514 THE NERVOUS SYSTEM. ‘ 
The ascending limb proceeds upwards, with a slight inclination forwards, into the 
lower part of the outer surface of the frontal lobe for a distance of about an inch. 
MID. JTEMPORAL = \ 
(= (Rus 
INF. TEMPORA, Me a 
Fic. 381.—Gyri AND SuLcI, on the outer surface of the cerebral hemisphere. 
te Sulcus frontalis superior. 1 Fissure of Rolando. 
1s Sulcus frontalis inferior. g.s. Superior genu. 
fm. Sulcus frontalis medius. g.i. Inferior genu. 
p.m. Sulcus paramedialis. d. Sulcus diagonalis. 
A. Pars basilaris. t!. Superior temporal sulcus (parallel). 
B. Pars triangularis. t”. Inferior temporal sulcus. 
C. Pars orbitalis. p'. Inferior postcentral sulcus. 
5. Sylvian fissure. p*. Superior postcentral suleus. 
Sas Anterior horizontal limb (Sylvian fissure). p®. Ramus horizontalis. 
s*. Ascending limb (Sylvian fissure). p*. Ramus occipitalis. 
S, Posterior horizontal limb (Sylvian fissure). s.o.t. Sulcus occipitalis transversus. 
p-c.l. Inferior preecentral sulcus. em. Calloso-inarginal suleus. 
pe.s. Superior precentral sulcus. c.t.r. Inferior transverse furrow. 
In many cases the two anterior limbs spring from a common stem of greater or 
less length, and not infrequently both are replaced by a single anterior limb. 
Limiting Sulcus of Reil (sulcus circularis Reilii)—If the lips of the posterior 
horizontal limb of the Sylvian fissure be widely pulled asunder from each other, the 
insula or island of Reil will be seen at the bottom. The insular district of the 
cortex is completely hidden from view when the Sylvian fissure is closed by over- 
lapping portions of the cerebral hemisphere, and, when brought into view in the 
manner indicated, it is observed to present a triangular outline ‘and Le be surrounded 
by a limiting sulcus, of which three parts may be recognised, viz.: an wpper part, 
bounding it “above and separating it from the parietal and froma lobes; a dower 
part, mar king it off below from the temporal lobe; and an anterior part, separating 
it in front from the frontal lobe. 
Opercula Insule.—The overlapping portions of the cerebral substance which 
cover over the insula are termed the insular opercula, and they form, by the apposi- 
tion of their margins, the three limbs of the Sylvian fissure. The opercula are four 
in number and are named : (1) temporal; (2) fronto-parietal ; (3) frontal; and (4) 
orbital. The limbs of the Sylvian fissure cut right through between the different 
opercula and extend from the exposed surface of “the hemisphere to the submerged 
surface of the insula, and, in this manner, separate the opercula from each other 
The temporal operculum extends upwards over the insula from the temporal lobe 
and its upper margin forms the lower lip of the posterior horizontal limb of the 
Sylvian fissure. 
The fronto-parietal operculum is carried downwards from the parietal and frontal — 
regions over the insula, and its lower margin, meeting the temporal operculum, 
forms the upper lip of the posterior limb of the Sylvian fissure. 
