res towards the left are not
confined to left-handed persons.

_Morbid Anatomy._--The original deviation or "primary curve" is
usually in the thoracic region, and has its convexity directed towards
the right side. To re-establish the equilibrium of the column,
"secondary" or "compensatory" curves, with their convexities to the
left, develop in the regions above and below the primary curve. It has
been proved experimentally that lateral deviation of the spine is
inevitably accompanied by rotation of the vertebrae around a vertical
axis, in such a way that their bodies look towards the convexity of
the curve, while their spines, laminae, and articular processes are
directed towards the concavity (Fig. 226).

[Illustration: FIG. 226.--Vertebrae from case of Scoliosis, showing
alteration in shape of bones.]

As the deformity increases, the individual vertebrae are distorted, the
bodies becoming wedge-shaped from side to side, the base of the wedge
looking towards the convexity of the curve, while the narrow end looks
towards the concavity (Fig. 228). As the spine, laminae, and articular
processes also undergo alterations in shape, a line uniting the tips
of the spinous processes does not furnish an accurate index of the
degree of lateral deviation but minimises it considerably. The muscles
and ligaments are altered in length in accordance with the changes in
the shape and position of the bones.

In the thoracic region, the ribs necessarily accompany the transverse
processes, so that on the side of the convexity they form an undue
prominence behind--the "rib-hump" (Fig. 227), while on the side of the
concavity the chest is flattened and the ribs crowded together so that
the intercostal spaces are diminished or even obliterated. The
converse--flattening on the side of the concavity--is seen on the
front of the chest.

[Illustration: FIG. 227.--Adolescent Scoliosis in a girl aet. 23.]

The general shape of the thorax is altered: on the side of the
convexity it is longer and narrower than normal and its capacity
diminished, while on the side of the concavity it is shorter and
broader and its capacity is increased.

The viscera are distorted and displaced in accordance with the altered
shape of the thoracic and abdominal cavities. The twisting of the
spine causes the patient to lose in stature, and the limbs appear to
be disproportionately long. In advanced cases the pelvis becomes
obliquely contracted--a deformity know