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Certain of the lower mammal-like reptiles show transitional stages, for in them one phalanx of the third digit and two phalanges of the fourth digit were much reduced in length and appear to be almost on the point of disappearing (Broom). Very possibly the reduction in the number of phalanges in cynodonts was associated with the newer method of walking more on the ends of the fingers and toes.

Thus it may be seen that man has inherited not only the number of his fingers and toes but even the number of the small bones on each finger and toe from the mammal-like reptiles of the Triassic period.

Man also owes to the higher mammal-like reptiles a whole series of structural improvements in his skull, teeth, and jaws, which the limits of space here compel us to deal with in a summary fashion, for the teeth of these reptiles are already reduced to two sets, corresponding to the milk teeth and the permanent teeth of man, and are differentiated into incisor, canine, premolar, and molar teeth, as in the mammals, including man. Moreover, the cynodonts clearly foreshadow the mammals in the progressive predominance of the dentary or tooth-bearing bone of the lower jaw, one on each side, which in the mammals is the only surviving one of the numerous separate pieces found in the lower jaw of reptiles.

The higher mammal-like reptiles take us almost to the threshhold of the mammals, and they almost exactly divide the structural differences between mammals and primitive reptiles. Meanwhile the typical or modernized reptiles, including the turtles, lizards, crocodiles, and dinosaurs, acquired divergently specialized characters that carried them far away from the mammal-like reptiles, which, as we