STRUCTURE OF THE BRAIK IK RODEKTS. 
709 
and sparse, 18 to 20 cells alone being seen in the quarter-inch field in striking contrast 
to their abundance in the areas A and B. 
Continuing to dimmish in depth and in the number of its cells, this layer becomes a 
very insignificant tract beyond E, being, however, always most richly developed along 
the sagittal angle of the hemisphere. The whole exposed or extra-limbic aspect of the 
hemisphere, from D to E, is distinctly five-laminated, and a typical linear arrangement 
of cells is maintained in the ganglionic layer—the cells being placed at wide distances 
apart, and all on the same plane or at a uniform depth from the surface of the cortex. 
Modified Upper Limbic Type (Plate 50, fig. 4) A 
It has been already inferred that the structural type of the posterior extremity of 
both upper and lower limbic arcs exhibit very important modifications. The change, 
as far as it affects the upper limbic arc, is as follows :—On the outer aspect of the 
hemisphere a shallow sulcus is seen (Plate 49, fig. 1, K) disposed parallel to the great 
longitudinal fissure and mapping off from the extra-limbic mass outside it, a portion of 
the hemisphere which in the convoluted brains of higher animals corresponds to the 
superior parietal or sagittal convolutions. 
Now this sulcus forms an abrupt boundary betwixt two forms of lamination; external 
to it lies the cortex typical of the larger mass of the extra-limbic lobe, internal to it is a 
cortex distinguished by a remarkable granule formation. It has been noted that as 
we examine the upper limbic cortex towards the posterior extremity of the callosal 
commissure an intercalated series of granule and angular elements becomes interposed 
betwixt the small pyramidal and ganglionic layers (vide Plate 50, fig. 4). Now, these 
small angular cells increase rapidly in number, and approaching the surface wholly replace 
the second or small pyramidal layer. In lieu of the latter, therefore, we eventually 
find here a deep belt of densely congregated small granule-like bodies, the granule-like 
character being due to the large size of their nucleus compared with their investing 
protoplasm. They are very closely crowded at the upper limits of the layer, but less 
so at deeper levels, taking a position in horizontal serried rank which is an especial 
feature of this formation—a peculiarity due to their separation into rows by the passage 
betwixt them of arciform fasciculi or bundles of medullated fibres running parallel to 
the surface of the cortex. In this region, therefore, the cortex is still four-laminated, 
consisting of— 
1 . Outer cortical zone (Plate 50, fig. 4, A). 
2 . Deep belt of granule-like cells (Plate 50, fig. 4, B). 
3. Ganglionic belt (Plate 50, fig. 4, C). 
4. Spindle-cell layer (Plate 50, fig. 4, D). 
This formation is not limited to the upper limbic arc, but stretching over on to the 
* The area covered by this formation is shaded by dots in Plate 49, figs. 1 and 3. 
