ey matter of the optic lobe, a part of the mid-brain, to
which the so-called anterior colliculus is equivalent in the mammalian
brain. In the optic lobe the axones of the neurones of the optic tract
meet neurones whose axones pass in turn to the motor neurones of the
muscles moving the eyeballs, and also to other motor neurones. But in
these fish the optic tract has no obvious connexion with the fore-brain
or with any cerebral pallium. Ascending, however, to the reptilian brain
is found an additional arrangement: a small portion of the optic tract
passes to grey matter in front of the optic lobe. This grey matter is
the lateral geniculate body. From this geniculate body a number of
neurones extend to the pallial portion of the cerebrum, for in the
reptilian brain the pallium is present. The portion of pallium connected
with the lateral geniculate body lies above and behind the olfactory or
archipallium. It is a part of what was mentioned above as neopallium.

In the mammalian brain the portion of the optic tract which goes to the
optic lobe (_ant. colliculus_ of the mammal) is dwarfed by great
development of the part which goes to the geniculate body and an
adjoining grey mass, the pulvinar (part of the optic thalamus). From
these latter pass large bands of fibres to the occipital region of the
neopallium. In mammals this visual region of the cortex is distinguished
in its microscopic features from the cortex elsewhere by a layer of
myelinate nerve-fibres, many of which are the axones of neurones of the
geniculate body and pulvinar. Thus, whereas in the bony fishes all the
third links of the conductive chain from the retina lead exclusively to
the final neurones of motor centres for muscles, in the mammal the
majority of the third links conduct to grey matter of the cortex
cerebri.

The application of electric stimuli to the surface of the cortex does
not for the greater part of the extent of the cortex evoke in higher
mammalian brains any obvious effect; no muscular act is provoked. But
from certain limited regions of the cortex such stimulation does evoke
muscular acts, and one of these regions is that to which the neurones
forming the third link of the conductive chain from the retina pass. The
muscular acts thus provoked from that region are movements of the
eyeballs and of the neck turning the head. In the monkey the movement is
the turning of both eyeballs and the head away from the side stimulated.
In short, the