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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