Covering, Support, and Movement of the Body
receptors in the nasal cavities to the brain. Projecting superiorly
between the cribriform plates is a triangular process called the
le; “rooster’s comb”). Te outermost
covering of the brain (the dura mater) attaches to the crista galli
and helps secure the brain in the cranial cavity.
of the ethmoid bone projects in-
feriorly in the median plane and forms the superior part of the
nasal septum, which divides the nasal cavity into right and leF
halves (±igure 7.5c and d). ±lanking the perpendicular plate on
each side is a
riddled with sinuses called
dal air cells
(±igures 7.10 and 7.14), for which the bone itself is
sieve). Extending medially from the lateral
masses, the delicately coiled
middle nasal con-
shell), named aFer the conch shells
found on warm ocean beaches, protrude into the nasal cavity
(±igures 7.10 and 7.13a). Te lateral surfaces of the ethmoid’s
lateral masses are called
because they contribute
to the medial walls of the orbits.
are tiny, irregularly shaped bones or bone clus-
ters that occur within sutures, most oFen in the lambdoid su-
ture (±igure 7.4b). Structurally unimportant, their number
varies, and not all skulls exhibit them. Te signiﬁcance of these
tiny bones is unknown.
Check Your Understanding
Look at Figure 7.4. Which of the skull bones illustrated in
view (a) are cranial bones?
Which bone forms the crista galli?
Which skull bones house the external ear canals?
What bones abut one another at the sagittal suture? At the
For answers, see Appendix H.
from the junction of the body and greater wings (±igure 7.9b).
Tey anchor the pterygoid muscles, which are important in
A number of openings in the sphenoid bone are visible in
±igures 7.7 and 7.9. Te
lie anterior to the sella
turcica; they allow the optic nerves (cranial nerves II) to pass to
the eyes. On each side of the sphenoid body is a crescent-shaped
row of four openings. Te anteriormost of these, the
, is a long slit between the greater and lesser wings.
It allows cranial nerves that control eye movements (III, IV, VI)
to enter the orbit. Tis ﬁssure is most obvious in an anterior
view of the skull (±igure 7.4; see also ±igure 7.9b). Te
le) provide passageways
for branches of cranial nerve V (the maxillary and mandibu-
lar nerves, respectively) to reach the face (±igure 7.7). Te fo-
ramen rotundum is in the medial part of the greater wing and
is usually oval, despite its name meaning “round opening.” Te
foramen ovale, a large, oval foramen posterior to the foramen
rotundum, is also visible in an inferior view of the skull (±ig-
ure 7.6). Posterolateral to the foramen ovale is the small
(±igure 7.7); it transmits the
, which serves the internal faces of some cranial bones.
Like the temporal and sphenoid bones, the delicate
has a complex shape
. Lying between the
sphenoid and the nasal bones of the face, it is the most deeply
situated bone of the skull. It forms most of the bony area be-
tween the nasal cavity and the orbits.
Te superior surface of the ethmoid is formed by the paired
rĭ-form) (see also ±igure 7.7),
which help form the roof of the nasal cavities and the ﬂoor of
the anterior cranial fossa. Te cribriform plates are punctured
by tiny holes (
low the ﬁlaments of the olfactory nerves to pass from the smell
The ethmoid bone.
Anterior view. (For related images, see
A Brief Atlas of the
, Figures 3 and 10.)