a case main body extending from one lateral side of an internal combustion engine to one lateral side of a rear wheel positioned rearwardly of said engine, said case main body being partitioned into front and rear casing sections and having {TAIL ~ a longitudinally extending lateral wall}, said rear casing section rotatably supporting a wheel axle of said rear wheel and having a recessed portion for partially housing a reduction gear means which includes said wheel axle, an unput shaft, and a gear train operatively interconnecting said input shaft to {HEAD ~ said wheel axle}, 
a case main body extending from one lateral side of an internal combustion engine to one lateral side of a rear wheel positioned rearwardly of said engine , said case main body being partitioned into front and rear casing sections and having { TAIL ~ a longitudinally extending lateral wall } , said rear casing section rotatably supporting a wheel axle of said rear wheel and having a recessed portion for partially housing a reduction gear means which includes said wheel axle , an unput shaft , and a gear train operatively interconnecting said input shaft to { HEAD ~ said wheel axle } ,
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