PEDIGREE OF MAMMALS. 



275 



is repeated, and Phylogenesis is unequivocally expressed 

 in Ontogenesis. The Anchitherium is a three-toed horse, 

 in which, however, the middle toe has already under- 

 taken the chief task. But in the Hipparion the two 

 side toes are entirely raised from the ground, and by 

 disuse are brought to the condition of arrest which is 

 completed in the horse. 



In the constitution of the molar teeth the tapirs have 

 remained most faithful to the ancestral type. The cir- 

 cumstance that the tapir has four toes in front, whereas 

 the Palaeotheridse known to us, have three shows, how- 

 ever, that the genus Palaeotherium cannot have been 

 the ancestral stock of the tapirs. For the supposition 

 that the tapir acquired the fourth toe is contrary to all 

 experience respecting the formation of the extremities. 

 Rhinoceroses are also four-toed in front, and their close 

 kindred with the tapirs is testified by the structure of 

 their toes and a series of details in the skeleton. 



Hippopotami. Pigs. Tragulidse. Deer. Antelopes. Oxen. 



Anoplotheridse. 



An isolated branch of the Palaeotheridse seems to be 

 the fossil genus Macrauchenidse, which combines the 



