PROF, marsh's researches. 95 



In the evolution of the horse from an animal of 

 about the size of a fox to his present proportions, it is 

 not strange that radical physical changes, of the teeth 

 as well as otlier organs, should have occurred, or that 

 they are in harmony with his bodily requirements as 

 well as his usefulness to man. Small, four-toed limbs 

 would support the body of an animal no larger than a 

 fox or a sheep, but they would require additional size 

 and strength to support the small horse (Hipparion) 

 of the Pliocene period, or the large horse of the present 

 period (Equus). This additional strength was gradu- 

 ally acquired by the enlargement of the limbs and the 

 sohdification, as it were, of four 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. 



During these metamorphoses equally varied and 

 interesting changes occurred in the horse's dental sys- 

 tem, which are described by Prof. O. C. Marsh, of Yale 

 College, in the article "Horse, Fossil," in "Johnson's 

 New Universal Cyclopedia (vol. ii, p. 906). He gives a 

 general description of the changes that have occurred 

 in species of three geological periods, namely, the 

 Pliocene, Miocene, and Eocene, those of the two last 

 named having forty-four functionally developed teeth. 

 Th ft part of the article which refers to the teeth is as 

 follows : 



"In the Pliocene tertiary period the horse was rep- 

 resented by several extinct genera, the best known be- 

 ing Hipparion (or Hippotherium). The species are 

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

 utive from the Greek hijipos, a Miorse.' In the upper 

 molar teeth there is in Hipparion, on the anterior por- 



