244
UNIT 2
Covering, Support, and Movement of the Body
7
Developmental Aspects
of the Skeleton
Define fontanelles and indicate their significance.
Describe how skeletal proportions change through life.
Discuss how age-related skeletal changes may affect health.
Te membrane bones of the skull start to ossify late in the second
month of development. Te rapid deposit of bone matrix at the
ossification centers produces cone-shaped protrusions in the de-
veloping bones. At birth, the skull bones are still incomplete and
are connected by as yet unossified remnants of fibrous membranes
called
fontanelles
(fon
0
tah-nelz
9
)
(Figure 7.36)
. Te fontanelles
allow the infant’s head to be compressed slightly during birth, and
they accommodate brain growth in the fetus and infant. A baby’s
pulse can be felt surging in these “soF spots”; hence their name
(
fontanelle
5
little fountain). Te large, diamond-shaped
anterior
fontanelle
is palpable for 1½ to 2 years aFer birth. Te others are
replaced by bone by the end of the first year.
Homeostatic Imbalance
7.9
Several congenital abnormalities may distort the skull. Most
common is
cleF palate
, a condition in which the right and leF
halves of the palate fail to fuse medially
(Figure 7.37)
. Te per-
sistent opening between the oral and nasal cavities interferes
with sucking and can lead to aspiration (inhalation) of food into
the lungs and
aspiration pneumonia
.
Te skeleton changes throughout life, but the changes in child-
hood are most dramatic. At birth, the baby’s cranium is huge
relative to its face, and several bones are still unfused (e.g., the
mandible and frontal bones). Te maxillae and mandible are
foreshortened, and the contours of the face are flat (±igure 7.39).
By 9 months aFer birth, the cranium is already half of its adult
size (volume) because of the rapid growth of the brain. By 8 to
9 years, the cranium has almost reached adult proportions.
Between the ages of 6 and 13, the head appears to enlarge
substantially as the face literally grows out from the skull. Te
jaws, cheekbones, and nose become more prominent. Tese fa-
cial changes are correlated with the expansion of the nose and
paranasal sinuses, and development of the permanent teeth.
±igure 7.39 tracks how differential bone growth alters body pro-
portions throughout life.
Only the thoracic and sacral curvatures are well developed
at birth. Tese so-called
primary curvatures
are convex pos-
teriorly, and an infant’s spine arches, like that of a four-legged
animal
(Figure 7.38)
.
Te
secondary curvatures
—cervical and lumbar—are convex
anteriorly and are associated with a child’s development. Tey
result from reshaping of the intervertebral discs rather than from
modifications of the vertebrae. Te cervical curvature is present
before birth but is not pronounced until the baby starts to liF
its head (at about 3 months). Te lumbar curvature develops
when the baby begins to walk (at about 12 months). Te lumbar
curvature positions the weight of the trunk over the body’s center
of gravity, providing optimal balance when standing.
Vertebral problems (scoliosis or lordosis; see ±igure 7.17a
and c) may appear during the early school years, when rapid
growth of the limb bones stretches many muscles. During the
Figure 7.37
A baby born with a cleft lip and palate.
Frontal bone
Ossification
center
Occipital
bone
(a) Superior view
Posterior fontanelle
Parietal bone
Anterior
fontanelle
Frontal suture
(b) Lateral view
Posterior
fontanelle
Mastoid
fontanelle
Parietal bone
Ossification
center
Occipital bone
Temporal bone
(squamous portion)
Frontal bone
Sphenoidal
fontanelle
Figure 7.36
Skull of a newborn.
Notice that the infant’s skull
has more bones than that of an adult. (For a related image, see
A
Brief Atlas of the Human Body
, Figure 16.)
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