Introduction 
3 
dwellers living in swampy forests. Most of their descendants left 
the forests and gradually became altered into such characteristic 
wanderers over the plains as horses, cattle, antelopes, deer and 
lions, in which the brain-growth was the accompaniment of many 
other changes in the body. Others remained in their original 
haunts, and the accession of brain-power was almost the only 
essential change that occurred in any of them. Now, the study 
of many kinds of fossils has shown that when, in successive 
generations, one part of the body begins to increase in size or com- 
plication much more rapidly than the other parts, this increase rarely 
stops until it becomes excessive. As a rule it passes the limit of 
utility, becomes a hindrance, and even contributes to the extermina- 
tion of the races of animals in which it occurs. In the case of the 
brain, however, a tendency to overgrowth might become an 
advantage, and it seems reasonable to imagine that such an over- 
growth in the early ape-like animals eventually led to the complete 
domination of the brain, which is the special characteristic of man. 
The little lemur-like animals of Eocene times would thus pass 
gradually into the larger apes of the Pliocene ; and as soon as 
animals of this kind could feed and defend themselves by craft, 
their teeth and other primitive weapons might degenerate, as 
in man. 
It has long been an aim of students of fossils to discover the 
links that are missing in this hypothetical chain connecting man 
with the early forest mammals, because, apart from adaptation to 
an upright gait, his skeleton is essentially identical with theirs. 
It would be interesting to trace the successive ancestors of the 
existing apes, with the slow improvement in their brain, the 
increasing power of their jaws and teeth, and the accession of 
strength to their arms. It would be still more interesting to 
follow the career of their " cousins," so to speak, in which the 
strengthening of the teeth and arms was ultimately checked and 
even diminished again by the rapid and excessive improvement 
of the brain. Monkeys, apes, and men, however, are remarkably 
wary in temperament, and they seem to have been always little 
liable to the accidents by which ordinary quadrupeds are destroyed, 
buried, and fossilised. Their remains are therefore very rare in 
the rocks, and their history in geological time is being but slowly 
revealed in a few scattered episodes or casual glimpses. These 
are illustrated in the Museum by a series of fossils and plaster 
copies of fossils, which it is the object of the present Guide-Book 
to explain. 
