Its
outer surface is smooth and
convex; it affords attachment to the
temporal muscle, and forms part of the
temporal fossa; on its hinder part is a vertical groove for the
middle temporal artery. A curved line, the
temporal line, or
supramastoid crest, runs backward and upward across its posterior part; it serves for the attachment of the temporal
fascia, and limits the origin of the temporalis muscle. The boundary between the squamous part and the mastoid portion of the bone, as indicated by traces of the original suture, lies about 1 cm. below this line. Projecting from the lower part of the squamous part is a long, arched process, the
zygomatic process. This process is at first directed lateralward, its two surfaces looking upward and downward; it then appears as if twisted inward upon itself, and runs forward, its surfaces now looking medialward and lateralward. The superior border is long, thin, and sharp, and serves for the attachment of the temporal fascia; the inferior, short, thick, and arched, has attached to it some fibers of the
masseter. The lateral surface is convex and
subcutaneous; the medial is
concave, and affords attachment to the masseter. The anterior end is deeply serrated and articulates with the
zygomatic bone. The posterior end is connected to the squamous part by two roots, the anterior and posterior roots. The posterior root, a prolongation of the upper border, is strongly marked; it runs backward above the
external auditory meatus, and is continuous with the temporal line. The anterior root, continuous with the lower border, is short but broad and strong; it is directed medialward and ends in a rounded eminence, the
articular tubercle (eminentia articularis). This tubercle forms the front boundary of the
mandibular fossa, and in the fresh state is covered with cartilage. In front of the articular tubercle is a small triangular area which assists in forming the
infratemporal fossa; this area is separated from the outer surface of the squamous part by a ridge which is continuous behind with the anterior root of the zygomatic process, and in front, in the articulated skull, with the
infratemporal crest on the great wing of the
sphenoid. Between the posterior wall of the
external acoustic meatus and the posterior root of the zygomatic process is the area called the suprameatal triangle (Macewen), or
mastoid fossa, through which an instrument may be pushed into the
tympanic antrum. At the junction of the anterior root with the zygomatic process is a projection for the attachment of the
temporomandibular ligament; and behind the anterior root is an oval depression, forming part of the mandibular fossa, for the reception of the condyle of the mandible. The mandibular fossa (glenoid fossa) is bounded, in front, by the articular tubercle; behind, by the tympanic part of the bone, which separates it from the external acoustic meatus; it is divided into two parts by a narrow slit, the petrotympanic fissure (
Glaserian fissure). The anterior part, formed by the squamous part, is smooth, covered in the fresh state with
cartilage, and articulates with the
condyle of the mandible. Behind this part of the fossa is a small conical eminence; this is the representative of a prominent tubercle which, in some mammals, descends behind the condyle of the mandible, and prevents its backward displacement. The posterior part of the mandibular fossa, formed by the
tympanic part of the bone, is non-articular, and sometimes lodges a portion of the
parotid gland. The
petrotympanic fissure leads into the
middle ear or
tympanic cavity; it lodges the anterior process of the
malleus, and transmits the tympanic branch of the
internal maxillary artery. The
chorda tympani nerve passes through a canal (canal of
Huguier), separated from the anterior edge of the petrotympanic fissure by a thin scale of bone and situated on the lateral side of the
auditory tube, in the retiring angle between the squamous part and the petrous portion of the temporal bone. The
internal surface of the squamous part is concave; it presents depressions corresponding to the convolutions of the temporal lobe of the brain, and grooves for the branches of the middle
meningeal vessels. == Borders ==