• The
mental foramina
are holes that allow passage
of the
mental nerve.
Dentists
use
the
mental
foramina as landmarks to inject anesthetics into
the mental nerve.
Zygomatic bones
(2), or cheekbones, form the cheek
prominences and part of the wall of the eye sockets.
They form joints with the frontal, maxilla, sphenoid,
and temporal bones.
Lacrimal bones
(
LAK-ri-mal
) (2) are the smallest,
thinnest bones on the medial eye socket. They house
the tear ducts, which tunnel through to the nasal
cavity. This is why your nose runs when you cry.
Inferior nasal conchae
(2) project into the nasal
cavity to filter air before it passes toward the trachea
and lungs.
The
vomer
(
VO-mer
) joins with the maxillae and the
palatine bones to form the floor of the nasal cavity.
Along with cartilage and the ethmoid bone, the single
vomer forms the nasal septum, which divides the nasal
cavity into right and left sides.
The Skull Has Many Unique Features
The skull has unique features, such as sutures, sinuses,
and fontanels (soft spots at birth and early infancy):
A
suture
(
SOO-chur
) is a special type of immovable
joint that joins most of the skull bones. There are 4
major sutures in the skull (Figure 5.8):
• The
coronal
(
ko-RO-nal
)
suture
unites the frontal
bone and two parietal bones.
• The
sagittal
(
SAJ-i-tal
)
suture
attaches the two
parietal bones.
• The
lambdoid
(LAM-doyd)
suture
joins the parietal
bones to the occipital bone.
• The
squamous
(
SKWÀ-mus
)
sutures
seal
the
parietal bones to the temporal bones.
Paranasal
sinuses
are
found
in
the
sphenoid,
frontal, ethmoid, and maxillary bones. They produce
mucus, lighten the weight of the skull, and serve as
echo chambers, which produce the unique sounds of
your voice.
F on tan els • Figure 5.9
The fontanels are the soft spots on a baby's head. They allow the bones of the skull to
compress during passage through the birth canal and provide room for the brain to
grow after birth.
Anterior Fontanel
• Diamond-shaped
• Largest fontanel
• Closes 18 - 24 months after birth
Posterior Fontanel
• Diamond-shaped
• Much smaller than anterior fontanel
• Closes 2 months after birth
Anterolateral Fontanels
(2)
• Small, irregular shape
• Normally close about 3 months after birth
Posterolateral Fontanels (2)
• Irregularly shaped
• Begin to close 1 - 2 months after birth
126 CHAPTER 5
The Skeletal System
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