(_b_) If the apes be thus rejected, the next question is, Would the Mauer jaw be appropriate to such a cranium as that of Pithecanthropus? I believe an affirmative answer is justifiable. It is true that an excellent authority (Keith[7]) hesitates on the ground that the mandible seems too massive for the skull, though the same writer recognises that, in regard to the teeth, the comparison is apt. This is a difficult point. For instance the _H. moust. hauseri_ (cf. Chapter II) has a mandible which is far 'lower' than the capacity of the brain-case would lead one to expect. Therefore it seems that the degree of correlation between mandible and capacity is small, and to predict the size of the brain from evidence given by the jaw is not always safe. It is to be remembered that special stress was laid by Professor Dubois (cf. p. 4) on the fact that the teeth of Pithecanthropus when compared with the skull-cap are inadequately small, if judged by the ape-standard of proportion. The characters of the teeth, in so far as upper and lower molars can be compared, present no obstacle to such an association, and in fact provide some additional evidence in its favour. The crucial point seems therefore to be the massiveness of the jaw. With regard to this, the following remarks may be made. First, that the skull-cap of Pithecanthropus is on all sides admitted to shew provision for powerful jaw-muscles. And further, in respect of actual measurements, the comparison of the transverse width of the Javanese skull-cap with that of the Mauer jaw is instructive. For the skull-cap measures 130 mm. in extreme width, the jaw 130 mm. The association of the two does not, in my opinion, make an extravagant demand on the variability in size of either part. A curious comparison may be instituted between the Mauer jaw and the corresponding bone as represented by Professor Manouvrier (cf. Dubois[8], 1896) in an attempted reconstruction of the whole skull of Pithecanthropus. Professor Manouvrier's forecast of the jaw differs from the Mauer specimen chiefly in regard to the size of the teeth, and the stoutness of the ascending ramus. The teeth are larger and the ascending ramus is more slender in the reconstruction than in the Mauer specimen. (_c_) Passing from the consideration of Pithecanthropus to that of human beings, the general results of the comparisons that can be made will shew that the gap separating the jaw of Mauer from all modern human representatives is filled by human jaws of great prehistoric antiquity.