TRANSACTIONS OF THE SECTIONS. 139 
was limited to the resent act in which the animal was engaged, or, at most, took 
in very little beyond it, the native impulse or desire seeking each step in succession 
by itself, because the animal’s power of thought could not take in the end of the 
series. 
A typical case of intelligence in the dog was similarly analyzed ; and it was shown 
that the dog had the power of thinking a particular act as a part of a series, combining 
with the idea of that act a thought of the series of acts, each with its effect, and all 
with their result. It was pointed out that this power of forming a plan to attain an 
end, which was possessed by the dog, differed from man’s power of design in this 
respect, that man can not only think an act as part of a series leading to a result, 
but that he has the further power of believing, with more or less certainty, that 
each step in the series of acts will be followed by the consequence connected with 
it in thought. This implies inference from laa experience, and inference is the 
process of imparting to the idea of a fact the degree of assurance which belongs to 
it as a case of a general principle. 
Characteristic instances of intelligence in the baboon and the orang-outang 
were minutely analyzed; and it was shown that while these manifested an intel- 
ligence to which the dog could not attain, the superiority consisted in the power 
of combining in an assured sense of reality with the idea of an object some abstract 
coexistence or succession which had been gathered from similar objects as a uni- 
formity of experience; that is, in the power of thinking a case of a general principle 
with the belief which belongs to it as such. 
This step of mental development in the orang-outang compared with the dog 
is similar in its essential nature to the previous step, which may be observed in the 
dog compared with the lower vertebrate animal. Each is a new power of combining 
thoughts which otherwise would have required a long course of repetition in con- 
junction with each other before they could by association have grown together; and 
each combines those thoughts in a closer and more vivid union through the medium 
of anew element—namely, sense of progress towards an end in the one case, and 
belief in the maintenance of a uniformity in the other. 
It was shown by a general survey of the highest kinds of intelligence manifested 
by the various classes and orders of vertebrate animals, coupled with a minute 
analysis of apparently contrary instances, that vertebrate animals may be divided in 
respect of their mental powers into three groups, of which the lowest can comprise 
in one act of thought only what can be perceived by sense all at the same time; 
the second can comprise in one act of thought a series of successions in time so as 
to think a single object of sense as part of such a series; and the third can comprise 
in one act of thought an entire class of coexistences or successions so as to combine 
with a particular fact the common element of coexistence or succession belonging to 
the class. To the first group belong the vertebrate animals below the Rodent order 
of Mammalia. In the second group the Rodents may claim a place (though their 
powers of purpose are small), along with the orders of Mamaia, above them up 
to the Quadrumana. To the third group belong the monkeys, the Anthropoid apes, 
and man. 
With these facts of the development of intelligence, the facts of the development 
of the brain are in striking correspondence. “Vor the cerebrum of the oviparous 
vertebrata corresponds only with the anterior lobe of the human cerebrum. It is 
among the Rodentia that we meet with the first distinct indication of a middle 
lobe; while the posterior lobe makes its first appearance in monkeys, and is 
distinctly present in the Anthropoid apes’ (Carpenter’s ‘Mental Physiology,’ 
p. 116). And the inference at once occurs, that the functions of the anterior lobe 
belong to the act of thinking single objects of sense, those of the middle lobe to 
the act of thinking such objects with a sense of a succession of them and as part 
of that succession, and those of the posterior lobe to the act of thinking a coex- 
istence or succession of them as a case of a general principle. 
In confirmation of this inference, the other features of brain-development were 
considered; and it was shown that the analogies of the nervous system seem to 
indicate that the increased development of the fibres of the brain serves to make 
the action of its different parts consentaneous, so as to give correspondence to the 
muscular action of the two sides of the body and strength and steadiness to 
