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70 ANATOMY. ;

eminence is ahvays one, and generally two, curved lines : the lower one
marks the superior boundary of the temporal fossa, and divides the
bone into two portions ; the upper one limits the attachment of the tem-
poral aponeurosis. The superior portion of the external surface is rough,
porous, and covered by the aponeurosis of the occipito-frontalis muscle.
Close to the upper border, near the posterior sujDerior angle, in one bone
or the other, is a small foramen, the parietal foramen, M^hich transmits a
vein to the superior longitudinal sinus. This foramen is not constant
it varies in size in different bones : sometimes it is situated between the
two bones. The inferior portion is flatter and smoother than the supe-
rior, and forms part of the temporal fossa.
The Infernal Surface (Fig. 26) is deeply concave, and forms the pari-
etal fossa. It presents eminences and depressions corresponding to the
Fig. 26.

Post Slip Ant. Sup
A iigle r* Angle

Left Parietal Bone, internal surface.
convolutions of the cerebrum. Near the anterior inferior angle, at
a point posterior to the middle of the inferior border, will be seen
the connncncement of grooves which extend upwardly and divide
into numerous branches. These grooves are for the accommodation
of the anterior and posterior branches of the middle meningeal arteries.
Sometimes the groove commencing at the anterior inferior angle has its
origin in a long canal. Along the inner aspect of the su])erior border
of this bone is a slight depression, which, together with itri fellow on