580 TRANSACTIONS OF SECTION H. 
has been wholly responsible for their dominant position, their world-wide distri- 
bution, and the plasticity which has manifested itself in the marvellous variety 
of adaptations to every mode of life which the mammals have undergone. 
If we search for the new feature in the brain which has made possible all 
their achievements it will be found in a cortical area to which eleven years ago 
I gave the name ‘neopallium.’ 
In the lowlier vertebrates each of the avenues of the senses leads to a special 
part of the brain, and although there are free communications between the 
regions allotted to the olfactory, visual, auditory, tactile, and other senses, there 
is no instrument for the adequate blending of impressions reaching the brain 
through these different portals, or for the storing of impressions, so as to awaken 
in consciousness the different properties of an object which appeals to several 
different senses. ‘The lowlier vertebrates do not see, hear, or feel an object 
in the sense that we associate with these terms. A biologically adequate 
stimulus, such, for example, as a splash in a pond to a frog, or the croaking 
of its fellows, will call forth an appropriate response; but an excitation such 
as would not normally come within the range of experience of the creature, 
however intense it may be, such as a loud noise from a gong, will leave it quite 
indifferent, because it lacks any mechanism to enable it to compare the novel 
stimulation either with former impressions or with its immediate effect upon other 
sense-organs, and to judge it in the light cf such standards of comparison. 
This must not be confused with the complex reflexes found in all vertebrates, 
where a response, or a whole train of complicated acts, is excited only by a series 
of stimuli entering the nervous system through various avenues of the senses, 
and elaborating in the central nervous system what Professor Sherrington would 
call a ‘common path’ to the nuclei of the motor nerves that excite the muscles 
to produce the appropriate response. 
Now it must be evident that unless there is some mechanism (a) for storing 
impressions so that they may be revived—i.e., recalled in associative memory 
at some later time, and (b) for blending in consciousness the sensory impulses 
entering the sensorium by different portals, there can be no learning by experi- 
ence. A fish that has swallowed a fly on a hook and got rid of the latter will 
repeat the process immediately, presumably because there is no intimate associa- 
tion in the brain between the receptor of the visual impression of the fly in the 
mid-brain and the receptor of the painful impression of the hook in the hind- 
brain; and therefore nothing to inhibit the normal response of the animal to the 
adequate biological stimulus provided by the visual image of the fly, whenever 
it occurs again. 
Some faint glimmering of an elementary kind of judgment makes its appear- 
ance in reptiles, in which the tactile paths have made their way into the hitherto 
almost exclusively olfactory cerebral hemispheres, and established some definite 
representation for the sense of touch in this dominant part of the brain.4* The 
snake which smells out some food-material, and then tests it by feeling it with 
its tongue, is checking by means of one sensory perception the information gained 
through another sense : it thus displays the germ of the power of contrasting the 
impressions and the memories of sensations reaching the brain by two distinct 
avenues of sense, from which eventually the power of instituting deliberate 
conscious judgments is developed. 
It is able to do so (and this is the important point for us to remember in this 
discussion) in virtue of the fact, which can be demonstrated by the comparative 
study of the structure of the brain, that both the senses of smell and touch are 
able not only to pour their impressions into contiguous and intimately associated 
areas of the cerebral cortex, but also because they are represented there by a mass 
of material serving as a storehouse for the impressions of these senses, which can 
be revived in memory. 
But such potentialities can be said to become first definitely established for 
% <The Natural Subdivision of the Cerebral Hemisphere,’ Journ. Anat. and 
Phys., vol. xxxv., 1901, p. 481. 
'* Arris and Gale Lectures on the Evolution of the Brain, Zancet, January 15, 
1910, p. 153. 
