Extinct Species. 189 



and neck were elongated, and the place for the bit 

 or diastema was well defined, and develops materi- 

 ally as we follow the line down. Compare this form 

 with the horse of the Lower Miocene (the Mesohip- 

 pus), and we find that the latter was larger, being 

 now about the size of a sheep. It has three toes 

 behind and in front, while the fourth toe, which we 

 saw in the previous form, is reduced to a mere 

 splint. Following it, in the Miocene proper, was the 

 Miohippus, in which the toes are about the same, 

 though the fourth one, or splint, is hardly dis- 

 tinguishable. Now, the animals, though small, had 

 well-defined horse-like shapes. Passing to the next 

 form in the Lower Pliocene, we find a skeleton 

 about as large as that of the present donkey. 

 The splint has entirely disappeared, and there are 

 three toes, the two outer ones being short, there 

 being very evident disposition to rely upon the 

 middle one, which was larger and stouter than in 

 previous forms. Moving upward to the Pliocene, we 

 come to a horse which scientists call Pliohippus, and 

 which was very similar to the horse of to-day. The 

 middle toe was now the hoof, while the other toes 

 were useless splints. Another step brings us to the 

 Quaternary and present horse, in which the middle 

 toe has become the hoof, upon which the genus 

 Equus stands, while the two toes are still represented 

 by the disappearing side splints. 



The striking nature of this evidence is shown in 

 the accompanying diagram. 



In referring to these animals Professor Marsh 

 says : " The most marked changes undergone by 



