304 TOWARDS THE HUMAN FORM 



to other causes besides the disproportionate growth of 

 certain individuals. Among the herbivorous animals the 

 Ruminants are the first examples of this. These animals, as 

 we have seen, appear to be derived from Oreodon of 

 Oliogocene times, which already had the molars of Ruminants 

 but five digits, of which one was very small on the front feet 

 and was absent in the hind ones. They appear to be descended 

 from the Condylarthra (Pantolestes) , and were followed by 

 Ccenotherium, which still had a complete dentition, though a 

 wide space known as the gap or diastema, in which the canine 

 occupied a variable position, had been produced between the 

 incisors and the molars. In their successors the lower jaw 

 preserved the complete dentition, in spite of this gap, except 

 that the canine was placed against the incisors, whose form it 

 took, and the first premolar, with a greatly reduced root, 

 united with it, so that it appeared to be hollowed out on its 

 cutting edge in the Giraffidae (Giraffe, Okapi). Thus apparently 

 there were only six molars in all, and that is the number that 

 persists in the other Ruminants. Things were far more com- 

 plicated in the upper jaw. There the dentition was still 

 probably complete in Leptotragulus and Proebrotherium of the 

 North American Eocene ; but in the Camels the middle 

 incisors disappeared, and the laterals, canines, and first 

 premolars, set very wide apart, took the form of sharp, curved- 

 back hooks. There are only two premolars in the upper jaw 

 and one in the lower, and in Halomeniscus and Eschatius 

 there is actually only one in each. As for the other Ruminants, 

 those forms with hollow horns have neither incisors nor canines 

 in the upper jaw. It may indeed be asked why the incisors 

 of Ruminants have disappeared while they remained in 

 Horses, which also browse on grass. Aristotle had already 

 pointed out, and after him Cuvier, that Ruminants with horns 

 had no canines, but both made use of this coincidence as an 

 argument in favour of finalism, on the grounds that animals 

 which could defend themselves with their teeth had no need 

 for horns, and vice versa. The correlation pointed out by 

 Aristotle is not, however, strictly accurate, nor is it an explana- 

 tion. Is it possible that the calcium employed in the formation 

 of the bony portion of the horns has been used up at the expense 

 of the teeth ? Triceratops, the only Reptile with real horns, 

 had no teeth in the anterior portion of its jaws, which were 



