THE ROOTS OF TEETH 259 



that of Reptiles is the possession of teeth with more than one 

 root. It is not true of all mammalian teeth and is more char- 

 acteristic of the molars than of the antemolar series. In the 

 Cynodonts we find the reptilian character of a single root even 

 in the flat quadrate molars of Sesamodon and the very mammal- 

 like molars of Diademodon. The cheek teeth of Protodonta 

 show incomplete separation of the root into two fangs (Fig. 

 13). In all known Triconodonta and Trituberculata on the 

 other hand the premolars and molars present at least two 

 roots. In the upper teeth these support the para- and metacones 

 respectively but in some genera, Dryolestes for example, the 

 upper molars differ from the premolars in possessing three 

 roots, a large medial one beneath the protocone and two smaller 

 lateral ones supporting the outer cusps of the crown. In most 

 primitive Mammals likewise, whether they are of marsupial or 

 placental stock, the premolars and molars are two-rooted al- 

 though the protocone and its supporting internal root in the 

 upper molars may be absent. We are justified then in con- 

 sidering the two-rooted brachyodont type as the primitive mam- 

 malian form. Further, it is by no means uncommon to find an 

 actual bifanged appearance in the canine. This condition oc- 

 curs in Talpa the Mole, and in Erinaceus the Hedgehog, both 

 being animals which from their lowly ordinal position are likely 

 to retain unchanged the primitive features of the tooth roots. 

 On reference to Fig. 94 it will be noted that evidence of separa- 

 tion of the root into two exists even in the incisors of certain 

 primitive animals.* Grooving of the root of a tooth must then 

 be taken as indicating a geologically older bifanged condition. 

 We have observed previously that there are various ways 

 whereby the teeth become elongated to compensate for marked 

 attrition, the result of a herbivorous diet. There is the elonga- 

 tion of the cusps so well seen in all lophodont Marsupials 

 especially in the grazing Kangaroos, and the elongation of the 

 body of the tooth so plainly marked in the Bandicoot Thala- 



*The Flying Lemur Galeopithecus has two roots in the outermost (third) incisor 

 as well as in the canine. 



