uished people, and even
in idiots 60 oz. has been recorded. On the other hand, microcephalic
idiots may have a brain as low as 10 or even 8-1/2 oz., but it is
doubtful whether normal intelligence is possible with a brain weighing
less than 32 oz. The taller the individual the greater is his brain
weight, but short people have proportionally heavier brains than tall.
The weight of the cerebellum is usually one-eighth of that of the
entire brain. Attempts have been made to estimate the surface area of
the grey matter by dissecting it off and measuring it, and also by
covering it with gold leaf and measuring that. The results, however,
have not been conclusive.

Further details of the brain, abundantly illustrated, will be found in
the later editions of any of the standard text-books on anatomy,
references to which will be found in the article on ANATOMY: _Modern
Human. Das Menschenhirn_, by G. Retzius (Stockholm, 1896), and
numerous recent memoirs by G. Elliot Smith and D.J. Cunningham in the
_Journ. Anat. and Phys._ and _Anatomisch Anzeig._, may be consulted.

_Histology of Cerebral Cortex._

The cerebral cortex (see fig. 15) consists of a continuous sheet of
grey matter completely enveloping the white matter of the hemispheres.
It varies in thickness in different parts, and becomes thinner in old
age, but all parts show a somewhat similar microscopic structure.
Thus, in vertical section, the following layers may be made out:--

1. _The Molecular Layer (Stratum zonale)._--This is made up of a large
number of fine nerve branchings both medullated and non-medullated.
The whole forms a close network, the fibres of which run chiefly a
tangential course. The cells of this layer are the so-called _cells of
Cajal_. They possess an irregular body, giving off 4 or 5 dendrites,
which terminate within the molecular layer and a long nerve fibre
process or neuraxon which runs parallel to the surface of the
convolution.

2. _The Layer of small Pyramidal Cells._--The typical cells of this
layer are pyramid-shaped, the apices of the pyramids being directed
towards the surface. The apex terminates in a dendron which reaches
into the molecular layer, giving off several collateral horizontal
branches in its course. The final branches in the molecular layer take
a direction parallel to the surface. Smaller dendrites arise from the
lateral and basal surfaces of