202
UNIT 2
Covering, Support, and Movement of the Body
7
nasal cavity and the orbits
(Figure 7.3)
. Te
orbits
house the
eyeballs. Several bones of the skull contain air-filled sinuses,
which lighten the skull.
Te skull also has about 85 named openings (foramina, ca-
nals, fissures, etc.). Te most important of these provide pas-
sageways for the spinal cord, the major blood vessels serving the
brain, and the 12 pairs of cranial nerves (numbered I through
XII), which transmit information to and from the brain.
As you read about the bones of the skull, locate each bone on the
different skull views in
Figures 7.4
,
7.5
, and
7.6
. Te skull bones
and their important markings are also summarized in
Table 7.1
(pp. 216–217). Te color-coded boxes before a bone’s name in the
text and in ±able 7.1 correspond to the color of that bone in the
figures. For example, note the color of the frontal bone in ±able 7.1
and see how you can easily find it in Figures 7.4 and 7.5.
Cranium
Te eight cranial bones are the paired parietal and temporal
bones and the unpaired frontal, occipital, sphenoid, and eth-
moid bones. ±ogether, these construct the brain’s protective
bony “helmet.” Because its superior aspect is curved, the cra-
nium is self-bracing. Tis allows the bones to be thin, and, like
an eggshell, the cranium is remarkably strong for its weight.
Frontal Bone
Te shell-shaped
frontal bone
(Figures 7.4a, 7.5, and 7.7) forms
the anterior cranium. It articulates posteriorly with the paired
parietal bones via the prominent
coronal suture
.
Te most anterior part of the frontal bone is the vertical
squamous part
, commonly called the
forehead
. Te frontal
squamous region ends inferiorly at the
supraorbital mar-
gins
, the thickened superior margins of the orbits that lie
under the eyebrows. From here, the frontal bone extends
posteriorly, forming the superior wall of the
orbits
and most
of the
anterior cranial fossa
(Figure 7.7a and b)
. Tis
fossa supports the frontal lobes of the brain. Each supraor-
bital margin is pierced by a
supraorbital foramen (notch)
,
which allows the supraorbital artery and nerve to pass to the
forehead (Figure 7.4a).
Te smooth portion of the frontal bone between the orbits is
the
glabella
(glah-bel
9
ah). Just inferior to this the frontal bone
meets the nasal bones at the
frontonasal suture
(Figure 7.4a).
Te areas lateral to the glabella are riddled internally with si-
nuses, called the
frontal
sinuses
(Figures 7.5c and 7.3).
Parietal Bones and the Major Sutures
Te two large
parietal bones
are curved, rectangular bones that
form most of the superior and lateral aspects of the skull; hence
they form the bulk of the cranial vault. Te four largest sutures
occur where the parietal bones articulate (form a joint) with
other cranial bones:
Te
coronal suture
(kŏ-ro
9
nul), where the parietal bones
meet the frontal bone anteriorly (Figures 7.2a and 7.5)
Te
sagittal suture
, where the parietal bones meet superiorly
at the cranial midline (Figure 7.4b)
Te
lambdoid suture
(lam
9
doid), where the parietal bones
meet the occipital bone posteriorly (Figures 7.2a, 7.4b, and 7.5)
Te
squamous suture
(one on each side), where a parietal
and temporal bone meet on the lateral aspect of the skull
(Figures 7.2a and 7.5)
Occipital Bone
Te
occipital bone
(ok-sip
9
ĭ-tal) forms most of the skull’s pos-
terior wall and base. It articulates anteriorly with the paired
parietal and temporal bones via the
lambdoid
and
occipitomas-
toid sutures
, respectively (Figure 7.5). Te basilar part of the
occipital bone also joins with the sphenoid bone in the cranial
base (Figure 7.6a).
Internally, the occipital bone forms the walls of the
posterior
cranial fossa
(Figures 7.7 and 7.2c), which supports the cerebel-
lum of the brain. In the base of the occipital bone is the
foramen
magnum
(“large hole”) through which the inferior part of the
brain connects with the spinal cord. Te foramen magnum is
flanked laterally by two occipital condyles (Figure 7.6). Te
rockerlike
occipital condyles
articulate with the first vertebra
of the spinal column in a way that permits a nodding (“yes”)
motion of the head. Hidden medially and superiorly to each
occipital condyle is a
hypoglossal canal
(Figure 7.7a), through
which a cranial nerve (XII) passes.
Just superior to the foramen magnum is a median protru-
sion called the
external occipital protuberance
(Figures 7.4b,
7.5, and 7.6). You can feel this knoblike projection just below
Frontal
sinus
Ethmoidal
air cells
Orbit
Orbit
Cranial cavity
Oral
cavity
Maxillary
sinus
Inferior
nasal
concha
Maxilla
Mandible
Ethmoid
bone
Frontal
bone
Zygomatic
bone
Vomer
Nasal
cavity
Figure 7.3
Major cavities of the skull, frontal section.
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