS.  91  in a needle penetration, pre-drug delivery operative orientation;  
         [0140]      FIGS. 114A and 114B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 113 ;  
         [0141]      FIGS. 115A and 115B  are sectional illustrations taken along respective section lines and directions CXVA-CXVA and CXVB-CXVB in  FIGS. 114A and 114B ;  
         [0142]      FIG. 116  is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in drug delivery operational orientation;  
         [0143]      FIGS. 117A and 117B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 116 ;  
         [0144]      FIGS. 118A and 118B  are sectional illustrations taken along respective section lines and directions CXVIIIA-CXVIIIA and CXVIIIB-CXVIIIB in  FIGS. 117A and 117B ;  
         [0145]      FIG. 119  is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in an immediate post-drug delivery operational orientation;  
         [0146]      FIGS. 120A and 120B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 119 ;  
         [0147]      FIGS. 121A and 121B  are sectional illustrations taken along respective section lines and directions CXXIA-CXXIA and CXXIB-CXXIB in  FIGS. 120A and 120B ;  
         [0148]      FIG. 122  is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in a needle protected operational orientation;  
         [0149]      FIGS. 123A and 123B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 122 ;  
         [0150]      FIGS. 124A and 124B  are sectional illustrations taken along respective section lines and directions CXXIVA-CXXIVA and CXXIVB-CXXIVB in  FIGS. 123A and 123B ;  
         [0151]      FIG. 125  is a simplified pictorial illustration of the automatic injection device of FIGS.  91  in a needle-guard push back misuse operational orientation;  
         [0152]      FIGS. 126A and 126B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 125 ;  
         [0153]      FIGS. 127A and 127B  are sectional illustrations taken along respective section lines and directions CXXVIIA-CXXVIIA and CXXVIIB-CXXVIIB in  FIGS. 126A and 126B ;  
         [0154]      FIG. 128  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a still further preferred embodiment of the present invention;  
         [0155]      FIG. 129  is a simplified pictorial illustration of a rear housing element which forms part of the automatic injection device of  FIG. 128 ;  
         [0156]      FIGS. 130A and 130B  are respective top and side view simplified planar illustrations of the rear housing element of  FIG. 129 ;  
         [0157]      FIGS. 131A, 131B  and  131 C are sectional illustrations taken along respective section lines and directions CXXXIA-CXXXIA, CXXXIB-CXXXIB and CXXXIC-CXXXIC in  FIGS. 130A and 130B ;  
         [0158]      FIG. 132  is a simplified pictorial illustration of a selectable driving assembly which forms part of the automatic injection device of  FIG. 128 ;  
         [0159]      FIGS. 133A and 133B  are respective top and side view simplified planar illustrations of the selectable driving assembly of  FIG. 132 ;  
         [0160]      FIGS. 134A, 134B  and  134 C are sectional illustrations taken along respective section lines and directions CXXXIVA-CXXXIVA, CXXXIVB-CXXXIVB and CXXXXIV-CXXXIVC in  FIGS. 133A and 133B ;  
         [0161]      FIG. 135  is a simplified pictorial illustration of a forward housing and actuator element which forms part of the automatic injection device of  FIG. 128 ;  
         [0162]      FIGS. 136A and 136B  are respective top and side view simplified planar illustrations of the forward housing and actuator element of  FIG. 135 ;  
         [0163]      FIGS. 137A, 137B  and  137 C are sectional illustrations taken along respective section lines and directions CXXXVIIA-CXXXVIIA, CXXXVIIB-CXXXVIIB and CXXXVIIC-CXXXVIIC in  FIGS. 136A and 136B ;  
         [0164]      FIG. 138  is a simplified pictorial illustration of a needle guard element which forms part of the automatic injection device of  FIG. 128 ;  
         [0165]      FIGS. 139A and 139B  are respective top and side view simplified planar illustrations of the needle guard element of  FIG. 138 ;  
         [0166]      FIGS. 140A, 140B  and  140 C are sectional illustrations taken along respective section lines and directions CXLA-CXLA, CXLB-CXLB and CXLC-CXLC in  FIGS. 139A and 139B ;  
         [0167]      FIGS. 141A, 141B ,  141 C,  141 D,  141 E,  141 F and  141 G are simplified pictorial illustration of various stages of typical use of the automatic injection device of  FIG. 128 ;  
         [0168]      FIG. 142  is a simplified assembled view illustration of the automatic injection device of  FIGS. 128 and 141 A in a pre-use operative orientation;  
         [0169]      FIGS. 143A and 143B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 142 ;  
         [0170]      FIGS. 144A and 144B  are sectional illustrations taken along respective section lines and directions CXLIVA-CXLIVA and CXLIVB-CXLIVB in  FIGS. 143A and 143B ;  
         [0171]      FIG. 145  is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 B in an optional titration operative orientation;  
         [0172]      FIGS. 146A and 146B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 145 ;  
         [0173]      FIGS. 147A and 147B  are sectional illustrations taken along respective section lines and directions CXLVIIA-CXLVIIA and CXLVIIB-CXLVIIB in  FIGS. 146A and 146B ;  
         [0174]      FIG. 148  is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 C in an actuated operative orientation;  
         [0175]      FIGS. 149A and 149B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 148 ;  
         [0176]      FIGS. 150A and 150B  are sectional illustrations taken along respective section lines and directions CLA-CLA and CLB-CLB in  FIGS. 149A and 149B ;  
         [0177]      FIG. 151  is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 D in a needle penetration, pre-drug delivery operative orientation;  
         [0178]      FIGS. 152A and 152B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 151 ;  
         [0179]      FIGS. 153A and 153B  are sectional illustrations taken along respective section lines and directions CLIIIA-CLIIIA and CLIIIB-CLIIIB in  FIGS. 152A and 152B ;  
         [0180]      FIG. 154  is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 E in drug delivery operational orientation;  
         [0181]      FIGS. 155A and 155B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 154 ;  
         [0182]      FIGS. 156A and 156B  are sectional illustrations taken along respective section lines and directions CLVIA-CLVIA and CLVIB-CLVIB in  FIGS. 155A and 155B ;  
         [0183]      FIG. 157  is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 F in an immediate post-drug delivery operational orientation;  
         [0184]      FIGS. 158A and 158B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 157 ;  
         [0185]      FIGS. 159A and 159B  are sectional illustrations taken along respective section lines and directions CLIXA-CLIXA and CLIXB-CLIXB in  FIGS. 158A and 158B ;  
         [0186]      FIG. 160  is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 G in its operation orientation as it is being disengaged from an injection site;  
         [0187]      FIGS. 161A and 161B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 160 ;  
         [0188]      FIGS. 162A and 162B  are sectional illustrations taken along respective section lines and directions CLXIIA-CLXIIA and CLXIIB-CLXIIB in  FIGS. 161A and 161B ;  
         [0189]      FIG. 163  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a yet further preferred embodiment of the present invention;  
         [0190]      FIG. 164  is a simplified assembled view illustration of the automatic injection device of  FIG. 163  in a pre-use operative orientation;  
         [0191]      FIGS. 165A and 165B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 164 ;  
         [0192]      FIGS. 166A and 166B  are sectional illustrations taken along respective section lines and directions CLXVIA-CLXVIA and CLXVIB-CLXVIB in  FIGS. 165A and 165B ;  
         [0193]      FIG. 167  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in an optional titration operative orientation;  
         [0194]      FIGS. 168A and 168B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 167 ;  
         [0195]      FIGS. 169A and 169B  are sectional illustrations taken along respective section lines and directions CLXIXA-CLXIXA and CLXIXB-CLXIXB in  FIGS. 168A and 168B ;  
         [0196]      FIG. 170  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in an actuated operative orientation;  
         [0197]      FIGS. 171A and 171B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 170 ;  
         [0198]      FIGS. 172A and 172B  are sectional illustrations taken along respective section lines and directions CLXXIIA-CLXXIIA and CLXXIIB-CLXXIIB in  FIGS. 171A and 171B ;  
         [0199]      FIG. 173  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in a needle penetration, pre-drug delivery operative orientation;  
         [0200]      FIGS. 174A and 174B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 173 ;  
         [0201]      FIGS. 175A and 175B  are sectional illustrations taken along respective section lines and directions CLXXVA-CLXXVA and CLXXVB-CLXXVB in  FIGS. 174A and 174B ;  
         [0202]      FIG. 176  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in drug delivery operational orientation;  
         [0203]      FIGS. 177A and 177B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 176 ;  
         [0204]      FIGS. 178A and 178B  are sectional illustrations taken along respective section lines and directions CLXXVIIIA-CLXXVIIIA and CLXXVIIIB-CLXXVIIIB in  FIGS. 177A and 177B ;  
         [0205]      FIG. 179  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in an immediate post-drug delivery operational orientation;  
         [0206]      FIGS. 180A and 180B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 179 ;  
         [0207]      FIGS. 181A and 181B  are sectional illustrations taken along respective section lines and directions CLXXXIA-CLXXXIA and CLXXXIB-CLXXXIB in  FIGS. 180A and 180B ;  
         [0208]      FIG. 182  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in its operation orientation as it is being disengaged from an injection site;  
         [0209]      FIGS. 183A and 183B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 182 ;  
         [0210]      FIGS. 184A and 184B  are sectional illustrations taken along respective section lines and directions CLXXXIVA-CLXXXIVA and CLXXXIVB-CLXXXIVB in  FIGS. 183A and 183B ;  
         [0211]      FIG. 185  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in a needle protected operational orientation;  
         [0212]      FIGS. 186A and 186B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 185 ;  
         [0213]      FIGS. 187A and 187B  are sectional illustrations taken along respective section lines and directions CLXXXVIIA-CLXXXVIIA and CLXXXVIIB-CLXXXVIIB in  FIGS. 186A and 186B ;  
         [0214]      FIG. 188  is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in a needle-guard push back misuse operational orientation;  
         [0215]      FIGS. 189A and 189B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 188 ;  
         [0216]      FIGS. 190A and 190B  are sectional illustrations taken along respective section lines and directions CXCA-CXCA and CXCB-CXCB in  FIGS. 189A and 189B ;  
         [0217]      FIG. 191  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with yet another preferred embodiment of the present invention;  
         [0218]      FIG. 192  is a simplified assembled view illustration of the automatic injection device of  FIG. 191  in a pre-use operative orientation;  
         [0219]      FIGS. 193A and 193B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 192 ;  
         [0220]      FIGS. 194A and 194B  are sectional illustrations taken along respective section lines and directions CXCIVA-CXCIVA and CXCIVB-CXCIVB in  FIGS. 193A and 193B ;  
         [0221]      FIG. 195  is a simplified pictorial illustration of the automatic injection device of  FIGS. 192-194B  in an optional vial adaptor mounted operative orientation;  
         [0222]      FIGS. 196A and 196B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 195 ;  
         [0223]      FIGS. 197A and 197B  are sectional illustrations taken along respective section lines and directions CXCVIIA-CXCVIIA and CXCVIIB-CXCVIIB in  FIGS. 196A and 196B ;  
         [0224]      FIG. 198  is a simplified pictorial illustration of the automatic injection device of  FIGS. 195-197B  in a vial communication operative orientation;  
         [0225]      FIGS. 199A and 199B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 198 ;  
         [0226]      FIGS. 200A and 200B  are sectional illustrations taken along respective section lines and directions CCA-CCA and CCB-CCB in  FIGS. 199A and 199B ;  
         [0227]      FIG. 201  is a simplified pictorial illustration of the automatic injection device of  FIGS. 198-200B  in a vial injection operative orientation;  
         [0228]      FIGS. 202A and 202B  are respective top and side view simplified planar illustrations ofthe automatic injection device of  FIG. 201 ;  
         [0229]      FIGS. 203A and 203B  are sectional illustrations taken along respective section lines and directions CCIIIA-CCIIIA and CCIIIB-CCIIIB in  FIGS. 202A and 202B ;  
         [0230]      FIG. 204  is a simplified pictorial illustration of the automatic injection device of  FIGS. 201-203B  in a vial aspiration operative orientation;  
         [0231]      FIGS. 205A and 205B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 204 ;  
         [0232]      FIGS. 206A and 206B  are sectional illustrations taken along respective section lines and directions CCVIA-CCVIA and CCVIB-CCVIB in  FIGS. 205A and 205B ;  
         [0233]      FIG. 207  is a simplified pictorial illustration of the automatic injection device of  FIGS. 204-206B  in a vial removed operative orientation;  
         [0234]      FIGS. 208A and 208B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 207 ;  
         [0235]      FIGS. 209A and 209B  are sectional illustrations taken along respective section lines and directions CCIXA-CCIXA and CCIXB-CCIXB in  FIGS. 208A and 208B ;  
         [0236]      FIG. 210  is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with still another preferred embodiment of the present invention;  
         [0237]      FIG. 211  is a simplified assembled view illustration of the automatic injection device of  FIG. 210  in a pre-use operative orientation;  
         [0238]      FIGS. 212A and 212B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 211 ;  
         [0239]      FIGS. 213A and 213B  are sectional illustrations taken along respective section lines and directions CCXIIIA-CCXIIIA and CCXIIIB-CCXIIIB in  FIGS. 212A and 212B ;  
         [0240]      FIG. 214  is a simplified pictorial illustration of the automatic injection device of  FIGS. 211-213B  in an optional vial adaptor mounted operative orientation;  
         [0241]      FIGS. 215A and 215B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 214 ;  
         [0242]      FIGS. 216A and 216B  are sectional illustrations taken along respective section lines and directions CCXVIA-CCXVIA and CCXVIB-CCXVIB in  FIGS. 215A and 215B ;  
         [0243]      FIG. 217  is a simplified pictorial illustration of the automatic injection device of  FIGS. 214-216B  in a vial communication operative orientation;  
         [0244]      FIGS. 218A and 218B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 217 ;  
         [0245]      FIGS. 219A and 219B  are sectional illustrations taken along respective section lines and directions CCXIXA-CCXIXA and CCXIXB-CCXIXB in  FIGS. 218A and 218B ;  
         [0246]      FIG. 220  is a simplified pictorial illustration of the automatic injection device of  FIGS. 217-219B  in an air injection operative orientation;  
         [0247]      FIGS. 221A and 221B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 220 ;  
         [0248]      FIGS. 222A and 222B  are sectional illustrations taken along respective section lines and directions CCXXIIA-CCXXIIA and CCXXIIB-CCXXIIB in  FIGS. 221A and 221B ;  
         [0249]      FIG. 223  is a simplified pictorial illustration of the automatic injection device of  FIGS. 220-222B  in a vial aspiration operative orientation;  
         [0250]      FIGS. 224A and 224B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 223 ;  
         [0251]      FIGS. 225A and 225B  are sectional illustrations taken along respective section lines and directions CCXXVA-CCXXVA and CCXXVB-CCXXVB in  FIGS. 224A and 224B ;  
         [0252]      FIG. 226  is a simplified pictorial illustration of the automatic injection device of  FIGS. 223-225B  in a vial removed operative orientation;  
         [0253]      FIGS. 227A and 227B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 226 ;  
         [0254]      FIGS. 228A and 228B  are sectional illustrations taken along respective section lines and directions CCXXVIIIA-CCXXVIIIA and CCXXVIIIB-CCXXVIIIB in  FIGS. 227A and 227B ;  
         [0255]      FIG. 229  is a simplified pictorial illustration of the automatic injection device of  FIGS. 226-228B  in a in a needle connection operative orientation;  
         [0256]      FIGS. 230A and 230B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 229 ;  
         [0257]      FIGS. 231A and 231B  are sectional illustrations taken along respective section lines and directions CCXXXIA-CCXXXIA and CCXXXIB-CCXXXIB in  FIGS. 230A and 230B ;  
         [0258]      FIG. 232  is a simplified pictorial illustration of the automatic injection device of  FIGS. 229-231B  in a needle cover removed operative orientation;  
         [0259]      FIGS. 233A and 233B  are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 232 ; and  
         [0260]      FIGS. 234A and 234B  are sectional illustrations taken along respective section lines and directions CCXXXIVA-CCXXXIVA and CCXXXIVB-CCXXXIVB in  FIGS. 233A and 233B ;  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0261]     Reference is now made to  FIGS. 1-13C , which illustrate the constituent elements of an automatic injection device constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0262]     As seen with particular clarity in  FIG. 1 , the automatic injection device comprises a rear housing element  10  in which is seated a main compression spring  20 , which provides selectable forward displacement to a selectable driving assembly  30 , which includes a selectable driving element  31  and a pair of elastomeric motion damping elements  32  and  34 , and selectably engages a plunger  40  and a pre-filled syringe  50  having a hypodermic needle  60  which is covered by a needle protection cover  62 . Pre-filled syringe  50  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0263]     Plunger  40  also operatively engages pre-filled syringe  50  and is selectably operated by selectable driving assembly  30  to inject liquid contents of pre-filled syringe  50  through hypodermic needle  60 .  
         [0264]     The forward portion of rear housing element  10  as well as spring  20 , selectable driving assembly  30 , plunger  40  and pre-filled syringe  50  are located within a forward housing and actuator element  70 . At a forward end of the interior of forward housing and actuator element  70  there is provided a needle guard element  80 , which is positioned by a compression spring  90 .  
         [0265]     Reference is now made to  FIG. 2 , which is a simplified pictorial illustration of a preferred rear housing element  10  which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 3A and 3B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 4A, 4B  and  4 C, which are sectional illustrations taken along respective section lines and directions IVA-IVA, IVB-IVB and IVC-IVC in  FIGS. 3A and 3B .  
         [0266]     As seen in  FIGS. 2-4C , the rear housing element  10  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  110 , which terminates in a back wall  112 , defining generally symmetric side-facing tabs  114  in front of which are generally symmetric side facing recesses  116 . Tubular portion  110  is preferably side-to-side symmetric about a longitudinal axis  120 .  
         [0267]     Tubular portion  110  is formed with a pair of generally symmetric side recesses  122  at which corresponding generally elongate engagement shaft portions  124  extend forwardly parallel to longitudinal axis  120 , each terminating in an outward facing protrusion  126 . Above each engagement shaft portion  124  there is provided an additional shaft portion  127 , which extends forwardly of protrusion  126  and has a somewhat curved cross sectional configuration. Shaft portions  127  on the two sides of the rear housing element  10  are separated from each other, as shown. A pair of mutually facing ribs  128  extend from shaft portions  127  parallel to longitudinal axis  120 , defining forward facing shoulders  129 . As seen particularly in  FIGS. 2 and 4 A, a central inward facing protrusion  130  is provided at a top interior surface of the rear housing element, between and rearward of ribs  128 .  
         [0268]     A bottom interior surface  131  of the rear housing element has a generally uniform, slightly concave cross section and includes a plurality of generally radially inwardly directed ribs  132 , which extend generally parallel to longitudinal axis  120 . A bottom exterior surface  134  of the rear housing element, which is the underside of surface  131 , includes a forward edge  136  and a plurality of radially outwardly directed ribs  138  which extend generally parallel to longitudinal axis  120 .  
         [0269]     Side interior surfaces  140  of the rear housing element  10  each define a forwardly pointed protrusion  142  which is engaged by an outwardly extending protrusion of a first finger of selectable driving assembly  30  and by elastomeric motion damping elements  32  and  34 , forming part of selectable driving assembly  30 , as described hereinbelow. The interior surface of back wall  112  of the rear housing element  10  further comprises a rear seat  160  for spring  20 .  
         [0270]     Reference is now made to  FIG. 5 , which is a simplified pictorial illustration of a preferred selectable driving assembly  30 , which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 6A and 6B , which are respective top and side view simplified planar illustrations of the selectable driving assembly and to  FIGS. 7A, 7B  and  7 C, which are sectional illustrations taken along respective section lines and directions VIIA-VIIA, VIIB-VIIB and VIIC-VIIC in  FIGS. 6A and 6B .  
         [0271]     As seen in  FIGS. 5-7C , the selectable driving element  31  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  310 , having an open back and having a pair of side-to-side symmetric actuation arms  312  which extend forwardly of tubular portion  310  parallel to a longitudinal axis  320 , which when selectable driving assembly  30  is assembled with the rear housing element  10 , is coaxial with longitudinal axis  120  ( FIGS. 2-4C ). A top engagement arm  322  also extends forwardly of tubular portion  310 . A narrowed tubular neck portion  324  is formed forwardly of tubular portion  310 . Elastomeric elements  32  and  34 , seated in side recesses  326  and  328  in the selectable driving element  31 , are located symmetrically at the junction of the tubular portion  310  and the neck portion  324 .  
         [0272]     Each of actuation arms  312  has a generally curved cross section and includes a rearwardly facing first finger  330  terminating in an outwardly extending protrusion  332  and an inwardly extending protrusion  333 , a second rearwardly extending finger  334  terminating in an inwardly inclined protruding portion  336  and a third rearwardly extending finger  338  having formed thereon, adjacent an extreme outward end thereof, an inwardly facing generally triangular tooth  342  having a forwardly facing inclined surface  344  and a rearwardly facing engagement surface  346  extending generally perpendicular to longitudinal axis  320 . Separated from tooth  342  by a notch  347  is an inwardly facing rounded tooth  348 . Additionally, third finger  338  has formed thereon top and bottom protrusions  349 .  
         [0273]     Top engagement arm  322  terminates in an outwardly facing protrusion  350  having an inclined forward facing surface  351 . Rearwardly of protrusion  350  and separated therefrom by an outwardly facing notch  352  is an outwardly facing protrusion  354 , having an inclined outwardly facing surface  356 .  
         [0274]     Plunger  40 , as seen in  FIG. 1 , is a generally circularly symmetric element, which is preferably formed in an overall ribbed configuration, as shown. Plunger  40  includes a rear portion  402  having a relatively large circular cross section which tapers forwardly to a neck portion  404 , having a relatively small circular cross section. Forwardly of neck portion  404  is an intermediate portion  406 , whose circular cross section is typically the same as that of rear portion  402 , and a forward portion  408 , whose circular cross section is typically the same as that of neck portion  404 . Plunger  40  terminates at its forward end in a male threaded protrusion  410  adapted to fit a corresponding female threaded socket formed in a piston described hereinbelow with reference to  FIG. 17A  which is movably located in pre-filled syringe  50 . Plunger  40  is preferably symmetrically disposed about a longitudinal axis  420 , which when assembled together with selectable driving assembly  30  and rear housing element  10 , is coaxial with longitudinal axes  120  ( FIGS. 2-4C ) and  320  ( FIGS. 5-7C ).  
         [0275]     As seen in  FIG. 1 , pre-filled syringe  50  includes a rear flange  502  which selectably engages notches  347  formed in respective third fingers  338  of each of side-to-side symmetric actuation arms  312  of selectable driving assembly  30  ( FIGS. 5-7C ).  
         [0276]     Reference is now made to  FIG. 8 , which is a simplified pictorial illustration of forward housing and actuator element  70  which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 9A and 9B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 10A, 10B  and  10 C, which are sectional illustrations taken along respective section lines and directions XA-XA, XB-XB and XC-XC in  FIGS. 9A and 9B .  
         [0277]     As seen in  FIGS. 8-10C , the forward housing and actuator element  70  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally truncated conical configuration arranged along a longitudinal axis  720 , which when the automatic injection device is assembled, is coaxial with longitudinal axes  120  ( FIGS. 2-4C ),  320  ( FIGS. 5-7C ) and  420  ( FIG. 1 ). Forward housing and actuator element  70  includes a generally tubular rear portion  710 , having an open back and formed with a pair of side-to-side symmetric snap fit engagement sockets  712  which receive the protrusions  126  of the rear housing element  10  during factory assembly of the automatic injection device.  
         [0278]     Forward of tubular rear portion  710  are formed a pair of top-bottom symmetric windows  714 , which allow the pre-filled syringe to be viewed, when the automatic injection device is assembled, including during use thereof.  
         [0279]     A pair of outer side surfaces  716  of forward housing and actuator element  70  are each formed with ribbed grip regions  718 . Corresponding inner side surfaces  721  each define a plurality of longitudinally extending ribs  722 ,  724 ,  726  and  728  which are used to slidably guide the needle guard element  80  during axial movement thereof as well as inner facing protrusions  730 , which together with ribs  722  and  724  define a forward facing spring seat for spring  90  ( FIG. 1 ). Inner facing protrusions  730  are operative to slidably support pre-filled syringe  50  and to slidably guide actuation arms  312  of selectable driving assembly  30 .  
         [0280]     Inner top and bottom surfaces  732  and  734  define respective pairs of ribs  736  and  738  which are operative to slidably guide the needle guard  80  during axial movement thereof. A cantilevered rearwardly extending actuation lever  750  extends from a location rearward of top window  714  and defines, at an extreme rearward top facing surface thereof, an actuation button  752 .  
         [0281]     As best seen in  FIG. 10A , inner facing protrusions  730  define at rearward facing portions thereof protrusions  760  and  762  which form a stopping point for flange  502 , thus limiting the forward movement of the pre-filled syringe  50 .  
         [0282]     Reference is now made to  FIG. 11 , which is a simplified pictorial illustration of a needle guard element  80  which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 12A and 12B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 13A, 13B  and  13 C, which are sectional illustrations taken along respective section lines and directions XIIIA-XIIIA, XIIIB-XIIIB and XIIIC-XIIIC in  FIGS. 12A and 12B .  
         [0283]     As seen in  FIGS. 11-13C , the needle guard element  80  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  810 , having a forward facing body engaging surface  812  including a pair of concentric ribbed circumferential forward facing rings  814  and  816 . The internal surface, located opposite from body engaging surface  812 , forms a spring-seat for spring  90 .  
         [0284]     Needle guard element  80  has a pair of side-to-side symmetric mounting arms  818  having rearwardmost ends  819 , arranged symmetrically about a longitudinal axis  820 . Each of arms  818  is formed with a rectangular window  821  having a relatively wider forward portion  822  and a relatively narrower rear portion  824 . Arms  818  extend along and rearwardly of tubular portion  810  parallel to longitudinal axis  820 , which when the automatic injection device is assembled, is coaxial with longitudinal axes  120  ( FIGS. 2-4C ),  320  ( FIGS. 5-7C ),  420  ( FIG. 1 ) and  720  ( FIGS. 8-10C ).  
         [0285]     A top engagement arm  832  also extends rearwardly of tubular portion  810  and includes a rearwardmost axial portion  834 , an inclined intermediate portion  836 , an axial intermediate portion  838  and an inclined mounting portion  840 , which extends from a top mounting arm  842 , formed with an elongate window  844 . An equivalent elongate window, also referenced by numeral  844 , is formed on a bottom mounting arm  845 . Elongate windows  844  and top-bottom symmetric windows  714  of forward housing and actuator element  70  are positioned in respective parallel locations, such that pre-filled syringe  50  is visible through the windows.  
         [0286]     Top and bottom engagement portions  846  and  848  are each formed with inwardly directed teeth, here designated by reference numerals  850  and  852  respectively.  
         [0287]     Reference is now made to  FIGS. 14A, 14B ,  14 C,  14 D,  14 E,  14 F,  14 G,  14 H and  14 I which are simplified pictorial illustrations of various stages of typical use of the automatic injection device of  FIG. 1 .  
         [0288]     As seen in  FIG. 14A , the automatic injection device of  FIG. 1  is stored prior to use, as indicated by reference numeral  900 , in a pre-use operative orientation, described hereinbelow with reference to  FIGS. 15-17B . While the automatic injection device is stored, it is preferably covered by needle protection cover  62 .  
         [0289]     As seen in  FIG. 14B , prior to use, after removing the needle protection cover  62 , air bubbles or some of the drug contained in pre-filled syringe  50  may optionally be manually expelled via the needle, as indicated by reference numeral  902 . The operative orientation of the automatic injection device for this functionality is described hereinbelow with reference to  FIGS. 18-20B .  
         [0290]     A user actuates the automatic injection device by pushing it against an injection site and depressing actuation button  752  ( FIGS. 8-10C ), as indicated by reference numeral  904  shown in  FIG. 14C  and as described hereinbelow with reference to  FIGS. 21-23B . In response to user actuation, needle penetration takes place at the injection site, as indicated by reference numeral  906  shown in  FIG. 14D . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 24-26B .  
         [0291]     As seen in  FIG. 14E , immediately following needle penetration, drug delivery takes place, as indicated by reference numeral  908 . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 27-29B . The operative orientation of the automatic injection device immediately following completion of drug delivery is indicated by reference numeral  910  shown in  FIG. 14F , as described hereinbelow with reference to  FIGS. 30-32B .  
         [0292]     As seen in  FIG. 14G , the automatic injection device is then manually disengaged from the injection site, as indicated by reference numeral  912 , during which time the needle guard  80  is automatically deployed. The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 33-35B . Immediately upon disengagement, the needle is automatically protected by the needle guard element  80 , as indicated by reference numeral  914  shown in  FIG. 14H . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 36-38B .  
         [0293]     As seen in  FIG. 14I , should the needle guard be forced axially rearward due to misuse, as indicated by reference numeral  916 , its rearward movement produces corresponding rearward motion of the syringe  50 , thus keeping the needle protected. The operative orientation of the automatic injection device in this case is described hereinbelow with reference to  FIGS. 39-41B .  
         [0294]     Reference is now made to  FIG. 15 , which is a simplified assembled view illustration of the automatic injection device of  FIGS. 1 and 14 A in a pre-use operative orientation, to  FIGS. 16A and 16B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 17A and 17B , which are sectional illustrations taken along respective section lines and directions XVIIA-XVIIA and XVIIB-XVIIB in  FIGS. 16A and 16B .  
         [0295]     As seen in  FIGS. 15-17B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the rear housing element  10  is joined to the forward housing and actuator element  70  by snap fit engagement of protrusions  126  of rear housing element  10  in the engagement sockets  712  formed in the forward housing and actuator element  70 .  
         [0296]     Selectable driving assembly  30  is retained in its axial position by engagement of inward facing protrusion  130  ( FIG. 4A ) with outwardly facing notch  352  of top engagement arm  322  ( FIG. 7A ) of selectable driving assembly  30 , as shown particularly in the enlarged portion of  FIG. 17A . In this arrangement, spring  20  is in a relatively compressed state and is held in that state by the selectable driving assembly  30 .  
         [0297]     Also seen in the enlarged portion of  FIG. 17A  is that the rearwardmost axial portion  834  of the top engagement arm  832  of the needle guard  80  ( FIGS. 11-13C ) is in a relatively forward position, only partially underlying actuation button  752  of forward housing and actuator element  70  ( FIGS. 8-10C ). Additionally, inward displacement of actuation button  752  is limited by ribs  128  ( FIGS. 2-4C ), thus ensuring that actuation button  752  does not directly engage protrusion  350  of engagement arm  322 . Accordingly, in this orientation of the needle guard  80 , inadvertent pressing of button  752  does not actuate the automatic injection device.  
         [0298]     The pre-filled syringe  50  is retained in a retracted orientation by engagement of flange  502  thereof with notches  347  formed in respective third fingers  338  of each of side-to-side symmetric actuation arms  312  of selectable driving assembly  30  ( FIGS. 5-7C ).  
         [0299]     Needle guard  80  is retained in its axial position, and is prevented from moving forward by engagement of inwardly directed teeth  850  and  852  with the flange  502  of the pre-filled syringe  50 . It is appreciated that in this operative orientation spring  90  is either at rest or in a semi-compressed state.  
         [0300]     Reference is now made to  FIG. 18 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 B in an optional titration operative orientation, to  FIGS. 19A and 19B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 20A and 20B , which are sectional illustrations taken along respective section lines and directions XXA-XXA and XXB-XXB in  FIGS. 19A and 19B .  
         [0301]     In an optional titration step, after the protective needle cover has been removed and while the needle guard  80  points upwards, a user may push rear portion  402  of plunger  40  forwardly as the syringe  50  is retained in place. This forces air bubbles and/or liquid out of the syringe via the needle  60 . At this stage, protrusions  349  formed on third fingers  338  ( FIGS. 5-7C ) engage the defining walls of narrower rear portion  824  of rectangular window  821  ( FIGS. 11-13C ), thus limiting the third fingers  338  from bending outward and therefore flange  502  continues to engage notches  347  thus inhibiting premature movement of syringe  50 . It is appreciated that except for the forward movement of the plunger  40 , the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0302]     Reference is now made to  FIG. 21 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 C in an actuated operative orientation, to  FIGS. 22A and 22B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 23A and 23B  which are sectional illustrations taken along respective section lines and directions XXIIIA-XXIIIA and XXIIIB-XXIIIB in  FIGS. 22A and 22B .  
         [0303]     As seen particularly in the enlarged portion of  FIG. 23A , due to engagement of the needle guard  80  with an injection site on a body, the needle guard  80  is forced to move axially in a rearward direction with respect to the remainder of the automatic injection device, thus compressing spring  90  and causing the rearwardmost axial portion  834  of the top engagement arm  832  of the needle guard  80  ( FIGS. 11-13C ) to assume a relatively rearward position, generally underlying actuation button  752  of forward housing and actuator element  70  ( FIGS. 8-10C ). The rearward motion of the needle guard  80  is limited by engagement of rearwardrnost ends  819  of arms  818  of the needle guard and the forward facing edge of outward facing protrusion  126  rear housing element  10  ( FIG. 23B ).  
         [0304]     In this orientation of the needle guard  80 , pressing of button  752  does actuate the automatic injection device, by causing portion  834  to engage protrusion  350 , thus disengaging notch  352  from protrusion  130  ( FIG. 4A ) and thus disengaging engagement arm  322  from the rear housing element  10  and permitting forward axial movement of the selectable driving assembly  30  under the urging of spring  20 .  
         [0305]     Reference is now made to  FIG. 24 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 D in a needle penetration, pre-drug delivery operative orientation, to  FIGS. 25A and 25B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 26A and 26B , which are sectional illustrations taken along respective section lines and directions XXVIA-XXVIA and XXVIB-XXVIB in  FIGS. 25A and 25B .  
         [0306]      FIGS. 24-26B  illustrate an initial stage in the forward motion of the selectable driving assembly  30  under the urging of spring  20  following user actuation of button  752 . It is seen that the axial forward motion of the selectable driving assembly  30  produces equivalent axial forward motion of the syringe  50 , due to engagement of flange  502  in notches  347  formed in respective third fingers  338  of each of side-to-side symmetric actuation arms  312  of selectable driving assembly  30  ( FIGS. 5-7C ).  
         [0307]     This forward motion results in forward motion of the needle  60  and needle penetration at the injection site as shown. The forward motion of syringe  50  and needle penetration stops as flange  502  reaches protrusions  760  and  762  of forward housing and actuator element  70 . During needle penetration, elastomeric elements  32  and  34  engage forwardly pointed protrusion  142  of side interior surface  140  causing friction therebetween, thus compensating for the force of spring  20  and resulting in damping of the needle movement and absorbance of the shock applied by protrusions  760  and  762  on the flange  502 . The forward motion of the selectable driving assembly  30  causes the outwardly extending protrusion  332  to engage forwardly pointed protrusion  142  of side interior surface  140 , thus bending the first finger  330  inwards. As will be described hereinbelow, drug delivery follows needle penetration.  
         [0308]     Reference is now made to  FIG. 27 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 E in drug delivery operational orientation, to  FIGS. 28A and 28B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 29A and 29B , which are sectional illustrations taken along respective section lines and directions XXIXA-XXIXA and XXIXB-XXIXB in  FIGS. 28A and 28B .  
         [0309]      FIGS. 27-29B  illustrate a further stage in the forward motion of the selectable driving assembly under the urging of spring  20  following user actuation of button  752 . It is seen that the axial forward motion of the selectable driving assembly  30  does not produce equivalent axial forward motion of the syringe  50 , due to engagement of flange  502  of syringe  50  with protrusions  760  and  762  of ribs of the forward housing and actuator element  70  ( FIG. 10A ).  
         [0310]     Continued urging of spring  20  and the selectable driving assembly  30  causes protrusions  349  formed on third fingers  338  ( FIGS. 5-7C ) to disengage the defining walls of narrower rear portion  824  of rectangular window  821 , and bend outward into the space formed by the wider forward portion  822  of the rectangular window ( FIGS. 11-13C ), resulting in disengagement of flange  502  and notches  347  formed in respective third fingers  338  of each of side-to-side symmetric actuation arms  312  of selectable driving assembly  30  ( FIGS. 5-7C ). This allows the inwardly extending protrusion  333  of the bended first finger  330  of the selectable driving assembly  30  to engage intermediate portion  406  of plunger  40 , causing it to continue its forward motion together with a piston  501 , which is threaded thereto.  
         [0311]     Forward motion of piston  501  forces the drug out of syringe  50  through needle  60  into the injection site. During drug delivery, the forward motion of the piston  501  is governed by friction between elastomeric elements  32  and  34  and forwardly pointed protrusions  142  of side interior surface  140 . The amount of friction may be selected by appropriately shaping the forwardly pointed protrusion and the elastomeric elements  32  and  34 .  
         [0312]     The forwardly pointed shape of the protrusions, causes a reduction in friction as selectable driving assembly  30  advances, which compensates for the reduction in the force applied by spring  20  as it extends. Friction between the protrusion and elastomeric elements  32  and  34  also damps shock resulting from engagement of inwardly extending protrusion  333  with intermediate portion  406  of plunger  40 , which is then transferred to flange  502  of the pre-filled syringe  50 , and may help control the drug injection rate.  
         [0313]     Reference is now made to  FIG. 30 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 F in an immediate post-drug delivery operational orientation, to  FIGS. 31A and 31B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 32A and 32B , which are sectional illustrations taken along respective section lines and directions XXXIIA-XXXIIA and XXXIIB-XXXIIB in  FIGS. 31A and 31B .  
         [0314]     Prior to this stage, forward motion of piston  501  in the syringe continued until the piston cannot move forward any more, thus terminating drug delivery. Additionally, outwardly extending protrusions  332  of first fingers  330  no longer engage the forwardly pointed protrusions, and are now supported by the internal surfaces of mounting arms  818 .  
         [0315]     Reference is now made to  FIG. 33 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 G in its operation orientation as it is being disengaged from an injection site, to  FIGS. 34A and 34B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 35A and 35B  which are sectional illustrations taken along respective section lines and directions XXXVA-XXXVA and XXXVB-XXXVB in  FIGS. 34A and 34B .  
         [0316]     At this stage, the automatic injection device is being removed from the injection site and the needle guard  80  is moving axially forward under the urging of spring  90 , so that the exposed portion of the needle  60  is protected by the needle guard  80 . Subsequent to the initial forward movement of the needle guard  80  forward, the first fingers  330  of each of side-to-side symmetric actuation arms  312  of the selectable driving assembly  30  are released and bend outwards to their initial position, thus disengaging from the plunger  40  and engaging the rearwardmost ends  819  of arms  818  of the needle guard  80 .  
         [0317]     At this stage the spring  20  applies more force than does spring  90  and thus pushes the needle guard  80  further forward. It is therefore appreciated that even if spring  90  were to be replaced by a shorter spring, for example a short plastic spring integrated with either forward housing and actuator element  70  or needle guard  80 , spring  20  would guarantee that needle guard  80  would be fully deployed, such that the auto injection device would be maintained in a protected position.  
         [0318]     Reference is now made to  FIG. 36 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 H in a needle protected operational orientation, to  FIGS. 37A and 37B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 38A and 38B  which are sectional illustrations taken along respective section lines and directions XXXVIIIA-XXXVIIIA and XXXVIIIB-XXXVIIIB in  FIGS. 37A and 37B .  
         [0319]     At this stage, the automatic injection device is fully disengaged from the injection site and the needle guard  80  is fully extended to fully enclose the needle  60 . When the needle guard is fully extended it is locked onto the syringe  50  by engagement of inwardly directed teeth  850  and  852  and flange  502  of the pre-filled syringe  50 , thus inhibiting further movement outwards of the needle guard  80 . During the movement of needle guard  80  and due to force exerted by spring  20 , inwardly extending protruding portions  336  of second fingers  334  snap over flange  502  within the narrower rear portion  824  of rectangular window  821 , thus enabling further locking of the needle guard as described hereinbelow.  
         [0320]     Reference is now made to  FIG. 39 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 1 and 14 I in a needle-guard push back misuse operational orientation, to  FIGS. 40A and 40B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 41A and 41B  which are sectional illustrations taken along respective section lines and directions XLIA-XLIA and XLIB-XLIB in  FIGS. 40A and 40B .  
         [0321]      FIGS. 39-41B  illustrate an important feature of the present invention provided by the locking of inwardly extending protruding portion  336  of second finger  334  of the selectable driving assembly  30  and the flange  502  of the pre-filled syringe  50 . Should the needle guard  80  be pushed rearwardly with respect to the forward housing and actuator element  70 , the rearwardmost ends  819  of arms  818  of the needle guard  80  push against protrusion  332  of the selectable driving assembly  30 . Selectable driving assembly  30  is therefore forced to move rearwardly together with the needle guard.  
         [0322]     Due to engagement of second fingers  334  and flange  502 , the selectable driving assembly  30  forces the needle  60  and syringe to  50  move rearwardly together with selectable driving assembly  30 , so that the needle  60  does not protrude from the needle guard  80 . During this rearward movement, first fingers  330  cannot bend inwards to cause outwardly extending protrusions  332  to disengage from rearwardrnost ends  819  of arms  818 , since the inwardly extending protrusions  333  of first fingers  330  are supported by intermediate portion  406  of the plunger  40 .  
         [0323]     Reference is now made to  FIGS. 42-58C , which illustrate the constituent elements of an automatic injection device constructed and operative in accordance with another preferred embodiment of the present invention.  
         [0324]     As seen with particular clarity in  FIG. 42 , the automatic injection device comprises a plunger  1002  which is partially located within a main housing element  1010  into which is seated a main compression spring  1020 , which provides selectable forward displacement to a selectable driving element  1030 , which selectably engages plunger  1002  and a pre-filled syringe  1050  having a hypodermic needle  1060  which is covered by a needle protection cover  1062 . Pre-filled syringe  1050  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0325]     Plunger  1002  also operatively engages pre-filled syringe  1050  and is selectably operated by selectable driving element  1030  to inject the liquid contents of pre-filled syringe  1050  through hypodermic needle  1060 . The forward portion of main housing element  1010  surrounds and is engaged with a forward housing element  1070 . At the forward end of the interior of forward housing element  1070  there is provided a needle guard element  1080 , which is positioned by a compression spring  1090 .  
         [0326]     Reference is now made to  FIGS. 43A and 43B , which are simplified pictorial illustrations of a preferred main housing element  1010  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 44A and 44B  which are simplified pictorial sectional illustrations of the main housing element  1010  of  FIGS. 43A and 43B , taken along lines XLIVA-XLIVA and XLIVB-XLIVB in  FIG. 43A , to  FIGS. 45A and 45B , which are respective top and side view simplified planar illustrations of the main housing element of  FIGS. 43A-44B  and to  FIGS. 46A, 46B  and  46 C which are sectional illustrations taken along respective section lines and directions XLVIA-XLVIA, XLVIB-XLVIB and XLVIC-XLVIC in  FIGS. 45A and 45B .  
         [0327]     As seen in  FIGS. 43A-46C , the main housing element  1010  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a rearward generally cylindrical portion  1110 , having a nearly circular cross section, which terminates in a back wall  1112 , defining a rearward-facing central opening  1115  communicating with a cylindrical bore  1116 . An interior surface of back wall  1112  defines a spring seat for spring  1020 , while bore  1116  slidably accommodates plunger  1002 . Rearward generally cylindrical portion  1110  is preferably side-to-side symmetric about a longitudinal axis  1120 .  
         [0328]     Rearward generally cylindrical portion  1110  is preferably formed on an interior surface thereof with a pair of generally symmetric axially extending upper interior ribs  1121  and a pair of generally symmetric axially extending lower interior ribs  1122  on each side of the interior surface. Also formed on opposite sides of an interior surface of rearward generally cylindrical portion  1110  are side-to-side symmetric axially extending guiding ribs  1123 . Cantilevered onto rearward generally cylindrical portion  1110  is an actuation button portion  1124  including a forward actuation button defining portion  1125  having a slightly curved finger engagement surface  1126 , defining an actuation button and a selectable syringe engagement portion  1128  having a rearward facing surface  1130  which selectably engages a forward facing surface of pre-filled syringe  1050  for selectably retaining it against forward axial motion. Actuation button portion  1124  is pivotally mounted with respect to the remainder of the main housing element  1010  about a pivot axis, transverse to longitudinal axis  1120 , which lies intermediate portion  1125  and portion  1128 , such that inward displacement of portion  1125  causes portion  1128  to move outwardly.  
         [0329]     Formed onto upper ribs  1121  and lower ribs  1122  are forwardly facing, outwardly extending ribs  1135 . A peripheral outwardly facing guard protrusion  1136  is formed around actuation button portion  1124 . Forwardly of actuation button portion  1124  and of protrusion  1136  there is formed a forwardly facing circular cylindrical portion  1140 .  
         [0330]     Circular cylindrical portion  1140  defines on an interior surface  1150  thereof a peripheral groove  1160 , which is in contact with top and bottom axial grooves  1162 .  
         [0331]     Reference is now made to  FIGS. 47A and 47B , which are simplified pictorial illustrations of a selectable driving element  1030  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 48A and 48B , which are simplified pictorial sectional illustrations of the selectable driving element of  FIGS. 47A and 47B , taken along lines XLVIIIA-XLVIIIA and XLVIIIB-XLVIIIB in  FIG. 47A , to  FIGS. 49A and 49B , which are respective top and side view simplified planar illustrations of the selectable driving element of  FIGS. 47A-48B  and to  FIGS. 50A and 50B , which are sectional illustrations taken along respective section lines and directions LA-LA and LB-LB in  FIGS. 49A and 49B .  
         [0332]     As seen in  FIGS. 47A-50B , the selectable driving element  1030  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  1310 , having an open back and having a pair of side-to-side symmetric actuation arms  1312  which extend forwardly of tubular portion  1310  generally parallel to a longitudinal axis  1320 , which when selectable driving element  1030  is assembled with the main housing element  1010 , is coaxial with longitudinal axis  1120  ( FIGS. 43-46C ). Overlying part of each actuation arm  1312  and extending axially rearwardly thereof along an outer surface of generally tubular portion  1310  is a guiding slot  1324 . Guiding slots  1324  cooperate with ribs  1123  formed on main housing element  1010  for guiding axial motion of the selectable driving element  1030  with respect to the main housing element  1010 .  
         [0333]     Each of actuation arms  1312  terminates in a forwardly facing end surface  1332  having oppositely directed transversely extending protrusions  1334  and defines a shoulder along the length of each arm  1312 .  
         [0334]     The selectable tubular portion  1310  defines a forward wall  1340  having an aperture  1342  for selectable slidable engagement with plunger  1002 . Forward of wall is formed a pair of side-to-side symmetric forward-facing tabs  1344 , each defining a forward shoulder surface  1346 . A rear facing surface of forward wall  1340  defines a spring seat for spring  1020 .  
         [0335]     Plunger  1002 , as seen in  FIG. 42  is a generally circularly symmetric element, which is preferably formed in an overall ribbed configuration, as shown. Plunger  1002  includes a rear wall portion  1402 . Forwardly of rear wall portion  1402  by approximately two thirds of the length of plunger  1002 , there are provided a pair of side-to-side symmetric, sideways extending protrusions  1404 . At a forward end of plunger  1002  there is provided a peripheral protrusion  1406  forward of which is provided a threaded end  1408 . Plunger  1002  is arranged along a longitudinal axis  1420 , which when the automatic injector device is assembled, is coaxial with longitudinal axes  1120  ( FIGS. 43-46C ), and  1320  ( FIGS. 47-50C ).  
         [0336]     As seen in  FIG. 42 , pre-filled syringe includes a rear flange  1502  which engages forwardly facing end surface  1332  formed in each of side-to-side symmetric actuation arms  1312  of selectable driver element  1030  ( FIGS. 47-50C ).  
         [0337]     Reference is now made to  FIGS. 51A and 51B , which are simplified pictorial illustrations of a forward housing element  1070  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 52A and 52B , which are simplified pictorial sectional illustrations of the forward housing element of  FIG. 51A and 51B , taken along lines LIIA-LIIA and LIIB-LIIB in  FIG. 51A , to  FIGS. 53A and 53B , which are respective top and side view simplified planar illustrations of the forward housing element of  FIGS. 51A-52B  and to  FIGS. 54A and 54B  which are sectional illustrations taken along respective section lines and directions LIVA-LIVA and LIVB-LIVB in  FIGS. 53A and 53B .  
         [0338]     As seen in  FIGS. 51A-54B , the forward housing element  1070  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally circular cylindrical truncated conical configuration arranged along a longitudinal axis  1720 , which when the automatic injector device is assembled, is coaxial with longitudinal axes  1120  ( FIGS. 43-46C ),  1320  ( FIGS. 47-50C ) and  1420  ( FIG. 1 ).  
         [0339]     Forward housing element  1070  includes a generally tubular forward portion  1710 , having an open front and having formed rearward thereof a top axially extending arm  1724  and a bottom axially extending arm  1725 . Each of arms  1724  and  1725  is formed with a pair of inwardly facing protrusions, respectively designated by reference numerals  1726  and  1727  and with a pair of outwardly facing protrusions, respectively designated by reference numerals  1728  and  1729 . Outwardly facing protrusions  1728  extend rearwardly only partially along the length of arm  1724 , while outwardly facing protrusions  1727  extend rearwardly along substantially the entire length of arm  1725 . Inwardly facing protrusions  1726  and  1727  are adapted to stop the forward motion of flange  1502  of pre-filled syringe  1050  following actuation as described hereinbelow with reference to  FIGS. 66-68A .  
         [0340]     A pair of teeth  1730  are formed on top of axially extending arms  1724 , which are operative to prevent premature activation of the automatic injection device as described hereinbelow with reference to  FIGS. 63-65B .  
         [0341]     A pair of side-to-side symmetric partial enclosures  1731  are formed rearwardly of forward portion  1710 , having a generally C-shaped cross section, in a plane perpendicular to longitudinal axis  1720 . Interior facing surfaces of enclosures  1731  together with arms  1724  and  1725  and protrusions  1726  and  1727  guide axial sliding motion of syringe  1050  relative to the main housing element  1010  and to forward housing element  1070 . Partially surrounded by each partial enclosure  1731  is an inwardly facing cantilevered engagement element  1732  terminated in a bifurcated tooth element  1733  having an inwardly extending tooth  1734  and a forwardly axially extending tooth  1736 .  
         [0342]     Forward portion  1710  has an interior facing cylindrical surface  1740  having formed thereon four pairs of inwardly facing, axially extending protrusions  1746 . Also formed interior of interior facing cylindrical surface  1740  are a plurality of spring seat defining portions  1750 , each of which defines a rearwardly facing shoulder  1752 . Spring  1090  sits on shoulders  1752  of spring seat defining portions  1750 ..  
         [0343]     Forward portion  1710  has an outer facing cylindrical surface  1760  having formed thereon a peripheral protrusion  1770  connected with top and bottom axial protrusions  1772 . Generally opposite peripheral protrusion  1770 , there are formed on inner facing cylindrical surface a pair of inwardly facing protrusions  1774 .  
         [0344]     Reference is now made to  FIGS. 55A and 55B  which are simplified pictorial illustrations of the needle guard element  1080  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 56A and 56B , which are simplified pictorial sectional illustrations of the needle guard element of  FIG. 55A and 55B , taken along lines LVIA-LVIA and LVIB-LVIB in  FIG. 55A , to  FIGS. 57A and 57B , which are respective top and side view simplified planar illustrations of the needle guard element of  FIGS. 55A and 55B  and to  FIGS. 58A, 58B  and  58 C, which are sectional illustrations taken along respective section lines and directions LVIIIA-LVIIIA, LVIIIB-LVIIIB and LVIIIC-LVIIIC in  FIGS. 57A and 57B .  
         [0345]     As seen in  FIGS. 55A-58C , the needle guard element  1080  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  1810 , having a forward wall  1811  defining forward facing body engaging surface  1812  including a pair of concentric circumferential forward facing rings  1814  and  1816 , and a rearward facing spring seat defining surface  1817 , which defines a spring seat for spring  1090 .  
         [0346]     Needle guard element  1080  has a pair of side-to-side symmetric mounting arms  1818  having rearwardmost ends  1819 , arranged symmetrically about a longitudinal axis  1820 . Arms  1818  extend along and rearwardly of tubular portion  1810  parallel to longitudinal axis  1820 , which when the automatic injector device is assembled, is coaxial with longitudinal axes  1120  ( FIGS. 43-46C ),  1320  ( FIGS. 47-50C ),  1420  ( FIG. 42 ) and  1720  ( FIGS. 51-54C ).  
         [0347]     Formed interiorly of each of mounting arms  1818  are a pair of spaced mutually facing circumferentially directed teeth  1822 , each pair of which is arranged for engagement with a corresponding axially extending tooth  1736  when the automatic injection device is in a pre-use operative orientation, as described hereinbelow with reference to  FIGS. 60-62B .  
         [0348]     A top engagement arm  1832  also extends rearwardly of tubular portion  1810  and includes a rearwardmost axial portion  1834 , an inclined intermediate portion  1836 , an axial intermediate portion  1838  and an inclined mounting portion  1840 , which extends from a top portion  1842 . Formed at an extreme rearward end of top engagement arm  1832  are a pair of oppositely circumferentially directed protrusions  1844 .  
         [0349]     A bottom engagement arm  1852  also extends rearwardly of tubular portion  1810  and includes an inclined portion  1856 , an axial intermediate portion  1858  and an inclined mounting portion  1860 , which extends from a bottom portion  1862 .  
         [0350]     Reference is now made to  FIGS. 59A, 59B ,  59 C,  59 D and  59 E, which are simplified pictorial illustration of various stages of typical use of the automatic injection device of  FIG. 42 .  
         [0351]     As seen in  FIG. 59A , the automatic injection device of  FIG. 42  is stored prior to use, as indicated by reference numeral  1900 , in a pre-use operative orientation, described hereinbelow with reference to  FIGS. 60-62B . While the automatic injection device is stored, it is preferably covered by needle protection cover  1062 .  
         [0352]     A user enables actuation of the automatic injection device by pushing it against an injection site, as indicated by reference numeral  1902  shown in  FIG. 59B  and as described hereinbelow with reference to  FIGS. 63-65B . Subsequently, in response to the user depressing actuation button  1125  ( FIGS. 43A-46C ), needle penetration takes place at the injection site, as indicated by reference numeral  1904  shown in  FIG. 59C . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 66-68B .  
         [0353]     As seen in  FIG. 59D , immediately following needle penetration, drug delivery takes place, as indicated by reference numeral  1906 . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 69-71B .  
         [0354]     As seen in  FIG. 59E , the automatic injection device is then manually disengaged from the injection site, as indicated by reference numeral  1908 , during which time the needle guard  1080  is automatically deployed. Immediately upon disengagement, the needle is automatically protected by the needle guard element  1080 . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 72-74B .  
         [0355]     Reference is now made to  FIG. 60 , which is a simplified assembled view illustration of the automatic injection device of  FIGS. 42 and 59 A in a pre-use operative orientation, to  FIGS. 61A and 61B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 60  and to  FIGS. 62A and 62B  which are sectional illustrations taken along respective section lines and directions LXIIA-LXIIA and LXIIB-LXIIB in  FIGS. 61A and 61B .  
         [0356]     As seen in  FIGS. 60-62B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the main housing portion  1010  is joined to the forward housing portion  1070  by engagement of peripheral protrusion  1770  with peripheral groove  1160 , and by engagement of top and bottom axial protrusions  1772  with top and bottom axial grooves  1162  of main housing  1010  ( FIGS. 43A-46C  and  51 A- 54 B).  
         [0357]     Selectable driving element  1030  is retained in a rearward axial position by engagement of forwardly facing surface  1332  ( FIGS. 47-50B ) with a rearward facing surface of flange  1502  of pre-filled syringe  1050 . Pre-filled syringe  1050  is, in turn, retained in its retracted axial position by engagement of a forward facing surface of flange  1502  by rearward facing surface  1130  of selectable syringe engagement portion  1128  of actuation button portion  1124  ( FIGS. 43A-46C ). Pre-filled syringe  1050  is also retained in its retracted axial position by engagement of inwardly extending teeth  1734  of bifurcated tooth elements  1733  of inwardly facing cantilevered engagement elements  1732  of forward housing element  1070  with a forward facing tapered peripheral surface of the pre-filled syringe  1050 .  
         [0358]     Inwardly facing cantilevered engagement elements  1732  cannot bend outwards to disengage inwardly extending teeth  1734  from pre-filled syringe  1050  due to engagement of forwardly axially extending teeth  1736  with respective pairs of spaced mutually facing circumferentially directed teeth  1822  formed in arms  1818  of needle guard element  1080 . The engagement of forwardly axially extending teeth  1736  with pairs of spaced mutually facing circumferentially directed teeth  1822  formed in arms  1818  of needle guard element  1080  also retains the needle guard element  1080  in its axial position and prevents it from moving outward.  
         [0359]     In the pre-use orientation shown in  FIGS. 60-62B , the actuation button is retained against inadvertent actuation by the needle guard element  1080  when in its relative forward orientation, as it is maintained in the storage orientation of the automatic injection device. When needle guard element  1080  is in its relative forward orientation, the pair of oppositely circumferentially directed protrusions  1844  of rearwardmost axial portion  1834  of top engagement arm  1832  is retained against radially inward displacement by pair of teeth  1730  of forward housing element  1070  and thus does not allow axial forward movement of selectable syringe engagement portion  1128  and of syringe  1050 .  
         [0360]     Reference is now made to  FIG. 63 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 42 and 59 B in an actuatable operative orientation, to  FIGS. 64A and 64B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 65A and 65B  which are sectional illustrations taken along respective section lines and directions LXVA-LXVA and LXVB-LXVB in  FIGS. 64A and 64B .  
         [0361]     As seen particularly in the enlarged portion of  FIG. 65A , due to engagement of the needle guard element  1080  with an injection site on a body following the removal of needle protection cover  1062 , the needle guard element  1080  is forced to move axially in a rearward direction with respect to the remainder of the automatic injection device, thus compressing spring  1090  and causing the rearwardmost axial portion  1834  of the top engagement arm  1832  of the needle guard element  1080  to assume a relatively rearward position, so that the pair of oppositely circumferentially directed protrusions  1844  does not overlie teeth  1730  of forward housing element  1070 . This permits inward pressing on the actuation button to cause disengagement of the forward facing surface of flange  1502  from rearward facing surface  1130  of selectable syringe engagement portion  1128  of actuation button portion  1124  ( FIGS. 43A-46C ), due to outward movement of surface  1130 .  
         [0362]     Disengagement of the forward facing surface of flange  1502  from rearward facing surface  1130  immediately releases the syringe  1050  to move forward under the urging of selectable driving element  1030 , due to engagement of flange  1502  with forwardly facing surface  1332  of selectable driving element  1030 . At the same time, rearward movement of the needle guard element  1080  causes the disengagement of the pairs of spaced mutually facing circumferentially directed teeth  1822  formed in arms  1818  of needle guard element  1080  from forwardly axially extending teeth  1736  of inwardly facing cantilevered engagement elements  1732 , thus allowing outward bending of inwardly facing cantilevered engagement elements  1732 .  
         [0363]     Reference is now made to  FIG. 66 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 42 and 59 C in an actuated needle penetration, pre-drug delivery operative orientation, to  FIGS. 67A and 67B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 66  and to  FIGS. 68A and 68B  which are sectional illustrations taken along respective section lines and directions LXVIIIA-LXVIIIA and LXVIIIB-LXVIIIB in  FIGS. 67A and 67B .  FIGS. 66-68B  illustrate an initial stage in the forward motion of the selectable driving element  1030  under the urging of spring  1020  following user actuation of portion  1125  of actuation button portion  1124 . It is understood that the axial forward motion of the selectable driving element  1030  produces equivalent axial forward motion of the syringe  1050 , due to engagement of flange  1502  by forwardly facing surface  1332  of selectable driving element  1030 .  
         [0364]     As seen particularly in  FIGS. 68A and 68B , as the syringe  1050  approaches its forward needle penetration axial position determined by flange  1502  reaching inwardly facing teeth  1726  and  1727  of forward housing  1070 , oppositely directed transversely extending protrusions  1334  at the forward facing surfaces  1332  of the engagement arms  1312  are deflected outwardly by outwardly extending ribs  1135 , thus enabling further forward motion of plunger  1002  under the urging of spring  1020 .  
         [0365]     Forward movement of pre-filled syringe  1050  forces inwardly facing cantilevered engagement elements  1732  to bend outwards and retain their bent state, thus allowing deployment of the needle guard element  1080  upon removal from the injection site as will be described hereinbelow with reference to  FIGS. 72-74B .  
         [0366]     The forward movement of pre-filled syringe  1050  also ensures that selectable syringe engagement portion  1128  of actuation button portion  1124  is retained in a raised position by engagement therewith of flange  1502 , which is located radially inwardly thereof. The raised positioning of selectable syringe engagement portion  1128  maintains the downward displacement of forward actuation button defining portion  1125  of actuation button portion  1124 , thus maintaining engagement thereof with rearwardmost axial portion  1834  of the top engagement arm  1832  of needle guard element  1080 . The engagement of rearwardmost axial portion  1834  and forward actuation button defining portion  1125  ensures non-interfered deployment of the needle guard element  1080  upon removal of the automatic injection device from the injection site.  
         [0367]     Reference is now made to  FIG. 69  which is a simplified pictorial illustration of the automatic injection device of  FIGS. 42 and 59 D in a post-drug delivery operative orientation, to  FIGS. 70A and 70B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 69  and to  FIGS. 71A and 71B  which are sectional illustrations taken along respective section lines and directions LXXIA-LXXIA and LXXIB-LXXIB in  FIGS. 70A and 70B .  
         [0368]      FIGS. 69-71B  illustrate a further stage in the forward motion of the selectable driving element  1030  under the urging of spring  1020  following user actuation of forward actuation button portion  1125 . As noted above, further axial forward motion of the selectable driving element  1030  does not produce equivalent axial forward motion of the syringe  1050 . Continued urging of spring  1020  and consequent forward axial motion of the selectable driving element  1030  causes engagement of forward wall  1340  of selectable driving member  1030  with corresponding protrusions  1404  located along the length of plunger  1002  thus forcing plunger  1002  forward along the interior of pre-filled syringe  1050  which results in drug delivery. Forward axial motion of selectable driving member  1030  and plunger  1002  is stopped when a piston attached to plunger  1002  engages the forward end of syringe  1050  and is prevented from moving further.  
         [0369]     Reference is now made to  FIG. 72  which is a simplified pictorial illustration of the automatic injection device of  FIGS. 41 and 59 E in post injection site disengagement operational orientation, to  FIGS. 73A and 73B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 72  and to  FIGS. 74A and 74B  which are sectional illustrations taken along respective section lines and directions LXXIVA-LXXIVA and LXXIVB-LXXIVB in  FIGS. 73A and 73B .  
         [0370]     At this stage, the automatic injection device has been removed from the injection site and the needle guard  1080  has moved axially forward under the urging of spring  1090 , so that the exposed portion of the needle  1060  is protected by the needle guard  1080 . Due to the forward movement of the needle guard  1080 , protrusion  1774  of the forward housing element  1070  engages axial intermediate portions  1838  and  1858  on the needle guard element  1080 , thus locking the needle guard  1080  against retraction and further forward movement.  
         [0371]     In accordance with an embodiment of the present invention, all or part of any or all of the housing element  1010  and forward housing element  1070  may be transparent, to enable the contents of the syringe  1050  to be viewed by a user from outside the automatic injection device.  
         [0372]     In an optional titration step, after the protective needle cover  1062  has been removed and while the needle guard  1080  points upwards a user may push rear wall portion  1402  of plunger  1040  forwardly as the syringe  1050  is retained in place. This forces air bubbles and/or liquid out of the syringe via the needle  1060 . It is appreciated that except for the forward movement of the plunger  1040 , the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0373]     Reference is now made to  FIGS. 75-90B , which illustrate automatic injection device constructed and operative in accordance with yet another preferred embodiment of the present invention.  
         [0374]     As seen with particular clarity in  FIG. 75 , the automatic injection device comprises a plunger  2002  which is partially located within a main housing element  2010  into which is seated a main compression spring  2020 , which provides selectable forward displacement to a pre-filled syringe  2050  having a hypodermic needle  2060  which is covered by a needle protection cover  2062 . Pre-filled syringe  2050  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0375]     Plunger  2002  also operatively engages pre-filled syringe  2050  and is selectably operable to inject liquid contents of pre-filled syringe  2050  through hypodermic needle  2060 .  
         [0376]     The forward portion of main housing element  2010  surrounds and is engaged with a forward housing element  2070 . At the forward end of the interior of forward housing element  2070  there is provided a needle guard element  2080 , which is positioned by a compression spring  2090 .  
         [0377]     Reference is now made to  FIGS. 43A and 43B , which are simplified pictorial illustrations of a preferred main housing element  1010  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 44A and 44B  which are simplified pictorial sectional illustrations of the main housing element  1010  of  FIGS. 43A and 43B , taken along lines XLIVA-XLIVA and XLIVB-XLIVB in  FIG. 43A , to  FIGS. 45A and 45B , which are respective top and side view simplified planar illustrations of the main housing element of  FIGS. 43A-44B  and to  FIGS. 46A, 46B  and  46 C which are sectional illustrations taken along respective section lines and directions XLVIA-XLVIA, XLVIB-XLVIB and XLVIC-XLVIC in  FIGS. 45A and 45B .  
         [0378]     Main housing element  2010  is similar to main housing element  1010  described hereinabove with reference to  FIGS. 43A-46C , except in the following respects:  
         [0379]     The main housing element  2010  is substantially shorter than main housing element  1010  and does not include various internal structural portions which are required in the embodiment of  FIGS. 42-58C  but are not required in the embodiment of  FIGS. 75-90B .  
         [0380]     The main housing element  2010  is formed at a rearward end thereof with side-to-side symmetric outwardly extending finger-engageable retainers  2091 .  
         [0381]     Plunger  2002 , as seen in  FIG. 75  is a generally circularly symmetric element, which is preferably formed in an overall ribbed configuration, as shown. Plunger  2002  includes a rear wall portion  2402 . At a forward end of plunger  2002  there is provided a peripheral protrusion  2406  forward of which is provided a threaded end  2408 . Plunger  2002  is arranged along a longitudinal axis  2420 , which when the automatic injector device is assembled, is coaxial with longitudinal axis  1120  ( FIGS. 43-46C ). As seen in  FIG. 75 , pre-filled syringe  2050  includes a rear flange  2502  which is engaged by a forward end of main spring  2020 .  
         [0382]     Reference is now made to  FIGS. 51A and 51B , which are simplified pictorial illustrations of a forward housing element  1070  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 52A and 52B , which are simplified pictorial sectional illustrations of the forward housing element of  FIG. 51A and 51B , taken along lines LIIA-LIIA and LIIB-LIIB in  FIGS. 51A , to  FIGS. 53A and 53B , which are respective top and side view simplified planar illustrations of the forward housing element of  FIGS. 51A-52B  and to  FIGS. 54A and 54B  which are sectional illustrations taken along respective section lines and directions LIVA-LIVA and LIVB-LIVB in  FIGS. 53A and 53B .  
         [0383]     Forward housing element  2070  is identical to forward housing element  1070  described hereinabove with reference to  FIGS. 51A-54B .  
         [0384]     Reference is now made to  FIGS. 55A and 55B  which are simplified pictorial illustrations of the needle guard element  1080  which forms part of the automatic injection device of  FIG. 42 , to  FIGS. 56A and 56B , which are simplified pictorial sectional illustrations of the needle guard element of  FIG. 55A and 55B , taken along lines LVIA-LVIA and LVIB-LVIB in  FIG. 55A , to  FIGS. 57A and 57B , which are respective top and side view simplified planar illustrations of the needle guard element of  FIGS. 55A and 55B  and to  FIGS. 58A, 58B  and  58 C, which are sectional illustrations taken along respective section lines and directions LVIIIA-LVIIIA, LVIIIB-LVIIIB and LVIIIC-LVIIIC in  FIGS. 57A and 57B .  
         [0385]     Needle guard element  2080  is identical to needle guard element  1080  described hereinabove with reference to  FIGS. 55A-58C .  
         [0386]     Reference is now made to  FIG. 76 , which is a simplified assembled view illustration of the automatic injection device of  FIG. 75  in a pre-use operative orientation, to  FIGS. 77A and 77B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 76  and to  FIGS. 78A and 78B  which are sectional illustrations taken along respective section lines and directions LXXVIIIA-LXXVIIIA and LXXVIIIB-LXXVIIIB in  FIGS. 77A and 77B .  
         [0387]     As seen in  FIGS. 76-78B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the main housing portion  2010  is joined to the forward housing portion  2070  by engagement of peripheral protrusion  2770  with peripheral groove  2160 , and by engagement of top and bottom axial protrusions formed in forward housing element  2070  with top and bottom axial grooves formed in main housing element  2010 .  
         [0388]     Pre-filled syringe  2050  is retained in its retracted axial position by engagement of a forward facing surface of flange  2502  by a rearward facing surface  2130  of a selectable syringe engagement portion  2128  of an actuation button portion  2124 . Pre-filled syringe  2050  is also retained in its retracted axial position by engagement of inwardly extending teeth  2734  of bifurcated tooth elements  2732  of inwardly facing cantilevered engagement elements  2730  of forward housing element  2070  with a forward facing tapered peripheral surface of the pre-filled syringe  2050 .  
         [0389]     Inwardly facing cantilevered engagement elements  2730  cannot bend outwards to disengage inwardly extending teeth  2734  from pre-filled syringe  2050  due to engagement of forwardly axially extending teeth  2736  with pairs of spaced mutually facing circumferentially directed teeth  2822  formed in arms  2818  of needle guard element  2080 . The engagement of forwardly axially extending teeth  2736  with pairs of spaced mutually facing circumferentially directed teeth  2822  formed in arms  2818  of needle guard element  2080  also retains the needle guard element  2080  in its axial position and prevents it from moving outward.  
         [0390]     In the pre-use orientation shown in  FIGS. 76-78B , the actuation button is retained against inadvertent actuation by the needle guard element  2080  when in its relative forward orientation, as it is maintained in the storage orientation of the automatic injection device. When needle guard element  2080  is in its relative forward orientation, the pair of oppositely circumferentially directed protrusions  2844  of rearwardmost axial portion  2834  of top engagement arm  2832  is retained against radially inward displacement by pair of teeth  2730  of forward housing element  2070  and thus does not allow axial forward movement of selectable syringe engagement portion  2128  and of syringe  2050 .  
         [0391]     Reference is now made to  FIG. 79 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in an actuatable operative orientation, to  FIGS. 80A and 80B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 81A and 81B  which are sectional illustrations taken along respective section lines and directions LXXXIA-LXXXIA and LXXXIB-LXXXIB in  FIGS. 80A and 80B .  
         [0392]     As seen particularly in the enlarged portion of  FIG. 81A , due to engagement of the needle guard element  2080  with an injection site on a body following the removal of the needle protection cover, the needle guard element  2080  is forced to move axially in a rearward direction with respect to the remainder of the automatic injection device, thus compressing spring  2090  and causing the rearwardmost axial portion  2834  of the top engagement arm  2832  of the needle guard element  2080  to assume a relatively rearward position, so that the pair of oppositely circumferentially directed protrusions  2844  does not overlie teeth  2730  of forward housing element  2070 . This permits inward pressing on the actuation button defining portion  2125  to cause disengagement of the forward facing surface of flange  2502  from rearward facing surface  2130  of selectable syringe engagement portion  2128  of actuation button portion  2124 , due to outward movement of surface  2130 .  
         [0393]     Disengagement of the forward facing surface of flange  2502  from rearward facing surface  2130  immediately releases the syringe  2050  to move forward under the urging of main spring  2020 . At the same time, rearward movement of the needle guard element  2080  causes the disengagement of the pairs of spaced mutually facing circumferentially directed teeth  2822  formed in arms  2818  of needle guard element  2080  from forwardly axially extending teeth  2736  of inwardly facing cantilevered engagement elements  2730 , thus allowing outward bending of inwardly facing cantilevered engagement elements  2730 .  
         [0394]     Reference is now made to  FIG. 82 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in an actuated needle penetration, pre-drug delivery operative orientation, to  FIGS. 83A and 83B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 82  and to  FIGS. 84A and 84B  which are sectional illustrations taken along respective section lines and directions LXXXIVA-LXXXIVA and LXXXIVB-LXXXIVB in  FIGS. 83A and 83B .  
         [0395]      FIGS. 82-84B  illustrate a final stage in the forward motion of the syringe  2050  under the urging of spring  2020  following user actuation of button defining portion  2125  of button portion  2124 .  
         [0396]     As seen particularly in  FIG. 84A , as the syringe  2050  approaches its forward, needle penetration axial position determined by flange  2502  reaching inwardly facing teeth  2726  and  2727  of forward housing  2070 , the user pushes plunger  2002 , thus enabling injection of fluid contained in syringe  2050 .  
         [0397]     Forward movement of pre-filled syringe  2050  forces inwardly facing cantilevered engagement elements  2730  to bend outwards and retain their bent state, thus allowing deployment of the needle guard element  2080  upon removal from the injection site as will be described hereinbelow with reference to  FIGS. 88-90B .  
         [0398]     The forward movement of pre-filled syringe  2050  also ensures that selectable syringe engagement portion  2128  of actuation button portion  2124  is retained in a raised position by engagement therewith of flange  2502 , which is located radially inwardly thereof. The raised positioning of selectable syringe engagement portion  2128  maintains the downward displacement of forward actuation button defining portion  2125  of actuation button portion  2124 , thus maintaining engagement thereof with rearwardmost axial portion  2834  of the top engagement arm  2832  of needle guard element  2080 . The engagement of rearwardmost axial portion  2834  and forward actuation button defining portion  2125  ensures non-interfered deployment of the needle guard element  2080  upon removal of the automatic injection device from the injection site.  
         [0399]     Reference is now made to  FIG. 85  which is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in a post-drug delivery operative orientation, to  FIGS. 86A and 86B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 85  and to  FIGS. 87A and 87B  which are sectional illustrations taken along respective section lines and directions LXXXVIIA-LXXXVIIA and LXXXVIIB-LXXXVIIB in  FIGS. 86A and 86B .  
         [0400]      FIGS. 85-87B  illustrate a further stage following user actuation of forward actuation button portion  2125 . The user continues to push plunger  2002  which results in drug delivery. Forward axial motion of plunger  2002  is stopped when a piston attached to plunger  2002  engages the forward end of syringe  2050  and is prevented from moving further.  
         [0401]     Reference is now made to  FIG. 88  which is a simplified pictorial illustration of the automatic injection device of  FIG. 75  in post injection site disengagement operational orientation, to  FIGS. 89A and 89B  which are respective top and side view simplified planar illustrations of the automatic injection device of  FIG. 75  and to  FIGS. 90A and 90B  which are sectional illustrations taken along respective section lines and directions XCA-XCA and XCB-XCB in  FIGS. 89A and 89B .  
         [0402]     At this stage, the automatic injection device has been removed from the injection site and the needle guard  2080  has moved axially forward under the urging of spring  2090 , so that the exposed portion of the needle  2060  is protected by the needle guard  2080 . Due to the forward movement of the needle guard  2080 , protrusions  2774  of the forward housing element  2070  engage sockets  2838  and  2858  on the needle guard element  2080 , thus locking the needle guard  2080  against retraction and further forward movement Reference is now made to  FIGS. 91-103C , which illustrate the constituent elements of another automatic injection device constructed and operative in accordance with another preferred embodiment of the present invention.  
         [0403]     As seen with particular clarity in  FIG. 91 , the automatic injection device comprises a rear housing element  4010  in which is seated a main compression spring  4020 , which provides selectable forward displacement to a selectable driving assembly  4030 , which includes a selectable driving element  4031  and a pair of elastomeric motion damping elements  4032  and  4034 , and selectably engages a plunger  4040  and a pre-filled syringe  4050  having a hypodermic needle  4060  which is covered by a needle protection cover  4062 . Pre-filled syringe  4050  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0404]     Plunger  4040  also operatively engages pre-filled syringe  4050  and is selectably operated by selectable driving assembly  4030  to inject the liquid contents of pre-filled syringe  4050  through hypodermic needle  4060 .  
         [0405]     The forward portion of rear housing element  4010  as well as spring  4020 , selectable driving assembly  4030 , plunger  4040  and pre-filled syringe  4050  are located within a forward housing and actuator element  4070 . At the forward end of the interior of forward housing and actuator element  4070  there is provided a needle guard element  4080 , which is positioned by a compression spring  4090 .  
         [0406]     Reference is now made to  FIG. 92 , which is a simplified pictorial illustration of a preferred rear housing element  4010  which forms part of the automatic injection device of  FIG. 91 , to  FIGS. 93A and 93B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 94A, 94B  and  94 C, which are sectional illustrations taken along respective section lines and directions XCIVA-XCIVA, XCIVB-XCIVB and XCIVC-XCIVC in  FIGS. 93A and 93B . As seen in  FIGS. 92-94C , the rear housing element  4010  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  4110 , which terminates in a back wall  4112 , defining generally symmetric side-facing tabs  4114  in front of which are generally symmetric side facing recesses  4116 . Tubular portion  4110  is preferably side-to-side symmetric about a longitudinal axis  4120 .  
         [0407]     Tubular portion  4110  is formed with a pair of generally symmetric side recesses  4122  at which corresponding generally elongate engagement shaft portions  4124  extend forwardly parallel to longitudinal axis  4120  each terminating in an outward facing protrusion  4126 . Above each engagement shaft portion  4124  there is provided a further shaft portion  4127 , which extends forwardly of protrusion  4126  and has a somewhat curved cross sectional configuration. Shaft portions  4127  on the two sides of the rear housing element are separated from each other, as shown. A pair of mutually facing ribs  4128  extend from shaft portions  4127  parallel to axis  4120 , defining forward facing shoulders  4129 . As seen particularly in  FIGS. 92 and 94 A, a central inward facing protrusion  4130  is provided at a top interior surface of the rear housing, between and rearward of ribs  4128 .  
         [0408]     A bottom interior surface  4131  of the rear housing element has a generally uniform, slightly concave cross section and includes a plurality of generally radially inwardly directed ribs  4132 , which extend generally parallel to longitudinal axis  4120 . A bottom exterior surface  4134  of the rear housing element, which is the underside of surface  4131 , includes a forward edge  4136  from which a plurality of radially outwardly directed ribs  4138  extend generally parallel to longitudinal axis  4120 .  
         [0409]     Side interior surfaces  4140  of the rear housing element  4010  each define a forwardly pointed protrusion  4142  which is engaged by an outwardly extending protrusion of a first finger of selectable driving assembly  4030  and by elastomeric motion damping elements  4032  and  4034  forming part of selectable driving assembly  4030 , as described hereinbelow. The interior surface of back wall  4112  of the rear housing element  4010  further comprises a rear seat  4160  for the spring  4020 .  
         [0410]     Reference is now made to  FIG. 95 , which is a simplified pictorial illustration of a preferred selectable driving assembly  4030 , which forms part of the automatic injection device of  FIG. 91 , to  FIGS. 96A and 96B , which are respective top and side view simplified planar illustrations of the selectable driving assembly and to  FIGS. 97A, 97B  and  97 C, which are sectional illustrations taken along respective section lines and directions XCVIIA-XCVIIA, XCVIIB-XCVIIB and XCVIIC-XCVIIC in  FIGS. 96A and 96B .  
         [0411]     As seen in  FIGS. 95-97C , the selectable driving element  4031  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  4310 , having an open back and having a pair of side-to-side symmetric actuation arms  4312  which extend forwardly of tubular portion  4310  parallel to a longitudinal axis  4320 , which when selectable driving assembly  4030  is assembled with the rear housing element  4010 , is coaxial with longitudinal axis  4120  ( FIGS. 92-94C ). A top engagement arm  4322  also extends forwardly of tubular portion  4310 . A narrowed tubular neck portion  4324  is formed forwardly of tubular portion  4310 . Elastomeric elements  4032  and  4034 , seated in side recesses  4326  and  4328  in the selectable driving element  4031 , are located symmetrically at the junction of the tubular portion  4310  and the neck portion  4324 .  
         [0412]     Each of actuation arms  4312  has a generally curved cross section and includes a rearwardly facing first finger  4330  terminating in an outwardly extending protrusion  4332  and an inwardly extending protrusion  4333  having a serrated edge  4334  and a second rearwardly extending finger  4338  having formed thereon, adjacent an extreme outward end thereof, an inwardly facing generally triangular tooth  4342  having a forwardly facing inclined surface  4344  and a rearwardly facing engagement surface  4346  extending generally perpendicular to longitudinal axis  4320 . Separated from tooth  4342  by a notch  4347  is an inwardly facing rounded tooth  4348 . Additionally, second finger  4338  has formed thereon top and bottom protrusions  4349 .  
         [0413]     Top engagement arm  4322  terminates in an outwardly facing protrusion  4350  having an inclined forward facing surface  4351 . Rearwardly of protrusion  4350  and separated therefrom by an outwardly facing notch  4352  is an outwardly facing protrusion  4354 , having an inclined outwardly facing surface  4356 . Plunger  4040 , as seen in  FIG. 91  is a generally circularly symmetric element, which is preferably formed in an overall ribbed configuration, as shown. Plunger  4040  includes a rear portion  4402  having a relatively large circular cross section which tapers forwardly to a neck portion  4404 , having a relatively small circular cross section. Neck portion  4404  has serrated edges herein referenced by numeral  4405 . Serrated edges  4405  of plunger  4040  are adapted to engage serrated edge  4334  of inwardly extending protrusion  4333  of first finger  4330 . Forwardly of neck portion  4404  is an intermediate portion  4406 , whose circular cross section is typically the same as that of rear portion  4402 , and a forward portion  4408 , whose circular cross section is typically the same as that of neck portion  4404 . Plunger  4040  terminates at its forward end in a male threaded protrusion  4410  adapted to fit a corresponding female threaded socket formed in a piston described hereinbelow with reference to  FIG. 106A  which is movably located in pre-filled syringe  4050 . Plunger  4040  is preferably symmetrically disposed about a longitudinal axis  4420 , which when assembled together with selectable driving assembly  4030  and rear housing element  4010 , is coaxial with longitudinal axes  4120  ( FIGS. 92-94C ) and  4320  ( FIGS. 95-97C ).  
         [0414]     As seen in  FIG. 91 , pre-filled syringe  4050  includes a rear flange  4502  which engages notches  4347  formed in respective second fingers  4338  of each of side-to-side symmetric actuation arms  4312  of selectable driving assembly  4030  ( FIGS. 95-97C ).  
         [0415]     Reference is now made to  FIG. 98 , which is a simplified pictorial illustration of forward housing and actuator element  4070  which forms part of the automatic injection device of  FIG. 91 , to  FIGS. 99A and 99B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 100A, 100B  and  100 C, which are sectional illustrations taken along respective section lines and directions CA-CA, CB-CB and CC-CC in  FIGS. 99A and 99B .  
         [0416]     As seen in  FIGS. 98-100C , the forward housing and actuator element  4070  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally truncated conical configuration arranged along a longitudinal axis  4720 , which when the automatic injection device is assembled, is coaxial with longitudinal axes  4120  ( FIGS. 92-94C ),  4320  ( FIGS. 95-97C ) and  4420  ( FIG. 91 ). Forward housing and actuator element  4070  includes a generally tubular rear portion  4710 , having an open back and formed with a pair of side-to-side symmetric snap fit engagement sockets  4712  which receive the protrusions  4126  of the rear housing element  4010  during factory assembly of the automatic injection device.  
         [0417]     Forward of tubular rear portion  4710  are formed a pair of top-bottom symmetric windows  4714 , which allow the pre-filled syringe to be viewed, when the automatic injection device is assembled, including during use thereof.  
         [0418]     A pair of outer side surfaces  4716  of forward housing and actuator element  4070  are each formed with ribbed grip regions  4718 . Corresponding inner side surfaces  4721  each define a plurality of longitudinally extending ribs  4722 ,  4724 ,  4726  and  4728  which are used to slidably guide the needle guard  4080  during axial movement thereof as well as inner facing protrusions  4730 , which together with ribs  4722  and  4724  define a forward facing spring seat for spring  4090  ( FIG. 91 ). Inner facing protrusions  4730  are operative to slidably support pre-filled syringe  4050  and to slidably guide actuation arms  4312  of selectable driving assembly  4030 .  
         [0419]     Inner top and bottom surfaces  4732  and  4734  define respective pairs of ribs  4736  and  4738  which are operative to slidably guide the needle guard  4080  during axial movement thereof A cantilevered rearwardly extending actuation lever  4750  extends from a location rearward of top window  4714  and defines, at an extreme rearward top facing surface thereof, an actuation button  4752 .  
         [0420]     As best seen in  FIG. 100A , inner facing protrusions  4730  define at rearward facing portions thereof protrusions  4760  and  4762  which form a stopping point for flange  4502 , thus limiting the forward movement of the pre-filled syringe  4050 .  
         [0421]     Reference is now made to  FIG. 101 , which is a simplified pictorial illustration of a needle guard element  4080  which forms part of the automatic injection device of  FIG. 91 , to  FIGS. 102A and 102B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 103A, 103B  and  103 C, which are sectional illustrations taken along respective section lines and directions CIIIA-CIIIA, CIIIB-CIIIB and CIIIC-CIIIC in  FIGS. 102A and 102B .  
         [0422]     As seen in  FIGS. 101-103C , the needle guard element  4080  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  4810 , having a forward facing body engaging surface  4812  including a pair of concentric ribbed circumferential forward facing rings  4814  and  4816 . The internal surface, located opposite from body engaging surface  4812 , forms a spring-seat for spring  4090 .  
         [0423]     Needle guard element  4080  has a pair of side-to-side symmetric mounting arms  4818  having rearwardmost ends  4819 , arranged symmetrically about a longitudinal axis  4820 . Each of arms  4818  is formed with a rectangular window  4821  having a relatively wider forward portion  4822  and a relatively narrower rear portion  4824 . Arms  4818  extend along and rearwardly of tubular portion  4810  parallel to longitudinal axis  4820 , which when the automatic injection device is assembled, is coaxial with longitudinal axes  4120  ( FIGS. 92-94C ),  4320  ( FIGS. 95-97C ),  4420  ( FIG. 91 ) and  4720  ( FIGS. 98-100C ).  
         [0424]     A top engagement arm  4832  also extends rearwardly of tubular portion  4810  and includes a rearwardmost axial portion  4834 , an inclined intermediate portion  4836 , an axial intermediate portion  4838  and an inclined mounting portion  4840 , which extends from a top mounting arm  4842 , formed with an elongate window  4844 . An equivalent elongate window, also referenced by numeral  4844 , is formed on a bottom mounting arm  4845 . Elongate windows  4844  and top-bottom symmetric windows  4714  of forward housing and actuator element  4070  are positioned in respective parallel locations, such that pre-filled syringe  4050  is visible through the windows.  
         [0425]     Top and bottom engagement portions  4846  and  4848  are each formed with backward inwardly directed teeth, here designated by reference numerals  4850  and  4852  respectively, and with forward inwardly directed teeth, here designated by reference numerals  4854  and  4856  respectively.  
         [0426]     Reference is now made to  FIG. 104 , which is a simplified assembled view illustration of the automatic injection device of  FIG. 91  in a pre-use operative orientation, to  FIGS. 105A and 105B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 106A and 106B , which are sectional illustrations taken along respective section lines and directions CVIA-CVIA and CVIB-CVIB in  FIGS. 105A and 105B .  
         [0427]     As seen in  FIGS. 104-106B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the rear housing element  4010 : is joined to the forward housing and actuator element  4070  by snap fit engagement of protrusions  4126  of rear housing element  4010  in the engagement sockets  4712  formed in the forward housing and actuator element  4070 .  
         [0428]     Selectable driving assembly  4030  is retained in its axial position by engagement of inward facing protrusion  4130  ( FIG. 94A ) with outwardly facing notch  4352  of top engagement arm  4322  ( FIG. 97A ) of selectable driving assembly  4030 . In this arrangement, spring  4020  is in a relatively compressed state and is held in that state by pressure from the selectable driving assembly.  
         [0429]     The rearwardmost axial portion  4834  of the top engagement arm  4832  of the needle guard  4080  ( FIGS. 91-93C ) is in a relatively forward position, only partially underlying actuation button  4752  of forward housing and actuator element  4070  ( FIGS. 98-200C ). Additionally, inward displacement of actuation button  4752  is limited by ribs  4128  ( FIGS. 92-94C ), thus ensuring that actuation button  4752  does not directly engage protrusion  4350  of engagement arm  4322 . Accordingly, in this orientation of the needle guard  4080 , inadvertent pressing of button  4752  does not actuate the automatic injection device.  
         [0430]     The pre-filled syringe  4050  is retained in a retracted orientation by engagement of flange  4502  thereof with notches  4347  formed in respective second fingers  4338  of each of side-to-side symmetric actuation arms  4312  of selectable driving assembly  4030  ( FIGS. 95-97C ).  
         [0431]     Needle guard  4080  is retained in its axial position, and is prevented from moving forward by engagement of forward inwardly directed teeth  4854  and  4856  with the flange  4502  of the pre-filled syringe  4050 . Forward inwardly directed teeth  4854  and  4856  are supported by ribs  4132  formed on surface  4131  and ribs formed on an inner surface of shaft portion  4127  of the rear housing element ( FIGS. 92-94C ) and thus are prevented from bending outward and disengaging from flange  4502 .  
         [0432]     Reference is now made to  FIG. 107 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in an optional titration operative orientation, to  FIGS. 108A and 108B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 109A and 109B , which are sectional illustrations taken along respective section lines and directions CIXA-CIXA and CIXB-CIXB in  FIGS. 108A and 108B .  
         [0433]     In an optional titration step, after the protective needle cover  4062  has been removed and while the needle guard  4080  points upwards a user may push rear portion  4402  of plunger  4040  forwardly as the syringe  4050  is retained in place. This forces air bubbles and/or liquid out of the syringe via the needle  4060 . At this stage, protrusions  4349  formed on second fingers  4338  ( FIGS. 95-97C ) engage the defining walls of narrower rear portion  4824  of rectangular window  4821 , thus limiting the third fingers  4338  from bending outward and therefore flange  4502  continues to engage notches  4347  thus inhibiting premature movement of syringe  4050 . It is appreciated that except for the forward movement of the plunger  4040 , the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0434]     Reference is now made to  FIG. 110 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in an actuated operative orientation, to  FIGS. 111A and 111B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 112A and 112B  which are sectional illustrations taken along respective section lines and directions CXIIA-CXIIA and CXIIB-CXIIB in  FIGS. 111A and 111B .  
         [0435]     As seen particularly in the enlarged portion of  FIG. 112A , due to engagement of the needle guard  4080  with an injection site on a body, the needle guard  4080  is forced to move axially in a rearward direction with respect to the remainder of the automatic injection device, thus compressing spring  4090  and causing the rearwardmost axial portion  4834  of the top engagement arm  4832  of the needle guard  4080  ( FIGS. 101-103C ) to assume a relatively rearward position, generally underlying actuation button  4752  of forward housing and actuator element  4070  ( FIGS. 98-100C ). The rearward motion of the needle guard  4080  is limited by engagement of rearwardmost ends  4819  of arms  4818  of the needle guard and the rear edge of the window formed in front of outward facing protrusion  4126  of rear housing element  4010  ( FIG. 112B ).  
         [0436]     In this orientation of the needle guard  4080 , pressing of button  4752  does actuate the automatic injection device, by causing portion  4834  to engage protrusion  4350 , thus disengaging notch  4352  from protrusion  4130  ( FIG. 94A ) and thus disengaging engagement arm  4322  from the rear housing element  4010  and permitting forward axial movement of the selectable driving assembly  4030  under the urging of spring  4020 .  
         [0437]     Reference is now made to  FIG. 113 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in a needle penetration, pre-drug delivery operative orientation, to  FIGS. 114A and 114B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 115A and 115B , which are sectional illustrations taken along respective section lines and directions CXVA-CXVA and CXVB-CXVB in  FIGS. 114A and 114B .  
         [0438]      FIGS. 113-115B  illustrate an initial stage in the forward motion of the selectable driving assembly  4030  under the urging of spring  4020  following user actuation of button  4752 . Immediately following user actuation of button  4752 , serrated edges  4334  of inwardly extending protrusions  4333  of first fingers  4330  engage serrated edges  4405  of plunger  4040 . The engagement point of serrated edges  4334  on serrated edges  4405  is dependent on the position of plunger  4040 , which in turn is dependent on the possible performance of titration prior to user actuation of the automatic injection device.  
         [0439]     The axial forward motion of the selectable driving assembly  4030  produces equivalent axial forward motion of the syringe  4050 , due to engagement of flange  4502  in notches  4347  formed in respective second fingers  4338  of each of side-to-side symmetric actuation arms  4312  of selectable driving assembly  4030  ( FIGS. 95-97C ).  
         [0440]     This forward motion results in forward motion of the needle  4060  and needle penetration at the injection site as shown. The forward motion of syringe  4050  and needle penetration stops as flange  4502  reaches protrusions  4760  and  4762  of forward housing and actuator element  4070 . The forward motion of the selectable driving assembly  4030  causes the outwardly extending protrusion  4332  to engage forwardly pointed protrusion  4142  of side interior surface  140 , thus bending the first finger  4330  inwards. During needle penetration, elastomeric elements  4032  and  4034  engage forwardly pointed protrusion  4142  causing friction therebetween, thus compensating for the force of spring  4020  and resulting in damping of the needle movement and absorbance of the shock applied by protrusions  4760  and  4762  on the flange  4502 . As will be described hereinbelow, drug delivery follows needle penetration.  
         [0441]     Reference is now made to  FIG. 116 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in drug delivery operational orientation, to  FIGS. 117A and 117B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 118A and 118B , which are sectional illustrations taken along respective section lines and directions CXVIIIA-CXVIIIA and CXVIIIB-CXVIIIB in  FIGS. 117A and 117B .  
         [0442]      FIGS. 116-118B  illustrate a further stage in the forward motion of the selectable driving assembly under the urging of spring  4020  following user actuation of button  4752 . It is seen that the axial forward motion of the selectable driving assembly  4030  does not produce equivalent axial forward motion of the syringe  4050 , due to engagement of flange  4502  of syringe  4050  with protrusions  4760  and  4762  of ribs of the forward housing and actuator element  4070  ( FIG. 100A ).  
         [0443]     Continued urging of spring  4020  and the selectable driving assembly  4030  causes protrusions  4349  formed on second fingers  4338  ( FIGS. 95-97C ) to disengage the defining walls of narrower rear portion  4824  of rectangular window  4821 , and bend outward into the space formed by the wider forward portion  4822  of the rectangular window ( FIGS. 101-103C ), resulting in disengagement of flange  4502  and notches  4347  formed in respective second fingers  4338  of each of side-to-side symmetric actuation arms  4312  of selectable driving assembly  4030  ( FIGS. 95-97C ).  
         [0444]     The disengagement of flange  4502  from notches  4347  and the engagement of serrated edges  4334  of inwardly extending protrusions  4333  and serrated edges  4405  cause plunger  4040  to continue its forward motion together with piston  4501 , which is threaded thereto.  
         [0445]     Forward motion of piston  4501  forces the drug out of syringe  4050  through needle  4060  into the injection site. During drug delivery, the forward motion of the piston  4501  is governed by friction between elastomeric elements  4032  and  4034  and forwardly pointed protrusion  4142  of side interior surface  140 . The amount of friction may be selected by appropriately shaping the forwardly pointed protrusion and the elastomeric elements  4032  and  4034 .  
         [0446]     The forwardly pointed shape of protrusions  4142  causes a reduction in friction as selectable driving assembly  4030  advances, which compensates for the reduction of the force applied by spring  4020  as it extends. Friction between the protrusion and elastomeric elements  4032  and  4034  also damps shock resulting from movement of the selectable driving element  4030  which is transferred by the engagement of serrated edges  4334  of inwardly extending protrusion  4333  and serrated edges  4405  of plunger  4040 , and is then transferred to flange  4502  of the pre-filled syringe  4050 , and may help control the drug injection rate.  
         [0447]     Reference is now made to  FIG. 119 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in an immediate post-drug delivery operational orientation, to  FIGS. 120A and 120B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 121A and 121B , which are sectional illustrations taken along respective section lines and directions CXXIA-CXXIA and CXXIB-CXXIB in  FIGS. 120A and 120B .  
         [0448]     Prior to this stage, forward motion of piston  4501  in the syringe continued until the piston cannot move forward any more, thus terminating drug delivery. Additionally, serrated edges  4334  of inwardly extending protrusions  4333  are maintained in touching engagement with serrated edges  4405  of plunger  4040  by pressure applied from forwardly pointed protrusion  4142 .  
         [0449]     Reference is now made to  FIG. 122 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in a needle protected operational orientation, to  FIGS. 123A and 123B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 124A and 124B  which are sectional illustrations taken along respective section lines and directions CXXIVA-CXXIVA and CXXIVB-CXXIVB in  FIGS. 123A and 123B .  
         [0450]     At this stage, the automatic injection device is fully disengaged from the injection site and the needle guard  4080  is fully extended to fully enclose the needle  4060 , by the force of spring  4090 . When the needle guard is fully extended it is locked onto the syringe  4050  by engagement of backward inwardly directed teeth  4850  and  4852  and flange  4502  of the pre-filled syringe  4050 , thus inhibiting further movement outwards of the needle guard  4080 . In addition, during the forward motion of the needle guard  4080  inwardly directed teeth  4854  and  4856  are released from the support of ribs  4132  formed on surface  4131  and ribs of shaft portions  4127  thus enabling them to bend outwardly and move forward of flange  4502 .  
         [0451]     Reference is now made to  FIG. 125 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 91  in a needle-guard push back misuse operational orientation, to  FIGS. 126A and 126B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 127A and 127B  which are sectional illustrations taken along respective section lines and directions CXXVIIA-CXXVIIA and CXXVIIB-CXXVIIB in  FIGS. 126A and 126B .  
         [0452]      FIGS. 125-127B  illustrate an important feature of the present invention provided by the locking of forward inwardly directed teeth  4854  and  4856  and the flange  4502  of the pre-filled syringe  4050 . Should the needle guard  4080  be pushed rearwardly with respect to the forward housing and actuator element  4070 , the forward inwardly directed teeth  4854  and  4856  push against flange  4502  of syringe  4050 , thus pushing rearwardly plunger  4040  together with syringe  4050 .  
         [0453]     Rearward motion of plunger  4040  forces selectable driving assembly  4030  to move rearwardly together with the needle guard, as serrated edges  4334  of inwardly extending protrusions  4333  still engage serrated edges  4405  of neck portion  4404  of plunger  4040 . As syringe  4050  and selectable driving assembly  4030  move rearwardly together with needle guard  4080 , needle  4060  does not protrude from the needle guard  4080 . During this rearward movement, first fingers  4330  cannot bend outward to disengage serrated edges  4334  of inwardly extending protrusions  4333  from serrated edges  4405  of plunger  4040  since the outwardly extending protrusions  4332  of first fingers  4330  are supported by forwardly pointed protrusions  4142  of rear housing element  4010 .  
         [0454]     Reference is now made to  FIGS. 128-140C , which illustrate the constituent elements of yet another automatic injection device constructed and operative in accordance with another preferred embodiment of the present invention.  
         [0455]     As seen with particular clarity in  FIG. 128 , the automatic injection device comprises a rear housing element  5010  in which is seated a main compression spring  5020 , which provides selectable forward displacement to a selectable driving assembly  5030 , which includes a selectable driving element  5031  and a pair of elastomeric motion damping elements  5032  and  5034 , and selectably engages a plunger  5040  and a pre-filled syringe  5050  having a hypodermic needle  5060  which is covered by a needle protection cover  5062 . Pre-filled syringe  5050  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0456]     Plunger  5040  also operatively engages pre-filled syringe  5050  and is selectably operated by selectable driving assembly  5030  to inject the liquid contents of pre-filled syringe  5050  through hypodermic needle  5060 .  
         [0457]     The forward portion of rear housing element  5010  as well as spring  5020 , selectable driving assembly  5030 , plunger  5040  and pre-filled syringe  5050  are located within a forward housing and actuator element  5070 . At the forward end of the interior of forward housing and actuator element  5070  there is provided a needle guard element  5080 , which is positioned by a compression spring  5090 .  
         [0458]     Reference is now made to  FIG. 129 , which is a simplified pictorial illustration of a preferred rear housing element  5010  which forms part of the automatic injection device of  FIG. 128 , to  FIGS. 130A and 130B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 131A, 131B  and  131 C, which are sectional illustrations taken along respective section lines and directions CXXXIA-CXXXIA, CXXXIB-CXXXIB and CXXXIC-CXXXIC in  FIGS. 130A and 130B .  
         [0459]     As seen in  FIGS. 129-131C , the rear housing element  5010  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  5110 , which terminates in a back wall  5112 , defining generally symmetric side-facing tabs  5114  in front of which are generally symmetric side facing recesses  5116 . Tubular portion  5110  is preferably side-to-side symmetric about a longitudinal axis  5120 .  
         [0460]     Tubular portion  5110  is formed with a pair of generally symmetric side recesses  5122  at which corresponding generally elongate engagement shaft portions  5124  extend forwardly parallel to longitudinal axis  5120  each terminating in an outward facing protrusion  5126 . Above each engagement shaft portion  5124  there is provided a further shaft portion  5127 , which extends forwardly of protrusion  5126  and has a somewhat curved cross sectional configuration. Shaft portions  5127  on the two sides of the rear housing element are separated from each other, as shown. A pair of mutually facing ribs  5128  extend from shaft portions  5127  parallel to axis  5120 , defining forward facing shoulders  5129 . As seen particularly in  FIGS. 129 and 131 A, a central inward facing protrusion  5130  is provided at a top interior surface of the rear housing, between and rearward of ribs  5128 .  
         [0461]     A bottom interior surface  5131  of the rear housing element has a generally uniform, slightly concave cross section and includes a plurality of generally radially inwardly directed ribs  5132 , which extend generally parallel to longitudinal axis  5120 . A bottom exterior surface  5134  of the rear housing element, which is the underside of surface  5131 , includes a forward edge  5136  from which a plurality of radially outwardly directed ribs  5138  extend generally parallel to longitudinal axis  5120 . Side to side parallel windows  5139 , having a relatively narrow forward portion and a relatively wide backward portion, are formed below shaft portions  5127  and in front of protrusion  5126 .  
         [0462]     Side interior surfaces  5140  of the rear housing element  5010  each define a forwardly pointed protrusion  5142  which is engaged by elastomeric motion damping elements  5032  and  5034  forming part of selectable driving assembly  5030 , as described hereinbelow. The interior surface of back wall  5112  of the rear housing element  5010  further comprises a rear seat  5160  for the spring  5020 .  
         [0463]     Reference is now made to  FIG. 132 , which is a simplified pictorial illustration of a preferred selectable driving assembly  5030 , which forms part of the automatic injection device of  FIG. 128 , to  FIGS. 133A and 133B , which are respective top and side view simplified planar illustrations of the selectable driving assembly and to  FIGS. 134A, 134B  and  134 C, which are sectional illustrations taken along respective section lines and directions CXXIVA-CXXXIVA, CXXXIVB-CXXXIVB and CXXXIVC-CXXXIVC in  FIGS. 133A and 133B .  
         [0464]     As seen in  FIGS. 132-134C , the selectable driving element  5031  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  5310 , having an open back and having a pair of side-to-side symmetric actuation arms  5312  which extend forwardly of tubular portion  5310  parallel to a longitudinal axis  5320 , which when selectable driving assembly  5030  is assembled with the rear housing element  5010 , is coaxial with longitudinal axis  5120  ( FIGS. 129-131C ). A top engagement arm  5322  also extends forwardly of tubular portion  5310 . A narrowed tubular neck portion  5324  is formed forwardly of tubular portion  5310 . Elastomeric elements  5032  and  5034 , seated in side recesses  5326  and  5328  in the selectable driving element  5031 , are located symmetrically at the junction of the tubular portion  5310  and the neck portion  5324 . Neck portion  5324  is formed with an internal thread  5325 .  
         [0465]     Each of actuation arms  5312  has a generally curved cross section and includes a rearwardly extending finger  5338  having formed thereon, adjacent an extreme outward end thereof, an inwardly facing generally triangular tooth  5342  having a forwardly facing inclined surface  5344  and a rearwardly facing engagement surface  5346  extending generally perpendicular to longitudinal axis  5320 . Separated from tooth  5342  by a notch  5347  is an inwardly facing rounded tooth  5348 . Additionally, finger  5338  has formed thereon top and bottom protrusions  5349 .  
         [0466]     Top engagement arm  5322  terminates in an outwardly facing protrusion  5350  having an inclined forward facing surface  5351 . Rearwardly of protrusion  5350  and separated therefrom by an outwardly facing notch  5352  is an outwardly facing protrusion  5354 , having an inclined outwardly facing surface  5356 .  
         [0467]     Plunger  5040 , as seen in  FIG. 128  is a generally circularly symmetric element, which is preferably formed in a tubular configuration, as shown. Plunger  5040  includes a rear portion  5402  having a relatively large circular cross section which continues forwardly to an externally threaded neck portion  5404  which is adapted to engage the internal thread  5325  of neck portion  5324  for advancing the plunger during titration. Forwardly of externally threaded neck portion  5404  is an intermediate portion  5406  and a forward portion  5408 . Plunger  5040  includes a forward end  5410  adapted to engage a piston described hereinbelow with reference to  FIG. 144A  which is movably located in pre-filled syringe  5050 . Plunger  5040  is preferably symmetrically disposed about a longitudinal axis  5420 , which when assembled together with selectable driving assembly  5030  and rear housing element  5010 , is coaxial with longitudinal axes  5120  ( FIGS. 129-131C ) and  5320  ( FIGS. 132-134C ).  
         [0468]     As seen in  FIG. 128 , pre-filled syringe  5050  includes a rear flange  5502  which engages notches  5347  formed in respective fingers  5338  of each of side-to-side symmetric actuation arms  5312  of selectable driving assembly  5030  ( FIGS. 132-134C ).  
         [0469]     Reference is now made to  FIG. 135 , which is a simplified pictorial illustration of forward housing and actuator element  5070  which forms part of the automatic injection device of  FIG. 128 , to  FIGS. 136A and 136B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 137A, 137B  and  137 C, which are sectional illustrations taken along respective section lines and directions CXXXVIIA-CXXXVIIA, CXXXVIIB-CXXXVIIB and CXXXVIIC-CXXXVIIC in  FIGS. 136A and 136B .  
         [0470]     As seen in  FIGS. 135-137C , the forward housing and actuator element  5070  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally truncated conical configuration arranged along a longitudinal axis  5720 , which when the automatic injection device is assembled, is coaxial with longitudinal axes  5120  ( FIGS. 129-131C ),  5320  ( FIGS. 132-134C ) and  5420  ( FIG. 128 ). Forward housing and actuator element  5070  includes a generally tubular rear portion  5710 , having an open back and formed with a pair of side-to-side symmetric snap fit engagement sockets  5712  which receive the protrusions  5126  of the rear housing element  5010  during factory assembly of the automatic injection device.  
         [0471]     Forward of tubular rear portion  5710  are formed a pair of top-bottom symmetric windows  5714 , which allow the pre-filled syringe to be viewed, when the automatic injection device is assembled, including during use thereof.  
         [0472]     A pair of outer side surfaces  5716  of forward housing and actuator element  5070  are each formed with ribbed grip regions  5718 . Corresponding inner side surfaces  5721  each define a plurality of longitudinally extending ribs  5722 ,  5724 ,  5726  and  5728  which are used to slidably guide the needle guard  5080  during axial movement thereof as well as inner facing protrusions  5730 , which together with ribs  5722  and  5724  define a forward facing spring seat for spring  5090  ( FIG. 128 ). Inner facing protrusions  5730  are operative to slidably support pre-filled syringe  5050  and to slidably guide actuation arms  5312  of selectable driving assembly  5030 .  
         [0473]     Inner top and bottom surfaces  5732  and  5734  define respective pairs of ribs  5736  and  5738  which are operative to slidably guide the needle guard  5080  during axial movement thereof. A cantilevered rearwardly extending actuation lever  5750  extends from a location rearward of top window  5714  and defines, at an extreme rearward top facing surface thereof, an actuation button  5752 .  
         [0474]     As best seen in  FIG. 137A , inner facing protrusions  5730  define at rearward facing portions thereof protrusions  5760  and  5762  which form a stopping point for flange  5502 , thus limiting the forward movement of the pre-filled syringe  5050 .  
         [0475]     Reference is now made to  FIG. 138 , which is a simplified pictorial illustration of a needle guard element  5080  which forms part of the automatic injection device of  FIG. 128 , to  FIGS. 139A and 139B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 140A, 140B  and  140 C, which are sectional illustrations taken along respective section lines and directions CXLA-CXLA, CXLB-CXLB and CXLC-CXLC in  FIGS. 139A and 139B .  
         [0476]     As seen in  FIGS. 138-140C , the needle guard element  5080  preferably is an integrally formed element, preferably injection molded of plastic and preferably has a generally cylindrical configuration including a generally tubular portion  5810 , having a forward facing body engaging surface  5812  including a pair of concentric ribbed circumferential forward facing rings  5814  and  5816 . The internal surface, located opposite from body engaging surface  5812 , forms a spring-seat for spring  5090 .  
         [0477]     Needle guard element  5080  has a pair of side-to-side symmetric mounting arms  5818  arranged symmetrically about a longitudinal axis  5820 . Each of arms  5818  has at a rearwardmost end thereof a pair of top and bottom facing teeth  5819 , and is formed with a rectangular window  5821  having a relatively wider forward portion  5822  and a relatively narrower rear portion  5824 . Arms  5818  extend along and rearwardly of tubular portion  5810  parallel to longitudinal axis  5820 , which when the automatic injection device is assembled, is coaxial with longitudinal axes  5120  ( FIGS. 129-131C ),  5320  ( FIGS. 132-134C ),  5420  ( FIG. 128 ) and  5720  ( FIGS. 135-137C ).  
         [0478]     A top engagement arm  5832  also extends rearwardly of tubular portion  5810  and includes a rearwardmost axial portion  5834 , an inclined intermediate portion  5836 , an axial intermediate portion  5838  and an inclined mounting portion  5840 , which extends from a top mounting arm  5842 , formed with an elongate window  5844 . An equivalent elongate window, also referenced by numeral  5844 , is formed on a bottom mounting arm  5845 . Elongate windows  5844  and top-bottom symmetric windows  5714  of forward housing and actuator element  5070  are positioned in respective parallel locations, such that pre-filled syringe  5050  is visible through the windows.  
         [0479]     Top and bottom engagement portions  5846  and  5848  are each formed with an inwardly directed tooth, here designated by reference numerals  5850  and  5852  respectively.  
         [0480]     Reference is now made to  FIGS. 141A, 141B ,  141 C,  141 D,  141 E,  141 F and  141 G which are simplified pictorial illustrations of various stages of typical use of the automatic injection device of  FIG. 128 .  
         [0481]     As seen in  FIG. 141A , the automatic injection device of  FIG. 128  is stored prior to use, as indicated by reference numeral  5900 , in a pre-use operative orientation, described hereinbelow with reference to  FIGS. 142-144B . While the automatic injection device is stored, it is preferably covered by needle protection cover  5062 .  
         [0482]     As seen in  FIG. 141B , prior to use, after removing the needle protection cover  5062 , air bubbles or some of the drug contained in pre-filled syringe  5050  may optionally be manually expelled via the needle, by rotation of rear portion  5402  of plunger  5040 , as indicated by reference numeral  5902 . The operative orientation of the automatic injection device for this functionality is described hereinbelow with reference to  FIGS. 145-147B .  
         [0483]     A user actuates the automatic injection device by pushing it against an injection site and depressing actuation button  5752  ( FIGS. 135-137C ), as indicated by reference numeral  5904  shown in  FIG. 141C  and as described hereinbelow with reference to  FIGS. 148-150B . In response to user actuation, needle penetration takes place at the injection site, as indicated by reference numeral  5906  shown in  FIG. 141D . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 151-153B .  
         [0484]     As seen in  FIG. 141E , immediately following needle penetration, drug delivery takes place, as indicated by reference numeral  5908 . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 154-156B . The operative orientation of the automatic injection device immediately following completion of drug delivery is indicated by reference numeral  5910  shown in  FIG. 141F , as described hereinbelow with reference to  FIGS. 157-159B .  
         [0485]     As seen in  FIG. 141G , the automatic injection device is manually disengaged from the injection site and the needle is automatically protected by the needle guard element  5080 , as indicated by reference numeral  5914 . The operative orientation of the automatic injection device at this stage is described hereinbelow with reference to  FIGS. 160-162B .  
         [0486]     Reference is now made to  FIG. 142 , which is a simplified assembled view illustration of the automatic injection device of  FIGS. 128 and 141 A in a pre-use operative orientation, to  FIGS. 143A and 143B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 144A and 144B , which are sectional illustrations taken along respective section lines and directions CXLIVA-CXLIVA and CXLIVB-CXLIVB in  FIGS. 143A and 143B .  
         [0487]     As seen in  FIGS. 142-144B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the rear housing element  5010  is joined to the forward housing and actuator element  5070  by snap fit engagement of protrusions  5126  of rear housing element  5010  in the engagement sockets  5712  formed in the forward housing and actuator element  5070 .  
         [0488]     Selectable driving assembly  5030  is retained in its axial position by engagement of inward facing protrusion  5130  ( FIG. 131A ) with outwardly facing notch  5352  of top engagement arm  5322  ( FIG. 5134 ) of selectable driving assembly  5030 . In this arrangement, spring  5020  is in a relatively compressed state and is held in that state by pressure from the selectable driving assembly.  
         [0489]     As seen clearly in the enlarged portion of  FIG. 144A , needle guard  5080  is retained in its position by engagement of inwardly directed teeth  5850  and  5852  of top and bottom engagement portions  5846  and  5848  with flange  5502  of pre-filled syringe  5050 .  
         [0490]     As seen clearly in the enlarged portion of  FIG. 144B , plunger  5040  is retained in place by engagement of externally threaded neck portion  5404  and internal thread  5325  of neck portion  5324 .  
         [0491]     The rearwardmost axial portion  5834  of the top engagement arm  5832  of the needle guard  5080  ( FIGS. 138-140C ) is in a relatively forward position, only partially underlying actuation button  5752  of forward housing and actuator element  5070  ( FIGS. 135-137C ). Additionally, downward displacement of actuation button  5752  is limited by ribs  5128  ( FIGS. 129-131C ), thus ensuring that actuation button  5752  does not directly engage protrusion  5350  of engagement arm  5322 . Accordingly, in this orientation of the automatic injection device, inadvertent pressing of button  5752  does not actuate the automatic injection device.  
         [0492]     The pre-filled syringe  5050  is retained in a retracted orientation by engagement of flange  5502  thereof with notches  5347  formed in respective fingers  5338  of each of side-to-side symmetric actuation arms  5312  of selectable driving assembly  5030  ( FIGS. 132-135C ).  
         [0493]     Reference is now made to  FIG. 145 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 B in an optional titration operative orientation, to  FIGS. 146A and 146B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 147A and 147B , which are sectional illustrations taken along respective section lines and directions CXLVIIA-CXLVIIA and CXLVIIB-CXLVIIB in  FIGS. 146A and 146B .  
         [0494]     In an optional titration step, after the protective needle cover  5062  has been removed and while the needle guard  5080  points upwards, a user may rotate rear portion  5402  of plunger  5040 , causing the externally threaded neck portion  5404  of the plunger to move the plunger forwardly by threading it further in the internal thread  5325  of neck portion  5324 . As the plunger moves forwardly, the syringe  5050  is retained in place, thus forcing air bubbles and/or liquid out of the syringe via the needle  5060 . At this stage, protrusions  5349  formed on fingers  5338  ( FIGS. 132-134C ) engage the defining walls of narrower rear portion  5824  of rectangular window  5821 , thus limiting the third fingers  5338  from bending outward and therefore flange  5502  continues to engage notches  5347  thus inhibiting premature movement of syringe  5050 . It is appreciated that except for the forward movement of the plunger  5040 , the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0495]     Reference is now made to  FIG. 148 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 C in an actuated operative orientation, to  FIGS. 149A and 149B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 150A and 150B  which are sectional illustrations taken along respective section lines and directions CLA-CLA and CLB-CLB in  FIGS. 149A and 149B .  
         [0496]     As seen particularly in the enlarged portion of  FIG. 150A , due to engagement of the needle guard  5080  with an injection site on a body, the needle guard  5080  is forced to move axially in a rearward direction with respect to the remainder of the automatic injection device, thus compressing spring  5090  and causing the rearwardmost axial portion  5834  of the top engagement arm  5832  of the needle guard  5080  ( FIGS. 138-140C ) to assume a relatively rearward position, generally underlying actuation button  5752  of forward housing and actuator element  5070  ( FIGS. 135-137C ). The rearward motion of the needle guard  5080  is limited by engagement of rearwardmost ends of top and bottom facing teeth  5819  of arms  5818  of the needle guard and the rear edge of window  5139  formed in front of outward facing protrusion  5126  of rear housing element  5010 .  
         [0497]     In this orientation of the needle guard  5080 , pressing of button  5752  does actuate the automatic injection device, by causing portion  5834  to engage protrusion  5350 , thus disengaging notch  5352  from protrusion  5130  ( FIG. 131A ) and thus disengaging engagement arm  5322  from the rear housing element  5010  and permitting forward axial movement of the selectable driving assembly  5030  under the urging of spring  5020 .  
         [0498]     Reference is now made to  FIG. 151 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 D in a needle penetration, pre-drug delivery operative orientation, to  FIGS. 152A and 152B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 153A and 153B , which are sectional illustrations taken along respective section lines and directions CLIIIA-CLIIIA and CLIIIB-CLIIIB in  FIGS. 152A and 152B .  
         [0499]      FIGS. 151-153B  illustrate an initial stage in the forward motion of the selectable driving assembly  5030  under the urging of spring  5020  following user actuation of button  5752 . It is seen that the axial forward motion of the selectable driving assembly  5030  produces equivalent axial forward motion of the syringe  5050 , due to engagement of flange  5502  in notches  5347  formed in respective fingers  5338  of each of side-to-side symmetric actuation arms  5312  of selectable driving assembly  5030  ( FIGS. 132-134C ).  
         [0500]     This forward motion results in forward motion of the needle  5060  and needle penetration at the injection site as shown. The forward motion of syringe  5050  and needle penetration stops as flange  5502  reaches protrusions  5760  and  5762  of forward housing and actuator element  5070 . During needle penetration, elastomeric elements  5032  and  5034  engage forwardly pointed protrusion  5142  of side interior surface  5140  causing friction therebetween, thus compensating for the force of spring  5020  and resulting in damping of the needle movement and absorbance of the shock applied by protrusions  5760  and  5762  on the flange  5502 . As will be described hereinbelow, drug delivery follows needle penetration.  
         [0501]     Reference is now made to  FIG. 154 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 E in drug delivery operational orientation, to  FIGS. 155A and 155B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 156A and 156B , which are sectional illustrations taken along respective section lines and directions CLVIA-CLVIA and CLVIB-CLVIB in  FIGS. 155A and 155B .  
         [0502]      FIGS. 154-156B  illustrate a further stage in the forward motion of the selectable driving assembly under the urging of spring  5020  following user actuation of button  5752 . It is seen that the axial forward motion of the selectable driving assembly  5030  does not produce equivalent axial forward motion of the syringe  5050 , due to engagement of flange  5502  of syringe  5050  with protrusions  5760  and  5762  of ribs of the forward housing and actuator element  5070  ( FIG. 137A ).  
         [0503]     Continued urging of spring  5020  and the selectable driving assembly  5030  causes protrusions  5349  formed on fingers  5338  ( FIGS. 132-134C ) to disengage the defining walls of narrower rear portion  5824  of rectangular window  5821 , and bend outward into the space formed by the wider forward portion  5822  of the rectangular window ( FIGS. 138-140C ), resulting in disengagement of flange  5502  and notches  5347  formed in respective fingers  5338  of each of side-to-side symmetric actuation arms  5312  of selectable driving assembly  5030  ( FIGS. 132-134C ).  
         [0504]     The urging of spring  5020  causes plunger  5040  to continue its forward motion together with piston  5501  which is engaged thereto.  
         [0505]     Forward motion of piston  5501  forces the drug out of syringe  5050  through needle  5060  into the injection site. During drug delivery, the forward motion of the piston  5501  is governed by friction between elastomeric elements  5032  and  5034  and forwardly pointed protrusion  5142  of side interior surfaces  5140 . The amount of friction may be selected by appropriately shaping the forwardly pointed protrusion  5142  and the elastomeric elements  5032  and  5034 .  
         [0506]     The forwardly pointed shape of protrusions  5142  causes a reduction in friction as selectable driving assembly  5030  advances, which compensates for the reduction of the force applied by spring  5020  as it extends. Friction between the protrusion and elastomeric elements  5032  and  5034  also damps shock resulting from engagement of the internal thread  5325  of neck portion  5324  and externally threaded neck portion  5404  of plunger  5040 , which is then transferred to flange  5502  of the pre-filled syringe  5050 , and may help control the drug injection rate.  
         [0507]     Reference is now made to  FIG. 157 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 F in an immediate post-drug delivery operational orientation, to  FIGS. 158A and 158B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 159A and 159B , which are sectional illustrations taken along respective section lines and directions CLIXA-CLIXA and CLIXB-CLIXB in  FIGS. 158A and 158B .  
         [0508]     Prior to this stage, forward motion of piston  5501  in the syringe continued until the piston cannot move forward any more, thus terminating drug delivery.  
         [0509]     Reference is now made to  FIG. 160 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 128 and 141 G in a needle protected operational orientation, to  FIGS. 161A and 161B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 162A and 162B  which are sectional illustrations taken along respective section lines and directions CLXIIA-CLXIIA and CLXIIB-CLXIIB in  FIGS. 161A and 161B .  
         [0510]     At this stage, the automatic injection device is fully disengaged from the injection site and the needle guard  5080  is fully extended to fully enclose the needle  5060 . When the needle guard is fully extended it is locked onto the syringe  5050  by engagement of inwardly directed teeth  5850  and  5852  and flange  5502  of the pre-filled syringe  5050 , thus inhibiting further movement outwards of the needle guard  5080 . As the needle guard disengages from the injection site and moves outwards, top and bottom facing teeth  5819  move along the narrow portion of window  5139 , until they engage forward edge  5136 , thus inhibiting the needle guard  5080  from moving inwards.  
         [0511]     Reference is now made to  FIG. 163  which is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a still further preferred embodiment of the present invention. The embodiment of  FIG. 163  is a modification of the embodiment of  FIGS. 1-41 . Accordingly, for the sake of conciseness, it is described hereinbelow in somewhat abbreviated form with reference to  FIGS. 164-190B .  
         [0512]     As seen with particular clarity in  FIG. 163 , the automatic injection device comprises a rear housing element  6010  in which is seated a main compression spring  6020 , which provides selectable forward displacement to a selectable driving assembly  6030 , which includes a selectable driving element  6031  and a pair of elastomeric motion damping elements  6032  and  6034 , and selectably engages a plunger  6040  and a pre-filled syringe  6050  having a hypodermic needle  6060  which is covered by a needle protection cover  6062 . Pre-filled syringe  6050  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0513]     Plunger  6040  also operatively engages pre-filled syringe  6050  and is selectably operated by selectable driving assembly  6030  to inject the liquid contents of pre-filled syringe  6050  through hypodermic needle  6060 .  
         [0514]     The forward portion of rear housing element  6010  as well as spring  6020 , selectable driving assembly  6030 , plunger  6040  and pre-filled syringe  6050  are located within a forward housing and actuator element  6070 . At a forward end of the interior of forward housing and actuator element  6070  there is provided a needle guard element  6080 , which is positioned by a compression spring  6090 .  
         [0515]     Plunger  6040 , as seen in  FIG. 163 , is a generally circularly symmetric element, which is preferably formed in an overall ribbed configuration, as shown. Plunger  6040  includes a rear portion  6402  having a relatively large circular cross section which tapers forwardly to a neck portion  6404 , having a relatively small circular cross section. Forwardly of neck portion  6404  is an intermediate portion  6406 , whose circular cross section is typically the same as that of rear portion  6402 , and a forward portion  6408 , whose circular cross section is typically the same as that of neck portion  6404 . Plunger  6040  terminates at its forward end in a male threaded protrusion  6410  adapted to fit a corresponding female threaded socket formed in a piston described hereinbelow with reference to  FIG. 166A , which is movably located in pre-filled syringe  6050 . Plunger  6040  is preferably symmetrically disposed about a longitudinal axis  6420 , which when assembled together with selectable driving assembly  6030  and rear housing element  6010 , is coaxial with longitudinal axes  6120  and  6320 .  
         [0516]     Reference is now made to  FIG. 2 , which is a simplified pictorial illustration of a preferred rear housing element  10  which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 3A and 3B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 4A, 4B  and  4 C, which are sectional illustrations taken along respective section lines and directions IVA-IVA, IVB-IVB and IVC-IVC in  FIGS. 3A and 3B .  
         [0517]     Rear housing element  6010  is identical to rear housing element  10  described hereinabove with reference to  FIGS. 2-4C .  
         [0518]     Reference is now made to  FIG. 5 , which is a simplified pictorial illustration of a preferred selectable driving assembly  30 , which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 6A and 6B , which are respective top and side view simplified planar illustrations of the selectable driving assembly and to  FIGS. 7A, 7B  and  7 C, which are sectional illustrations taken along respective section lines and directions VIIA-VIIA, VIIB-VIIB and VIIC-VIIC in  FIGS. 6A and 6B .  
         [0519]     Selectable driving assembly  6030  is nearly identical to selectable driving assembly  30  described hereinabove with reference to  FIGS. 5-7C  except for the following differences:  
         [0520]     In contrast to the embodiment of  FIGS. 1-41 , third fingers  6338  including notches  6347  and inwardly facing rounded teeth  6348  are obviated. Teeth  6342  having inclined surface  6344  and a rearward surface  6346  are formed directly on inwardly facing surfaces of side to side symmetric actuation arms  6312 .  
         [0521]     Reference is now made to  FIG. 8 , which is a simplified pictorial illustration of forward housing and actuator element  70  which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 9A and 9B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 10A, 10B  and  10 C, which are sectional illustrations taken along respective section lines and directions XA-XA, XB-XB and XC-XC in  FIGS. 9A and 9B .  
         [0522]     Forward housing and actuator element  6070  is identical to forward housing and actuator element  70  described hereinabove with reference to  FIGS. 8-10B .  
         [0523]     Reference is now made to  FIG. 11 , which is a simplified pictorial illustration of a needle guard element  80  which forms part of the automatic injection device of  FIG. 1 , to  FIGS. 12A and 12B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 13A, 13B  and  13 C, which are sectional illustrations taken along respective section lines and directions XIIIA-XIIIA, XIIIB-XIIIB and XIIIC-XIIIC in  FIGS. 12A and 12B .  
         [0524]     Needle guard element  6080  is identical to needle guard element  80  described hereinabove with reference to  FIGS. 11A-13C .  
         [0525]     Reference is now made to  FIG. 164 , which is a simplified assembled view illustration of the automatic injection device of  FIG. 163  in a pre-use operative orientation, to  FIGS. 165A and 165B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 166A and 166B , which are sectional illustrations taken along respective section lines and directions CLXVIA-CLXVIA and CLXVIB-CLXVIB in  FIGS. 165A and 165B .  
         [0526]     As seen in  FIGS. 164-166 , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the rear housing element  6010  is joined to the forward housing and actuator element  6070  by snap fit engagement of protrusions  6126  of rear housing element  6010  in the engagement sockets  6712  formed in the forward housing and actuator element  6070 .  
         [0527]     Selectable driving assembly  6030  is retained in its axial position by engagement of inward facing protrusion  6130  with outwardly facing notch  6352  of top engagement arm  6322  of selectable driving assembly  6030 , as shown with particularly in the enlarged portion of  FIG. 604A . In this arrangement, spring  6020  is in a relatively compressed state and is held in that state by the selectable driving assembly  6030 .  
         [0528]     Also seen in the enlarged portion of  FIG. 166  is that the rearwardmost axial portion  6834  of the top engagement arm  6832  of the needle guard  6080  is in a relatively forward position, only partially underlying actuation button  6752  of forward housing and actuator element  6070 . Additionally, inward displacement of actuation button  6752  is limited by ribs  6128 , thus ensuring that actuation button  6752  does not directly engage protrusion  6350  of engagement arm  6322 . Accordingly, in this orientation of the needle guard  6080 , inadvertent pressing of button  6752  does not actuate the automatic injection device.  
         [0529]     The pre-filled syringe  6050  is retained in a retracted orientation by engagement of flange  6502  thereof with rearwardly facing engagement surfaces  6346  of teeth  6342  formed on side-to-side symmetric actuation arms  6312  of selectable driving assembly  6030 .  
         [0530]     Needle guard  6080  is retained in its axial position, and is prevented from moving forward by engagement of inwardly directed teeth  6850  and  6852  with the flange  6502  of the pre-filled syringe  6050 . It is appreciated that in this operative orientation spring  6090  either at rest or in a semi-compressed state.  
         [0531]     Reference is now made to  FIG. 167  which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in an optional titration operative orientation, to  FIGS. 168A and 168B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 169A and 169B , which are sectional illustrations taken along respective section lines and directions CLIXA-CLIXA and CLIXB-CLIXB in  FIGS. 168A and 168B .  
         [0532]     In an optional titration step, after the protective needle cover has been removed and while the needle guard  6080  points upwards, a user may push rear portion  6402  of plunger  6040  forwardly as the syringe  6050  is retained in place. This forces air bubbles and/or liquid out of the syringe via the needle  6060 . At this stage, flange  6502  continues to engage rearwardly facing engagement surfaces  6346  of teeth  6342  thus inhibiting premature movement of syringe  6050 . It is appreciated that except for the forward movement of the plunger  6040 , the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0533]     Reference is now made to  FIG. 170 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in an actuated operative orientation, to  FIGS. 171A and 171B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 172A and 172B  which are sectional illustrations taken along respective section lines and directions CLXXIIA-CLXXIIA and CLXXIIB-CLXXIIB in  FIGS. 609A and 609B .  
         [0534]     As seen particularly in the enlarged portion of  FIG. 172A , due to engagement of the needle guard  6080  with an injection site on a body, the needle guard  6080  is forced to move axially in a rearward direction with respect to the remainder of the automatic injection device, thus compressing spring  6090  and causing the rearwardmost axial portion  6834  of the top engagement arm  6832  of the needle guard  6080  to assume a relatively rearward position, generally underlying actuation button  6752  of forward housing and actuator element  6070 . The rearward motion of the needle guard  6080  is limited by engagement of rearwardmost ends  6819  of arms  6818  of the needle guard with a forward facing edge of outward facing protrusion  6126  rear housing element  6010 .  
         [0535]     In this orientation of the needle guard  6080 , pressing of button  6752  does actuate the automatic injection device, by causing portion  6834  to engage protrusion  6350 , thus disengaging notch  6352  from protrusion  6130  and thus disengaging engagement arm  6322  from the rear housing element  6010  and permitting forward axial movement of the selectable driving assembly  6030  under the urging of spring  6020 .  
         [0536]     Reference is now made to  FIG. 173 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in a needle penetration, pre-drug delivery operative orientation, to  FIGS. 174A and 174B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 175A and 175B , which are sectional illustrations taken along respective section lines and directions CLXXVA-CLXXVA and CLXXVB-CLXXVB in  FIGS. 174A and 174B .  
         [0537]      FIGS. 173-175B  illustrate an initial stage in the forward motion of the selectable driving assembly  6030  under the urging of spring  6020  following user actuation of button  6752 . It is seen that the axial forward motion of the selectable driving assembly  6030  produces equivalent axial forward motion of the syringe  6050 , due to engagement between inwardly extending protrusion  6333  of the bended first finger  6330  of the selectable driving assembly  6030  and intermediate portion  6406  of plunger  6040 , which, in turn, forces the syringe to move forward.  
         [0538]     This forward motion results in forward motion of the needle  6060  and needle penetration at the injection site as shown. The forward motion of syringe  6050  and needle penetration stops as flange  6502  reaches protrusions  6760  and  6762  of forward housing and actuator element  6070 . During needle penetration, elastomeric elements  6032  and  6034  engage forwardly pointed protrusion  6142  causing friction therebetween, thus compensating for the force of spring  6020  and resulting in damping of the needle movement and absorbance of the shock applied by protrusions  6760  and  6762  on the flange  6502 . The forward motion of the selectable driving assembly  6030  causes the outwardly extending protrusion  6332  to engage a forwardly pointed protrusion formed on surface  6140 , thus bending the first finger  6330  inwards. As will be described hereinbelow, drug delivery follows needle penetration.  
         [0539]     Reference is now made to  FIG. 176 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in drug delivery operational orientation, to  FIGS. 177A and 177B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 178A and 178B , which are sectional illustrations taken along respective section lines and directions CLXXVIIIA-CLXXVIIIA and CLXXVIIIB-CLXXVIIIB in  FIGS. 177A and 177B .  
         [0540]      FIGS. 176-178B  illustrate a further stage in the forward motion of the selectable driving assembly under the urging of spring  6020  following user actuation of button  6752 . It is seen that the axial forward motion of the selectable driving assembly  6030  does not produce equivalent axial forward motion of the syringe  6050 , due to engagement of flange  6502  of syringe  6050  with protrusions  6760  and  6762  of ribs of the forward housing and actuator element  6070 .  
         [0541]     Continued urging of spring  6020  and the selectable driving assembly  6030  in addition to the engagement between inwardly extending protrusion  6333  of the bended first finger  6330  of the selectable driving assembly  6030  and intermediate portion  6406  of plunger  6040 , cause the plunger  6040  to continue its forward motion together with piston  6501 , which is connected thereto.  
         [0542]     Forward motion of piston  6501  forces the drug out of syringe  6050  through needle  6060  into the injection site. During drug delivery, the forward motion of the piston  6501  is governed by friction between elastomeric elements  6032  and  6034  and a forwardly pointed protrusion formed on surface  6140 . The amount of friction may be selected by appropriately shaping the forwardly pointed protrusion and the elastomeric elements  6032  and  6034 .  
         [0543]     The forwardly pointed shape of the protrusion causes a reduction in friction as selectable driving assembly  6030  advances, which compensates for the reduction in the force applied by spring  6020  as it extends. Friction between the protrusion and elastomeric elements  6032  and  6034  also damps shock resulting from engagement of inwardly extending protrusion  6333  with intermediate portion  6406  of plunger  6040  may help control the drug injection rate.  
         [0544]     Reference is now made to  FIG. 179 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in an immediate post-drug delivery operational orientation, to  FIGS. 180A and 180B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 181A and 181B , which are sectional illustrations taken along respective section lines and directions CLXXXIA-CLXXXIA and CLXXXIB-CLXXXIB in  FIGS. 180A and 180B .  
         [0545]     Prior to this stage, forward motion of piston  6501  in the syringe continued until the piston cannot move forward any more, thus terminating drug delivery. Additionally, outwardly extending protrusions  6332  of first fingers  6330  no longer engage the forwardly pointed protrusion, and are now supported by the internal surfaces of mounting arms  6818 .  
         [0546]     Reference is now made to  FIG. 182 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in its operation orientation as it is being disengaged from an injection site, to  FIGS. 183A and 183B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 184A and 184B  which are sectional illustrations taken along respective section lines and directions CLXXXIVA-CLXXXIVA and CLXXXIB-CLXXXIB in  FIGS. 183A and 183B .  
         [0547]     At this stage, the automatic injection device is being removed from the injection site and the needle guard  6080  is moving axially forward under the urging of spring  6090 , so that the exposed portion of the needle  6060  is protected by the needle guard  6080 . Subsequent to the initial forward movement of the needle guard  6080 , the first fingers  6330  of each of side-to-side symmetric actuation arms  6312  of the selectable driving assembly  6030  are released and bend outwards to their initial position, thus disengaging from the plunger  6040  and engaging the rearwardmost ends  6819  of arms  6818  of the needle guard  6080 .  
         [0548]     At this stage the spring  6020  applies more force than does spring  6090  and thus pushes the needle guard  6080  further forward. It is therefore appreciated that even if spring  6090  were to be replaced by a shorter spring, for example a short plastic spring integrated with either forward housing and actuator element  6070  or needle guard  6080 , spring  6020  would guarantee that needle guard  6080  would be fully deployed, such that the auto injection device would be maintained in a protected position.  
         [0549]     Reference is now made to  FIG. 185 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in a needle protected operational orientation, to  FIGS. 186A and 186B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 187A and 187B  which are sectional illustrations taken along respective section lines and directions CLXXXVIIA-CLXXXVIIA and CLXXXVIIB-CLXXXVIIB in  FIGS. 186A and 186B .  
         [0550]     At this stage, the automatic injection device is fully disengaged from the injection site and the needle guard  6080  is fully extended to fully enclose the needle  6060 . When the needle guard is fully extended it is locked onto the syringe  6050  by engagement of inwardly directed teeth  6850  and  6852  and flange  6502  of the pre-filled syringe  6050 , thus inhibiting further movement outwards of the needle guard  6080 . During the movement of needle guard  6080  and due to force exerted by spring  6020 , inwardly extending protruding portions  6336  of second fingers  6334  snap over flange  6502  within the narrower rear portion  6824  of rectangular window  6821 , thus enabling further locking of the needle guard as described hereinbelow.  
         [0551]     Reference is now made to  FIG. 188 , which is a simplified pictorial illustration of the automatic injection device of  FIG. 163  in a needle-guard push back misuse operational orientation, to  FIGS. 189A and 189B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 190A and 190B  which are sectional illustrations taken along respective section lines and directions CXCA-CXCA and CXCB-CXCB in  FIGS. 189A and 189B .  
         [0552]      FIGS. 188-190B  illustrate an important feature of the present invention provided by the locking of inwardly extending protruding portion  6336  of second finger  6334  of the selectable driving assembly  6030  and the flange  6502  of the pre-filled syringe  6050 . Should the needle guard  6080  be pushed rearwardly with respect to the forward housing and actuator element  6070 , the rearwardmost ends  6819  of arms  6818  of the needle guard  6080  push against protrusion  6332  of the selectable driving assembly  6030 . Selectable driving assembly  6030  is therefore forced to move rearwardly together with the needle guard.  
         [0553]     Due to engagement of second fingers  6334  and flange  6502 , the selectable driving assembly  6030  forces the needle  6060  and syringe  6050  to move rearwardly together with selectable driving assembly  6030 , so that the needle  6060  does not protrude from the needle guard  6080 . During this rearward movement, first fingers  6330  cannot bend inwards to cause outwardly extending protrusions  6332  to disengage from rearwardmost ends  6819  of arms  6818 , since the inwardly extending protrusions  6333  of first fingers  6330  are supported by intermediate portion  6406  of the plunger  6040 .  
         [0554]     Reference is now made to  FIG. 191  which is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a still further preferred embodiment of the present invention. The embodiment of  FIG. 191  is a modification of the embodiment of  FIGS. 1-41  with the addition of a vial adapter and vial contents mixing functionality. Accordingly, for the sake of conciseness, it is described hereinbelow in somewhat abbreviated form with reference to  FIGS. 192-209B .  
         [0555]     As seen with particular clarity in  FIG. 191 , the automatic injection device comprises a rear housing element  7010  into which is seated a main compression spring  7020 , which provides selectable forward displacement to a selectable driving assembly  7030 , which includes a selectable driving element  7031  and a pair of elastomeric motion damping elements  7032  and  7034 , and selectably engages a plunger  7040  and a pre-filled syringe  7050  having a hypodermic needle  7060  which is covered by a needle protection cover  7062 . Pre-filled syringe  7050  may be a conventional pre-filled syringe, such as a commercially available syringe sold under the catalog designation BD-Hypak™ or may be any other suitable syringe or cartridge.  
         [0556]     Plunger  7040  also operatively engages pre-filled syringe  7050  and is selectably operated by selectable driving assembly  7030  to inject the liquid contents of pre-filled syringe  7050  through hypodermic needle  7060 . The forward portion of rear housing element  7010  as well as spring  7020 , selectable driving assembly  7030 , plunger  7040  and pre-filled syringe  7050  are located within a forward housing and actuator element  7070 . At the forward end of the interior of forward housing and actuator element  7070  there is provided a needle guard element  7080 , which is positioned by a compression spring  7090 .  
         [0557]     The above-described apparatus is identical to that described hereinabove with reference to  FIGS. 1-13C  other than in that plunger  7040  is somewhat longer than plunger  40  in order to provide the vial contents mixing functionality.  
         [0558]     As seen, the embodiment of  FIG. 191  also includes a vial adaptor  7091  and an associated septum  7092 , typically formed of rubber, which are adapted for selectable operative engagement with a conventional drug vial  7093 .  
         [0559]     The vial adaptor  7091  preferably comprises three concentric cylindrical portions including a needle engagement portion  7094  defining a rearward facing bore  7095  in which is seated septum  7092 . Forward of bore  7095  is an intermediate bore  7096  which terminates in a hollow vial puncturing spike  7097 . Surrounding vial puncturing spike  7097  is a forward cowl  7098  and partially surrounding needle engagement portion  7094  is a rearward cowl  7099 . A radially extending wall  7100  is common to cylindrical portions  7094 ,  7098  and  7099 .  
         [0560]     Reference is now made to  FIG. 192  which is a simplified assembled view illustration of the automatic injection device of  FIG. 191  in a pre-use operative orientation, to  FIGS. 193A and 193B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 194A and 194B , which are sectional illustrations taken along respective section lines and directions CXCIVA-CXCIVA and CXCIVB-CXCIVB in  FIGS. 193A and 193B .  
         [0561]     As seen in  FIGS. 192-194B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the rear housing element  7010  is joined to the forward housing and actuator element  7070  by snap fit engagement of protrusions  7126  of rear housing element  7010  in the engagement sockets  7712  formed in the forward housing and actuator element  7070 .  
         [0562]     Selectable driving assembly  7030  is retained in its axial position by engagement of inward facing protrusion  7130  with outwardly facing notch  7352  of top engagement arm  7322  of selectable driving assembly  7030 . In this arrangement, spring  7020  is in a relatively compressed state and is held in that state by the selectable driving assembly.  
         [0563]     As seen in  FIG. 194A , the rearwardmost axial portion  7834  of the top engagement arm  7832  of the needle guard  7080  is in a relatively forward position, only partially underlying actuation button  7752  of forward housing and actuator element  7070 . Additionally, inward displacement of actuation button  7752  is limited by ribs  7128 , thus ensuring that actuation button  7752  does not directly engage protrusion  7350  of engagement arm  7322 . Accordingly, in this orientation of the needle guard  7080 , inadvertent pressing of button  7752  does not actuate the automatic injection device.  
         [0564]     The pre-filled syringe  7050  is retained in a retracted orientation by engagement of flange  7502  thereof with notches  7347  formed in respective third fingers  7338  of each of side-to-side symmetric actuation arms  7312  of selectable driving assembly  7030 . At this stage, and in all the further orientations of the automatic injection device, protrusions formed on third fingers  7338  engage the defining walls of a narrower rear portion of a rectangular window formed in needle guard element  7080 , thus limiting third fingers  7338  from bending outward and ensuring that flange  7502  will continue to engage notches  7347  resulting in prevention of premature movement of syringe  7050 .  
         [0565]     Needle guard  7080  is retained in its axial position and is prevented from moving forward by engagement of inwardly directed teeth  7850  and  7852  with the flange  7502  of the pre-filled syringe  7050 . It is appreciated that in this operative orientation spring  7090  is either at rest or in a semi-compressed state.  
         [0566]     Reference is now made to  FIG. 195 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 192-194B  in an optional vial adaptor mounted operative orientation, to  FIGS. 196A and 196B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 197A and 197B , which are sectional illustrations taken along respective section lines and directions CXCVIIA-CXCVIIA and CXCVIIB-CXCVIIB in  FIGS. 196A and 196B .  
         [0567]     In an optional vial adaptor mounting step, after the protective needle cover  7062  has been removed a user may push vial adaptor  7091  onto needle  7060  so that needle  7060  extends through septum  7092  so that a forward edge of forward housing and actuator element  7070  engages a rearward facing edge of radially extending wall  7100 , thus preventing premature actuation by not allowing needle guard element  7080  to be pressed rearwardly as required for firing the needle. It is appreciated that the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0568]     Reference is now made to  FIG. 198 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 195-197B  in a vial communication operative orientation, to  FIGS. 199A and 199B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 200A and 200B  which are sectional illustrations taken along respective section lines and directions CCA-CCA and CCB-CCB in  FIGS. 199A and 199B .  
         [0569]     As seen in  FIGS. 198-200B , the interior of the vial  7093  communicates with the interior of the syringe  7050  via needle  7060 , septum  7092 , bore  7095 , bore  7096  and puncturing spike  7097 . It is appreciated that as the plunger moves forwardly, the syringe  5050  is retained in place, thus forcing air bubbles or a portion of the liquid out of the syringe via the needle  5060 .  
         [0570]     Reference is now made to  FIG. 201 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 198-200B  in a vial injection operative orientation, to  FIGS. 202A and 202B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 203A and 203B  which are sectional illustrations taken along respective section lines and directions CCIIIA-CCIIIA and CCIIIB-CCIIIB in  FIGS. 202A and 202B .  
         [0571]     As seen in  FIGS. 201-203B , the plunger  7040  is forced axially forwardly, thus injecting at least part of the contents of the syringe  7050  into the vial  7093 , via needle  7060 , septum  7092 , bore  7095 , bore  7096  and puncturing spike  7097 , thus producing mixing in the vial of the contents of the syringe  7050  with the contents of the vial  7093 . It is appreciated that as the plunger  7040  moves forwardly, the syringe  7050  is retained in place.  
         [0572]     Reference is now made to  FIG. 204 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 201-203B  in a vial aspiration operative orientation, to  FIGS. 205A and 205B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 206A and 206B  which are sectional illustrations taken along respective section lines and directions CCVIA-CCVIA and CCVIB-CCVIB in  FIGS. 205A and 205B .  
         [0573]     As seen in  FIGS. 204-206B , the plunger  7040  is pulled axially rearwardly, preferably to its position shown in  FIGS. 198-200B , thus drawing at least part of the mixed contents of the syringe  7050  and the vial  7093  from the vial  7093  into the syringe  7050 , via needle  7060 , septum  7092 , bore  7095 , bore  7096  and puncturing spike  7097 . It is appreciated that as the plunger  7040  moves rearwardly, the syringe  7050  is retained in place.  
         [0574]     Reference is now made to  FIG. 207 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 204-206B  in a vial removed operative orientation, to  FIGS. 208A and 208B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 209A and 209B  which are sectional illustrations taken along respective section lines and directions CCIXA-CCIXA and CCIXB-CCIXB in  FIGS. 208A and 208B .  
         [0575]     As seen in  FIGS. 207-209B , the vial  7093  and the vial adaptor  7091  are separated from the automatic injection device, which is now ready for use as described hereinabove with respect to  FIGS. 18-41B .  
         [0576]     It is appreciated that in each of the operative orientations in which fluid is transferred between different elements prior to removal of the vial adaptor  7091 , the automatic injection device is maintained in a safe orientation, ensuring that the needle guard will not be rearwardly displaced, and there will be no premature actuation of the device, as the vial adaptor covers the needle guard  7080  making it inaccessible.  
         [0577]     Reference is now made to  FIG. 210  which is a simplified exploded view illustration of an automatic injection device constructed and operative in accordance with a still further preferred embodiment of the present invention. The embodiment of  FIG. 210  is a modification of the embodiment of  FIGS. 1-41  with the addition of a vial adapter including a luer and vial contents mixing functionality. Accordingly, for the sake of conciseness, it is described hereinbelow in somewhat abbreviated form with reference to  FIGS. 211-234B .  
         [0578]     As seen with particular clarity in  FIG. 210 , the automatic injection device comprises a rear housing element  8010  into which is seated a main compression spring  8020 , which provides selectable forward displacement to a selectable driving assembly  8030 , which includes a selectable driving element  8031  and a pair of elastomeric motion damping elements  8032  and  8034 , and selectably engages a plunger  8040  and a needle-less syringe  8050  adapted to have attached thereto a hypodermic needle. Needle-less syringe  8050  may be a conventional needle-less syringe, or may be any other suitable syringe or cartridge.  
         [0579]     Plunger  8040  also operatively engages syringe  8050  and is selectably operated by selectable driving assembly  8030  to inject the liquid contents of syringe  8050  through a hypodermic needle (not shown). The forward portion of rear housing element  8010  as well as spring  8020 , selectable driving assembly  8030 , plunger  8040  and syringe  8050  are located within a forward housing and actuator element  8070 . At the forward end of the interior of forward housing and actuator element  8070  there is provided a needle guard element  8080 , which is positioned by a compression spring  8090 .  
         [0580]     The above-described apparatus is identical to that described hereinabove with reference to  FIGS. 1-13C  other than in that syringe  8050  is a needle-less syringe and plunger  8040  is somewhat longer than plunger  40  in order to provide the vial contents mixing functionality.  
         [0581]     As seen, the embodiment of  FIG. 210  also includes a vial adaptor  8091  integrally formed with a vial puncturing spike  8092 , which is adapted for selectable operative engagement with a conventional drug vial  8093 .  
         [0582]     The vial adaptor  8091  preferably comprises three concentric cylindrical portions including a luer engagement portion  8094  defining a rearward facing bore  8095 . Forward of bore  8095  is an intermediate bore  8096  which terminates in vial puncturing spike  8092 . Surrounding vial puncturing spike  8092  is a forward cowl  8098  and partially surrounding luer engagement portion  8094  is a rearward cowl  8099 . A radially extending wall  8100  is common to cylindrical portions  8094 ,  8098  and  8099 .  
         [0583]     Reference is now made to  FIG. 211  which is a simplified assembled view illustration of the automatic injection device of  FIG. 210  in a pre-use operative orientation, to  FIGS. 212A and 212B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 213A and 213B , which are sectional illustrations taken along respective section lines and directions CCXIIIA-CCXIIIA and CCXIIIB-CCXIIIB in  FIGS. 212A and 212B .  
         [0584]     As seen in  FIGS. 211-213B , in a pre-use operative orientation of the automatic injection device which is suitable for storage, the rear housing element  8010  is joined to the forward housing and actuator element  8070  by snap fit engagement of protrusions  8126  of rear housing element  8010  in the engagement sockets  8712  formed in the forward housing and actuator element  8070 .  
         [0585]     Selectable driving assembly  8030  is retained in its axial position by engagement of inward facing protrusion  8130  with outwardly facing notch  8352  of top engagement arm  8322  of selectable driving assembly  8030 . In this arrangement, spring  8020  is in a relatively compressed state and is held in that state by the selectable driving assembly.  
         [0586]     As seen in  FIG. 213A , the rearwardmost axial portion  8834  of the top engagement arm  8832  of the needle guard  8080  is in a relatively forward position, only partially underlying actuation button  8752  of forward housing and actuator element  8070 . Additionally, inward displacement of actuation button  8752  is limited by ribs  8128 , thus ensuring that actuation button  8752  does not directly engage protrusion  8350  of engagement arm  8322 . Accordingly, in this orientation of the needle guard  8080 , inadvertent pressing of button  8752  does not actuate the automatic injection device.  
         [0587]     The syringe  8050  is retained in a retracted orientation by engagement of flange  8502  thereof with notches  8347  formed in respective third fingers  8338  of each of side-to-side symmetric actuation arms  8312  of selectable driving assembly  8030 .  
         [0588]     Needle guard  8080  is retained in its axial position and is prevented from moving forward by engagement of inwardly directed teeth  8850  and  8852  with the flange  8502  of the pre-filled syringe  8050 . It is appreciated that in this operative orientation spring  8090  is either at rest or in a semi-compressed state.  
         [0589]     Reference is now made to  FIG. 214 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 211-213B  in an optional vial adaptor mounted operative orientation, to  FIGS. 215A and 215B , which are respective top and side view simplified planar illustrations thereof and to  FIGS. 216A and 216B , which are sectional illustrations taken along respective section lines and directions CCXVIA-CCXVIA and CCXVIB-CCXVIB in  FIGS. 215A and 215B .  
         [0590]     In an optional vial adaptor mounting step, a user may push vial adaptor  8091  onto a forward tapered portion of syringe  8050  so that rearward facing bore  8095  sealingly engages the forward tapered portion of syringe  8050 . It is appreciated that the remainder of the operative orientation of the automatic injection device remains identical to the pre-use operative orientation.  
         [0591]     Reference is now made to  FIG. 217 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 214-216B  in a vial communication operative orientation, to  FIGS. 218A and 218B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 219A and 219B  which are sectional illustrations taken along respective section lines and directions CCXIXA-CCXIXA and CCXIXB-CCXIXB in  FIGS. 218A and 218B .  
         [0592]     As seen in  FIGS. 217-219B , the interior of the vial  8093  communicates with the interior of the syringe  8050  via spike  8092 , bore  8095  and bore  8096  It is appreciated that as the plunger moves forwardly, the syringe  5050  is retained in place.  
         [0593]     Reference is now made to  FIG. 220 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 217-219B  in an air injection operative orientation, to  FIGS. 221A and 221B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 222A and 222B  which are sectional illustrations taken along respective section lines and directions CCXXIIA-CCXXIIA and CCXXIIB-CCXXIIB in  FIGS. 221A and 221B .  
         [0594]     As seen in  FIGS. 220-222B , the plunger  8040  is forced axially forwardly, thus injecting air contained in the syringe  8050  into the vial  8093 , via spike  8092 , bore  8095  and bore  8096 . It is appreciated that as the plunger  8040  moves forwardly, the syringe  8050  is retained in place.  
         [0595]     Reference is now made to  FIG. 223 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 220-222B  in a vial aspiration operative orientation, to  FIGS. 224A and 224B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 225A and 225B  which are sectional illustrations taken along respective section lines and directions CCXXVA-CCXXVA and CCXXVB-CCXXVB in  FIGS. 224A and 224B .  
         [0596]     As seen in  FIGS. 223-225B , the plunger  8040  is pulled axially rearwardly, preferably to its position shown in  FIGS. 217-219B , thus drawing at least part of the content of the vial  8093  into the syringe  8050 , via spike  8092 , bore  8095  and bore  8096 . It is appreciated that as the plunger  8040  moves rearwardly, the syringe  8050  is retained in place.  
         [0597]     Reference is now made to  FIG. 226 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 223-225B  in a vial removed operative orientation, to  FIGS. 227A and 227B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 228A and 228B  which are sectional illustrations taken along respective section lines and directions CCXXVIIIA-CCXXVIIIA and CCXXVIIIB-CCXXVIIIB in  FIGS. 227A and 227B .  
         [0598]     As seen in  FIGS. 226-228B , the vial  8093  and the vial adaptor  8091  are separated from the automatic injection device.  
         [0599]     Reference is now made to  FIGS. 229A and 229B , which are simplified pictorial illustrations of the automatic injection device of  FIGS. 226-228B  in a needle connection operative orientation, to  FIGS. 230A and 230B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 231A and 231B  which are sectional illustrations taken along respective section lines and directions CCXXXIA-CCXXXIA and CCXXXIB-CCXXXIB in  FIGS. 230A and 230B .  
         [0600]     As seen in  FIGS. 229-231B , a needle  8902  is attached to the forward tapered portion of syringe  8050 , and is covered by a needle protection cover  8104 .  
         [0601]     Reference is now made to  FIG. 232 , which is a simplified pictorial illustration of the automatic injection device of  FIGS. 229-231B  in a needle cover removed operative orientation, to  FIGS. 233A and 233B  which are respective top and side view simplified planar illustrations thereof and to  FIGS. 234A and 234B  which are sectional illustrations taken along respective section lines and directions CCXXXIVA-CCXXXIVA and CCXXXIVB-CCXXXIVB in  FIGS. 233A and 233B .  
         [0602]     As seen in  FIGS. 232-234B , the needle protection cover  8904  is removed from the automatic injection device, which is now ready for use as described hereinabove with respect to  FIGS. 18-41B .  
         [0603]     It is appreciated that in each of the operative orientations in which fluid is transferred between different elements prior to removal of the vial adaptor  8091 , the automatic injection device is maintained in a safe orientation, ensuring that the needle guard will not be rearwardly displaced, and there will be no premature actuation of the device, as the vial adaptor covers the needle guard  8080  making it inaccessible.  
         [0604]     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as modifications thereof which would occur to persons skilled in the art upon reading the foregoing specification and which are not in the prior art.
An automatic injection device including a housing element, at least one resilient element arranged to be located within the housing element, a syringe including at least one syringe piston, a needle guard adapted for selectable positioning with respect to the housing element and a selectable driving element adapted, when actuated, to be driven by the at least one resilient element for initially displacing the syringe relative to the housing element from a non-penetration position to a penetration position and thereafter displacing the at least one syringe piston in the syringe to effect drug delivery and displacing the needle guard into a needle guarding position.