EXTINCT ANIMALS 



number, four in front which are replaced 

 — that means that second teeth come to take 

 the place of the first — and three hinder ones, 

 which are never replaced. If you look at the 

 surface of these cheek teeth you will find they 

 are broad, with many tubercles, fitted for grind- 

 ing great varieties of food. There are seven of 

 these cheek teeth on each side in each jaw, 

 upper and lower, one canine, and three 

 incisors, so that eleven on each side in upper 

 and in lower jaw or forty-four teeth in all is the 

 complete number, the typical number — the 

 most characteristic number in the group of 

 hairy mammals. Many have less, but among 

 the immediate ancestors of those mammals with 

 " reduced dentition " we find a larger number 

 of teeth, and in their remote ancestors the com- 

 plete typical number is discovered. 



It is important to notice that whereas the 

 front teeth have a single fang by which they are 

 implanted in the jaw the cheek teeth have two 

 fangs, as shown in Fig. 51. Teeth with two 

 fangs appear to be peculiar to mammals. Other 

 animals have only single fangs to all their teeth, 

 as mammals have for their incisors and canines 

 (as a rule). 



78 



