Two babies, one sitting up with arms raised and one creeping.

Three lateral images of a child in sitting position with vertebral column visible to illustrate development of normal curvature; (left) fetus, (middle) newborn, and (right) child.

Illustration of boy using upper extremity muscles to stand up. Upper left: child on knees and elbows. Upper right: child supports himself on extended arms. Lower left: child straightens legs, hands still on floor. Lower right: hands "climb" up to

Child sitting on floor.