Chapter 7
The Skeleton
201
7
Check Your Understanding
1.
What are the three main parts of the axial skeleton?
2.
Which part of the skeleton—axial or appendicular—is
important in protecting internal organs?
For answers, see Appendix H.
The Skull
Name, describe, and identify the skull bones. Identify their
important markings.
Compare and contrast the major functions of the cranium
and the facial skeleton.
Te
skull
is the body’s most complex bony structure. It is
formed by
cranial
and
facial bones
, 22 in all. Te cranial bones,
or
cranium
(kra
9
ne-um), enclose and protect the fragile brain
and furnish attachment sites for head and neck muscles. Te
facial bones (1) form the framework of the face, (2) contain
cavities for the special sense organs of sight, taste, and smell,
(3) provide openings for air and food passage, (4) secure the
teeth, and (5) anchor the facial muscles of expression, which
we use to show our feelings. As you will see, the individual skull
bones are well suited to their assignments.
Most skull bones are flat bones. Except for the mandible,
which is connected to the rest of the skull by freely movable
joints, all bones of the adult skull are firmly united by interlock-
ing joints called
sutures
(soo
9
cherz). Te suture lines have a
saw-toothed or serrated appearance.
Te major skull sutures, the
coronal
,
sagittal
,
squamous
, and
lambdoid sutures
, connect cranial bones (Figures 7.2a, 7.4b, and
7.5a). Most other skull sutures connect facial bones and are
named according to the specific bones they connect.
Overview of Skull Geography
It is worth surveying basic skull “geography” before describing
the individual bones. With the lower jaw removed, the skull re-
sembles a lopsided, hollow, bony sphere. Te facial bones form
its anterior aspect, and the cranium forms the rest of the skull
(Figure 7.2a)
.
Te cranium can be divided into a vault and a base. Te
cra-
nial vault
, also called the
calvaria
(kal-va
9
re-ah; “bald part of
skull”), forms the superior, lateral, and posterior aspects of the
skull, as well as the forehead. Te
cranial base
forms the skull’s
inferior aspect. Internally, prominent bony ridges divide the
base into three distinct “steps” or fossae—the
anterior
,
middle
,
and
posterior cranial fossae
(Figure 7.2b and c). Te brain sits
snugly in these cranial fossae, completely enclosed by the cra-
nial vault. Overall, the brain is said to occupy the
cranial cavity
.
In addition to the large cranial cavity, the skull has many
smaller cavities. Tese include the middle and internal ear cavi-
ties (carved into the lateral side of its base) and, anteriorly, the
Bones of cranium
Lambdoid
suture
Facial
bones
Anterior cranial
fossa
Middle cranial
fossa
Posterior cranial
fossa
Frontal lobe
of cerebrum
Temporal lobe
of cerebrum
Cerebellum
Posterior
Middle
Anterior
Cranial
fossae
Squamous
suture
(a) Cranial and facial divisions of the skull
(b) Superior view of the cranial fossae
(c) Lateral view of cranial fossae showing the contained
brain regions
Coronal
suture
Figure 7.2
The skull:
Cranial and facial divisions and fossae.
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