Applied anatomy and kinesiology, the mechanism of muscular movement . reader will recall that inward rotation of the arm is per-formed incidentally by the large muscles having the larger dutyof swinging the arm, and that outward rotation is performed by aspecial group of two muscles, the infraspinatus and teres is interesting to find that in case of the hip we have a similarartangement, inward rotation being performed incidentally by thegreat flexors and extensors along with their main work and out- THE SIX OUTWARD ROTATORS 173 ward rotation by a special group, in this case of six in
Applied anatomy and kinesiology, the mechanism of muscular movement . reader will recall that inward rotation of the arm is per-formed incidentally by the large muscles having the larger dutyof swinging the arm, and that outward rotation is performed by aspecial group of two muscles, the infraspinatus and teres is interesting to find that in case of the hip we have a similarartangement, inward rotation being performed incidentally by thegreat flexors and extensors along with their main work and out- THE SIX OUTWARD ROTATORS 173 ward rotation by a special group, in this case of six in place of two;the pyriformis, obturator externus, obturator internus, gemellussuperior, gemellus inferior, quadratus femoris. Origin.—The posterior portions of the pelvis. Insertion.—The great trochanter of the femur. Structure.—Fig. 96 shows five of these muscles; three of themare named in the figure and the gemellus superior and inferior areassistants of the obturator internus, the former above and thelatter below. The obturator externus is shown in Fig. Fig. 99.—Rotation in the hip-joints during walking. The amount of rotation isindicated by the position of the stick. Action.—The position of this group of six muscles indicates out-ward rotation as their main action, and electric experiment givesthe same answer. It is true here, just as in case of the arm, thatforward movement of the limb through a right angle puts the groupin a position to produce abduction as well as rotation; it is easy to 174 MOVEMENTS OF THE HIP-JOINT observe on a mounted skeleton that contraction of the outwardrotators while skting will separate the knees. If in walking and running the hips do not swing forward andbackward there is no rotation in the hip-joints, but usually thehip goes forward as the foot goes forward, the amount of the swingvarying considerably in different individuals. Now a forwardswing of the hip as the limb swings forward will swing the toe inunless there is outward r
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