THE NERVOUS SYSTEM AND CONSCIOUSNESS. 67 



striatum. The fissure of Rolando separates the frontal lobe, F, from 

 the rest of the brain. It begins at the great longitudinal division be- 

 tween the hemispheres, and pursues an uninterrupted course to within 

 a short distance of the horizontal branch of the Sylvian fissure. Back 

 of the fissure of Rolando is the external perpendicular fissure (E) ; it 



AT 



MP 



F3- 



T.S. 



Fig. 1. Fissures and Convolutions of the Human Brain. (Wundt.) Left side. S, Sylvian 

 fissure s, perpendicular, s\ horizontal, branches of this fissure; R, fissure of Rolando; E, 

 external perpendicular fissure ; F 3 , third frontal convolution or convolution of Broca ; AF, 

 ascending frontal convolution; AP, ascending parietal convolution; AG, angular gyrus or pli 

 courbe ; F, frontal lobe ; P, parietal lobe ; T.S, temporo-sphenoidal lobe ; 0, occipital lobe. 



appears as a simple notch on the upper edge of the hemisphere. It is 

 a prolongation, on the convex or lateral surface of the brain, of the 

 deep fissure of the internal zone. This fissure marks the rear limit of 

 the parietal lobe (P), which therefore lies between the fissure of Ro- 

 lando and this furrow. Back of the parietal lobe is the occipital lobe 

 (O). This region is less exactly defined ; an ideal prolongation of the 

 external perpendicular fissure would determine its anterior and inferior 

 limits. The temporo-sphenoidal lobe (T) has already been noticed as 

 lying below the fissure of Sylvius. Among the various convolutions 

 formed by these fissures there are three or four which must be named, 

 because it is with them that the experiments in brain-functions are 

 chiefly concerned. In the frontal lobe there are two of these convo- 

 lutions (F 3), the third frontal convolution, or the convolution of 

 Broca, and (A F) the fourth frontal convolution or ascending frontal 

 fold. Broca's convolution has somewhat the shape of a horseshoe, 

 and is formed around the ascending branch of the Sylvian fissure. 

 The ascending frontal fold lies directly to the left of the fissure of 

 Rolando, which it follows throughout. In the parietal lobe we notice 

 (A P) the ascending parietal convolution immediately to the right of 

 the fissure of Rolando, and (A G) the angular gyrus or pli courbe. 

 This latter convolution is very complex in man. 



