cial excitation, chiefly electric, of various parts of the brain,
and the defects produced by destruction or removal of circumscribed
portions. The clinico-pathological proceeds by observing the
disturbances of body and mind occurring in disease or injury, and
ascertaining the extent of the disease or injury, for the most part
_post mortem_. The histological method examines the microscopic
structure of the various regions of the brain and the characters and
arrangement of the nerve-cells composing it. The zoological follows and
compares the general features of the brain, as represented in the
various types of animal creation.

It is on the functions of the fore-brain that interest now mainly
focuses, for the reasons mentioned above. And the interest in the
fore-brain itself chiefly attaches to the functions of its cortex. This
is due to several causes. In man and the animals nearest him the cortex
forms by far the larger part of the whole cerebral hemisphere. More than
any other part it constitutes the distinctively human feature. It lies
accessible to various experimental observations, as also to traumatic
lesions and to the surgeon's art. It is composed of a great unbroken
sheet of grey matter; for that reason it is a structure wherein
processes of peculiar interest for the investigation in view are likely
to occur. To make this last inference more clear a reference to the
histology of nervous tissue must be made. The whole physiological
function of the nervous system may be summed up in the one word
"conduction." This "conduction" may be defined as the transmission of
states of excitement (nerve-impulses) along the neural arcs composing
the system. The whole nervous system is built up of chains of
nerve-cells (neurones) which are nervous conductors, the chains often
being termed arcs. Each neurone is an elongated cell which transmits
nerve-impulses from its one end to its other, without so far as is known
modifying the impulses in transit, unless in that part of the nerve-cell
where the nucleus lies. That part of the neurone or nerve-cell is called
the perikaryon or cell-body, and from that part usually many branches of
the cell (each branch being a nerve-fibre) ramify. There is no evidence
that impulses are modified in transit along a branch of a nerve-cell,
but there is clear evidence of manifold modification of nerve-impulses
in transit along the nerve-arcs of the nervous system. These nerve-arcs
are neurone-chain