CHAP. Vl] THE DENTAL SYSTEM OF THE PEIMATES 



293 



Forsyth-Major, who (Proc. Zool. Sue. 1893), for Rodents, proposed 

 the alternative theory known as that of Multituberculisin or Poly- 

 buny. Forsyth -Major is able to point to the facts (a) that in the 

 most ancient of the fossil mammals (Fig. 208) the molar teeth arc not 

 tritubercular, but multitubercular, i.e. furnished with many small 

 cusps 1 ; (b) that the Prototheria, which include the most primitive 



Lingual 

 aspect. 



X5 



Pig. 208. To the left. Two upper molar teeth of Ornithorhyachus. To the 

 right. A molar tooth of Microlestes moorei. (After Thomas and Osborn.) 



of known mammals (whether recent or fossil), the teeth are also of 

 multitubercular type. Fossil remains of animals clearly ancestral 

 to the existing Prototheria are not definitely known. One fossil 

 form with characters suggestive of such a relation is Tritylodon 

 (Jurassic), with multituberculate molar teeth. According to this 

 theory the evolution of molar teeth has involved the loss of cusps 



1 The multituberculate form Microlestes is of Upper Triassic antiquity, whereas 

 the most ancient trituberculate form, viz. Amphitherium, is of Mid-Jurassic 

 antiquity only. 



