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Mr. Victor Horsley—Cranio-Cerebral Topography.

321

In the adult.—In the adult, on the contrary, it is usually conceded by
most observers that the posterior limb of the Sylvian fissure coincides with
the highest point of the squamo-parietal suture. While this is sufficiently
generally true, it is to be noted that the correspondence may be incomplete
, and the fissure consequently above or below the suture. This is
possibly to be chiefly ascribed to defect of the growth, which, as Professor
Cunningham has sufficiently shown, occurs in the squamous part of the
temporal bone, causing the latter to push upwards and overlap the corresponding
portion of the parietal bone. In any case, however, the possible
error of localization ought* not in absolute measurement amount to more
than five millimetres, except in very rare cases, indeed; therefore, for
" practical" purposes (which usually means the employment of a fairly
large opening), the removal of even a centimetre disc would expose the
fissure with almost absolute certainty.

The determination of the topography of the hinder extremity of the
posterior limb is, however, not so simple.

The posterior limb of the Sylvian fissure customarily terminates in one
of two ways—(a) it suddenly turns upwards at an angle (about 100°),
often bifurcating and ending close to the parietal eminence; (b) it continues
in the line of the limb and terminates below the parietal eminence,
but little further back than the vertical plane of the termination in (a),

The possibility of correctly estimating the situation of the end of this
limb is not rendered easy by these variations. Further, the absolute
necessity of dealing only with brains hardened in situ limits greatly the
material on which to found an answer to the problem. From an examination
of fifteen heads, of all ages, prepared by Professor Cunningham, the
termination was in ten cases as in (a) ; and in the remainder, i.e. 33 per cent.,
as in {b), but with tendency towards (a) in two cases.

The impossibility of determining which form of termination exists in

* This is not an inappropriate place to point out the very serious and dangerous defects
(especially on the point here described) of the large folio plates recently constructed by Adam-
kiewicz: Wien. 1892. These plates, which purport to be a guide to the surgeon, Trill, if
relied upon, be a fertile source of disaster rather than success, and, as such, should, in the
interests of humanity, be withdrawn from publication.

UOYAL IRISH ACADEMY. — CUNNINGHAM MEMOIRS, NO. TIT. [411