When all these differences between races are given, the question arises, whether they have any significance in regard to mental faculty. I may be permitted to disregard for the moment differences in the size and structural development of the nervous system, and confine myself to the mental significance of other traits. The general analogy of mental development of animals and of man prompts us to associate lower mental traits with theromorphic features. In our naïve, every-day parlance, brutish features and brutality are closely connected. We must distinguish here, however, between the anatomical characteristics of which we have been speaking and the muscular development of the face, trunk, and limbs, due to habitual activity. The hand, which is never employed in activities requiring those refined adjustments which are characteristic of psychologically complex actions, will lack the modelling brought about by the development of each muscle. The face whose muscles have not responded to the innervations accompanying deep thought and refined sentiment will lack in individuality and refinement. The neck that has supported heavy loads, and has not responded to the varied requirements of delicate changes of position of head and body, will appear massive and clumsy. These physiognomic differences must not mislead us in our interpretations. But even without them, we are inclined to draw inferences in regard to mentality from a receding forehead, a heavy jaw, large and heavy teeth, perhaps even from an inordinate length of arms or an unusual development of hairiness. From a strictly scientific point of view, these inferences seem to be open to the most serious doubt. Only a few investigations have been made in relation to these problems, but their results have been entirely negative. Most important among them is the elaborate attempt made by Karl Pearson to investigate the relationship of intelligence to size and shape of the head. His conclusions are so significant that I will repeat them here: “The onus of proof that other measurements and more subtle psychological observations would lead to more definite results may now, I think, be left to those who _a priori_ regard such an association as probable. Personally, the result of the present inquiry has convinced me that there is little relationship between the external physical and the psychical character in man.” I think all the investigations that have been made up to the present time compel us to assume that the characteristics of the osseous, muscular, visceral, or circulatory system, have practically no direct relation to the mental ability of man (Manouvrier).