The 33 vertebrae fit
together to form a flexible, yet extraordinarily tough,
column that serves to support the back through a full range
of motion. It also protects the spinal cord, which runs
from the brain through the hollow space in the middle of
the vertebral column. There are seven cervical (C1-C7), 12
thoracic (T1-T12), five lumbar (L1-L5), five sacral (S1-
S5),and four coccygeal vertebrae in this column, each
separated by intervertebral disks.
The first cervical
vertebra, known as the atlas, supports the head. It pivots
on the odontoid process of the second cervical vertebra,
the axis. The cervical vertebrae end at their juncture
with the thoracic vertebrae. The seventh cervical vertebra
(the prominent vertebra, so named because of its long spiny
projection) adjoins the first thoracic vertebrae.
The thoracic
vertebrae provide an attachment site for the true ribs, and
make up part of the back of the chest (thorax). This part
of the spine is very flexible to permit bending and
twisting. The thoracic vertebrae join the lumbar vertebrae,
which are particularly study and large, as they support the
entire structure. The lumbar vertebrae are nonetheless
quite flexible.
At the top of the pelvis, the lumbar
vertebrae join the sacral vertebrae. By adulthood these
five bones have usually fused to form a triangular bone
called the sacrum. At the tip of the sacrum, the final part
of the vertebral column projects slightly outward. This is
the coccyx, better known as the tailbone. It is made up of
three to five coccygeal vertebrae: small, rudimentary
vertebrae that fuse together.
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