PRESIDENTIAL ADDRESS. 581 
all the senses in mammals. The neopallium of the mammal ™ provides a receptive 
organ for impressions of all the senses—touch, vision, and hearing, as well as 
taste and smell, among the rest—which enables the effects of all such perceptions 
to manifest themselves unified in consciousness, and to become recorded in some 
way so that they can be revived again, each discrete sensory impression or the 
one idea excited by all of them, in associative memory. Moreover, it is the 
instrument by means of which all these perceptions, past and present, can be 
freely blended in consciousness, so that the animal is able to appreciate all the 
properties of any object, to whatever sense they may appeal, and can benefit by 
past experience, and so be educated. 
In spite of the opinion of Prof. C. J. Herrick,* I maintain that the neo- 
pallium is a feature distinctive of the mammalian brain, and that it represents 
in itself the unity of the apparatus concerned with psychical phenomena, the 
sensorium commune, which Aristotle postulated as the counterpart of the unity 
of consciousness.?® I am well aware that psychologists may consider this the 
rankest heresy, to judge from the writings of my friend Dr. William Mc- 
Dougall 7; but the anatomical evidence is quite definite and unequivocal that in 
the neopallium of the lowlier Mammalia we have a ‘unitary organ the physical 
processes of which might be regarded as corresponding to the unity of conscious- 
ness.’ Moreover, it fulfils Aristotle’s claim for his sensorium commune of possess- 
ing ‘especially the perceptual functions that are common to the several senses.’ 
Nothing that happens in this area in the course of its enormous expansion and 
differentiation in the higher mammals materially affects this fundamental purpose 
of the neopallium, which continues to remain a unifying organ that acts as a 
whole, though each part is favourably placed to receive and transmit to the rest its 
special quota to the sum-total of what we may call the materials of conscious life. 
Thus the area in which the tract from the eyes ends in the neopallium 
naturally becomes the mechanism for visual perception, but it also serves as a 
means of union between visual and other perceptual parts of the cortex; for if 
the eyes are destroyed, the visual area does not wholly atrophy ; or again, in the 
intact individual the visual impression of an apple is capable of awakening 
memories of perceptions of its ‘feel,’ its weight, its smell and its taste, all of 
which were originally acquired by impressions made upon the receptive area of 
each of the senses concerned. 
The consciousness which resides, so to speak, in this neopallium, and is fed 
by the continual stream of sensory impressions pouring into it and awakening 
memories of past sensations, can express itself directly in the behaviour of the 
animal through the intermediation of a part of the neopallium itself, the so-called 
motor area, which is not only kept in intimate relation with the muscles, tendons, 
and skin by sensory impressions, but controls the voluntary responses of the 
muscles of the opposite side of the body. 
The possession of this higher type of brain enormously widened the scope for 
the conscious and intelligent adaptation of the animal to varying surroundings ; 
a sensory impression once received no longer remained only half an experience, 
which left no lasting impression behind it to influence behaviour in the future, 
or at most a perception uninfluenced by those simultaneously received by other 
sense-organs, and thus incapable of being checked, so to speak; and in the exer- 
cise of this newly acquired power of choice the way was opened for adaptations 
to varying environments entailing manifold structural modifications, in which the 
enhanced plasticity of the new type of animal found expression. 
Nature tried innumerable experiments with the new type of brain almost as 
soon as the humble Therapsid-like mammal felt the impetus of its new-found 
144 T am omitting all reference to birds, in which a new formation makes its 
appearance in the cerebral hemisphere and performs functions in a sense analo- 
gous to those of the neopallium in mammals. It is, however, a specialisation 
incapable of great extension, just as the structure and functions of a bird are so 
highly specialised for flight as to lose the high degree of plasticity of the primi- 
tive mammal. 
18 «The Morphology of the Forebrain in Amphibia and Reptilia,’ Journ. 
Comp. Neur. and Psych., October 1910, p. 439. 
16 See op: cit., Journ. Anat. and Phys., vol. xxxv., p. 453. 
17 Body and Mind, 1911, p. 286. 
