Kyphosis, Or The Angular Projection, which is formed by two sides of an angle, is counterbalanced by a curvature forward (lordosis). The compensation is sometimes effected chiefly by the upper, sometimes by the lower part of the spine: as a general rule, it is the longer side of the angle by which the balance is restored; though sometimes its two sides are equally curved. These compensatory curves, again, whenever it is possible, become the occasion of further curvatures in the opposite direction; and the cervical vertebrae and sacrum, by their projection backward, make up for the deviation of the adjoining regions forward.

The compensation in Lordosis, or curvature forward, is obtained in two ways, according as it arises from too great inclination of the pelvis, or from angular projection in the dorsal region. In the former case, the natural curvature in the dorsal region is slightly increased; in the latter the sacrum, and therefore the pelvis, incline backwards.

When there is a combination of lateral and angular projection, or of lateral, with a primary curvature forwards, the form of the compensatory distortions of course corresponds with those of the compound primary curves.

Distortions of the spine diminish the capacity of the two great cavities of the trunk to such an extent as materially to interfere with the development and free action of the thoracic and abdominal viscera, while they also produce various changes in those organs, as regards both their position and their form; but the most serious consequences are those which ensue from extreme lateral and angular curvatures, as such distortions narrow and deform the thorax, and impair the functions of the lungs, and consequently of the heart. They occasion an increase of density in the tissue of the lung, and thereby give rise to active dilatation of the right side of the heart, and enlargement and permanent congestion of the whole venous system, - cyanosis. And hence, though a contrary opinion is very commonly entertained, they establish that general immunity from tuberculous disease, of which I have already spoken.

The deformities of the thorax and pelvis resulting from curvature of the spine are so intimately associated with the subject before us, that they must be treated of at once; and it will add to the interest with which we shall enter upon the study of the distortions of the pelvis in general, and more especially of the consequent curvatures of the spine, when we can refer again to our present conclusions, and find how the results of analysis in the two cases agree.