30 EVOLUTION 



Dr. Matthew notices, "to subsist on the 

 hard, comparatively innutritions grasses of 

 the dry plains, which require much more 

 thorough mastication before they can be of 

 any use as food than do the softer green foods 

 of the swamps and forests." 



We must not leave this question of the 

 horse's evolution without calling attention to 

 a fact of great interest, that in the individual 

 development there is LJ>eries of changes 

 which to some extent correspond with the 

 historical steps represented by forms like 

 Eohippus, Mesohippus, Protohippus, Mery- 

 chippus, and so on. Professor Cossar Ewart 

 has shown, for instance, that the small nodule 

 at the end of the splint bone is separate in 

 the embryo, and is the representative of 

 one or more of the joints of the second or the 

 fourth digit which, apart from this, would 

 seem to have entirely passed away. It is 

 well known that in a monstrosity of our 

 Jamiliar one-toed horse the splint bone^oix 

 each side of the main ca.nnmi-honp fc pn- 

 larged, and bears a complete digit, so that a 

 Ihree-tQed. horse, such as the one Juliys 

 Caesar rode, occasionally still walks upon the 

 earth. Such cases of symmetrical threejo^d 

 development may be f amy interpreted as 

 ^reversions to the ancestral type, and are to 

 be distinguished from unsymmetrical extra 



