Two years later (1867), Flower contributed to the same journal a paper on the anatomy of the West African chevrotain, _Hyomoschus aquaticus_, or, as it is now called, _Dorcatherium aquaticum_. The specimen on which the paper was based was the first of its kind which had ever been dissected—at least in this country; and the result of its examination was to confirm the view that the mouse-deer, or chevrotains, cannot be included among the true ruminants, or Pecora, but rather that they form a group (Tragulina), in many respects intermediate between the latter and the pigs and hippopotamuses, or Suina. To the essential difference between the chevrotains and the musk-deer, which have often been confounded, Flower was very fond of recurring in his later writings. About the year 1866 Sir William began to turn his attention to the teeth of mammals, more especially as regards the mode in which the milk or baby series is succeeded by the permanent teeth, and the general homology of the milk with the permanent, and of the individual teeth of both series with one another. As the result of these investigations he published during the next few years the following papers on this subject. First and most important, one on the development and succession of the teeth of marsupials, which appeared in the _Philosophical Transactions_ for 1867. In the following year he delivered before the British Association at Norwich a paper entitled “Remarks on the Homologies and Relation of the Teeth of the Mammalia,” which was published in the _Journal of Anatomy and Physiology_ for the same year. In that year he also published, in the _Proceedings_ of the Zoological Society, an account of the homology and succession of the teeth in the armadillos. A general sketch from his pen of the dentition of mammals was published in the _British Medical Journal_ for 1871, while in the _Transactions_ of the Odontological Society for the same year, appeared a paper on the first, or milk, dentition of the Mammalia. By far the most important of this series of papers is undoubtedly the one on the succession and homologies of the teeth in the marsupials or pouched mammals; and it is the one which contains, perhaps, the most noteworthy discovery made by Flower.