190 1.] Gidley^ The North American Species of Equus. 



95 



netastyle 



hypostylle'— 

 hypocom — 



■pr.otoconule 



-protocone 



—prefossette 



has been worn away they have all become united by narrow 



isthmuses, and the fun- mesostyls parastyle 



damental tooth pattern 

 of the horse is pre- 

 sented. (Fig. 2, C, D.) 

 The five prominent 

 points or cusps on the 

 triturating surface of a 

 newly erupted molar or 

 premolar tooth are the 

 paracone, met aeon e, 

 protocone, protoconule, 

 and a cusp apparently 

 formed by the union of 

 a ridge thrown out from 

 the hypostyle meeting 

 the metaloph at about 

 its middle point. (Fig. 

 2, A.) The cusps form- 

 ing the ectoloph are very 

 early united, as is also 

 the protocone with the 

 protoconule. The next 

 points of union are 

 usually at the anterior 

 and posterior walls of 

 the tooth, where the pro- 

 toloph unites with the 

 parastyle, and where the 

 . hypostyle unites with the 

 metastyle ; usually then 

 the antecrochet and 

 crochet unite, and final- 

 ly the metaloph extend- 

 ing across from the 

 metaconule unites with 

 the ectoloph directly op- 

 posite the mesostyle ; 

 this is because the metaloph is usually much depressed opposite 



C 



r/-ocAef--j__ 



D 



vietdlftplL 



2irotoloj}h 



Fig. 2. Cusps, Crests, Styles, Crochets, and Fossettes 

 in the molar teeth of the Horse {E. complicatus). A , 

 unwornlcrown. B-D, successive stages of wear. 



