462 



THE BRAIN 



of the blood to the grey cortex is in this way rendered 

 uniform. 



Cerebral Lobes and Interlobar Fissures. Certain of the 

 fissures which traverse the surface of the cerebrum are 

 arbitrarily chosen for the purpose of subdividing the surface 

 into districts, termed lobes. These fissures, which receive 

 the name of interlobar, are the following (i) the lateral 

 fissure (O.T. Sylvian) ; (2) the central (O.T. fissure of 

 Rolando) ; (3) the parieto-occipital ; (4) the collateral ; and 

 (5) the circular sulcus (O.T. limiting sulcus of Reil). 



Post-central sulcus 

 Central sulcus | 

 Sulcus cinguli 



Ranius horizontalis 



Upper prascentral sulcus 



Lower praecentral sulcus 



Sup. frontal sulcus 



ateral occip. 

 FIG. 



Sup. temp. sulc. 

 Mid. temp. sulc. 

 sulcus Pre-occipital notch 



Fis. lat. i 

 ant. hori; 

 Fis. lat. ran 

 asc. 



\ Pars triangulari 

 Pars orbitalis 

 Pars basilaris 



Post, ramus of lateral fissure 

 186. Gyri and Sulci on the Lateral Surface of the Cerebral Hemisphere. 



The lobes which are mapped out by these fissures are 

 (i) the frontal; (2) the parietal; (3) the occipital; (4) the 

 temporal ; (5) the insula. To these may be added a sixth 

 lobe, in no way related to the interlobar fissures, viz., the 

 olfactory lobe. 



Lateral Fissure (O.T. Sylvian). This is the most con- 

 spicuous fissure on the surface of the cerebrum. It is 

 composed of a short main stem, from the lateral extremity of 

 which three branches radiate. The stem is placed on the 

 inferior surface of the cerebrum (Fig. 182). It begins at 

 the substantia perforata anterior. Thence it passes laterally, 

 forming a deep cleft between the temporal pole and the 

 orbital surface of the frontal lobe. Appearing on the lateral 



