74 Thomas Henry Huxley 



horses — which in fact are so similar to horses, that j-oii may 

 follow descriptious given in works upon the anatomy of the 

 horse, upon the skeletons of these animals — but which differ 

 in some important particulars. For example, the structure of 

 their fore and hind limbs is somewhat diflFerent. The bones, 

 which, in the horse are represented by two long splints, im- 

 perfect below, are as long as the middle metacarpal and meta- 

 tarsal bones ; and, attached to the extremity of each, is a digit 

 with three joints of the same general character as those of the 

 middle digit, only very nmch smaller. These small digits are 

 so disposed that they could have had but very little functional 

 importance, and they must have been rather of the nature of 

 the dew-claws, such as are to be found in many ruminant 

 animals. The Hipparioti, as the extinct European three-toed 

 horse is called, in fact presents a foot similar to that of the 

 American Pfotohippus except that in Hipparion the smaller 

 digits are situated further back, and are of smaller proportional 

 size than in the Protohippus. 



"The ulna is slightly more distinct than in the horse ; and 

 the whole length of it, as a very slender shaft, intimately 

 united with the radius, is completely traceable. The fibula 

 appears to be in the same condition as in the horse. The teeth 

 of the Hipparion are essentially similar to those of the horse, 

 but the pattern of the grinders is in some respects a little more 

 complex, and there is a depression on the face of the skull in 

 front of the orbit, which is not seen in existing horses. 



" In the earlier Miocene and perhaps in the Eocene deposits 

 of some parts of Europe, another distinct animal has been dis- 

 covered, which Cuvier, who first described some fragments of 

 it, considered to be a Palceotherium, but as further discoveries 

 threw new light on its structure, it was recognised as a distinct 

 genus, under the name oi Anchithcriuin. 



"In its general characters the skeleton of A^ichithcriuvi is 

 very similar to that of the horse, in fact Lartet and De Blain- 

 ville called it Palceotheriutn equinum or Hippoides ; and 

 De Cristol, in 1847, said that it differed from Hipparion in little 

 more than the characters of the teeth, and gave it the name of 

 Hipparitheriuni. Each foot possesses three complete toes : 

 while the lateral toes are much larger in proportion to the 

 middle toe than in Hipparion, and doubtless rested on the 



