Cerebral Convolutions 



47 



tudinal fissure, and runs a short distance on to the convex surface of 

 the hemisphere between the parietal and occipital lobes. 



This figure shows the relative position of the sutures of skull and the fissures of brain. (QUAIN.) 



Lobes. The frontal lobe reaches back to the fissure of Rolando ; 

 that part of it which rests in the anterior fossa of the skull constitutes 

 its orbital surface. The frontal lobe is marked by two horizontal 

 sulci which map it into superior, middle, and inferior frontal convolu- 

 tions, which, like the sulci, are directed from before backwards. Be- 

 hind these horizontal lobes is a vertical furrow, the transverse frontal 

 fissure, or, because it lies in front of the central (Rolando's) fissure, the 

 prce-central sulcus. The vertical convolution which lies between this 

 transverse frontal sulcus and the fissure of Rolando is the important 

 ascending: frontal convolution. 



The infra-parietal fissure ascends for a while behind the fissure 

 of Rolando and then turns backwards, perhaps to join the parieto- 

 occipital fissure. The convolution between it and the fissure of Ro- 

 lando is the ascending parietal convolution, and below the fissure 

 of Rolando it becomes continuous with the ascending frontal convolu- 

 tion, the junction between their lower ends forming a thick flap which 

 has to be lifted up in order to expose the island of Reil. Acting thus 

 like a lid, the flap is called the operculum (operio, -ertum, cover, hide), 

 the convolutions of the island being the gyri operti. 



