The diagrams below show the development of the horse
The diagrams below show the development of the horse 3bPbw
The pictures illustrate the evolution of the horse.
Overall, the whole procedure consists of 4 stages, starting with Eohippus and finishing with the development of the modern horse.
40 million years ago, the first horse, Eohippus, was comparatively small with a short tail. Its defining characteristic. However, the feature was shown clearly about the structure of its foot, which had 4 digits. Particularly, each of the digits was relatively small. 10 million years later, it had evolved into the larger Mesohippus, with a longer tail and a foot structure of 3 digits.
Then, in the next stage of development, Merychippus evolved 15 million years ago. It was a similar size to Mesohippus, and also had 3 digits on its feet, but now the digits on the feet were larger, divided into segments, and the middle digit was very prominent.
Finally, the modern horse evolved. It is bigger than its predecessors, with a large mane and its foot structure is a single, extremely large digit. 
The pictures illustrate the evolution of the horse.
 Overall
, the whole procedure consists of 4 stages, starting with  
Eohippus
 and finishing with the development of the modern horse.
40 million years ago, the  
first
 horse,  
Eohippus
, was  
comparatively
  small
 with a short tail. Its defining characteristic.  
However
, the feature  
was shown
  clearly
 about the structure of its foot, which had 4 digits.  
Particularly
, each of the digits was  
relatively
  small
. 10 million years later, it had evolved into the larger  
Mesohippus
, with a longer tail and a foot structure of 3 digits.
Then, in the  
next
 stage of development,  
Merychippus
 evolved 15 million years ago. It was a similar size to  
Mesohippus
, and  
also
 had 3 digits on its feet,  
but
  now
 the digits on the feet were larger, divided into segments, and the middle digit was  
very
 prominent. 
Finally
, the modern horse evolved. It is bigger than its predecessors, with a large mane and its foot structure is a single,  
extremely
 large digit.