s, and the root of the zygoma--are taken, and connected by
lines, which are further subdivided--_always being bisected_. Figs.
179 and 181 explain the method. The head being shaved, a line (GO) is
drawn along the vertex from the glabella (G) to the external occipital
protuberance (O). This line is bisected in M, which constitutes the
"mid-point." The posterior half of the line MO is bisected in T,
constituting the "three-quarters point," and the posterior half TO is
bisected in S--"the seven-eighths point." The lateral angular process
(E) is next connected to the root of the zygoma (P) by a line EP, and
the root of the zygoma with the seven-eighths point by PS; the line
EPS thus forms the base line. The lateral angular process is now
joined to the three-quarters point by ET. The two segments of the base
line EP and PS are bisected in N and R respectively, and these points
connected with the mid-point (M) by lines NM and RM. These lines cut
off a part of ET--AB, which is now bisected in C, and from C the line
CD is drawn parallel to AM.

[Illustration: FIG. 181.--Chiene's Method of Cerebral Localisation.]

In this way practically all the points of the brain which are wanted
for operative purposes may be mapped out. Thus the quadrilateral space
MDCA contains the Rolandic area. MA represents the praecentral sulcus,
and if it be trisected in K and L, these points will correspond to the
origins of the superior and inferior frontal sulci. The pentagon ABRPN
corresponds to the temporal lobe. The apex of the temporal lobe
extends a little in front of N. The supra-marginal convolution lies in
the triangle HBC. The angular gyrus is at B. A is over the anterior
branch of the middle meningeal artery, and the bifurcation of the
lateral or Sylvian fissure; AC follows the horizontal limb of the
lateral fissure. The transverse or lateral sinus at its highest point
touches the line PS at R (Fig. 181).

The _fissure of Rolando_ or _central sulcus_ may be marked out by
taking a point half an inch behind the mid-point (M) (Fig. 181), and
drawing a line downwards and forwards for a distance of about three
and a half inches, at an angle of 67.5 deg. with the line GO. The angle of
67.5 deg. can be readily determined by folding a square piece of paper on
itself so as to make a triangle. The angle at the fold equals 45 deg.. By
folding the paper again upon itself in the same direction, the right
angle of the paper is divided into four angles