THE ONE BIG DIGIT OF THE HORSE 263 



Atrophy and subsequent suppression, enlargement and fusion, 

 are some of the factors of modification in the skeletons of verte- 

 brates ; and we have seen that in the hand of the Plesiosaur and 

 the Round-headed Dolphin there is no distinction between the 

 metacarpal bones and the phalanges. 



The more one makes researches to discover at what period the 

 so-called archetypal hand with five digits took form, the more one 

 loses faith in there ever having been such a thing. From the hand 

 with many digits the hand with five digits evolved, and this 

 continued to lose other digits till only one has remained, as is 

 supposed, in the Horse. All that can be said in favour of an 

 archetypal hand is, that a large number of vertebrates have five 

 digits in their fore-limb, and that probably they evolved from a 

 many-digited type after it had lost several of its original digits, and 

 was temporarily reduced to jive. We have seen that some of the 

 specimens of Ichthyosaurs in the Natural History Museum have 

 as many as eight digits in their hand. 



I suppose there is no osteologist who believes that this so- 

 called archetypal hand was created ab initio with five digits ! 



It is not only in extinct animals, but also in recent ones, that 

 we find a large number of phalanges as shown by Professor Flower 

 in the two fingers of the Round-headed Dolphin. Curiously 

 enough, although this mammal has retained some of the general 

 characters of the Plesiosaurian hand, it has got rid of its legs 

 entirely. We have seen that in the Ichthyosaurs the hind-limbs 

 were already dwindling. We cannot know which set of extinct 

 animals eventually branched off into the mammal type, and we 

 have no means of knowing whether that immense series of extinct 

 animals, provisionally grouped under the name of Dinosaurs, were 

 oviparous or viviparous. Indeed, as I said, this distinction is not of 

 much importance, seeing that viviparous means hatched inside the 



