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BONES. 67

with the lateral border forms the anterior clinoid process. The inter-
nal aspect of this border at the point where it joins the body of the bone
is pierced by the optic foramen, which follows the line of junction of the
lesser wing with the body.
The Lateral Border is free, smooth, and rounded, and is received into
the fissure of Sylvius of the brain.
The Superior Pedicle is broad, thin, and forms the roof of the optic
foramen.
The Inferior Pedicle forms the base and external boundary of the
ojjtie foramen. It is in shaj^e a three-sided prism.
The Optic Foramen transmits the optic nerve and the ophthalmic
artery.
The Pterygoid Processes project downward from the junction of the
great wings with the body of the bone. Each process is composed of
two plates, which separate at their lower third, forming a triangular
notch for the reception of the pyramidal process of the palate bone, with
which it articulates by a serrated surface. Above the pterygoid notch,
anteriorly, is a smooth, triangular surface of bone which forms the pos-
terior wall of the spheno-maxillary fossa. At the upper border of this
triangular surface is seen the foramen rotund um, while at its superior
inner angle, or apex, will be found the anterior opening of the Vidian
canal. It is just at this point that the spheno-palatine or Meckel's gan-
glion is situated.
The external plate is broader than the internal. It is a continuation
of the great wing, passing downward and outward, forming a concavity
externally. Its anterior border articulates with the palate bone near to
the tuberosity of the superior maxilla. Its external surface gives origin
to the lower head of the external pterygoid muscle. The upper two-
thirds of these two plates of bone are joined anteriorly. Posteriorly
they diverge, forming the pterygoid fossa.
The Pterygoid Fossa.—The internal pterygoid muscle in this fossa
arises from the outer plate only.
The inner plate is vertical, longer, and thinner than the outer plate.
Its anterior border articulates M'ith the palate bone. The posterior bor-
der is free, and forms the distal and lateral boundary of the posterior
naris.
The Scaphoid Fossa.—Above the pterygoid fossa, and between it and
the posterior opening of the Vidian canal, is situated the scaphoid fossa.
It gives origin to the tensor palati muscle, the tendon of which descends
the outer siu'face of the internal pterygoid plate to its inferior extremity,
winds around the hook-like projection, the hamular process, and is
inserted into the soft palate.
The hamular process can be felt at the posterior lateral portion of
the mouth, behind the tuberosity of the superior maxilla.
Vaginal Process.—The internal pterygoid plate at its upper internal
surface curves inwardly until it meets and partially leaves the body of
the bone. The extremity of this curve is called the vaginal process.
The internal surface of the external pterygoid plate forms part of the
external wall of the nasal chamber.
Development.—The sphenoid bone is developed from fourteen cen-