Brooklyn medical journal. . n outward they fall to the opposite side. Inthis process of equilibration the spinal column plays a most activepart; made up as it is of movable segments, it permits this processof shifting the weights, by curving upon itself; shortening uponone side and lengthening upon the other; at the same time ro-tating, if necessary, upon its axis. The ribs through their articulation with the spinal vertebrae,participate in its movements, becoming approximated upon theconcave side of its curve, and separated upon its convexity. Thescapulae being attached to it only by muscles,
Brooklyn medical journal. . n outward they fall to the opposite side. Inthis process of equilibration the spinal column plays a most activepart; made up as it is of movable segments, it permits this processof shifting the weights, by curving upon itself; shortening uponone side and lengthening upon the other; at the same time ro-tating, if necessary, upon its axis. The ribs through their articulation with the spinal vertebrae,participate in its movements, becoming approximated upon theconcave side of its curve, and separated upon its convexity. Thescapulae being attached to it only by muscles, move with the armsand head, independent somewhat of the movements of the possess, by virtue of their attachment, however, a powerfulleverage upon the dorsal region of the spine. THE INFLUENCE OF HABITUAL POSTURE., ETC. 395 In the sitting posture the weight of the* lower extremities, as amodifier of posture, is removed. The pelvis becomes fixed in theposition which obtained, when it rested equally upon both Fig. i. Influence of weight of arms and head on shape of back in sitting posture. (Com-mon posture of child at study.) The lumbar region now becomes the pivot upon which the re-mainder of the trunk moves. The balance of power is vested in 396 ELIZA M. MO SHER, the arms, which hang- like weights upon the base of an inverted cone;suspended at the sides upon the hip line, they balance each other,permitting the spinal column to poise itself upon the pelvis, and the
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