This question is, however, wrapped up in a wider one. Its solution depends upon the ancestry of mammals. If the Mammalia are to be derived from reptiles with simple conical teeth, then the first stage in the development of trituberculy is proved. On the other hand, however, the evidence is gradually growing that the Theromorpha represent more nearly than any non-mammalian group with which we are acquainted the probable ancestral form of the mammals. These animals offer some support to both the leading views. _Cynognathus_ had triconodont teeth which, as will be pointed out later, are a theoretically intermediate stage in the evolution of tritubercular teeth; on the other hand, the teeth of _Diademodon_ and some others are multituberculate, and have been very properly compared to the multitubercular teeth of such primitive mammalia as the Ornithorhynchus. Professor Osborn is no doubt correct in italicising a remark of an anonymous writer in _Science_ to the effect that in _Diademodon_ the teeth, though multitubercular, show the prevalence of three cusps arranged in the tritubercular fashion. {57} But this may be only a proof that the multitubercular antedates the tritubercular. It may be, indeed, that the mammalian tooth was already differentiated among the mammal-like Saurians and that from such a form as _Cynognathus_ the Eutheria and other forms in which a tritubercular arrangement can be detected were evolved, and from such form as _Tritylodon_ the Monotrematous branch of the mammals. This way of looking at the matter harmonises a much-disputed question, but involves a diphyletic origin of the mammals--an origin which for other reasons is not without its supporters. We shall now attempt to give a general idea of the facts and arguments which support or tend to support "trituberculy." As a matter of fact the name is inaccurate; for the holders of this view do not derive the mammalian molar from a trituberculate condition, but in the first place from a simple cone such as that of a crocodile!