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Cunningham Memoirs.

ptero-frontal suture to reach the posterior point of the pterion, whence it
runs downwards or beneath the ptero-temporal suture, but leaving it before
reaching the ridge of the pterygoid aspect and surface of the temporal bone
to pass backwards to the root of the zygoma, along which it lies at the junction
of the process with the skull. Further backwards the line rises gently close
above the auditory meatus. Immediately behind the vertical diameter of the
meatus the margin of the hemisphere is seen to rise steeply to clear the
roof of the tympanum and vestibule as previously described. Having
accomplished this, the line passes just above, or at the change of the
squamous suture into the parieto-mastoid suture. Above this last it runs,
rising gently to reach an acme vertically over the asterion, and thus forms
the prse-occipital notch. Descending again, it soon crosses the lambdoid
suture a short distance above the asterion, and then runs down to almost
reach the superior curved line ; thence turning up again at an angle of
about 30° as far as the middle of the curved line, and following consequently
the direction of the latter to reach horizontally the middle line
just above the Torcular Herophili, or in other words (i. e. externally) the
occipital protuberance.

II. Topography of the Cerebrum viewed as a whole—its Surfaces.—

The customary anatomical description of the surface of the cerebral hemisphere
requires a little alteration to adapt it to our present purpose.
Topographically speaking the principal points to be studied are :—

1. The inclination and direction of the surfaces.

2. The external position of limiting points, chiefly with reference to

the basal aspect.

The inferior {and outer, as it actually is) surface of the frontal lobe rests
on the orbital plate of the frontal bone, and adjoining parts of the ethmoid
and sphenoid in so far as these enter into the composition of the anterior
fossa, the anterior and outer limits having been already described. The
posterior margin of the orbital surface is easily defined externally as a line
joining the posterior extremities of both portions. This line consequently