Covering, Support, and Movement of the Body
lumbar vertebral structure. Te thoracic vertebrae increase in
size from the ﬁrst to the last. Unique characteristics of these
vertebrae include the following:
Te body is roughly heart shaped. It typically bears two small
facets, commonly called
(half-facets), on each
side, one at the superior edge (the
superior costal facet
the other at the inferior edge (the
inferior costal facet
demifacets receive the heads of the ribs. (Te bodies of ±
vary from this pattern by having only a single facet to
receive their respective ribs.)
Te vertebral foramen is circular.
Te spinous process is long and points sharply downward.
With the exception of ±
, the transverse processes
have facets, the
transverse costal facets
, that articulate with
the tubercles of the ribs.
Te superior and inferior articular facets lie mainly in the
frontal plane, a situation that prevents ﬂexion and extension,
but which allows this region of the spine to rotate. Lateral
ﬂexion, though possible, is restricted by the ribs.
Te lumbar region of the vertebral column, commonly referred
to as the small of the back, receives the most stress. Te en-
hanced weight-bearing function of the ﬁve lumbar vertebrae
) is reﬂected in their sturdier structure. Teir bodies are
massive and kidney shaped in a superior view (see ±able 7.2,
Figure 7.16, and Figure 7.21). Other characteristics typical of
Te pedicles and laminae are shorter and thicker than those
of other vertebrae.
Te spinous processes are short, ﬂat, and hatchet shaped and
are easily seen when a person bends forward. Tese pro-
cesses are robust and project directly backward, adaptations
for the attachment of the large back muscles.
Te vertebral foramen is triangular.
Te orientation of the facets of the articular processes of the
lumbar vertebrae diﬀers substantially from that of the other
vertebra types (see ±able 7.2). Tese modiﬁcations lock the
lumbar vertebrae together and provide stability by prevent-
ing rotation of the lumbar spine. Flexion and extension are
possible (as when you do sit-ups), as is lateral ﬂexion.
Te triangular sacrum, which shapes the posterior wall of
the pelvis, is formed by ﬁve fused vertebrae (S
) in adults
, and see Figure 7.16). It articulates superiorly (via
superior articular processes
) with L
and inferiorly with
the coccyx. Laterally, the sacrum articulates, via its
, with the two hip bones to form the
e-ak) of the pelvis.
e; “high point of
land projecting into the sea”), the anterosuperior margin of
the ﬁrst sacral vertebra, bulges anteriorly into the pelvic cavity.
Te body’s center of gravity lies about 1 cm posterior to this
costal facet (for
tubercle of rib)
Dens of axis
facet (for head
(a) Cervical vertebrae
(c) Lumbar vertebrae
(b) Thoracic vertebrae
Posterolateral views of articulated vertebrae.
Notice the bulbous tip on the spinous process of C
, the vertebra
prominens. (For a related image, see
A Brief Atlas of the Human
, Figures 19, 20, and 21.)