208
UNIT TWO
skulls) through which blood vessels and nerves pass
to the tissues of the forehead. Within the frontal bone
are two
frontal sinuses,
one above each eye near the
midline. The frontal bone is a single bone in adults, but
it develops in two parts (see F
g. 7.31
b
). These halves
grow together and usually completely fuse by the F
fth
or sixth year of life.
2.
Parietal bones.
One parietal (pah-ri
e
˘-tal) bone is
located on each side of the skull just behind the frontal
bone. Each is shaped like a curved plate and has four
borders. Together, the parietal bones form the bulging
sides and roof of the cranium. They are fused at the
midline along the
sagittal suture,
and they meet the
frontal bone along the
coronal suture.
3.
Occipital bone.
The occipital (ok-sip
i-tal) bone joins
the parietal bones along the
lambdoid
(lam
doid)
suture.
It forms the back of the skull and the base of
the cranium. A large opening on its lower surface is
the
foramen magnum,
where the inferior part of the
brainstem connects with the spinal cord. Rounded
processes called
occipital condyles,
located on each
side of the foramen magnum, articulate with the F
rst
vertebra (atlas) of the vertebral column.
or lower jawbone, is a movable bone held to the cranium
by ligaments
(f
gs. 7.17
and
7.19)
. Some facial and cranial
bones together form the orbit of the eye
(f
g. 7.18)
. Plates
26–54 on pages 245–259 show a set of photographs of the
human skull and its parts.
Cranium
The
cranium
(kra
ne-um) encloses and protects the brain,
and its surface provides attachments for muscles that make
chewing and head movements possible. Some of the cranial
bones contain air-filled cavities called
paranasal
sinuses,
lined with mucous membranes and connected by passage-
ways to the nasal cavity. Sinuses reduce the weight of the
skull and increase the intensity of the voice by serving as
resonant sound chambers.
The eight bones of the cranium
(table 7.5)
are as follows:
1.
Frontal bone.
The frontal (frun
tal) bone forms the
anterior portion of the skull above the eyes, including
the forehead, the roof of the nasal cavity, and the roofs
of the orbits (bony sockets) of the eyes. On the upper
margin of each orbit, the frontal bone is marked by a
supraorbital foramen
(or
supraorbital notch
in some
TABLE
7.4
|
Terms Used to Describe Skeletal Structures
Term
Def
nition
Example
Condyle (kon
dīl)
Rounded process that usually articulates with another bone
Occipital condyle of the occipital bone (F
g. 7.20)
Crest (krest)
Narrow, ridgelike projection
Iliac crest of the ilium (F
g. 7.48)
Epicondyle (ep
ı˘-kon
dı¯l)
Projection situated above a condyle
Medial epicondyle of the humerus (F
g. 7.43)
±acet (fas
et)
Small, nearly ²
at surface
±acet of a thoracic vertebra (F
g. 7.36
b
)
±issure (F
sh
ūr)
Cleft or groove
Inferior orbital F
ssure in the orbit of the eye (F
g. 7.18)
±ontanel (fon
tah-nel
)
Soft spot in the skull where membranes cover the space
between bones
Anterior fontanel between the frontal and parietal bones (F
g. 7.31
a
)
±oramen (fo-ra
men)
Opening through a bone that usually serves as a
passageway for blood vessels, nerves, or ligaments
±oramen magnum of the occipital bone (F
g. 7.20)
±ossa (fos
ah)
Relatively deep pit or depression
Olecranon fossa of the humerus (F
g. 7.43
b
)
±ovea (fo
ve-ah)
Tiny pit or depression
±ovea capitis of the femur (F
g. 7.51
b
)
Head (hed)
Enlargement on the end of a bone
Head of the humerus (F
g. 7.43)
Linea (lin
e-ah)
Narrow ridge
Linea aspera of the femur (F
g. 7.51
b
)
Meatus (me-a
tus)
Tubelike passageway within a bone
External acoustic meatus of the temporal bone (F
g. 7.19)
Process (pros
es)
Prominent projection on a bone
Mastoid process of the temporal bone (F
g. 7.19)
Ramus (ra
mus)
Branch or similar extension
Ramus of the mandible (F
g. 7.29
a
)
Sinus (si
nus)
Cavity within a bone
±rontal sinus of the frontal bone (F
g. 7.25)
Spine (spīn)
Thornlike projection
Spine of the scapula (F
g. 7.41
a, b
)
Suture (soo
cher)
Interlocking line of union between bones
Lambdoid suture between the occipital and parietal bones (F
g. 7.19)
Trochanter (tro-kan
ter)
Relatively large process
Greater trochanter of the femur (F
g. 7.51
a
)
Tubercle (tu
ber-kl)
Small, knoblike process
Tubercle of a rib (F
g. 7.39)
Tuberosity (tu
bĕ-ros
ĭ-te)
Knoblike process usually larger than a tubercle
Radial tuberosity of the radius (F
g. 7.44
a
)
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