Il TRITUBERCULY sy, 
Sut this may be only a proof that the multitubercular ante- 
dates 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 TZvitylodon the Monotre- 
matous 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 1s not without its supporters. 
We shall now attempt to give a general idea of the tacts 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 ! 
To this main and at first oniy cusp came as a reinforcement 
an additional cusp at each side, or rather at each end, having 
regard to their position with reference to the long axis of the 
jaw. This stage is the “ triconodont ” stage, and teeth exist among 
living as well as extinct mammals which show this early form of 
tooth. We have, indeed, the genus 7vriconodon, so named on that 
very account. Among living mammals the Seals and the Thyla- 
cine all show some triconodont teeth. A Toothed Whale, it may 
be remarked, is a living example of a mammal with monocono- 
dont teeth. The three primary cusps, as the supporters of Cope’s 
theory of trituberculism denominate them, are termed respectively 
the protocone, paracone, and metacone, or, if they are in the teeth of 
the lower jaw, protoconid, paraconid, and metaconid. At a slightly 
later stage, or coincidently, a rim partly surrounded the crown of 
the tooth; the rim is known as the cingulum, and from a pro- 
minent elevation of this rim a fourth cusp, the hypocone, was 
developed. The three main cones then moved, or rather two of thena 
moved, so as to form a triangle; this is the tritubercular stage. 
Teeth of this pattern are common, and occur in such ancient 
forms as Ingectivora and Lemurs, besides numerous extinct groups. 
An amendment has been suggested, and that is to term the teeth 
with the simple primitive triangle “trigonodont,” and to reserve 
the term tritubercular for those teeth in which the hypocone has 
appeared. The platform bearing the hypocone widened into the 
