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126 ANAT03IY.

one side, across the body of the sphenoid ])one, to the same process on
the other side.
This region is symmetrically divided by the descending plate of the
ethmoid and the rostrum of the sphenoid bone.
Tlie structures forming the anterior division on each side of this cen-
tral division, from within outwardly, arc, tirst, the cribriform plate of
the ethmoid bone, which forms the roof to the nasal chamber ; second,
the lateral masses of the ethmoid, which, through its os planum, forms
third, the orbital
a portion of the inner >vall of the orbital cavity ;
plate of the frontal bone and a portion of the lesser wing of the sphe-
noid ; and fourch, the great wing of the sphenoid, together with the
rough articulating surface of the external angular process of the frontal
bone.
Immediately in front of the ethmoid bone, and between the internal
angular processes of the frontal bone, will be found the articulating sur-
faces for the lachrymal, maxillary, and nasal bones.
The foramina of this region have already been described. They are
as follows : The perforations of the cribriform plate of the ethmoid
bone, the anterior and posterior ethmoidal Ibramina, the supraorbital,
anterior lacerated, and optic foramina within the orbital cavity, and the
foramen rotundum and Vidian canal.
The Median or Cervical Region is bounded anteriorly by the inferior
border of the great wing of the sphenoid bone, and by a line drawn from
the base of the anterior surface of the pterygoid process on one side,
across the body of the sphenoid bone, to the same point on the other.
The lateral boundary is formed by a line drawn along the pterygoid
ridge of the sphenoid bone, extending to the extreme outer point of the
glenoid fossa, and thence to the apex of the mastoid portion of the tem-
poral bone. The posterior boundary is formed by a line drawn from
the apex of the mastoid portion of the temporal bone on one side to the
same point on the other, crossing the centre of the condyloid processes
of the occi])ital bone and the foramen magnum.
A line drawn froiu the anterior portion of the rostrum of the sphenoid
bone to the centre of the anterior portion of the foramen magnum Avill
divide the middle region into two symmetrical halves.
The structures forming this division on each side of the central
line from its anterior to its })osterior portion are as folloM's
:
First : the P(eri/e/oid Process^ which extends downwardly.
Second : the Pterygoid Fossa, which is situated posteriorly between the
plates composing the jiterygoid jirocess. The outer plate of this process
gives origin witliin the fossa to the internal pterygoid muscle.
Tiiird : the XcapJioid Fossa, at the base of the roots of the pterygoid
fossa posteriorly. This fossa gives origin to the tensor palati muscle.
Fourth : the Vaginal Process, situated at the base of the internal
pterygoid plate, at its junction with the body of the bone.
Fifth: the Inferior Surface of the Great Wing of the Sphenoid Bone.
—This surface is smooth, concave, and quadrilateral ; it is situated just
external to i\\v jitcrygoid jiroccss. It gives origin to the external liead
of the external ])terygoid nuiscle.
Sixth : the Foramen Ovale, situated in the posterior portion of the