TOOTH-GENBSlS I2f THE CANIDJE. 475 



the upper carnassial of the Dog forms the posterior part of the 

 Metacone, and in the lower the posterior (smaller) part of the 

 Hypoconid. Consequently, it will be seen that the talon of 

 the lower carnassial appears very early. This is in accordance 

 with the early appearance, geologically, of the trituberculo- 

 sectorial type of tooth. Moreover, Forsyth Major (11) asserts 

 that the talon, though reduced, as compared with the rest of the 

 tooth, in the Carnivora, is well developed in all other orders — 

 therefore, cL priori, it is not a late development ; and he also 

 points to the fact that several Archaic Eutheria, including- some 

 Creodonta from the Cernaysian fauna of Eheims, have a more 

 distinctly marked talon than in many later forms, both in longi- 

 tudinal extension and in height of cusps. Again, Goodrich affirms 

 (5) that we must conclude that the common ancestors of both 

 Placentals and Marsupials possessed this (trituberculo-sectorial) 

 type of tooth. 



Following upon this, the next structure to be added is what 

 I propose to term the Secondary Cone. It arises upon the 

 posterior slope of the Primary cone, and is of mechanical origin 

 due to contact with the Primary cone of the opposite jaw. This 

 cone is seen in its most rudimentary form in the anterior pre- 

 molars of the Dog. The more it becomes developed the more 

 the opposing cusp would tend to wedge it backwards and 

 separate it from the Primary cone from which it has been de- 

 veloped. This cone forms the anterior part of the Metacone of 

 the upper carnassial, and the Metacone of the upper true molars. 

 In the lower carnassial it forms the anterior, larger portion of 

 the talon, and postero-external cusp of m^^. This cusp oulj 

 develops, to any extent, in the premolars of those forms whose 

 dentition approximates to the Carnivorous type. 



Upon the internal cingulum there develops a Centro-internal 

 cusp, situated slightly posteriorly to the middle of the antero- 

 posterior line of the tooth. This cusp is not developed in the 

 premolars of the Canidae. It forms in the molars the cusp ci 

 (fig. 3, B) and gives rise to the Metaconid of the lower carnassial. 



As the upper jaw comes to overlap the lower, the opposing 

 cusps would so interlock that the internal cingula of the molars 

 would tend to be wedged inwards away from the main mass of 

 the tooth ; the depression thus formed, other cusps would tend 

 to be formed, giving rise to those marked pr and i in the same 

 figures. 



