EXTINCT ANIMALS 



shows seven cheek-teeth in position on each side 

 ineach jawat once — of which the front ones are 

 second-teeth and were preceded by milk-teeth 

 — whilst the three big back ones are not pre- 

 ceded. In tracing the ancestry of living mam- 

 mals through extinct ancestors of different suc- 

 ceeding geological ages, we expect to find even 

 the strangest and most curiously modified 

 creatures, such as are the elephants in regard to 

 their teeth and jaws and the horses in regard 

 to their toes — preceded by forms which bring 

 us nearer and nearer, as we recede into the past, 

 to a sort of common form or " type " of the 

 mammahan group — a hairy-coated creature, 

 with five toes on each foot, the typical dentition 

 or tooth series of three incisors, one canine, 

 four front or fore-molars, and three back molars 

 on each side of each jaw, with three or four 

 tubercles or knobs on the crowns of the molar 

 teeth. And we do not expect this remote an- 

 cestor to be very big — not much bigger than a 

 dog — since great size is a peculiarity implying 

 long and special predominance. 



A further point in which the American masto- 

 don is more like the ordinary run of mammals 

 than are the elephants, is that it has front teeth 



114 



