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Me. Victor Horsley—Cranio-Cerebral Topography.

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level of the upper border of the zygoma. It is extraordinary to what a
degree this simple projection has been misrepresented by all previous
authors. Vide the drawings of Turner, Hefftler, Foulhouze, &c.

Finally, from 7 tracings which Professor Cunningham has kindly given
me of infants and foetuses, full term, as follows :—No. 1, new born, <? ; No. 2,
new born, 2 ; No. 3, three months, ? ; No. 4, six months, & ; No. 5, seven
and a-half months; No. 6, seven and a-half months; No. 7, eight months, $ —
it is evident that in early life the lower border of the temporal lobe either
coincides with or only just passes beneath the upper border of the zygoma.
Hence the relationship of the two lines as given for children of maturer age
and for adults is one of further development.

Viewed sagittally the margin of the hemisphere is readily traced. The
line of the edge of the hemisphere runs parallel to the middle line of the
skull, i.e. the sagittal suture, and distant from it about 5 mm. in the adult,
owing to the presence of the longitudinal sinus. As this vessel often lies
rather to the right of the middle line, the margin of the left hemisphere
commonly approaches the sagittal suture more closely than does the right;
but in either case the separation only involves the actual margin, since the
sinus is triangular in transverse section, and consequently the mesial
surfaces of the hemispheres lie close to the falx cerebri in the middle line,
immediately below the depth of the sinus. Similarly the margins of the
hemispheres are more separated posteriorly than anteriorly on account of
the sinus widening from before backwards. In surgical practice, of course,
the localization of the sinus is of far more importance than that of the
edge of the hemisphere, but the necessity of defining the margin is obvious
when the determination of a lesion therein is required.

In front the margin of the hemisphere descending to the level of the
olfactory bulb reaches almost to the nasal suture, connecting the frontal and
nasal bones, hence the choice of this point in estimating the length of the
hemisphere. From this lowest point a line to indicate the margin may be
drawn upwards and outwards over the superciliary ridge (the supra-orbital
line) curving round to just below the points uniting the minimal breadth of
the frontal bone (Broca), (the end of the supra-orbital diameter of the anthropologists
). From this point the marginal line runs backward across the

ROYAL IRISH ACADEMY.-CUNNINGHAM MEilOIRS, NO. YII. [40]