1394 A MANUAL OF ANATOMY 



Opercula Insulse. — ^The parts of the cerebral hemisphere which 

 bound the three hmbs of the fissure of Sylvius and overhang the 

 insula are called the opercula insulae. They are four in number, 

 namely, fronto-parietal, temporal, frontal, and orbital. 



The fronto-parietal operculum forms the upper lip, and the 

 temporal operculum forms the lower lip, of the posterior limb of the 

 fissure of Sylvius. The frontal operculum represents the pars 

 triangularis of the inferior frontal gyrus — that is to say, the part 

 which lies between the ascending and the anterior limbs of the fissure 

 of Sylvius. The orbital operculum represents the pars orbitalis of 

 the inferior frontal gyrus, and lies below the anterior limb of the 

 fissure of Sylvius. 



Limbic Lobe. — ^This lobe is situated on the internal or mesial 

 surface of the cerebral hemisphere. It is composed of two convo- 



Fissure of Rolando 



Superior Part of Limiting Sulcus^ 



Anterior Part of Limiting 

 Sulcus 



Postero-inferior Part of 

 ''OLE I Limiting Sulcus 



Central Sulcus 



Fig. 587. — The Left Island of Reil (Poirier, from Eberstaller). 

 1, 2, 3, Gyri Breves ; 4, 5, Gyri Longi ; x , Limen Insulae. 



lutions, namely, the callosal gyrus, or gyrus fomicatus, and the 

 hippocampal gyrus, so disposed as to form an almost complete 

 ring round the corpus callosum and subjacent parts. The open part 

 of the ring, which is very small, is situated at the locus perforatus 

 anticus, and is occupied by the roots of the olfactory tract. Around 

 its circumference the limbic lobe is bounded superiorly by the 

 calloso-marginal fissure, posteriorly by the postlimbic sulcus, and 

 inferiorly by the anterior part of the collateral fissure and the 

 incisura temporalis. The callosal and hippocampal gyri become con- ■ 

 tinuous beneath the splenium of the corpus callosum, the connecting 

 portion, which is narrow, being known as the isthmus of the limbic lobe. 

 The callosal gyrus, or gyrus cinguli, arches round the corpus 

 callosum: hence the name gyrus fornicatus. It commences at the 



