208
UNIT 2
Covering, Support, and Movement of the Body
7
slope of this ridge lies in the posterior cranial fossa; the anterior
slope is in the middle cranial fossa. Together, the sphenoid bone
and the petrous portions of the temporal bones construct the
middle cranial fossa
(Figures 7.7 and 7.2b), which supports the
temporal lobes of the brain.
Several foramina penetrate the bone of the petrous region
(Figure 7.6). ±e large
jugular foramen
at the junction of the
occipital and petrous temporal bones allows passage of the in-
ternal jugular vein and three cranial nerves (IX, X, and XI). ±e
carotid canal
(kar-rot
9
id), just anterior to the jugular foramen,
transmits the internal carotid artery into the cranial cavity. ±e
two internal carotid arteries supply blood to over 80% of the cer-
ebral hemispheres of the brain; their closeness to the internal ear
cavities explains why, during excitement or exertion, we some-
times hear our rapid pulse as a thundering sound in the head.
±e
foramen lacerum
(la
9
ser-um) is a jagged opening (
lacerum
5
torn or lacerated) between the petrous temporal bone and the
sphenoid bone. It is almost completely closed by cartilage in a
living person, but it is conspicuous in a dried skull, and students
usually ask its name. ±e
internal acoustic meatus
, positioned
superolateral to the jugular foramen (Figures 7.5c and d, and
7.7), transmits cranial nerves VII and VIII.
A conspicuous feature of the petrous part of the temporal
bone is the
mastoid process
(mas
9
toid; “breast”), which acts
as an anchoring site for some neck muscles (Figures 7.5, 7.6,
and 7.8). ±is process can be felt as a lump just posterior to the
ear. ±e needle-like
styloid process
(sti
9
loid; “stakelike”) is an
attachment point for several tongue and neck muscles and for
a ligament that secures the hyoid bone of the neck to the skull
(see Figure 7.15). ±e
stylomastoid foramen
, between the sty-
loid and mastoid processes, allows cranial nerve VII (the facial
nerve) to leave the skull (Figure 7.6).
Temporal Bones
±e two
temporal bones
are best viewed on the lateral skull
surface (Figure 7.5). ±ey lie inferior to the parietal bones and
meet them at the squamous sutures. ±e temporal bones form
the inferolateral aspects of the skull and parts of the cranial base.
±e use of the terms
temple
and
temporal
, from the Latin word
temporum
, meaning “time,” came about because gray hairs, a
sign of time’s passing, usually appear first at the temples.
Each temporal bone has a complicated shape
(Figure 7.8)
and is
described in terms of its three major parts, the
squamous
,
tympanic
,
and
petrous parts
. ±e flaring
squamous part
abuts the squamous
suture. It has a barlike
zygomatic process
that meets the zygomatic
bone of the face anteriorly. Together, these two bony structures form
the
zygomatic arch
, which you can feel as the projection of your
cheek (
zygoma
5
cheekbone). ±e small, oval
mandibular fossa
(man-dib
9
u-lar) on the inferior surface of the zygomatic process re-
ceives the condylar process of the mandible (lower jawbone), form-
ing the freely movable
temporomandibular joint
.
±e
tympanic part
(tim-pan
9
ik; “eardrum”) (Figure 7.8) of
the temporal bone surrounds the
external acoustic meatus
,
or external ear canal, through which sound enters the ear. ±e
external acoustic meatus and the eardrum at its deep end are
part of the
external ear
. In a dried skull, the eardrum has been
removed and part of the middle ear cavity deep to the external
meatus can also be seen.
±e thick
petrous part
(pet
9
rus) of the temporal bone houses
the
middle
and
internal ear cavities
, which contain sensory re-
ceptors for hearing and balance. Extending from the occipital
bone posteriorly to the sphenoid bone anteriorly, it contrib-
utes to the cranial base (Figures 7.6 and 7.7). In the floor of the
cranial cavity, the petrous part of the temporal bone looks like
a miniature mountain ridge (
petrous
5
rocky). ±e posterior
Petrous
part
External acoustic
meatus
Mastoid process
Styloid process
Tympanic
part
Mandibular
fossa
Zygomatic
process
Squamous
part
Figure 7.8
The temporal bone.
Right lateral view. (For related images, see
A Brief Atlas of
the Human Body
, Figures 2 and 8.)
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