722 
ME. W. BE VAN LEWIS ON THE COMPARATIVE 
their close approximation renders their outlines obscure except in extremely fine and 
carefully prepared sections. Near the commencement of the first involution where the 
cells are more widely scattered, these elements are observed to be encircled usually by 
a number of nucleated protoplasts, as are also the spindle cells, which latter have fre¬ 
quently such numbers heaped upon their surface as quite to conceal their real contour. 
These pericellular elements also tend to render the ganglionic cells of the true cornu 
ammonis obscure in outline. The more elongated or fusiform cell is prevalent in the 
lower end of the cornu ammonis or that portion bounded externally by the lower 
limbic arc. That portion, however, lying internal to the upper limbic arc has the 
characteristic pegtop-shaped cell throughout its whole extent. Each ganglionic cell 
besides its apex process, gives off several secondary processes from its basal extremity, 
and especially a primary branch from the base, which becomes an axis cylinder process. 
The secondary branches are directed towards the medulla and rapidly divide and sub¬ 
divide within the subjacent formation (stratum moleculare). The axis cylinder process 
passes into the medulla of the alveus. The involuted cornu ammonis is most fully 
developed just posterior to the corpus callosum, and sections taken across the hemi¬ 
sphere at this site will therefore present us with the most extensive tracts of the 
ganglionic and other layers, the reticulated portion of the peripheral zone being also 
best studied here. The nearer we approach the inferior extremity of the cornu the more 
contracted is the area of section, and consequently the less extended are its nerve-cell 
layers, whilst the individual cells of the ganglionic series not only become more 
elongated in contour, but exhibit less and less of the striate formation from early sub¬ 
division of their apex processes. In the latter site, therefore, in lieu of the straight, 
elongated apex process of the cells becoming more and more attenuated and thus form¬ 
ing a forest-like structure of delicate twigs (striate layer) they commence as coarse con¬ 
torted branches, which at the distance of ‘046 mm. from the cell sub-divide into brush¬ 
like groups of filaments. The dimensions attained by these cells are an average length 
of 23/x and a width of 18/x, the nucleus measuring 13/x. At the commencement of its 
involution, however, where the cells are larger, more scattered, and elongated in 
contour, the dimensions are 37/xXl8/x (nucleus 13/x), the apex process becoming 
bifurcate at from 30/x to 60/x from the cell. A few spindle cells or even pyramidal cells 
are found occasionally here and there at wide distances apart within the striate layer 
separated from the main body of cells. 
Spindle-cell layer .—Beneath the ganglionic layer we come to a belt in which the 
neuroglia basis supports the fine fibrillar network formed by the secondary processes of 
the super-imposed cells. The presence of this nervous network accounts for the uniform 
faint staining which is here seen in aniline black preparations—a staining common to 
all parts of the grey cortex possessed of a network of non-medullated nerve fibrils and 
contrasted strongly with the perfectly white unstained layer of medullated fibres 
beneath this belt. Passing up from the ventricular ependyma covering the medulla of 
the cornu through this stratum numerous large blood-vessels are seen on their way to 
