“ THE CRANIUM. 1161 
Two inches vertically above the pre-auricular point is the lower end of the 
fissure of Rolando. ‘T'wo fingers’-breadth (14 in.) vertically above the middle of the 
zygomatic arch is the pterion (spheno- parieti al suture), a point which cannot be felt, 
but which is nevertheless of topographical importance, as it overlies the Sylvian 
point (the poit where the Sylvian fissure breaks up into its three branches) and 
the anterior branch of the middle meningeal artery. A point three fingers’-breadth 
vertically above the middle of the zygomatic arch, on the left side, will mark the 
position of the centre of Broca’s convolution (posterior extremity of the left inferior 
frontal convolution). 
The frontal eminence (better marked in the child) overlies the middle frontal 
convolution. The parietal eminence, which varies considerably in the definiteness 
with which it can be recognised, overlies the termination of the posterior hori- 
zontal limb of the fissure of Sylvius, and therefore also the supra-marginal convolution, 
which is named by Turner the convolution of the parietal eminence. The part of 
the temporal crest which intervenes between the external angular process and the 
coronal suture lies a little above the level of the inferior frontal suleus. The 
highest part of the temporal crest crosses the Rolandic area at the junction of its 
middle and lower thirds, that is to say, at the junction of the motor areas for the 
arm and face. In the child, the temporal muscle, which is relatively much smaller 
than in the adult, reaches only a short distance above the squamous suture, and, 
therefore, only as far as the level of the lower end of the fissure of Rolando. 
The thickness of the skull-cap varies at different parts and in different dividuals. The 
inner table is only half the thickness of the outer table, but both possess the same degree of elas- 
ticity. When the vault is fractured from direct violence, the inner table is more extensiv ely 
fissured than the outer table because the elements of the latter are compressed, while those of the 
former are stretched apart. The weak areas at the base of the skull through which fractures are 
liable to extend are: in the anterior cranial fossa, the orbital plates of the frontal bone and the 
eribriform plate of the ethmoid ; in the middle cranial fossa, the region of the glenoid fossa of 
the temporal bone, and of the foramen ovale of the sphenoid ; in the posterior fossa, the cerebellar 
fossee of the occipital bone. The strong petrous temporal is weakened by the tympanic cavity 
and by the deep jugular fossa. ; 
Cranio-Cerebral Topography.—Of the many methods which have been 
devised for mapping out the relations of the cranial contents to the scalp, that 
introduced by Professor Chiene is, probably, the most useful from a clinical 
point of view; no figures or angles have to be remembered, and the primary 
surface lines are drawn from bony points which are not variable, whilst the 
secondary lines are drawn, for the most part, between mid-points of the primary 
lines. The method is as follows (Figs. 792 and 793) :— 
“The head being shaved, find in the mesial line of the skull between the 
glabella (G) and the ‘external occipital protuberance (O) the following points :— 
“ First, the mid-point (M) ; second, the three-quarter point (T); third, the seven- 
eighth point (S). 
“Find also the external angular process (EK), and the root of the zygoma (pre- 
auricular point) (P), immediately above and in front of the external auditory 
meatus. Having found these five points, jom EP, PS, and ET. Bisect EP and 
PS at Nand R. Join MN and MR. Bisect also AB at C, and draw CD parallel 
to AM.” 
The line MA corresponds to the superior and inferior precentral sulci, and may 
therefore be termed the pre-central line. The origins of the superior and inferior 
frontal sulci may be indicated by trisecting MA at the points K and L, the latter 
point being at the level of the temporal crest. 
The line ET, termed the oblique or Sylvian line, intersects the pre-central line at 
the point A, which corresponds to the Sylvian point of the fissure of Sylvius and 
to the anterior division of the middle meningeal artery. AC overlies the posterior 
horizontal limb of the fissure of Sylvius, which terminates at the level of the 
temporal crest, in the lower part of the triangle HCB. This triangle contains 
the parietal eminence, and may, therefore, be termed the swpra- marginal triangle. 
The termination of the Sy lvian line, at the three-quarter sagittal point T, overlies 
the parieto-occipital fissure. 
By joining TR, RO, a triangle is mapped out which delimits the outer surface 
