Applied anatomy and kinesiology, the mechanism of muscular movement . egrees, whenit is brought to a stop by contact of the tissues on the back of thethigh and leg and by tension of the front of the capsular ligamentand the crucial ligaments. Overextension is usual to a slight extentso that in the erect position the weight of the body tends to causefurther overextension; the crucial and posterior ligaments preventfurther movement and thus the extensor muscles are not neededto hold the joint in extension, as long as one stands still and thereis nothing happening to disturb the balance., There a
Applied anatomy and kinesiology, the mechanism of muscular movement . egrees, whenit is brought to a stop by contact of the tissues on the back of thethigh and leg and by tension of the front of the capsular ligamentand the crucial ligaments. Overextension is usual to a slight extentso that in the erect position the weight of the body tends to causefurther overextension; the crucial and posterior ligaments preventfurther movement and thus the extensor muscles are not neededto hold the joint in extension, as long as one stands still and thereis nothing happening to disturb the balance., There are ten muscles acting on the knee-joint, all but four MOVEMENTS OF THE KNEE-JOINT 177 of which have been described; three of the four will be describedin this chapter and the fourth, which acts mainly on the ankle-joint, will be described in the next chapter. Six flexors: semitendinosus, semimembranosus, biceps, sartorius,adductor gracilis, gastrocnemius. OUTER BERO STYLOID, PROCESS NNER TU-BEROSITY BORDER ftNTERO-l INTER-NAL BORDER OUTER MALLEOLU. INNERALLEOLUS Fig. 101.—The right tibia and fibula, front view. (Gerrish.) Four extensors: rectus femoris, vastus externus, vastus internus,vastus intermedius. Four rotators inward: semitendinosus, semimembranosus, sarto-rius, adductor 178 MOVEMENTS OF THE KNEE-JOINT One rotator outward: biceps. Among the flexors the semitendinosus and sartorius have thebest leverage, since they attach lowest on the tibia; next to themare the gracilis and the biceps, with the semimembranosus nearestthe joint. The angle of pull is least at the start, when the knee isin complete extension, and is best when it is flexed through a littlemore than 90 degrees. This group of muscles acts to lift the foot from the ground inwalking, running, hopping, climbing, jumping, and dancing, butthe resistance to be overcome is small, the weight of the leg andfoot being slight in comparison with the weight of the body, whichmost of the mu
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