498 



THE NERVOUS SYSTEM. 



convolutions, while from the lower extremity extends the inferior 

 frontal sulcus, separating the middle and inferior frontal convolu- 

 tions. Thus the frontal lobe is divided into the ascending, 

 superior, middle, and inferior frontal convolutions. 



(2) The parietal lobe is behind the frontal and in front of the 

 occipital lobe, the fissure of Rolando being its anterior, and the 

 parieto-occipital fissure its posterior boundary. Its inferior 

 boundary is the fissure of Sylvius and the imaginary continuation 

 of it to the superior occipital sulcus. It has 2 sulci, the intra- 

 parietal and the post-central, and 3 convolutions, the ascending, 

 superior, and inferior parietal. 



(3) The occipital lobe is posterior to the parietal, and has 2 



Lobulus paracentralis, 



FIG. 289. Lateral view of the brain : gyri and lobuli marked with antique type, 

 the sulci and fissures with italic type (combined from Ecker). 



sulci, the superior and middle, and 3 convolutions, the superior, 

 middle, and inferior occipital, the latter being subdivided into the 

 supramarginal and the angular. 



(4) The Temporosphenoidal Lobe. The fissure of Sylvius forms 

 the anterior and superior boundaries of this lobe, while its posterior 

 boundary is the imaginary continuation of the occipitoparietal 

 fissure. It presents 2 sulci, the superior temporosphenoidal or 

 parallel, and the middle temporosphenoidal. Its convolutions are 

 3, the superior, middle, and inferior temporosphenoidal. 



(5) The central lobe, or island of Reil, is situated at the base of 

 the brain, in the fissure of Sylvius. It consists of 6 convolutions, 

 the gyri operti. 



