RUDIMENTARY STRUCTURES. 241 



fifth is rather small ; while in the Rhinoceros the 

 disappearance of the fifth leaves only three functional 

 toes, of which the middle one (third) is much the 

 largest. Passing over some intermediate forms, we 

 find in the extinct horse-like animal known as the 

 Hipparion, the lateral toes have become very small, 

 short, and useless, while their metacarpals are reduced 

 to slender bones lying along the sides of the large 

 third metacarpal. Finally, the modern horse has 

 totally lost the lateral toes, and their metacarpals 

 (2nd and 4th) are merely represented by small splints 

 lying parallel to the upper end of the third meta- 

 carpal now known as the cannon-bone in the same 

 position as the upper splints (2nd and 5th) in Fig. 80. 

 Here then, again, we have true rudimentary organs 

 the remnants of bones once functional which are 

 not only of no sort of use to their owner, but, on the 

 contrary, are absolutely injurious to him, since it is 

 from inflammation, due to hard work, arising in these 

 bones which gives rise to the disease known as " splint " 

 in horses. 



Except for the presence of these " splints " the 

 horse appears to our ideas to be an absolutely perfect 

 type of animal ; and, indeed, so far as we can see, is 

 the supreme development of which the Odd-toed Ungu- 

 late stock is susceptible. If the horse were unknown, 

 and the rhinoceros and tapir the only representatives 

 of the Odd-toed group, it might have been readily con- 

 ceived that their speed and agility could be improved by 

 diminishing the number of their toes, and lengthening 



Q 



