DOMESTIC ANIMALS. 



155 



adapting him more closely to the new con- 

 ditions in which he was to live. The three 

 toes he possessed in the preceding age were 

 consolidated into one the hoof; the teeth 

 became at the same time better adapted for 

 grinding hard food, and a new substance- 

 cement appeared on the crown of the tooth. 

 Further, the diastema (the toothless gap in 

 the jaw) lengthened. The changes in the 

 feet and teeth were advantageous to the 

 animal itself, and at the same time rendered 

 him more serviceable for the use of man ; but 

 the benefit of the diastema to the Horse 

 himself is not apparent. Its advantage to 

 man is, however, great ; for if the diastema 

 did not provide a recess for the bit of the 

 bridle, it would be extremely difficult to 

 control him. 1 



Now these modifications, from their 

 nature, could not have arisen either from 

 the accumulation of slight beneficial varia- 

 tions or from use or disuse, and it is signif- 

 icant that these modifications, necessary 

 for the existence of the Horse in his new 

 conditions of life, occurred at the same time 

 in organs so distinct from each other as 

 the jaws and the feet. Whatever the 



1 Hence the metaphor describing the action of a head- 

 strong man, "He has got the bit between his teeth." 



