DISSECTING MANUAL. 



Reil; it is triangular, apex downward, and consists of three 

 parts, upper, lower, and anterior. The opercula insulce are 

 brain folds overlapping the insula; from behind forward they 

 consist of the temporal, fronto-parietal, frontal, and orbital 

 opercula; their margins are the limbs of the Sylvian fis- 

 sure. [556] 



Fissure of Rolando. This begins in the supero-mesial bor- 

 der just behind its midpoint, winds downward and forward on 

 the outer surface, and ends above the centre of the posterior 

 Sylvian limb. It bends (superior genu), with the concavity 

 forward, between its upper and middle thirds, and again (in- 

 ferior genu), with the concavity backward, lower down and in 

 front. The upper end runs a short way backward on the 

 mesial surface. [558] 



Parieto-occipital Fissure. The internal portion begins in 

 the supero-mesial border an inch and a half to two inches in 

 front of the occipital pole, descends almost vertically on the 

 mesial surface, and joins the calcarine fissure just in front of 

 its centre. The external portion runs for about half an inch 

 outward on the external surface. [558] 



Collateral Fissure. Beginning near the occipital pole this 

 runs forward on the tentorial surface toward the temporal pole ; 

 a shallow sulcus (incisura temporalis), which is rarely contin- 

 uous with it, prolongs its course round the end of the temporal 

 lobe. [559] 



Calloso-marginal Fissure. Beginning near the locus per- 

 foratus anticus, below the genu of the corpus callosum, this 

 curves around in front of the genu on the mesial surface, then 

 runs backward to just behind the middle of this surface, and 

 then upward into the supero-mesial border just behind the 

 upper end of the fissure of Rolando. [560] 



Frontal Lobe. This is bounded on the outer surface by the 

 fissure of Rolando behind and the posterior Sylvian limb be- 

 low, on the mesial surface by the calloso-marginal fissure, 

 and on the inferior surface by the Sylvian stem. External sur- 



[38] 



