68 COMPAEATIVE DENTAL ANATOMY 



very conclusively that the mammals have evolved 

 from the reptiles. The concrescence theory is 

 that the large number of teeth which we find in 

 the fish and reptiles have fused together and made 

 a number of large teeth with a varying number of 

 cusps. There is very little to support this theory 

 except a few fossil forms that have been found in 

 various parts of the country. The teeth of the 

 mastodon and mammoth seem to be made up of 

 a number of cusps fused together. The plates of 

 the elephant's teeth might also come under this 

 form of evolution, but there is nothing to prove 

 that the majority of mammals have had their 

 molars evolved in that manner. Briefly, the 

 argument against the concrescence theory is that 

 the number of teeth have decreased from the 

 fishes to reptiles and we find the primitive reptiles 

 having single conical teeth. The majority of the 

 teeth of the fishes were located on the palates and 

 vomer and in the higher reptiles and mammals 

 the maxillae and mandible carry the teeth. The 

 low forms of mammals generally have few teeth 

 and they are all conical as in the ant-eaters and 

 armadillos. As we reach the higher forms we 

 find that the cusps begin to appear on these coni- 

 cal teeth. 



The Tritubercular Theory. The tritubercular 

 theory is that the molars of mammals have 

 evolved from a molar with three cusps. This 



