TOOTH-GENESIS IN THE CANID^. 



451 



absurdum " to derive the remainder of the tooth from this, a 

 structure of admittedly later appearance than the tooth itself. 



From this it will be seen that I regard the Protocone of the 

 upper carDassial and the anterior cinguluin-cusps of the anterior 

 premolar, the canine, and the incisors as homologous. 



Fig. 2. 



3-^ 



Permanent dentition of Canisjamiliaris. Lettering explained in text. 

 Description of the Permanent Teeth of the Bog. CFig. 2.) 



The cusp hy is homologous with the cusp inadvertently lettered g in fig. 1. 



Upper Jaw. — The central incisor has a well-marked central cone and decided 

 lateral cusps, continuous with and formed by the cingulum. 



The outer cusp is more distinct than the inner. 



i.^ possesses the same characters, but is somewhat larger. 



i.^ is more caniniform. The anterior (inner) cusp (ca) is scarcely noticeable, 

 while the posterior is marked and situated nearer to the base of the tooth {cp). 



All these teeth have well-marked internal cingula continuous with these small 

 cusps. 



The canine is a long, somewhat compressed, recurved tooth ; the lateral cusps 

 are not so distinct as in the deciduous canine, though the posterior cusp (cp) 

 is still to be made out. 



The first premolar ( pm.^ ) is small and conical, its posterior slope being 

 greater than the anterior. There is a posterior prominence (cp), hardly to be 

 called a cusp, into which the well-marked internal cingulum runs. The cingulum 



