FISSURES OF THE HEMISPHERES. 193 



in the interior of the brain, and is perforated by numerous vessels for that 

 body. 



Position of the part. Now the base of the cerebrum lias been dissected, 

 the brain should be turned over for the examination of the upper part. 

 Something should then be placed beneath the front, in order that it may 

 be raised to the same level as the back ; and a rolled-up cloth should 

 loosely encircle the whole, to support the hemispheres. 



UPPER SURFACE OF THE CEREBRUM. On the upper surface the cere- 

 brum, taken as a whole, is oval in form, and is convex in its outline, in 

 accordance with the shape of the skull. 



A median longitudinal fissure divides the cerebrum incompletely into 

 two halves. At the front and back the hemispheres are quite separated 

 by it ; but at the middle and under parts they are united by connecting 

 pieces, the largest of which is the white corpus callosum. In it the falx 

 cerebri is lodged. 



Each hemisphere is larger in front than behind. Its outer surface is 

 convex; but the inner is Hat, and in contact in front with the opposite 

 half. On the upper aspect the surface of the hemisphere is divided by 

 fissures into lobes, and on the under aspect it is cleft into two large pieces 

 by the fissure of Sylvius. The superficies of the hemisphere is marked 

 by tortuous eminences, the projections on it being named convolutions or 

 gyri, and the intervening depressions, sulci or anfractuosities. 1 



FISSURES OF THE HEMISPHERE. The larger fissures separate the 

 lobes, and the smaller sulci mark the extent of particular convolutions. 

 The fissures dividing the hemisphere into lobes are the three following: 



The fissure of Sylvius (S, fig. 60) begins below at the anterior perfo- 

 rated spot, and directed out between the frontal and temporo-sphenoidal 

 lobes, divides into two parts, anterior and posterior. 



The anterior limb, 'S, ascends for a short distance into the frontal 

 lobe. 



The posterior limb, the continuation of the fissure, is directed obliquely 

 upwards and backwards to about the middle of the outer face of the hemi- 

 sphere. At its extremity it is sometimes divided into smaller sulci. 



fissure of Rolando (It, fig. GO). Beginning above, about half way 

 along the hemisphere, in or near the longitudinal fissure of the cerebrum, 

 it is prolonged outwards between the frontal and parietal lobes nearly to 

 the posterior part of the Sylvian fissure, about the middle of that limb. 



The external parieto-occipital fissure (opposite P 0, fig. 60) begins 

 in the median longitudinal fissure half way between the preceding and the 

 hinder end of the hemisphere. It is very variable in extent, being some- 

 times an inch long, and at others only a slight indentation ; but it may be 

 always recognized by its continlity with the perpendicular fissure on the 

 inner face of the hemisphere (fig. 62). 



LOBES OF THE HEMISPHERE. Each hemisphere is divided into five 

 lobes, which have the following names and limits : 



The frontal lobe (Fr, fig. 60) forms the anterior half of the hemisphere. 

 It is limited below by the fissure of Sylvius, , and behind by the fissure 



1 In the following description of the surface anatomy of the cerebrum I have 

 followed chiefly the arrangement of Professor Turner in his paper "ON THE CON- 

 VOLUTIONS OF THE HUMAN CEREBRUM ;" and to him I am indebted for permission to 

 copy the wood-cuts employed in illustration of his publication. 

 ]3 



