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62 ANATOMY.

The Sphenoid Bone.
The sphenoid bone is situated across the base of the skull, extending
upward and anteriorly until it joins the frontal and parietal bones. It
is placed mostly in front of, but partially internal to, the temporal bones.
The posterior face of the body of the sphenoid bone articulates Avith the
basilar process of the occipital bone ; anteriorly the articulation is with
the malar and palate bones, the ethmoid, and the vomer, and occasion-
ally, through the inferior angle of its anterior border, with the superior
maxilla. Acting as a key or wedge, the central location of this bone
causes it to enter into the formation of the anterior and middle Ibssa of
the brain-case by the inner, and of the temporal, zygomatic, and spheno-
maxillary fossa by the external, surface ; also the orbital and nasal cav-
ities internally. It forms part of the roof of the pharynx, and the
hamular process of its internal pterygoid plate can be reached through
the mouth just posterior to the tuberosity of the superior maxillary
bone. It gives support to the superior dental arch and origin to three
of the four muscles of mastication. The great sensory nerve of the
teeth and lace and the branch of this nerve governing the muscles of
mastication pass from the brain-case through three of the foramina of
this bone. It also gives passage to the optic, motor oculi, pathetic, and
abducens nerves, the ophthalmic artery and veins, and to two of the
meningeal arteries.
For convenience of study the sphenoid bone is divided into a body
and six processes, three on each side, a greater and lesser wing, and a
pterygoid process composed of two plates. The body of the bone is
cuboidal in shape, having six surfaces—a superior, inferior, anterior,
posterior, and two lateral.
The /Superior Surface (Fig. 21), the most irregular of the six, is
situated within the brain-case. Its anterior border, known as the eth-
moidal spine, is thin, projects forward and slightly upward, and by its
centre articulates with the crista galli of the ethmoid bone. Just poste-
rior to this spine is a smooth, slightly concave surface extending back-
ward to the optic groove and laterally into the lesser wings. This
surface forms i)art of the floor of the anterior fossa of the brain-case.
The optic groove, slightly curved, passes nearly transversely across the
body of the bone, and terminates on either side in the optic foramina.
These foramina transmit the o])tic nerves and the ophthalmic arteries,
wliile the groo\e lodges tlie optic commissure. Just behind the optic
groove, and between it and the pituitary fossa (sella turcica), is a small
surface of bone, the olivary process, \Ahich assists in supporting the
optic commissure. Posterior to this process is a deep concavity, the
pituitary fossa (sella turcica) for the reception of the pituitary body.
All that portion of the bone situated behind this fossa, and between it
and the spheno-oceipital articulation, is termed the dorsum sellse. At
the superior lateral angles of this ])ortion of the bone are the })osterior
clinoid jn'ocesses. The posterior border of the lesser wings terminates
in rounded points, the anterior clinoid processes. At the superior
lateral angle of the anterior border of the pituitary fossa, on the poste-
rior margin of the olivary process, is sometimes seen a small tubercle