96 THE fcEMtfAStf? TEETS. 



tion of the inner side, an isolated ellipse of enamel 

 inclosing dentine, and not joined with the main body 

 of the tooth by an isthmus of dentine, as in Equus, at 

 least until the teeth are nearly worn out. Anchippus, 

 also from the Pliocene, resembled in its teeth Anchi- 

 therium of the Miocene, a genus now considered as 

 typical of a family distinct from that of the horse. In 

 Anchitherium the molars have short crowns, devoid of 

 cement, and are inserted by distinct roots. The Mio- 

 cene species were not larger than a sheep. The Eocene 

 representatives of the group were still smaller, the 

 largest hardly exceeding a fox in size. They belong 

 to the genus Orohippus. The dentition is very simi- 

 lar to that of Anchitherium, but the first upper pre- 

 molar is larger and the succeeding ones smaller than 

 in that genus. The diastema, or 'place for the bit,' is 

 distinct. The canines are large, and near the incisors. 

 The crowns of the molars are short and destitute of 

 cement, and the skeleton is decidedly equine in its 

 general features. 



" The gradual elongation of the head and neck may 

 be said to have already begun in Orohippus, if we 

 compare that form with other most nearly allied mam- 

 mals. The diastema was well developed even then, but 

 increased materially in succeeding genera. The num- 

 ber of teeth remained the same until the Pliocene, 

 when the front lower premolar was lost, and subse- 

 quently the corresponding upper tooth ceased to be func- 

 tionally developed.* The next upper premolar, which 

 in Orohippus was the smallest of the six posterior 



* The italics are mine. This " corresponding upper tooth 

 that ceased to be functionally developed," is the identical tooth 

 that now appears as a mere remnant. 



