Page 118 - My FlipBook

128 ANAT03IY.
the centre of the basilar process of the occipital bone. This spine gives
attachment to what is known as the raphe of the pharynx.
Twenty-first: the Anterior Concti/loid Foramen is just in front of the
condyles of the occipital bone, on the lateral surface of the basilar pro-
cess. This foramen is the external orifice of the hypoglossal canal.
Twenty-second : the Condyloid Processes of the Occipital Bone are
situated on each side of the foramen magnum anteriorly. They are
double-convex articulating facets, upon which the head rocks within the
corresponding concavities of the atlas or first cervical vertebra.

Posterior Region.
The Posterior Division of the base^ of the brain-case is semicircular
in outline. Its anterior boundary extends from the apex of the mastoid
portion of the temporal bone on one side, across the articnlating condyles
of the occipital bone, to the same point on the other side. Its posterior
or semicircular boundary extends from the apex of the mastoid portion
of the temporal bone on one side, upward and backward, joining the
superior curved line of the occipital bone, and passing along this ridge
to the occipital protuberance, from which point it runs forward and
downward on the ridge of the other side to the apex of the mastoid
portion of the temporal bone. The surface of bone included within this
semicircular outline, excluding the condyles, the posterior condyloid
foramina, and the foramen magnum, affords attachment to muscles.
The line forming the anterior boundary of the posterior region not
only separates it from the middle region, but is the axis between the
anterior muscles, which act as the motor power in bowing the head,
from those which antagonize these and raise and draw the head back-
ward : this, therefore, is tlie axis upon which the head oscillates ; its
centre is the point around which the head rotates.
On either side, immediately behind the condyles, are depressions
pierced by foramina leading to the lateral sinuses. These are known
respectively as the posterior condyloid fossae and foramina.

Lateral Regions op the Skull.
The points of interest on the lateral region (see Fig. 60) from the
posterior to the anterior Ijoundary are the mastoid process, the external
auditory meatus, the auditory process, the glenoid fossa, all of which
are parts of tlic tcmpoi-al bone ; the zygomatic arch, formed by union
of the zygomatic; ])rocesses of the temporal and the malar bones ; the
condyloid and coronoid processes of the inferior maxilla.
Two deep fosste mark the lateral region of the skull—one above the
zygomatic arch, known as tlic tcmj)oral fossa, and the other below the
arch, known as the zygomatic fi)ssa.
The Temporal Fossa occupies the greater portion of the lateral region
^ In comparative anatomy this is the posterior half of the roof of the brain-case in
animals, it being above the spinal cord or neural cavity, and the only portion of the
roof formed from cartilage.