296 TOWARDS THE HUMAN FORM 



fourth digits are almost equal they share the task of supporting 

 the body and become almost exactly alike. The foot then 

 assumes the cleft form characteristic of the Artiodactyla. 

 In both cases the lateral toes tend to disappear thiough lack 

 of use and all the stages in this retrogression can be followed. 

 In the order of Perissodactyla, where the foot is reduced to a 

 single toe, as in Horses, this reduction and disappearance 

 takes place onlv after the bones of the carpus and the tarsus 

 have gone on for some time being displaced in order to afford 

 mutual support, piling up over one another and articulating 

 one on the other. They may unite, but do not disappear. It 

 is otherwise with the Artiodactyla. Here the reduction was 

 produced in a first series of forms, while the carpus and 

 tarsus were still seriated. The bones of the carpus and the 

 corresponding bones of the tarsus are either reduced or dis- 

 appear,, and both hind and fore feet have preserved their 

 frailty. This is what Woldemar Kowalevsky, brother of the 

 famous embryogenist, called non-adaptive reduction. The 

 Artiodactyla that underwent it all disappear from Miocene 

 times onwards : they were Dichobune and Hyopotamus, provided 

 with four digits ; Anoplotherium , an aquatic animal which had 

 only two to the fore limbs, with a third much reduced 

 digit to each hind limb ; and Xiphodon, more graceful than our 

 gazelle, which had only two toes on all four feet, and whose 

 molars were the first to show the Ruminant tendency, although 

 Xiphodon must not be considered as their ancestor. To 

 these must be added Anthracotherium, Cheer opotamus, and 

 Hyothcrium, related both to the Wild Boar and the Peccary, 

 and particularly Entelodon, large as a Rhinoceros. In the 

 persisting forms which have led in one direction to the Pig 

 and in another to the Ruminants, the heads of the third and 

 fourth metacarpals have been broadened as though crushed 

 under the animal's weight. They have encroached upon the 

 carpals supporting the lateral toes, and thus assured the 

 preservation of these last. When the reduction in the number of 

 toes begins only after this modification has taken place, 

 W. Kowalevsky describes it as adaptive reduction. This is 

 the condition in the Hippopotamus, Wild Boar, Peccary, and 

 the other existing Pigs. The metacarpals and metatarsals 

 in these animals are never united, nor were they united in 

 primitive Ruminants. The latter series begins with Oreodon, 



