THE ONE BIG DIGIT OF THE HORSE 259 



case of reversion, because the metacarpal and metatarsal bones of 

 the Horse, unlike those of the Ox, were single bones. I remarked 

 that the case, in his book on The Horse, of a metatarsal bone with 

 two nutrient foramina, threw some doubt on the theory that these 

 bones in the Horse were originally only one bone. He replied — 

 ' Then, if these bones are made up of a fusion of two, you would 

 have to credit the Horse with having had six digits originally.' I 

 said that would exactly correspond to the six digits in the hand 

 and foot of numerous persons mentioned by Darwin and others. 



I do not think that we are justified in beginning to count from 

 either a Pkcenacodus, or any other extinct anirnal previous to it, 

 with five digits to its hand and foot, and then call these ' archetypal ' 

 hand and foot, for these extinct animals were not the conimence- 

 ment of the vertebrate type, and behind them there may have been 

 other extinct animals which may have had six digits. True 

 enough, we have not yet found fossil animals with normally six 

 digits, but we have found some with more than six. 



There can be no doubt that certain digits can become hyper- 

 trophied, and then, through natural selection, the enlargement 

 might be continued, and even increased ; but what I have some 

 doubt about is whether the Horse's digit was originally an enlarged 

 one, or a fusion of two digits. 



The abnormal examples given by Chauveau and M'Fadyean, 

 which are like the cloven foot of the Ox, and the example of two 

 nutrient foramina in the metatarsal bone of a Horse, certainly tend 

 to throw doubt on the accepted origin of the Horse's digit as a 

 hypertrophied one digit. These abnormalities may be as im- 

 portant, in a sense, as the discovery of the archeopteryx. 



When we begin to search lower down in the scale of vertebrates 

 than Phcenacodus to try and find out where it got its five digits 

 from, what do we find ? , / 



