Active Muscular Contraction, arising from some idiopathic and substantive, or from a secondary, affection of the nervous system, especially of the nervous centres, and usually combined with other deformities of the skeleton, contractions, palsies, etc, which also owe their origin to muscular contraction.

B. In most cases it arises from neglecting or impeding the action of the muscles of inspiration of one side. All the scolioses traced by Stro-mayer to paralysis of the muscles of inspiration on one side are of this class, as well as those in which the spine is bent in consequence of chronic pleurisy, and narrowing of one side of the thorax. In such cases, the primary curvature is at the dorsal part of the column; and as, in most occupations, it is the left side of the thorax, the function of which is impeeled or neglected, the spine inclines far more frequently towards the right side than towards the left.

The curvature may be in consequence of rickets: the pelvis deriving some one-sided deformity from the lower extremities, propagates it to the vertebral column. The first curve is then in the lumbar region, and that in the dorsal region is consecutive, and slighter than the other.

§. Lastly, scoliosis may ensue after a one-sided deformity of the pelvis has been produced by dislocation of either femur upwards, whether the dislocation be the result of violence or of disease (spontaneous).

Every considerable lateral curvature is accompanied by a twisting of the vertebrae upon their axes; and this rotation or torsion is of importance in reference to the diagnosis. The vertebrae are always turned towards the curved side, that is, the bodies face the convexity, and the spinous processes the concavity of the curve: that vertebra is the most rotated which forms the most prominent point of the curve, and for the same reason, the spinous process of the same vertebra is the deepest in the row of distorted spines. Upon these facts Guérin rests the solution of the problem, from a given curvature of spinous processes to determine the degree of deviation of the vertebral bodies.

This rotation of the vertebrae upon their axes produces the deviation of the vertebral column backwards, and the rounded hump, which are the peculiar result of lateral curvature (excurvation of Bampfield). It is a compound distortion, which has been named kyphosis scoliotica; but which, inasmuch as the lateral curvature - the scoliosis, is the primary evil, would be better called scoliosis kyphotica.

The changes which take place in the several vertebrae and their processes, as well as those in the ribs, become more palpable in proportion to the degree and the duration of the lateral curvature. The vertebrae on the side of the concavity are less deep than natural; sometimes they scarcely measure one-third of their normal height; they slope considerably from above downward, their margins seem pressed forward, and their form, in short, bespeaks their having undergone gradual compression. The intervertebral bodies are more or less wasted, and sometimes are entirely removed: when this is the case the vertebrae at last become anchylosed. The processes in the concavity of the curvature become slender; they are frequently elongated, pressed together, and flattened against one another, and the articular processes are anchylosed. And the ribs, in like manner, attenuated, compressed, and flattened where they adjoin the vertebral column, become anchylosed to the vertebrae and to one another.