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Throughout all these modifications it must be recollected 
that the foot loses no one of its essential characters. Every 
Monkey and Lemur exhibits the characteristic arrangement 
of tarsal bones, possesses a short flexor and short extensor 
muscle, and a peroneus longus. Varied as the proportions and 
appearance of the organ may be, the terminal division of the 
hind limb remains, in plan and principle of construction, a 
foot, and never, in those respects, can be confounded with a 
hand. 
Hardly any part of the bodily frame, then, could be found 
better calculated to illustrate the truth that the structural 
differences between Man and the highest Ape are of less value 
than those between the highest and the lower Apes, than the 
hand or the foot, and yet, perhaps, there is one organ the 
study of which enforces the same conclusion in a still more 
striking manner—and that is the Brain. 
But before entering upon the precise question of the 
amount of difference between the Ape’s brain and that of Man, 
it is necessary that we should clearly understand what consti- 
tutes a great, and what a small difference in cerebral structure ; 
and we shall be best enabled to do this by a brief study of the 
chief modifications which the brain exhibits in the series of 
vertebrate animals. 
The brain of a fish is very small, compared with the spinal 
cord into which it is continued, and with the nerves which 
come off from it: of the segments of which it is composed 
—the olfactory lobes, the cerebral hemisphere, and the suc- 
ceeding divisions—no one predominates so much over the rest 
as to obscure or cover them ; and the so-called optic lobes are, 
frequently, the largest masses of all. In Reptiles, the mass of 
the brain, relatively to the spinal cord, increases and the cere- 
bral hemispheres begin to predominate over the other parts ; 
while in Birds this predominance is still more marked. The 
brain of the lowest Mammals, such as the duck-billed Platypus 
and the Opossums and Kangaroos, exhibits a still more 
definite advance in the same direction. The cerebral hemi- 
spheres have now so much increased in size as, more or less, 
