4 MAMMALS OF THE PACIFIC WORLD 



cisors are absent in cattle and deer, while in the elephant the 

 lower ones are missing and the two upper incisors are modified 

 to form the tusks. 



The canines, or eye-teeth, are usually longer and more 

 rounded in cross section than the other teeth. While the upper 

 incisors are set into the front upper jaw bone, the upper canine 

 is the first tooth in the maxillary or side bone of the upper jaw. 

 The lower canine fits in front of the upper one. Bats, meat- 

 eaters, the seal group, and most monkeys, especially males, 

 have large canine teeth. These teeth are tusk-like in pigs and 

 dagger-like in the mouse-deer. They are the killing teeth of 

 beasts of prey, the fighting teeth of these and animals such as 

 pigs and monkeys which tear and hurt rivals. Rabbits, rodents, 

 and most kinds of kangaroos have no canines ; cattle and most 

 true deer have only lower ones, similar in shape to the incisors. 



In each toothrow the cheek-teeth, from few to as many as 

 seven in number, stand behind the canine, or the gap (diastema) 

 which is present when this tooth is undeveloped. In elephants 

 only one enormous grinder with parts of others is used at a 

 time. The tooth, as it wears away, travels forward in the jaw 

 and the next behind it moves upward and forward gradually 

 to take its place. These teeth are very large. Their grinding 

 surfaces may have fifteen or twenty cross-ridges of hard enamel 

 which make the teeth efficient mills to grind leaves and twigs. 

 The grinders of other plant-eaters such as rhinoceros and tapir, 

 cattle and deer, have different patterns ; but the ridges, whether 

 they are shaped like the Greek letter tt or are crescent-like, 

 serve similar purposes. 



The cheek-teeth of many meat-eaters are reduced in number, 

 and a pair of very large ones on each side works together like 

 shears to cut up meat. The cheek-teeth of bears, otters, and 

 many of the civet family have mound-shaped cusps, better suited 

 for crushing than shearing. Insect-eaters and the insect-eating 

 bats have sharp-cusped teeth for crushing and cutting up hard- 

 bodied insects. 



