682 



THE XERVOUS SYSTEM 



for a short distance on to tlie convex surface. Tlie ])iirtion on the mesial surface 

 is (listintruislied as the internal parieto-occipital or internal perpendicular fis- 

 sure. It will be more itarticularly dcscrilicd with the hssurcs and convolutions of 

 the inner surface of the hemisphere. The ]iortion which a])pears on the convex 

 surface is distin<:uished as the external parieto-occipital fissure. 



The fissure of Sylvius is situated jtartly on the base and partly on the external 

 surface of the hemisi)liere, and is, with the exception of the great longitudinal fis- 

 sure, the most conspicuous sulcus in the brain. It connnences at the outer angle 

 of a depression called the vallecula Sylvii, in which the anterior perforated space 

 is situated. It passes outwards and upwards with an inclination backwards, and 

 <livi(U's into tln-ee l)ranches or limbs, a posterior, an ascending, and an anterior. The 

 posterior limb is by far the largest, and is to be regarded as the continuation of the 



Fici. 409. — The Fissures and Coxvolutioxs of the Cerebrum, viewed from above. 



OnBITA L 



MARiiiy 

 svPEnion 



FROXTA I. 



COXVOLLTIOX 



MIDDLE 



FRONTAL 

 COyvOLLTION 



IXFERIOR 



FRONTAL 



CONVOLVTIOS 



ASCEXDiya 



FRONT A I 



C0NV0LVTIO.\ 



ASCENDING 



PARIETAL 



CONVOLUTION 



SUPRA- 

 MARGINAL 

 CONVOLUTION 



SUPERIOR PARI- 

 ETAL LOBUL 



ANGULAR GYR 

 AND POST-PA RI 

 ETAL GYRUS 



MIDDLE OrriPITAL 

 CONVOLUTION 



SUPERIOR OCCIPITAL 

 CONVOLUTION 



SUPERIOR 

 FRONTA L 

 FISSURE 



INFERIOR 

 PR^E- 

 CENTRA L 

 FISSURE 



SUPERIOR 

 PR.E- 

 CENTRA L 

 FISSURE 



INTRA- 

 PARIETAL 

 FISSURE 



CALLOSO- 

 MARGINAL 

 FISSURE 



SULCUS Or- 

 CIPITA LIS 

 ANTERIOR 



EXTERNA I. 

 PARIETn- 

 OCCIPITA L 

 FISSURE 



TRANSVERSE 

 OCCIPITAL 

 FISSURE 



SUPERIOR 

 OCCIPITAL 

 FISSURE 



main fissure; it passes backwards and slightly U]nvards, separating the temporo- 

 sphenoidal from the frontal and parietal lobes, and finally, taking a more upward 

 direction, ends in the parietal lolie. The ascending limb is short and ])asses 

 vertically upwards; the inferior frontal convolution arches around it. The anterior 

 limb is about the same length as the ascending; it passes directly forwards into 

 the substance of the inferior frontal convolution. 



The convolutions Avhich surround the fissure of Sylvius cover in and conceal 

 the central lobe and are therefore called the opercula. The opercula are four in 

 number — the tem])oral, the fronto-parietal, the frontal, and the orbital. The 

 temporal operculum is fonncd liy the upper temporo-sphenoidal convolution, 

 thi' fronto-parietal operculum by the lower ends of the ascending frontal and 

 parietal c(jnv(jlutions and tiie jtosterior end of the inferior frontal convolution. 



