these cells, but do not extend far from
the body of the cell. The neuraxon always arises from the base of the
cell and passes towards the central white matter, thus forming one of
the nerve-fibres of that substance. In its path it gives off a number
of collaterals at right angles, which are distributed to the adjacent
grey matter.

[Illustration: From Cunningham, _Text-book of Anatomy_.

Fig. 15.--Diagram to illustrate Minute Structure of the Cerebral
Cortex.

A. Neuroglia cells.
B. " "
C. Cell with short axon (N) which breaks up in a free arborization.
D. Spindle-shaped cell in stratum zonale.
E. Small pyramidal cell.
F. Large pyramidal cell.
G. Cell of Martinotti.
H. Polymorphic cell.
K. Corticipetal fibres.]

3. _The Layer of large Pyramidal Cells._--This is characterized by the
presence of numbers of cells of the same type as those of the
preceding layer, but of larger size. The nerve-fibre process becomes a
medullated fibre of the white matter.

4. _The Layer of Polymorphous Cells._--The cells of this layer are
irregular in outline, and give off several dendrites branching into
the surrounding grey matter. The neuraxon gives off a number of
collaterals, and then becomes a nerve-fibre of the central white
matter.

Scattered through these three layers there are also a number of cells
(_cells of Golgi_) whose neuraxon divides at once, the divisions
terminating within the immediate vicinity of the cell-body. Some cells
are also found in which the neuraxon, instead of running into the
white matter of the brain, passes toward the surface; these are called
_cells of Martinotti_.

The medullated nerve-fibres of the white matter when traced into the
cortex are seen to enter in bundles set vertically to the surface.
These bundles taper and are resolved into isolated fibres in the upper
parts of the pyramidal layers. The fibres constituting the bundles
form two sets. (a) The centrifugal fibres consist as above described
of the fibre processes of the pyramidal and polymorphous cells. (b)
The centripetal fibres ascend through the cortex to terminate within
the molecular layer by horizontally running branches. As they pass
through they give off a number of collaterals. The position of the
cells from which these fibres arise is not known. In addition to the
radially arranged bundles of fibres, networks ar