STRUCTURE OF THE CORTEX CEREBRI. 
37 
that of Rolando. The crucial sulcus, figs. 1 and 2 (7), separates the parietal from 
the anterior exposed part of the limbic lobe, figs. I and 2 (4) ; the fissure of Rolando, 
fig. 2 (9), separates the latter from the frontal lobe, fig. 2 (10); whilst the inter¬ 
parietal, fig. 2 (12), runs between the upper and lower series of parietal convolutions. 
The Sylvian fissure, fig. 2 (13), is directed obliquely upwards and backwards, the lower 
parietal gyri arching around the fissure. All the parietal convolutions take origin 
Fig. 2 . 
from a region termed by Broca the temporal lobule of the parietal lobe, and, after 
winding around the fissure of Sylvius, terminate near the fissure of Rolando, in a 
region corresponding to the ascending parietal convolution of higher Mammals, 
fig. 2 (11). 
Above the interparietal fissure we find the third and fourth parietal convolutions, 
the latter being also called the sagittal, figs. 1 and 2 (18). The sagittal gyrus is 
almost invariably split up posteriorly by secondary sulci. The first parietal or Sylvian 
convolution, although separated from the second parietal behind the fissure of Sylvius, 
fig. 2 (15, 16), is in front of that fissure blended with the second parietal often as far 
as the gyrus post-Rolandique (11). 
3. The frontal lobe .—This lobe is limited to the extreme anterior tip of the hemi¬ 
sphere and its inner aspect as far as the sub-frontal sulcus. The portion appearing 
upon the outer surface of the hemisphere anteriorly is the representative of the 
ascending frontal convolution (10), and is separated from the parietal lobe by the 
fissure of Rolando. Its inner surface is separated from the great limbic lobe by the 
sub-frontal sulcus, fig. 1 (5), or anterior extremity of the limbic fissure. 
Lamination of the Cortex of the Brain in the Pig. 
Number and arrangement of layers. —The general arrangement of the varied series 
of cells, constituting the greater portion of the cortex of the brain, is very similar to 
