The =temporal bone= (Os temporale) forms the greater part of the lateral
wall of the cranium. It is situated between the occipital behind, the
parietal above, the frontal in front, and the sphenoid below. It
consists of two distinct parts, =squamous= and =petrous=.
1. The =squamous temporal= (Squama temporalis) is a shell-like plate
which has two surfaces and four borders.
The =internal surface= (Facies cerebralis) is largely overlapped by the
surrounding bones, but its central part is free and presents digital
impressions and vascular grooves.
The =external surface= (Facies temporalis) is convex, and enters into
the formation of the temporal fossa. From its lower part there springs
the =zygomatic process= (Processus zygomaticus), which forms the
external boundary of the temporal fossa. It is at first directed
outward, and is wide and flattened dorso-ventrally. It then turns
forward, becomes narrower, and is twisted so that its surfaces are
internal and external. Its anterior end is pointed and joins the
zygomatic process of the malar bone, with which it forms the =zygomatic
arch= (Arcus zygomaticus). The narrow anterior part has a convex outer
surface and a concave inner one. Its upper border has a rough area for
articulation with the supraorbital process of the frontal. Its lower
border is wide and rough. The wide posterior part presents on its
ventral face a surface for articulation with the condyle of the
mandible. This surface consists of a transversely elongated =condyle=
(Tuberculum articulare), behind which is the =glenoid fossa= (Fossa
mandibularis). The fossa is limited behind by the =postglenoid process=,
the anterior surface of which is articular. Behind this process is a
fossa in which is the external opening of the parieto-temporal canal.
The dorsal surface is concave and forms the outer boundary of the
temporal fossa. The superior border is sinuous and is continuous behind
with the temporal crest.
The =posterior process= (Processus posterior) springs from the posterior
part of the squama. Its external surface is crossed by the temporal
crest, which forms here the outer limit of the temporal fossa. The
internal surface forms the outer boundary of the parieto-temporal canal,
and is elsewhere applied to the petrous portion. It divides into two
branches, upper and lower; the upper branch unites with the occipital
bone, while the lower one curves downward behind the external auditory
process and overlaps the mastoid process.
The =superior border= of the squamous temporal articulates with the
parietal, forming the =parieto-temporal suture=. The =inferior border=
joins the temporal wing of the sphenoid at the =spheno-squamous suture=.
The =anterior border= unites with the frontal bone, and the =posterior=
with the parietal.
2. The =petrous temporal= (Os petrosum) is placed between the occipital
behind and the parietal in front, and is largely overlapped externally
by the squamous temporal. It has the form of a four-sided pyramid, the
base of which is ventral.
The =external surface= is mainly concealed by the squamous temporal, but
two features are visible. A short tube of bone, the =external auditory
process=, protrudes from the lowest part through the notch of the
squamous temporal. The process is directed outward, upward, and a little
forward. It gives attachment to the annular cartilage of the ear. Its
lumen, the =external auditory meatus= (Meatus acusticus externus),
conducts to the cavity of the middle ear (tympanum) in the dry skull,
but is separated from it by the tympanic membrane in the natural state.
The =mastoid process= projects ventrally in the interval between the
posterior process of the squamous temporal and the root of the
paramastoid (or styloid) process of the occipital bone; its outer
surface is crossed by a curved groove which leads to the
parieto-temporal canal.
The =internal surface= faces into the cerebellar fossa of the cranium.
It is concave and smooth but irregular. In its lower part is the
entrance to a short canal, the =internal auditory meatus=, which
transmits the seventh and eighth cranial nerves.
The fundus of the meatus is divided by a crest into a superior and an
inferior fossa. In the superior one is the origin of the =facial
canal=, which curves through the bone and opens externally at the
stylo-mastoid foramen; it transmits the facial (seventh cranial)
nerve. The inferior fossa presents small foramina for the passage of
fibers of the auditory (eighth cranial) nerve.
Behind the meatus and near the posterior margin of the surface is the
slit-like opening of the aquæductus vestibuli, covered by a scale of
bone. Below this is a narrow fissure, the orifice of the aquæductus
cochleæ.
The =anterior surface= looks upward and forward. The outer part
articulates with the parietal bone and the inner part faces into the
cerebral fossa of the cranium. A sharp border, the =petrosal crest=
(Crista petrosa), separates this surface from the inner one.
The =posterior surface= joins the lateral part of the occipital bone.
The =base forms= the outer boundary of the foramen lacerum basis cranii.
It is very irregular and presents a number of important features. The
=hyoid process= is a short rod which projects downward and forward below
the base of the external auditory process, inclosed in a bony tube; it
is connected by a bar of cartilage with the hyoid bone. The
=stylo-mastoid foramen= is situated between the root of the hyoid
process and the mastoid process; it is the external opening of the
facial canal, through which the facial nerve emerges. The =bulla ossea=
is a considerable eminence situated centrally; it is thin-walled and
incloses a cavity which is part of the tympanum. The =muscular
process=[14] is a sharp spine which projects downward and forward from
the anterior part of the base; it gives origin to the tensor and levator
palati muscles. External to the root of the preceding is the small
=petro-tympanic= or =Glaserian fissure= (Fissura petro-tympanica) for
the passage of the chorda tympani nerve. The osseous =Eustachian tube=
is a semicanal at the inner side of the root of the muscular process; it
leads to the tympanum. At the inner side of the preceding is the
slit-like orifice of the petrosal canal, which communicates with the
facial canal.
The =apex= projects upward and backward between the squamous temporal
and the occipital bone.
=Development.=—The petrous temporal may be regarded as consisting of
petro-mastoid and tympanic parts. The latter includes the external
auditory process, the bulla ossea, and the muscular process; it is
developed in membrane. The petro-mastoid is developed in the
cartilaginous ear capsule. Its petrous part consists of very dense bone
which contains the labyrinth or internal ear and forms the inner wall of
the tympanum.
The =parieto-temporal canal= (Meatus temporalis) is a continuation of
the transverse groove which extends outward from the base of the
tentorium osseum. It is directed downward, forward, and somewhat
outward, and opens externally in front of the root of the auditory
process. It is bounded by the squamous temporal externally, the petrous
behind, and the parietal in front and internally. Several foramina open
from it into the temporal fossa. It contains a large vein (Vena
cerebralis dorsalis), the continuation of the transverse sinus of the
dura mater.
The =foramen lacerum basis cranii= (Foramen lacerum et jugulare) is a
large irregular opening in the cranial base, bounded internally by the
basilar part of the occipital bone, externally by the petrous temporal,
and in front by the temporal wing of the sphenoid. It consists of a
large anterior part (Foramen lacerum anterius), and a narrow posterior
part (Foramen lacerum posterius s. jugulare). It transmits the internal
carotid artery, the middle meningeal artery, the mandibular, ninth,
tenth, and eleventh cranial nerves, and the inferior cerebral vein.
In the fresh state the foramen is occupied by a dense fibrous membrane
which is perforated by apertures for the various structures
transmitted. Thus there are three openings in front for the internal
carotid artery, the mandibular nerve, and the middle meningeal artery;
these are (from within outward) the foramen caroticum, ovale,
spinosum.
(B) BONES OF THE FACE
The bones of the face (Ossa faciei) are the Maxilla, Premaxilla,
Palatine, Pterygoid, Nasal, Lacrimal, Malar, Superior Turbinal, Inferior
Turbinal, Vomer, Mandible, and Hyoid. The last three are single, the
others paired.