194 CRITIQUES AND ADDRESSES. [ix. 



to a mere style ankylosed throughout nearly its whole 

 length with the radius, and appearing to be little more 

 than a ridge on the surface of the latter bone until it is 

 carefully examined. The front toes are still three, but 

 the outer ones are more slender than in Anchitherium, 

 and their hoofs smaller in proportion to that of the 

 middle toe ; they are, in fact, reduced to mere dew- 

 claws, and do not touch the ground. In the leg, the 

 distal end of the fibula is so completely united with the 

 tibia that it appears to be a mere process of the latter 

 bone, as in the Horses. 



In Equus, finally, the crowns of the grinding-teeth 

 become longer, and their patterns are slightly modified ; 

 the middle of the shaft of the ulna usually vanishes, and 

 its proximal and distal ends ankylose with the radius. 

 The phalanges of the two outer toes in each foot dis- 

 appear, their metacarpal and metatarsal bones being left 

 as the " splints." 



The Hipparion has large depressions on the face in 

 front of the orbits, like those for the " larmiers " of many 

 ruminants ; but traces of these are to be seen in some 

 of the fossil horses from the Sewalik Hills ; and, as 

 . Leidy's recent researches show, they are preserved in 

 Anchitherium. 



When we consider these facts, and the further circum- 

 stance that the Hipparions, the remains of which have 

 been collected in immense numbers, were subject, as 

 M. Gaudry and others have pointed out, to a great 

 range of variation, it appears to me impossible to resist 

 the conclusion that the types of the Anchitherium, of 

 the Hipparion, and of the ancient Horses constitute the 

 lineage of the modern Horses, the Hipparion being the 

 intermediate stage between the other two, and answer- 

 ing to B in my former illustration. 



The process by which the Anchitherium has been con- 



