Friction and pressure changed their lines of incidence with the increasing tendency of man to assume the upright posture, for the surfaces exposed to pressure and friction were only affected when the extensor surface or back of the forearm rested on some supporting object, an attitude extremely common in man as we know him now. Then came the opportunity of the primitive barbarian host, the lemur fashion, by a prolonged counter-attack to recover on the greater part of the forearm the ground lost millions of years before by the ape, and then was engraved on the forearm of man the permanent treaty which we have before us to-day. [46] _Prehistoric Man and His Story_, p. 60 This small and apparently trivial battle-ground has been described at what may seem undue length, but it is a miniature of the rise and fall of little empires such as here engage our attention, and I make no apology for this to the reader who has gone thus far with me, for, on the principle of _ex uno disce omnes_, all that follows in other areas of the hairy coat of mammals will be the clearer, and little repetition will be needed. NOTE.--Two terms have been used somewhat freely in this Introduction, “vestige” and “normal,” and a few remarks upon them are not out of place, for they are both somewhat ambiguous and apt to be carelessly employed. A vestige in biological writings is almost the exclusive property of the Pan-Selectionists, and no one can doubt that on the one hand it is a far more correct term than that of rudiment which Darwin employed so freely, on the other that they have a perfectly legitimate claim to it in a large number of obsolete structures of animal forms. But vestiges, footsteps, footprints, have another and equally correct meaning, even if less often thus employed, in the fact that a vestige or footprint may just as well be a relic of what the race and individuals have _done_, as a relic of what they have _retained_ in the way of possession, and I submit that the facts and arguments I have here advanced afford a valid claim to the term “vestige” in the results of certain _doings_ on the part of animals--as will appear later still more clearly.