dial (nasal) half of one
visual field and the lateral (temporal) half of the other is affected,
so that there is an inability to see objects situated on the side
opposite to the lesion.

_Auditory impulses_ are received in the posterior part of the superior
temporal convolution.

_Aphasia._--The use of language, spoken or written, as a means of
expression depends upon the co-ordination of four different centres:
the visual, the auditory, the graphic, and the articulatory. These are
situated in different parts of the brain and are connected by
sub-cortical association tracts, the main pathway of which lies in the
vicinity of the upper end of the fissure of Sylvius. Marie has proved
that aphasia results from lesions in this area.

The _olfactory_ and _gustatory_ centres are situated in the uncus
close to the pituitary fossa.

Lesions of the frontal cortex anterior to the motor centres, even if
extensive, may produce few or no symptoms, and in consequence this
region has been called a "silent" area. Occasionally there results a
change in temperament or intelligence, and the region is on this
account supposed to be concerned with the higher psychical functions.
There is evidence that the pre-frontal cortex has a centre for the
conscious initiation of movements, and that lesions produce "apraxia,"
_i.e._, inability to perform, or clumsiness in voluntarily performing
fine movements such as touching the nose with the finger, though such
movements may be perfectly carried out unintentionally. This centre is
probably situated in the superior and middle left frontal convolutions
in right-handed people. The fibres from the centre to the right motor
area cross in the anterior part of the corpus callosum.

#Cerebral Localisation.#--The various parts of the brain can be
localised in relation to the surface by various methods. That devised
by Professor Chiene has been found reliable.

#Relation of Cerebral Centres to the Surface.#--Numerous attempts have
been made to formulate rules for locating the different parts of the
brain in relation to the surface of the head. The method devised by
Chiene is free from many of the difficulties and fallacies common to
most other methods, inasmuch as the results obtained do not depend
upon making definite measurements in inches, or determining particular
angles. Certain fixed and easily recognised bony landmarks--the
glabella, the external occipital protuberance, the lateral angular
proces