Covering, Support, and Movement of the Body
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
. 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
little fountain). Te large, diamond-shaped
is palpable for 1½ to 2 years aFer birth. Te others are
replaced by bone by the end of the ﬁrst year.
Several congenital abnormalities may distort the skull. Most
, a condition in which the right and leF
halves of the palate fail to fuse medially
. 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
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
are convex pos-
teriorly, and an infant’s spine arches, like that of a four-legged
—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
A baby born with a cleft lip and palate.
(a) Superior view
(b) Lateral view
Skull of a newborn.
Notice that the infant’s skull
has more bones than that of an adult. (For a related image, see
Brief Atlas of the Human Body
, Figure 16.)