FIVE TOES SOLIDIFIED IKTO OtfE. 95 



toed limbs would support the body of an animal no 

 larger than a fox, but they would require additional 

 size and strength to support either the larger fossil 

 horses of the Pliocene period or a modern horse. 

 This additional strength was gradually acquired by 

 the enlargement of the limbs and the solidification, 

 as it were, of five toes into one, it being as natural, 

 in conformity to the law of adaptation, for a line of 

 succeeding animal forms to undergo bodily changes 

 as for an individual form to do so. * (See p. 306.) 



During these changes of the toes equally interest- 

 ing changes occurred in the teeth, concerning which 

 Prof. Marsh says (Johnson's N". U. Cyc. ii, 996) : f 



" In the Pliocene tertiary period the horse was rep- 

 resented by several extinct genera, the best known 

 being Hipparion (Hippotherium). The species are 

 small, as the name implies, Hipparion being a dimin- 

 utive from the Greek hippos, a horse. In the upper 

 molars there is in Hipparion, on the anterior por- 



* W. H. Flowers, F.R.S., says : " If we were not so habituated to 

 the, sight of the horse as hardly ever to consider its structure, we 

 should greatly marvel at being told of a mammal so strangely con- 

 structed that it had but a single toe on each extremity, on the end 

 of the nail of which it walked or galloped. Such a formation is 

 without a parallel in the vertebrate series, and is one of the most 

 remarkable instances of specialization, or deviation from the usual 

 type, in accordance with special conditions of life. It can be demon- 

 strated, both by the structure of the foot itself and also by an exam- 

 ination of the intermediate forms, that this toe corresponds to the 

 middle or 3d of the complete typical or pentadactyle foot, the ' ring- 

 finger ' of man ; and there is very strong evidence to show that by 

 a gradual concentration of all the power of the limb upon this toe, 

 and the concurrent dwindling away and final disappearance of all the 

 others, the present condition of the horse's foot has been produced." 



f The five-toed fossil horse had not been discovered when this 

 article was written. See pages 260 to 265. 



