Curves
Viewed laterally the vertebral column presents
several curves, which correspond to the different regions
of the column, and are called cervical, thoracic, lumbar,
and pelvic.
The cervical
curve, convex forward, begins
at the apex of the odontoid (tooth-like) process,
and ends at the middle of the second thoracic
vertebra; it is the least marked of all the
curves. The thoracic
curve, concave forward, begins
at the middle of the second and ends at the
middle of the twelfth thoracic vertebra. Its
most prominent point behind corresponds to
the spinous process of the seventh thoracic
vertebra. This curve is known as a kyphotic
curve.
The lumbar curve is
more marked in the female than in the male; it begins at
the middle of the last thoracic vertebra, and ends at the
sacrovertebral angle. It is convex anteriorly, the convexity
of the lower three vertebrae being much greater than that
of the upper two. This curve is described as a lordotic
curve.
The pelvic curve begins
at the sacrovertebral articulation, and ends at the point
of the coccyx; its concavity is directed downward and forward.
The thoracic and pelvic curves are termed primary
curves, because they alone are present during fetal life.
In the early embryo, the vertebral column is C-shaped, and the cervical
and lumbar curvatures are not yet present in a newborn infant. The cervical
and lumbar curves are compensatory or secondary, and are developed after
birth, the former when the child is able to hold up its head (at three
or four months), and to sit upright (at nine months), the latter at twelve
or eighteen months, when the child begins to walk.
The thoracic portion of the vertebral column also has a slight lateral
curvature, the convexity of which is directed toward the right side.
This may be produced by muscular action, most persons using the right
arm in preference to the left, especially in making long-continued efforts,
when the body is curved to the right side. In support of this explanation
it has been found that in one or two individuals who were left-handed,
the convexity was to the left side. This curvature is regarded by others
as being produced by the aortic arch and upper part of the descending
thoracic aorta – a view which is supported by the fact that in
cases of situs inversus where the viscera are transposed and the aorta
is on the right side, the convexity of the curve is directed to the left
side.
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Different
regions (curvatures) of the vertebral column and
names of individual vertebrae.
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The vertebral column seen from the side.
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