504 



Vertebrata. 



" accessory toes," which did not touch the ground in walking * Hippaiion lived 

 in recent Miocene times as weU as in the Pliocene. The Genus AncUtherivm is 

 more remote from Equus ; it has toes like Hipparion, but the second and fourth 

 are considerably stronger than in the latter, although stiU much weaker than the 

 thii-d ; the crowns of the molars are shorter than in Equus, the folding more like 

 that of the Rhinoceros (or Pateotherium), the cement little developed ; the wolf 



Fig. 405. Left fore foot of AncUtherium (A, A'), Hipparion (B, B'), Horse (0, 0'), 

 from in front and from within. All similarly decreased (about |). tm trapezium, id 

 trapezoid, m os magTium, u unciform. II, III, IV, second — fourth metacarpals, v rudi- 

 mentary fifth metacarpal. — After Gaudry. 



tooth (first premolar) is larger, and present also in the lower jaw ; the front teeth 

 without the mai-k ; the ulna and fibula better developed than in Equus. This 

 genus, which lived in Miocene times, is very like the Eocene Palseotherium 

 mentioned above. 



Sub-Order 2. Artiodactyla. 



The third and fourth digits on both fore and hind feet are each 

 asymmetrical in themselves, but the two correspond, as does an 

 object with its image in a mirror ; the median plane of the 

 foot passes between these two toes. The third and 

 fifth are smaller, do not usually touch the ground in walking, and 

 are situated somewhat behind the others ; indeed they are often 

 rudimentary or absent. The trochanter tertius is wanting. The two 

 articular facets on the distal edge of the astragalus, for the naviculare 

 and cuboid, respectively, are of about equal size, and both are much 

 arched from before backwards ; the stomach is more or less compli- 



* The fifth metacarpal is present (Fig. 405 B), but quite rudimentary; it may 

 also be present in the horse. 



