In one sense the reception accorded by palaeontologists to the fossil jaw of Mauer differs remarkably from most of the comparable instances. That difference consists in the comparative absence of controversy excited by its discovery. This must not be ascribed to any lack of ardour on the part of archaeologists. More probable is it that with the lapse of time, the acceptance of an evolutionary interpretation of the origin of man has gained a wider circle of adherents, so that the claims of even so sensational a specimen as this, are sifted and investigated with a judicial calm much more appropriate and certainly more dignified than the fierce outbursts occasioned by some of the earlier discoveries. It remains to institute brief anatomical comparisons between the Mauer jaw and those of the highest apes on the one hand, and of the most primitive of human beings on the other. (_a_) Of the three larger anthropoid apes available for comparison, it is hard to say which presents the closest similarity. The Gibbons do not appear to approach so nearly as these larger forms. Among the latter, no small range of individual variations occurs. My own comparisons shew that of the material at my disposal the mandible of an Orang-utan comes nearest to the Mauer jaw. But other mandibles of the same kind of ape (Orang-utan) are very different. The chief difficulty in assigning the possessor of the Mauer jaw to a pithecoid stock has been mentioned already. It consists in the inadequate size of the teeth. In addition to this, other evidence comes from the results of an examination of the grinding surfaces (crowns) of the molar teeth. These resemble teeth of the more primitive human types rather than those of apes. Finally the convergence of the two rows when traced towards the canine or eye-tooth of each side, points in the same direction.