THE TEETH OE VERTEBKATES 69 



theory as first advocated has been modified some 

 by various investigators nntil it may be briefly 

 stated as follows: Eealizing that all teeth have 

 developed from the primitive conical teeth which 

 we find in the reptiles by the addition of other 

 cones, this first or primitive cone is called the 

 protocone in the upper arch and the protoconid in 

 the lower. In the evolution of the premolars, 

 such as we find in the upper teeth of man, the 

 protocone becomes the lingual cusp (some writers 

 claim the protocone becomes the buccal cusp in 

 the upper premolars but there is little fo support 

 that theory), and the second cusp becomes the 

 buccal cusp and is called the deuterocone. In the 

 lower premolars the protoconid becomes the buc- 

 cal cusp and the deuteroconid becomes the lingual 

 cusp. Some of the premolars, often the lower 

 second premolar of man, are three cusp teeth, 

 made so by the addition of the third cusp which is 

 called the tritoconid, and when present in the 

 upper arch is called the tritocone. In some of the 

 mammals, a fourth cusp is found which is called 

 the tetarocone in the upper and the tetaroconid in 

 the lower. In the carnivora, we find the cusps of 

 the premolars arranged in a row antero-pos- 

 teriorly. 



In the evolution of the true molars, there is 

 added to the protocone a small anterior cusp 

 which is called the paracone and a small posterior 



