584 TRANSACTIONS OF SECTION H. 
Primates, the significance of which it would be difficult to exaggerate in the 
later stages, when the simian are giving place to the distinctively human charac- 
teristics. 
The high specialisation of the sense of sight awakened in the creature the 
curiosity to examine the objects around it with closer minuteness, and supplied 
guidance to the hands in executing more precise and more skilled movements 
than the Tree-Shrew attempts. Such habits not only tended to develop the 
motor cortex itself, trained the tactile and kinesthetic senses, and linked up 
their cortical areas in bonds of more intimate associations with the visual cortex, 
but they stimulated the process of specialisation within or alongside the motor 
cortex of a mechanism for regulating the action of that cortex itself—an organ of 
attention which co-ordinated the activities of the whole neopallium so as the 
more efficiently to regulate the various centres controlling the muscles of the 
whole body. In this way not only is the guidance of all the senses secured, 
but the way is opened for all the muscles of the body to act harmoniously so as 
to permit the concentration of their action for the performance at one moment 
of some delicate and finely adjusted movement. 
In some such way as this there was evolved from the motor area itself, in the 
form of an outgrowth placed at first immediately in front of it, a formation, 
which attains much larger dimensions and a more pronounced specialisation of 
structure in the Primates than in any other order; it is the germ of that great 
prefrontal area of the human brain which is said to be ‘ concerned with attention 
and the general orderly co-ordination of psychic processes,’ ** and as such is, in 
far greater measure than any other part of the brain, deserving of being regarded 
as the seat of the higher mental faculties and the crowning glory and distinction 
of the human fabric. 
But the high development of certain other parts of the cortex was necessary 
to minister to these high functions of the prefrontal cortex and to supply the 
materials, if the term can be applied to anything so immaterial as perceptions 
and memories, upon which its own activities are expended. For before an animal 
like Tarsius could attempt to concentrate its attention upon the performance of 
some delicately skilled action, its large and highly specialised visual, tactile, and 
motor areas must have had impressed upon them countless numbers of records 
of things seen and felt and of memories of the experience acquired in perform- 
ing innumerable simpler acts. 
Whether the exceedingly primitive Tarsius-like Primates, of which I have 
been speaking, originated in the extreme south-west of Asia, where its modern 
representative now lives, or in North America, it is not possible to say with 
certainty ; but the fact that the Eocene beds of North America contain remains 
_ of both the Tarsius-like Anaptomorphus and Tupaia-like Insectivores** seems 
to suggest that North America may have been the original home of the Primate 
phylum, and the centre from which, quite early in Eocene times, there radiated 
to South America, Asia, Europe, and Africa the ancestors not only of the 
Tarsier itself, but of the Lemurs also, as well as specialised varieties of lemu- 
roids, such as Adapis, which may perhaps be related to the progenitors of the 
Lemurs, What remained of the original undifferentiated Primate stock in North 
America became transformed into primitive monkeys of Platyrrhine type, from 
which in turn sprang not only the later New World apes, but also the Catar- 
rhine or Old World apes, which were undoubtedly derived from primitive 
Platyrrhines, possibly after their migration into the Old World in Oligocene 
times, or perhaps even earlier. 
In the present state of our knowledge it is not possible to give the precise 
history of the wanderings of the early Primates. For not only are there vast 
ages of time in which we lose sight of them altogether, but in addition we are 
still far from an agreement as to the intercontinental land-bridges along which 
our simian ancestors must have travelled in their wanderings. How great are 
the discrepancies between the conclusions reached by leading authorities on this 
subject is revealed only too clearly in the recent monographs by Professor 
23 J. §. Bolton, ‘The Functions of the Frontal Lobes,’ Brain, 1903. 
*« Tf. F. Osborn, Vhe Age of Mammals, 1910, p. 155. 
