HORSE. 575 



Cuvier(l) was unable from the materials at his command to 

 detect any characters in the bones or teeth of the different existing 

 species of Equus or in the fossil remains of the same genus, by 

 which he could distinguish them, save by their difference of size. 

 Amongst the numerous teeth of a species of Equus, as large as a 

 horse fourteen hands and a half high, collected from the Oreston 

 cavernous fissures, I have found specimens clearly indicating two 

 distinct species, so far as specific differences may be founded on 

 well-marked modifications of the teeth. 



One of these, like the ordinary Equus fossilis of the drift and 

 pleistocene formations, differs from the existing Equus caballus by 

 the minor transverse diameter of the molar teeth ; the other, in the 

 more complex and elegant plication of the enamel, and in the 

 bilobed posterior termination of the grinding surface of the last upper 

 molar more closely approximates to the extinct Horse of the miocene 

 period, which H. v. Meyer has characterised under the name of 

 the Equus caballus primigenius. The Oreston fossil teeth differ, 

 however, from this in the form of the fifth or internal prism of 

 dentine in the upper molars, and in its continuation with the anterior 

 lobe of the tooth ; the fifth prism p being oval and insulated in the 

 Equus primigenius of v. Meyer, {Hippotherium, Kaup. PI. 136, fig. 3). 



The Oreston fossil molar teeth, which in their principal 

 characters manifest so close a relationship with the miocene Equus 

 primigenius, differ, like the later drift species {Eq. fossilis), from the 

 recent Horse in a greater proportional antero-posterior diameter of 

 the crown and also in a less produced anterior angle of the first 

 molar. I have named this ancient British fossil Horse Equus 

 plicidens{2). The fossil Horse {Equus curvidens) of South America 

 which coexisted with the Megatherium and, like it, became extinct 

 apparently before the introduction of the Human Race, differs from 

 the existing Horse by the greater degree of curvature of the upper 

 molars. (3). 



(1) 'Ossemens Fossiles,' 4to. 1822, torn. ii. pt. i, p. HI. 



(2) * History of Brit. Fossil Manamalia, 8vo. p. 392. 



(3) See * Catalogue of Fossil Mammalia in the Museum of the Royal College of Surgeons,' 

 4to. p. 235. 



