be described
in a general way as following a sequence resembling that of the motor
representation in the spinal cord, the top of the gyrus being taken as
corresponding with the caudal end of the spinal cord. The sequence as
the gyrus is followed downwards runs: perineum, foot, knee, hip,
abdomen, chest, shoulder, elbow, wrist, hand, eyelids and ear, nose,
mouth and tongue. The nature of the movement is very fairly constant for
separate points of this motor cortex as observed both in the same and in
similar experiments. Thus flexion of the arm will be excitable from one
set of points, and extension of the arm from another set of points;
opening of the jaw from one set and closure from another, and so on.
These various movements if excited strongly tend to have characters like
those of the movements seen in an epileptic convulsion. Strong
stimulation excites in fact a convulsion like that of epilepsy,
beginning with the movement usual for the point stimulated and spreading
so as to assume the proportions of a convulsion affecting the entire
skeletal musculature of one half or even of the whole body. The
resemblance to an epileptic seizure is the closer because the movement
before it subsides becomes clonic (rhythmic) as in epilepsy. The
determination of the exact spots of cortex in which are represented the
various movements of the body has served a useful practical purpose in
indicating the particular places in the cortex which are the seat of
disease. These the physician can localize more exactly by reason of this
knowledge. Hence the surgeon, if the nature of the disease is such as
can be dealt with by surgical means, can without unnecessarily damaging
the skull and brain, proceed directly to the point which is the seat of
the mischief.

The motor representation of certain parts of the body is much more
liberal than is that of others. There is little correspondence between
the mere mass of musculature involved and the area of the cortex devoted
to its representation. Variety of movement rather than force or energy
of movement seems to demand extent of cortex. The cortical area for the
thumb is larger than those for the whole abdomen and chest combined. The
cortical area for the tongue is larger than that for the neck. Different
movements of one and the same part are very unequally represented in the
cortex. Thus, flexion of the leg is more extensively represented than is
extension, opening of the jaw has a much larger