518 THE NERVOUS SYSTEM. | 4 
of the collateral fissure; at the same time it must be admitted that the two are 
seldom continuous with each other. The collateral fissure and the incisura 
temporalis intervene between the limbic and temporal lobes. 
ES 
& 
70. 
ANTERIOR 
Fic, 386.—THE GyRI AND SULCI ON THE MESIAL ASPECT OF THE CEREBRAL HEMISPHERE. 
7, Fissure of Rolando. 7.0, Rostral suleus. 7.¢, Incisura temporalis. 
The collateral fissure is developed, as a rule, in three portions—a hinder or occipital, an 
intermediate, and an anterior or temporal part. These ultimately run into each other and form 
the continuous fissure. The middle part is usually a complete fissure and responsible for the pro- 
duction of the eminentia collateralis posterior in the floor of the trigonum of the lateral ventricle ; 
the temporal part is sometimes a complete fissure, forming when it is so the eminentia collateralis 
anterior ; the occipital part is always incomplete. 
Calloso-marginal Fissure.—This fissure is a strongly-marked sulcus on the 
forepart of the mesial surface of the hemisphere. It divides the front portion of 
the mesial surface into an upper marginal and a lower callosal convolution, and 
intervenes between the frontal and limbic lobes. Beginning below the fore end of 
the corpus callosum, close to the locus perforatus anticus, the calloso-marginal 
fissure curves round in front of the genu of the corpus callosum, and then extends 
backwards to a point a short distance behind the middle of the mesial surface. 
It then turns upwards and cuts the supero-mesial border of the hemisphere, 
immediately behind the upper end of the fissure of Rolando. The relation presented 
by the two extremities of these fissures is such that they can both be readily 
recognised either when examined on the outer or mesial aspect of the cerebrum. 
The calloso-marginal suleus is developed in two or three separate pieces, which, as growth 
proceeds, run into each other and form the continuous fissure. The numerous cases of irregular 
arrangement met with in connection with this fissure can generally be explained by this inter- 
rupted mode of development. 
FrontaL Lope.—tThe frontal lobe is the largest of the cerebral lobes. On the 
outer surface of the hemisphere, it is bounded behind by the fissure of Rolando and 
below by the posterior horizontal limb of the fissure of Sylvius. On the mesial 
face it is limited by the calloso-marginal fissure, whilst on the inferior surface of 
the hemisphere the stem of the Sylvian fissure forms its posterior boundary. It 
presents an outer surface, a mesial surface, and an inferior or orbital surface. 
On the outer surface of the frontal lobe the following sulci and gyri may be 
recognised :— 
‘Sulcus preecentralis inferior. /Gyrus frontalis ascendens or gyrus 
Sulcus preecentralis superior. centralis anterior. ; 
Sule paramedialis, Gyrus frontalis superior spars superior. 
Sulcus frontalis superior. Cun / \ pars inferior. 
Sulcus frontalis medius. J f pars superior. 
Sulcus frontalis inferior. \ pars inferior. 
Sulcus diagonalis. pars basilaris. 
Sulcus fronto-marginalis. ee triangul- 
aris. 
tears orbitalis. 
Sulei 
[> 
Gyrus frontalis medius 
Gyrus frontalis inferior  - 
alle 
