‘PRESIDENTIAL ADDRESS. 587 
Fayoum monkeys, described by Schlosser as belonging to the Oligocene Age, 
there is a strange association of Platyrrhine and Catarrhine traits. 
In their new environment these primitive Catarrhines felt the impetus of 
their newly acquired faculties; and an army of variously specialised Apes set out 
to invade the rest of the warmer regions of the Old World. In the course of 
these differentiations some of the Catarrhines fell away in some respects from 
the high standard their ancestors had attained; the Baboons, for example, took 
to quadrupedal progression, and thereby sacrificed all chance of further advance 
in the Anthropoid direction. But in Early Oligocene times certain of the 
Catarrhines probably developed still further the powers of walking erect, which 
their remote Tarsioid ancestor possessed in‘'some measure, and became modified’ 
in structure so as to be able to walk upright upon their hind limbs, and use their 
hands and arms for other purposes. Thus, one group of Catarrhines became 
transformed into Anthropoid Apes very soon after the evolution of the first 
monkey of the Old World. 
The assrmption of the erect attitude is not the simple matter that most 
anthropologists suppose it to be : it is not a question merely of learning to balance 
the body on the hinder extremities: but, as Professor Keith has well shown,** 
it entailed profound structural changes for the fixation of the contents of the 
body so that the organs would not fall, and also the loss of the tail, so that the 
tail muscles could be turned to other uses as visceral supports; moreover, the 
freeing of the arms, which in a pronigrade animal, as Dr, Wood Jones has shown, 
are fixed supports for the muscles of respiration, interfered with this function 
of the extrathoracic muscles, and made the diaphragm the chief respiratory 
muscle. Thus was effected the most far-reaching changes in the mode of 
breathing. Such fundamental modifications of the structure and functions of 
the body must have been fashioned when the primitive Catarrhine was far more 
plastic than any of the modern Old World Apes we are familiar with; and | 
should not have been at all surprised, even without any knowledge of Schlosser’s 
Oligocene Propliopithecus, to find that an erect Anthropoid Ape had already 
emerged from the Proto-Catarrhine stock soon after the close of the Eocene 
period. 
In the modern Gibbon, which is a true Anthropoid, Nature has preserved 
for us with relatively only slight changes the type of the original ancestor of 
the phylum common to Man and the giant Apes. 
The additional freedom which the degree of erectness of the Gibbon affords 
to the arms gave an immense impetus to the development of more highly skilled 
movement and a phenomenal agility; and such potentialities are the expression 
of still further stages of growth and elaboration of the brain. In all probability 
it is not strictly accurate to speak of the freeing of the arms as supplying the 
stimulus to the brain by permitting the acquisition of more highly skilled move- 
ments, expressed in a higher state of cultivation and growth of the motor cortex. 
here can be no question that the primary stimulus to the fuller use of the arms 
as organs, not of mere progression, but of prehension and the more skilled acts 
came from the steady growth and specialisation of the brain itself; but the con- 
sequences of the acquisition of this skill were the freeing of the arms and the 
possibility of still further cultivation of the powers of the hands, which no 
doubt reacted so as to call for yet further growth and specialisation of the brain. 
Thus, there was a reciprocal influence of brain and the erect attitude, both help- 
ing to achieve the result which various writers are too apt to attribute exclusively 
to one factor only. 
That this explanation is the correct one is shown by the gradual increase in 
the size of the motor area, the degree of specialisation of the movements that 
become possible, and especially in the progressive expansion of the prefrontal 
area found at each step, when we compare Lemurs with Platyrrhines, the latter 
with Catarrhines, and these, in turn, with Anthropoids.*’ 
This is especially seen in the increase in the control of the independent move- 
ments of the fingers. Such actions are very poorly developed in Lemurs, a little 
°6 Keith, Hunterian Lectures on Certain Phases in the Evolution of Man, 
Brit. Med. Journ., April 6, 1912, p. 788. 
37 CG. and O. Vogt, op. cit., pp. 392, 393, and 394; also Brodmann, op, cit., 
supra. 
