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56 ANATOMY.
The styloid process may also be added to this division, and studied sepa-
rately, as it has its own centre of ossification.
The Squwnous Portion is divided into three parts—the ascending, the
horizontal, and the part forming the wall of the glenoid cavity. The
ascending portion is concavo-convex, the convexity, which is almost per-
pendicular, being smooth and giving origin to the temporal muscle. It
is marked by two grooves running upward, one near its anterior border,
the other at the posterior termination of the zygomatic arch. They in-
dicate the position of the deep temporal arteries at the upper border of
the squamous portion, where it articulates with the parietal bone, form-
ing the temporo-parietal suture (squamous) ; the outer table is extended
considerably beyond the inner, thus forming a scale or bevel at the
expense of the inner border. This scale overlaps the corresponding
surface of the parietal bone. That portion which forms the suture is
bevelled inwardly, the middle portion is serrated, and the lower portion
anteriorly is bevelled outwardly.
The zygomatic process (horizontal portion) has a triangidar origin
from the squamous portion of the bone, where it bends abruptly inward
toward the base of the skull, and has three roots. Its large posterior
root passes backward, above the external auditory meatus, behind which
it forms the boundary betAveen the squamous and the mastoid portions
of the bone, and is called the supramastoid ridge ; this then curves
upward, and, uniting with the temporal ridge of the parietal bone,
forms the posterior boundary of the temporal fossa. The middle root
forms the outer boundary of the glenoid fossa; then bends inwardly
and terminates in the posterior glenoid process at the outer extremity
of the t»:lenoid fissure. The anterior root runs directlv inward in front
of the glenoid fossa, forming its anterior border, which is also known
as the eminentia articularis. At the juncture of this root with the
zygomatic process is a rounded eminence, called the tubercle, for the
attachment of the external lateral ligament of the inferior maxilla.
The zygomatic process projects outwardly from the skull about one-
fourth of an inch, and has an upper and a lower surface ; it then turns
upon itself, and its posterior edge, which is thin, forms the superior
border. The inferior border is about half an inch in length, its
extremity being serrated and bevelled at the expense of the inferior
border, where it articulates with the zygomatic process of the malar
bone. The masseter muscle arises in part from the lower border of this
process, and each side of the upper border gives attachment to the two
layers of the tem])oral fascia.
The Glenoid Fo^m is situated at the base of the squamous portion
of the bone. It is bounded in front by the anterior root of the zygoma,
behind by the tympanic plate of the petrous portion, externally by the
auditory process and middle root of the zygoma. It is divided into an
anterior and posterior ])ortion by the glenoid fissure (fissure Glaserius,
the squamoso-tympanic suture). The anterior Jialf is the articulating
portion of the fossa, and is occupied by the condyle of the inferior
maxilla. In man this is a complicated articulation, which will be
described subsequently. The posterior half accommodates the upper
portion of the parotid gland.