Between the years 1879 and 1885 inclusive, Flower appears to have devoted much of his attention to elaborating a satisfactory biological classification of the various races of mankind. In the former he drew up a preliminary scheme of this nature, which was published in the _British Medical Journal_ for 1879 and 1880, under the title of “Anatomical Characters of the Races of Man.” Impressed with the importance of having some well-marked feature, other than those afforded by the skull, by means of which the skeletons of such races could easily be distinguished, he turned his attention to the scapula, or shoulder-blade, and in 1880, with the assistance of Dr. J. G. Garson, published in the _Journal of Anatomy and Physiology_ a paper “On the Scapular Index as a Race-Character in Man.” On the whole, although the number of skeletons examined was confessedly insufficient, the results obtained were decidedly satisfactory, and agreed fairly well with those of other observers. The Australians and Andamanese, for instance, accorded in this respect with the Negro type. On the other hand, Bushman skeletons, as had been observed in Paris, approached in this respect to the Caucasian type, while the Tasmanians were unexpectedly found to differ markedly from the other black races in their scapular index. In 1884, in a paper published in the _Journal_ of the Anthropological Society, Sir William recorded the results of a large series of observations in regard to the value of the size of the teeth as a race-character, and was enabled, by means of a “dental index,” to divide the human species into a “Microdont,” or small-toothed group, a “Mesodont” group and a “Macrodont,” or large-toothed group. In the first group were included Europeans and other members of the Caucasian stock, as well as Polynesians, and many of the non-Aryan tribes of Central and Southern India. In the second group came Chinese, American Indians, Malays, and African Negroes; while in the third were included Melanesians, Andamanese, Australians, and Tasmanians. If it be borne in mind, as explained in the original paper, that the teeth in African Negroes are actually larger than in Europeans, although the “index” is reduced by the great length of the base of the cranium (which forms a factor in the index) in the former, the results accord remarkably well with the under-mentioned classification of the human species, which is indeed partly based on the character in question.