ORDINAL TYPES OF MOLARS: MONOTl: KM ATA 



107 



cannot truly be said that they actually resemble those of any Multituber- 

 culate in the strict sense, because all the higher Multituberculates exhibit 

 an extremely regular mechanical disposition of the cusps, whereas in this 

 living Monotreme the cusps are extremely irregular. Secondly, it does 





External Internal 

 Inferior 



xio 



Internal External 

 Superior 



Fig. to. Molar teeth of Oi~nithorhynchus /IC.-.K'O./'KS, before being shed and functionally re- 

 placed by the horny epithelial plates. After Oldfield Thomas. Xos. 1, 2. Superior and inferior 

 teeth and horny dental pads. X'o. 5. Crown view of a molar of " Microlestes" 



not appear that the Oniithorliynclius molars can be cited as evidence either 

 for or against the tritubercular theory because of the evidently secondary 

 and largely degenerative changes which they have undergone ; they 

 bear evidence (Fig. 56) of descent from a more primitive regularly 



'2. Ptiloilus. First and second inferior molars, worn considerably. These teeth belong to two 

 individuals. 



3. 1'tilvilim. First superior molar of the left side. 



4. Ptiloiltis. Fourth superior prevuolar, first and second molars placed together and reversed 

 in outline to show probable relations. The three shaded teeth on the left side of drawing belong 

 to three individuals. 



.">. ii. Ptilmli's. External and superior views of two lower jaws, showing proportions of the 

 teeth. 



7. -V. nixt-nfxsiix. First and second inferior molars of two individuals placed to u ,-tliri- ,'ind 

 reversed to exhibit the natural position. 



8. A/< /uV(.i/.<xi!.v - i-iiiHiuisti's. First and second superior molars of two individuals placed to- 

 gether and reversed to show the natural position. 



9. Mi iiixruexgH.*. Composition side view of upper and lower dentition as far as known. Teeth 

 and jaws combined from eight individuals. The superior premolars are not yet known with 

 certainty. 



