Chapter 7
The Skeleton
221
7
cervical vertebrae (C
3
–C
7
) have the following distinguishing
features (see Figure 7.21 and Table 7.2):
±e body is oval—wider from side to side than in the antero-
posterior dimension.
Except in C
7
, the spinous process is short, projects directly
back, and is
bifid
(bi
9
fid), or split at its tip.
±e vertebral foramen is large and generally triangular.
Each transverse process contains a
transverse foramen
through which the vertebral arteries pass to service the brain.
±e spinous process of C
7
is not bifid and is much larger than
those of the other cervical vertebrae (see Figure 7.21a). Because
its spinous process is palpable through the skin, C
7
can be used
as a landmark for counting the vertebrae and is called the
verte-
bra prominens
(“prominent vertebra”).
±e first two cervical vertebrae, the atlas and the axis, are
somewhat more robust than the typical cervical vertebra. ±ey
have no intervertebral disc between them, and they are highly
modified, reflecting their special functions. ±e
atlas
(C
1
) has
no body and no spinous process
(Figure 7.20a and b)
. Es-
sentially, it is a ring of bone consisting of
anterior
and
poste-
rior arches
and a
lateral mass
on each side. Each lateral mass
has articular facets on both its superior and inferior surfaces.
±e superior articular facets receive the occipital condyles of
the skull—they “carry” the skull, just as Atlas supported the
heavens in Greek mythology. ±ese joints allow you to nod
“yes.” ±e inferior articular facets form joints with the axis
(C
2
) below.
±e
axis
, which has a body and the other typical vertebral
processes, is not as specialized as the atlas. In fact, its only unu-
sual feature is the knoblike
dens
(denz; “tooth”) projecting su-
periorly from its body. ±e dens is actually the “missing” body
of the atlas, which fuses with the axis during embryonic devel-
opment. Cradled in the anterior arch of the atlas by the trans-
verse ligament
(Figure 7.21a)
, the dens acts as a pivot for the
rotation of the atlas. Hence, this joint allows you to rotate your
head from side to side to indicate “no.”
Thoracic Vertebrae
±e 12 thoracic vertebrae (T
1
–T
12
) all articulate with the ribs
(see Table 7.2, Figure 7.16, and Figure 7.21b). ±e first looks
much like C
7
, and the last four show a progression toward
respectively, from the pedicle-lamina junctions. ±e smooth joint
surfaces of the articular processes, called
facets
(“little faces”), are
covered with hyaline cartilage. ±e inferior articular processes
of each vertebra form movable joints with the superior articu-
lar processes of the vertebra immediately below. ±us, successive
vertebrae join both at their bodies and at their articular processes.
Regional Vertebral Characteristics
Beyond their common structural features, vertebrae exhibit
variations that allow different regions of the spine to perform
slightly different functions and movements. In general, move-
ments that can occur between vertebrae are (1) flexion and
extension (anterior bending and posterior straightening of the
spine), (2) lateral flexion (bending the
upper body
to the right
or le²), and (3) rotation (in which vertebrae rotate on one an-
other in the longitudinal axis of the spine). ±e regional verte-
bral characteristics described in this section are illustrated and
summarized in
Table 7.2
on p. 223.
Cervical Vertebrae
±e seven cervical vertebrae, identified as C
1
–C
7
, are the small-
est, lightest vertebrae (see Figure 7.16). ±e first two (C
1
and C
2
)
are unusual and we will skip them for the moment. ±e “typical”
Anterior arch
Superior articular
facet
Transverse foramen
Posterior arch
Posterior tubercle
Anterior tubercle
Posterior
Lateral
masses
(a) Superior view of atlas (C
1
)
C
1
C
2
Facet for dens
Transverse
process
Lateral
masses
Transverse foramen
Posterior arch
Posterior tubercle
Posterior
Anterior tubercle
Anterior arch
(b) Inferior view of atlas (C
1
)
Inferior
articular
facet
Posterior
Dens
(c) Superior view of axis (C
2
)
Inferior
articular
process
Body
Superior
articular
facet
Transverse
process
Pedicle
Lamina
Spinous process
Figure 7.20
The first and second cervical vertebrae.
(For a
related image, see
A Brief Atlas of the Human Body
, Figure 18.)
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