Page 342 - Clinical Anatomy

ECA5 7/18/06 6:51 PM Page 327

The vertebral column 327

C7 is the vertebra prominens, so called because of its relatively long and
easily felt non-bifid spine; it is the first clearly palpable spine on running
one’s fingers downwards along the vertebral crests, although the spine of
T1 immediately below it is, in fact, the most prominent one.
The vertebral artery enters its vertebral course nearly always at the
foramen transversarium of C6; it is not surprising, therefore, that the
foramen of C7, which transmits only the vein, is small or even sometimes
absent.

The thoracic vertebrae (12)
These vertebrae are characterized by demifacets on the sides of their bodies
for articulation with the heads of the ribs and by facets on their transverse
processes (apart from those of the lower two or three vertebrae) for the rib
tubercles. The spines are long and downward sloping and the articular
facets are also relatively vertical. The lowest couple are rather ‘lumbar’ in
appearance, have a single facet on the side of the body and no facet on the
transverse process.
The bodies of T5 and T8 are worth noting; they come into relationship
with the descending aorta and are a little flattened by it on their left flank. If
the descending aorta becomes aneurysmally dilated, these four vertebral
bodies become eroded by its pressure, although their avascular interverte-
bral discs remain intact. You can make this diagnosis confidently when
shown a specimen of four partly worn-away vertebrae with normal inter-
vening discs.

The lumbar vertebrae (5)
These are of great size with strong, square, horizontal spines and with
articular facets which lie in the sagittal plane (Fig. 232).
L5 is distinguished by its massive transverse process which connects
with the whole lateral aspect of its pedicle and encroaches on its body; the
transverse processes of the other lumbar vertebrae attach solely to the junc-
tion of pedicle with lamina.

The sacrum (5 fused)
The coccyx (3, 4 or 5 fused)
These are considered with the bony pelvis (see page 125).

Development

Each vertebra ossifies from three primary centres, one for each side of the
arch and one for the body. The body occasionally develops from two
centres and failure of one of these to form results in formation of a hemiver-
tebra with a consequent congenital scoliosis. Failure of the two arch centres
to fuse posteriorly results in the condition of spina bifida, which occurs