STRUCTURE OF THE CORTEX CEREBRI. 
51 
A most noteworthy feature presented by this layer is its tendency to take a higher 
position than is observed in the same region in the Pig ; in other words, it appears 
to encroach upon the third layer, which becomes unusually shallow, whilst the 
ganglionic stratum is proportionately increased. 
Parietal lobe. —Throughout the greater mass of the parietal lobe the six-laminated 
type prevails, and the solitary or laminar arrangement of the ganglionic series is 
found. Exceptions occur, however, near the crucial sulcus, in the ascending and lower 
parietal convolutions. Along the whole of the first parietal or Sylvian convolution 
the same structural peculiarities exist that were apparent in the Pig. The five¬ 
layered cortex and the clustered ganglion cells reappear here. The nests in this 
Sylvian convolution are dense in cells, and so closely approximated as frequently 
to become quite confluent, and especially is this the case towards the lower aspects 
of this convolution. They usually occupy areas '325 mm. in depth by TG2 mm. in 
breadth, and the cells average 40/x X 13y, with a nucleus having a diameter of 13 p. 
The largest cell observed measured 60pX27p. It will be apparent from the fore¬ 
going statement that, as in the similarly stratified portion of the limbic lobe, the 
elements of this layer are peculiar from their elongated form and their rich dense 
clustering. Posterior to the fissure of Sylvius these nests become thinned out, the 
lamination assumes the transitional characters, passing eventually into the six- 
laminated type. The second parietal convolution anterior to the Sylvian fissure 
presents us with a realm transitional between a five and six-layered cortex. The 
ganglion cells assume a distinctly laminar arrangement, the angular cells increasing- 
in number but not forming in this region a very distinct layer. 
Frontal lobe .—Throughout the whole extent of this lobe the cortex is constituted 
of five layers. The cells of the ganglionic layer are small, well nested, and often 
confluent, but do not approach in their development the corresponding series in the 
exposed portion of the limbic lobe. The third layer in this lobe is constituted of 
cells maintaining uniform dimensions throughout the depth of this layer; but they 
approach close to the ganglionic series and fail to exhibit the pale zone betwixt 
these two layers, which is apparent in realms nearer the six-laminated cortex. 
The Cortex Cerebri of the Cat. 
Taking the great limbic lobe as presenting in its most perfect development the 
cortical formation characteristic of the motor area, we proceed to note the essential 
features of its individual layers. For the present we restrict our examination to the 
anterior half of its superior arc, fig. 5 (*). 
First layer. —A narrow, pale, white streak, averaging '325 mm. in depth, con¬ 
stitutes this stratum as seen by the naked eye. It is found to consist of an extremely 
delicate meshwork of connective and nerve-fibrils, in which two forms of nucleated 
cells may be observed—the perivascular following the course of blood-vessels, and 
H 2 
