I20 TTNDKRIIILL : 



while the next to the last is beginning to become so. The 

 canines are well forward and the diastema, or " place for the 

 bit," is distinct. 



The Epihippus is from the Upper I{ocene, and is about as 

 large as a fox. In this stage the four fingers and three toes 

 of the Orohippus are still retained, but the central finger and 

 central toe are becoming larger. The once rounded knobs of 

 the molar teeth are now almost completely converted into 

 crests, while the third, as well as the fourth premolar, have 

 become like the molars. 



The fourth in the line is the Mesohippus, found in the 

 Lower Miocene White River Formation. It is somewhat 

 smaller than a sheep, and stands upon three fingers and three 

 toes, the fifth finger of its Eocene ancestors being reduced to 

 a splint. The side digits are now bearing little weight, while 

 the central ones are much the largest. The crests on the 

 molars are completely formed and three of the premolars have 

 become true molars. 



The Miohippus from the Upper Miocene is about as large 

 as a sheep. Like its predecessors in the series, it has three 

 fingers and three toes, a rudiment of the fifth finger still 

 remaining. The radius and ulna are loosely united, and the 

 tibia and fibula are co-ossified at their distal ends. 



The Protohippus is found in the Lower Pliocene. It is 

 nearly as large as an ass, and represents the first stage where 

 the lateral hoofs are not functional. It stands upon the 

 middle finger and middle toe. The side digits, that is, the 

 second and fourth, are still complete, but much more slender 

 than in the preceding stage,- and they are clear of the ground. 

 The hand still retains tiny nodules of bone at the back of the 

 wrist, or so-called knee, which are the remains of the first 

 and fifth digits. 



In the Pliohippus from the Upper Pliocene we have the 

 last stage l)efore reaching the true horse. It is as large as an 

 ass, and in some species the side digits have almost if not 

 completely disappeared. 



