TKITUBERCULY 5/ 



Tint this may be only a proof that the multitubercular ante- 

 dates the tritiibercular. It may be, indeed, that the mammalian 

 tooth was already differentiated among the mammal-like Saurians, 

 and that from such a form as Ci/no[inathus the Eutheria, and other 

 forms in which a trituljercular arrangement can Ije detected were 

 evolved, and from such form as Tritylodfm the Monotre- 

 matous branch of the mammals. This way of looking at the 

 matter harmonises a much -disputed question, l)ut 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 " trituljerculy." As 

 a matter of fact the name is inaccurate ; for the holders of this 

 view do not derive the mammalian moLir from a tritul)erculate 

 condition, but in the first place from a simple cone such as that 

 of a crocodile ! 



To this main a.nd at first only 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 Trir.onodon, so named on that 

 very account. Among living mammals the Seals and the 1'hyla- 

 cine all show sonie triconodont teeth. A Toothed Whale, it may 

 be remarked, is a living examjile of a mammal with monocono- 

 tlont teeth. The three primary cusps, as the supporters of Cope's 

 theory of tritulierculism 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 sliglitly 

 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 hy})ocone, was 

 developed. The three main cones then moved, or rather two of them 

 moved, so as to form a triangle : this is the trituljercular stage. 

 Teeth of this pattern are common, and occur in such ancient 

 forms as Insectivora 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 reser^'e 

 the term trituliercular for those teeth in which the hypocone has 

 appeared. The platform bearing the hypocone widened into the 



