428 ORDERS OF MAMMALIA. 



Three fossil genera of this family are known viz., Anchi- 

 therium, Hipparion, and Equus, the last of which is represented 

 at the present day by the existing Horses, Asses, and Zebras. 



Anchitherium comprises some singular forms from the Upper 

 Eocene and Lower Miocene. In this genus each foot is fur- 

 nished with a single functional hoofed toe, flanked by two 

 small hoofed digits, which are sufficiently developed to touch 

 the ground. Anchitherium is nearly related to Palizotherium. 



Hipparion is confined to the Upper Miocene and Pliocene 

 deposits, and is distinguished by the fact that each foot pos- 

 sessed a single fully-developed toe, bordered by two function- 

 ally useless toes, which did not touch the ground, but simply 

 dangled on each side of the central toe. 



In the genus Equus, the foot consists of a single developed 

 toe, but there are two rudimentary toes in the form of little 

 bony spines the so-called " splint-bones " which are attached 

 to the carpus on either side of the metacarpal of the single 

 functional toe. In the Pliocene period appear, for the first 

 time, remains of horses which, like the present form, possessed 

 only a single toe encased in a single hoof. It is interesting to 

 observe that one of the Pliocene horses (Equus curvideiis) 

 occurs in South America, though this continent certainly pos- 

 sessed no native horse at the time of its discovery by the 

 Spaniards. About twenty horses one of them standing no 

 more than two and a half feet in height have been described 

 from North America, in which continent no indigenous horse 

 existed at the time of its discovery. The Equus fossilis of the 

 Post-Pliocene and Recent deposits is specifically undistinguish- 

 able from the common horse (Equus caballus). 



SECTION B. ARTIODACTYLA. In this section of the Ungu- 

 lates the number of the toes is even either two or four and 

 the third toe in each foot forms a symmetrical pair with the 

 fourth. The dorso-lumbar vertebrae are nineteen in number, 

 and there is no third trochanter on the femur. If true horns 

 are present, these are always in pairs, and are supported by 

 bony horn-cores. The antlers of the Deer are also paired, but 

 they are not to be regarded as true horns. The stomach is 

 always more or less complex, or is divided into separate com- 

 partments, and the caecum is comparatively small and simple. 



The section Artiodactyla comprises the Hippopotamus, the 

 Pigs, and the whole group of the Ruminants, including Oxen, 

 Sheep, Goats, Antelopes, Camels, Llamas, Giraffes, Deer, &c. 

 Besides these there is an extensive series of fossil forms com- 

 mencing in the Eocene or Lower Tertiary period, and in many 

 respects filling up the gaps between the living forms. 



