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Mr. Victor Horsley—Cranio-Cerebral Topography.

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indications for the localization on the surface of an average head of the
chief fissures in the cortex, but what is now required is the topographical
determination of the same in the following cases :—

(a) Variations due to variation of cephalic index;

(b) Variations due to age;

(c) Variations due to race;

(d) Variations due to sex;

(e) Variations due to pressure distortion ;*

and it may not be out of place to here allude to the chief points on which
further information is most required.

Some anatomists have, it will be seen, already arranged their facts under
such a classification as permits of these cardinal divisions being preserved,
but unfortunately the methods employed have been so different, and the
measurements given so often only absolute and not relative to some general
index (e. g. the length of the hemisphere, &c), that comparison of the
results obtained by different observers is hardly possible. A very moderate
experience of the practical application of topographical procedure shows
soon that the systems involving arbitrary lines (especially verticals raised
from a base line)f and measurements are apt to mislead, and though giving
perfectly true results in some instances, more frequently fail completely
with serious consequences. I shall endeavour, therefore, to describe the
position of each sulcus and region of the brain with reference to the parts
of the skull covering them, and shall supplement the description of each
by reference to the arbitrary measurements which have from time to time
been recorded; for while disallowing the primary value of such absolute
statements, no one is more ready to admit their worth as corroborative
adjuncts. It ought to be specially noted that even what should be
essential features in such researches are often omitted. Thus it should be

* Not merely has the deformity of the cranium (Broca, Fere, Ecker) to he borne in mind,
but the displacement of the sulci and gyri due to increased intra-cranial pressure.

f Merkel has shown, moreover, that in children the base-line, from the external auditory
meatus to the inferior margin of the orbit, is untrustworthy.

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