Section III. THE VERTEBRAL COLUMN
a. General. Twenty-six vertebrae make up the vertebral column. These bones
are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal
according to the regions they occupy. When viewed from the side (figure 2-18), the
vertebral column presents four normal curves that correspond with the different regions
of the column: cervical, thoracic, lumbar, and sacral (or pelvic). Anteriorly, the cervical
curve is convex, the thoracic curve is concave, the lumbar curve is convex, and the
sacral curve is concave (this curve includes the coccyx). The thoracic and sacral
curves are termed primary curves because they develop before birth. They are
sometimes indicated as the accommodation curvatures because they tend to increase
the size of the thoracic and pelvic cavities. The cervical and lumbar curves are known
as secondary curves because they develop after birth. The cervical curve develops
when the infant is able to hold up its head (at 3 or 4 months) and sit upright (at about 9
months). The lumbar curve develops when the child begins to walk (at 12 to 18
months). In addition to these alternate curvatures, the vertebral column normally has a
slight lateral curvature when viewed from the anterior aspect. In most cases, the
convexity of the lateral curvature is directed toward the right side and is associated with
right-handedness. It is considered to be produced by the normal pull of the muscles.
b. Abnormal Curves of the Vertebral Column. A complex lateral curvature of
the entire vertebral column, curves in thoracic and lumbar regions is called scoliosis.
An exaggerated dorsal curvature is called kyphosis, or "humpback". Exaggerated
curvature of the lumbar region is called lordosis, or swayback.
c. Numbering System for Vertebrae. Region and number generally designate
vertebrae. For convenience, abbreviations are used. Beginning superiorly at the first
cervical vertebra, or atlas, the abbreviation is C-1; the second cervical vertebra, or axis
is C-2; and numbering continues inferiorly to C-7. Because C-7 has a prominent spine,
it is called vertebra prominens. In the thoracic region, the abbreviations are T-1 to T-12.
The vertebrae in the lumbar region are abbreviated L-1 inferiorly to L-5.