warming, and f ltering air as it enters the respiratory
tract. The lateral portions oF the ethmoid bone contain
many small air spaces, the
shows various structures in the nasal cavity.
Projecting upward into the cranial cavity between the
cribriForm plates is a triangular process oF the ethmoid
bone called the
li) (cock’s comb).
Membranes that enclose the brain attach to this process.
shows a view oF the ﬂ oor oF the cranial cavity.
consists oF thirteen immovable bones
and a movable lower jawbone. In addition to Forming the
basic shape oF the Face, these bones provide attachments For
muscles that move the jaw and control Facial expressions.
The bones oF the Facial skeleton are as Follows:
The maxillary (mak
(sing., maxilla, mak-sil
ah; pl., maxillae, mak-sı˘l
Form the upper jaw; together they Form the keystone
oF the Face, because the other immovable Facial bones
articulate with them.
Portions oF these bones comprise the anterior rooF oF
the mouth (
), the ﬂ
oors oF the orbits, and the
sides and ﬂ
oor oF the nasal cavity. They also contain the
sockets oF the upper teeth. Inside the maxillae, lateral to
the nasal cavity, are
These spaces are
the largest oF the sinuses, and they extend From the ﬂ
oF the orbits to the roots oF the upper teeth.
shows the locations oF the maxillary and other paranasal
During development, portions oF the maxillary
grow together and Fuse
along the midline, or median palatine suture. This Forms
the anterior section oF the hard palate (see f
The inFerior border oF each maxillary bone projects
downward, Forming an
projects anteriorly From the
temporal bone in the region oF the external acoustic
meatus. It joins the temporal process oF the zygomatic
bone and helps Form the prominence oF the cheek, the
The sphenoid (sFe
(f g. 7.21)
is wedged between several other bones in the anterior
portion oF the cranium. It consists oF a central part and
two winglike structures that extend laterally toward each
side oF the skull. This bone helps Form the base oF the
cranium, the sides oF the skull, and the ﬂ oors and sides oF
the orbits. Along the midline within the cranial cavity, a
portion oF the sphenoid bone indents to Form the saddle-
si-ka) (Turk’s saddle). In
this depression lies the pituitary gland, which hangs From
the base oF the brain by a stalk.
The sphenoid bone also contains two
These lie side by side and are separated by a bony
septum that projects downward into the nasal cavity.
The ethmoid (eth
is located in Front oF the sphenoid bone. It consists oF
two masses, one on each side oF the nasal cavity, joined
horizontally by thin
These plates Form part oF the rooF oF the nasal cavity,
and nerves associated with the sense oF smell pass
through tiny openings (
) in them.
Portions oF the ethmoid bone also Form sections oF the
oor, orbital walls, and nasal cavity walls. A
projects downward in the midline
From the cribriForm plates to Form most oF the nasal
Delicate, scroll-shaped plates called the
kah) and the
middle nasal concha
project inward From the lateral portions oF the ethmoid
bone toward the perpendicular plate. These bony plates
support mucous membranes that line the nasal cavity.
The mucous membranes, in turn, begin moistening,
The ethmoid bone. (
) Superior view and (
) Posterior view.