Fontanels
(fonta-NELZ) are mesenchyme-filled spaces
between the cranial bones of infants at birth (
Figure
5.9
). These soft spots compress as the baby passes
through the birth canal. For a short time after birth,
the fontanels also provide room for the brain to grow.
Within the first two years of life, they are replaced
by bone via intramembranous ossification. As the
fontanels close, the bones of the skull fuse to form the
sutures.
The
hyoid bone
(Hl-oyd)
is located in the neck,
between the mandible and larynx (see Figure 5.8). It
is suspended from the styloid process of each temporal
bone by ligaments and muscle. It supports the tongue,
stabilizes the airways, and provides attachment points
for tongue, neck, and pharyngeal muscles.
The Vertebral Column Contains 26
Vertebrae
The vertebral column (also called the
spine, spinal column,
or
backbone)
protects the spinal cord, supports the head and
neck, permits movement, and provides attachment points
for the back muscles, ribs, and pelvis. The vertebral col-
umn consists of 26 bones called
vertebrae
(VER-te-bre;
singular is vertebra). Vertebrae have the following general
structures (see
Figure 5.10
on the next page): •
The
body
is the thick, disc-shaped anterior portion
that bears weight.
The
vertebral arch
extends posteriorly from the body.
It consists of two short, thick processes called
pedicles
(PED-i-kuls) that project backward and join with two
flat parts called
laminae
(LAM-i-ne). The
vertebral
foramen
is an opening through which the spinal cord
passes.
Seven processes arise from the vertebral arch:
Spinous process
(1) projects from the laminae; it serves
as attachment point for muscles.
Transverse processes
(2) are lateral extensions that
serve as attachment points for muscles.
Superior articular processes
(2) attach to vertebra above.
Inferior articular processes
(2) attach to vertebra below.
The exact shape and structure of the vertebrae vary with
the region where they are located:
Cervical vertebrae
(7) are in the neck region. Each
cervical vertebra has three openings (foramina): a
larger, central opening (vertebral foramen) for the
spinal cord, and two transverse foramina, passages for
blood vessels and nerves.
Thoracic vertebrae
(12) are posterior to the chest
cavity and serve as attachments for the ribs.
Lumbar vertebrae
(5) form the lower back.
The
sacrum
(SA-krum) consists of 5 fused vertebrae
and forms the posterior wall of the pelvis. Blood vessels
and nerves pass through the openings.
The
coccyx
(KOK-siks), sometimes referred to as the
tailbone, consists of 4 fused vertebrae.
Note that the adult vertebral column has four curved re-
gions: cervical, thoracic, lumbar, and sacral. The curves
develop from a single, concave curve in the fetus. When
the infant begins holding its head erect (at approximate-
ly three months of age), the cervical curve develops. The
lumbar curve develops later, when the child starts sit-
ting up, standing, and walking. Sometimes, abnormal
curvatures develop in the spine due to uneven growth
or weakening of the bones and/or musculature associated
with the spine (see Figure 5.10):
Scoliosis
—A lateral curvature that causes the spine to
“lean” to one side more than the other. This condition
is seen more commonly in females than in males.
Kyphosis
—An exaggeration of the thoracic curve that
forms a “humpback” appearance.
Lordosis
—An exaggeration of the lumbar curve that
causes a “sway back.”
CONCEPT CHECK
1.
Which
cranial bones form the floor of the cra-
nium?
2.
How
do sutures form from the anterior fontanel?
3.
Compare
and contrast the five types of verte-
brae.
The Axial Skeleton is Composed of 80 Bones 127
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