Chapter 7
The Skeleton
215
7
Paranasal Sinuses
Five skull bones—the frontal, sphenoid, ethmoid, and paired
maxillary bones—contain mucosa-lined, air-filled sinuses that
give them a rather moth-eaten appearance in an X-ray image.
Tese particular sinuses are called
paranasal
sinuses
because
they cluster around the nasal cavity
(Figure 7.14)
.
Small openings connect the sinuses to the nasal cavity and
act as “two-way streets”: Air enters the sinuses from the nasal
cavity, and mucus formed by the sinus mucosae drains into the
nasal cavity. Te mucosa of the sinuses also helps to warm and
humidify inspired air. Te paranasal sinuses lighten the skull
and enhance the resonance of the voice.
Check Your Understanding
10.
What bones contain the paranasal sinuses?
11.
The perpendicular plates of the palatine bones and the
superior and middle conchae of the ethmoid bone form a
substantial part of the nasal cavity walls. Which bone forms
the roof of that cavity?
12.
What bone forms the bulk of the orbit floor and what sense
organ is found in the orbit of a living person?
For answers, see Appendix H.
The Hyoid Bone
Tough not really part of the skull, the
hyoid bone
(hi
9
oid; “U-
shaped”) lies just inferior to the mandible in the anterior neck, and
looks like a miniature version of it
(Figure 7.15)
. Te hyoid bone is
unique in that it is the only bone of the body that does not articulate
directly with any other bone. Instead, it is anchored by the narrow
stylohyoid ligaments
to the styloid processes of the temporal bones.
Horseshoe-shaped, with a body and two pairs of
horns
, or
cornua
,
the hyoid bone acts as a movable base for the tongue. Its body and
greater horns are attachment points for neck muscles that raise and
lower the larynx during swallowing and speech.
maxillae and the palatine bones. Te nasal cavity is divided into
right and le± parts by the
nasal septum
. Te bony portion of the
septum is formed by the vomer inferiorly and the perpendicular
plate of the ethmoid bone superiorly (Figure 7.13b). A sheet of car-
tilage called the
septal cartilage
completes the septum anteriorly.
Te nasal septum and conchae are covered with a mucus-
secreting mucosa that moistens and warms the entering air and
helps cleanse it of debris. Te scroll-shaped conchae increase the
turbulence of air flowing through the nasal cavity. Tis swirling
forces more of the inhaled air into contact with the warm, damp
mucosa and encourages trapping of airborne particles (dust,
pollen, bacteria) in the sticky mucus.
Frontal
sinus
Ethmoidal
air cells
(sinus)
Maxillary
sinus
Sphenoidal
sinus
Frontal
sinus
Ethmoidal
air cells
Maxillary
sinus
Sphenoidal
sinus
(a) Anterior aspect
(b) Medial aspect
Figure 7.14
Paranasal sinuses.
Greater horn
Lesser horn
Body
Figure 7.15
The hyoid bone, anterior view.
(Text continues on p. 218.)
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