592 TRANSACTIONS OF SECTION H. 
of Man and other mammals is obviously correlated with the great expansion of 
the temporo-parietal area, which is the fundamental distinctive feature of the 
human brain. 
In other Primates, even in the Anthropoid Apes, there is relatively only a 
small area intervening between the great visual, tactile, and auditory territories, 
and the fringing bands intimately associated with them, so that practically the 
whole of this part of the brain is under the direct influence of sensations that 
are constantly pouring in to keep the animal ‘ absorbed in direct responses to the 
demands of its environment’ ; but the part of the temporo-parietal area which is 
not under such direct influences undergoes a steady increase in size as we ascend 
the Primate series, until in the Anthropoid Apes the three sensory territories are 
definitely being pushed asunder, the visual to the occipital pole, the auditory to 
the temporal region, and the sensory to the central. The time eventually 
arrives when a sufticiently large area is formed where the functions of correlation 
of sensory images can go on undisturbed by the new stream of incoming impres- 
sions, and provide the physical mechanism for storing up records of the conse- 
quences of actions excited by the frontal areas, which must be the materials out 
of which the anticipation of what the result of any given action must be com- 
pounded. 
It may seem wildly speculative to speak in this manner of the way in which 
these great temporo-parietal and frontal areas perform their functions, when 
we are so profoundly ignorant of the precise nature of their working. But they 
present the outstanding features of contrast in the brains of Men and Anthro- 
poid Apes: we know that these two areas show a progressive and unbroken 
increase in size in the series of Primates, with which we can associate the grow- 
ing power of skill in manipulation, of intelligent action, and the faculty of learn- 
ing to perform most complex movements; and the records of clinical medicine 
and psychiatry have given us some faint glimmerings of the way in which they 
perform their functions in Man. 
Thus there seems to be some justification for framing a definite working 
hypothesis to cover the factors that are known to us. The temporo-parietal area 
is the storehouse for the memories of the states of consciousness compounded of 
visual, auditory, and tactile sensations, and its progressive growth and specialisa- 
tion is the measure of the efficiency with which it performs these functions. 
The central area is the storehouse for the memories of actions and the feelings 
associated with them. The prefrontal area is concerned with attention and the 
orderly control of the psychical activities of the whole cortex; and its great 
expansion and high differentiation in Man may be taken to mean, among other 
things, that it correlates the actions of the central and temporo-parietal areas, 
and supplies the mechanism for recording the experience of the casual relation- 
ship between the states of consciousness, causes, and effects, with which the 
central and the temporo-parietal areas respectively are more immediately con- 
cerned. 
I am aware that this is a rather clumsy and crude attempt at psychological 
analysis; but the idea I am striving to express is this: that the Gibbon and the 
other Anthropoid Apes are ‘strictly bound down to experience’ and have not 
learned ‘to anticipate to any extent what is going to happen,’ because the parts 
ot the brain, temporo-parietal and prefrontal areas, which provide the 
mechanisms for correlating causes and effects and making such experience avail- 
able to regulate conduct, are still small and relatively undifferentiated. They 
are not yet sufliciently large to be removed far from the great sensory avenues 
along which a constant stream of tratlic is surging and overflowing into these 
areas, compelling the latter to-attune their activities to the immediate demands 
ot the animal’s environment. 
And so the Gibbon, not yet mentally endowed to anticipate the consequences 
of its acts and to do any great variety of useful things with its hands, developed 
its arms in size and cunning, and became the most expert gymnast the world 
has known. Nor, again, when Man’s nearer relatives, the Chimpanzee and the 
Gorilla, branched off from his ancestral line, were they any the more able to use 
their arms for the highest skilled work: but they developed great strength, 
which enabled them to hold their own upon the ground and wax in size when 
pitted in competition with the animals of their African forest home. In these 
specialisations of their limbs they lost something of the mechanisms that were 
